Why do LF/HF RFID tags use the near field (magnetic coupling) and not the far field? Well, I guess it's easier. The two antennas can just be modeled as a "transformer" and power transfer is straight forward.
But would it be possible to use the far field as well (assuming we antenna size is not the issue)? How would the energy transfer change?
Why are "long distance" RFID tags UHF tags?
According to Frii's transmission equation, the received power is indirectly proportional to frequency. So a lower frequency would mean more power at the tag.
Is the reason just the large required antenna or something else?