Yes, there is. With all UHF interrogators, the read field is not uniform. There are null spots—or holes in the read field—caused by reflections in the waves coming from the reader antenna. These null spots can change as objects in the environment change. They are not a problem in applications where objects are moving through the read field or the reader antenna is moving, because the tag will pass into and out of the null spot and be read. But null spots can be an issue if you are trying to read stationary objects with a fixed reader antenna. If you’re running into this problem, you’ll need to work with a systems integrator who has strong knowledge of RF fields to resolve it.
—Mark Roberti, Editor, RFID Journal
How Is Tag Read Range Measured? »