Masters Theses

Date of Award

5-1989

Degree Type

Thesis

Degree Name

Master of Science

Major

Electrical Engineering

Major Professor

James D. Tillman

Committee Members

G. W. Hoffman

Abstract

Horn antennas play a vital role in modern microwave communication systems. An accurate determination of their fields is essential to the design and implementation of these antennas. A simple and reliabale method to determine these fields is needed.

Two methods for the calculation of the electric fields of an E-plane sectoral horn are discussed in this thesis. The exact method uses the asymptotic approximation of the Hankel function to calculate the field and pattern. The asymptotic approximations are used whenever possible due to the large amount of computer time involved when evaluating Hankel functions.

The Fresnel approximation method uses the sine and cosine Fresnel integrals and divides the horn into one, two, or three sections. The field is found for each of these sections and then combined for a more accurate approximation. The major problem associated with the Fresnel approximation is the phase error. When a wave travels down the length of the horn, different parts of the wave reach the aperture at different times. The result is phase error. By dividing the horn into two or three sections, the phase error is reduced and the electric field approximation more accurately.

The Fresnel approximation was found to approach the exact method as the flare angle of the horn decreased. However, the calculation of the field by the Fresnel approximation required more computer time than for the exact method.

Although the broadness of the patterns for both methods matched closely, the exact method failed to show the lobes of these patterns. This results from the horn being of finite length. In the derivation of the exact method, the sides of the horn are assumed to extend to infinity.

From this evaluation, it is obvious that each method has its advantages. The Fresnel approximation consumes more computer time, but gives an accurate projection of the lobes. The exact method gives a good general shape of the pattern and takes less computer time, but does not give a good description of the lobes.

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