Research On The Theory And Design Method Of Dieletric Resonator Antennas

With the rapid progress in modern wireless communication systems, antennas have drawn significant attention as one o- their key components. Dielectric resonator antennas (DRAs) have attractive features such as small size, wide bandwidth, and high radiation efficiency. They are not only suitable for the traditional wireless communication systems, but also have prospects in millimeter wave regions. The operating principle of DRAs is researched in this dissertation, and a systematic design method for DRAs is presented. Moreover, several new design concepts for DRAs are proposed, and DRA designs with good antenna performance are achieved. The major contributions of this dissertation are as follows:1. The operating principle and design method of DRA are studied. The relationship between the stored energy and radiated energy of a dielectric resonator in a source-free region is researched. The reason why a dielectric resonator can be used as an antenna radiating structure is studied based on theoretical derivation. Two work stages of DRAs are defined in time domain, and the energy relations of the DRAs in the two work stages are discussed. Then a first-order approximate design model for DRAs is proposed based on dividing a DRA into radiating structure and feeding structure. The correlations between the antenna performance and the two structures are presented.Moreover, the influence of feeding structure on the radiating structure is introduced to improve the proposed model. Finally, a systematic design method for DRAs is carried out on the basis of the model, with the principle for choosing radiating structure and feeding structure. In addition, the operating principle of hybrid DRAs is explained based on the electromagnetic theory, and a wideband hybrid circularly polarized (CP)DRA with a wide CP bandwidth of 24.6% is achieved.2. New radiating structure designs for DRAs are studied. Firstly, stratified dielectric rectangular resonators are theoretically discussed based on the dielectric waveguide model method and effective dielectric constant method. Equations for computing the resonant frequencies and corresponding field distributions of stratified dielectric rectangular resonators are carried out. On the basis of the obtained equations,the operating principle of wideband stratified dielectric DRAs is explained and the air gap effect on DRAs is theoretically studied. Besides, the stair-shaped dielectric resonator is researched, and the resonant modes in it are defined. Then a wide dual-band CP stair-shaped DRA is presented, with the CP bandwidths of 9.7% and 20.0% for the lower and upper bands, respectively.3. New feeding structure designs for DRAs are studied. A new concept for DRA bandwidth optimal design is presented, which is based on utilizing a broadband feeding structure to excite the resonant modes in the dielectric resonator. Two new broadband feeding structures are introduced, including the monofilar-spiral-slot and the Archimedean spiral slot, and three wideband CP DRAs are presented based on the two feeding structures. The Archimedean spiral slot excited rectangular DRA realizes a wide CP bandwidth of 25.5% based on its TE111x/TE111y, mode, and the Archimedean spiral slot excited stair-shaped DRA obtains a wide CP bandwidth of 53.4% by exciting the quasi-TE111x/ quasi-TE111y and quasi-TE111x13/ quasi-TE113y modes.4. A new directivity design method for DRAs is studied. A new design concept for DRA directivity design is presented. The design concept is based on combining different operating modes in a DRA to achieve the desired antenna radiating pattern.Based on the proposed concept, an omnidirectional rectangular DRA is realized by combining its TE121x and TE211y modes, and the synthetic mode is named as quasi- TM011 mode. Equations for calculating the resonant frequency and field distribution of the quasi-TM011 mode are presented. The existence conditions and feeding method for the quasi-TM011 mode are discussed. Moreover, it is demonstrated that the TE411x and TE411y, modes of a rectangular DRA can also be used to construct a higher-order omnidirectional quasi- TM012 mode. A dual-band omnidirectional rectangular DRA is realized by using a probe to simultaneously excite the quasi-TM011 and quasi-TM012 modes, and its operating frequency band covers the 3.5GHz WiMAX and 5.8GHz WLAN bands.5. New antenna material for DRAs is studied. A DRA based on pure water is presented. A method for improving radiation efficiency of water DRAs is carried out,which effectively solves the bottleneck of water DRAs. In addition, a design concept for frequency-reconfigurable antennas based on combining a broadband feeding structure with a frequency-reconfigurable radiating structure is proposed. Two frequency-reconfigurable water DRAs are designed. The Archimedean spiral slot excited frequency-reconfigurable water DRA exhibits a wide continuous tuning frequency range from 155 MHz to 400 MHz with a radiation efficiency of about 90% and good CP performance. The conical probe excited frequency-reconfigurable water DRA has a wide continuous tuning frequency range from 165 MHz to 700 MHz with stable omnidirectional pattern and an average radiation efficiency of about 80%. The two water DRAs have the advantages of wide frequency range and high radiation efficiency over the traditional frequency-reconfigurable antennas.