Unidirectional Antenna for Cognitive Radio Applications

A novel band-reconfigurable antenna with stable unidirectional radiation patterns is presented for cognitive radio applications. One wideband mode based on a magneto-electric (ME) dipole and four narrowband modes based on a length-reconfigurable thin dipole are achieved for operation between 0.83 to 2.16 GHz. PIN diodes are used as switches for choosing different operating modes. The ME dipole technology makes the wideband mode with flat gain (8.7 +/- 1 dBi) and well-controlled radiation patterns (cross polarization <= -25 dB, back radiation <= -20 dB). Moreover, as parts of the ME dipole, four hollow metal posts can hide the DC bias lines from the RF radiation, which provides the advantages of high efficiency and simple structure.