In CPW waveguide without back grounded plane, which kind of port is better?

I am using a coplanar waveguide (CPW) without back grounded plane, which kind of port is better?

I have tried waveports, but observing asymmetric electric field using HFSS in the perpendicular direction (z) of the CPW board (in x-y plane). Is lumped ports will help me to get symmetric electric field?

I assume your port is centered/symmetric and that your board is too. The waveport port needs to touch both of the ground planes. Double check material assignments. I am guessing that you have an integration line between the signal and one of the grounds. Please confirm or correct these assumptions.

Thank you for your reply. I have exactly used the waveports as you described. But it has given me asymmetric electric field. My part of question is that..... Do lumped ports help me to get a symmetric electric field?