Miniaturized Omnidirectional UHF RFID Antennas

UHF RFID reader antennas are often patches operating in the fundamental mode, with broadside radiation patterns. For some applications, it is convenient to have planar antennas with omni-directional patterns, which can have greater angular coverage than conventional reader antennas. A circular-patch antenna operating in a monopole mode is presented. Using both shorting pins and slots, the antenna is highly miniaturized. The effect of different antenna tuning parameters are presented, and their trade-offs are considered. An optimized design is presented and its properties are discussed.