What are radar sidelobes and why can they cause false returns?

• A. Sidelobes are weaker radiation lobes away from the main beam; energy reflecting from off-axis targets can appear as false echoes.
• B. Sidelobes are the main beam's strongest lobe echo.
• C. Sidelobes are only present in weather radar, not ATC radar.
• D. Sidelobes refer to the limit of minimum detectable signal.

Answer: (B)

Radar sidelobes are weaker radiation patterns that surround the main beam. They occur because the antenna radiates energy in multiple directions, not just along the central lobe. If there’s a strong target off to the side, energy can be reflected back into the receiver via these sidelobes, so the radar can interpret it as echoes from a target at an angle different from where the main beam is pointed. That’s why sidelobes can produce false returns on the display.

The idea that sidelobes are the main beam’s strongest lobe is not correct—the main beam (the main lobe) is the strongest part of the pattern. Sidelobes exist in many radar systems, not just weather radar. And sidelobes are not about the minimum detectable signal; that relates to system sensitivity and noise, not the presence of sidelobes.