Coplanar Waveguide Gap

How critical is it that the gap be an air gap in a coplanar waveguide structure? I have never had this built before, but what if the gap were filled with solder resist. How will this affect the performance? I could not figure out how to simulate this in ADS using the standard CPWG model.

thanks

I think you should use HFSS to simulate it, not ADS.

solder resist varies by vendor, but a typical one (Taiyo 4000BN) has er-4.71, Tandel=0.033 and thickness of 0.0005". You can use free sonnet (or other emag) simulator to see the effect.

I would not use HFSS for this. The EM problem can be easily solved in ADS Momentum or Sonnet (or other planar solvers).

Not sure if there is a relevant effect. I think we need to consider not only on the gap, but also the slight increase in capacitance between center and ground conductor surfaces from the solder resist layer above.

If lehomme specifies the dimensions and substrate, I can run the model in Sonnet to see what effect the solder resists has, with the solder resist data that biff44 has supplied.

I have had reasonable success with HFSS. Polar Instruments also has a transmission simulator, Polar 9000, that may be useful in your situation. Simon and Waddell have books and models on the subject as well. Without details a guess is uncertain, nevertheless, I would not anticipate a significant disturbance from solder mask in the vicinity of your traces.

The best simulator is the one you have not the one someone else has so I would not get wrapped up in that debate.