Hi Drax,
If S11 > 1 it means it is not unconditional stable, i.e. it might
oscillate...
Your formula for input impedance is only valid if s12 or s21 = 0, and I
think that is not the case.
Otherwise: Gamma(Inp)=S11+(S12*S21*Gamma(outp))/(1-S22*Gamma(outp))
73's Carel.
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Drax Felton
Sent: dinsdag 16 juni 2015 21:53
To: amps@contesting.com
Subject: [Amps] Understanding S Parameters
I am trying to understand S Parameters for a RD00HHS1 transistor.
The S11 parameters listed in the datasheet are as follows:
10 MHz 1.002 (mag) -3.6(ang)
30 MHz 1.003 -9.9
50 MHz 1.005 -16.8
100 1.007 -33.5
150 0.989 -49.8
I'm trying to estimate the input impedance at 0.475MHz. But I am uncertain
what it means when the mag is greater than 0.999.
Using the 10 MHz S11 value because it's available I get:
Gamma = 1.002 = (ZL-50)/(ZL+50) --> ZL= -50050 ohm impedance or a VSWR of
negative 1001:1.
What am I doing wrong? What does this mean?
My other attempts at calculating input Z also result in negative impedances
in linear form like -50.58-1589j My RF books do not seem to say anything
about this.
Kb3x
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