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# S-parameters - an ideal value?

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#### dd2001

##### Full Member level 4
S-parameters?

What is ideal value of S11 and S22?

Are they have to be real number like S11=100+j0, and S22=4+j0?
Does S11=100+j0 is better than S11=50+j0?

Thanks

reflection coefficients

These are reflection coefficients. It all depends upon what the circuit is to do. In amplifiers, making them zero is best. In filters they have to be not zero in the stop band.

armaniranfar

### armaniranfar

Points: 2
In VSWR a good value for S11 and S22(Exept for HPA's)
would be <1.2 in dB this ~ -20dB. If your plotting S11/S22
on a smith chart a good place is dead center of the graph.
This region = 1+j0 on the smith chart.
(when normalized by Zo (Most of the time Zo=50 Ohms)

P.S. Hp has a good App note on S-parameters you might find it
in MCU fileman
Good luck

Element_115 said:
on a smith chart a good place is dead center of the graph.
This region = 1+j0 on the smith chart.
(when normalized by Zo (Most of the time Zo=50 Ohms)

perhaps, 0+j0.

Refection coefficient 0+j0
Normalized impedance 1+j0

Basically they are same thing.

:!: :idea: :?:

marcomdd said:
Element_115 said:
on a smith chart a good place is dead center of the graph.
This region = 1+j0 on the smith chart.
(when normalized by Zo (Most of the time Zo=50 Ohms)

perhaps, 0+j0.

Re: S-parameters?

You did a small mistake. The values are actually impedance and not S11. S11 is same as reflection coefficient and its real component varies from +1 to -1.

:!: :idea: :?:

dd2001 said:
What is ideal value of S11 and S22?

Are they have to be real number like S11=100+j0, and S22=4+j0?
Does S11=100+j0 is better than S11=50+j0?

Thanks

S11 means the reflection coefficient at port 1 provided that the other ports are matched. The same thing applies to S22. Plotting Sxx in the smith chart can give you information to extract the normalized impedance.

S parameters

what does it mean if s parameters given for a HF FET gate input?

It means that FET in amplifier mode: source is grounded, gate (port 1) is input, drain (port 2) is output. Usually S-parametrs gives for some operating modes (Vds and Ids).

Regards,
Kit-the-great

Hi,

How can I get S-parameter in a HPA and how get it's K value?

Hi GaAs FET ,

but............