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

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


 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?


 
   
 
 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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