Wave port definition for a conductor backed CPW in HFSS

[sayantan]

I would like to know how to define the waveport for a conductor backed CPW.. If no integration line is provided the port modes show the electric field lines converging on the central conductor from the ground planes. Can someone provide a suitable answer. I can mail my design if its required.

Thanks

 

[tallface65]

Treat the CPW as a microstrip. Have the Waveport extend from the groundplane to a height 10*h where h is the substrate thickness. It is not necessarily unreasonable for the fields to look as though converging on the center conductor, particularly if the CPW is quite far from the ground plane.

 

[sayantan]

Treat the CPW as a microstrip. Have the Waveport extend from the groundplane to a height 10*h where h is the substrate thickness. It is not necessarily unreasonable for the fields to look as though converging on the center conductor, particularly if the CPW is quite far from the ground plane.

Thanks!! Will look into it and willl let you know

 

[sayantan]

I did as you suggested but my results don't seem to be correct. My question is, if the E field lines are converging on the central conductor then it will start acting as a ground plane and the two ground planes on either side starts acting as the signal line. This might be leading to a complete change in the return loss characteristics. Kindly advice.

 

[tallface65]

OK...I believe that you may have a pretty bad misconception about interpreting the E fields on a transmission line cross section. First, you have to remember that you are dealing with AC fields, therefore the fields will be alternating from pointing "to" the center conductor and "from" the center conductor to the coplanar grounds. The Return Loss of a transmission line dies not change just because you switch the E fields from pointing to the center conductor. By switching the direction of the E field vector from center conductor to coplanar grounds, you have simply shifted your reference along the transmission line by 180 degrees.

You may want to brush up on Pozar to get a little more comfortable with these concepts if you can. Have Fun