Circularly Polarized Wide Axial Ratio Beamwidth Omnidirectional Bifilar Helix Antennas

In this paper, analysis and design of omnidirectional single feed circularly polarized, wide axial ratio beamwidth resonant side-fed bifilar helix antennas not requiring 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 & around nulls, at a certain turn angle that corresponds to the formula A = rho l given in [1] where A is the area of loop, rho is the pitch of the helix and l is the radianlength. Helix with smaller radii gives 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 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 >= -3dB) varies from 3.96 pi to 4 pi steradian. The gain and 3dB beamwidth of the antennas are 2dB and 90 degrees respectively. The polarization bandwidth varies from 34% to 65%. The simulated results are verified by experimental measurements.