Novel designs of three-dimensional patch antennas for beamdwidth enhancement and broadband peration have been proposed in this dissertation. For the beamwidth enhancement, the patch antenna with an inverted V-shaped patch has been proposed, and the antenna¡¦s radiation beamwidths have been broadened. Another beamwidth enhancement design using a three-dimensional square ground structure has also been demonstrated, and the 3-dB beamwidth of the CP radiation can reach more than 110¢X. In addition to the designs of beamwidth enhancement, the broadband patch antennas with a V-shaped patch, a W-shaped ground plane and a short probe-pin have been proposed. These novel structures can have significantly reduced probe-pin length and obtain a good impedance matching over a wide frequency range. Finally, a 1 ¡Ñ 2 broadband patch antenna array, suitable for base-station antenna applications for mobile communications systems, has also been studied.

Novel designs of planar antennas including the feed network for improving the antenna performance improvement (CP axial-ratio bandwidth, XPL, port decoupling for dual-polarized operation, and harmonic control) or achieving dual-band operation are presented. This thesis, comprises five sections. Firstly, for obtaining broadband CP designs, the Wilkinson power divider and branch-line coupler are used. The 3-dB axial ratio CP bandwidths of all proposed antennas are larger than 30%. Secondly, the dual broadband patch antennas including a stopband network are proposed. Thirdly, the dual-polarized patch antenna with high XPL and isolation between two ports by using a Wilkinson power divider with a 180¢X phase shift between its two ports is proposed. Fourthly, the dual-band and dual-polarized patch antenna suitable for base-station antenna applications for mobile communications systems is studied. Finally, the harmonic control study of a square microstrip antenna is presented.

Several broadband dual-polarized patch antenna designs are presented and studied. Good isolation (< ¡V30 dB) between the two feeding ports of the proposed broadband dual-polarized patch antenna has been obtained. This dissertation reports four different innovative designs. Firstly, a new design of the aperture-coupled patch antenna with modified H-shaped coupling slots for achieving dual-polarized radiation with high isolation over a wide bandwidth is studied. Secondly, Optimized feeding of the dual-polarized aperture-coupled patch antenna with H-shaped coupling slots for achieving highly decoupled feeding ports is experimentally investigated. Thirdly, an aperture-coupled patch antenna with a cross slot for compact dual-polarized operation in the 1800-MHz band suitable for applications in personal communication system is presented. Finally, new designs of the broadband dual-polarized patch antenna with hybrid feeds suitable for DCS base-station application are proposed.