Design of an electrically small and near-3D omnidirectional loop antenna for UHF band RFID tag

A novel planar and electrically small (0.1×0.1×0.002λ³) RFID tag antenna is proposed whose radiation pattern is near-3D omnidirectional. The proposed antenna is comprised of a small loop and an open-loop element with an inverted Z-shaped slot on it. The inverted Z-shaped slot is used to make the antenna smaller and improve the radiation performance. The proposed antenna is easy to change its shape in order to suit different applications without making great impact on performance. A rectangular version and a circular version of the proposed antenna are simulated for comparison. It´s confirmed that the performance of the circular version has little difference with the rectangular one. Both simulated operating bandwidths of the two version antennas are near 13.3 MHz and the gain deviations in all directions are less than 4dB.