EMC Filter & Matching Circuit for MINI RFID-RC522 (MFRC522)

[JoSt]

Hi

I am working on a University project where we need to impliment 24 of the same Mini RFID-RC522 onto a single PCB. Instead of buying the full reader 24 times per PCB and using the PCB only as a connection board to an ESP32 (as we have done so far), we want to build the full reader (incl. antenna) onto the PCB directly. My issue is now that I cant find the full EMC Filter & Matching Circuits for (example) this Reader in the schematics provided with the product online (its missing 2 caps and a couple of resistors and the LED, the issue is only the caps with the antenna).
Also we don't have access to the equipment to build and then determine the antenna characteristics on our own as would have been outlined how to do in this document.

If it helps in any capacity, size of the antenna is:
outer lenght: 30mm
inner lenght: 24.5mm
outer width: 24mm
inner width: 18mm

Any help would be greatly appriciated.

PS: Attached I have a drawn version of cap locations on the MINI RFID-RC522, here the same highlight of the cap corresponds to same capacitance of the cap, but measurements dont reflect values found in the schematic found above (factor +-1.5-2), therefore I left them out (capacitor measurement has been done using a frequency generator and high ohm resistors looking at their chargecurve on a oscilloscope). The cap names are derived from this version of the product

Correction, the resistors R4 and R5 are not shorted, and their inner (left) pads are connected to the antenna. The outer pads are connected either up/down to the caps (R4 is connected to C9, C11, C15 and R5 is connected to C13, C14, C16)

[Fabian_R]

Hello, my name is Fabian, I've been assigned to support your case.
Please notice that MFRC522 isn´t recommended for new designs, unfortunately, the support for custom boards is out of the scope of this free online support. My recommendation is to please take a look at the following Application Note for Antenna Design. https://www.nxp.com/docs/en/application-note/AN1445_An1444.zip
This document will be very helpful for building your own antenna design.
Please keep in mind that even though the document you posted is from an NFC Reader, the requirements for PN7120 and MFRC522 are different.
Please take a look at AN1445 for a better implementation.

[JoSt]

Thanks Fabian,
I wasn't aware (and a bit of searching honestly only confused me more about whats right or wrong) that there was such a major difference between the PN7120 and the MFRC522. Also I am still unsure if it will solve my problem, I will see that in the near future.
For now thank you though.
Best Regards
Jo

[Fabian_R]

Yes, please explore the possibility of using MFRC630 plus since it is a similar recommendation for your project.
You are very welcome sir!