STEVAL-25R3916B with external antenna

[Dilip]

Hi ST team, 

Can I connect an external antenna to STEVAL-25R3916B board ? In my project i need to connect the external antenna through a SAM connector cable. what  changes i have to do in this board for antenna tuning and matching network?

[Travis Palmer · Accepted solution]

Hi Dilip,

please have a look at AN5592.

https://www.st.com/resource/en/application_note/an5592-st25r-single-ended-antenna-matching-stmicroelectronics.pdf

It describes how external antennas, which are connected via coaxial cables are connected to the ST25R3916/B.

It also applies to ST25R3916B. 

Please let me know, if you have any specific questions.

br Travis

[mgscasso]

Hi Travis,

I'm interested in implementing an external antenna, specifically the one referenced in this datasheet https://www.mouser.mx/datasheet/2/18/1/ST0812_21_N01_A_FPC_Antenna_NFC_Reader_Datasheet_R-3370083.pdf

While I've reviewed the AN5592 application note, I'm still uncertain about the optimal approach to take. Do you have any additional examples of external antenna implementations? Could you recommend an off-the-shelf antenna with a 'standard' matching network that would be suitable for most applications?"

[Travis Palmer]

Hello Mgscasso,

Matching this antenna:

Inside the datasheet you can find the antenna parameter in free air. 

If you don't have a VNA, this is a good starting point for you. There is no parallel resistance at resonance frequency state, but i think you can calculate it from the Q-factor.

If you have a VNA  i would propose to bring the antenna in the final position (integrated into your device including the environment of the antenna (display, battery, PCB, metallic parts) which can change the antenna parameter. 

Once you have decided, which antenna parameters to continue with, you can follow the process mentioned in AN5276 - chapter 6 Antenna Matching. 

You should also look into chapter 7 - Design verification.

Single ended antenna:

If you want to continue with another antenna, which is already tuned to 50Ohm. 

For example the Taoglas FXR.01.07.0100C.A. and continue like mentioned in AN5592 single ended with cable and just skip the cable.

BR Travis