A compact coaxial-fed unidirectional circularly polarized antenna with wide beamwidth

A new compact coaxial-fed unidirectional circularly polarized antenna with wide beamwidth is presented in this paper. Firstly, multiple metal segments and helical wires are connected in series to form an antenna radiator. Secondly, a meandered ground with a cylindrical side wall is used for miniaturization. The length of metal segments and helical wires are designed to the half-wavelength length through controlling the parameters. By carefully selecting the turns of the helical wires, the antenna obtains unidirectional circularly polarized radiation characteristics. Finally, a 50 Ω coaxial line is utilized to feed the antenna and the ground size is optimized for a best performance. A prototype is fabricated and tested. Measured results show that the antenna obtains a matching bandwidth of 17.04% from 2.2 to 2.61 GHz (|S11|<−10 dB) and an axial ratio bandwidth of 28.11% from 2.14 to 2.84 GHz (AR<3 dB). Thus, the antenna has an overlapped bandwidth of 17.04% with a peak realized gain of 6.1 dB. This proposed antenna has the characteristic of a wide horizontal beamwidth, a simpler structure, and more convenient processing and practical applications.