Optimal design of a symmetric monopole antenna with spiral geometry

Conventional monopole antennas have narrow bandwidth and this bandwidth can slightly be improved by using dual arms for the monopole structure. Folding both ends of the dual monopole antenna can result in further improvement of bandwidth of the dual monopole structure. Spiral antennas have large bandwidth. This paper proposes an optimal symmetric antenna combining spiral geometry with a dual monopole structure. Modeling of the proposed antenna is done using the number of turns, segment lengths and spiral geometrical parameters. The antenna parameters, gain and input impedance, are calculated using NEC2 and the proposed structure is optimized using Particle Swarm Optimization(PSO). The proposed structure is optimized for maximizing gain subject to the prescribed input impedance. Simulated results of the proposed antenna shows better gain, impedance and bandwidth characteristics compared to L-shape folded dual monopole.