Hi，
I am trying to design NFC antenna with ST25R3911B，the antenna size is about 30*30cm，and the read range need 35cm；
I want to know the target matching impedance ，and is it possible to fulfill this requirement with the ST25R3911B NFC reader?
Hello Sky,
Following this two threads, you should succeed.
https://community.st.com/s/question/0D50X0000AvgiHoSQI/st25r3911b-with-antenna-size-30x40cm
https://community.st.com/s/question/0D50X00009XkWCSSA3/design-questions-around-st25r3911b
In the second thread we achieved a read range of 24cm using a 14x10 cm antenna. For you purpose I would recommend a 25x25cm or 30x30 cm antenna.
The Register 0x27 should be kept at 0x00. I would start with a target matching impedance around 15 to 20. The Q-factor should be around 35. The capacitive voltage divider should be setup in a way you achieve 2.7Vpp on the RFI (using the Measure Amplitude command).
Further information can be found in the application note "AN4974 Antenna matching for ST25R3911B/ST25R391x devices".
BR Travis
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