# How to convert S11and S22 to complex impedance

1. ## converting s11 to impedance

Dear all.
I'm a new comer, i wish to learn alot from you.
I have designed a PA module using BLF278. but datasheet only give me S11,S12.S21.S22 and I need convert to Zin and Zout in complex impedance. (or how to use S-paramter)
Thanks

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2. ## s11 impedance

Z = (1 + ρ)/(1-ρ)

ρ = (Z-Z0)/(Z+Z0)

Z0 is usually 50 ohms. These calculations are, of course, complex.

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3. ## s11 to impedance

You can use the calculations from the link
http://www.rfcafe.com/references/electrical/s-h-y-z.htm

1 members found this post helpful.

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4. ## convert s11 to impedance

Thanks you very much for so many helps.
But BLF278 only give me S11 and Φ; (see table). I must convert to Zs and Zl in complex impedance.
Thanks.

5. ## s11 convert s22

Maybe I wasn't clear enough.

Zin = 50*(1 + S11)/(1 - S11)

And

Zout = 50*(1 + S22)/(1 - S22)

where Zin and Zout are the impedances looking INTO the device. You have to mutiply by 50 to convert the normalized impedance into ohms (assuming your S parameters were measured on a 50 ohm network analyzer).

The table you published has S11 as mag[s11] and ang[s11] for various frequencies. These are complex numbers. You do the complex division, one frequency at a time, and the answer is also a complex quantity, either in magnitude and angle, or Real and Imaginary parts, depending on how you choose to do the arithmetic.

Rich
www.MaguffinMicrowave.com

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See below:

thanks alot

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