A coupling or a coupler are one and the same object. Today still rf couplers continue to be utilized in piping and plumbing works. The coupling (or coupler) is usually quite a short length of piping or tube. It usually has a socket one or both ends of the pipe. This makes provision for two pipes to be conjoined, welded, brazed or soldered together. Soldering will be considered when brass or copper materials are utilized.
Welding work will be considered when steel is being worked with. In the event that two ends of the coupling are indicative of differing standards or joining methods, the coupling reverts to being termed as an adapter. Such an example would be where one end of the pipe is BSP (UK) threaded whilst the other will be NPT (USA) threaded. A more basic example could be where one piping end is threaded whilst the other holds just a plain socket for brazing purposes.
A coupling that utilizes the same connecting methods but has different sizes on each end will be called a reduced coupling or reducer. Directional couplers, as well as power dividers (also called power splitters, or power combiners when used in reverse) are passive devices. These are mostly used in the field of radio technology. Such a coupling will couple defined amounts of electromagnetic power into a transmission line through to a port that enables signals to be used within another circuit.
Directional couplers that are designed to split power in equal measures between two ports are known as hybrid couplers. These couplers are made from two coupled transmission lines held close together. It is a favored technique that accommodates microwave frequencies within transmission lines used to initiate numerous circuit elements.