3dB hybrid couplers and directional couplers are passive devices used in microwave field.
Directional coupler is a reciprocal 4 port device. When a signal is applied to its input port, it provides 2 amplitude ports, coupling is the ratio in dB of the incident power fed into the input port of the main line of the directional coupler to the coupled port of the secondary line when all ports are terminated on matched load.
A 3db Hybrid coupler is a special class of directional couplers in which signals at the two outputs are equal to split RF signal in 2 equal parts or to combine 2 RF signals on one port.
Many applications :
- providing a signal sample for measurement or monitoring, feedback, combining feeds to and from antennae, antenna beam forming.