With the rapid development of wireless systems, dielectric resonator antennas?DRAs? draw wide attention owing to their advantages of wide bandwidth, low loss and high efficiency. Circularly polarized and dual-linearly polarized antennas have been widely used in satellite communications, navigations and other fields. Therefore, this dissertation is mainly concerned with the dual-band circularly polarized and wideband dual-linearly polarized dielectric resonator antennas. The major contributions are summarized as follows: 1. A dual-band circularly polarized DRA has been studied. A novel single-fed dual-band circularly polarized DRA is presented. The proposed antenna is excited by a microstrip line through the narrow underneath rectangular aperture, and its HE111 and HE11??2<?<3? modes are utilized for the dual-band operation. By cutting two notches from the cylindrical DRA, two sets of orthogonal modes for HE111 and HE11??2<?<3? can be excited simultaneously for dual-band circularly polarized design. A pair of equal arc-shaped slots are employed to enhance the axial-ratio?AR? and impedance bandwidths. The broadband circularly polarized characteristic has been achieved in the lower band by using two radiators, DRA and arc-shaped slots. The simulated results indicate that the antenna features impedance bandwidths?|S11|<-10dB? of 26.25%?4.5-5.88GHz? and 11.17%?8.54-9.55GHz?, and 3-dB AR bandwidths of 15.8%?4.78-5.6GHz? and 5.02%?8.94-9.4GHz? in the lower and upper bands, respectively. Finally, prototype of the proposed antenna is fabricated and measured. Reasonable agreement between measured and simulated results is obtained. 2. Two broadband dual-linearly polarized DRAs have been studied. Firstly, a broadband dual-linearly polarized DRA is proposed using the probe- and slot-fed excitation methods. By introducing an air gap between dielectric resonator and ground plane, the Q-factor of the DRA is reduced and the impedance bandwidth is expanded. To achieve dual-polarized operation, a hybrid feed mechanism with a probe feed and a slot feed is used. The simulated results show that the impedance bandwidth for port1 and port2 is 50.84%?4.24-7.13GHz? and 41.75%?4.7-7.18GHz?, respectively. The isolation is more than 25 dB across the overlapping band. Then, a broadband dual-linearly polarized DRA excited by inverted-L probes is designed. By introducing a low-permittivity??2=2.2? dielectric layer between dielectric resonator and ground plane, the Q-factor of the DRA is reduced effectively and the impedance bandwidth is widened. To achieve dual-polarization and high-gain characteristics, two pairs of rectangular dielectric resonators fed by two T-junction power dividers are placed to be orthogonal. The simulated results show that the impedance bandwidth for port1 and port2 is 58.43%?4.47-8.16GHz? and 52.47%?4.78-8.18GHz?, respectively. The isolation is more than 20 dB across the overlapping band. Finally, the second antenna is fabricated and measured. Reasonable agreement between measured and simulated results is obtained. |