A light dual-band AMPS/GSM top-loaded retractable antenna

This paper presents a new type of top-loaded retractable antenna for mobile phone applications. The antenna consists of a straight radiating element top-loaded with a helical radiating element. The antenna top-loading reduces antenna physical length without decreasing its electrical length. In this way, although physically shorter, the antenna still produces low SAR values. A novel matching circuit with two contacts is placed within a mobile phone. One contact provides matching of the high input impedance of the antenna in extended position, while the lower input impedance of the antenna in retracted position is matched using the second contact. A detailed explanation of the matching circuit operation is given. The input impedance bandwidth (VSWR 2:1) of around 200 MHz, covering both AMPS and GSM frequency bands is achieved. Special attention is paid to reducing the antenna weight. A careful choice of materials used in the antenna fabrication and the development of appropriate production techniques enable a light antenna, weighing about 1.5 g, to be manufactured.