Most manufacturers seem to offer active RFID in the ranges of 433 MHz or 2.45 GHz. Why is this the case?
That's an interesting question. There were a few companies that offered active systems in the 900 MHz frequency band, including RFind and Radarfind. Both companies are no longer in business, though I am unsure whether or not this is due to their choice of frequency. I believe there are not a lot of companies that chose 900 MHz for their active system because RF energy is absorbed by water at this frequency, which means the systems wouldn't perform as well as those using higher or lower frequencies outdoors. Perhaps some RF engineers will chime in with more technical responses below.
—Mark Roberti, Founder and Editor, RFID Journal
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