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Antenna for RFID reader

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beni_annis

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Hello Everyone,

I want to design a reader with frequency changing frequency from 10 to 20 MHz does anyone know who to design the reader antenna, I want to have the center frequency at 15 Mhz. Thank for the help in advance :)
 

Hello,

in HF-RFID Applications the antennas are simple coils. So for example for 13,56 MHz (passive RFID-Tags ISO 14443) a reader antenna can be a 60*40 mm coil with 4 to 6 windings. It's because the system relies on inductive coupling (for RFID-systems I know).
 

yes i know that, but in the case where you do not have a simple reader but reader with band of frequency which is my case, is it possible to choose a center frequency and than make a antenna design and the coupling based on this value ?
 

yes it's possible. The Antenna itself is independent of the center frequency (in the Range of some MHz) because it is a coil (inductance). For tuning it to a special frequency a matching circuit of C's are applied. The goal is to make a resonance-circuit. For more details you can look at AN710 from Microchip and AN1445 from NXP. But the way for tuning the antenna depends on the concrete reader-ic you use.
 
Usual RFID systems are small band, due to both existing regulations and technical advantages. To generate suffcient field strength with small power (e.g. a few 10 mW), you have to rely on resonance. Reader coils are tuned to the center frequency of 13.56 MHz, the Q value is set according to the modulation bandwith. Increasing the bandwidth by a factor of 10 also demands tenfold transmitter power. Keeping this relations in mind, it's surely possible.

Although your project seems to involve wide band operation, it can be meaningful to check, wether it can be legally used at all.
 

yeah sure, I will have a look (no break of rules :) )
 

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