Optimum design of axial mode helical antenna with nonlinear pitch profile modeled using Catmull-Rom spline and Particle Swarm Optimization

This paper presents a novel method for design of circularly polarized axial mode helical antenna with maximum directive gain. In this work helical antenna is compactly modeled by the following parameters - helix radius (a), number of turns (N) and nonlinear pitch profile represented by a Catmull-Rom spline curve. This spline curve consists of six pitch angles α₁, α₂, α₃, α₄, α₅ and α₆ at six equidistant points along the axial length of the helix. For a given number of turns, optimum values of radius and pitch profile are determined for maximizing the gain subject to unity axial ratio. The gain and axial ratio are determined using NEC2 (Numerical Electromagnetics Code) simulation and optimization is performed using Particle Swarm Optimization (PSO). The original NEC2 source code has been modified to incorporate Catmull-Rom spline modeling and PSO to suite the requirement of this work. Simulated and experimental results show that there is significant improvement in gain characteristics compared to design based on Kraus method which uses constant pitch profile.