1/4 Wave

Refers to wavelengths of audio or electromagnetic radiation (i.e., radio waves). One quarter of a wave denotes some dimension having a relationship with a signal such that it is 25% (or 1/4) as large as the space required for the entire wave of the signal. For example, in an RF (Radio Frequency) or wireless system, 1/4-wave antennas are common. A 1/4-wave (typically pronounced “quarter wave”) antenna’s length is a quarter of the wavelength of the carrier frequency used by the system. There are also 1/2-wave antennas, and so on. Similar relationships exist in the field of acoustics (see quarter space), though they aren’t usually this specific (audio systems generally have to respond to a wide range of frequencies), and it’s not as common to hear things referred to in this manner.