الفهرس 
CHAPTER 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
This thesis addresses radiation, scattering and applications of plasma antennas.
Plasma antenna is a special type of antenna which uses ionized noble gases (argon, neon,
xenon…) as a conducting medium to perform similar to a metal which is usually used in
traditional antenna. Plasma antennas have many advantages as their design permit
electrical, rather than mechanical control for their radiation characteristics. They are light
weight, reconfigurable, and can be energized, and de-energized in a fraction of a second.
When a particular plasma antenna is de-energized, it does not affect the nearby elements
and allowing other antennas to transmit or receive without any effect due to the notenergized
plasma antenna.
For plasma to be excited, ionization is necessary. Plasma density usually refers to the
electron density, the number of free electrons per unit volume. The plasma is a kind of a
reconfigurable dispersion material with different conducting and dielectric properties. The
dispersion material properties can be reconstructed with different electron densities and
collision frequencies. So, the radiation characteristics of plasma antenna are controlled
using such factors. plasma antenna can be used in military application in which we can
control the amount of the reflected power by varying the applied voltage and once the
plasma is de-energized the plasma antenna is simply a dielectric tube with a very little radar
cross section.
The radiation characteristics of plasma antennas are investigated and analyzed using a
finite integral technique. The input impedance of the antenna at the feeding terminals
depends on many factors, including the operating frequency, the method of excitation, its
geometry and its proximity to the surrounding objects. It is often convenient to represent
the input impedance of the antenna by frequency dependent lumped elements equivalent
circuit. A five lumped elements equivalent circuit for the plasma dipole antenna is
investigated and optimized by using the genetic algorithm (GA). The effect of plasma
frequency and collision frequency of the ionized gas on input impedance variations of theplasma dipole antenna is studied with the help of the equivalent circuit model. Another
form of equivalent circuit is synthesized by using a rational function and GA. The Cauer’s
realization method is used to deduce a new more accurate structure of the lumped elements
equivalent circuit. Plasma antenna can be used in RFID applications to overcome the multireader
collision, and jamming issue. So a broadband circularly polarized plasma curl
antenna for portable RFID reader at 2.45 GHz is proposed. The antenna consists of a glass
tube filled with argon gas and of about 1.4 wavelengths curled into one turn. A parametric
study for the plasma curl antenna parameters is carried out. A simulated compact model for
the portable RFID reader is designed. The radiation characteristics of the plasma curl
antenna enclosed inside a portable reader device are determined. The behavior of plasma
curl antenna is similar to a metal antenna when the signal is transmitted and received.
Because Plasma is a reconfigurable medium with different conductor and dielectric
properties, it has been used to design a multi-objective plasma reflectarray/transmitarray
antenna which reflects/transmits the incident waves radiating from a feed antenna in
different directions using a single structure. An electronic beam steering is achieved using
a DC applied voltage on the array elements. A 13×13 unit cell reflectarray/transmitarray
antenna covering an area of 13.52×13.52 cm2 is proposed. The dimensions of the unit cells
are identical with different argon gas ionization density according to the relative phases of
the reflected/transmitted wave. Each unit cell consists of two plasma cylindrical ring tubes
positioned along the top and bottom of a plasma square ground plane filled with argon gas.
The reflectarray is designed for 19.39 GHz, and the transmitarray is operating at 19.75 GHz
using a single structure. The plasma frequency of the argon gas is varied by changing the
applied ionizing DC voltage at both ends of the dielectric cylinder. The gain and frequency
bandwidth for the new configuration are presented. An electronic beam steering plasma
transmitarray antenna from −30° to +30° is introduced. The radiation characteristics of the
steering plasma reflectarray/transmitarray are investigated.