Profile optimisation in planar ultra-wideband monopole antennas for minimum return losses

Optimised profile ultra-wideband planar monopole antennas designed for minimum return losses are presented. Two different procedures based upon the simulated annealing algorithm and the finite element method are considered in order to achieve the minimum return losses possible in the 2-11-GHz frequency band. As a result of both procedures, two different designs have been obtained. Simulations using an infinite ground plane show that lower than 14 and 18-dB, respectively, return losses were obtained for each design. With these results, two prototypes were built and measured, one for each procedure. Lower than 13 and 18-dB return losses were measured in each final design using a 10-cm radius ground plane. Very good agreement between experimental and numerical results is achieved. To conclude the analysis, radiation characteristics of both prototypes are also studied both using an infinite ground plane and taking into account the 10-cm radius ground plane.