What Is a Directional Coupler?
A directional coupler is a specialized piece of equipment with four ports, designed to extract radio waves proportional to the forward and reflected waves in a transmission line.
Of these four ports, two are designated for the transmission line’s input and output, one typically serves as an isolation port, and the other as a coupling port for extracting radio waves. Variants known as bidirectional couplers have no isolation ports and feature two coupling ports instead.
The efficiency of directional couplers is gauged by their ability to differentiate between forward and reflected waves, a trait known as directionality. This directionality is quantified as 10 log(P1 / P4) – 10 log(P1 / P3), and is measured in decibels (dB).
Using directional couplers to measure radio waves helps in assessing the signal conditions within transmission lines. They are crucial in monitoring applications, such as mobile phone base stations, antennas, and cable television networks.