Title

Circular loop antennas radiating in the presence of symmetrically placed scatterers

Date of Award

2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering and Computer Science

Advisor(s)

Ercument Arvas

Second Advisor

Joseph R. Mautz

Keywords

Antennas, Circular loop antennas, Scatterers, Conducting spheres

Subject Categories

Electrical and Computer Engineering | Engineering

Abstract

Electromagnetic radiation from electrically large circular loop antennas of different radii and of different nonuniform current values in the presence of symmetrically placed conducting and/or dielectric objects is considered. A single or multiple parallel loops) lie on an imaginary sphere of radius a . The p th loop, of radius e p at the angle [straight theta] p is driven by a delta-function generator V p and carries a nonuniform current I p ([straight phi]) . The loop(s) would be radiating in the presence of one or more of the following objects: a dielectric sphere of radius b < a , a spherical dielectric shell of inner radius b and outer radius a , another dielectric shell of inner radius a and outer radius c > a , another such shell of inner radius c and outer radius d , a perfectly conducting sphere or cap at radius b , and another such cap at radius d . In some particular cases, it will be possible to model the following geometries: A loop antenna in front of (a) a circular disc, (b) a conducting plane, and (c) a perforated plane and the loop (d) on or near a planar interface. These structures could include dielectric layers.

Eigenfunction series solutions for the field are assumed in different regions. Unknown field coefficients are computed by enforcing boundary conditions at the interfaces of these different regions. The current distribution on each of the thin-wire circular loops, driven by a voltage source, is determined by Fourier series expansion in terms of tesseral harmonics and all necessary harmonics are taken into account. Exact analytical field expressions in closed forms are derived for most of the cases and accurate results are obtained. For the cases when a conducting cap exists, a semi-analytical solution with the Method of Moments is presented. It is demonstrated how the presence of the conducting and/or dielectric objects can change and direct radiation characteristics of the loop antennas.

The master antenna model presented here addresses numerous loop antenna problems which can be solved by the powerful formulation given in this dissertation. There will be no need to use various methods for various loop antenna problems, nor will there be a need to have expensive commercial electromagnetic simulation software thanks to this dissertation. The unique analytical formulation given here for design and synthesis is a handy tool for antenna analysts.

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