| dc.description.abstract | The spherical inverted-F antenna (SIFA) is a relatively new conformal antenna
design that consists of a microstrip patch resonator on a spherical ground. The SIFA
resembles a planar inverted-F antenna (PIFA) that has been conformally recessed onto a
sphere. The basic design, simulation, and fabrication of a SIFA were recently reported.
The aim of this thesis is to provide a three-fold improvement to the study of the SIFA:
the fabrication of a dielectric-coated SIFA, a new analytical model based on the cavity
method, and the analysis of a randomly oriented SIFA’s operation in a remote
networking scenario.
A key improvement to the basic SIFA design is the addition of a lossy dielectric
coating to the outside of the sphere for purposes of impedance stability, bandwidth
control, and physical ruggedization. The first contribution of this thesis is the fabrication
of such a dielectric-coated SIFA. Two antennas are fabricated: a coated SIFA operating
at 400 MHz, and an uncoated SIFA operating at 1 GHz for comparison. Both SIFAs are
constructed of foam and copper tape; the coating is comprised of silicone rubber and carbon fiber. The fabricated designs perform with reasonable agreement to
corresponding simulations, providing a basic proof of concept for the coated SIFA.
The SIFA was previously studied analytically using a transmission line model.
The second task of this thesis is to present a new model using the cavity method, as
employed in microstrip patches. The SIFA cavity model uses a curvilinear coordinate
system appropriate to the antenna’s unique geometry and is able to predict the antenna’s
performance more accurately than the transmission line model.
The final portion of this thesis examines the performance of the SIFA in a remote
network scenario. Specifically, a line-of-sight link between two SIFAs operating in the
presence of a lossy dielectric ground is simulated assuming that each SIFA is randomly
oriented above the ground. This analysis is performed for both uncoated and coated
SIFAs. A statistical analysis of the impedance match, efficiency, and power transfer
between these antennas for all possible orientations is presented that demonstrates a
design tradeoff between efficiency and predictability. | en |
