diff --git a/Makefile b/Makefile
index 21cdd78..a208742 100644
--- a/Makefile
+++ b/Makefile
@@ -37,6 +37,7 @@ ORCH_SOURCES := \
 
 PREPROC_SOURCES := \
 	data_acq_and_processing/preprocessing/calibration_master/src/calibration_master.cpp \
+	data_acq_and_processing/preprocessing/calibration_master/src/channel_bundle_support.cpp \
 	data_acq_and_processing/preprocessing/calibration_master/src/through_calibrator.cpp \
 	data_acq_and_processing/preprocessing/reference_master/src/reference_master.cpp \
 	data_acq_and_processing/preprocessing/data_preprocessor/src/data_preprocessor.cpp \
diff --git a/data_acq_and_processing/common_cpp/config/include/run_config.hpp b/data_acq_and_processing/common_cpp/config/include/run_config.hpp
index eea690c..b5a4af7 100644
--- a/data_acq_and_processing/common_cpp/config/include/run_config.hpp
+++ b/data_acq_and_processing/common_cpp/config/include/run_config.hpp
@@ -75,10 +75,14 @@ struct RuntimeConfig {
 
 struct PreprocessConfig {
     // Names and bundle paths selected by Python GUI layer.
-    std::string calibration_set{};
-    std::string reference_set{};
-    std::string calibration_bundle_path{};
-    std::string reference_bundle_path{};
+    std::string s21_calibration_set{};
+    std::string s21_reference_set{};
+    std::string s21_calibration_bundle_path{};
+    std::string s21_reference_bundle_path{};
+    std::string s11_open_calibration_bundle_path{};
+    std::string s11_short_calibration_bundle_path{};
+    std::string s11_load_calibration_bundle_path{};
+    std::string s11_reference_bundle_path{};
 };
 
 struct GprTxGeometry {
diff --git a/data_acq_and_processing/common_cpp/config/src/run_config.cpp b/data_acq_and_processing/common_cpp/config/src/run_config.cpp
index 1cec13d..7d389fe 100644
--- a/data_acq_and_processing/common_cpp/config/src/run_config.cpp
+++ b/data_acq_and_processing/common_cpp/config/src/run_config.cpp
@@ -438,10 +438,18 @@ auto load_run_config(const std::string& path) -> RunConfig {
 
     {
         const auto* preprocess_obj = as_object(required_field(*root_obj, "preprocess"), "preprocess");
-        config.preprocess.calibration_set = optional_string(*preprocess_obj, "calibration_set", "");
-        config.preprocess.reference_set = optional_string(*preprocess_obj, "reference_set", "");
-        config.preprocess.calibration_bundle_path = optional_string(*preprocess_obj, "calibration_bundle_path", "");
-        config.preprocess.reference_bundle_path = optional_string(*preprocess_obj, "reference_bundle_path", "");
+        config.preprocess.s21_calibration_set = optional_string(*preprocess_obj, "s21_calibration_set", "");
+        config.preprocess.s21_reference_set = optional_string(*preprocess_obj, "s21_reference_set", "");
+        config.preprocess.s21_calibration_bundle_path =
+            optional_string(*preprocess_obj, "s21_calibration_bundle_path", "");
+        config.preprocess.s21_reference_bundle_path = optional_string(*preprocess_obj, "s21_reference_bundle_path", "");
+        config.preprocess.s11_open_calibration_bundle_path =
+            optional_string(*preprocess_obj, "s11_open_calibration_bundle_path", "");
+        config.preprocess.s11_short_calibration_bundle_path =
+            optional_string(*preprocess_obj, "s11_short_calibration_bundle_path", "");
+        config.preprocess.s11_load_calibration_bundle_path =
+            optional_string(*preprocess_obj, "s11_load_calibration_bundle_path", "");
+        config.preprocess.s11_reference_bundle_path = optional_string(*preprocess_obj, "s11_reference_bundle_path", "");
     }
 
     if (const auto* gpr_value = optional_field(*root_obj, "gpr"); gpr_value != nullptr) {
diff --git a/data_acq_and_processing/preprocessing/calibration_master/include/calibration_master.hpp b/data_acq_and_processing/preprocessing/calibration_master/include/calibration_master.hpp
index a0489fc..5508d1a 100644
--- a/data_acq_and_processing/preprocessing/calibration_master/include/calibration_master.hpp
+++ b/data_acq_and_processing/preprocessing/calibration_master/include/calibration_master.hpp
@@ -1,32 +1,51 @@
 #pragma once
 
 #include <memory>
+#include <span>
 #include <string>
-#include <unordered_map>
 #include <vector>
 
 #include "calibrator_interface.hpp"
+#include "channel_bundle_support.hpp"
 #include "shared_types.hpp"
 
 namespace radar::preprocessing {
 
 class CalibrationMaster {
   public:
-    // `calibrator` encapsulates the actual calibration algorithm (v1: through).
-    explicit CalibrationMaster(std::unique_ptr<CalibratorInterface> calibrator);
+    // `s21_calibrator` encapsulates the S21 calibration algorithm.
+    explicit CalibrationMaster(std::unique_ptr<CalibratorInterface> s21_calibrator);
 
-    // Loads a serialized raw sweep bundle with one calibration standard per combo.
-    void load_bundle(const std::string& path);
+    // Loads a serialized raw sweep bundle with one S21 calibration standard per combo.
+    void load_s21_calibration_bundle(const std::string& path);
+    // Loads optional one-port OSL calibration data for S11 from raw sweep bundles.
+    void load_s11_calibration_bundle(
+        const std::string& open_path,
+        const std::string& short_path,
+        const std::string& load_path
+    );
     // Ensures all runtime combos are present in loaded standards.
     void validate_combos(const std::vector<ipc::ComboKey>& combos) const;
-    // Applies calibration standard corresponding to measured trace combo.
-    [[nodiscard]] auto apply(const ipc::SweepTraceBlock& measured_trace) const -> ipc::SweepTraceBlock;
+    // Applies both channel calibrations to one measured trace.
+    [[nodiscard]] auto apply_to_trace(const ipc::SweepTraceBlock& measured_trace) const -> ipc::SweepTraceBlock;
+    [[nodiscard]] auto apply_s21(
+        const ipc::ComboKey& combo,
+        std::span<const float> frequency_hz,
+        const std::vector<ipc::Complex32>& measured_s21
+    ) const -> std::vector<ipc::Complex32>;
+    [[nodiscard]] auto apply_s11(
+        const ipc::ComboKey& combo,
+        std::span<const float> frequency_hz,
+        const std::vector<ipc::Complex32>& measured_s11
+    ) const -> std::vector<ipc::Complex32>;
+    [[nodiscard]] auto has_s11_calibration() const noexcept -> bool;
 
   private:
-    std::unique_ptr<CalibratorInterface> calibrator_impl_;
-    std::unordered_map<ipc::ComboKey, ipc::SweepTraceBlock, ipc::ComboKeyHash> standards_by_combo_{};
+    std::unique_ptr<CalibratorInterface> s21_calibrator_;
+    S21CalibrationBundle s21_calibration_bundle_{};
+    S11CalibrationBundle s11_calibration_bundle_{};
 };
 
-[[nodiscard]] auto make_through_calibrator() -> std::unique_ptr<CalibratorInterface>;
+[[nodiscard]] auto make_s21_through_calibrator() -> std::unique_ptr<CalibratorInterface>;
 
 }  // namespace radar::preprocessing
diff --git a/data_acq_and_processing/preprocessing/calibration_master/include/channel_bundle_support.hpp b/data_acq_and_processing/preprocessing/calibration_master/include/channel_bundle_support.hpp
new file mode 100644
index 0000000..4a85258
--- /dev/null
+++ b/data_acq_and_processing/preprocessing/calibration_master/include/channel_bundle_support.hpp
@@ -0,0 +1,91 @@
+#pragma once
+
+#include <span>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include "shared_types.hpp"
+
+namespace radar::preprocessing {
+
+class CalibratorInterface;
+
+struct ChannelTrace {
+    std::vector<float> frequency_hz{};
+    std::vector<ipc::Complex32> samples{};
+};
+
+class S21CalibrationBundle {
+  public:
+    void load(const std::string& path);
+
+    [[nodiscard]] auto is_enabled() const noexcept -> bool;
+    void validate_combos(const std::vector<ipc::ComboKey>& combos) const;
+    [[nodiscard]] auto apply(
+        const ipc::ComboKey& combo,
+        std::span<const float> frequency_hz,
+        const std::vector<ipc::Complex32>& measured,
+        const CalibratorInterface& calibrator
+    ) const -> std::vector<ipc::Complex32>;
+
+  private:
+    [[nodiscard]] auto resolve(const ipc::ComboKey& combo) const -> const ChannelTrace&;
+
+    std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash> traces_by_combo_{};
+};
+
+class S21ReferenceBundle {
+  public:
+    void load(const std::string& path);
+
+    [[nodiscard]] auto is_enabled() const noexcept -> bool;
+    void validate_combos(const std::vector<ipc::ComboKey>& combos) const;
+    [[nodiscard]] auto resolve(const ipc::ComboKey& combo) const -> const ChannelTrace&;
+
+  private:
+    std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash> traces_by_combo_{};
+};
+
+class S11CalibrationBundle {
+  public:
+    struct Coefficients {
+        std::vector<float> frequency_hz{};
+        std::vector<ipc::Complex32> directivity{};
+        std::vector<ipc::Complex32> source_match{};
+        std::vector<ipc::Complex32> reflection_tracking{};
+    };
+
+    void load(
+        const std::string& open_path,
+        const std::string& short_path,
+        const std::string& load_path
+    );
+
+    [[nodiscard]] auto is_enabled() const noexcept -> bool;
+    void validate_combos(const std::vector<ipc::ComboKey>& combos) const;
+    [[nodiscard]] auto apply(
+        const ipc::ComboKey& combo,
+        std::span<const float> frequency_hz,
+        const std::vector<ipc::Complex32>& measured
+    ) const -> std::vector<ipc::Complex32>;
+
+  private:
+    [[nodiscard]] auto resolve(const ipc::ComboKey& combo) const -> const Coefficients&;
+
+    std::unordered_map<ipc::ComboKey, Coefficients, ipc::ComboKeyHash> coefficients_by_combo_{};
+};
+
+class S11ReferenceBundle {
+  public:
+    void load(const std::string& path);
+
+    [[nodiscard]] auto is_enabled() const noexcept -> bool;
+    void validate_combos(const std::vector<ipc::ComboKey>& combos) const;
+    [[nodiscard]] auto resolve(const ipc::ComboKey& combo) const -> const ChannelTrace&;
+
+  private:
+    std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash> traces_by_combo_{};
+};
+
+}  // namespace radar::preprocessing
diff --git a/data_acq_and_processing/preprocessing/calibration_master/src/calibration_master.cpp b/data_acq_and_processing/preprocessing/calibration_master/src/calibration_master.cpp
index 126f61c..f9ae484 100644
--- a/data_acq_and_processing/preprocessing/calibration_master/src/calibration_master.cpp
+++ b/data_acq_and_processing/preprocessing/calibration_master/src/calibration_master.cpp
@@ -1,107 +1,60 @@
 #include "calibration_master.hpp"
 
-#include <cstdint>
-#include <fstream>
-#include <iterator>
 #include <stdexcept>
-#include <string>
-#include <vector>
 
 namespace radar::preprocessing {
-namespace {
 
-[[nodiscard]] auto combo_to_string(const ipc::ComboKey& combo) -> std::string {
-    return "input=" + std::to_string(combo.input_pos) + " output=" + std::to_string(combo.output_pos);
-}
-
-[[nodiscard]] auto read_binary_file(const std::string& path, const std::string& bundle_label)
-    -> std::vector<std::uint8_t> {
-    std::ifstream stream(path, std::ios::binary);
-    if (!stream.is_open()) {
-        throw std::runtime_error("Failed to open " + bundle_label + " bundle: " + path);
-    }
-
-    return std::vector<std::uint8_t>(std::istreambuf_iterator<char>(stream), std::istreambuf_iterator<char>());
-}
-
-void validate_trace_layout(const ipc::SweepTraceBlock& trace, const std::string& trace_label) {
-    if (trace.frequency_hz.size() != trace.s21.size()) {
-        throw std::runtime_error(
-            trace_label + " frequency/complex vector size mismatch for combo " + combo_to_string(trace.combo)
-        );
-    }
-    if (trace.frequency_hz.size() != trace.s11.size()) {
-        throw std::runtime_error(
-            trace_label + " frequency/S11 vector size mismatch for combo " + combo_to_string(trace.combo)
-        );
-    }
-}
-
-}  // namespace
-
-CalibrationMaster::CalibrationMaster(std::unique_ptr<CalibratorInterface> calibrator)
-    : calibrator_impl_(std::move(calibrator)) {
-    if (!calibrator_impl_) {
+CalibrationMaster::CalibrationMaster(std::unique_ptr<CalibratorInterface> s21_calibrator)
+    : s21_calibrator_(std::move(s21_calibrator)) {
+    if (!s21_calibrator_) {
         throw std::runtime_error("CalibrationMaster requires a non-null calibrator");
     }
 }
 
-void CalibrationMaster::load_bundle(const std::string& path) {
-    if (path.empty()) {
-        throw std::runtime_error("Calibration bundle path must not be empty");
-    }
+void CalibrationMaster::load_s21_calibration_bundle(const std::string& path) {
+    s21_calibration_bundle_.load(path);
+}
 
-    const auto bytes = read_binary_file(path, "calibration");
-    if (bytes.empty()) {
-        throw std::runtime_error("Calibration bundle is empty: " + path);
-    }
-
-    const auto collection = ipc::deserialize_raw_collection(bytes);
-    standards_by_combo_.clear();
-    standards_by_combo_.reserve(collection.traces.size());
-    for (const auto& trace : collection.traces) {
-        validate_trace_layout(trace, "Calibration standard");
-        standards_by_combo_.insert_or_assign(trace.combo, trace);
-    }
-
-    if (standards_by_combo_.empty()) {
-        throw std::runtime_error("Calibration bundle does not contain traces: " + path);
-    }
+void CalibrationMaster::load_s11_calibration_bundle(
+    const std::string& open_path,
+    const std::string& short_path,
+    const std::string& load_path
+) {
+    s11_calibration_bundle_.load(open_path, short_path, load_path);
 }
 
 void CalibrationMaster::validate_combos(const std::vector<ipc::ComboKey>& combos) const {
-    for (const auto& combo : combos) {
-        if (!standards_by_combo_.contains(combo)) {
-            throw std::runtime_error("Calibration data is missing for combo " + combo_to_string(combo));
-        }
-    }
+    s21_calibration_bundle_.validate_combos(combos);
+    s11_calibration_bundle_.validate_combos(combos);
 }
 
-auto CalibrationMaster::apply(const ipc::SweepTraceBlock& measured_trace) const -> ipc::SweepTraceBlock {
-    validate_trace_layout(measured_trace, "Measured trace");
-
-    const auto found = standards_by_combo_.find(measured_trace.combo);
-    if (found == standards_by_combo_.end()) {
-        throw std::runtime_error(
-            "Calibration standard is missing for measured combo " + combo_to_string(measured_trace.combo)
-        );
-    }
-
-    const auto& standard = found->second;
-    validate_trace_layout(standard, "Calibration standard");
-    if (measured_trace.s21.size() != standard.s21.size()) {
-        throw std::runtime_error(
-            "Calibration standard point count mismatch for combo " + combo_to_string(measured_trace.combo)
-        );
-    }
-
+auto CalibrationMaster::apply_to_trace(const ipc::SweepTraceBlock& measured_trace) const -> ipc::SweepTraceBlock {
     ipc::SweepTraceBlock output{};
     output.combo = measured_trace.combo;
     output.frequency_hz = measured_trace.frequency_hz;
-    output.s11 = measured_trace.s11;
-    output.s21 = calibrator_impl_->apply(measured_trace.s21, standard.s21);
-
+    output.s21 = apply_s21(measured_trace.combo, measured_trace.frequency_hz, measured_trace.s21);
+    output.s11 = apply_s11(measured_trace.combo, measured_trace.frequency_hz, measured_trace.s11);
     return output;
 }
 
+auto CalibrationMaster::apply_s21(
+    const ipc::ComboKey& combo,
+    std::span<const float> frequency_hz,
+    const std::vector<ipc::Complex32>& measured_s21
+) const -> std::vector<ipc::Complex32> {
+    return s21_calibration_bundle_.apply(combo, frequency_hz, measured_s21, *s21_calibrator_);
+}
+
+auto CalibrationMaster::apply_s11(
+    const ipc::ComboKey& combo,
+    std::span<const float> frequency_hz,
+    const std::vector<ipc::Complex32>& measured_s11
+) const -> std::vector<ipc::Complex32> {
+    return s11_calibration_bundle_.apply(combo, frequency_hz, measured_s11);
+}
+
+auto CalibrationMaster::has_s11_calibration() const noexcept -> bool {
+    return s11_calibration_bundle_.is_enabled();
+}
+
 }  // namespace radar::preprocessing
diff --git a/data_acq_and_processing/preprocessing/calibration_master/src/channel_bundle_support.cpp b/data_acq_and_processing/preprocessing/calibration_master/src/channel_bundle_support.cpp
new file mode 100644
index 0000000..631a17e
--- /dev/null
+++ b/data_acq_and_processing/preprocessing/calibration_master/src/channel_bundle_support.cpp
@@ -0,0 +1,405 @@
+#include "channel_bundle_support.hpp"
+
+#include <algorithm>
+#include <cmath>
+#include <complex>
+#include <cstddef>
+#include <cstdint>
+#include <fstream>
+#include <iterator>
+#include <span>
+#include <stdexcept>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include "calibrator_interface.hpp"
+
+namespace radar::preprocessing {
+namespace {
+
+enum class RawTraceChannel {
+    S11,
+    S21,
+};
+
+constexpr float kFrequencyRelativeTolerance = 1e-5F;
+constexpr float kFrequencyAbsoluteTolerance = 1e-3F;
+constexpr float kComplexMagnitudeSquaredEpsilon = 1e-12F;
+
+[[nodiscard]] auto combo_to_string(const ipc::ComboKey& combo) -> std::string {
+    return "input=" + std::to_string(combo.input_pos) + " output=" + std::to_string(combo.output_pos);
+}
+
+[[nodiscard]] auto read_binary_file(const std::string& path, const std::string& bundle_label)
+    -> std::vector<std::uint8_t> {
+    std::ifstream stream(path, std::ios::binary);
+    if (!stream.is_open()) {
+        throw std::runtime_error("Failed to open " + bundle_label + " bundle: " + path);
+    }
+
+    return std::vector<std::uint8_t>(std::istreambuf_iterator<char>(stream), std::istreambuf_iterator<char>());
+}
+
+void validate_raw_trace_layout(const ipc::SweepTraceBlock& trace, const std::string& trace_label) {
+    if (trace.frequency_hz.size() != trace.s11.size()) {
+        throw std::runtime_error(
+            trace_label + " frequency/S11 vector size mismatch for combo " + combo_to_string(trace.combo)
+        );
+    }
+    if (trace.frequency_hz.size() != trace.s21.size()) {
+        throw std::runtime_error(
+            trace_label + " frequency/S21 vector size mismatch for combo " + combo_to_string(trace.combo)
+        );
+    }
+}
+
+void validate_channel_trace_layout(
+    const ChannelTrace& trace,
+    const std::string& trace_label,
+    const ipc::ComboKey& combo
+) {
+    if (trace.frequency_hz.size() != trace.samples.size()) {
+        throw std::runtime_error(
+            trace_label + " frequency/channel vector size mismatch for combo " + combo_to_string(combo)
+        );
+    }
+}
+
+[[nodiscard]] auto frequency_axes_match(std::span<const float> left, std::span<const float> right) -> bool {
+    if (left.size() != right.size()) {
+        return false;
+    }
+
+    for (std::size_t index = 0; index < left.size(); ++index) {
+        const auto delta = std::fabs(left[index] - right[index]);
+        const auto scale = std::max(std::fabs(left[index]), std::fabs(right[index]));
+        const auto tolerance = std::max(kFrequencyAbsoluteTolerance, scale * kFrequencyRelativeTolerance);
+        if (delta > tolerance) {
+            return false;
+        }
+    }
+    return true;
+}
+
+void ensure_frequency_axis_match(
+    std::span<const float> expected,
+    std::span<const float> actual,
+    const std::string& label
+) {
+    if (!frequency_axes_match(expected, actual)) {
+        throw std::runtime_error(label + " frequency axis mismatch");
+    }
+}
+
+[[nodiscard]] auto to_std_complex(const ipc::Complex32& value) -> std::complex<float> {
+    return std::complex<float>(value.re, value.im);
+}
+
+[[nodiscard]] auto from_std_complex(const std::complex<float>& value) -> ipc::Complex32 {
+    return ipc::Complex32{
+        .re = value.real(),
+        .im = value.imag(),
+    };
+}
+
+[[nodiscard]] auto pick_channel_samples(const ipc::SweepTraceBlock& trace, RawTraceChannel channel)
+    -> const std::vector<ipc::Complex32>& {
+    if (channel == RawTraceChannel::S11) {
+        return trace.s11;
+    }
+    return trace.s21;
+}
+
+[[nodiscard]] auto to_channel_trace(
+    const ipc::SweepTraceBlock& trace,
+    RawTraceChannel channel,
+    const std::string& bundle_label
+) -> ChannelTrace {
+    validate_raw_trace_layout(trace, bundle_label + " trace");
+
+    ChannelTrace channel_trace{};
+    channel_trace.frequency_hz = trace.frequency_hz;
+    channel_trace.samples = pick_channel_samples(trace, channel);
+    validate_channel_trace_layout(channel_trace, bundle_label + " trace", trace.combo);
+    return channel_trace;
+}
+
+[[nodiscard]] auto load_channel_traces(
+    const std::string& path,
+    const std::string& bundle_label,
+    RawTraceChannel channel
+) -> std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash> {
+    const auto bytes = read_binary_file(path, bundle_label);
+    if (bytes.empty()) {
+        throw std::runtime_error(bundle_label + " bundle is empty: " + path);
+    }
+
+    const auto collection = ipc::deserialize_raw_collection(bytes);
+    std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash> traces_by_combo{};
+    traces_by_combo.reserve(collection.traces.size());
+    for (const auto& trace : collection.traces) {
+        traces_by_combo.insert_or_assign(trace.combo, to_channel_trace(trace, channel, bundle_label));
+    }
+
+    if (traces_by_combo.empty()) {
+        throw std::runtime_error(bundle_label + " bundle does not contain traces: " + path);
+    }
+    return traces_by_combo;
+}
+
+void validate_bundle_combos(
+    const std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash>& traces_by_combo,
+    const std::vector<ipc::ComboKey>& combos,
+    const std::string& bundle_label
+) {
+    if (traces_by_combo.empty()) {
+        return;
+    }
+
+    for (const auto& combo : combos) {
+        if (!traces_by_combo.contains(combo)) {
+            throw std::runtime_error(bundle_label + " is missing combo " + combo_to_string(combo));
+        }
+    }
+}
+
+template <typename TValue>
+auto resolve_required(
+    const std::unordered_map<ipc::ComboKey, TValue, ipc::ComboKeyHash>& values_by_combo,
+    const ipc::ComboKey& combo,
+    const std::string& value_label
+) -> const TValue& {
+    const auto found = values_by_combo.find(combo);
+    if (found == values_by_combo.end()) {
+        throw std::runtime_error(value_label + " is missing for combo " + combo_to_string(combo));
+    }
+    return found->second;
+}
+
+void ensure_combo_coverage(
+    const std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash>& expected,
+    const std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash>& actual,
+    const std::string& expected_label,
+    const std::string& actual_label
+) {
+    for (const auto& entry : expected) {
+        const auto& combo = entry.first;
+        if (!actual.contains(combo)) {
+            throw std::runtime_error(
+                actual_label + " is missing combo " + combo_to_string(combo) +
+                " required by " + expected_label
+            );
+        }
+    }
+}
+
+[[nodiscard]] auto solve_osl_coefficients(
+    const ipc::ComboKey& combo,
+    const ChannelTrace& open_trace,
+    const ChannelTrace& short_trace,
+    const ChannelTrace& load_trace
+) -> S11CalibrationBundle::Coefficients {
+    validate_channel_trace_layout(open_trace, "S11 open calibration", combo);
+    validate_channel_trace_layout(short_trace, "S11 short calibration", combo);
+    validate_channel_trace_layout(load_trace, "S11 load calibration", combo);
+    ensure_frequency_axis_match(open_trace.frequency_hz, short_trace.frequency_hz, "S11 short calibration");
+    ensure_frequency_axis_match(open_trace.frequency_hz, load_trace.frequency_hz, "S11 load calibration");
+
+    S11CalibrationBundle::Coefficients coefficients{};
+    coefficients.frequency_hz = open_trace.frequency_hz;
+    coefficients.directivity.resize(open_trace.frequency_hz.size());
+    coefficients.source_match.resize(open_trace.frequency_hz.size());
+    coefficients.reflection_tracking.resize(open_trace.frequency_hz.size());
+
+    for (std::size_t index = 0; index < open_trace.frequency_hz.size(); ++index) {
+        const auto load = to_std_complex(load_trace.samples[index]);
+        const auto open_delta = to_std_complex(open_trace.samples[index]) - load;
+        const auto short_delta = to_std_complex(short_trace.samples[index]) - load;
+        const auto denominator = open_delta - short_delta;
+
+        std::complex<float> source_match = std::complex<float>(0.0F, 0.0F);
+        std::complex<float> reflection_tracking = std::complex<float>(1.0F, 0.0F);
+        if (std::norm(denominator) > kComplexMagnitudeSquaredEpsilon) {
+            source_match = (open_delta + short_delta) / denominator;
+            reflection_tracking = open_delta * (std::complex<float>(1.0F, 0.0F) - source_match);
+        }
+
+        coefficients.directivity[index] = load_trace.samples[index];
+        coefficients.source_match[index] = from_std_complex(source_match);
+        coefficients.reflection_tracking[index] = from_std_complex(reflection_tracking);
+    }
+
+    return coefficients;
+}
+
+}  // namespace
+
+void S21CalibrationBundle::load(const std::string& path) {
+    traces_by_combo_.clear();
+
+    if (path.empty()) {
+        throw std::runtime_error("S21 calibration bundle path must not be empty");
+    }
+
+    traces_by_combo_ = load_channel_traces(path, "S21 calibration", RawTraceChannel::S21);
+}
+
+auto S21CalibrationBundle::is_enabled() const noexcept -> bool {
+    return !traces_by_combo_.empty();
+}
+
+void S21CalibrationBundle::validate_combos(const std::vector<ipc::ComboKey>& combos) const {
+    validate_bundle_combos(traces_by_combo_, combos, "S21 calibration bundle");
+}
+
+auto S21CalibrationBundle::apply(
+    const ipc::ComboKey& combo,
+    std::span<const float> frequency_hz,
+    const std::vector<ipc::Complex32>& measured,
+    const CalibratorInterface& calibrator
+) const -> std::vector<ipc::Complex32> {
+    const auto& calibration_trace = resolve(combo);
+    ensure_frequency_axis_match(calibration_trace.frequency_hz, frequency_hz, "S21 calibration");
+    if (measured.size() != calibration_trace.samples.size()) {
+        throw std::runtime_error("S21 calibration vector size mismatch");
+    }
+    return calibrator.apply(measured, calibration_trace.samples);
+}
+
+auto S21CalibrationBundle::resolve(const ipc::ComboKey& combo) const -> const ChannelTrace& {
+    return resolve_required(traces_by_combo_, combo, "S21 calibration trace");
+}
+
+void S21ReferenceBundle::load(const std::string& path) {
+    traces_by_combo_.clear();
+
+    if (path.empty()) {
+        throw std::runtime_error("S21 reference bundle path must not be empty");
+    }
+
+    traces_by_combo_ = load_channel_traces(path, "S21 reference", RawTraceChannel::S21);
+}
+
+auto S21ReferenceBundle::is_enabled() const noexcept -> bool {
+    return !traces_by_combo_.empty();
+}
+
+void S21ReferenceBundle::validate_combos(const std::vector<ipc::ComboKey>& combos) const {
+    validate_bundle_combos(traces_by_combo_, combos, "S21 reference bundle");
+}
+
+auto S21ReferenceBundle::resolve(const ipc::ComboKey& combo) const -> const ChannelTrace& {
+    return resolve_required(traces_by_combo_, combo, "S21 reference trace");
+}
+
+void S11CalibrationBundle::load(
+    const std::string& open_path,
+    const std::string& short_path,
+    const std::string& load_path
+) {
+    coefficients_by_combo_.clear();
+
+    if (open_path.empty() && short_path.empty() && load_path.empty()) {
+        return;
+    }
+    if (open_path.empty() || short_path.empty() || load_path.empty()) {
+        throw std::runtime_error("S11 calibration requires open, short, and load raw bundle paths");
+    }
+
+    const auto open_traces = load_channel_traces(open_path, "S11 open calibration", RawTraceChannel::S11);
+    const auto short_traces = load_channel_traces(short_path, "S11 short calibration", RawTraceChannel::S11);
+    const auto load_traces = load_channel_traces(load_path, "S11 load calibration", RawTraceChannel::S11);
+
+    ensure_combo_coverage(open_traces, short_traces, "S11 open calibration", "S11 short calibration");
+    ensure_combo_coverage(open_traces, load_traces, "S11 open calibration", "S11 load calibration");
+    ensure_combo_coverage(short_traces, open_traces, "S11 short calibration", "S11 open calibration");
+    ensure_combo_coverage(load_traces, open_traces, "S11 load calibration", "S11 open calibration");
+
+    coefficients_by_combo_.reserve(open_traces.size());
+    for (const auto& [combo, open_trace] : open_traces) {
+        coefficients_by_combo_.insert_or_assign(
+            combo,
+            solve_osl_coefficients(combo, open_trace, short_traces.at(combo), load_traces.at(combo))
+        );
+    }
+}
+
+auto S11CalibrationBundle::is_enabled() const noexcept -> bool {
+    return !coefficients_by_combo_.empty();
+}
+
+void S11CalibrationBundle::validate_combos(const std::vector<ipc::ComboKey>& combos) const {
+    if (!is_enabled()) {
+        return;
+    }
+
+    for (const auto& combo : combos) {
+        if (!coefficients_by_combo_.contains(combo)) {
+            throw std::runtime_error("S11 calibration data is missing for combo " + combo_to_string(combo));
+        }
+    }
+}
+
+auto S11CalibrationBundle::apply(
+    const ipc::ComboKey& combo,
+    std::span<const float> frequency_hz,
+    const std::vector<ipc::Complex32>& measured
+) const -> std::vector<ipc::Complex32> {
+    if (!is_enabled()) {
+        return measured;
+    }
+    if (frequency_hz.size() != measured.size()) {
+        throw std::runtime_error("S11 calibration input frequency/sample size mismatch");
+    }
+
+    const auto& coefficients = resolve(combo);
+    ensure_frequency_axis_match(coefficients.frequency_hz, frequency_hz, "S11 calibration");
+    if (measured.size() != coefficients.directivity.size()) {
+        throw std::runtime_error("S11 calibration vector size mismatch");
+    }
+
+    std::vector<ipc::Complex32> corrected{};
+    corrected.reserve(measured.size());
+    for (std::size_t index = 0; index < measured.size(); ++index) {
+        const auto numerator = to_std_complex(measured[index]) - to_std_complex(coefficients.directivity[index]);
+        const auto denominator =
+            to_std_complex(coefficients.reflection_tracking[index]) +
+            (to_std_complex(coefficients.source_match[index]) * numerator);
+
+        if (std::norm(denominator) > kComplexMagnitudeSquaredEpsilon) {
+            corrected.push_back(from_std_complex(numerator / denominator));
+        } else {
+            corrected.push_back(from_std_complex(numerator));
+        }
+    }
+    return corrected;
+}
+
+auto S11CalibrationBundle::resolve(const ipc::ComboKey& combo) const -> const Coefficients& {
+    return resolve_required(coefficients_by_combo_, combo, "S11 calibration coefficients");
+}
+
+void S11ReferenceBundle::load(const std::string& path) {
+    traces_by_combo_.clear();
+
+    if (path.empty()) {
+        return;
+    }
+
+    traces_by_combo_ = load_channel_traces(path, "S11 reference", RawTraceChannel::S11);
+}
+
+auto S11ReferenceBundle::is_enabled() const noexcept -> bool {
+    return !traces_by_combo_.empty();
+}
+
+void S11ReferenceBundle::validate_combos(const std::vector<ipc::ComboKey>& combos) const {
+    validate_bundle_combos(traces_by_combo_, combos, "S11 reference bundle");
+}
+
+auto S11ReferenceBundle::resolve(const ipc::ComboKey& combo) const -> const ChannelTrace& {
+    return resolve_required(traces_by_combo_, combo, "S11 reference trace");
+}
+
+}  // namespace radar::preprocessing
diff --git a/data_acq_and_processing/preprocessing/calibration_master/src/through_calibrator.cpp b/data_acq_and_processing/preprocessing/calibration_master/src/through_calibrator.cpp
index 5aff8cd..a146397 100644
--- a/data_acq_and_processing/preprocessing/calibration_master/src/through_calibrator.cpp
+++ b/data_acq_and_processing/preprocessing/calibration_master/src/through_calibrator.cpp
@@ -69,7 +69,7 @@ class ThroughCalibrator final : public CalibratorInterface {
 
 }  // namespace
 
-auto make_through_calibrator() -> std::unique_ptr<CalibratorInterface> {
+auto make_s21_through_calibrator() -> std::unique_ptr<CalibratorInterface> {
     return std::make_unique<ThroughCalibrator>();
 }
 
diff --git a/data_acq_and_processing/preprocessing/data_preprocessor/src/data_preprocessor.cpp b/data_acq_and_processing/preprocessing/data_preprocessor/src/data_preprocessor.cpp
index 3729de4..9b2c05a 100644
--- a/data_acq_and_processing/preprocessing/data_preprocessor/src/data_preprocessor.cpp
+++ b/data_acq_and_processing/preprocessing/data_preprocessor/src/data_preprocessor.cpp
@@ -74,8 +74,8 @@ auto DataPreprocessor::preprocess_collection(const ipc::RawSweepCollection& raw_
 
     for (const auto& raw_trace : raw_collection.traces) {
         // Pipeline order is fixed: calibration first, then reference subtraction.
-        const auto calibrated = calibration_master_.apply(raw_trace);
-        const auto referenced = reference_master_.apply(calibrated);
+        const auto calibrated = calibration_master_.apply_to_trace(raw_trace);
+        const auto referenced = reference_master_.apply_to_trace(calibrated);
         preprocessed.traces.push_back(referenced);
     }
 
diff --git a/data_acq_and_processing/preprocessing/data_preprocessor/src/main.cpp b/data_acq_and_processing/preprocessing/data_preprocessor/src/main.cpp
index 48f671a..db4745a 100644
--- a/data_acq_and_processing/preprocessing/data_preprocessor/src/main.cpp
+++ b/data_acq_and_processing/preprocessing/data_preprocessor/src/main.cpp
@@ -62,12 +62,20 @@ int main(int argc, char** argv) {
         );
 
         // Load preprocessing assets once before entering run loop.
-        radar::preprocessing::CalibrationMaster calibration_master(radar::preprocessing::make_through_calibrator());
-        calibration_master.load_bundle(config.preprocess.calibration_bundle_path);
+        radar::preprocessing::CalibrationMaster calibration_master(
+            radar::preprocessing::make_s21_through_calibrator()
+        );
+        calibration_master.load_s21_calibration_bundle(config.preprocess.s21_calibration_bundle_path);
+        calibration_master.load_s11_calibration_bundle(
+            config.preprocess.s11_open_calibration_bundle_path,
+            config.preprocess.s11_short_calibration_bundle_path,
+            config.preprocess.s11_load_calibration_bundle_path
+        );
 
         radar::preprocessing::ReferenceMaster reference_master;
-        reference_master.load_bundle(config.preprocess.reference_bundle_path);
-        reference_master.prepare_calibrated(calibration_master);
+        reference_master.load_s21_reference_bundle(config.preprocess.s21_reference_bundle_path);
+        reference_master.load_s11_reference_bundle(config.preprocess.s11_reference_bundle_path);
+        reference_master.prepare_calibrated(calibration_master, config.run_combos);
 
         radar::preprocessing::DataPreprocessor preprocessor(
             config,
diff --git a/data_acq_and_processing/preprocessing/reference_master/include/reference_master.hpp b/data_acq_and_processing/preprocessing/reference_master/include/reference_master.hpp
index cb23ca1..2d3ae70 100644
--- a/data_acq_and_processing/preprocessing/reference_master/include/reference_master.hpp
+++ b/data_acq_and_processing/preprocessing/reference_master/include/reference_master.hpp
@@ -1,9 +1,11 @@
 #pragma once
 
+#include <span>
 #include <string>
 #include <unordered_map>
 #include <vector>
 
+#include "channel_bundle_support.hpp"
 #include "shared_types.hpp"
 
 namespace radar::preprocessing {
@@ -12,19 +14,33 @@ class CalibrationMaster;
 
 class ReferenceMaster {
   public:
-    // Loads a serialized raw sweep bundle with one reference trace per combo.
-    void load_bundle(const std::string& path);
+    // Loads a serialized raw sweep bundle with one S21 reference trace per combo.
+    void load_s21_reference_bundle(const std::string& path);
+    // Loads optional raw S11 reference data.
+    void load_s11_reference_bundle(const std::string& path);
     // Builds calibrated references in memory using currently loaded raw references.
-    // Must be called after load_bundle() and after calibration standards are loaded.
-    void prepare_calibrated(const CalibrationMaster& calibration_master);
+    // Must be called after load_s21_reference_bundle() and after calibration standards are loaded.
+    void prepare_calibrated(const CalibrationMaster& calibration_master, const std::vector<ipc::ComboKey>& combos);
     // Ensures all runtime combos are present in loaded references.
     void validate_combos(const std::vector<ipc::ComboKey>& combos) const;
-    // Subtracts per-combo reference trace from calibrated trace.
-    [[nodiscard]] auto apply(const ipc::SweepTraceBlock& calibrated_trace) const -> ipc::SweepTraceBlock;
+    // Subtracts both channel references from one calibrated trace.
+    [[nodiscard]] auto apply_to_trace(const ipc::SweepTraceBlock& calibrated_trace) const -> ipc::SweepTraceBlock;
+    [[nodiscard]] auto apply_s21(
+        const ipc::ComboKey& combo,
+        std::span<const float> frequency_hz,
+        const std::vector<ipc::Complex32>& calibrated_s21
+    ) const -> std::vector<ipc::Complex32>;
+    [[nodiscard]] auto apply_s11(
+        const ipc::ComboKey& combo,
+        std::span<const float> frequency_hz,
+        const std::vector<ipc::Complex32>& calibrated_s11
+    ) const -> std::vector<ipc::Complex32>;
 
   private:
-    std::unordered_map<ipc::ComboKey, ipc::SweepTraceBlock, ipc::ComboKeyHash> raw_references_by_combo_{};
-    std::unordered_map<ipc::ComboKey, ipc::SweepTraceBlock, ipc::ComboKeyHash> calibrated_references_by_combo_{};
+    S21ReferenceBundle raw_s21_reference_bundle_{};
+    std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash> calibrated_s21_references_by_combo_{};
+    S11ReferenceBundle raw_s11_reference_bundle_{};
+    std::unordered_map<ipc::ComboKey, ChannelTrace, ipc::ComboKeyHash> calibrated_s11_references_by_combo_{};
 };
 
 }  // namespace radar::preprocessing
diff --git a/data_acq_and_processing/preprocessing/reference_master/src/reference_master.cpp b/data_acq_and_processing/preprocessing/reference_master/src/reference_master.cpp
index 53d487d..afea007 100644
--- a/data_acq_and_processing/preprocessing/reference_master/src/reference_master.cpp
+++ b/data_acq_and_processing/preprocessing/reference_master/src/reference_master.cpp
@@ -1,8 +1,8 @@
 #include "reference_master.hpp"
 
-#include <cstdint>
-#include <fstream>
-#include <iterator>
+#include <algorithm>
+#include <cmath>
+#include <span>
 #include <stdexcept>
 #include <string>
 #include <utility>
@@ -15,132 +15,195 @@
 namespace radar::preprocessing {
 namespace {
 
+constexpr float kFrequencyRelativeTolerance = 1e-5F;
+constexpr float kFrequencyAbsoluteTolerance = 1e-3F;
+
 [[nodiscard]] auto combo_to_string(const ipc::ComboKey& combo) -> std::string {
     return "input=" + std::to_string(combo.input_pos) + " output=" + std::to_string(combo.output_pos);
 }
 
-[[nodiscard]] auto read_binary_file(const std::string& path, const std::string& bundle_label)
-    -> std::vector<std::uint8_t> {
-    std::ifstream stream(path, std::ios::binary);
-    if (!stream.is_open()) {
-        throw std::runtime_error("Failed to open " + bundle_label + " bundle: " + path);
+void validate_channel_trace_layout(
+    const ChannelTrace& trace,
+    const std::string& trace_label,
+    const ipc::ComboKey& combo
+) {
+    if (trace.frequency_hz.size() != trace.samples.size()) {
+        throw std::runtime_error(
+            trace_label + " frequency/channel vector size mismatch for combo " + combo_to_string(combo)
+        );
     }
-
-    return std::vector<std::uint8_t>(std::istreambuf_iterator<char>(stream), std::istreambuf_iterator<char>());
 }
 
-void validate_trace_layout(const ipc::SweepTraceBlock& trace, const std::string& trace_label) {
-    if (trace.frequency_hz.size() != trace.s21.size()) {
-        throw std::runtime_error(
-            trace_label + " frequency/complex vector size mismatch for combo " + combo_to_string(trace.combo)
-        );
+[[nodiscard]] auto frequency_axes_match(std::span<const float> left, std::span<const float> right) -> bool {
+    if (left.size() != right.size()) {
+        return false;
     }
-    if (trace.frequency_hz.size() != trace.s11.size()) {
-        throw std::runtime_error(
-            trace_label + " frequency/S11 vector size mismatch for combo " + combo_to_string(trace.combo)
-        );
+
+    for (std::size_t index = 0; index < left.size(); ++index) {
+        const auto delta = std::fabs(left[index] - right[index]);
+        const auto scale = std::max(std::fabs(left[index]), std::fabs(right[index]));
+        const auto tolerance = std::max(kFrequencyAbsoluteTolerance, scale * kFrequencyRelativeTolerance);
+        if (delta > tolerance) {
+            return false;
+        }
     }
+    return true;
 }
 
 }  // namespace
 
-void ReferenceMaster::load_bundle(const std::string& path) {
-    if (path.empty()) {
-        throw std::runtime_error("Reference bundle path must not be empty");
-    }
-
-    const auto bytes = read_binary_file(path, "reference");
-    if (bytes.empty()) {
-        throw std::runtime_error("Reference bundle is empty: " + path);
-    }
-
-    const auto collection = ipc::deserialize_raw_collection(bytes);
-    raw_references_by_combo_.clear();
-    raw_references_by_combo_.reserve(collection.traces.size());
-    calibrated_references_by_combo_.clear();
-    for (const auto& trace : collection.traces) {
-        validate_trace_layout(trace, "Reference trace");
-        raw_references_by_combo_.insert_or_assign(trace.combo, trace);
-    }
-
-    if (raw_references_by_combo_.empty()) {
-        throw std::runtime_error("Reference bundle does not contain traces: " + path);
-    }
+void ReferenceMaster::load_s21_reference_bundle(const std::string& path) {
+    raw_s21_reference_bundle_.load(path);
+    calibrated_s21_references_by_combo_.clear();
 }
 
-void ReferenceMaster::prepare_calibrated(const CalibrationMaster& calibration_master) {
-    if (raw_references_by_combo_.empty()) {
+void ReferenceMaster::load_s11_reference_bundle(const std::string& path) {
+    raw_s11_reference_bundle_.load(path);
+    calibrated_s11_references_by_combo_.clear();
+}
+
+void ReferenceMaster::prepare_calibrated(
+    const CalibrationMaster& calibration_master,
+    const std::vector<ipc::ComboKey>& combos
+) {
+    if (!raw_s21_reference_bundle_.is_enabled()) {
         throw std::runtime_error("Reference bundle must be loaded before prepare_calibrated()");
     }
 
-    calibrated_references_by_combo_.clear();
-    calibrated_references_by_combo_.reserve(raw_references_by_combo_.size());
-    for (const auto& [combo, raw_reference] : raw_references_by_combo_) {
-        auto calibrated = calibration_master.apply(raw_reference);
-        calibrated.combo = combo;
-        calibrated_references_by_combo_.insert_or_assign(combo, std::move(calibrated));
+    calibrated_s21_references_by_combo_.clear();
+    calibrated_s21_references_by_combo_.reserve(combos.size());
+    for (const auto& combo : combos) {
+        const auto& raw_reference = raw_s21_reference_bundle_.resolve(combo);
+        ChannelTrace calibrated{};
+        calibrated.frequency_hz = raw_reference.frequency_hz;
+        calibrated.samples = calibration_master.apply_s21(combo, raw_reference.frequency_hz, raw_reference.samples);
+        calibrated_s21_references_by_combo_.insert_or_assign(combo, std::move(calibrated));
+    }
+
+    calibrated_s11_references_by_combo_.clear();
+    if (!raw_s11_reference_bundle_.is_enabled()) {
+        return;
+    }
+    if (!calibration_master.has_s11_calibration()) {
+        throw std::runtime_error("S11 reference bundle requires S11 calibration bundle");
+    }
+
+    calibrated_s11_references_by_combo_.reserve(combos.size());
+    for (const auto& combo : combos) {
+        const auto& raw_reference = raw_s11_reference_bundle_.resolve(combo);
+        ChannelTrace calibrated{};
+        calibrated.frequency_hz = raw_reference.frequency_hz;
+        calibrated.samples = calibration_master.apply_s11(combo, raw_reference.frequency_hz, raw_reference.samples);
+        calibrated_s11_references_by_combo_.insert_or_assign(combo, std::move(calibrated));
     }
 }
 
 void ReferenceMaster::validate_combos(const std::vector<ipc::ComboKey>& combos) const {
-    if (calibrated_references_by_combo_.empty()) {
+    if (calibrated_s21_references_by_combo_.empty()) {
         throw std::runtime_error(
             "Calibrated references are not prepared. Call ReferenceMaster::prepare_calibrated() at startup."
         );
     }
 
+    raw_s21_reference_bundle_.validate_combos(combos);
     for (const auto& combo : combos) {
-        if (!raw_references_by_combo_.contains(combo)) {
-            throw std::runtime_error("Raw reference data is missing for combo " + combo_to_string(combo));
+        if (!calibrated_s21_references_by_combo_.contains(combo)) {
+            throw std::runtime_error("Calibrated S21 reference data is missing for combo " + combo_to_string(combo));
         }
-        if (!calibrated_references_by_combo_.contains(combo)) {
-            throw std::runtime_error("Calibrated reference data is missing for combo " + combo_to_string(combo));
+    }
+
+    raw_s11_reference_bundle_.validate_combos(combos);
+    if (!raw_s11_reference_bundle_.is_enabled()) {
+        return;
+    }
+    if (calibrated_s11_references_by_combo_.empty()) {
+        throw std::runtime_error("Calibrated S11 references are not prepared");
+    }
+    for (const auto& combo : combos) {
+        if (!calibrated_s11_references_by_combo_.contains(combo)) {
+            throw std::runtime_error("Calibrated S11 reference data is missing for combo " + combo_to_string(combo));
         }
     }
 }
 
-auto ReferenceMaster::apply(const ipc::SweepTraceBlock& calibrated_trace) const -> ipc::SweepTraceBlock {
-    validate_trace_layout(calibrated_trace, "Calibrated trace");
-
-    const auto found = calibrated_references_by_combo_.find(calibrated_trace.combo);
-    if (found == calibrated_references_by_combo_.end()) {
-        throw std::runtime_error(
-            "Calibrated reference trace is missing for combo " + combo_to_string(calibrated_trace.combo)
-        );
-    }
-
-    const auto& reference = found->second;
-    validate_trace_layout(reference, "Calibrated reference trace");
-    if (calibrated_trace.s21.size() != reference.s21.size()) {
-        throw std::runtime_error(
-            "Reference point count mismatch for combo " + combo_to_string(calibrated_trace.combo)
-        );
-    }
-
+auto ReferenceMaster::apply_to_trace(const ipc::SweepTraceBlock& calibrated_trace) const -> ipc::SweepTraceBlock {
     ipc::SweepTraceBlock output{};
     output.combo = calibrated_trace.combo;
     output.frequency_hz = calibrated_trace.frequency_hz;
-    output.s11 = calibrated_trace.s11;
-    output.s21.resize(calibrated_trace.s21.size());
+    output.s21 = apply_s21(calibrated_trace.combo, calibrated_trace.frequency_hz, calibrated_trace.s21);
+    output.s11 = apply_s11(calibrated_trace.combo, calibrated_trace.frequency_hz, calibrated_trace.s11);
+    return output;
+}
+
+auto ReferenceMaster::apply_s21(
+    const ipc::ComboKey& combo,
+    std::span<const float> frequency_hz,
+    const std::vector<ipc::Complex32>& calibrated_s21
+) const -> std::vector<ipc::Complex32> {
+    const auto found = calibrated_s21_references_by_combo_.find(combo);
+    if (found == calibrated_s21_references_by_combo_.end()) {
+        throw std::runtime_error("Calibrated S21 reference is missing for combo " + combo_to_string(combo));
+    }
+
+    const auto& reference = found->second;
+    validate_channel_trace_layout(reference, "Calibrated S21 reference", combo);
+    if (calibrated_s21.size() != reference.samples.size()) {
+        throw std::runtime_error("S21 reference point count mismatch for combo " + combo_to_string(combo));
+    }
+    if (!frequency_axes_match(frequency_hz, reference.frequency_hz)) {
+        throw std::runtime_error("S21 reference frequency axis mismatch for combo " + combo_to_string(combo));
+    }
+
+    std::vector<ipc::Complex32> output(calibrated_s21.size());
 
     static_assert(sizeof(ipc::Complex32) == sizeof(float) * 2U, "Complex32 layout must be two contiguous floats");
     using InterleavedComplexView = Eigen::Matrix<float, Eigen::Dynamic, 2, Eigen::RowMajor>;
-    const auto point_count = static_cast<Eigen::Index>(calibrated_trace.s21.size());
+    const auto point_count = static_cast<Eigen::Index>(calibrated_s21.size());
 
     Eigen::Map<const InterleavedComplexView> calibrated_view(
-        reinterpret_cast<const float*>(calibrated_trace.s21.data()),
+        reinterpret_cast<const float*>(calibrated_s21.data()),
         point_count,
         2
     );
     Eigen::Map<const InterleavedComplexView> reference_view(
-        reinterpret_cast<const float*>(reference.s21.data()),
+        reinterpret_cast<const float*>(reference.samples.data()),
         point_count,
         2
     );
-    Eigen::Map<InterleavedComplexView> output_view(reinterpret_cast<float*>(output.s21.data()), point_count, 2);
+    Eigen::Map<InterleavedComplexView> output_view(reinterpret_cast<float*>(output.data()), point_count, 2);
 
     output_view = calibrated_view - reference_view;
+    return output;
+}
 
+auto ReferenceMaster::apply_s11(
+    const ipc::ComboKey& combo,
+    std::span<const float> frequency_hz,
+    const std::vector<ipc::Complex32>& calibrated_s11
+) const -> std::vector<ipc::Complex32> {
+    if (!raw_s11_reference_bundle_.is_enabled()) {
+        return calibrated_s11;
+    }
+
+    const auto found = calibrated_s11_references_by_combo_.find(combo);
+    if (found == calibrated_s11_references_by_combo_.end()) {
+        throw std::runtime_error("Calibrated S11 reference is missing for combo " + combo_to_string(combo));
+    }
+
+    const auto& reference = found->second;
+    validate_channel_trace_layout(reference, "Calibrated S11 reference", combo);
+    if (calibrated_s11.size() != reference.samples.size()) {
+        throw std::runtime_error("S11 reference point count mismatch for combo " + combo_to_string(combo));
+    }
+    if (!frequency_axes_match(frequency_hz, reference.frequency_hz)) {
+        throw std::runtime_error("S11 reference frequency axis mismatch for combo " + combo_to_string(combo));
+    }
+
+    std::vector<ipc::Complex32> output(calibrated_s11.size());
+    for (std::size_t index = 0; index < calibrated_s11.size(); ++index) {
+        output[index].re = calibrated_s11[index].re - reference.samples[index].re;
+        output[index].im = calibrated_s11[index].im - reference.samples[index].im;
+    }
     return output;
 }
 
diff --git a/data_acq_and_processing/preprocessing/testdata/s11_load_calibration_bundle.bin b/data_acq_and_processing/preprocessing/testdata/s11_load_calibration_bundle.bin
new file mode 100644
index 0000000..6cee6b2
Binary files /dev/null and b/data_acq_and_processing/preprocessing/testdata/s11_load_calibration_bundle.bin differ
diff --git a/data_acq_and_processing/preprocessing/testdata/s11_open_calibration_bundle.bin b/data_acq_and_processing/preprocessing/testdata/s11_open_calibration_bundle.bin
new file mode 100644
index 0000000..283d22a
Binary files /dev/null and b/data_acq_and_processing/preprocessing/testdata/s11_open_calibration_bundle.bin differ
diff --git a/data_acq_and_processing/preprocessing/testdata/s11_reference_bundle.bin b/data_acq_and_processing/preprocessing/testdata/s11_reference_bundle.bin
new file mode 100644
index 0000000..1d64a3b
Binary files /dev/null and b/data_acq_and_processing/preprocessing/testdata/s11_reference_bundle.bin differ
diff --git a/data_acq_and_processing/preprocessing/testdata/s11_short_calibration_bundle.bin b/data_acq_and_processing/preprocessing/testdata/s11_short_calibration_bundle.bin
new file mode 100644
index 0000000..8b7e104
Binary files /dev/null and b/data_acq_and_processing/preprocessing/testdata/s11_short_calibration_bundle.bin differ
diff --git a/data_acq_and_processing/processing/data_processor/include/processing_live_config.hpp b/data_acq_and_processing/processing/data_processor/include/processing_live_config.hpp
index d5da5a3..935fc26 100644
--- a/data_acq_and_processing/processing/data_processor/include/processing_live_config.hpp
+++ b/data_acq_and_processing/processing/data_processor/include/processing_live_config.hpp
@@ -18,6 +18,7 @@ struct ProcessingLiveConfig {
     std::string processor_mode = "pass_through";
     float gain_db = 0.0F;
     float phase_deg = 0.0F;
+    std::string pass_through_channel = "s21";
     bool pass_through_fixed_y_enabled = false;
     float pass_through_y_min_db = -100.0F;
     float pass_through_y_max_db = 0.0F;
diff --git a/data_acq_and_processing/processing/data_processor/src/processing_live_config.cpp b/data_acq_and_processing/processing/data_processor/src/processing_live_config.cpp
index e74e8d0..3d1989b 100644
--- a/data_acq_and_processing/processing/data_processor/src/processing_live_config.cpp
+++ b/data_acq_and_processing/processing/data_processor/src/processing_live_config.cpp
@@ -30,6 +30,13 @@ using Json = nlohmann::json;
     throw std::runtime_error("processing.history_command must be one of: none, remove_last, clear_all");
 }
 
+[[nodiscard]] auto parse_pass_through_channel(const std::string& value) -> std::string {
+    if (value == "s21" || value == "s11") {
+        return value;
+    }
+    throw std::runtime_error("processing.pass_through_channel must be one of: s21, s11");
+}
+
 [[nodiscard]] auto parse_u64_number(const Json& value, const std::string& field_name) -> std::uint64_t {
     if (!value.is_number()) {
         throw std::runtime_error(field_name + " must be number");
@@ -101,6 +108,12 @@ using Json = nlohmann::json;
         }
         config.phase_deg = static_cast<float>(found->get<double>());
     }
+    if (const auto found = root.find("pass_through_channel"); found != root.end()) {
+        if (!found->is_string()) {
+            throw std::runtime_error("processing.pass_through_channel must be string");
+        }
+        config.pass_through_channel = parse_pass_through_channel(found->get<std::string>());
+    }
     if (const auto found = root.find("pass_through_fixed_y_enabled"); found != root.end()) {
         if (!found->is_boolean()) {
             throw std::runtime_error("processing.pass_through_fixed_y_enabled must be bool");
diff --git a/data_acq_and_processing/processing/processors/src/passthrough_processor.cpp b/data_acq_and_processing/processing/processors/src/passthrough_processor.cpp
index d55244a..247737a 100644
--- a/data_acq_and_processing/processing/processors/src/passthrough_processor.cpp
+++ b/data_acq_and_processing/processing/processors/src/passthrough_processor.cpp
@@ -29,7 +29,11 @@ auto PassThroughProcessor::process_collection(
         payload.processing_name = name();
         payload.kind = ipc::ResultKind::TraceComplex;
         payload.frequency_hz = trace.frequency_hz;
-        payload.trace = trace.s21;
+        if (live_config.pass_through_channel == "s11") {
+            payload.trace = trace.s11;
+        } else {
+            payload.trace = trace.s21;
+        }
 
         const float linear_gain = std::pow(10.0F, live_config.gain_db / 20.0F);
         const float phase_rad = live_config.phase_deg * (kPi / 180.0F);
diff --git a/python_app/gui/app_window.py b/python_app/gui/app_window.py
index c4a188b..af6b1b9 100644
--- a/python_app/gui/app_window.py
+++ b/python_app/gui/app_window.py
@@ -78,8 +78,8 @@ class AppWindow(
     def _init_preprocess_state(self) -> None:
         """Initialize preprocessing dialog and selected set names."""
         self._preprocess_dialog: PreprocessDialog | None = None
-        self._selected_calibration_set = str(self._defaults_config.preprocess.calibration_set)
-        self._selected_reference_set = str(self._defaults_config.preprocess.reference_set)
+        self._selected_s21_calibration_set = str(self._defaults_config.preprocess.s21_calibration_set)
+        self._selected_s21_reference_set = str(self._defaults_config.preprocess.s21_reference_set)
 
     def _init_capture_state(self) -> None:
         """Initialize one-shot capture and sequence-control flags."""
diff --git a/python_app/gui/controllers/app_window_config_mixin.py b/python_app/gui/controllers/app_window_config_mixin.py
index bee62aa..7389e17 100644
--- a/python_app/gui/controllers/app_window_config_mixin.py
+++ b/python_app/gui/controllers/app_window_config_mixin.py
@@ -118,8 +118,8 @@ class AppWindowConfigMixin:
         if self._switches_are_effectively_static(config):
             config.combos = [ComboModel(input=0, output=0)]
 
-        config.preprocess.calibration_set = self._selected_calibration_set
-        config.preprocess.reference_set = self._selected_reference_set
+        config.preprocess.s21_calibration_set = self._selected_s21_calibration_set
+        config.preprocess.s21_reference_set = self._selected_s21_reference_set
         config.gpr.mode = self._gpr_config_mode.currentText()
         config.gpr.relative_permittivity = float(self._gpr_relative_permittivity.value())
         config.gpr.tx_geometry = self._parse_gpr_tx_geometry_text(self._gpr_tx_geometry_input.toPlainText())
@@ -153,6 +153,7 @@ class AppWindowConfigMixin:
             processor_mode=self._processing_mode.currentText(),
             gain_db=float(self._processing_gain_db.value()),
             phase_deg=float(self._processing_phase_deg.value()),
+            pass_through_channel=self._pass_through_channel.currentText(),
             pass_through_fixed_y_enabled=bool(self._pass_through_fixed_y_enabled.isChecked()),
             pass_through_y_min_db=min(y_min_db, y_max_db),
             pass_through_y_max_db=max(y_min_db, y_max_db),
diff --git a/python_app/gui/controllers/app_window_pipeline_mixin.py b/python_app/gui/controllers/app_window_pipeline_mixin.py
index 3628249..9c3550d 100644
--- a/python_app/gui/controllers/app_window_pipeline_mixin.py
+++ b/python_app/gui/controllers/app_window_pipeline_mixin.py
@@ -38,28 +38,28 @@ class AppWindowPipelineMixin:
             run_signature = self._build_run_history_signature(config)
             radar_key = self._radar_key(config)
 
-            if not config.preprocess.calibration_set or not config.preprocess.reference_set:
+            if not config.preprocess.s21_calibration_set or not config.preprocess.s21_reference_set:
                 raise RuntimeError("Select calibration and reference sets in Preprocessing Panel before Start")
 
             combo_keys = [ComboKey(input_pos=combo.input, output_pos=combo.output) for combo in config.combos]
 
             if not self._store.has_combo_coverage(
-                "calibration", radar_key, config.preprocess.calibration_set, combo_keys
+                "calibration", radar_key, config.preprocess.s21_calibration_set, combo_keys
             ):
                 raise RuntimeError("Selected calibration set does not cover requested run combos")
             if not self._store.has_combo_coverage(
-                "reference", radar_key, config.preprocess.reference_set, combo_keys
+                "reference", radar_key, config.preprocess.s21_reference_set, combo_keys
             ):
                 raise RuntimeError("Selected reference set does not cover requested run combos")
 
-            calibration_bundle, reference_bundle = self._config_writer.prepare_bundles(
+            calibration_bundle, reference_bundle = self._config_writer.prepare_s21_bundles(
                 self._store,
                 radar_key,
-                config.preprocess.calibration_set,
-                config.preprocess.reference_set,
+                config.preprocess.s21_calibration_set,
+                config.preprocess.s21_reference_set,
             )
-            config.preprocess.calibration_bundle_path = str(calibration_bundle)
-            config.preprocess.reference_bundle_path = str(reference_bundle)
+            config.preprocess.s21_calibration_bundle_path = str(calibration_bundle)
+            config.preprocess.s21_reference_bundle_path = str(reference_bundle)
             config.runtime.continuous = not single_capture
 
             if not single_capture:
diff --git a/python_app/gui/controllers/app_window_plot_mixin.py b/python_app/gui/controllers/app_window_plot_mixin.py
index 7b85246..0aa0fe8 100644
--- a/python_app/gui/controllers/app_window_plot_mixin.py
+++ b/python_app/gui/controllers/app_window_plot_mixin.py
@@ -106,6 +106,7 @@ class AppWindowPlotMixin:
         show_phase = self._show_phase_curves()
         magnitude_plot = self._trace_magnitude_plot
         phase_plot = self._trace_phase_plot
+        pass_through_channel = self._pass_through_channel.currentText().upper()
 
         magnitude_plot.setVisible(show_magnitude)
         phase_plot.setVisible(show_phase)
@@ -119,6 +120,7 @@ class AppWindowPlotMixin:
             mag_item.showAxis("left", show=True)
             mag_item.showAxis("bottom", show=not show_phase)
             magnitude_plot.setLabel("left", "Magnitude", units="dB")
+            magnitude_plot.setTitle(f"Pass-Through {pass_through_channel}")
             if not show_phase:
                 magnitude_plot.setLabel("bottom", "Frequency", units="Hz")
 
@@ -130,6 +132,7 @@ class AppWindowPlotMixin:
             phase_item.showAxis("bottom", show=True)
             phase_plot.setLabel("left", "Phase", units="deg")
             phase_plot.setLabel("bottom", "Frequency", units="Hz")
+            phase_plot.setTitle(f"Pass-Through {pass_through_channel}")
 
         palette = [
             "#4cc9f0",
diff --git a/python_app/gui/controllers/app_window_preprocess_mixin.py b/python_app/gui/controllers/app_window_preprocess_mixin.py
index 6fa05d1..946d074 100644
--- a/python_app/gui/controllers/app_window_preprocess_mixin.py
+++ b/python_app/gui/controllers/app_window_preprocess_mixin.py
@@ -40,14 +40,14 @@ class AppWindowPreprocessMixin:
 
     def _on_preprocess_selection_changed(self, calibration_set: str, reference_set: str) -> None:
         """Persist selected preprocessing set names from dialog."""
-        self._selected_calibration_set = calibration_set.strip()
-        self._selected_reference_set = reference_set.strip()
+        self._selected_s21_calibration_set = calibration_set.strip()
+        self._selected_s21_reference_set = reference_set.strip()
         self._refresh_preprocess_summary_labels()
 
     def _refresh_preprocess_summary_labels(self) -> None:
         """Update compact summary labels in the main window."""
-        self._selected_calibration_label.setText(self._selected_calibration_set or "<not selected>")
-        self._selected_reference_label.setText(self._selected_reference_set or "<not selected>")
+        self._selected_calibration_label.setText(self._selected_s21_calibration_set or "<not selected>")
+        self._selected_reference_label.setText(self._selected_s21_reference_set or "<not selected>")
 
     def _refresh_sets(self) -> None:
         """Refresh calibration/reference set lists for current radar key."""
@@ -60,12 +60,12 @@ class AppWindowPreprocessMixin:
         dialog.set_calibration_sets(calibration_sets)
         dialog.set_reference_sets(reference_sets)
 
-        if self._selected_calibration_set not in calibration_sets:
-            self._selected_calibration_set = calibration_sets[0] if calibration_sets else ""
-        if self._selected_reference_set not in reference_sets:
-            self._selected_reference_set = reference_sets[0] if reference_sets else ""
+        if self._selected_s21_calibration_set not in calibration_sets:
+            self._selected_s21_calibration_set = calibration_sets[0] if calibration_sets else ""
+        if self._selected_s21_reference_set not in reference_sets:
+            self._selected_s21_reference_set = reference_sets[0] if reference_sets else ""
 
-        dialog.set_selected_sets(self._selected_calibration_set, self._selected_reference_set)
+        dialog.set_selected_sets(self._selected_s21_calibration_set, self._selected_s21_reference_set)
         self._refresh_preprocess_summary_labels()
         self._log(f"Set lists refreshed for key={radar_key}")
 
@@ -147,9 +147,9 @@ class AppWindowPreprocessMixin:
                 self._cleanup_capture_session()
 
                 if kind == "calibration":
-                    self._selected_calibration_set = set_name
+                    self._selected_s21_calibration_set = set_name
                 else:
-                    self._selected_reference_set = set_name
+                    self._selected_s21_reference_set = set_name
 
                 self._refresh_sets()
                 dialog.set_status(f"{kind.title()} set saved: {set_name} ({len(collection.traces)} traces)")
diff --git a/python_app/gui/controllers/app_window_ui_mixin.py b/python_app/gui/controllers/app_window_ui_mixin.py
index f500fa3..f184e08 100644
--- a/python_app/gui/controllers/app_window_ui_mixin.py
+++ b/python_app/gui/controllers/app_window_ui_mixin.py
@@ -79,7 +79,7 @@ class AppWindowUiMixin:
 
         # Default view on startup is pass-through traces.
         self._plot_stack.setCurrentWidget(self._trace_plots_container)
-        root_layout.addWidget(self._plot_stack, stretch=11)
+        root_layout.addWidget(self._plot_stack, stretch=12)
 
     def _build_bscan_plot_page(self) -> None:
         """Create B-scan page in plot stack."""
@@ -141,7 +141,7 @@ class AppWindowUiMixin:
     def _build_settings_panel(self, root_layout: QHBoxLayout, root: QWidget) -> None:
         """Build right settings panel with controls, status labels, and log."""
         self._settings_panel = QWidget(root)
-        self._settings_panel.setMinimumWidth(659)
+        self._settings_panel.setMinimumWidth(530)
         right_layout = QVBoxLayout(self._settings_panel)
         right_layout.setContentsMargins(0, 0, 0, 0)
         right_layout.setSpacing(10)
@@ -163,7 +163,7 @@ class AppWindowUiMixin:
         right_layout.addWidget(self._history_label)
 
         right_layout.addWidget(self._log_box, stretch=0)
-        root_layout.addWidget(self._settings_panel, stretch=8)
+        root_layout.addWidget(self._settings_panel, stretch=6)
 
     def _build_settings_scroll(self) -> QScrollArea:
         """Build scroll area with all control groups in display order."""
diff --git a/python_app/gui/controllers/sections/data_actions_section.py b/python_app/gui/controllers/sections/data_actions_section.py
index e1c5b7d..8a68f69 100644
--- a/python_app/gui/controllers/sections/data_actions_section.py
+++ b/python_app/gui/controllers/sections/data_actions_section.py
@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+from PyQt6.QtCore import Qt
 from PyQt6.QtWidgets import QGroupBox, QHBoxLayout, QLabel, QLineEdit, QPushButton, QSpinBox, QVBoxLayout
 
 
@@ -11,16 +12,13 @@ def build_data_actions_group(owner) -> QGroupBox:
     layout = QVBoxLayout(group)
     layout.setSpacing(8)
 
-    save_row = QHBoxLayout()
-    save_row.setSpacing(8)
-
-    save_button = QPushButton("Save Numpy Snapshot")
+    save_button = QPushButton("Save Snapshot")
     save_button.clicked.connect(owner._save_snapshot)
-    save_vna_json_button = QPushButton("Save VNA History JSON")
+    save_vna_json_button = QPushButton("Save VNA JSON")
     save_vna_json_button.clicked.connect(owner._save_vna_history_json)
-    remove_last_button = QPushButton("Remove Last Runtime Measurement")
+    remove_last_button = QPushButton("Remove Last Measurement")
     remove_last_button.clicked.connect(owner._remove_last_runtime_history)
-    clear_history_button = QPushButton("Clear ALL Runtime History")
+    clear_history_button = QPushButton("Clear Runtime History")
     clear_history_button.clicked.connect(owner._clear_all_runtime_history)
     owner._save_count = QSpinBox()
     owner._save_count.setMinimum(1)
@@ -35,14 +33,20 @@ def build_data_actions_group(owner) -> QGroupBox:
     owner._vna_json_output_index.setMaximum(65_535)
     owner._vna_json_output_index.setValue(0)
 
-    save_row.addWidget(save_button)
-    save_row.addWidget(save_vna_json_button)
-    save_row.addWidget(remove_last_button)
-    save_row.addWidget(clear_history_button)
-    save_row.addWidget(QLabel("Last N"))
-    save_row.addWidget(owner._save_count)
-    save_row.addStretch(1)
-    layout.addLayout(save_row)
+    button_column = QVBoxLayout()
+    button_column.setSpacing(8)
+    button_column.addWidget(save_button, alignment=Qt.AlignmentFlag.AlignLeft)
+    button_column.addWidget(save_vna_json_button, alignment=Qt.AlignmentFlag.AlignLeft)
+    button_column.addWidget(remove_last_button, alignment=Qt.AlignmentFlag.AlignLeft)
+    button_column.addWidget(clear_history_button, alignment=Qt.AlignmentFlag.AlignLeft)
+    layout.addLayout(button_column)
+
+    count_row = QHBoxLayout()
+    count_row.setSpacing(8)
+    count_row.addWidget(QLabel("Last N"))
+    count_row.addWidget(owner._save_count)
+    count_row.addStretch(1)
+    layout.addLayout(count_row)
 
     json_row = QHBoxLayout()
     json_row.setSpacing(8)
diff --git a/python_app/gui/controllers/sections/hardware_actions_section.py b/python_app/gui/controllers/sections/hardware_actions_section.py
index 70d5c87..db9b9ac 100644
--- a/python_app/gui/controllers/sections/hardware_actions_section.py
+++ b/python_app/gui/controllers/sections/hardware_actions_section.py
@@ -2,24 +2,25 @@
 
 from __future__ import annotations
 
-from PyQt6.QtWidgets import QGroupBox, QHBoxLayout, QPushButton
+from PyQt6.QtCore import Qt
+from PyQt6.QtWidgets import QGroupBox, QPushButton, QVBoxLayout
 
 
 def build_hardware_actions_group(owner) -> QGroupBox:
     """Create hardware action buttons section."""
     group = QGroupBox("Hardware Actions")
-    layout = QHBoxLayout(group)
+    layout = QVBoxLayout(group)
     layout.setSpacing(8)
 
-    apply_radar_button = QPushButton("Apply Radar Settings")
+    apply_radar_button = QPushButton("Apply Radar")
     apply_radar_button.clicked.connect(owner._apply_radar_settings)
-    layout.addWidget(apply_radar_button)
+    layout.addWidget(apply_radar_button, alignment=Qt.AlignmentFlag.AlignLeft)
 
-    save_config_button = QPushButton("Save Current Config")
+    save_config_button = QPushButton("Save Config")
     save_config_button.clicked.connect(owner._save_current_config)
-    layout.addWidget(save_config_button)
+    layout.addWidget(save_config_button, alignment=Qt.AlignmentFlag.AlignLeft)
 
-    preprocess_button = QPushButton("Preprocessing Panel")
+    preprocess_button = QPushButton("Preprocessing")
     preprocess_button.clicked.connect(owner._open_preprocess_panel)
-    layout.addWidget(preprocess_button)
+    layout.addWidget(preprocess_button, alignment=Qt.AlignmentFlag.AlignLeft)
     return group
diff --git a/python_app/gui/controllers/sections/pipeline_section.py b/python_app/gui/controllers/sections/pipeline_section.py
index 65ee644..ab6be87 100644
--- a/python_app/gui/controllers/sections/pipeline_section.py
+++ b/python_app/gui/controllers/sections/pipeline_section.py
@@ -2,7 +2,8 @@
 
 from __future__ import annotations
 
-from PyQt6.QtWidgets import QGroupBox, QHBoxLayout, QLabel, QPushButton, QVBoxLayout
+from PyQt6.QtCore import Qt
+from PyQt6.QtWidgets import QGroupBox, QLabel, QPushButton, QVBoxLayout
 
 
 def build_pipeline_group(owner) -> QGroupBox:
@@ -11,22 +12,17 @@ def build_pipeline_group(owner) -> QGroupBox:
     layout = QVBoxLayout(group)
     layout.setSpacing(8)
 
-    action_row = QHBoxLayout()
-    action_row.setSpacing(8)
-
     start_button = QPushButton("Start")
     start_button.clicked.connect(owner._start_run)
-    action_row.addWidget(start_button)
+    layout.addWidget(start_button, alignment=Qt.AlignmentFlag.AlignLeft)
 
     single_button = QPushButton("Single Capture")
     single_button.clicked.connect(owner._start_single_capture)
-    action_row.addWidget(single_button)
+    layout.addWidget(single_button, alignment=Qt.AlignmentFlag.AlignLeft)
 
     stop_button = QPushButton("Stop")
     stop_button.clicked.connect(owner._stop_run)
-    action_row.addWidget(stop_button)
-
-    layout.addLayout(action_row)
+    layout.addWidget(stop_button, alignment=Qt.AlignmentFlag.AlignLeft)
 
     hint = QLabel("Start continuous run or single processed collection capture.")
     hint.setObjectName("hintLabel")
diff --git a/python_app/gui/controllers/sections/processing_section.py b/python_app/gui/controllers/sections/processing_section.py
index 611a872..0d0cb63 100644
--- a/python_app/gui/controllers/sections/processing_section.py
+++ b/python_app/gui/controllers/sections/processing_section.py
@@ -61,6 +61,9 @@ def build_processing_group(owner) -> QGroupBox:
     owner._processing_phase_deg.setSingleStep(1.0)
     owner._processing_phase_deg.setValue(0.0)
 
+    owner._pass_through_channel = QComboBox()
+    owner._pass_through_channel.addItems(["s21", "s11"])
+
     owner._show_magnitude_checkbox = QCheckBox("Show magnitude")
     owner._show_magnitude_checkbox.setChecked(True)
 
@@ -91,6 +94,7 @@ def build_processing_group(owner) -> QGroupBox:
 
     pass_through_form.addRow("Gain dB (live)", owner._processing_gain_db)
     pass_through_form.addRow("Phase deg (live)", owner._processing_phase_deg)
+    pass_through_form.addRow("Channel", owner._pass_through_channel)
     pass_through_form.addRow(owner._show_magnitude_checkbox)
     pass_through_form.addRow(owner._show_phase_checkbox)
     pass_through_form.addRow(owner._pass_through_fixed_y_enabled)
@@ -206,6 +210,7 @@ def build_processing_group(owner) -> QGroupBox:
     owner._processing_mode.currentTextChanged.connect(owner._on_processing_mode_changed)
     owner._processing_gain_db.valueChanged.connect(owner._on_processing_live_settings_changed)
     owner._processing_phase_deg.valueChanged.connect(owner._on_processing_live_settings_changed)
+    owner._pass_through_channel.currentTextChanged.connect(owner._on_processing_live_settings_changed)
     owner._show_magnitude_checkbox.toggled.connect(owner._on_trace_visibility_changed)
     owner._show_phase_checkbox.toggled.connect(owner._on_trace_visibility_changed)
     owner._pass_through_fixed_y_enabled.toggled.connect(sync_pass_through_y_controls)
diff --git a/python_app/gui/main.py b/python_app/gui/main.py
index 5bc6bc9..4aec4c6 100644
--- a/python_app/gui/main.py
+++ b/python_app/gui/main.py
@@ -23,7 +23,7 @@ def main() -> int:
     apply_dark_theme(app)
     pg.setConfigOptions(antialias=True, foreground="#dbe4f1")
     window = AppWindow(PROJECT_ROOT)
-    window.show()
+    window.showMaximized()
     return app.exec()
 
 
diff --git a/python_app/gui/runtime/history.py b/python_app/gui/runtime/history.py
index e4790ae..1d7c25e 100644
--- a/python_app/gui/runtime/history.py
+++ b/python_app/gui/runtime/history.py
@@ -79,8 +79,8 @@ def build_run_history_signature(
         str(config.output_switch.driver),
         int(config.output_switch.positions),
         bool(config.output_switch.invert_logic),
-        str(config.preprocess.calibration_set),
-        str(config.preprocess.reference_set),
+        str(config.preprocess.s21_calibration_set),
+        str(config.preprocess.s21_reference_set),
         combos_signature,
     )
 
diff --git a/python_app/models/run_config_codec.py b/python_app/models/run_config_codec.py
index c423d90..4d32564 100644
--- a/python_app/models/run_config_codec.py
+++ b/python_app/models/run_config_codec.py
@@ -65,13 +65,47 @@ def run_config_from_dict(payload: dict[str, Any]) -> RunConfigModel:
         run_payload.get("processing_live_config_path", model.runtime.processing_live_config_path)
     )
 
-    model.preprocess.calibration_set = str(preprocess_payload.get("calibration_set", model.preprocess.calibration_set))
-    model.preprocess.reference_set = str(preprocess_payload.get("reference_set", model.preprocess.reference_set))
-    model.preprocess.calibration_bundle_path = str(
-        preprocess_payload.get("calibration_bundle_path", model.preprocess.calibration_bundle_path)
+    model.preprocess.s21_calibration_set = str(
+        preprocess_payload.get("s21_calibration_set", model.preprocess.s21_calibration_set)
     )
-    model.preprocess.reference_bundle_path = str(
-        preprocess_payload.get("reference_bundle_path", model.preprocess.reference_bundle_path)
+    model.preprocess.s21_reference_set = str(
+        preprocess_payload.get("s21_reference_set", model.preprocess.s21_reference_set)
+    )
+    model.preprocess.s21_calibration_bundle_path = str(
+        preprocess_payload.get(
+            "s21_calibration_bundle_path",
+            model.preprocess.s21_calibration_bundle_path,
+        )
+    )
+    model.preprocess.s21_reference_bundle_path = str(
+        preprocess_payload.get(
+            "s21_reference_bundle_path",
+            model.preprocess.s21_reference_bundle_path,
+        )
+    )
+    model.preprocess.s11_open_calibration_bundle_path = str(
+        preprocess_payload.get(
+            "s11_open_calibration_bundle_path",
+            model.preprocess.s11_open_calibration_bundle_path,
+        )
+    )
+    model.preprocess.s11_short_calibration_bundle_path = str(
+        preprocess_payload.get(
+            "s11_short_calibration_bundle_path",
+            model.preprocess.s11_short_calibration_bundle_path,
+        )
+    )
+    model.preprocess.s11_load_calibration_bundle_path = str(
+        preprocess_payload.get(
+            "s11_load_calibration_bundle_path",
+            model.preprocess.s11_load_calibration_bundle_path,
+        )
+    )
+    model.preprocess.s11_reference_bundle_path = str(
+        preprocess_payload.get(
+            "s11_reference_bundle_path",
+            model.preprocess.s11_reference_bundle_path,
+        )
     )
 
     model.gpr.mode = str(gpr_payload.get("mode", model.gpr.mode))
@@ -127,6 +161,7 @@ def run_config_from_dict(payload: dict[str, Any]) -> RunConfigModel:
     model.ensure_combos()
     return model
 
+
 def run_config_to_dict(model: RunConfigModel) -> dict[str, Any]:
     """Encode :class:`RunConfigModel` to C++ pipeline-compatible JSON structure."""
     model.ensure_combos()
@@ -178,10 +213,14 @@ def run_config_to_dict(model: RunConfigModel) -> dict[str, Any]:
             "combos": [{"input": combo.input, "output": combo.output} for combo in model.combos],
         },
         "preprocess": {
-            "calibration_set": model.preprocess.calibration_set,
-            "reference_set": model.preprocess.reference_set,
-            "calibration_bundle_path": model.preprocess.calibration_bundle_path,
-            "reference_bundle_path": model.preprocess.reference_bundle_path,
+            "s21_calibration_set": model.preprocess.s21_calibration_set,
+            "s21_reference_set": model.preprocess.s21_reference_set,
+            "s21_calibration_bundle_path": model.preprocess.s21_calibration_bundle_path,
+            "s21_reference_bundle_path": model.preprocess.s21_reference_bundle_path,
+            "s11_open_calibration_bundle_path": model.preprocess.s11_open_calibration_bundle_path,
+            "s11_short_calibration_bundle_path": model.preprocess.s11_short_calibration_bundle_path,
+            "s11_load_calibration_bundle_path": model.preprocess.s11_load_calibration_bundle_path,
+            "s11_reference_bundle_path": model.preprocess.s11_reference_bundle_path,
         },
         "gpr": {
             "mode": model.gpr.mode,
diff --git a/python_app/models/run_config_schema.py b/python_app/models/run_config_schema.py
index 995bd62..89bb5ef 100644
--- a/python_app/models/run_config_schema.py
+++ b/python_app/models/run_config_schema.py
@@ -89,10 +89,14 @@ class RuntimeModel:
 class PreprocessModel:
     """Selected preprocessing artifacts for live acquisition."""
 
-    calibration_set: str = ""
-    reference_set: str = ""
-    calibration_bundle_path: str = ""
-    reference_bundle_path: str = ""
+    s21_calibration_set: str = ""
+    s21_reference_set: str = ""
+    s21_calibration_bundle_path: str = ""
+    s21_reference_bundle_path: str = ""
+    s11_open_calibration_bundle_path: str = ""
+    s11_short_calibration_bundle_path: str = ""
+    s11_load_calibration_bundle_path: str = ""
+    s11_reference_bundle_path: str = ""
 
 
 @dataclass(slots=True)
diff --git a/python_app/orchestration/config_writer.py b/python_app/orchestration/config_writer.py
index adc5c3d..f356c93 100644
--- a/python_app/orchestration/config_writer.py
+++ b/python_app/orchestration/config_writer.py
@@ -17,19 +17,19 @@ class ConfigWriter:
         self._runtime_dir = runtime_dir
         self._runtime_dir.mkdir(parents=True, exist_ok=True)
 
-    def prepare_bundles(
+    def prepare_s21_bundles(
         self,
         store: NpzStore,
         radar_key: str,
-        calibration_set: str,
-        reference_set: str,
+        s21_calibration_set: str,
+        s21_reference_set: str,
     ) -> tuple[Path, Path]:
         """Export calibration/reference sets into binary bundles for preprocessor."""
-        calibration_bundle = self._runtime_dir / "calibration_bundle.bin"
-        reference_bundle = self._runtime_dir / "reference_bundle.bin"
+        calibration_bundle = self._runtime_dir / "s21_calibration_bundle.bin"
+        reference_bundle = self._runtime_dir / "s21_reference_bundle.bin"
 
-        store.export_set_bundle("calibration", radar_key, calibration_set, calibration_bundle)
-        store.export_set_bundle("reference", radar_key, reference_set, reference_bundle)
+        store.export_set_bundle("calibration", radar_key, s21_calibration_set, calibration_bundle)
+        store.export_set_bundle("reference", radar_key, s21_reference_set, reference_bundle)
         return calibration_bundle, reference_bundle
 
     def write(self, config: RunConfigModel, output_path: Path) -> Path:
diff --git a/python_app/orchestration/live_processing_config.py b/python_app/orchestration/live_processing_config.py
index 1b67761..2ae98c2 100644
--- a/python_app/orchestration/live_processing_config.py
+++ b/python_app/orchestration/live_processing_config.py
@@ -14,6 +14,7 @@ class ProcessingLiveConfig:
     processor_mode: str = "pass_through"
     gain_db: float = 0.0
     phase_deg: float = 0.0
+    pass_through_channel: str = "s21"
     pass_through_fixed_y_enabled: bool = False
     pass_through_y_min_db: float = -100.0
     pass_through_y_max_db: float = 0.0
@@ -52,6 +53,7 @@ class ProcessingLiveConfig:
             "processor_mode": str(self.processor_mode),
             "gain_db": float(self.gain_db),
             "phase_deg": float(self.phase_deg),
+            "pass_through_channel": str(self.pass_through_channel),
             "pass_through_fixed_y_enabled": bool(self.pass_through_fixed_y_enabled),
             "pass_through_y_min_db": float(self.pass_through_y_min_db),
             "pass_through_y_max_db": float(self.pass_through_y_max_db),
diff --git a/python_app/runtime/run_config_smoke.json b/python_app/runtime/run_config_smoke.json
index cb081c4..16410ba 100644
--- a/python_app/runtime/run_config_smoke.json
+++ b/python_app/runtime/run_config_smoke.json
@@ -79,10 +79,14 @@
     ]
   },
   "preprocess": {
-    "calibration_set": "smoke_cal",
-    "reference_set": "smoke_ref",
-    "calibration_bundle_path": "/home/europa/Documents/radar_system/python_app/runtime/calibration_bundle.bin",
-    "reference_bundle_path": "/home/europa/Documents/radar_system/python_app/runtime/reference_bundle.bin"
+    "s21_calibration_set": "smoke_cal",
+    "s21_reference_set": "smoke_ref",
+    "s21_calibration_bundle_path": "/home/europa/Documents/radar_system/python_app/runtime/s21_calibration_bundle.bin",
+    "s21_reference_bundle_path": "/home/europa/Documents/radar_system/python_app/runtime/s21_reference_bundle.bin",
+    "s11_open_calibration_bundle_path": "/home/europa/Documents/radar_system/data_acq_and_processing/preprocessing/testdata/s11_open_calibration_bundle.bin",
+    "s11_short_calibration_bundle_path": "/home/europa/Documents/radar_system/data_acq_and_processing/preprocessing/testdata/s11_short_calibration_bundle.bin",
+    "s11_load_calibration_bundle_path": "/home/europa/Documents/radar_system/data_acq_and_processing/preprocessing/testdata/s11_load_calibration_bundle.bin",
+    "s11_reference_bundle_path": "/home/europa/Documents/radar_system/data_acq_and_processing/preprocessing/testdata/s11_reference_bundle.bin"
   },
   "gpr": {
     "mode": "point",
diff --git a/python_app/scripts/manual_smoke_run.py b/python_app/scripts/manual_smoke_run.py
index c6eb350..a9b1107 100644
--- a/python_app/scripts/manual_smoke_run.py
+++ b/python_app/scripts/manual_smoke_run.py
@@ -113,11 +113,16 @@ def main() -> int:
     store.save_set("calibration", radar_key, "smoke_cal", calibration_set)
     store.save_set("reference", radar_key, "smoke_ref", reference_set)
 
-    calibration_bundle, reference_bundle = config_writer.prepare_bundles(store, radar_key, "smoke_cal", "smoke_ref")
-    config.preprocess.calibration_set = "smoke_cal"
-    config.preprocess.reference_set = "smoke_ref"
-    config.preprocess.calibration_bundle_path = str(calibration_bundle)
-    config.preprocess.reference_bundle_path = str(reference_bundle)
+    calibration_bundle, reference_bundle = config_writer.prepare_s21_bundles(
+        store,
+        radar_key,
+        "smoke_cal",
+        "smoke_ref",
+    )
+    config.preprocess.s21_calibration_set = "smoke_cal"
+    config.preprocess.s21_reference_set = "smoke_ref"
+    config.preprocess.s21_calibration_bundle_path = str(calibration_bundle)
+    config.preprocess.s21_reference_bundle_path = str(reference_bundle)
 
     config_path = config_writer.write(config, project_root / "python_app/runtime/run_config_smoke.json")
 
diff --git a/run_config.json b/run_config.json
index 5c95a31..0bf5510 100644
--- a/run_config.json
+++ b/run_config.json
@@ -55,10 +55,14 @@
     ]
   },
   "preprocess": {
-    "calibration_set": "",
-    "reference_set": "",
-    "calibration_bundle_path": "python_app/runtime/calibration_bundle.bin",
-    "reference_bundle_path": "python_app/runtime/reference_bundle.bin"
+    "s21_calibration_set": "",
+    "s21_reference_set": "",
+    "s21_calibration_bundle_path": "python_app/runtime/s21_calibration_bundle.bin",
+    "s21_reference_bundle_path": "python_app/runtime/s21_reference_bundle.bin",
+    "s11_open_calibration_bundle_path": "",
+    "s11_short_calibration_bundle_path": "",
+    "s11_load_calibration_bundle_path": "",
+    "s11_reference_bundle_path": ""
   },
   "gpr": {
     "mode": "point",