الفهرس 
An OverviewOnly 14 pages are availabe for public view
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Abstract
Synthetic Aperture Radar (SAR) is used for remote sensing to create twodimensional
images of land covers on the earth’s surface. Such a land-imaging system
has a great importance in many civilian and military applications. The SAR uses the radar
antenna to scan a ground area to provide microwave images with fine spatial resolution.
The SAR is typically mounted on an aircraft or spacecraft, and usually has a form of sidelooking
radar. It uses the Doppler and time delay information of the ground reflected
wave to generate a two-dimensional image with the desired azimuth resolution (direction
of motion) and range resolution (normal to the direction of motion), respectively.
The SAR operation requires a physical antenna of radiation pattern with foot print of
high aspect ratio and a mechanism capable of achieving beam steering and beam shaping.
The SAR antenna array should be rigid, planar, deployable, and as lightweight as
possible. A side-looking SAR system requires an antenna with a flat-topped beam pattern
in the plane of the azimuth direction and a cosecant-squared beam shape in the plane of
the range direction. For satellite communications with the ground stations, an isoflux
beam is required for uniform coverage and continuity during the communication session.
In the present work, both linearly and circularly polarized beams with all the shapes
described above are synthesized using the Particle Swarm Optimization (PSO) algorithm
and then produced by practical planar rectangular and circular arrays of the appropriate
microstrip patch elements.
In this thesis, the PSO optimization algorithm is applied using a developed technique
to synthesize the radiation patterns required for high-resolution land imaging SAR and
satellite communications using planar rectangular or concentric circular arrays. The goal
of the PSO algorithm is to get the excitation coefficients of the array elements, which are,
then, applied to practical arrays of printed microstrip patch antennas to produce the
corresponding beam shape.
Microstrip patch antennas with linear or circular polarization are proposed to
construct the synthesized-beam arrays required for the considerd application. A wideband
Abstract
rectangular patch antenna with U-slot is proposed for planar arrays with linear
polarization. A square patch antenna with four truncated corners and four axial slots is
designed for planar rectangular and circular arrays. Finally, a square patch antenna with
two L-shaped slots inserted at diagonaly opposite corners is designed for planar
concentric circular arrays. Turnstile arrays of either dipole elements or U-slotted
microstrip patch antennas excited with circulating phase shift are proposed to construct
planar arrays with circular polarization for land-imaging SAR systems and satellite
communications. Overlapping between the adjacent turnstile elements in a planar array is
proposed, to reduce the array size and the sidelobe level of the resulting beam.
A computationally efficient optimization technique using particle swarm algorithm to
synthesize radiation patterns for planar rectangular arrays is proposed. This is achieved
by applying excitation coefficients obtained for -element and -element linear arrays
to the elements of a two-dimensional × planar array. Also, the present work
develops a computationally efficient PSO algorithm to synthesize three-dimensional
beams which are circularly symmetric in the azimuth plane. The excitation coefficients of
all the elements on the same circle are kept equal to each other allowing the magnitudes
to vary only in the radial direction to achieve the optimization goals. This can be
considered a major improvement that considerably reduces the computational time and
the required memory space to about 6.5% of their original values for the considered case.
Experimental measurements of fabricated prototypes of some linearly and circularly
polarized microstrip patches and two-element arrays of them show good agreement with
the electromagnetic simulation results regarding the impedance matching, bandwidth,
mutual coupling between the nearby elements and the radiation patterns of the circularly
polarized field. Also, some of the three-dimensional beams produced in the present work
are compared to the corresponding beams produced by other published work and show
good agreement.