Date of Award

1-1-2013

Document Type

Open Access Thesis

Department

Electrical Engineering

Sub-Department

Electrical Engineering

First Advisor

Mohammod Ali

Abstract

Conformal antennas have been increasingly playing an important role in a vast number wireless of communication applications. More specifically, Conformal Load Bearing Antenna Structures (CLAS) have drawn a great deal of interest among researchers and engineers because of their advantages of multiple functionality, e.g. antenna and structure both. The objectives of this thesis are to investigate and design innovative conformal Ultrawideband (UWB) endfire antenna arrays and reconfigurable aperture coupled pixel patch antennas both of which are good candidates for CLAS. First, a broadband VHF-UHF end-fire Yagi-Uda array is proposed for possible air vehicle integration and operation within the 240-465 MHz frequency band. The array consists of a driven dipole, a reflecting dipole, and three directing dipoles. The broadband impedance, pattern, and gain responses are obtained by adding two parasitic metal strips adjacent to a fat driven strip dipole. The array has a peak gain greater than 7 dBi and Forward to Backward ratio (F/B) greater than 13 dB throughout most of the operating frequency band. Second, a novel size reduced bi-layer UWB Log Periodic Dipole Array (LPDA) is proposed for operation in the 350-750 MHz UHF frequency band. The LPDA's overall size is reduced by using printed double meander-line elements on two separate dielectric surfaces. The array proposed in this work is fed using a coaxial cable and a conducting tube. The effects of the diameter of each on the VSWR bandwidth of the array are thoroughly investigated. Simulations are also conducted considering dielectric support members between the layers and their effect on the antenna performance is studied. Finally, an array is fabricated and measured for VSWR, pattern, and gain all of which show satisfactory performance, e.g. 350-750 MHz operation bandwidth with good pattern coverage and peak gain greater than 7 dBi at most frequencies.

Finally, an aperture coupled reconfigurable pixel patch antenna is proposed that can be reconfigured in three frequencies with the help of low loss MEMs switches. Starting from the basic idea of a probe fed pixel patch controlled using MEMs switches investigations on an aperture coupled reconfigurable pixel patch are presented. The effects of substrate thickness, dielectric constant and loss tangent, bias networks, bias pads and vias are investigated and their effects on the performance of the reconfigurable antenna are evaluated. The proposed work shows that with an array of 5 mm by 5 mm pixels controlled by MEMs switches a patch can be reconfigured for operation at three frequencies with peak gain in the vicinity of 8 dBi. It is expected that the pixel patch concept can be further generalized to encompass a wide frequency range of reconfiguration providing more than an octave of bandwidth.

Cleared for public release: Case Number: 88ABW-2013-2995

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