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Output Power Measurement Using Network Analyzer - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

 Post subject: Output power measurement using network analyzer
Posted: Fri Jul 07, 2006 2:48 pm 

Joined: Tue Apr 18, 2006 10:40 pm
Posts: 11

i new to using network analyzer and doing microwave/RF measurements. i am using Agilent 8364B network analyzer. i did full 2-port caliberation for power sweep and got s21 vs. Pin curve. now, i wanted to get Pout vs. Pin curve but the one i got didn't correspond to s21 data.

i did an unratioed trace on receiver B (in side the VNA port 2) to see the absolute output power on receiver B but instead of showing a curve that is Pin+s21=Pout it shows me in fact a loss of 10 dB, which doesn't make sense. i did the full two-port caliberation so i think caliberation shouldn't be the issue. do i need to do a receiver caliberation for B. is that required, though? would i see this bad a Pout curve if I don't do receiver calibeartion? any help or feedback will be nice. thanks

 Post subject:
Posted: Tue Jul 11, 2006 4:40 pm 
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Joined: Sun May 14, 2006 8:53 pm
Posts: 20
Location: Earth
I'm not sure if I understand you correctly, but if I do I think the relative numbers should match. Meaning you the compression levels for input power should be the same for both results. I would stick with the one with S21 since the calibration is fully accounted for.

For the measurement of "raw" power into PortB, since the measurement is unratioed (as you mentioned) the levels have to be checked for. The VNA has internal attenuators (plus the couplers) that are automatically accounted for when you use the VNA "normally". Check the settings and also check the actual output port power (PortA) with a Spectrum Analyzer.

But I think you already found this out:

 Post subject:
Posted: Tue Aug 29, 2006 6:13 pm 

Joined: Tue Aug 29, 2006 6:10 pm
Posts: 1
You will need to calibrate the "B" receiver in order to see accurate power levels. What you are trying to accomplish can be done. Set up a B channel measurement. Perform a source power calibration on port 1, so the output power of port 1 is calibrated over your desired frequency range. Then make a through connection between ports 1 and 2, and perform a receiver cal (which is essentially a normalization). Now the values on the B receiver are accurate. When you connect your amp, the B will show you the output power in dBm.

Posted  11/12/2012

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