Broadband Circularly-polarized And Dual-Polarized Dielectric Resonator Antennas

The rapid development of modern wireless communications, satellite communications, navigation and radar systems demands for advanced antennas in terms of polarization characteristics, wide bandwidth, miniaturization and low loss. Circularlypolarized(CP) antennas have been widely used in communications and radar systems because of their ability to reduce multipath effect, suppress interference from rainy or foggy weather and increase the channel capacity. The synthetic aperture radar(SAR) with dual-polarized(DP) antennas is featured by all-time and all-weather capability and high-quality imaging, which has found wide range applications in both military and civilian systems. Therefore, several innovative designs on broadband CP and DP dielectric resonator antennas(DRAs) are proposed in the paper. Moreover, the corresponding experimental demonstrations are accomplished. Three main subjects are included in the thesis:Firstly, a dual-feed CP DRA with new wideband quadrature coupler is presented. The feed network provides good impedance matching, equal power splitting and consistent 90° phase shifting over a relative bandwidth of 50%. The antenna exhibits good performance on impedance matching and CP property over a broadband bandwidth of 41.8%. Moreover, the compact design of the mentioned antenna achieves impedance bandwidth of 48.46% and axial ratio(AR) bandwidth of 47.69%, respectively. Some parameters of the proposed dual-feed CP DRAs keep advanced level in the world. Also, a wideband CP DRA fed with a sequentially rotated feed network is developed, whose AR bandwidth and impedance bandwidth are promoted obviously.Secondly, a broadband DP DRA with high performance is proposed. The antenna is excited by balanced feed structure and in turn the cross-polarization fields are suppressed effectively. The DP DRA with balanced-slot feed demonstrates that the port isolation reaches 51 dB, the worst cross-polarization level below –35dB, and the relative impedance bandwidth is over 15%, from 8.85 GHz to 10.45 GHz. The X band DP dielectric resonator array with balanced-slot feed also demonstrates good performance on cross-polarizations and port isolations.Thirdly, a novel feed structure named as coplanar waveguide(CPW)-to-slotline is presented, with which a high radiation-efficiency CP DRA is designed. Since the absence of conductor and surface-wave losses of the dielectric resonator and the inherent low loss of CPW-to-slotline structure, the CP DRA reaches the highest radiation efficiency of 97.7% in the operating band. Additionally, a high gain CP DRA employing higher-order TEδ13 mode radiation is proposed for the first time, and the antenna gain is higher than 9.0dBi. The analysis on the mechanism of gain enhancement is presented theoretically.