Application Of Artificial Magnetic Conductor On Low Profile Antennas Design

With the rapid development of artificial electromagnetic structure, using a variety of unconventional electromagnetic parameters of AMC to improve the conventional devices has been attracted widespread concern in industry and academia. On the other hand, miniaturization trend of the wireless terminal device put forward stricter request for the antenna design. The antenna miniaturization issues become more prominent. In this thesis, concerning the problem of high profile of the traditional antennas, several low profile antennas are proposed based on the zero reflection phase characteristics of AMC within a specific frequency range.Firstly, a wideband low-profile quasi-Yagi antenna operating above a metal surface is proposed. A design approach combining a printed double-element Quasi-Yagi antenna and an Artificial Magnetic Conductor(AMC) reflector is proposed to eliminate the negative effect of the metal on the antenna performance, such as impedance mismatch and low radiation efficiency. A prototype has been fabricated for validation, and experimental results show that the antenna provides a wide operation band of 1.68 GHz(8.8–10.48 GHz) and a low profile of 0.14λg. The antenna also features a broadband off-axis radiation pattern with a maximum radiation direction of 37o-47 o at from 9 GHz to 10 GHz, which is suitable for applications requiring tilted beam pointing the end-fire direction.Secondly, a coax-feed low profile dual-polarized circular patch antenna with ±45o polarization is presented. The antenna consists of a dual-polarized circular patch excited by two coax-lines and an AMC reflector. By using the AMC reflector as the ground plane of the patch antenna, the profile of the antenna is reduced to λ/8 of the operation frequency, which is much lower than that of the conventional dual-polarized patch antenna. The experimental results show that the proposed design obtained a wide bandwidth(2.12–2.77 GHz) and a high isolation(>35dB) over the entire band. In addition, the front-back radio of the antenna is improved significantly by using the AMC reflector. The wide bandwidth, low-profile and high front-to-back ratio make the antenna a good candidate as a base station antenna for WLAN, WiMAX and LTE applications.Finally, concerning the contradictions of traditional AMC structure between bandwidth and miniaturization, complementary AMC structure is proposed based on the defect ground AMC. Compared with the conventional AMC structure, complementary AMC structure is more simple and easy to optimize. Using electromagnetic characteristics of the proposed AMC structure is analyzed using electromagnetic simulation software. At the same time, combined with folded monopole antenna, a new low-profile broadband folded monopole antenna is proposed based on the complementary AMC structure. This kind of antenna can achieve a good impedance matching over a wide frequency band, high gain and radiation efficiency.