April 18, 2009
As I mentioned in my previous blog about the million dollar question, “How far will it read?”, two of the factors are the reader and antennas (and remember we are discussing passive RFID).
Passive UHF RFID readers can affect the read range depending on the manufacturer and the power level. In the US, FCC regulations cap the output power at 4 watts, whereas in Europe it is only 1 watt. There are studies available for purchase that detail the testing results of readers and antennas in a controlled, RF-friendly environment. These are appropriate for general guidelines, but each environment is different and a reader that did not test at #1 in the study may be the better one in your environment.
Passive UHF RFID antennas can also affect the read range depending on the manufacturer, the type of polarization and the gain. Antennas can be either linearly polarized or circularly polarized. When the direction of the electric field is in one plane, it is called “linear polarization”. When the direction of the electric field is rotated around the axis of propagation, it is called “circular polarization”. Linear polarized antennas will provide a longer read range as compared to circular. Also, an improvement in antenna gain is achieved by focusing the radiated RF into narrower patterns for the purpose of increasing the power in a specific direction. In general, the higher the gain the longer the read range.
My next post will cover how RFID tags affect the read range.