# External Antenna connection on MFRC522

New to RFID world.

I am working on a Healthcare product. One of the feature includes authentication of patients which will be done through RFID reader MFRC522. Application schematic in the datasheet explains about the matching and tuning circuits. But I couldn't find anything related to interfacing an external 13.56MHz antenna.

Can I use an external antenna 1462360001 from Molex in place of Lant (Antenna in datasheet pg.81)?

Datasheet of External antenna - https://www.molex.com/pdm_docs/sd/1462360001_sd.pdf

Edited:

I do not have much filter experience. Those application notes are really helpful. I am using AN1491 to design EMC filter & matching circuit for the chosen external antenna 1462360001.

Antenna datasheet doesn't specify all the parameters needed in the calculation tool to design like Ca & Ra values are not mentioned.

Here is the snapshot of the calculation.

La = 2.11uH (from antenna datasheet), Ca = Ra = 0 (missing in datasheet) Which gives L0, C0, C1 & C2 values.

Please let me know if I am doing anything wrong.

A quick search for this Molex “part number + Application note “ shows a variety of sizes each with a specific inductance , L with a series capacitor added to resonate at this NFC frequency. Bigger is better for range in the 10 cm + ballpark.

Molex also have some with ferrite substrates that raises L slightly using a slightly smaller cap. The ferrite substrate is not used to increase the possible gain but rather improves the immunity to nearby metal objects from detuning.

$$\Z_o(f)=\sqrt{\dfrac{L}{C}} ~~Q=\dfrac{Z_o}{Rs}\$$

Application note — MFRC52x Reader IC Family Directly Matched Antenna Design

Application note — MIFARE (ISO/IEC 14443 A) 13.56 MHz RFID Proximity Antennas

An Eng. with sim tools can compute the desired Rx/Tx duplex passive values.

If you do not have much filter experience with all the necessary test equipment, it is wiser to use the recommended differential antenna and filter matching circuit in their App Notes above. The antennae are not compatible to the same circuit. The external antenna would have to be the same differential loop type and impedance based on geometry and substrate materials.

As you see, the Tx/Rx coils form a weakly coupled resonant transformer.

Here you can see data rate is 16th of the carrier frequency which limits the Q possible for gain vs BW to about 4.

A quick review shows that the Lant has complimentary design (first sentence on P.81 of the data-sheet). This is also true for a coil antenna such as the one you found from Molex.

Short answer: Yes. Not as short: You should verify antenna parameters to understand whether you need to tune the antenna to your reader. The typical application example shows there are components used to tuning so overall it seems possible.

Can I use an external antenna 1462360001 from Molex in place of Lant

The MFRC22 is a 32 pin chip therefore, any mention of an antenna is always going to be an external antenna i.e. the chip doesn't have an internal antenna.

Regarding whether the Molex antenna is suitable, there is nothing in the data sheet that states it is used for 13.56 MHz so, without wishing to dig deeper, you will have to dig deeper and ascertain these things: -

• Whether it is suitable for 13.56 MHz
• Whether the range of inductance it has is suitable for the tuning arrangements mentioned in the NXP data sheet.