A dual-band antenna for cellular applications: influence of plastic embedding

With the increasing demand for cellular phones operating in two frequency bands, several new antenna designs have been proposed. Previously, a dual-band (GSM and DCS) antenna design using three elements with one feed point was was proposed (Liu 1998). For the elements not clad by plastic, the radiation patterns were shown to be basically omnidirectional (though maximum radiation directions were not in the horizontal plane), and the antenna was tunable by adjusting the length of the wire elements. In this paper, we report FDTD modeling results for a practical situation wherein the wire elements are formed in a plastic rod. Our modeling study indicates a large shift of the antenna´s radiation pattern in the elevation plane. This shift likely negates the usefulness of the design of Liu.