Antenna parameters measurement for ST25R3911B

[JPehl.1]

We have a custom board which have a ST25R95 transceiver with a PCB copper made NFC antenna/coil that is double side. Now we want to switch to ST25R3911B transceiver to be able to reach a higher reading distance for NFC tags. We do have some bare boards to make tests with the antenna/coil alone.

When I calculated the components for RF circuit of ST25R95 through a spreadsheet, it was required to input only the inductance and the DC resistance values. But for ST25R3911B there are other inputs like "Parallel resistance" and "Self resonance frequency". This is required by the tool "ST25R Antenna Matching Tool" in order to calculate the values of components for the RF circuit.

The "Parallel resistance", should it be measured at 13.56MHz or other given frequency?

And about "Parallel resistance" and "Self resonance" parameters, which kind of equipment could be used to measure them? 

Regards. 

[Ulysses HERNIOSUS · Accepted solution]

Hi,

AN4974 should contain the necessary information. Did you study it already?

Regards, Ulysses

[JPehl.1]

Thanks for your help.

I have read the document, but don't have much knowledge about RF circuits.

I have forwarded a bare PCB for tests of the copper trace made NFC antenna/coil using a network analyzer. They will make the same setup and measurements of page 15 and 16 of the document you quoted.

[Travis Palmer]

Hello JPehl,

The measured smith chart should look like this:

The necessary data can be taken from Marker 2 and Marker 3.

This measurement can be done using a "miniVNA PRO".

It is also sufficient for antenna matching and fine tuning.

br Travis

BR Travis.