¿ªÔÆÌåÓý

ctrl + shift + ? for shortcuts
© 2025 Groups.io
  1. Nanovna-Users
  2. Messages
Single Messages Topics Expanded

Re: NanoVNA for RFID design

 

I am one of several engineers who worked for the company that originally
introduced RFID to the world, AMTEK. They no longer exist as many
start-ups go. The company was fresh off "The Hill", Los Alamos, where RFID
was originally developed to log and to some extent, track, Pu and other
radioactive carrying trucks. Dr. Gary Seawright purchased the patent
rights from Los Alamos and formed the company. Those systems operated in
the 915 MHz and 2.45 GHz ISM bands with an experimental license from the
FCC. When AMTEK was bought out by the Texans (that was the end of a good
beginning!!), Gary resigned. Another engineer, Dr. Jerry Landt, also left
shortly after. Jerry wrote and still participates in authoring most of the
RFID standards we have today for the RFID industry. The rest is
history........

So much for history. I was there. However your system is a low-frequency
inductively coupled system that likely operates below 150 kHz. Even though
the coupling element is referred to as an "antenna" is it not. You are
dealing with inductive coupling between the tag or badge and the reader
coils. I did not work on these systems, but am quite familiar with them
from much later work before I retired.

I note the required equipment lists only a Network Analyzer. There is a
big difference between a Scalar and Vector network analyzer, both in
performance and cost. The NANOVNAs are vector analyzers, but can be used
as a scalar analyzer as well. A scalar analyzer can not produce Smith
Charts as it does not measure the angle of the measurements and, therefore,
can not represent complex impedances or deal with Smith charts. That is
accomplished with a VECTOR network analyzer which is far more complex and
dwells with the Smith Chart. So,........., if there is no need for
measuring complex portions of the impedances of the antennas (inductors)
(which I do not read in AN4974) you're off the hook for a lot of complex
arithmetic and the Smith Chart!

Dave - W?LEV

On Tue, Jun 14, 2022 at 8:20 PM tjackson382000 <tedj1@...> wrote:

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





--
*Dave - W?LEV*
*Just Let Darwin Work*
--
Dave - W?LEV
Join [email protected] to automatically receive all group messages.