Which of the following is NOT a common calibration target for radar?

• A. Weather Balloon
• B. Corner Reflector
• C. Trihedral
• D. Transponder

Answer: (B)

Calibration targets in radar are chosen for predictable, repeatable returns so you can verify range, angle, and reflectivity measurements. A corner reflector and a trihedral are classic passive calibrators because their geometry yields strong, well-defined radar returns from many directions, giving reliable benchmarks for the radar’s response. A transponder acts as an active calibrator: it answers with a known signal, allowing you to check timing, range accuracy, and decoding performance. A weather balloon, however, does not provide a stable, known target—the balloon’s size, shape, and orientation change with altitude and wind, making its radar return unpredictable. That variability makes it unsuitable as a standard calibration target, which is why it’s not commonly used for calibration.