A Study Of Dual-band Circularly Polarized And Wideband Dual-Linearly Polarized Dielectric Resonator Antennas

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 HE11δ（2<δ<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 HE11δ（2<δ<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（ε₂=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.