modeling frequency dependent resistor

How can I define a frequency dependent resistor? I have tried a normal lump resistor with R=k*sqrt(freq). ADS does not like that. It told me to use Equation base component. I used one port z-parameter equation base component with Z(1,1) = k*sqrt(freq). It is ok for S-parameter simulation but when I ask for Z-paramater data in S-parameter simulation. All Z parameters are zero. Any better way to define a frequency dependent resistor?

I don't think there is something like "frequency dependant resistor".
Maybe because of that all values are ZERO ..

Dear IanP. The frequnecy-dependent resister is for modeling purpose. I am trying to model some Coilcraft inductor, in the model,provided by coilcraft, there is a frequency-dpendent resistor. R = k*sqrt(freq). where k is given.

Did you solve this problem?

Replace R value of lumped Resistor to an equation defined variable. Otherwise, use a equation-defined 2-port to set the equation.

"Otherwise, use a equation-defined 2-port to set the equation.". How can u set parameters in 2-port Z-parameters? I use 1-port equation based. it works ok but when I turn the Z-parameter simulation on and use it to simulate 2-port. i get the warning message,

From your structure, I think the Z parameters are all infinite so you need to use only one port and connect another to the ground. This should work for the Z parameters.