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Monday, May 11, 2009

Strange RFID reading holes

Besides the well documented orientation reading holes, testing reading range on several scenarios usually observes the following: testing reading distance while moving away from the antenna, tags can be read on continuous basis until a certain distance, then they stop reading, and then they start reading again, and so on and so forth until they finally stop reading. And this reading hole phenomena seems stronger as we power up the antennas.

image The reason for this strange reading holes is reflection. When multipath signals re-unite in phase the combined effect creates an extended reading range. When they re-unite out of phase the combined effect effectively reduces de reading range.

So should we use this extra-mileage reading range? Well, I hate to say this but… it really depends on your scenario. As a rule of thumb you should always privilege lower power and stay away from edge reading scenarios, but there are times when we really have to depend on this inter-reading-hole area to get some edge cases.

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