Bandwidth Enhancement of Dielectric Resonator Antennas using Stacked and Fractal Geometries

Abstract

In recent times, the Dielectric Resonator Antennas (DRAs) have shown great potential as an alternative to microstrip patch antennas in various practical applications. Their inherent properties like wide bandwidth (BW), high gain, low losses, high mechanical strength, high power handling capacity, three degrees of freedom, compatibility with diverse feeding techniques, and many more make DRAs the preferred choice over microstrip antennas. Various techniques have been employed by the researchers for bandwidth improvement of Dielectric Resonator Antennas. This thesis focusses on the concept of using fractal geometry, stacking and a hybrid of fractal geometry and stacking for achieving wide bandwidth. Various novel DRA designs with wideband and ultrawideband (UWB) performance have been proposed. The proposed antennas have been analyzed using a FEM-based EM simulator Ansys HFSS. The prototypes have been fabricated and their results compared with simulated results to validate the designs. Further, it was found that very little work had been carried out in the field of mutual coupling isolation in ultrawideband DRA array. Using novel Defected Ground Structures (DGS), reduction in mutual coupling in different DRA array designs has been achieved. In the first approach to enhance the bandwidth of DRAs, two novel fractal-based DRA designs have been proposed. The use of fractal geometry also offers the benefit of antenna miniaturisation. The first design is a Triangular Prism-shaped DRA with Sierpinski Gasket fractal geometry. An impedance bandwidth of 72.3% has been achieved in this prototype. Secondly, the design of the innovative Surya Yantra-shaped fractal UWB DRA has been proposed. Measured impedance bandwidth of 113.3% covering the frequency range from 2.6 to 9.4 GHz has been achieved. In the second approach, two novel DRA designs based on the concept of stacking have been proposed. Apart from bandwidth improvement this approach also provides the benefit of high gain. Stacked T- and Z-shaped DRA designs have been proposed. Measured impedance bandwidth of 110.5% in stacked T-shaped DRA, and 114.5% in case of stacked Z-shaped DRA has been achieved. The simulated results of both the antennas have been validated. In the third approach, two novel DRA designs using a hybrid configuration based on the combined concept of fractal geometry and stacking have been proposed. This approach helps in achieving all three benefits of wide bandwidth, high gain, and antenna miniaturisation. Stacked fractal Maltese Cross and Triangular Prism-shaped DRA designs have been proposed. UWB of 111% covering 3.6–12.6 GHz and 120.9% covering 3.3–13.4 GHz have been achieved in stacked fractal Maltese Cross- and Triangular Prism-shaped DRA designs, respectively. Finally, the aspect of mutual coupling reduction has been addressed by the use of different defected ground structures. Mutual coupling reduction is the most essential factor for the use of antennas in multiple-input multiple-output (MIMO) applications. Four DRA array designs with novel DGS structures have been proposed. In the first two designs namely, fractal Tree- and stacked fractal Maltese Cross-shaped DRA array, periodic defected ground structure (PDGS) of C-shape has been incorporated to achieve mutual coupling reduction (< -15 dB). Elliptical-shaped DGS is used to reduce mutual coupling in the Triangular Prism-shaped fractal DRA array (third design). The fourth design is a Surya Yantra-shaped fractal DRA array with rectangular loop-shaped DGS for better isolation between DR elements. In all, ten novel designs have been proposed along with their detailed study.