| Summary: | In recent years there has been a growing demand for reduced mass, small launch
volume, and, at the same time, high-gain large-aperture antenna systems in modern
space-borne applications. This dissertation introduces new techniques for dual-band
reflectarray antennas to meet these requirements. A series of developments is presented
to show the dual-band capability of the reflectarray.
A novel microstrip ring structure has been developed to achieve circular
polarization (CP). A C/Ka dual-band front-fed reflectarray antenna has been designed to
demonstrate the dual-band circular polarized operation. The proposed ring structure
provides many advantages of compact size, more freedom in the selection of element
spacing, less blockage between circuit layers, and broader CP bandwidth as compared to
the patches.
An X/Ka dual-band offset-fed reflectarray is made of thin membranes, with their
thickness equal to 0.0508 mm in both layers. Several degrading effects of thin substrates
are discussed. To overcome these problems, a new configuration is developed by
inserting empty spaces of the proper thickness below both the X and Ka band
membranes. More than 50 % efficiencies are achieved at both frequency ranges, and the proposed scheme is expected to be a good candidate to meet the demand for future
inflatable antenna systems.
An X/Ka dual-band microstrip reflectarray with circular polarization has also been
constructed using thin membranes and a Cassegrain offset-fed configuration. It is
believed that this is the first Cassegrain reflectarray ever developed. This antenna has a
0.75-meter-diameter aperture and uses a metallic sub-reflector and angular-rotated
annular ring elements. It achieved a measured 3 dB gain bandwidth of 700 MHz at Xband
and 1.5 GHz at Ka-band, as well as a CP bandwidth (3 dB axial ratio) of more than
700 MHz at X-band and more than 2 GHz at Ka-band. The measured peak efficiencies
are 49.8 % at X-band and 48. 2 % at Ka-band.
In summary, this dissertation presents a series of new research developments to
support the dual-band operation of the reflectarray antenna. The results of this work are
currently being implemented onto a 3-meter reflectarray with inflatable structures at the
Jet Propulsion Laboratory and are planned for other applications such as an 8-meter
inflatable reflectarray in the near future.
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