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

Termination by Means of Coupled Sections

Author: Edmund A. Laport

Standing waves on a feeder can be suppressed by means of an open-end quarter-wave section or a half-wave short-circuited section coupled to the feeder ( and ) provided that the position of the coupled section along the line is correct, as well as the degree of coupling to the feeder.

FIG. 4.40. Feeder matching, using series reactances.

The open end of the quarter-wave coupled section is pointed toward the load end of the feeder, and the standing waves are eliminated on the feeder opposite the closed end of the coupled section. The schematic diagram of this arrangement is given in Fig. 4.41.

Mechanically this method is not very convenient until the frequency is high enough to give a short coupled section that can be easily slid along its support wires to the position that accomplishes the desired result. The method has singular merit due to the fact that the termination of a feeder is selective to the frequency for which it is adjusted, within 1 or 2 percent, and outside this range the coupled section gives the effect of nonexistence. Therefore, when two or more different frequencies are to be propagated over a common feeder, a separate coupled section can be used to terminate the feeder for each frequency without influencing the other frequencies being transmitted. This provides a means of connecting several generators to a common load over a common feeder and also of using a common feeder to carry power from several generators to several loads selectively, using suitable stopper circuits at the branches of the feeder for correct routing of the different frequencies.

FIG. 4.41. Coupled sections for impedance matching.


Last Update: 2011-03-19