Design of dual-polarized patch antennas for wireless communications

Abstract

Patch antennas are widely used in wireless communication systems, due to their features of low profile, lightweight and ease of integration with other microwave circuits. Dual-polarized antennas have the ability of increasing system capacity and frequency reuse. In this thesis, three original dual-polarized patch antennas are designed. The first dual-polarized antenna is designed for outdoor cellular base stations covering the frequency band of 1.7 to 2.7 GHz for efficient support of 2G/3G/LTE systems. Aiming at overcoming the disadvantages of unstable radiation patterns of previous dual-polarized patch antennas, a low-profile dual-polarized patch antenna is proposed. The antenna consists of a square patch radiator placed at 20 mm above a square ground plane. For bandwidth enhancement, the square patch radiator is dual fed using four probes, each having a U-shape. The radiation pattern is stabilized using four slot groups on the ground plane and a metallic ground wall around the radiating patch. Both simulation and measurement results show that the antenna has stable radiation pattern with small HPBW variation in both E- and H-planes. The second dual-polarized patch antenna is designed for indoor base station applications, including WLAN. Notably, there is an increasing demand of aesthetics for indoor antennas. In this part, we present the design of a transparent dual-polarized patch antenna using micro-metal mesh conductive (MMMC) film covering the frequency band of 5.15-5.85 GHz. The MMMC film is constructed by CIMA NanoTech using SANTE self-assembling nanoparticle technology, and has a high transmittance of above 75% and a low sheet resistance of 0.05 Ω/sq. A smartphone screen is used as substrate and a layer of MMMC film is used as ground. The radiating patch made of MMMC film, is aperture fed through two H-shaped coupling slots in orthogonal direction on the ground plane. Results show that our transparent antenna has higher efficiency than other transparent antennas. Our third dual-polarized patch antenna is targeted for long distance wireless systems, where antennas with high-gain are essential. The design of our third dual-polarized patch antenna has high-gain by using a microwave-lens. Based on the microwave-lens for linearly polarized antenna composed of 13 layers of purely dielectric sheets in parallel, a lens for dual-polarized antenna is also designed. It consists of two groups of dielectric sheets in parallel, and these two groups of dielectric sheets are placed in orthogonal directions. Simulation results show that the microwave lens has little effect on the impedance bandwidths (IMBWs) and isolation of dual-polarized patch antenna, but can significantly increase the boresight gain of the dual-polarized patch antenna from 4.5 to 16.6 dBi for port 1 and 5.1 to 16.8 GHz for port 2, at center frequency of 8.5 GHz. In conclusion, three original dual-polarized antennas are designed in this thesis, including a low-profile dual-polarized patch antenna with stable radiation pattern using ground-slot groups and metallic ground wall, a transparent dual-polarized patch antenna suitable for indoor deployment, and a dual-polarized patch antenna with high gain using microwave-lens.