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how to measure UHF RFID antenna port impedance

how to measure UHF RFID antenna port impedance

how to measure UHF RFID antenna port impedance

(OP)
Hi everyone,
How do I measure the complex port impedance of an UHF RFID port antenna? I have tried measuring differential port impedance using VNA with a probe, but the results do not seem to be correct.
Thanks
 

RE: how to measure UHF RFID antenna port impedance

"using VNA with a probe" - that doesn't make much sense, can you provide more detail or a photo of your test setup?  

What was your test environment?  You can easily get unexpected results by having your antenna too near a metal surface, or more likely not having the same physical ground structure at your test fixture as you have in your application.  

Have you verified your test setup by measuring a known impedance?  

A crude technique I've used in the past is to use two identical antennas, one as source and one as receptor and then make a couple of S21 measurements with the setup and extract the parameters from there.  If you can get a decent S11 setup you'll probably get much better results though.  

John D

RE: how to measure UHF RFID antenna port impedance

Hello,
In what range of frequency works your RF ID antenna?
Is the setup used by you calibrated somehow? Is there any offsets taken in consideration?
Maybe a picture  would be very helpful for us ,like zappedagain said in the above post.
Mishu

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