rf directional coupler is the important part in rf passive component filed.It's a electronic item that couple a defined amount of the electromagnetic power in a transmission line to a port enabling the signal to be used in another circuit.

One key feature of directional couplers is that they only couple power flowing in one direction. In this way, power entering the output port is coupled to the isolated port but not to the coupled port.

3dB directional coupler,6dB directional coupler***40dB directional couplers can be implemented using a variety of techniques including stripline, coaxial feeder and lumped or discrete elements. They may also be contained within a variety of packages from blocks with RF connectors, or solder pins, or they may be contained on a substrate carrier, or they may be constructed as part of a larger unit containing other functions.