Design of a small antenna for wideband mobile direction finding systems

In this study, the authors propose a novel small antenna for use in mobile direction finding (DF) systems covering the range 20-1300-MHz. The proposed antenna has a multiconical sleeve to increase the input resistance at low frequencies while reducing the antenna size. A skirt-shaped disk on top of the antenna body maintains the omnidirectional radiation pattern over a wide frequency band without radiation nulls in the broadside direction. The detailed design parameters of the proposed antenna were optimised using a Pareto genetic algorithm (GA) with the FEKO EM software package. Below 200-MHz, the proposed antenna shows a receiving performance comparable to a 60-cm conventional dipole but at only half the size. Above 200-MHz, the antenna maintains an omnidirectional radiation pattern up to 1300-MHz with a stable realised gain, whereas the 60-cm dipole has a broadside radiation null at about 850-MHz.