A multi-band, closely spaced yagi antenna with helical-shaped directors

This paper presents the design of a multi-band, closed spaced Yagi antenna which consists of a folded driver and multiple helical-shaped directors. If one or more straight directors are added to the folded driver, more than one resonant frequency is observed. However, the maximum realized gain and the front-to-back ratio at each resonant frequency are not good because radiation from directors interfere with each other. By introducing a helical-shaped director, however, the multiple resonances with high realized gain and good front-to-back ratio at each frequency are achieved. IE3D is used to simulate the antennas. Copper wire of 0.5 mm radius is used for all simulations.