Title page for ETD etd-12112003-095406


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
  • NEC-4
Date of Defense 2003-10-31
Availability unrestricted
Abstract
Helices 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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