waveport size

I am trying to build a bandgap transmission line(similar to the CPW), but I donot think the result is correct espacially above 20 GHz. I think there are some problem in my defining of the size and the location of the waveport and the boundary.

Could you help and tell me how to choose the waveport size and the boundary size, and also which kind of boundary should I choose, perfect E or perfect H?

Thank you very much!!!!

Hello :)

First you could inform us which simulator are you using or even post the zipped project here

Boundary settings depending of your project details, if it's boxed, you can set PEC at the boundaries, otherwise open. Definitely no PMC (if you're not using field symmetry).

Waveport size depends on fringe fields of the given line. Generally the waveport size should be enough to cover all the transversal fields. Port impedance shouldn't change with further extending port size. Make the port as big as possible but take care about higher modes!!
My opinion is that at higher freqs you mention there could be higher modes appearing. You have to investigate possible cut-off frequencies of your port and eventually divide the calculation for different modes.
Also take care on deembeding, is port impedance calculated in whole frequency band?

Kind regards

eirp

Oh, thank you very much for your kind help!
I used HFSS9.2 to simulate. I used two non-assigned retangulars to begin and end the microstrip line. And then I setup the two retangulars as waveports. I think the length and the height of the waveports should be determined by the wideth of the strip and the height of the substrate. But I am not sure how much bigger it will be. Also I put an air box out of the board. I donot know how large it should be. Are there also some relationship between the size of the substrate and the air box?
Thank you!