Variable leaky feeders for cellular radio systems

The leaky cable is an electromagnetic coupling element whose application is becoming very important because of the growing use of cellular telecommunication systems. Used in fixed radio systems the leaky cable generally offers a favourable electromagnetic field distribution even in such particular areas as road tunnels or closed environments where communication through antennae is critical. A serious limit of the leaky cable at high frequencies is its longitudinal attenuation which causes high signal dynamics. In plants employing amplified cable sections, longitudinal cable attenuation severely affects the dimensioning of the line amplifiers and the section length. The author provides a description of specially designed leaky cable sections with an increasing radiation performance along their length (VARIO concept). Nonhomogeneous cable sections allow reduced dynamics in a consistent portion of the frequency bandwidth and should permit the implementation of UHF systems with high section length and reduced amplifier power even with a reasonably low cable diameter