ANTENNA_1356 Datasheet, PDF (3/6 Pages) rfsolutions.ltd – Micro RWD MF (Mifare) Antenna Specification

ib technology
0.7 – 1.4uS
RWD to transponder communication – pulse pause modulation, ISO14443A timing
specification and waveform envelope for ideal Quality factor
7) For optimum performance the antenna Q (Quality factor) should not exceed 40.
Practically the Quality factor effects the shape of the waveform envelope and if too
low or too high then read/write performance (range) will be poor or the system will
not work at all.
The formula for calculating Q = 2*pi*fL / Rant = 102 / Rant
where f = Resonant frequency, 13.56 MHz, L = Antenna inductance, 1.2 uH
Rant = Overall antenna resistance = Rdriver + Rext + (Rcu + Rrf)
Rdriver = Resistance of FET driver (from IC spec)
Rcu = Resistance of Copper (coil)
Rrf = RF resistive component (eddy current losses etc)
For Q = 35, Rant = 102 / Q = 102 / 35 = 3 R
By measurement (and IC spec) Rdriver + (Rcu + Rrf) = approx 2R
Therefore Rext = 1R
8) The Micro RWD has been designed to work at optimum performance with a
Quality factor of 35-40 using 1uH inductor and Rant < 3 R.
For practical purposes Rext will be <1R and may be omitted and a thinner
gauge of wire used for the coil.
(Note that Rext would be shared between two series resistors of value Rext/2)
9) When designing and winding antenna coils, the wire gauge and its DC resistance
must be considered to keep close to the design optimum. Significant differences in
Rant will affect EMC and overall performance.
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