Complex source impedance for lumped ports

[yuanshen-flexcompute]

Currently lumped port only support real source impedance. It will be useful (particularly in antenna/RFID cases) to be able to define a complex source impedance.

[weiliangjin2021]

Do you mean this impedance

tidy3d/tidy3d/plugins/smatrix/ports/base_lumped.py

Lines 27 to 33 in 6b8e1c6

	impedance: Complex = pd.Field(
	DEFAULT_REFERENCE_IMPEDANCE,
	title="Reference impedance",
	description="Reference port impedance for scattering parameter computation.",
	units=OHM,
	)

? It does allow complex-valued impedance.

[yuanshen-flexcompute]

Not entirely. The impedance field supports complex values for the purposes of S-matrix renormalization but the LinearLumpedElement that gets created only has the real part of it. So the underlying physical system is incorrect. The reason is because some additional work is necessary to fit the imaginary part to appropriate L and C values.

In fact, I would say that before we implement this feature, we should actually only permit real impedance values to prevent user confusion.