A high-gain beam-steering quasi-Yagi antenna

Recently, beam-steering reconfigurable antennas have gained considerable attention due to their capability of enhancing the performance of wireless communication systems [1]-[5]. By changing the main beam direction, they have the potential to avoid noise sources, to mitigate the multipath fading, to provide larger coverage, and to save energy. Unfortunately, most of the currently reported beam steering antennas suffer from either the low realized gain or the very small overlapped impedance bandwidth. In [1] and [2], rectangular single-arm spiral antennas are employed to realize beam scanning. The gains of the antennas in [1] and [2] are between 3-6 dBi and 4 dBi, respectively, and the bandwidths of the two antennas are about 6% (axial ratio bandwidth) and about 1.4% (50MHz at 3.7 GHz), respectively. In addition, a four-element L-shaped antenna array is proposed that can switch the main beam to 8 directions [3]. The gain of this design is around -0.5-2.1 dBi and the impedance bandwidth is 4% (2.42-2.54 GHz). In [4], a reconfigurable patch-slot-ring antenna is designed with both elevation and azimuth beam switching. The 6-dB impedance bandwidth for all modes is 2.6% centred at 2.05 GHz, and the measured peak gains are 6.1-6.7 dBi. Furthermore, a beam-tilting pattern reconfigurable microstrip parasitic dipole array is shown in [5] with an impedance bandwidth of 5%. The gain of this antenna is not reported. There is no doubt that the small impedance bandwidth or the low gain of the above antennas can significantly limit their applications.