Using Lumped Ports and Wave ports in HFSS

Hi!!
I am simulating a CPW (attached picture), using 2 dielectric materials as substrate. I know the rule of thumb for defining wave ports when I use only one dielectric (width wave port =3(2*w+s)) and (length wave port=4h)and it woks!, but when I applied this rule for two dielectrics assuming the total thickness equal to the sum of two dielectrics, it did not work!.

I do not know if I should use the same rule when I am designing the CPW with 2 dielectric substrates or its better use Lumped port than wave ports in this case. I got wrong characteristic impedance.

I will appreciate your help:D

I see no picture...

CPW is a little bit tricky in HFSS. Just try to increase/decrease both in x- and y- dimensions of the wave port rectangle. I had to reduce a bit the size of the wave port from the recommended values to get proper characteristic impedance.

Take a look in help at the note on "calculating characteristic impedance". They recommend using the Zpv form of the calculation. I usually place an impedance line from a sideground and the center, even if there is a lower groundplane present. Then check the port fields display to make sure you are exciting the desired mode.

This is an obscure point and I hope that it is helpful.