Standards and calibration: Standard mismatches (precision opens, shorts, and loads) are used to calibrate SWR and impedance-measuring equipment in microwave labs.

Introduction / Context:
Accurate measurements of VSWR, reflection coefficient, and impedance require instrument calibration against known standards. In microwave practice, precision terminations and known mismatches (open, short, and matched load) define reference points on the measurement plane and enable traceable results.

Given Data / Assumptions:

• SWR meters, slotted lines, and modern VNAs all require calibration.
• Standards have well-characterized magnitude and phase of reflection.
• Connections are made at a defined reference plane with suitable adapters.

Concept / Approach:

Calibration consists of measuring known standards and using those results to remove systematic errors. For scalar instruments (e.g., SWR meters), a matched load sets the 1.0 reference while an open or short defines strong reflections. For vector instruments, SOL (short-open-load) or SOLT (including through) calibrations establish error terms for directivity, source match, and tracking.

Step-by-Step Solution:

Verification / Alternative check:

Post-calibration, plotting data on a Smith chart should position standards at expected points: short at −1 on the real axis, open at +1, and load at the center. Agreement confirms correct calibration.

Why Other Options Are Wrong:

• False or 'random loads': would not remove systematic errors and are not traceable.
• Only at extreme frequencies: calibration is necessary from HF through mmWave.

Common Pitfalls:

Ignoring connector repeatability, not de-embedding adapters, and using contaminated or worn standards, all of which degrade accuracy.

Final Answer:

True