The port discontinuity for boxwall ports is described in the section that follows. The discontinuity for the other types of ports may be different, but the process outlined below is similar for all port types. Boxwall ports have one port terminal connected to a polygon inside the metal box, and the second port terminal connected to ground (see the figure below). The port discontinuity is modeled as a series resistor, R, and capacitor, C, shunted to ground as shown below. If the circuit being analyzed is completely lossless, the resistor value, R, is zero. Even with loss in the circuit, the capacitive reactance is normally very large compared to the resistance.
When enabled, em’s de-embedding feature automatically calculates the values of R and C for each box-wall port present in the circuit. The port discontinuities are then removed by cascading a negative R and C as illustrated below.