Low-profile, Ultra-wideband, Cavity-backed Spiral Antennas.
Rahman, Nahid.
2012
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Abstract: Spiral
antennas are a popular class of antennas that demonstrate exceptionally large
bandwidths, uniform input impedance, stable gains and the ability to radiate circularly
polarized waves over their entire frequency coverage. Circularly polarized radiators are
integral components of all space-based communication, SATNAV and SATCOM services,
microwave direction finding systems, GPS ... read moreapplications, in-flight connectivity etc. As a
result, spiral and helical elements have become a distinctive branch in the field of
antenna engineering. Spiral antennas are often configured with a metallic cavity that
restricts the radiation to one hemisphere for unidirectional operation. With
ever-decreasing dimensions of communication devices and to focus on issues concerning
space constraints arising from installation of numerous antenna elements, low-profile
geometries have drawn considerable research interest over the years. In this
dissertation, we have addressed the problem of designing low-profile, ultra-wideband
(UWB), 2-18 GHz cavity-backed spiral antennas. First, we discuss the development of UWB
shallow, absorptive cavities from a microwave material characterization standpoint. We
then proceed onto geometrically modifying regular spirals to obtain more compact
structures that incorporate certain radiation properties. Axial ratio is one the most
important bandwidth factors in measuring the performance of a circularly polarized
radiator. In developing low-profile geometries, one most often encounters the problem of
deterioration of the axial ratio. This is particularly evident in rectangular spiral
antennas, where the purity of the circularly polarized waves is highly compromised as a
tradeoff with available aperture. It therefore becomes essential to design spiral
geometry in such a way so as to preserve the lowest possible antenna aperture with the
best possible axial ratio performance. In our work, we have presented a detailed study
of slow wave spirals, elliptical spirals and modified Archimedean polygonal spiral
antenna designs that address the problem of maintaining high axial ratio performance
with low-profile planar geometries. The designed antenna systems have been fabricated
and tested for performance validation, and they demonstrate excellent axial ratio
characteristics across their bandwidth.
Thesis (Ph.D.)--Tufts University, 2012.
Submitted to the Dept. of Electrical Engineering.
Advisor: Mohammed Afsar.
Committee: Joseph Noonan, Sameer Sonkusale, and Robert Mailloux.
Keywords: Electrical engineering, and Electromagnetics.read less - ID:
- 2b88qq31n
- Component ID:
- tufts:20987
- To Cite:
- TARC Citation Guide EndNote
