I'm interested in the distance that an ultrahigh-frequency interrogator can actually reach, and not in the theoretical distance for reading a passive tag.
It would be impossible to answer this question with any precision. In a vacuum, such as in space, radio waves travel forever. On Earth, however, electromagnetic energy grows weaker as it travels through the air. Water absorbs UHF energy, so moisture in the air or products with a lot of water in the read field will reduce the signal. If the wave needs to travel through cardboard or other materials, that will impact the distance the waves can travel.
Moreover, the power output of the reader antenna, the antenna gain and whether you are using a circular- or linear-polarized antenna will have an impact on how far the waves can travel. The size and design of the receiving antenna might also be relevant here. Waves might reach more than one mile away, but if you cannot pick them up with your receiver, what good would that do?
If you can explain what you are trying to accomplish, perhaps I can reach out to an RF engineer and get a precise answer for you.
—Mark Roberti, Founder and Editor, RFID Journal
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