High Gain Wide Bandwidth Layered Dielectric Resonator Antennas

Dielectric resonator antennas (DRAs) are promising candidates for the next-generation wireless communication systems since they offer wider bandwidth and higher radiation efficiency. In addition, higher gain can be accomplished by exciting a higher order resonance mode in order to meet the high-frequency application requirements. However, several challenges exist in the design of higher-order mode DRAs such as the narrow bandwidth and the possibility of impractical dimensions. This thesis presents a novel design approach that offers high gain in conjunction with wide impedance and axial ratio bandwidths by utilizing layered DRAs that are excited in higher order mode. A number of known approaches for gain enhancement have been investigated such as higher order mode operation of standalone DRAs, dielectric superstrate as well as DRA arrays. Generally, each of these design approaches is associated with at least one of key limitations such as narrower impedance bandwidth, impractical dimension, considerable sensitivity to fabrication errors and the requirements for a complex and lossy feed network in the case of arrays. On the other hand, the reported literature designs that incorporate multi-layer DRAs have been limited only for impedance bandwidth improvements. This research extends the potential of incorporating a dielectric coat layer to enhance the gain and axial ratio as well as impedance bandwidth.
X-band and mm wave rectangular DRAs that operate at multi-high order modes have been considered, where each one of them has been coated by an additional dielectric layer that has increased the order of the excited modes so that an enhanced gain of ~12dBi can be accomplished in conjunction with wider matching impedance and axial ratio bandwidths as well as a considerable robustness to fabrication errors. The proposed design concept offers an alternative approach to the existing mechanisms that are either based on a lower gain single mode operation or a higher order mode operation with narrow bandwidth and noticeable sensitivity to fabrication tolerances. This framework has been applied to cylindrical DRA that offered a remarkably gain of ~ 14 dBi, which is the highest for a single wideband DRA and in line with those offered by arrays. Therefore, the proposed layered DRA designs represent alternative to the classical approach of employing arrays for gain enhancement with additional appealing radiation characteristics. Moreover, the proposed concept has been adopted to design a high gain wide band mm-wave hemispherical DRA. However, owing to the nature of the modal field distribution inside the DRA, the design has been modified to utilize a two-layer dielectric coat in order to create a multi-stage transitional region between the DRA element and free space. This has provided an enhanced gain of 9.5dBi in conjunction with a wide impedance bandwidth. Several prototypes have been fabricated and measured at the x-band and mm-wave frequency range with good agreement between simulated and measured results.