What is the working principle of radar?

Radar emits electromagnetic waves and bats emit ultrasonic waves, both of which are located by echoes. However, electromagnetic waves travel faster than sound waves. Ultrasonic means that the vibration frequency is above 20000Hz, and the number of vibrations per second (frequency) is very high, which exceeds the upper limit of human hearing (20000Hz). People call this inaudible sound wave ultrasonic. This is a mechanical wave.

Electromagnetic wave is a form of movement of electromagnetic field. Electricity and magnetism can be said to be two sides of the same body. Current will produce a magnetic field, and changing the magnetic field will produce current. The changing electric field and the changing magnetic field constitute an inseparable and unified field, which is the electromagnetic field. The changing electromagnetic field propagates in space to form electromagnetic waves.

The function of radar is similar to that of eyes. Of course, it is no longer a masterpiece of nature. At the same time, its information carrier is radio waves. In fact, visible light and radio waves are essentially the same thing, both are electromagnetic waves, and their propagation speed is C, but the difference is that they occupy different bands. Its principle is that the transmitter of radar equipment emits electromagnetic wave energy to a certain direction in space through an antenna, and the object in this direction reflects the electromagnetic wave it encounters; After receiving this reflected wave, the radar antenna sends it to the receiving equipment for processing, and extracts some information of the object (the distance from the target object to the radar, the change rate of distance or radial speed, azimuth, altitude, etc.). ). A lot. Ultrasonic attenuation in the air is too serious to achieve the purpose of directional detection as required, so radar uses electromagnetic waves.

Let's talk about radar again.

Composition of radar: The specific uses and structures of various radars are different, but the basic form is the same, including five basic components: transmitter, transmitting antenna, receiver, receiving antenna and display. There are also auxiliary equipment such as power supply equipment, data acquisition equipment and anti-interference equipment. How it works: Radar functions like eyes and ears. Of course, it is no longer a masterpiece of nature, and its information carrier is radio waves. In fact, visible light and radio waves are essentially the same thing, both electromagnetic waves, and the propagation speed is C, but the difference is that the frequency and wavelength occupied are different. Its principle is that the transmitter of radar equipment emits electromagnetic wave energy to a certain direction in space through an antenna, and the object in this direction reflects the electromagnetic wave it encounters; After receiving this reflected wave, the radar antenna sends it to the receiving equipment for processing, and extracts some information of the object (the distance from the target object to the radar, the change rate of distance or radial speed, azimuth, altitude, etc.). ).

Measuring the distance is actually measuring the time difference between the transmitted pulse and the echo pulse. Because electromagnetic waves travel at the speed of light, they can be converted into the exact distance of the target.

Measuring the target azimuth is a sharp azimuth beam measurement using an antenna. Measurement of elevation beam with narrow elevation angle. According to the elevation and distance, the target height can be calculated.

Velocity measurement is the principle that radar produces frequency Doppler effect according to its relative motion with the target. The target echo frequency received by radar is different from the radar transmission frequency, and the difference between them is called Doppler frequency. One of the main information that can be extracted from Doppler frequency is the range change rate between radar and target. When the target and jamming clutter exist in the same spatial resolution unit of the radar, the radar can detect and track the target from the jamming clutter by using the difference of their Doppler frequencies. Classification of radars: There are many kinds of radars, which can be classified in many ways:

(1) can be divided into active radar and passive radar according to the types of radiation sources.

(2) According to the platform, it can be divided into: ground radar, shipborne radar, airborne radar, spaceborne radar, etc.

(3) According to the waveform, it can be divided into pulse radar and continuous wave radar.

(4) According to the working band, it can be divided into meter wave radar, decimeter wave radar, centimeter wave radar and millimeter wave radar.

(5) It can be divided into surveillance radar, search radar, fire control radar, guidance radar, weather radar and navigation radar.

(6) According to the scanning mode, it can be divided into mechanical scanning radar and electric scanning radar.

Electric scanning radar refers to a radar using an electric scanning antenna. The typical method is to control the feed phase of antenna elements to achieve the purpose of flexibly controlling the beam pointing, also known as phased array radar, which is an important development direction of radar in the future.