how to measure the S parameters of an unequal power divider? - RF Cafe Forums

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alpergenc

Post subject: how to measure the S parameters of an unequal power divider?

Posted: Thu Jun 18, 2009 8:46 pm

Lieutenant

Joined: Thu Jun 18, 2009 8:36 pm
Posts: 1

I have to measure the S-parameters of an unequal dual-band power divider using VNA. I have set Z0=50ohm during the calibration. The problem is the output impedences of the divider is different than 50 ohm. can I set the impedences of the two ports of the VNA seperately during the calibration? can anyone please help me about this?

skywave

Post subject: Re: how to measure the S parameters of an unequal power divider?

Posted: Thu Jul 09, 2009 8:17 pm

Lieutenant

Joined: Wed Sep 10, 2008 5:49 pm
Posts: 4
Location: Central England

What springs to mind is this:

If you know the impedances that the O/P ports want to 'see' - i.e. what will match them, then a suitable resistive pad between the O/P under test and the 50-ohm input of the VNA will keep everything matched, thus enabling you to make the measurements. The unused port will need to be terminated in its appropriate R, for which you may - or may not - need a pad, depending on just what the O/P Z of that port actually is. Of course, you then need to correct the measurements (return loss, insertion loss, etc.) to take into account the attenuation of the pad(s). As for the pads themselves, you might have to make these yourself, and if the freqs. invloved are many tens of MHz, that could be difficult without introducing stray L and C, thus putting errors into your measurement. If, however, you have a 75-ohm to 50-ohm requirement, suitable coaxial pads are available commercially.

HTH.

Skywave.

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