selectable calkit load model

Software/PC_Application/Calibration/calkit.cpp

@@ -80,6 +80,13 @@ Calkit Calkit::fromFile(QString filename)
         qDebug() << "JSON format detected";
         // calkit file uses json format, parse
         Savable::parseJSON(j, c.descr);
+        auto jSOLT = j["SOLT"];
+        if (!jSOLT.contains("loadModelCFirst")) {
+            // older version which did not allow the user to choose the load model. CFirst seems to be the more
+            // used standard so it is the default for newer calkits. However, old calkits used LFirst so we need
+            // to keep that to not mess with older calkit files
+            c.SOLT.loadModelCFirst = false;
+        }
         // adjust Z0/resistance in case of older calkit file version with missing resistance entries
         if(isnan(c.SOLT.load_f.resistance)) {
             c.SOLT.load_f.resistance = c.SOLT.load_f.Z0;
@@ -207,14 +214,20 @@ class Calkit::SOLT Calkit::toSOLT(double frequency, bool male_standards)
         ref.Load = ts_load->interpolate(frequency).S[0];
     } else {
         auto imp_load = complex<double>(Load.resistance, 0);
+        if (SOLT.loadModelCFirst) {
+            // C is the first parameter starting from the VNA port. But the load is modeled here starting from
+            // the other end, so we need to start with the inductor
+            imp_load += complex<double>(0, frequency * 2 * M_PI * Load.Lseries);
+        }
         // Add parallel capacitor to impedance
         if(Load.Cparallel > 0) {
             auto imp_C = complex<double>(0, -1.0 / (frequency * 2 * M_PI * Load.Cparallel));
             imp_load = (imp_load * imp_C) / (imp_load + imp_C);
         }
-        // add series inductor to impedance
+        if (!SOLT.loadModelCFirst) {
-        auto imp_L = complex<double>(0, frequency * 2 * M_PI * Load.Lseries);
+            // inductor not added yet, do so now
-        imp_load += imp_L;
+            imp_load += complex<double>(0, frequency * 2 * M_PI * Load.Lseries);
+        }
         ref.Load = (imp_load - complex<double>(50.0)) / (imp_load + complex<double>(50.0));
         ref.Load = addTransmissionLine(ref.Load, Load.Z0, Load.delay*1e-12, 0, frequency);
     }

Software/PC_Application/Calibration/calkit.h

@@ -79,6 +79,7 @@ private:
             int Sparam;
         };
         Load load_m, load_f;
+        bool loadModelCFirst;
         struct {
             double Z0, delay, loss;
             QString file;
@@ -152,6 +153,7 @@ private:
         {&SOLT.short_f.file, "SOLT.Short.Measurements.File_Female", ""},
         {&SOLT.short_f.Sparam, "SOLT.Short.Measurements.Port_Female", 0},
 
+        {&SOLT.loadModelCFirst, "SOLT.loadModelCFirst", true},
         {&SOLT.load_m.resistance, "SOLT.Load.Param.Resistance", 50.0},
         {&SOLT.load_m.Z0, "SOLT.Load.Param.Z0", 50.0},
         {&SOLT.load_m.delay, "SOLT.Load.Param.Delay", 0.0},

Software/PC_Application/Calibration/calkitdialog.cpp

@@ -249,6 +249,7 @@ void CalkitDialog::parseEntries()
     ownKit.SOLT.short_m.L2 = ui->short_L2->value();
     ownKit.SOLT.short_m.L3 = ui->short_L3->value();
 
+    ownKit.SOLT.loadModelCFirst = ui->load_C_first->isChecked();
     ownKit.SOLT.load_m.resistance = ui->load_resistance->value();
     ownKit.SOLT.load_m.Z0 = ui->load_Z0->value();
     ownKit.SOLT.load_m.delay = ui->load_delay->value();
@@ -336,6 +337,8 @@ void CalkitDialog::updateEntries()
     ui->short_L2->setValueQuiet(ownKit.SOLT.short_m.L2);
     ui->short_L3->setValueQuiet(ownKit.SOLT.short_m.L3);
 
+    ui->load_C_first->setChecked(ownKit.SOLT.loadModelCFirst);
+    ui->load_L_first->setChecked(!ownKit.SOLT.loadModelCFirst);
     ui->load_resistance->setValueQuiet(ownKit.SOLT.load_m.resistance);
     ui->load_Z0->setValueQuiet(ownKit.SOLT.load_m.Z0);
     ui->load_delay->setValueQuiet(ownKit.SOLT.load_m.delay);

Software/PC_Application/Calibration/calkitdialog.ui

@@ -722,7 +722,7 @@
                <item>
                 <widget class="QTabWidget" name="mf_load">
                  <property name="currentIndex">
-                  <number>1</number>
+                  <number>0</number>
                  </property>
                  <widget class="QWidget" name="tab_7">
                   <attribute name="title">
@@ -940,6 +940,35 @@
                  </widget>
                 </widget>
                </item>
+               <item>
+                <widget class="QGroupBox" name="groupBox">
+                 <property name="title">
+                  <string>Load Parameter Model</string>
+                 </property>
+                 <layout class="QHBoxLayout" name="horizontalLayout_15">
+                  <item>
+                   <widget class="QRadioButton" name="load_L_first">
+                    <property name="text">
+                     <string>Series L first</string>
+                    </property>
+                    <attribute name="buttonGroup">
+                     <string notr="true">LoadModel</string>
+                    </attribute>
+                   </widget>
+                  </item>
+                  <item>
+                   <widget class="QRadioButton" name="load_C_first">
+                    <property name="text">
+                     <string>Shunt C first</string>
+                    </property>
+                    <attribute name="buttonGroup">
+                     <string notr="true">LoadModel</string>
+                    </attribute>
+                   </widget>
+                  </item>
+                 </layout>
+                </widget>
+               </item>
               </layout>
              </item>
             </layout>
@@ -1477,12 +1506,13 @@
  </connections>
  <buttongroups>
   <buttongroup name="LoadType_f"/>
-  <buttongroup name="OpenType"/>
-  <buttongroup name="LoadType"/>
   <buttongroup name="ShortType"/>
-  <buttongroup name="ThroughType"/>
   <buttongroup name="OpenType_f"/>
   <buttongroup name="TRL_Rtype"/>
+  <buttongroup name="LoadType"/>
   <buttongroup name="ShortType_f"/>
+  <buttongroup name="OpenType"/>
+  <buttongroup name="ThroughType"/>
+  <buttongroup name="LoadModel"/>
  </buttongroups>
 </ui>