Hello, imado_60. Unfortunately, ADS has limited number of coplanar components, only transmission lines i think. If you want to simulate an interdigital capacitor in ADS you can only in Momentum, from the EM field point of view (depends now what kind of result do you want from the simulation!!). As far as I know, i don't think any kind of microwave software or RF can simulate a CPW interdigital capacitor, the whole idea is to actually build it yourself in a EM software, like CST, AWR MO, etc. so that you can define the whole geometry accordingly to your needs. But this also depends very much on what kind of data you want from the simulation of it.