An antenna coupler is a device which makes it possible for one or two antennas to do the electrical work of many, as opposed to using a separate antenna for each individual wavelength. Ideally, every signal would have an individual antenna perfectly measured to resonate to its frequency. Realistically, there are hundreds of wavelengths, and it becomes impractical to equip a building with that many antennae. Technicians, therefore, change their electrical length instead of their physical length.

The process of changing an antenna's electronic abilities is known as "antenna tuning." Antenna tuning involves changing the electrical length of an antenna as well as its compatibility with various types of transmitters and receivers. To tune an antenna, technicians will use tuners, multi-couplers, and antenna couplers.

Antenna tuners and couplers perform the same essential function. Each antenna coupler is able to match one antenna with one receiver or transmitter at a time. Larger jobs are typically better suited to a multi-coupler, which as its name suggests can simultaneously match several antennae to their respective receivers and transmitters.