| In recent years, with mobile communication technology developed rapidly, mobile communication system has been updated faster and faster. As the important components of the mobile communication system, antennas have been put forward more different requirements. Therefore, the research on the key techniques of mobile communication antenna has become a hot topic. In consideration of research subiects and practical requiement of moblie communication systems, this dissertation is mainly concerned with the dual-polarized antennas, the analog beam forming networks and the novel wideband array antennas in the key techniques of mobile communication antennas. The author’s major works and contributions are as follows:1. Dual-polarized microstrip array antennas are investigated. Based on the probe fed microstrip patch antenna, two dual-polaried microstrip array antennas are proposed.1) For broadening the bandwidth of dual-polarized microstrip antenna element, a capacitive coupling slot and tapered feed plate are introduced. An 8×1 broadband low profile dual-polarized microstrip array antenna is developed for base station application.2) A dual-band dual-polarized low profile microstrip antenna element is proposed. By introducing a wideband 180°power divider with simple struture, the cross polarization and port isolation of the antenna is improved. Based on the element antenna, a 4×1 dual-band dual-polarized low profile antenna array is developed for micro base station applications.2. Dual-polarized dipole antennas are researched. Based on the crossed-dipole antenna with reflector plate, three kinds of dual-polarized dipole antennas are designed.1) A wideband dual-polarized dipole antenna covering the band of 2.32-4.03GHz is proposed based on the planar overlapping open sleeve antenna structure.2) Based on the abvoe antenna, a dual-band dual-polarized dipole antenna which can over 2.4/5.8GHz band is proposed. By introducing a horizontally-extruded square ring, the impedance bandwidth and pattern bandwidth at the upper band is broadened.3) A broadband dual-polarized dipole antenna which can cover the band of 1.7-3.8GHz is proposed. By adding a vertically-extruded square ring, the antenna achieves a broadband bandwidth and a stable radiation pattern over the whole operating band. The three kinds of dual-polarized dipole antennas above have the wide band/multi band-characteristics, which can be used in the micro base station of the mobile communication system.3. Beam-forming networks (BFNs) are studied.1) According to the three orthogonal beams requirement of the mobile communication system, a 3×3 orthogonal beam-forming network is designed to provide three orthogonal beams simultaneously.2) For beam reconfiguration requirements of the mobile communication system, a 2×3 reconfigurable beam-forming network is designed to achieve two beams reconfigurable at the same time through a 2-bit phase shifter.3) For different scenarios in the mobile communication, a beam-forming network with different number of the orthogonal beams is required. In order to design the beam-forming networks with arbitrary orthogonal beam number, two synthesis methods based on Givens transform matrix are proposed. The correctness of the above synthesis methods are validated with simulation.4. Microstrip array antenna fed by slot on a substrate integrated waveguide(SIW) is studied.1) A 4×1 microstrip array antenna is proposed using series feed network. The proposed array breaks the limitions of narrow impedance bandwidth of regular array antenna with series feed network, achieveing a bandwidth of 20.1%(VSWR<1.5).2) By using a multi-section height-stepped waveguide, a broad bandwidth substrate intergated waveguide (SIW) waveguide to rectangular waveguide direct transition is designed.3) Based the above 4×1 microstrip array antenna and the broad band transition, a 4×8 microstrip array antenna fed by standrad rectangular metal waveguide is proposed. Experimental results show that the 4×8 array has a wide impedance bandwidth (24-26.5GHz) and high gain.5. Dual-polarized array antenna based on tightly coupled theory is studied.1) A broadband dual-polarized array unit which uses crossed-dipole structure is proposed for infinitely periodic array.2) A 4×7 finite array is designed which composed of the above array unit. By using open-circuit termination, resistive termination and quasti-ridge-waveguide loading techniques, the truncation effect for the 4×7 finite array is overcome. The proposed array obtains a wide impedance bandwidth (100-350 MHz). In addition, the active standing wave is under 3 when phase scans±45° in horizontal plane. 3) A broadband impedance converter is desgined to match the impedance of the antenna unit and achieve unbalanced to balanced conversion. Also a broadband divider with four outputs is designed to combine the four elements in the vertical dimension.4) The proposed dual-polarized 4×7 array prototype is fabricated and tested, and the simulated and measured results are analyzed.
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