Thanks erveybody!
Maybe I agree with Vfone. Yes, the dynamic range of the RFID receiver is pool, but this system is FSK modulation, I think FSK system have more anti-jamming capbility than ASK system. So if the tag's antenna circuit gets detuned, then how to explain the tag is worked well at the 1.5cm distance,except something is make the tag worked in a detuned condition. Somebody can ell me what's that?
Now I put my test step in the attachment, it is a very particular account of the test.
Attachment:
View attachment 50441