Novel designs of three-dimensional patch antennas for beamdwidth enhancement and broadband operation 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