Modelling a non-linear resistor on ADS
Aldrich—I am not really familiar with Advanced Design System or AWR Microwave Office, but your post is tagged with &quot;spice&quot;, so that implies one or both of the packages supports SPICE netlists? And supports behavioral current sources? If so, you could try coding the non-linear resistor's behavior like this:
.subckt Rmicrowave pin1 pin2
  Br pin1 pin2 I = V(pin1,pin2) - V(pin1,pin2)**2 - V(pin1,pin2)**3
.ends Rmicrowave