(a) Wave guide directional couplers possess properties which make them useful for power monitoring purposes and for impedance measuring or matching. They are used to provide test points in ultra high frequency transmission systems, at which transmitter power may be measured, or at which signals of known amplitude may be introduced in order to measure receiver sensitivity, in a manner that is relatively free from standing Waves in the guide. Wave guide directional couplers may also be used to aid in determining standing wave ratio in a wave guide, a knowledge of which is valuable in providing correct termination for the wave guide.
(b) A wave guide directional coupler is a device which, when inserted into a main wave guide in which waves travel in both directions, delivers to an output device in an auxiliary wave guide energy which is largely a function of the amplitude of the wave going in a preferred direction in the main wave guide, and relatively independent of the amplitude of the wave going in the opposite direction in the main wave guide.
(c) A wave guide directional coupler may be further described as a device comprising sections of a main and auxiliary wave guide, and all regions in which there is coupling between the two. Some means of electrical coupling between the two sections of wave guide is included, this means generally taking the form of coupling elements.