6 dB directional coupler: An RF passive device used to tap off or sample a portion of the signal from a main transmission line, featuring a coupling value of 6 dB—meaning about 25% of the input power is coupled to the secondary port while the rest continues through the main path. Commonly used in RF and microwave systems for signal monitoring, measurement, combining, and feedback applications, it offers low insertion loss on the through line, good directivity, and stable performance across a wide frequency range.