Broadband Circularly Polarized Antenna Employing Cascaded Water Dipole and Helix

This article presents a compact directional circularly polarized (DCP) antenna employing cascaded water dipole and helix. It consists of five half-wavelength water cylinders as vertical dipoles for generating vertical electric component and six half-wavelength open helices for horizontal electric component. The dipoles and helices are connected in series and the central dipole is splitted for a differential feed. Owing to the 90° phase difference between the vertical and horizontal fields and an asymmetric distribution of the dipole radiators, a relative broadband unidirectional CP radiation is achieved by only using a single radiator with compact size. A prototype is fabricated employing 3D printing technology, reducing the difficulty of practical realization of the antenna. Measured results show that a matching bandwidth of 30% and an axial ratio bandwidth of 10.1% are achieved. This antenna features a broadband DCP radiation while having a simple, compact, and highly transparent structure, which is potentially useful for CP wireless communications.