What is the detection principle of radar?

A typical radar is pulse radar, which is mainly composed of antenna, transceiver switch, transmitter, receiver, timer, display and power supply.

The transmitter generates high-power high-frequency oscillation pulses. Directional antenna converts this high-frequency oscillation into an electromagnetic wave similar to a beam, which propagates in space at the speed of light. When the electromagnetic wave meets the target in the propagation process, the target is excited to generate secondary radiation, and a small part of the electromagnetic wave in the secondary radiation returns to the radar and is collected by the antenna, which is called echo signal.

The receiver amplifies and transforms the echo signal and sends it to the display for display, thus detecting the existence of the target. In order to enable radar to search, find and track targets in a wide airspace, the method of mechanically rotating the antenna or electronically controlling beam scanning is usually used to make the directional beam of the antenna scan in space in a certain way.

The timer is used to control all parts of the radar to keep synchronous work. The transceiver switch allows the same antenna to act as both a transmitter and a receiver. The power supply supplies the electric energy required by each part of the radar. The distance of the target is the time required for the electromagnetic wave to travel from the radar to the target (that is, half the arrival time of the echo signal) multiplied by the speed of light (300,000 kilometers per second). The azimuth and elevation of the target are measured by using the directional characteristics of the antenna beam.

According to the distance and elevation angle of the target, the height of the target can be determined. When there is relative motion between the target and the radar, the frequency of the target echo received by the radar will change. This frequency shift is called Doppler frequency shift, and its value is proportional to the radial component of the target velocity. Based on this, the radial velocity of the target can be measured.