HFSS: Effect of Number of Modes on a Desired Mode's Solution (say that at Mode 1)

Hi

I am simulating a simple microstrip transmission line (TL) based impedance matching network through HFSS. Important factor in this design is to check the input impedance (Zin1), that is observed while looking into the matching network.

However, simulations indicate different values of Zin1, when different number of modes are set for the ports in the circuit.
Specifically, there are two ports in the circuit. Same number of modes (say 'n') are set for these two ports. Now as this 'n' value is changed, Zin1 value (calculated in desired mode 1) changes.

May someone suggest the value of 'n' that can ensure correct and consistent simulation results?

I wish to keep as low value of 'n' as possible, so that optimization (based on repetition of this simulation) is fast.

Thanks in Advance!
Vivs

Hi engrvivs,

With solutions involving multiple modes, the question to ask is always: how likely is it that these modes will be excited? There are a few easy way to get around answering this question.

1) Simulate your feeding connector. I assume you will be using something like a coaxial SMA connector eventually, what you can do is include this in your model and excite the coaxial mode only. All of the other modes will be excited in the correct proportions on the microstrip line.

2) Assume that you only have the microstrip mode. This usually isn't a bad assumption, but it depends on your setup, frequency range, etc.

If you can post some information about your Microstrip design, I can give you my best guess.