Quad hybrid microstrip coupler
Image of the Quad hybrid microstrip coupler.

The quadrature hybrid may be implemented in microstrip or stripline, and is also known as a branch-line coupler. It is a four-port network which produces a 90 degree phase shift between the two output ports, hence the name "90 degree hybrid junction".

With reference to the port numbering in the image below - when fed at port 1, two equal signals are received at ports 2 and 3 with a 90 degree phase shift between them; while good isolation is achieved between the input and output ports (1 and 4). Unequal power division may be achieved by using different impedances at the output ports.

The quadrature hybrid with its relevant line lengths and impedances

Since the quadrature hybrid has a high degree of symmetry, any port may be used as the input port. The output ports will always be on the opposite side of the junction, and the isolated port will be the remaining port on the same side as the input port.

Typical reflection coefficient behavior versus frequency
Typical phase behavior versus frequency