SMA end launch optimization

end launch ghz

Hey everyone...
I am trying to get on and off a PCB at about 6GHz with the best S11 I can muster. I have been using a Johnson SMA end launch connector attaching directly to microstrip which has worked reasonably well below 3GHz. Above 4GHz this approach is probably not what I want to do. I have started looking at a CPWG structure at the initial launch point which transitions to plain microstrip but HFSS and CPWG do not seem to play well together. Specifically my port definitions are most likely incorrect.
So the question I ask is: A) Are there any suggestions for >4GHz SMA to PCB launch? B) Does anyone have an example HFSS file using CPWG?

Thanks,

Dan

sma end launch for microstrip

In general terms things get fun above about 2 GHz. You will need to model and evaluate the footprint and the connection to your transmission line carefully. Pay attention to the way the ground is connected to the connector housing and model via's if they are in the picture. You describe CPW but you may be considering grounded cpw as well. Unless you are really lucky you may find the dimensions of the transmission line, components installed downstream, and the connector dimensions force you into incompatibility in your model.

I would expect that without too much pain you could get into the -15 to -20 dB range with s11 over a useful bandwidth.

BTW a microstrip could easily work in this situation as well. You might not need to shift to cpw to get a good match.

"BTW a microstrip could easily work in this situation as well. You might not need to shift to cpw to get a good match. "

Exactly! No need to bother with (G)CPW at relatively low 6GHz... And (G)CPW port definition in HFSS is tricky. Also the meshing at port rectangle must be very fine to get useful impedance. Still I find HFSS very unreliable with CPW structure, cos you can get easily wrong Zo...