Bandwidth Enhancement of Dielectric Resonator Antennas using Stacked and Fractal Geometries by Kedar Trivedi

Guided by: Dr. Dhaval Pujara With Synopsis and CD
15EXTPHDE152

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.