Radio Antenna Engineering is a free introductory textbook on radio antennas and their applications. See the editorial for more information....

Multiple-star Ground System

Author: Edmund A. Laport

The star ground system utilizes the principle that if a number of short buried-wire radial systems, simulating large ground plates, are placed at uniform distance around the antenna base and their centers connected together at the base of the antenna with overground bus wires, the current densities in the soil can be made relatively small. A system of such star radials can reduce the current densities at the collecting areas to almost any degree desired depending on the number used. When two or more concentric circles of stars are used, inductors are placed in series with the busses for the inner stars to equalize the currents - otherwise the inner ones would collect the most current. The inductors may be simply a few turns in the bus wire wrapped around the supporting poles for the over-ground return circuit. The size and number of radial wires in each star and the number of stars used per circle have to be determined by tests. The greater the amount of current to be collected, the greater should be the number of stars and the number of circles of stars. This will in turn depend upon the antenna resistance and the power input. A star of eight 50-foot radials may be mentioned as a suggestion for 100-kilocycle use. At higher frequencies the radials can be decreased eventually to 25 feet in length. It is better to use more stars of short radial length than to use fewer stars with long radials. The need for ground rods at the ends of each radial must be determined by experimental tests.

Last Update: 2011-03-19