|dc.description.abstract||Antennas that use the radiating mode of a dielectric resonator are called Dielectric Resonator Antennas (DRAs). They are used extensively in microwave communication in today’s world. They can be of any three-dimensional shape such as cylindrical, rectangular, hemispherical, etc. Such a resonator typically has low loss (no conductor loss) and frequency bandwidth is dependent on the dielectric permittivity. They are generally smaller in size than an equivalent metallic cavity, and can be incorporated into microwave circuits and coupled to planar transmission lines.
DRAs are much more difficult to batch fabricate along with microwave circuits compared to their metal counterparts. This is due to the fact that most DRAs are generally made of high permittivity ceramics, which require high temperature firing which is not generally compatible with microwave fabrication processes. The fabrication of miniature DRAs for high frequency bands is even more challenging. Machining of the extremely hard ceramics becomes difficult. This resulted in a new approach proposed in the research group, which enabled one to fabricate DRAs using lower permittivity ‘soft’ polymer materials. These so called ‘meta-DRAs’ were formed by incorporating metal inclusions within a polymer base material. The polymer-base has a very low permittivity, and hence does not naturally resonate as a DRA in the 20-60 GHz region. In order to achieve resonance at the desired frequencies, the relative permittivity of the DRA has to be increased considerably. This was done by introducing metal inclusions in the polymer base of the DRA to affect the electric flux density. In this thesis, a wide variety of such meta-DRAs have been designed and simulated considering various structural design parameters. The simulations have been done using HFSS version 15.0 and a layout for fabrication was developed with the help of AutoCAD and ADS. The antennas were designed for two principal resonating frequencies, 24 GHz and 60 GHz. Various designs were evaluated and the ones with the best results were included in the layout. Small physical variations such as lateral metal width and gap have been carried out. The height of the inclusions was also altered. The layout was used to fabricate an X-Ray mask at the Karlsruhe Institute of Technology (KIT), Germany. Using this mask, X-Ray lithography and metal electroplating were used to demonstrate the feasibility of fabricating the proposed structure.
In the thesis, the entire process used to design and simulate these meta-DRAs has been explained and the simulation results have been compared. The primary objective of this project, to demonstrate through simulations an increase in the effective permittivity of a polymer based DRA and the effect on permittivity of varying the inclusion properties, has been successfully satisfied.
Generally, the use of metal inclusions can increase the effective relative permittivity of the DRA in the range of 12-16. Different metal inclusion geometries behave differently. Out of the geometries tested, the “H shaped” inclusions generally perform most favorably. Other geometries include “window” and “half-window”. Certain meta-DRAs with unusual shapes or special meta arrays have been designed and results compared. Varying the gap/width of the meta inclusions affects the resonance. This also depends on the number of elements (metal inclusions) in the polymer base. Some designs have non-uniform metal widths. Non-uniform height of the meta samples results in multiple resonances in some cases.||