Synthesis of circular polarized normal mode helical antenna

A synthesizing cross-normal mode helical antenna (NHMA) having a circular polarized wave and giving an omnidirectional pattern in the plane of the antenna is given. The moment method solution is used to formulate the problem and the Gram-Schmit orthogonalization method is utilized to calculate the driving voltages of the structure to give the desired pattern. A piecewise triangular expansion function for the current distribution is assumed along the cross-NMHA, considering one triangle along one complete turn of the helix. The driving voltages are calculated against the variation of the parameters of the helix, like the pitch angle, the number of turns and the total length of the helix. Approximate relations are obtained using polynomial curve fitting for the results and can be used for the design of the antenna. It is found that the magnitudes of the driving voltages are almost equal but the phase is more sensitive to the changing parameters of the helix in keeping the circular polarization in the axial direction. Also, as the number of turns is increased little change in the relative phase is required.