Directional Coupler

Some articles on directional coupler, coupler, directional couplers:

Power Dividers And Directional Couplers - Transmission Line Types - Directional Couplers - Coupled Transmission Lines
... The most common form of directional coupler is a pair of coupled transmission lines ... in figure 4 of a quarter-wavelength (λ/4) directional coupler ... reason it is sometimes called a backward coupler ...
Power Dividers And Directional Couplers - Applications - Making Use of Isolation
... If isolation is high, directional couplers are good for combining signals to feed a single line to a receiver for two-tone receiver tests ... Because of the symmetry of the directional coupler, the reverse injection will happen with the same possible modulation problems of signal generator F2 by F1 ... the isolators are used in figure 20 to effectively increase the isolation (or directivity) of the directional coupler ...