| abstract |
An antenna structure for two frequency ranges including two antenna elements. The first antenna element is a cylindrical coil conductor (2) forming a helical antenna and includes in the direction of its longitudinal axis, a first portion (2a) and a second portion (2b). The second antenna element (3; 6) is connected to the cylindrical coil conductor by a fixed connection at a junction (2c) lying between the first and second portions of the first antenna element. The second antenna element may be for example, a filamentous conductor (5a), a conductive pattern (5) formed on the surface of an insulating plate (3), or a small-diameter helical antenna (6). The first operating frequency is dependent on the combined electrical length of the portions of the first antenna element while the second operating frequency is dependent on the combined electrical length of the lower part of the first antenna element and the second antenna element. The bandwidth of the operating frequencies is dependent on the positioning of the junction in the first antenna element. |