Low-Profile Helical Quasi-Yagi Antenna Array With Multibeams at the Endfire Direction

This letter presents a novel helical quasi-Yagi antenna array with low profile and multibeams at the endfire direction. First, a planar normal-mode helical quasi-Yagi antenna with top-hat loading for low profile is designed to achieve endfire radiation. It is mounted on a conducting plane, consisting of a top-loaded folded helix as the driven element and three top-loaded unfolded helices as parasitic elements. A broadband can be achieved by controlling the resonance difference between the driven and parasitic elements. Second, a microstrip beamforming network based on Butler matrix is designed to feed a 1 × 4 helical quasi-Yagi array. The proposed antenna array is fabricated and tested. Measured results show that three endfire beams at ϕ = 90°, (90 ± 47)° are obtained while the antenna has a very low profile of 0.054λ at its center frequency, showing that the antenna may be useful in many airborne applications such as unmanned aerial vehicles.