Two-frequency operation in secondary radar transactions helps reduce which type of clutter?

• A. Direct reflections clutter
• B. Multipath interference
• C. Atmospheric attenuation
• D. Thermal noise

Answer: (C)

Two-frequency operation leverages the fact that atmospheric attenuation changes with frequency. In secondary radar links, weather conditions and atmospheric constituents can weaken the interrogation and reply paths differently at two distinct frequencies. By comparing how each frequency is attenuated, the system can compensate for these losses and distinguish legitimate returns from clutter caused by atmospheric effects. This targeted use of frequency diversity reduces clutter tied to atmospheric attenuation, making detections more reliable under adverse weather.

Direct reflections (ground clutter) and multipath interference are not inherently mitigated by simply using two frequencies, and thermal noise is a broadband phenomenon not specifically addressed by this approach.