Type of Document Master's Thesis Author Clark, Jeffrey R URN etd-12112003-095406 Title Multifilar Hemispherical Helical Antennas Degree Master of Science Department Electrical and Computer Engineering Advisory Committee
Advisor Name Title Safaai-Jazi, Ahmad Committee Chair Besieris, Ioannis M. Committee Member Davis, William A. Committee Member Keywords
- quadrifilar helix
- helical antennas
- multifilar helices
Date of Defense 2003-10-31 Availability unrestricted AbstractHelices are broadband antennas that provide moderate gain, largely real input impedance and circular polarization when operating in the axial mode regime. A modified form of the helix, the spherical helix, has been shown to yield similar polarization and gain characteristics over a narrow bandwidth but a much larger beamwidth. This investigation examines multifilar hemispherical helices and produces two specific designs with some desirable radiation characteristics. The side-fed quadrifilar helix and the top-fed bifilar helix are the new hemispherical designs which are studied in detail both numerically and experimentally.
The Numerical Electromagnetics Code 4 is used to analyze the radiation
characteristics of the proposed multifilar hemispherical helices. Directivity, E- and H-
plane radiation patterns, axial ratio and input impedance of a few example designs are
calculated. Measurements, taken in the anechoic chamber at the Virginia Tech antenna
range, generally confirmed the simulation results. It is shown that the bifilar
hemispherical helix provides a flat gain curve over the measured bandwidth (~14%) and
generally elliptical polarization with near circular polarization in limited case.
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