Design and Simulation of Reconfigurable Yagi-Uda Antenna for Cognitive Radio

A frequency reconfigurable Yagi-Uda antenna with varactor diode is being presented for Cognitive Radio systems. The antenna consists of a driven dipole element loaded with pair of varactor diode in two arms, four directors with an additional varactor diode, a microstrip-to-coplanar stripline transition for feed, and a resistive biasing circuitry. Antenna is made to operate over TV spectrum band of 450-750 MHz. The above configuration will maintain high gain and constant endfire pattern while the operating frequency of antenna is tuned. It should have the ability to reconfigure itself to communicate based on sensed spectrum from the environment. Reconfigurability is achieved by varying the reverse bias voltage to the diode so that its capacitive effect will adjust the electrical length of the driver and director element which inturn tune the operating frequency. Results show a better gain variation of about 5-6 dB and return loss less than -10 dB. A better frequency tuning bandwidth is achieved, which makes the antenna as an user terminal antenna that can be used for mobile or fixed point-to-multipoint enabled cognitive radio broadband access.