Computing Characteristic Impedance

The Desktop must calculate the characteristic impedance of each port in order to compute a renormalized S-matrix.

The characteristic impedance of microstrip and stripline ports is calculated using a variation of the voltage-current definition of impedance

where the voltage (V,I) is a weighted average of the voltage on the strip defined as

Since the path of the integral of the electric field is not path-independent for time-varying fields, the voltage on the strip varies with position. This definition uniquely defines a voltage.

For coupled microstrip and stripline ports, the characteristic impedance is defined as power over the square of the current. The power is defined as

The definition of characteristic impedance for coplanar waveguides and slotline ports is defined as the square of the voltage over power. The power definition is the same for coupled ports, and the voltage is defined as the integral of the electric field across a slot.