| 摘要 |
A multi-band antenna (10) is adapted to receive signals in the AM/FM bands and to receive and transmit signals in a significantly higher frequency band such as that used for cellular telephone. An AM/FM band antenna is formed of a tubular rod (14,16), and a higher frequency band antenna is formed using a center-fed coaxial dipole (12) mounted on top of and coaxially with the AM/FM antenna. The dipole (44,46) is fed by a coaxial rod (48) attached to a coaxial cable (26) extending through the AM/FM antenna (14,16). A cylindrical choke (50) is disposed about the coaxial rod and is spaced a predetermined distance from the dipole antenna to reduce coupling between the AM/FM antenna (14,16) and the high-frequency antenna (12). The choke (50) functions to position the input impedance of the high-frequency antenna at the base of the choke in a manner so that a short matching transformer may be used at the base of the choke for connection to the coaxial cable. In matching the antenna in this manner at the base of the choke, the best possible VSWR characteristics of the antenna are preserved and the radiation pattern of the antenna's main lobe extends horizontally along a horizontal axis. <IMAGE> |
