How Radar Detects

Radar has an exceptionally wide range of applications, capable of accurately determining an object’s position, distance, and speed. Its effectiveness becomes especially evident in conditions of low visibility or when the line of sight is obstructed. So, how exactly does radar detect targets?

Radar operates by exploiting the properties of electromagnetic waves, primarily microwaves, to obtain information about a target. Electromagnetic waves are generated by the oscillation of electric and magnetic fields. Although they resemble water waves in form, they do not require a medium and can propagate through a vacuum. Different frequencies of electromagnetic waves exhibit distinct physical characteristics, which is why they are widely applied in various fields. In general, lower frequencies correspond to longer wavelengths, stronger diffraction ability, and longer propagation distances; higher frequencies correspond to shorter wavelengths, greater energy, but increased absorption or scattering in matter. Based on frequency ranges, electromagnetic waves can be classified as:

• Radio waves: Longest wavelengths, capable of diffracting around obstacles and penetrating the atmosphere, commonly used in broadcasting, television signals, and mobile communications.
• Microwaves: Higher energy than radio waves, widely used in microwave ovens, radar detection, and Wi-Fi communication.
• Infrared: Primarily thermal radiation, invisible to the human eye, used in remote controls, thermal imaging, and night vision devices.
• Visible light: The spectrum detectable by the human eye, broadly applied in illumination, photography, and optical instruments.
• Ultraviolet: Higher energy, capable of triggering chemical and biological reactions, used in sterilization and industrial curing.
• X-rays: Strong penetrating power, able to pass through soft tissue and certain materials, used in medical imaging and security inspection.
• Gamma rays: Highest energy, with intense ionizing effects, used in cancer radiotherapy, nuclear physics research, and astronomical observation.

The operating principle of radar is to emit electromagnetic waves outward; when the beam encounters a target, it reflects back. The receiver then analyzes the reflected signal to determine the target’s position, direction, and speed. Because different frequencies of electromagnetic waves have different properties, microwaves are most commonly used in radar. Their wavelength is moderate, striking a balance between resolution and propagation capability: if the wavelength is too long, attenuation is low and propagation distance is far, but resolution is insufficient for precise localization; if the wavelength is too short, resolution is high but performance is easily degraded by fog, clouds, or rain. Microwaves, however, can effectively penetrate clouds, fog, and partial rainfall, and reflect strongly from metals or solid objects, making them particularly suitable for detecting aircraft, ships, and vehicles.

Radar today serves many purposes. In aviation navigation, it monitors aircraft position and altitude, supporting air traffic control and ensuring flight safety. In maritime navigation, ships use radar to detect nearby vessels and land, preventing collisions and maintaining safe passage in adverse weather. In meteorology, radar tracks rainfall, cloud formations, and typhoon structures, providing forecasts and disaster warnings. In military defense, radar detects enemy aircraft, missiles, or warships, and supports weapon targeting and air defense systems. In traffic management, police radar measures vehicle speed for law enforcement, while autonomous vehicles rely on radar to sense their surroundings. In space exploration, radar is used to study planetary surfaces and asteroid trajectories, supporting scientific research and space missions.