The 3 dB couplers can be used as power-splitters or as power combiners and their most common application is as components in the design of combiners.

They consist of two identical parallel transmission lines coupled over a length equal or approximately equal to l/4 and mounted in a common exterior conductor.

The couplers are designed to achieve coupling differences in the operating frequency range at the output ports. The phase-shift between the two outputs is always 90° and is independent of frequency. The isolation between these two ports depends heavily on the VSWR of the port loads.

Couplers can be used for air-pressured systems on request.