Power monitoring and reflectometry – Underlying principle Modern microwave power monitors and reflectometers primarily rely on which fundamental microwave component principle?

Introduction / Context:
Measuring forward and reflected power on transmission lines requires separating the two traveling waves. Directional couplers provide this separation, enabling direct sampling of forward and reverse waves for power monitoring and VSWR/return-loss measurement in reflectometers.

Given Data / Assumptions:

• Coupled-line or waveguide directional couplers are available.
• Detectors or power sensors can be attached to coupled ports.
• Goal is to measure forward and/or reflected power accurately.

Concept / Approach:

A directional coupler couples a known fraction of power from the main line into auxiliary ports with a preferred directionality. By attaching detectors to the forward and reverse coupled ports, instruments compute power, return loss, and VSWR. This principle underpins reflectometers and most in-line wattmeters used in microwave labs and systems.

Step-by-Step Solution:

Verification / Alternative check:

Calibrated couplers with known coupling enable absolute power estimation; dual-directional couplers permit simultaneous forward and reverse readings for reflectometry.

Why Other Options Are Wrong:

Klystrons, Gunn diodes, and TWTs are sources/amplifiers, not measuring elements; a DRO is an oscillator, not a wave-separating device.

Common Pitfalls:

Confusing coupling with insertion loss; ignoring directivity limits which set the floor for measurement accuracy in high-return-loss systems.

Final Answer:

directional coupler.