Date of Award

8-11-2017

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Systems Engineering

First Advisor

Hussain AL-Rizzo

Abstract

Circularly polarized microstrip antennas are attractive due to their low profile, conformability, compatibility with MMIC, and low cost. Numerous circularly polarized microstrip antenna designs have been proposed to achieve high gain with an axial ratio typically less than 3 dB for a narrow range of elevation and azimuth angles around the boresight. One well-known and popular design approach is the sequentially rotated antenna array, in which sufficiently separated, arbitrarily polarized antenna elements and their excitation are progressively rotated and phase shifted in the spatial and temporal domains, respectively. Traditionally, the antenna elements must be excited by a separate feeding network situated beneath the array, which must provide equal amplitude and a progressive phase shift for the adjacent elements. The major drawbacks of this conventional approach are the complexity, size, undesired radiation and loss causes by the feeding network. In this dissertation, a novel sequentially rotated virtual microstrip antenna array is presented for the first time without using a separate feeding network. The antenna is termed virtual since the array consists of a single conducting patch that mimics the performance, in terms of gain, axial ratio bandwidth, and purity of circular polarization, of a sequentially rotated antenna array. The proposed design, on the other hand, utilizes the fields induced on the feeding element to satisfy the phase-shift requirement of the feeding network. Two realizations of the proposed antenna have been demonstrated using three and four circular elements symmetrically overlapped with a circularly polarized circular patch operating in the dominant TM11 mode with two orthogonal and 900 phase-shifted excitations.

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