External antenna for NUCLEO-NFC08A1?

[Jose_eflow]

Hi, 

Could you please confirm whether an external NFC antenna can be connected to the X-NUCLEO-NFC08A1 board? I see P200 and P202 in the schematic, but it is not clear to me whether these are intended for external antenna connection or only for optional/test points. If an external antenna can be used, could you explain how the on-board etched PCB antenna should be disconnected from the ST25R3916B antenna path, where the external antenna should be connected instead, and what antenna inductance or electrical parameters should be targeted before tuning the matching network?

Thanks!

Best regards, 

Jose
 

[Ulysses HERNIOSUS]

Hello Jose,

 

U.FL P200 and P202 are connected to AAT_A/B. They can be used to observe these signals coming from ST25R3916B.

If you want to connect and external antenna I recommend to attach to the pads (pink arrow) or the vias and cut the board around the dotted lines and break the antenna (4) off:

 

This way you have the matching at 3 at your disposal to change for your antenna. Please refer to the Antenna Design guide AN5276 for details on the target values and process.

 

BR, Ulysses

[Jose_eflow]

Thanks for your response Ulysses, 

Regarding the NFC antenna integrated on the NUCLEO-NFC08A1 board, I used the antenna design tool available at https://eds.st.com/ and calculated an inductance of approximately 1.34 µH for the existing antenna.

Using this value as the target inductance, I designed a rectangular NFC antenna using 1mm diameter copper wire with the goal of matching the same inductance. Could you please review my calculations and confirm whether the resulting inductance is correct? I would also appreciate your feedback on whether using the estimated antenna inductance as the design target is a valid approach for replicating the antenna's performance.

Thanks 

Best regards, 

Jose

[Travis Palmer]

Hi Jose,

 

The ST25R supports a wide range of antenna inductance. A safe range is between 0.5uH to 1.5uH. But it does not mean that an inductance of 2uH is not useable. 

Regarding your design, 1.34uH is perfectly fine. Once you have produced your antenna and measured the antenna parameter we can help you designing the matching network. 

Please let us know, if you have additional questions.

 

br Travis