Considering the high speed RoF (Radio over Fiber) based cognitive radio which is suggested for the future communication systems, one of the important problems to be solved is the necessity of antennas in different sizes or structures for each frequency band. Additionally, in order to keep up with the high speed RoF systems, cognitive radio antennas should have the reconfigurable multiband properties. In this PhD thesis, to get rid of the need of different antenna structures when the cognitive radio changes its operating frequency bands, a novel reconfigurable antenna system is proposed. The proposed antenna system has the ability of changing its operating frequency depending on the antenna reconfiguration controller output. Unless the antenna characteristic is changed dynamically, the necessity of having many antennas to operate at each specific band makes cognitive radio unusable. With the antenna system proposed in this PhD thesis, one of the important problems limits the high speed multiband cognitive radio applications is removed.
Key Words: Cognitive Radio, Fractal Antennas, Radio over Fiber systems, CO-OFDM systems, Particle Swarm Optimization