Is it possible to guarantee communication distance of more than 50cm by using ST25R3911B?

[zhulev uri]

Posted on March 20, 2018 at 03:12

Hi all 

I am making RF reader using ST25R3911B.

Communication distance should be more than 50cm.

Please let me know if is possible without an external power amp.

#st25r3911b

[Travis Palmer]

Posted on April 09, 2018 at 10:46

Dear Zhulev,

The communication distance depends very much on both - reader and tag.

Only if there is a good coupling from reader to tag a good communication distance is guaranteed. This will also ensure that the tag has a good LMA (Load Modulation Amplitude). A good coupling is given, if the tag antenna is similar size than the reader antenna. Usually the reader antenna is a bit bigger. 

Also the used protocol will have an influence on the communication range. ISO15693 for example will allow bigger distances than ISO14443 A or B. A rule of thumb says that the communication distance is approximately the length of a square antenna. Which means if you have a 10cm times 10cm antenna the communication distance should also be at least 10cm using a tag as described above. Also the Q-Factor of your reader plays a role here. The higher the Q-Factor will be, the more power will resonate in the LC antenna tank and the harder it will be to be ISO compliant or even produce decode-able wave shapes.

Achieving 50cm you will then need to upscale the antenna sizes for tag and reader accordingly. 

An alternative would be to add additional amplifier circuit to boost output power beyond the 1.4W and add additional filtering to the RFI receiver path.

BR Travis

[z3361]

HOW to set the registers to the power of 1.4W