changed default reference impedance to conjugate of the load, and fixed the calculation of voltage/current for lossy modes

Author: dmarek-flex

CHANGELOG.md

@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 or `Absorber` classes (or when invoking `pml()`, `stable_pml()`, or `absorber()` functions)
 with fewer layers than recommended.
 - Warnings and error messages originating from `Structure`, `Source`, or `Monitor` classes now refer to problematic objects by their user-supplied `name` attribute, alongside their index.
+- Default reference impedance used for calculating power waves in the `TerminalComponentModeler`, which is now equal to the conjugate of the load impedance.
 
 ### Fixed
 - Arrow lengths are now scaled consistently in the X and Y directions, and their lengths no longer exceed the height of the plot window.
@@ -32,6 +33,7 @@ with fewer layers than recommended.
 - Fixed incorrect gradient computation in PyTorch plugin (`to_torch`) for functions returning multi-element arrays.
 - `MonitorData.get_amplitude()` no longers multiplies by a factor of `1j` and now directly returns the complex value of the data.
 - `EMESimulationData.port_modes_tuple` is now symmetry-expanded.
+- Calculation of voltage and current in the `WavePort` when one type of path integral is supplied and the transmission line mode is lossy.
 
 ## [2.9.0rc1] - 2025-06-10
 

tidy3d/plugins/smatrix/component_modelers/terminal.py

@@ -459,7 +459,14 @@ def s_to_z(
 
     @cached_property
     def port_reference_impedances(self) -> PortDataArray:
-        """The reference impedance used at each port for definining power wave amplitudes."""
+        """The reference impedance used at each port for definining power wave amplitudes.
+
+        Note
+        ----
+        By default, we choose reference impedances to be the conjugate of the load impedance.
+        For wave ports, this corresponds with the conjugate of the characteristic impedance.
+        This choice corresponds with Equation 4.64 - Pozar - Microwave Engineering 4ed.
+        """
         return self._port_reference_impedances(self.batch_data)
 
     def _port_reference_impedances(self, batch_data: BatchData) -> PortDataArray:
@@ -486,7 +493,9 @@ def _port_reference_impedances(self, batch_data: BatchData) -> PortDataArray:
                 # LumpedPorts have a constant reference impedance
                 port_impedances.loc[{"port": port.name}] = np.full(len(self.freqs), port.impedance)
 
-        port_impedances = TerminalComponentModeler._set_port_data_array_attributes(port_impedances)
+        port_impedances = TerminalComponentModeler._set_port_data_array_attributes(
+            port_impedances.conj()
+        )
         return port_impedances
 
     @staticmethod

tidy3d/plugins/smatrix/ports/wave.py

@@ -82,8 +82,9 @@ def _mode_voltage_coefficients(self, mode_data: ModeData) -> FreqModeDataArray:
         """
         mode_data = mode_data._isel(mode_index=[self.mode_index])
         if self.voltage_integral is None:
+            flux_sign = 1 if mode_data.monitor.store_fields_direction == "+" else -1
             current_coeffs = self.current_integral.compute_current(mode_data)
-            voltage_coeffs = 2 * np.abs(mode_data.flux) / np.conj(current_coeffs)
+            voltage_coeffs = 2 * flux_sign * mode_data.complex_flux / np.conj(current_coeffs)
         else:
             voltage_coeffs = self.voltage_integral.compute_voltage(mode_data)
         return voltage_coeffs.squeeze()
@@ -94,8 +95,9 @@ def _mode_current_coefficients(self, mode_data: ModeData) -> FreqModeDataArray:
         """
         mode_data = mode_data._isel(mode_index=[self.mode_index])
         if self.current_integral is None:
+            flux_sign = 1 if mode_data.monitor.store_fields_direction == "+" else -1
             voltage_coeffs = self.voltage_integral.compute_voltage(mode_data)
-            current_coeffs = (2 * np.abs(mode_data.flux) / voltage_coeffs).conj()
+            current_coeffs = (2 * flux_sign * mode_data.complex_flux / voltage_coeffs).conj()
         else:
             current_coeffs = self.current_integral.compute_current(mode_data)
         return current_coeffs.squeeze()