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I'm trying to model the input impedance of a MESFET by using a series RLC circuit.

For example I have the following reflection coefficients:

.575 angle(-138) at 6 GHz

.617 angle(170) at 8 GHz

.610 angle(128) at 10 GHz

As you can see, as the frequency changes so too does the angle. Does anyone have any suggestions for how I can analytically or graphically determine a fairly close approximation using a series RLC?

Right now I'm trying to plot the 3 frequencies and the reflection coefficients on a Smith Chart and come up some values but the best I've been able to do so far is

.61 angle(-150)

.59 angle(178)

.61 angle(164)

using L = .442 nH, C = .917 pF and R = 12.85 ohms.

I'd like to get some more accuracy but it seems my method is not working too well.

Thanks,

roeb