Thesis Abstracts 2002
Research and Graduate Studies Electrical and Computer Engineering
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Antenna Miniaturization Using Non-Planar Rings
By: LCdr Spencer Collins
Supervisor: Dr. Y.M.M. Antar
Abstract
The current trend in personal computing devices is to make them smaller while at the same time integrating the device into a wireless network. This application obviously requires a small antenna to fit on the host device. Recent research published in the literature concentrates on the reduction in size of the radiating element. Typical methods of reducing the size of a microstrip antenna incorporates the use of high dielectric substrates, slotted patches, and shorted patches. All of these antennas require a ground plane. The size of the ground plane is a critical part of a microstrip antenna. Its size will affect the impedance of the antenna, its radiation pattern shape, the gain and the back radiation. These performance characteristics of an antenna will degrade when the size of the ground plane is reduced. The aim of this thesis is to investigate a method of reducing the size of a microstrip antenna's ground plane while at the same time preserving the good performance of a similar antenna on a much larger ground plane.
Preliminary research focused on the optimization of a shorted circular patch antenna on a large ground plane. The effects of truncating the ground plane are then studied. By reducing the ground plane to a radius of 0.23 l, it was found that the impedance of the antenna is adversely affected and the radiation pattern becomes severely distorted. A 4.5 dB decrease in gain over the same antenna on a large ground plane was noted. To compensate for this poor performance a unique configuration that overcomes the adverse effects of truncating the ground plane is introduced in here.
This unique design consists of a metallic cylindrical ring attached to the perimeter of the ground plane to control the diffraction off the small ground plane. A smaller cylindrical ring, which is suspended off the ground plane, is mainly responsible for the improvement in performance. The analysis of the current distribution on this antenna leads to a hypothesis about the principle of operation of the antenna. To validate this hypothesis a different variation of the antenna was implemented. This variant replaces the inner cylindrical ring with two planar rings. The experimental results are as expected and they serve to validate the principle of operation. The result in both cases is a well-matched antenna with good radiation characteristics on a much smaller ground plane. The implementation of this antenna configuration in a 2x2 array is also studied and successfully implemented.
All the new antenna configurations studied in this thesis achieved good performance while at the same time having a small ground plane. These characteristics make them a viable solution for small wireless devices.
