الفهرس 
Principle Operation of Leaky-Wave AntennasOnly 14 pages are availabe for public view
 |  | from | 107 |  |  |
| | | from | 107 | | |
Abstract
This thesis addresses the analysis and design of reconfigurable leaky wave antennas
(RLWAs). RLWAs are introduced by modifying the leaky-mode complex propagation
constant to produce a desired scanning beam. The radiation characteristics of a RLWA are
desired in beam scanning applications such as tracking systems, and mobile
communications. Several antennas have been designed using different materials such as
graphene and plasma to operate in different frequency ranges as THz, and GHz ranges
which covers a wide range of applications.
In this thesis, a reconfigurable graphene leaky-wave antenna (GLWA) with
electronic beam scanning capability for THz communications system is proposed. It
consists of graphene strips printed on silicon oxide substrate. The tunable graphene
conductivity using DC-bias is used to control the GLWA radiated beam direction without
changing its physical structure. By selecting the proper periodicity of the biased/unbiased
graphene strips (codes) of the GLWA the beam direction, scanning range, gain and SLL are
changed without changing layout. A parametric study on the effect of GLWA dimensions
on the radiation characteristics is studied. The radiated beam is electronically scanned from
-68˚ to 26˚ at a fixed frequency of 2 THz using different codes. The proposed antenna is
simple in design, easy to control via the biased/unbiased periodic graphene strips. It has a
compact size of 1350 × 300 × 35 𝜇𝑚3. The GLWA coded by 1111111000 has a peak gain
of 19.7 dBi, SLL of -10.8 dB and beam radiated in 8o direction at 2 THz. The code 11111000
has beam scanning from -35o to -3o with frequency varying from 1.8 THz to 2.2 THz with
20.0 dBi gain. An investigation of the radiation characteristics of different codes of GLWA
is introduced. The antenna structure is full-wave simulated and studied using the finite
integral technique.
The effect of different plane wave launchers on the radiation characteristics of GSLWA is investigated. A planar substrate integrated waveguide (SIW) horn antenna is
investigated. It introduces a peak gain of 18.2 dBi with a bandwidth of 21.95% and SLL ofAbstract
10.6 dB. End-fire radiation from parabolic reflector is employed to launch plane-wave in
the GS-LWA. A matching BW of 0.82 THz is achieved with peak gain of 18 dBi. A coplanar
fed Yagi-Uda like structure element is studied using a single element and two elements
array. The two elements provided the highest matching of -40 dB over BW of 6% and gain
of 16.5 dBi. Finally, tapered microstrip line is investigated, it introduced the lowest SLL -
16.1 dB with a gain of 17.5 dBi and BW of 39.57% (1.5-2.24 THz). The selection of proper
feeding structure depends on the required matching BW, peak radiated gain, and the lowest
SLL. Full-wave analysis of the GS-LWA excited by different feeding methods is
introduced.
Electronic beam scanning 2D leaky-wave antenna (LWA) based on reconfigurable
conductivity of the plasma is introduced. The antenna consists of a fixed number (112) of
Plexiglass semi-elliptical gratings filled with a noble gas printed on a grounded dielectric
substrate. A coplanar fed Yagi-like dipole printed antenna is integrated with the LWA to
launch a cylindrical exciting wave. By controlling the periodicity of ionized/non-ionized
plasma gratings, the radiated beam direction, gain and side lobe level (SLL) can be
controlled. The antenna has a compact structure of 241 × 262.5 × 2.67 𝑚𝑚3. The effect
of curvature of semi-elliptical grating on the LWA operation is investigated. A fan-shaped
beam is obtained from semi-elliptical grating LWA with different aspect-ratio. The semicircular grating introduces a pencil beam with 23 dBi and bandwidth (BW) of 1.52 GHz.
The effect of ON/OFF plasma periodicity and codes is investigated. At fixed frequency, the
beam is electronically scanned from -28˚ to 34˚ with a gain of 23 dBi for different
periodicity. For fixed periodicity, P=8, the beam is scanned from 8˚ to 23˚ with high gain
of 20.3 dBi. Using the proposed semi-circular grating LWA, the beam direction is
controlled without changing the physical structure of the antenna.
A planar leaky-wave antenna (LWA) based on reconfigurable conductivity of
plasma is designed for MIMO applications with electronic beam scanning. The system
contains a number of plasma leaky wave antenna elements. Both two and four LWA
elements are arranged in MIMO structure for high data rate applications.