How radar sensors work: Technology and application guide

Radio waves detect, locate, and track objects

Radar, which stands for Radio Detection and Ranging, is a technology using radio waves to detect, locate, and track objects. The basic principle behind radar involves transmitting radio frequency (RF) signals, or waves, and receiving their reflections back from objects in the radar path. 

The round-trip time for the waves is also known as time-of-flight. That time provides information about object presence, distance, velocity, and direction through signal analysis.

The Doppler effect

Radar sensors use the Doppler effect to measure the speeds of moving objects. The Doppler effect is the apparent frequency change in a wave when the source and observer move relative to each other. Frequencies increase as objects approach each other, and lower as they move apart.

Radar also uses the Doppler effect to determine a target’s velocity (a vector quantity indicating speed and direction). When targets move toward or away from the sensor, reflected RF signal frequencies change accordingly. Greater shifts indicate faster movement.

Radar sensor components

• The transmitter generates electromagnetic waves in the microwave frequency range. Emitted radio waves travel through the air at the speed of light, imperceptible to humans. 

• The antenna emits these radio waves and receives the signals. Various systems use single antennas for both functions, dedicated antennas for each, or sophisticated antenna arrays for expanded coverage. 

• The receiver filters out noise from the returning signals and prepares them for processing.

• The signal processing unit analyzes returning signals for object information.

The display unit presents a visual representation of the processed object information about detected objects for human interpretation. Not all radar systems include this feature.

Radar sensor technologies

Various radar technologies enable different industrial and mobile applications: 

• Pulsed radar emits short bursts of high-frequency radio energy and measures return time from targets.
• Continuous wave (CW radar) continuously transmits a known, stable frequency signal and measures Doppler shift in returned signals.
• Frequency-Modulated Continuous Wave Radar (FMCW)  transmits continuously varying frequency signals and analyzes frequency changes in received echoes versus transmitted signals.
• Frequency shift keying switches between two or more signal frequencies to determine range and velocity by analyzing differences in each one’s received signals.
• Deep Dive Continuous Wave Radar (CW) provides advanced analysis of standard CW radar through continuous transmission and Doppler shift.

Measurements

Radar sensors use advanced signal processing for precise distance, velocity, and direction measurements: 

• Distance: Calculated from reflected signal time delay. Since radio waves travel at light speed, return time directly corresponds to object distance.
• Velocity: Determined through Doppler effect motion detection. Doppler analysis determines moving target velocity by examining reflected wave frequency shifts.
• Direction:Achieved through antenna arrays and phase differences. Comparing phase differences between signals received at multiple antenna elements enables precise determination of reflected signal arrival direction.

Varying radar dimensionalities provide different measurements: 

• 1D radar measures one characteristic, usually velocity, using CW technology or distance using pulsed technology. Without distance or angular resolution, it cannot separate multiple objects with identical velocity.
• 2D radar commonly measures velocity and distance using FMCW or FSK technology.
• 3D radar measures distance, velocity, and angle (direction or object orientation) in three-dimensional space using antenna arrays.

• Narrow beam radar technology features 1-10 degree beam angles, delivering superior precision and resolution. This focused configuration enables single-axis measurement, providing length-based data detection. Through length measurement, these systems identify object presence, determine sensor-to-target distances, and calculate velocity for approaching or retreating objects. These sensors are often called "radar distance sensors."

Typical applications:

• Precise distance measurement
• Level detection of liquids or bulk materials
• Object detection 
• Speed measurement'

• Wide beam radar technology operates with beam angles exceeding 10 degrees, offering expanded coverage for dual-axis measurement combining length and depth data. This broader detection zone facilitates enhanced object identification and spatial positioning in three-dimensional environments, though with reduced resolution compared to narrow beam systems. These sensors are frequently called "radar area sensors."

Typical applications:

• Area monitoring
• Collison avoidance 
• Driver assistance and blind spot monitoring in challenging conditions
• 2D/3D profiling

Radar resolution, or separability, is a radar's ability to distinguish closely-positioned targets as separate objects. When targets have similar measured values, sensors may fail to detect them individually.

• Distance resolution depends on transmission signal bandwidth, enabling object differentiation based on distance differences. Objects at similar lateral and elevation angles can still be separated reliably based on their mutual distances.
• Angular resolution describes differentiation capability based on target angle information. This includes azimuth resolution (lateral angles) and elevation resolution (elevation angles). Objects farther from the sensor require greater separation distances for reliable detection.

A= Angular resolution B= Distance resolutions

Radar cross-section (RCS)

Radar cross-section (RCS) describes how detecible an object is for a radar sensor. The more detecible an object is, the further away it can be detected. RCS value is based on the target's characteristics including size, orientation, dielectrical constant, material, and coating.