Abstract
A frequency reconfigurable printed Yagi-Uda antenna is presented for cognitive radio applications. A 46% continuous frequency tuning bandwidth is obtained by loading the driver dipole arms and four directors with varactor diodes. This configuration allows a high-gain and an almost constant end-fire pattern to be maintained while the antenna operating frequency is tuned. A parametric study was undertaken considering the inter-director spacing, director length tapering, and reflector geometry. It was found possible over the band that the front-to-back ratio is >; 16 dB, the sidelobe level is <; -14 dB and the cross polarization levels in the principal planes are <; - 15.5 dB. From 1-dB compression point measurements, the maximum input power of the antenna with the present diodes is limited to 17.6 dBm at 700 MHz. This suggests that reconfigurable antennas which use active components should have an IIP3 specification placed on them. The frequency selective feature of the antenna makes it as an attractive user terminal antenna for fixed point-to-multipoint cognitive radio enabled broadband wireless access.
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