CPW open end stub and other discontinuities

Hi,

I have been reading a lot on CPW design from many sources but I don't know how to design an open end stub or a T on CPW. I can use ADS or CST for the design but I don't know where to start to select the dimensions of the stub since many equations take into account the gap but not the actual lenght of the stub.

Any guidance is much appreciated.

Regards