directional coupler

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directional coupler

[də′rek·shən·əl ′kəp·lər]
(electronics)
A device that couples a secondary system only to a wave traveling in a particular direction in a primary transmission system, while completely ignoring a wave traveling in the opposite direction. Also known as directive feed.

Directional Coupler

 

a device consisting of two sections of radio waveguides. A fraction of the electromagnetic-wave energy propagating through the main waveguide is shunted into an auxiliary waveguide by using coupling links; in the auxiliary waveguide the energy is transmitted only in a specific direction. If the wave-propagation direction in the main waveguide is reversed, then the propagation direction of the shunted wave in the auxiliary waveguide will also be reversed. The unidirectional propagation in the auxiliary waveguide results from the interference of the waves that are excited in it. The superposition of these waves in one direction results in cancellation of the waves; superposition in the other direction results in the formation of the summed shunted wave. Examples of coupling links between two waveguides are (1) apertures in adjacent walls and (2) loops. Directional couplers are widely used in superhigh-frequency apparatus (frequencies from 30 megahertz to 300 gigahertz) for splitting or combining the energies of waves; for determining the wave direction, power, and phase; and for other applications.

REFERENCES

Lebedev, I. V. Tekhnika i pribory sverkhvysokikh chastot, vol. 1. Moscow-Leningrad, 1961.
Altman, J. Ustroistva sverkhvysokikh chastot. Moscow, 1968. (Translated from English.)

L. S. OSIPOV

directional coupler

(communications)
(tap) A passive device used in cable systems to divide and combine radio frequency signals. A directional coupler has at least three ports: line in, line out, and the tap. The signal passes between line in and line out ports with loss referred to as the insertion loss. A small portion of the signal power applied to the line in port passes to the tap port. A signal applied to the tap port is passed to the line in port less the tap attenuation value. The tap signals are isolated from the line out port to prevent reflections. A signal applied to the line out port passes to the line in port and is isolated from the tap port. Some devices provide more than one tap output line (multi-taps).