Radar is an essential electronic equipment in modern warfare. It is not only used in the military, but also in the national economy (such as transportation, weather forecasting and resource exploration, etc.) and scientific research (such as aerospace, atmospheric physics, ionospheric structure and celestial body research, etc.) and some other fields. The basic concept of radar was formed in the early 20th century. But it wasn't until around World War II that radar developed rapidly.
As early as the beginning of the 20th century, some scientists in Europe and the United States have known that electromagnetic waves are reflected by objects.
In 1922, Italian G. Marconi published a paper on the possibility of radio waves detecting objects.
The United States Naval laboratory found that bistatic CW radar could detect ships passing in between.
In 1925, the United States began to develop pulse modulation radar capable of ranging, and first used it to measure the height of the ionosphere.
In the early 1930s, some countries in Europe and the United States began to develop pulse modulation radar for detecting aircraft.
In 1936, the United States developed a pulse radar with a range of 40 kilometers and a resolution of 457 meters to detect aircraft.
By 1938, the British had placed a chain of early warning radars along their home coast near France to detect enemy aircraft.
Early warning radar chain During World War II, radar technology developed rapidly due to operational needs.
In terms of the frequency bands used, pre-war devices and technologies could only reach tens of megahertz.
In the early days of the war, Germany first developed high-power three - and four-pole tubes to increase the frequency to more than 500 MHZ.
This not only improves the accuracy of radar searching and guiding aircraft, but also improves the performance of anti-aircraft gun control radar, so that anti-aircraft guns have a higher hit rate.
In 1939, the British invented the 3000 MHZ power magnetron, and microwave radars using this magnetron were equipped on the ground and in aircraft, giving the Allies an advantage in air and air-sea operations.
Later in the war, the United States further increased the frequency of the magnetron to 10 GHZ, achieving miniaturization of airborne radar and improving measurement accuracy.
In terms of anti-aircraft gun fire control, the precision automatic tracking radar SCR-584 developed by the United States has improved the anti-aircraft gun hit rate from thousands of shells to shoot down an aircraft in the early years of the war to tens of rounds to hit an aircraft.
In the late 1940s, moving target display technology appeared, which is conducive to finding targets in the clutter background such as ground clutter and cloud rain.
High performance moving target display radar must transmit coherent signals, so the devices such as power traveling wave tube, klystron and forward wave tube are developed.
The emergence of high-speed jet aircraft in the 1950s, and the emergence of low-altitude penetration aircraft and medium - and long-range missiles and military satellites in the 1960s, promoted the rapid improvement of radar performance.
In the 1960s and 1970s, electronic computers, microprocessors, microwave integrated circuits and large-scale digital integrated circuits were applied to radar, which greatly improved radar performance, reduced volume and weight, and improved reliability.
In the aspect of new radar system and new technology, moving target display, monopulse Angle measurement and tracking and pulse compression technology have been widely used in the 1950s. Phased array radar appeared in the 1960s; In the 1970s, solid-state phased array radar and pulse Doppler radar were introduced.
In China, radar technology has only been developed since the early 1950s. Radar developed by China has been equipped with the army.
China has developed two - and three-coordinate warning and guidance radars for air defense, ground-to-air missile guidance radars, long-range missile initial range measurement radar and reentry range measurement and recovery radar.
The large radar developed by China is also used to observe satellites launched by China and other countries.
In the civil aspect, navigation and collision avoidance radar for ocean-going ships, navigation control radar for airports and weather radar have been produced and applied.
The airborne synthetic aperture radar developed by China has been able to obtain clear mapping of large areas.
The new generation of radars developed in China have adopted computers or microprocessors, and applied digital information processing technology of medium and large scale integrated circuits, and the frequency has been extended to millimeter bands. The radar antenna shoots the electromagnetic wave energy provided by the transmitter into a certain direction in space, and the object in this direction reflects the electromagnetic wave it encounters.
These reflected waves contain information about the object and are received by the radar antenna, sent to the radar receiving equipment for processing, to extract useful information needed by people and filter out useless information. Radar can be divided into two categories: continuous wave radar and pulse radar.
Single-frequency CW radar is the simplest form of radar, and it is easy to obtain the range change rate (radial velocity) between the moving target and the radar.
Its main disadvantages are:
(1) The target distance can not be measured directly, if you want to measure the target distance, you must adjust the frequency, but the target distance measured by the frequency modulated continuous wave is far less accurate than the pulse radar;