Reflectarray performance improvement using the element spacing reduction technique
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Date
2016
Authors
Safari, Faezeh
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Abstract
This thesis presents the design, analysis and performance improvement of reflectarray (RA) antennas. The considered RA consists of a feed antenna and an array of 'small' elements that are distributed on a flat surface using printed circuit technology. The feed antenna is used to generate an incident field to illuminate the elements of the RA. Each element acts as a partial reflector with a specific reflection coefficient. The resulting reflected field on the RA aperture should have the desired amplitude and phase distribution to create the antenna`s far field radiation pattern. The RA element reflection coefficient versus its geometrical parameters in a uniform infinite array environment is used as a data table to design the RA elements. The RA element geometry is comprised of a simple rectangular patch on the top of a at single-layer grounded dielectric substrate.
Reflectarray technology suffers from several degrading factors such as low efficiency and gain bandwidth. In this thesis it is shown that as the element spacing reduces, a better control over the RA aperture is achieved. This improves the efficiency of the RA. Also, as the element spacing reduces, the reflection coefficient phase versus frequency becomes more linear. This improves the gain bandwidth of the RA.
The beam squint, which is the deviation of the RA beam angle from the desired beam angle, is another degrading factor of the RA technology. Only a few attempts have been made in the literature to investigate or reduce the RA beam squint. These attempts are either incomplete or complicated. In this thesis, it is shown that as the element spacing reduces the beam squint of the RA improves. It is also shown that as the element spacing reduces the side lobe level and cross-polarization of the RA improves. These two far field parameters are important but not investigated in the literature.
Sixteen RA designs and associated analyses are presented. One design was selected for fabrication utilizing a feed antenna from the University of Manitoba's Antenna Laboratory. The measured radiation patterns agree well with the analysis results and demonstrate the validity of the element spacing reduction technique.
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Keywords
Antennas, Reflectarray, Radiation Pattern, Far-Field Parameters, Element Spacing Reduction