الفهرس 
Chapter 1 : IntroductionOnly 14 pages are availabe for public view
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Abstract
Mushroom-like electromagnetic band gap materials have numerous
applications. One of these applications is its use as a polarization
converter. The polarization converter transforms the polarization of an
incident wave from any type of polarization to any other required type. In
this thesis a simple technique for the design of polarization converters
was developed. Given the polarization of the incident wave, the working
frequency, and bandwidth, the technique is capable of designing the
structure that gives the required polarization. The design technique is
based upon the effective medium model. In this model the material is
treated as a parallel resonant circuit. The accuracy of the design depends
upon the dimensions of the material compared to the wavelength. The
smaller the dimensions, the more accurate the results will be. However, a
procedure was developed to increase the accuracy of the technique. The
developed design technique was used to design materials for the
following five cases: (a) Avoidance of blockage due to subreflector in
Cassegrain antennas. In this case the polarization converter transforms an
incident linearly polarized wave to another linearly polarized wave but
the electric field is normal to the incident field. (b) Simplifying the
structure of dual polarized satellite communications reflector antennas.
The antenna structure reflects two incident waves linearly polarized with
their electric fields perpendicular to each other. The designed polarization
converter reflects the two incident linearly polarized waves keeping their
polarization without any change after reflection. (c ) Simplifying the feed
structure of circularly polarized parabolic reflector antennas. The
designed polarization converter transforms the polarization of the incident
wave from linear to circular. Thus avoiding the use of complicated wave
guide sections used for that purpose. (d) Enhancement of radar cross section of trihedral corner reflectors used for civil maritime radar.
Circular polarization is used in such cases to overcome clutter due to rain.
But right handed circular polarization is reflected fro trihedral corner
reflector to be left handed circular. Thus it can not be received by the
radar, effectively reducing the radar cross section of the trihedral corner
reflector. The designed polarization converter covers one face of the
reflector and transforms the circularly polarized incident wave to a
linearly polarized one. Thus enabling the radar to receive the
backscattered signal, effectively increasing the radar cross section of the
trihedral corner reflector. (e) Calibration of polarimetry radar.
Polarimetry radar uses two linearly polarized waves with their electric
fields normal to each other for the study of weather conditions. The radar
sends the two waves ( H and V) and receives four ( HH, HV, VV, VH).
Calibration of the radar needs several targets. One of these targets must
return strong cross polar field. The thesis suggest the use of a trihedral
corner reflector with one face covered by a polarization converter. The
converter transforms the incident linearly polarized wave to a linearly
polarized wave with its electric field normal to the incident electric field.
The polarization converter was designed. The HFSS and CST packages
were used for the simulations.