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UBC Theses and Dissertations
Diffraction of antenna radiation patterns by local obstacles Cheung, Hong D.
Abstract
Radiowave blockage by buildings is a problem common to mobile radio and cellular telephone systems in high-density urban areas. Plane wave incidence is an approximation which simplifies analysis of the scattering problem, but this is not an accurate assumptions if the obstacle is near the antenna. If the transmitting antenna has an omnidirectional pattern and the obstacle is large in wavelengths the scattered field can be calculated by the techniques of high frequency diffraction theory such as the geometrical theory of diffraction. If the antenna pattern is directive and the obstacle is local, the omnidirectional source solution can be converted to a beam source solution by the complex source point (CSP) method. Antenna patterns with sidelobes can be synthesized from arrays of CSP beams, each with appropriate amplitude, phase and direction. Their individual scattering from apertures and buildings may be calculated and the result summed for the total field. The complex source point method is used here to produce the basis elements of an array of linearly and directionally equispaced two-dimensional CSP beams and compared with Gaussian beam results obtained by others earlier. For efficiency a limited number of significant beams and beam directions is required. Approximately twice as many beams as the aperture width in wavelengths, with all beam directions normal to the aperture, is found to be sufficient here for simple uniform and cosinusoidal distributions in apertures of moderate size at ranges outside the evanescent field zone of the aperture. Now the exact solution for the far field of a line source, or here a beam source in the presence of a conducting half plane, is used as our basis element, to give the solution for antenna pattern diffraction by a local half plane. In this work a beam source in the presence of a conducting half plane, is used as our basis element, to give the solution for antenna pattern diffraction by a local half plane. Antenna pattern diffraction by an aperture near a wide slit is presented as simply a superposition of the solutions for two coplanar half planes with separated parallel edges. Antenna pattern distortion by various other local obstacles, such as conducting wedges and rectangular cylinders, can be obtained similarly. Numerical results, including both extended apertures and a single beam source, represented by arrays of complex source point beams and by a single CSP beam are given. From scattering patterns the latter are shown to accurately represent in some cases aperture distributions such as cosine-squared and with less accuracy uniform aperture distributions. The exact series solution and the moment method solution are used to verify the accuracy of the solution for conducting wedges and a rectangular cylinder of moderate size. Two dimensional scattering by conducting circular cylinders of small to moderate size in wavelengths, in the presence of local directive sources, is also rigorously analyzed. Calculated scattering cross sections show that for E-polarized local sources the cross section first decreases and then increases with increasing directivity whereas for H-polarized sources the reverse occurs.
Item Metadata
Title |
Diffraction of antenna radiation patterns by local obstacles
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1999
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Description |
Radiowave blockage by buildings is a problem common to mobile radio and
cellular telephone systems in high-density urban areas. Plane wave incidence is an
approximation which simplifies analysis of the scattering problem, but this is not an
accurate assumptions if the obstacle is near the antenna. If the transmitting antenna has an
omnidirectional pattern and the obstacle is large in wavelengths the scattered field can be
calculated by the techniques of high frequency diffraction theory such as the geometrical
theory of diffraction. If the antenna pattern is directive and the obstacle is local, the
omnidirectional source solution can be converted to a beam source solution by the
complex source point (CSP) method. Antenna patterns with sidelobes can be synthesized
from arrays of CSP beams, each with appropriate amplitude, phase and direction. Their
individual scattering from apertures and buildings may be calculated and the result
summed for the total field.
The complex source point method is used here to produce the basis elements of an
array of linearly and directionally equispaced two-dimensional CSP beams and compared
with Gaussian beam results obtained by others earlier. For efficiency a limited number of
significant beams and beam directions is required. Approximately twice as many beams
as the aperture width in wavelengths, with all beam directions normal to the aperture, is
found to be sufficient here for simple uniform and cosinusoidal distributions in apertures
of moderate size at ranges outside the evanescent field zone of the aperture. Now the
exact solution for the far field of a line source, or here a beam source in the presence of a
conducting half plane, is used as our basis element, to give the solution for antenna
pattern diffraction by a local half plane. In this work a beam source in the presence of a
conducting half plane, is used as our basis element, to give the solution for antenna
pattern diffraction by a local half plane. Antenna pattern diffraction by an aperture near a
wide slit is presented as simply a superposition of the solutions for two coplanar half
planes with separated parallel edges. Antenna pattern distortion by various other local
obstacles, such as conducting wedges and rectangular cylinders, can be obtained
similarly. Numerical results, including both extended apertures and a single beam source,
represented by arrays of complex source point beams and by a single CSP beam are
given. From scattering patterns the latter are shown to accurately represent in some cases
aperture distributions such as cosine-squared and with less accuracy uniform aperture
distributions. The exact series solution and the moment method solution are used to
verify the accuracy of the solution for conducting wedges and a rectangular cylinder of
moderate size.
Two dimensional scattering by conducting circular cylinders of small to moderate
size in wavelengths, in the presence of local directive sources, is also rigorously
analyzed. Calculated scattering cross sections show that for E-polarized local sources the
cross section first decreases and then increases with increasing directivity whereas for H-polarized
sources the reverse occurs.
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Extent |
5310725 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-07-02
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0065036
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1999-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.