Abstract
In this letter, the novel ladder-like directors are proposed and investigated for antenna gain and bandwidth enhancement. First, single-stage director is introduced to the quasi-Yagi antenna design to improve directivity in the endfire direction. Then, to further enhance the performance, multistages of directors form ladder-like structures that are co-designed with the antenna, with careful considerations of mutual coupling effects. To validate the concept, a 60-GHz antenna using proposed directors is designed and fabricated. The simulation results reveal an antenna gain improvement of 2.2-3.4 dB and bandwidth improvement of 30% by using the proposed directors. The measured antenna achieves a gain of 11.7 dB at 60 GHz and in-band cross polarization of less than 15 dB. The antenna occupies a compact size of 9.2 x 10 mm(2).