A tunable filter antenna for cognitive radio systems

A simple frequency-tunable antenna for cognitive radio is proposed. It features a narrow bandpass filter, rendered tunable with a single varactor, and embedded in the feed line of an ultrawideband antenna. A modified version capable of both ultrawideband and tunable narrowband operations is also presented. Due to the topology of the antenna, the required DC biasing lines are easy to design and leave little effect on the antenna performance. Simulated and measured results show the good functioning of the presented design, for both channel sensing and communication.