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But why would anyone want an RFID reader that can read cards over 10" away except to read someone's Credit card or Debit card without the person knowing about it... then you just watch them type in their pin number and you have complete access to their credit/debit card....

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From: [email protected] <[email protected]> on behalf of tjackson382000 <tedj1@...>
Sent: Tuesday, June 14, 2022 8:20 PM
To: [email protected] <[email protected]>
Subject: [nanovna-users] NanoVNA for RFID design

I'm sure that at least a few here are familiar with the following section from the STMicro application note "AN4974: Antenna matching for ST25R3911B/ST25R391x devices", since it calls for the use of a VNA and the ST25R391x is an RFID reader chip, supporting several standards. What I'm confused about is line 4. And I'm not sure of the nanoVNA setting for line 5 (Q factor measurement). Can anyone brief me on what the author is saying there exactly? I'm by now familiar with the open/short/50ohm calibration procedure of course, but intermediate level in re-exploring the many curvy zen mysteries of... the dreaded Smith Chart and applying the procedures within AN4974.

Also, does anyone here have actual experience with the design of reader impedance matching and tag antenna design for those chips? In other words, has anyone ever survived AN4974 and lived to tell about it? Finally, I need to design an RFID system (I chose the ISO-15693 standard for its relatively long range, although I would LOVE to hear about any other standard for which cheap front end chip solutions exist). Requires a 3" diameter tag antenna and any diameter below 5.5" for the reader antenna and a read range of up to 10" and must merely read out its unique UID code when detected. Am I dreaming? Sound feasible? Many thanks to anyone who might be willing to offer a little experience and advice, and I'd discuss compensation if an expert is willing.


7.3 Verification of the Q factor in the frequency domain

The Q factor can be measured using a vector network analyzer and an ISO10373-6 Class 1-3 calibration coil. The following steps should be carried out:

1. The network analyzer shall be calibrated for a frequency sweep from about 10 to 20 MHz
2. S11 measurement in log mag format shall be displayed.
3. The calibration coil is connected to the VNA.
4. “Short” calibration of the coil and conversion to “Z: Reflection”
5. Set marker 1 and enable the bandwidth/Q factor measurement
6. Place the PCD antenna on the measurement coil Note: If the reader is plugged and powered, ensure that register 0x27 is set to 0xFF to avoid an high power transfer to the VNA ports, which can damage the VNA.
7. Adjust the suitable trim value via the register map (register 0x21) in the GUI of the reader
8. Place a 3 ? resistor between the RFO pin to simulate the chip resistance during operation.
9. Press “max search” to align the marker on the resonance frequency peak of the PCD antenna Figure 33 shows the results of such a measurement.

#applications #coils #design #matching #nanovna