Triple-band dipole antenna with artificial magnetic conductor for radio frequency identification

Abstract

The radiation characteristics and input impedance of the dipole antenna will be distorted when the antenna is placed on a metal object. The electromagnetic wave of the antenna is reflected almost entirely by the metallic surface and a 180° phase shift is occurred. In addition, a common dipole antenna has low gain which is about 2.15 dBi. Owing to the high impedance, surface structure called Artificial Magnetic Conductor (AMC) is developed as a ground plane for the dipole antenna to prevent the performance degradation of the antenna caused by metallic objects and to increase the antenna’s gain. Due to the reflected wave of the AMC is in-phase with the antenna current (reflection phase equals to zero), it improves the radiation efficiency and subsequently enhances the gain of the dipole antenna. Thus, due to the great demand in multiband antenna, this research has developed a triple-band dipole antenna with straight and meander structures at Ultra-high Frequency (UHF) and Microwave Frequency (MWF) Radio Frequency Identification (RFID) frequencies; 0.92 GHz, 2.45 GHz and 5.8 GHz respectively. Firstly, the single-band square-patches AMCs are investigated. Then, to obtain a smaller structure of AMC and suitable for RFID applications, two new structures of AMC-HIS are developed. They are single-band AMC called zigzag dipole and dual-band AMC called rectangular-patch with slotted rectangular and I-shaped slot. The parameters that affect the AMC performance are discussed and the performances of the antenna with and without the AMC GP are investigated in terms of return loss, total gain, total efficiency and directivity. From the results gained, in general the power received of the dipole antenna with AMC GP is higher than the power received of the dipole antenna with the absent of AMC GP. Furthermore, a longer reading distance is recorded for the dipole tag antenna backed by AMC structures. For instance, the reading distance for the UHF meandered dipole tag antenna with the 2x2 rectangular-patch with slotted rectangular and I-shaped slot has achieved two times higher compared with the dipole antenna without the AMC GP. While at MWF, its reading distance is increased from 0.8 m to 1.25 m. The performance of the dipole tag antenna with AMC GP attached to the metallic plate size is also tested to verify the dipole tag antenna with AMC GP can be used for metallic object detection in RFID applications.