DESIGN OF CIRCULARLY POLARIZED OMNIDIREC- TIONAL BIFILAR HELIX ANTENNAS WITH OPTIMUM WIDE AXIAL RATIO BEAMWIDTH

Abstract—In this paper, design and analysis of omnidirectional single feed circularly polarized, wide axial ratio beamwidth resonant side-fed bifilar helix antennas that do not require a ground plane is presented. The simulation and measurement results show that side-fed helix antennas of various radii gives near perfect circular polarization (CP) almost over the whole sphere except at and around nulls, at a certain turn angle by properly proportioning the area of loop (A) with the product of pitch (ρ) and radianlength (l) of helix. Helix antennas with smaller radii give axial ratio (AR) close to one at higher values of turn angle with lower value of resonant input impedances but CP is less sensitive to inaccuracy in turn angle. However helix antennas with larger radii results in AR close to one at lower values of turn angle and provides better values of input resistance but its AR is more sensitive to variations in turn angle. The simulated results show that the polarization solid angle beamwidth (for AR ≤ 3 dB) varies from 3.96pi to 4pi steradian. The gain and 3 dB beamwidth of the antennas are 2 dBi and 90 ◦ respectively. The polarization bandwidth varies from 34 % to 65%. The simulated results are verified by experimental measurements. 1