Antenna problems in RFID systems

As the frequency of choice for RFID devices rises into the microwave region, the problem of designing antennas to match the devices on the protected object becomes more acute. The objective of any such antenna must be to maximise the transfer of power into and out of the device on the protected object. This requires careful design to match the antenna to free space and to the following ASIC. The frequency bands considered in this paper are 435 MHz, 2.45 GHz and 5.8 GHz and the usage is for retail goods only. The major considerations in choosing an antenna are: the type of antenna; its impedance; RF performance when applied to the object; and RF performance when the object has other structures around it. Antennas which are omnidirectional should be avoided and, wherever possible, directional antennas should be used because they have the advantage of less disturbance to the radiation pattern and to the return loss. (5 pages)