My PhD Dissertation

Innovative Antenna Designs for Broadband Circularly-Polarized Wireless Systems and Software Radios

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Brief Motivation and Summary

Sustaining current increases in wireless data rates has driven engineers of all related backgrounds to seek fresh and innovative approaches in wireless system design. With the advancement of RF switching technology, transceiver architectures, and digital signal processing capabilities, the pressure now falls on the antenna designs for future broadband and adaptive wireless services. The first part of the work focuses on enhancing the bandwidth of low-profile patch antennas for circularly-polarized (CP) wireless systems. We start with an in-depth examination of the CP patch antenna cavity model, revealing that traditional circularly polarized (CP) patch antennas are not being utilized to their full potential for bandwidth. Some new modifications to enable broader bandwidths are proposed. A high-performance antenna for future Mars Rover missions is also discussed, and a novel CP Half E-shaped patch antenna subarray was developed and prototyped to demonstrate its use. Another concept uses composite right/left-handed (CRLH) transmission lines towards creating wideband CP arrays. Our resulting array prototype using a CRLH transmission line feed network showed an overall bandwidth of 60%, which is a formidable increase compared to designs using conventional quarter-wavelength transmission lines.

In the second part of this work, reconfigurable antenna functionalities for software and cognitive radios are pursued. With the development of practical reconfigurable antenna simulation models in conjunction with nature-inspired optimization techniques, two reconfigurable E-shaped patch antenna implementations are evaluated for potential use as frequency or polarization reconfigurable antennas. This is particularly useful for systems wanting to achieve unidirectional patterns with a low-profile antenna. Both the frequency and polarization reconfigurable designs were optimized, fabricated, and characterized through measurement. Our frequency reconfigurable E-shaped patch antenna design is able to support an overall bandwidth of 50% by incorporating MEMS switches. The CP reconfigurable version design provided CP bandwidths of 17% and 20% for an element and array concept, respectively. Lastly, a rejection reconfigurable array element is developed. The design uses a reconfigurable frequency rejection slot within a wideband monopole antenna, and some simulation and experimental measurement studies are undertaken. By integrating another reconfigurable filter, a higher-order filter capability is achieved, leading to stronger rejection levels from strong blockers.