Reason for Different Results between Wave Port, Lumped Port, and Coax. Thank You.

[jianke]

Hi all,

I measured a circuit with input/output SMA connectors. But the measured results are much different from (worse than) the simulation results using WavePort.

To find out the reason, I compare the simulation results between WavePort(rectangular), LumpedPort, and Coax(using waveport).
I found the measured results are much similar with the simulation results using Coax excitation (waveport on coax face).

The Discontinuity from the SMA connectors to the PCB board causes impedance mismatch and result in the worse reflection coefficients (S11).
Is the Discontinuity ONLY reason for the worse performance?
The simulation results using WavePort is reliable or not?
The problem is that if the WavePort (rectangular) is correct and reliable, we cannot measure it since the connectors must be used.

The simulation results are attached for review. Thank you very much.


jianke

 

[Andryuha]

Waveport is reliable if you intend for direct waveguide-to waveguide connection of your circuit. Of course, connectors introduce mismatch and a phase shift. Therefore people simulate connectors as well (and it takes time and RAM).
BTW, don't forget that the waveport for open-boundary waveguide, like microstrip, should be considerably larger than the microstrip model. BUT you still should provide integration lines from top to bottom planes of the stripline, not between the port boundaries.