conductor backed coplanar waveguide

halo i am want to design a 100ohm and 50 ohm CBCPW as shown in figure now my question is what should be the optimum ration between g and w.how to avoid unnwanted modes .i have designed line using hfss now the thing is using different values of g and w i can get the same impedance are there limitation's between ration of g and w i have to avoid.
i need help urgently

There are two unwanted propagation modes you want to avoid in a GCPW:

1. Slot line mode: This is avoided by keeping the grounds on the signal layer at the same potential by shorting them with an air bridge.

2. Parallel plate mode: This can be avoided by shorting the grounds on the signal layer to the substrate ground with the help of a via.

After that, it is advisable to keep the width of the ground line on the G-S-G layer at least 2.5 times the gap between the ground and signal lines to avoid return currents.

You may find more information on this at:
http://www.ece.tamu.edu/~kentesar/EL...89_passive.pdf

i have linewith s=0.3mm and g=1.2 for 100 ohms line is it ok ?

Yes, that line width is ok as long as the manufacturing process allows such tolerances. This should still be ok in a standard PCB manufacturing processes where the tolerances are better than 0.1mm.

the substrate i am using is 0.762mm in that case are the values right ?

Although, its too old thread, but still I have some problem in my design using HFSS so kindly help in this regard. I am sending the HFSS file that I made. I s my str. dimensions and waveport size is OK?

Thanx if somebody comes up with the help.

sorry i dont see your file

Hello leaps

I am attaching you the file...that was missed that time.....
i want to design a 50 ohm CPW line with right mode propagating...can u help in this regard..?


I will b thnkful 4 ur help...