Application of Particle Swarm Optimization to the Design of Multi-Band Antennas with Lumped Loads

This paper investigates the use of nonresonant LC loads in the design of multi-band antennas. In this approach, the loads are made to have inductive reactances at some operating frequencies and capacitive reactances at other frequencies; the loads are never resonant. This has the effect of increasing or decreasing the effective electrical length of the antenna. Also, the entire structure supports significant radiating currents at all operating frequencies. Although this approach is not new, the design process has historically been relatively complicated or has relied on trial-and-error. A much more straightforward and automatic approach based on the particle swarm optimization (PSO) method is described here. The PSO method was chosen because of its speed and relatively simple implementation. The focus is on achieving an input impedance with zero reactance and not on obtaining a specific radiation pattern shape, since the patterns of short monopoles and dipoles are essentially invariant with respect to length