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Description
This thesis focuses on two aspects: triple mode feedhorn as a feed source to reflector antennas and a compact spiral loaded planar dipole antenna with frequency reconfiguration. For the first aspect, parabolic symmetric and offset reflector antennas are adaptively illuminated using a novel triple (TE__+ TM__+ TE21__) modes feedhorn with different mode combinations and impedance and radiation performances are presented. The combination of the radiating modes in a feedhorn with proper amplitude and fixed phase values helps in electronically pointing the main beam of the radiating patterns such as obtained in a beam steering antenna with limited beam scan range. This type of radiation performance virtually creates a displaced phase center location for the feedhorn, which consequently, adaptively illuminates the reflector antenna surface. Impedance matching bandwidths are preserved for both reflector antennas similar to the case of feedhorn alone. The co-polarization gain and peak cross-polarization levels are far better with the offset reflector antenna than the symmetric reflector antenna. Such reflector antennas find applications in radars. The simulation and analysis have been performed using EMSS's FEKO tool which is a Method of Moments (MOM) based Maxwell equation solver. The other design performed is a reconfigurable spiral loaded planar dipole antenna design which is frequency reconfigurable in the 0.76 GHz, 1.47 GHz and 2.2 GHz bands by employing PIN diodes as switching elements. This design is implemented to show the compactness achieved using spiraling in a planar dipole antenna. This antenna was fabricated and tested with nearly matching results. It can be used in wireless communication applications and for many other devices which operate over these frequency bands
