Since is a metallic device used to radiate

Since human beings are social animals, they need to communicate with
each other. In early days of civilization, various acoustic methods like drums,
horns and optical communication methods as smoke signals and fireworks were
used for signaling and communication. In nineteenth century, as technology
developed, communication using the electromagnetic spectrum outside the visible
region was explored.

Maxwell (1831-1879), first introduced the concept of electromagnetic
waves and related its behavior with optical waves travelling at the same speed.
First rigorous mathematical partial differential equations of Electrodynamics were
presented by Maxwell, a fundamental unification of electric and magnetic fields
describing an electromagnetic wave phenomenon i.

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An important fact
from physics, namely, “accelerated charges radiate” along with the outcomes of
Maxwell’s equations, namely, “existence of EM waves traveling at the speed of
light” forever have changed how we live, enjoy life and protect ourselvesii. However same could not
have been possible without the design and development of an antenna. An antenna
is an integral part of any communication device. Usually an antenna is a
metallic device used to radiate or receive radio frequency (RF) waves. An
antenna can be defined as a specialized transducer which converts RF fields
into alternating current or vice-versa. Thus,
antenna is a transitional structure between free space and a guiding device
like coaxial cable, waveguide, complainer line, microstrip line etciii.
First wire antennas were inaugurated in 1842 by Professor Joseph Henry,
inventor of wire telegraphy. He found
that by “throwing a spark” to a circuit of wire in an upper room,
current received in a parallel circuit in a cellar, 30 ft below, could magnetize needles. In 1885 Edison patented
first communication system to radiate key clicks to a distance using vertical,
top-loaded, grounded antenna. In 1887 H. Hertz launched, processed, and
received radio waves systematically using a balanced dipole antenna.iv Since the invention of
wire antennas in middle of nineteenth century, various types of antennas like
wire, loop, parabolic & corner reflectors, horns, slots, helix, lenses, log
periodic, arrays, microstrip etc. have been developed over centuries.

Before World War
II, antenna and electromagnetic waves were utilized for communication purpose
only and hence used to be low power system. However, after first world war, due
to threat and success of bombing by an aircraft, in the late 1930s research
groups in at least eight countries— United States, the Soviet Union, the United
Kingdom, France, Germany, Japan, Italy and Netherlands independently developed
radar. A radar system transmits radio waves and detect any aerial object by receiving
reflected signals from aerial object. Radar, which is essentially “seeing” with
radio waves, were utilized for various applications like aiming anti-aircraft
guns, locating enemy ships and aircraft, and to direct gunfire. It was installed
on aircrafts, where it could detect hostile aircraft or ships, or to navigate
the aircraft, or to find bombing targets. During this large number of reflector
antenna in huge size, able to transmit several megawatts of peak power were
developed.

As discussed above,
early days all communication systems and radars were analog system,
transmitting around carrier frequency and used to be narrow band. Since the
invention of transistor
in 1947 by Walter Brattain, John Bardeen, and William Shockley and further
integrated circuits by circuit in 1958 by Jack Kilby, the development of
communication system over last 75 years has been phenomenal including wideband
microwave radio systems, and satellite communication systems.

With the exponential growth of
wireless communication system including
voice, data, and video transmission and the introduction and use of personal
communications services, communications systems are required to operate in multiple
bands. In some case bandwidth requirement includes few octave to several
decades. Hence antenna designers have been forced to design a low cost, compact
Ultra Wide Band (UWB) antenna. In 1990 a report defines UWB system operating
with more than 0.25 fractional BW while in Feb 2002, U.S. Federal
Communications Commission (FCC) v1 defines UWB technology
with a bandwidth exceeding the lesser of 500 MHz or 20% of the arithmetic
center frequency. In Feb 2002FCC has authorized the unlicensed use of UWB in
the frequency range from 3.1 to 10.6 GHz for short distance communication.
For UWB system, fractional BW is defined as below:

Where
is the higher band of
operating frequency while is the lower operating frequency.
Historically there have been three different classvi of
antenna as discussed below:

(a)          DC to Daylight Class: these class of antennas are designed to have
bandwidth as much as possible and application includes ground penetrating
radars, field measurement and electromagnetic compatibility (EMC),
electromagnetic weapons and covert communication systems.

(b)          Multi narrowband class: These antennas
are designed to collect RF information for Signal intelligence (SIGINT) and
communication intelligence (COMMINT). They operate in large bandwidth but at any
given time, they operate in narrow band and sweeps to entire band.

(c)          Modern Ultra-wideband Class: These are
the antennas designed to operate with approximately 3:1 frequency from 3.1 to
10.6 GHz as defined by FCC. The bandwidth requirement of modern communication
system is much smaller than DC to daylight antennas.

iTaflove, A,
Computational Electrodynamics. I ed, Boston: Artech House.

iiYahya Rahmat-Samii , “From Maxwell’s equations to modern
antenna marvels: From tiniest capsule antennas to largest space antennas” General Assembly and Scientific
Symposium (URSI GASS), 2014 XXXIth URSI ,Pages: 1 – 1, DOI: 10.1109/URSIGASS.2014.6929136

iiiBalanis, C. A.,
Antenna Theory, Analysis and Design, New York: John Wiley & Sons,

1997.

ivJ.
Ramsay, “Highlights of antenna history”, IEEE
Antennas and Propagation Society Newsletter,
Year: 1981, Volume: 23, Issue:
6 , Pages: 7 – 20, DOI: 10.1109/MAP.1981.27575

vFederal Communications Commission (FCC), Revision of Part 15 of the
Commission’s Rules Regarding Ultra-Wideband Transmission Systems, First
Report and Order, FCC 02-48, 2002

vi Hans G. Schantz,
The art and science of ultrawideband antennas, 2nd ed., Artech
House, 2015.