29-05-2014, 12:06 PM
Antenna Theory: A Review
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ABSTRACT
Thispaper is a tutorial on the theory of antennas, and it has been
written as an introduction for the nonspecialist and as a review for
the expert. The paper traces the history of antennas and some of
the most basic radiating elements, demonstrates the fundamental
principles of antenna radiation, reviews Maxwell’s equations and
electromagnetic boundary conditions, and outlines basic proce-
dures and equations of radiation. Modeling of antenna source
excitation is illustrated, and antenna parameters and fisures-of-
merit are reviewed. Finally, theorems, arraying principles, and
advanced asymptotic methods for antenna analysis and design are
summarized.
INTRODUCTION
For wireless communication systems, the antenna is
one of the most critical components. A good design of
the antenna can relax system requirements and improve
overall system performance. A typical example is TV for
which the overall broadcast reception can be improved by
utilizing a high performance antenna. An antenna is the
system component that is designed to radiate or receive
electromagnetic waves. In other words, the antenna is the
electromagnetic transducer which is used to convert, in the
transmitting mode, guided waves within a transmission line
to radiated free-space waves or to convert, in the receiving
mode, free-space waves to guided waves. In a modern
wireless system, the antenna must also act as a directional
device to optimize or accentuate the transmitted or received
energy in some directions while suppressing it in others [l].
The antenna serves to a communication system the same
purpose that eyes and eyeglasses serve to a human.
ANTENNA ELEMENTS
Prior to World War I1 most antenna elements were of
the wire type (long wires, dipoles, helices, rhombuses,
fans, etc.), and they were used either as single elements
or in arrays. During and after World War 11, many other
radiators, some of which may have been known for some
time and others of which were relatively new, were put
into service. This created a need for better understanding
and optimization of their radiation characteristics. Many
of these antennas were of the aperture type (such as
open-ended waveguides, slots, horns, reflectors, lenses,
and others), and they have been used for communication,
radar, remote sensing, and deep space applications both on
airborne and earth based platforms. Many of these operate
in the microwave region. In this issue, reflector antennas
are discussed in “The current state of the reflector antenna
art-Entering the 1990’s,” by W. V. T. Rusch.
CONCLUSIONS
Antenna engineering has enjoyed a very successful
period during the past four decades. Responsible for
its success have been the introduction and technological
advances of some new elements of radiation, such
as aperture antennas, reflectors, frequency independent
antennas, and microstrip antennas. Excitement has been
created by the advancement of the low-frequency and
high-frequency asymptotic methods which have been
instrumental in analyzing many previously intractable
problems. A major factor in the success of antenna
technology has been the advances in computer ar-
chitecture and numerical computation methods. Today
antenna engineering is considered a truly fine engineering
art.