Radar (Radio Detection and Ranging) can detect the speed of an object even when it is moving at a 90-degree angle relative to the radar antenna. The principle behind this is known as the Doppler effect.
The Doppler effect refers to the change in frequency or wavelength of a wave when there is relative motion between the source of the wave and the observer. In the case of radar, the radar system emits electromagnetic waves (usually in the form of radio waves) toward the target object. These waves bounce off the object and return to the radar system.
When the object is stationary or moving directly toward or away from the radar, the frequency of the returned waves remains unchanged. However, when the object is moving perpendicular to the radar (at a 90-degree angle), the frequency of the returned waves changes. This change in frequency is known as the Doppler shift.
The Doppler shift can be measured by the radar system, and by analyzing the shift, the radar can determine the speed of the object. The radar measures the difference in frequency between the transmitted and received waves and uses this information to calculate the object's velocity relative to the radar.
By employing advanced signal processing techniques, radar systems can extract and analyze the Doppler shift accurately, even for objects moving at different angles relative to the radar antenna. This allows radar to detect and measure the speed of objects moving in various directions, not just toward or away from the radar system.