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Which Antenna Should I Use?
Is there a specific antenna that is better than others?
The short answer is: Whichever one works.
The longer answer is more complicated. In some cases, you need to match tag and reader antennas. All passive low-frequency (LF) and high-frequency (HF) systems utilize coiled reader and tag antennas that form an electromagnetic field with which they communicate.
With passive ultrahigh-frequency (UHF) systems, you can choose linear- or circular-polarized antennas. A linear-polarized antenna directs RF energy in a narrow horizontal or vertical beam. If you are using dipole tag antennas and can control the tag's orientation to the reader antenna, then a linear-polarized antenna will give you a longer read range than a circular-polarized version.
If you cannot control the tag's orientation to the reader antenna, then a circular-polarized antenna is probably preferable. The circular-polarized model emits energy in a cone-shaped spiral, so some energy can reach the tag antenna regardless of its orientation.
There are also some new phased-array antennas on the market. These provide some relative information on a tag's location. So, for instance, if you were to put one in the ceiling, it would project a cone of energy down to the floor, and could then tell you if a tag was located near the center of the circle on the floor, or near the edge on the left or right.
In the end, the choice of antenna depends on a variety of factors, as well as what you are trying to achieve.
—Mark Roberti, Founder and Editor, RFID Journal
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