BROADBAND FLAT GAIN ENHANCEMENT OF PLANAR DOUBLE-DIPOLE QUASI-YAGI ANTENNA USING MULTIPLE DIRECTORS

In this article, a method of broadband flat gain enhancement for a planar double-dipole quasi-Yagi antenna using multiple directors is proposed. The proposed antenna consists of two dipole drivers with different lengths, a truncated ground plane, and three parasitic strip directors. First, the length ratio of the two dipoles is adjusted to increase the gain in the low-frequency region. Next, three parasitic strip directors are employed to increase the impedance bandwidth and improve the gain of the antenna in the middleand high-frequency regions. A detailed design procedure for the proposed antenna, covering a frequency band of 1.70–2.70 GHz with a gain > 8 dBi, is explained, along with a step-by-step analysis of the effects of placing each director on input impedance, voltage standing wave ratio (VSWR), and gain characteristics. Experiment results show that the proposed antenna has the desired impedance characteristics with a frequency band of 1.66–2.88 GHz (53.7%) for a VSWR < 2, and a stable flat gain of 8.0–8.4 dBi in the 1.70–2.70 GHz frequency range. Moreover, a measured front-to-back ratio > 11 dB within the band is achieved.