I'm designing a combline filter in ADS using stripline and microstrip. Can someone please tell me why stripline need a 3 layer substrate (MLSUBSTRATE3) and microstrip a 2 layer substrate (MLSUBSTRATE2)?
Stripline Comb-line filter from the ADS passive circuit design guide is based on the multi-layer transmission line library. Stripline by definition has top and bottom ground planes, adding the signal layer in the middle so there are three metal layers in total. That is why stripline comb-line filter needs the 3 metal layer substrate of MLSUBSTRATE3.