matching of transformer coupled circuit

doneirik · Aug 29, 2005

dear forum,

I´m using a passive circuit with two coils (one at each end) for relaying a signal between an RFID tranceiver and a transponder. The system operates at 13.56 MHz.
So far I only use a series resistor and a series capacitor for resonance frequency in the passive relay circuit. The distance between the two coils is only 2 -3 cm, and I have connected it by twisting a copper wire.

I´m wondering if I have to macth each end of the passive circuit to 50 ohm? (or to each other) to avoid reflections?
Any opinions on this?

zappedagain · Aug 30, 2005

While I can't picture your circuit exactly, I expect that if you go through the RLC calculations you'll see that 50 ohms will severely detune your resonator (very low Q) and you'll have poor coupling between the two antennas.

Matching the transceiver and transponder antennas to each other might give some improvement; think of it as a transformer.

At 13.56 MHz your wavelength is extremely long (about 22 meters) so reflections over 2-3 cm will not be a problem.

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matching of transformer coupled circuit

doneirik

Electrical

zappedagain

Electrical

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