Re: CPW T-junction
Hi,
The pictures shown above are really good and valuable! You must have air bridges around T junction or the current in direct path (left to right) will be broken for the bottom arm. Likewise, both of the bottom arm of T junction excite parasitic microstrip-like mode at discontuity unless this mode is blocked out by adding symmetrically the airbridges so that the potential is equalized around the discontinuity.
To conclude, if airbridges are not arranged as on the picture, you will have some undefined circuit that will look like CPW T junction but will not function as one.
My advice is as Sinatra's: Do T junction first and make sure that it works more-less as sugested from general transmission line theory (3x50 OHm lines connected in a common point), then add the switch circuitry. You will, of course, see the effect of discontinuities, but generally you should see something like:
S21, S31 ~-6dB
S11, S22, S33 ~-6dB.
flyhigh