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Impact of Q factor in spiral antenna design for RFID

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Sep 12, 2008
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10 khz spiral antenna

Hi everyone,

I was surprised to find a forum like this where there is some activities. I try to expose my problem.

I'm currently doing my diploma work. I must create a complete RFID system (reader and tag) at 13.56 MHz. My question concern the antennas which are spiral inductors. I have already well documented about them. I have understand eg about modelisation that we can do complicate as well we can do simply. But I keep in my mind that the quality factor of antenna must be severly considered if we want avoid problems in communication.

Thus, the deal is as follows :

If we want to get a good read range, we must increase this quality factor. For ISO15693, because of the subcarrier of 423 kHz, the bandwidth must be 846 kHz, thus the quality factor can be maximised only to 16. I have showed that if quality factor of antenna is too big one add a resistor to decrease it. That's ok, but how should we now consider the design of antenna if in all case we ensure that Q don't exceeds 16. Does the own quality factor of antenna reach a big value in such a way that we increase the read range or does it have any impact because we finaly decrease Q of global system ?

I thank the one who can answer me if there is an answer :)

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