- A unidirectional (UNI) directional coupler samples RF power in only one direction, usually forward power, and cannot measure reflections.
- A bidirectional (BI) coupler samples both forward and reflected power, enabling VSWR and return-loss measurements.
- A dual directional coupler also measures forward and reflected power but uses two independent sensing paths, giving higher accuracy and better tolerance to load mismatches, especially under high-VSWR conditions.
