Browse Prior Art Database

NOVEL APPLICATIONS OF RADIATING FEEDER

IP.com Disclosure Number: IPCOM000006720D
Original Publication Date: 1992-Dec-01
Included in the Prior Art Database: 2002-Jan-25
Document File: 3 page(s) / 188K

Publishing Venue

Motorola

Related People

Brian R. Cook: AUTHOR

Abstract

Radiating feeder cables are primarily designed to distribute radio signals in confined areas. They are used where discrete antennas would be unsuitable by reason of inadequate coverage, excessive coverage overlapping adjacent areas, or unsightly appearance. Typical applica- tions are tunnels, stairwells, underground stations, mili- tary bunkers and similar locations.

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MOTOROLA INC. Technical Developments Volume 17 December 1992

NOVEL APPLICATIONS OF RADIATING FEEDER

by Brian R. Cook

1. lNTRODUCTlON

  Radiating feeder cables are primarily designed to distribute radio signals in confined areas. They are used where discrete antennas would be unsuitable by reason of inadequate coverage, excessive coverage overlapping adjacent areas, or unsightly appearance. Typical applica- tions are tunnels, stairwells, underground stations, mili- tary bunkers and similar locations.

  It is often the case, particulary in tunnels, that other circuits are required along the route of the radiating cable and this report investigates the extent to which it could be used for applications in addition to its primary role for radio.

2. RADlATlNG FEEDER

  Radiating feeders are generally used for carrying two- way radio, paging and broadcast radio in the frequency range 30 MHz to 2 GHz, though there are some uses at lower frequencies.

  Many types of radiating feeder are similar in design to standard coaxial cables except that the outer screen- ing sheath contains holes or slots through which a lim- ited amount of RF radiation, and signal pick-up, is pos- sible. The dimensions, quantity and spacing of the holes determine the radiating efficiency. Manufacturers gener- ally offer a range of cables, some with low radiation and a correspondingly low attenuation per unit length of cable, other types have higher radiation and hence more rapid attenuation.

  The radiating efficiency of the cable varies with fre- quency. This is usually expressed in terms of the cou- pling loss to a dipole antenna at a set distance between 2 and 10 metres from the cable. Cables currently available vary in their characteristics, some claim an essentially constant coupling loss, some have a minimum and 150 MHz, others drop steadily from 150 MHz to 900 MHz. This, and the fact that coupling loss can vary 10 to 20 dR as the detector is moved slightly, merely serve to

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illustrate that it is unwise to generalize and the quantita- tive studies can only apply to particular types of cable.

3. LOW FREQUENCY APPLICATIONS

  Radiating feeder has similar impedance and loss fig- ures to standard coaxial cables and so could be suitable for carrying various types of signals normally carried by them. The special requirements are that the amount of spurious radiation from the radiating cable must not inter- fere with adjacent circuits, and that the cables must not pick up an unacceptable level of interference t?om exter- nal sources at the frequencies of interest.

  In a long underground tunnel where there are no other cables or electrical machinery this may not be a problem. In other applications 'electromagnetic com- patibility is an important practical requirement and fur- thermore, note must be taken of the current EC direc- tives on the subject.

  At low frequenices the coupling loss of many types of cable is increased. This means that the cables will perform reasonably we...