What is Multiple Degree of Reconfiguration

Cognitive Radio presents promising applications in creating a more intelligent and flexible radio and wireless system structures considering the increasing demands faced by spectrum usage and spectrum regulators for specific frequency bands. The flexibility and reconfigurability required by such systems place a significant burden on engineers and radio designers specifically on the radio front-end and antenna elements. This chapter aims to study and analyse the various reconfiguration techniques and types that could be employed in the antenna front-end that will allow cognitive radio to be more flexible and adaptable to different bands and environments. The chapter focuses on theoretical and experimental analyses of novel methods to frequency-reconfigure compact ultra-wideband antennas to work in different bands, and it also explores the possibility of pattern and polarisation reconfiguration of the antenna element. It ultimately shows a method of combining all reconfiguration techniques to realise an original antenna structure capable of adapting the cognitive radio unit to work in congested electromagnetic spectrum bands based on availability of other free gaps, usage rate, and environmental factors. The authors strongly believe the proposed design meets the growing demand of cognitive and smart radio devices for more intelligent and multi-functional antennas.