Date of Award

Summer 2000

Document Type

Thesis

Degree Name

Master of Science in Electrical Engineering - (M.S.)

Department

Electrical and Computer Engineering

First Advisor

Ibrahim Akduman

Second Advisor

Gregory A. Kriegsmann

Third Advisor

Edip Niver

Fourth Advisor

Bruce Mitchell Nyman

Abstract

Traditionally beam steering in phase array antenna systems is achieved using tunable phase shifters or switched feed networks. Here, a tunable patch antenna element is suggested as a novel alternative to a combination of a radiating element and a phase shifter. A conductor backed coplanar waveguide patch antenna is chosen due to its suitability to mounted external tuning elements, using varactor diodes. Limited types of lumped tuning circuits, using varactor diodes, have been tested, though a lumped as well as distributed tuning is feasible in the chosen antenna configuration. Approximate analytical models for coplanar waveguide patch antennas with finite ground plane have been developed; in the literature, such approach is limited to infinite ground plane coplanar waveguide patch antenna only. Numerical results from approximate model were used as initial values in optimized simulations using JE31) software tool. Coplanar waveguide patch antennas were constructed; re-tuned to the desired frequency and tuning element were surface mounted. Experimental measurements for input return loss and phase variation as a function of frequency are carried out using various bias voltages applied in tuning circuits. Despite observed small losses and incremental changes in the resonance frequency, significant phase shifts were obtained within the desired bandwidth (low VSWR.) Alternative tuning with ferroelectric elements and distributed tuning is suggested as further research.

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