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[SOLVED] RFID CP Antenna (Why is sensing resistor required ?)

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vedagarbhamsandeep

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I have designed a RFID CP Antenna (8.2dBi) and when we connected the same to a Reader, it failed to detect / work.

But after some R&D and study of specs of the reader, I understood that they required a sensing resistor (10 Kilo ohms). Immediately I connected the 1/4W resistor between the ground plane and the radiating patch .. it worked very fine.

Can anyone tell me why the resistor was required ? I also wrote to quite a few antenna manufacturing companies but did not get a satisfactory answer though we are blindly manufacturing the antennas with resistors.
 

Maybe it's needed so that the circuit doesn't transmit unless the antenna is connected. (Obvious answer).
 
I would like to share another observation as well.

When the same spec antenna was designed using a shorted patch where the ground and radiating patch were shorted, the sensing resistor was not required. Here the resistance is 0 but the reader worked. Any comments on this as well would be highly appreciated.

We had to discard the same as the performance was not up to the mark.
 

The 10K resistor is just only for antenna detection which means the transmitter will not work if the antenna is not connected well. This is to protect PA .

It's a usual method in RFID application.
 
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