An improved-gain omnidirectional circularly polarized antenna based on helical dipoles

This paper presents the design of a circularly polarized omnidirectional antenna based on an inclined dipole structure. The antenna features four helix-shaped dipoles distributed evenly around the cylinder, exhibiting a helical arrangement with 1.5 turns on the cylindrical surface. By exciting all four pairs of dipoles with equal amplitude and in phase, the antenna achieves omnidirectional circular polarization with an improved gain compared to conventional half-wavelength dipole elements. Optimization of various design parameters has yielded a relative bandwidth of 6.8% (1.54 GHz to 1.65 GHz) with a return loss better than 10 dB, a gain higher than 3.5 dBi, and an axial ratio less than 2 dB. Moreover, the gain variation in the azimuth plane is less than 1 dB.