| 摘要 |
A detachable mast antenna for a vehicle is operable in two mobile telecommunications frequency bands (eg 900 MHz, 1.8 GHz GSM), and also receives longer wavelength transmissions (eg FM, AM, DAB). A first choke 30, formed as a helical coil, delineates the extent of the highest resonant frequency (eg 1800 HMz) radiating region of the antenna. Similarly a second choke 32 delineates the extent of the second highest resonant frequency (eg 900 Mhz) radiating region. The overall length of the conductive path, which includes a metal tape 42 helically wound around a glass fibre rod 40, is one half wavelength of the mid-wavelength of the M band. A steel coil spring 36 provides flexibility. The mast can be unscrewed 12 from a mounting (see figure 1d) which contains two PCBs with circuitry (eg amplifier AGC) to process signals. |
