Single feed circularly polarised omnidirectional bifilar helix antennas with wide axial ratio beamwidth

This study presents design and analysis of single feed omnidirectional circularly polarised resonant side-fed bifilar helix antennas with wide axial ratio (AR) beamwidth that does not require a ground plane. The simulation results show that side-fed helix antennas of various radii give polarisation beamwidth (for AR <= 3 dB) from 170 degrees to 178 degrees in elevation planes at a certain turn angle where area of the loop equals the product of pitch and radianlength of the helix. Circularly polarised helix antennas with smaller radii are of higher turn angle, have lower value of resonant input impedances but AR is less sensitive to inaccuracy in turn angle and vice versa for helix with larger radii. The gain and 3 dB beamwidth of the antennas are 2 dBi and 90 degrees, respectively. The polarisation bandwidth (for AR <= 3 dB) varies from 34 to 65%. The simulated results are verified by experimental measurements.