Bandwidth enhancement of the monopole antenna by using a parasitic normal-mode helix

An innovative monopole antenna coupled with a parasitic normal-mode helix h as been designed and studied both experimentally and theoretically. The eff ects of various dimensions of the monopole and the parasitic helix were inv estigated extensively. This simple combination can significantly enhance th e antenna bandwidth over that of the conventional monopole antenna. It is f ound that, with suitably chosen antenna dimensions, the VSWR bandwidth (VSW R less than or equal to2) of the antenna can be increased to 36%, almost do uble that of the monopole antenna alone. The far-field pattern of the combi ned antenna is basically the same as that of the monopole antenna. This ant enna is designed to operate at 1.8 GHz. The substantially enhanced bandwidt h of this simple and small antenna is a useful feature for future mobile co mmunications.