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Directive Broadcast Arrays

Author: Edmund A. Laport

In the middle of the 1930's, spectrum congestion in the medium-frequency broadcasting band began to be solved by the use of directive antennas. These were composed of two or more vertical radiators, usually towers, disposed geometrically and excited electrically to produce radiation patterns that control the field strength radiated toward another station. By this method, the interference can be maintained within prescribed limits in the area of other stations on the same or adjacent frequency assignments.

The success of the directive-antenna technique in North America has led to a much more intensive utilization of the available frequency band than would have been possible otherwise. At the present time several hundred broadcast stations employ directive systems for mutual protection, administered under precise technical standards by international treaty.

This remarkable branch of antenna engineering has developed rapidly under the ever-increasing complexity of the allocation situation as the number of stations in service increased. The number of radiators needed to produce the more complex radiation patterns has been increasing year by year until, at the present time, systems of nine radiators are being used or proposed, with even more extensive systems likely to be used in the future.

Appendix VIII is included to show the development of the 620-kilo-cycle channel as of 1949, using directive antennas.

Last Update: 2011-03-19