One of the simplest and probably the most widely used microwave antenna is the horn.
Its existence and early use dates back to the late 1800s. Although neglected somewhat
in the early 1900s, its revival began in the late 1930s from the interest in microwaves
and waveguide transmission lines during the period of World War II. Since that time a
number of articles have been written describing its radiation mechanism, optimization
design methods, and applications. Many of the articles published since 1939 which deal
with the fundamental theory, operating principles, and designs of a horn as a radiator
can be found in a book of reprinted papers  and chapters in handbooks , .
The horn is widely used as a feed element for large radio astronomy, satellite
tracking, and communication dishes found installed throughout the world. In addition
to its utility as a feed for reﬂectors and lenses, it is a common element of phased arrays
and serves as a universal standard for calibration and gain measurements of other high-
gain antennas. Its widespread applicability stems from its simplicity in construction,
ease of excitation, versatility, large gain, and preferred overall performance.
An electromagnetic horn can take many different forms, four of which are shown in
Figure 13.1. The horn is nothing more than a hollow pipe of different cross sections,
which has been tapered (ﬂared) to a larger opening. The type, direction, and amount of
taper (ﬂare) can have a profound effect on the overall performance of the element as
a radiator. In this chapter, the fundamental theory of horn antennas will be examined.
In addition, data will be presented that can be used to understand better the operation
of a horn and its design as an efﬁcient radiator.
13.2 E-PLANE SECTORAL HORN
The E-plane sectoral horn is one whose opening is ﬂared in the direction of the E-ﬁeld,
and it is shown in Figure 13.2(a). A more detailed geometry is shown in Figure 13.2(b).
Portions of this chapter on aperture-matched horns, multimode horns, and dielectric-loaded horns were
ﬁrst published by the author in , Copyright 1988, reprinted by permission of Van Nostrand Reinhold Co.
Antenna Theory: Analysis Design, Third Edition, by Constantine A. Balanis
ISBN 0-471-66782-X Copyright
2005 John Wiley & Sons, Inc.