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Introduction
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Fundamentals
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Source: ANTENNA ENGINEERING HANDBOOK
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Introduction and Fundamentals
1-3
Fundamentals
of Antennas,
Arrays, and Mobile
Communications
Thomas F. Eibert
Universität Stuttgart
John L. Volakis
The Ohio State University
CONTENTS
1.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
1.2 HUYGENS’ AND EQUIVALENCE PRINCIPLES. . . . . . . . . . . . . . . . . . 1-5
1.3 HERTZIAN AND FITZGERALD ELEMENTARY RADIATORS . . . . . . . 1-7
1.4 FAR-FIELD ANTENNA PROPERTIES, POWER TRANSFER,
AND RECIPROCITY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
1.5 ANTENNAS AS ELECTROMAGNETIC CIRCUITS. . . . . . . . . . . . . . . 1-11
1.6 POLARIZATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14
1.7 DIRECTIVITY PATTERNS FROM CONTINUOUS
LINE SOURCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-17
1.8 DIRECTIVITY PATTERNS FROM AREA
SOURCE DISTRIBUTIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21
1.9 FUNDAMENTALS OF ANTENNA ARRAYS . . . . . . . . . . . . . . . . . . . . 1-27
1.10 BASIC CONCEPTS IN MOBILE COMMUNICATIONS . . . . . . . . . . . 1-32
Chapter 1
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Source: ANTENNA ENGINEERING HANDBOOK
1-4 CHAPTER ONE
1.1 INTRODUCTION
*
Antennas are key components of any wireless communication system.
1,2
They are the
devices that allow for the transfer of a signal (in a wired system) to waves that, in turn,
propagate through space and can be received by another antenna. The receiving antenna
is responsible for the reciprocal process, i.e., that of turning an electromagnetic wave into
a signal or voltage at its terminals that can subsequently be processed by the receiver. The
receiving and transmitting functionalities of the antenna structure itself are fully char-
acterized by Maxwell’s equations and are fairly well understood.
3
The dipole antenna
(a straight wire, fed at the center by a two-wire transmission line) was the first antenna ever
used and is also one of the best understood.
1,2
For effective reception and transmission, it must
be approximately l/2 long (l = wavelength) at the frequency of operation (or multiples of
this length). Thus, it must be fairly long (or high) when used at low frequencies (l = 1 m at
300 MHz), and even at higher frequencies (UHF and greater), its protruding nature makes it
quite undesirable. Further, its low gain (2.15 dB), lack of directionality, and extremely narrow
bandwidth make it even less attractive. Not surprisingly, the Yagi-Uda antenna (typically seen
on the roof of most houses for television reception) was considered a breakthrough in antenna
technology when introduced in the early 1920s because of its much higher gain of 8–14 dB.
Log-periodic wire antennas introduced in the late 1950s and 1960s and wire spirals allowed
for both gain and bandwidth increases. On the other hand, even today high gain antennas rely
on large reflectors (dish antennas) and waveguide arrays (used for many radar systems).
Until the late 1970s, antenna design was based primarily on practical approaches using
off-the-shelf antennas such as various wire geometries (dipoles, Yagi-Uda, log-periodics,
spirals), horns, reflectors, and slots/apertures as well as arrays of some of these. The antenna
engineer could choose or modify one of them based on design requirements that characterize
antennas, such as gain, input impedance, bandwidth, pattern beamwidth, and sidelobe
levels (see References 4 and 5 for a description of these quantities). Antenna development
required extensive testing and experimentation and was, therefore, funded primarily by
governments. However, in recent years, dramatic growth in computing speed and develop-
ment of effective computational techniques for realistic antenna geometries has allowed for
low-cost virtual antenna design. Undoubtedly, the explosive growth of wireless communi-
cations and microwave sensors, microwave imaging needs, and radars has been the catalyst
for introducing a multitude of new antenna designs over the past decade and an insatiable
desire for using modern computational techniques for low-cost designs. Requirements for
∗
Heinrich R. Hertz was the first to demonstrate the generation of radio waves at UHF using a gap dipole in 1885–
1886 at Karlsruhe University (Germany). Hertz was able to detect radio waves 20 m away using a high-voltage
electrical spark discharge to excite the dipole gap. From recorded conversations, Hertz did not seem to understand
the impact of his experiments, but instead did it as a validation of the newly developed Maxwell’s equations. Within
ten years, Tesla at the Franklin Institute in the U.S., Marconi in Bologna, Italy, Popov in Russia, and Bose in India,
demonstrated wireless telegraphy. In 1892, Tesla delivered a widely distributed presentation at the IRE of London
about “transmitting intelligence without wires,” and in 1895, he transmitted signals detected 50 miles (80 km) away.
Concurrently, in 1894 Bose used wireless signals to ring a bell in Calcutta, and Popov presented his radio receiver
to the Russian Physical & Chemical Society on May 7, 1895. Marconi is certainly considered the key individual for
his contributions to the commercialization of radio waves, and he received the Nobel prize for his work in 1909.
Nevertheless, Marconi’s widely advertised first radio wave transmission experiment was in 1895, and his British pat-
ent application in 1897 was preceded by that of Tesla. A culmination of Marconi’s experiments was the December 12,
1901, trans-Atlantic radio wave transmission of the Morse code for the letter S. The success of this experiment is often
disputed, possibly due to strong atmospheric noise during the time of the experiment, but by the 1920s the U.S. had
hundreds of radio stations, and in 1922, the BBC began transmitting in England. Subsequent development of radio
detectors, vacuum tubes, and the tiny transistor in 1947 played a critical role in the practical everyday use of radio
waves for communication and wireless transmission of information.
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Fundamentals of Antennas, Arrays, and Mobile Communications