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 are also used to combine power amplifiers to the transmitters and translators.
They consist of two identical parallel transmission lines coupled over a length equal to 1/4 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 º and is independent of frequency. The isolation between the two ports depends heavily on the VSWR of the port loads.