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

[vedagarbhamsandeep]

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.

 

[sky_123]

Maybe it's needed so that the circuit doesn't transmit unless the antenna is connected. (Obvious answer).

 

[vedagarbhamsandeep]

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.

 

[rf1008]

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.