History and classification of radar?

Development history and classification of radar

194110am10at a sentry post in the northern part of Oahu in the Pacific Ocean, soldiers reported the discovery of an unknown plane to the US Air Defense Command, but the Air Defense Command thought it was just a false alarm and did not adopt it. Only half an hour later, the Hawaiian base of the US Pacific Fleet turned into a sea of fire, and the Pearl Harbor incident that shocked the world broke out. So why did the sentinel who had the opportunity to save this disaster predict the Japanese attack in advance? Does he really have clairvoyance? Are there spies in the Japanese army?

There is only one answer: he is not an ordinary sentry, he is a radar station sentry. He has no clairvoyance, but he has a radar that is more magical than clairvoyance.

The invention of radar can be traced back to19th century. 1887, when the German scientist Hertz confirmed the existence of electromagnetic waves, he found that electromagnetic waves would reflect back when they met metal objects in the process of propagation, just like light would be reflected by a mirror. This is essentially the working principle of radar. However, Hertz did not think of applying this principle to radio communication at that time.

1897, when Russian scientist popov conducted a 5-kilometer communication test directly on the cruiser Africa and the training ship Europe, the communication was suddenly interrupted and returned to normal in a few minutes. This phenomenon has appeared one after another. At first, he thought there was something wrong with the machine. After inspection, everything is normal. After troubleshooting the machine, popov began to pay attention to other details. He found that whenever the contact ship "Captain Ilya" passed between the two ships, communication would be interrupted. With his keen sense of smell, popov immediately realized that it was the ship that blocked the radio waves when passing between two ships. In his work diary, he recorded the influence of obstacles on the propagation of electromagnetic waves, and put forward the possibility of using electromagnetic waves for navigation in his test records. But unfortunately, he didn't put this idea into practice. However, this can be said to be the bud of radar thought.

1934, Watson, UK? Watt was appointed director of the Royal Institute of Radio, in charge of radio scientific investigation of the earth's atmosphere. One day, as usual, he sat in front of the screen and observed the received electromagnetic wave image. Suddenly, his eyes were attracted by a series of bright spots on the screen. From the analysis of brightness and distance, these spots are completely different from the radio echo signals reflected by the ionosphere. It turns out that these bright spots are radio signals reflected from a nearby high-rise building. This discovery made him very excited. Since the radio signals reflected by buildings can be clearly displayed on the screen, can planes in the air also be reflected on the screen? You know, under the technical conditions at that time, there was no way to find the plane in advance except to see and hear the sound of the plane.

At that time, when Britain stepped up the development of air defense forces, the British Air Force also specially found a group of blind people with sensitive hearing to search for enemy planes with their ears. When Watt wrote his findings and ideas into a report, the Air Force immediately ordered funding for the experiment if it got the treasure. According to the above idea, Watt and a group of British electrical engineers finally developed the first radar that can be used to detect aircraft at 1935.

By 1939, radar technology has reached a completely practical level. This year, World War II broke out, and this invention showed its great power in World War II, and radar technology with the functions of ground-to-air, air-to-ground (search) bombing, air-to-air (interception) fire control, and friend-or-foe identification appeared. The advantage of radar is that it can detect long-distance targets day and night without being blocked by fog, clouds and rain. It has the characteristics of all-weather and all-day, and has certain penetration ability.

The wavelength of electromagnetic wave used by radar is longer than that of infrared ray, and the range is 0.0 1 ~ 10 meter (corresponding frequency is 30 GHz ~ 30 MHz), so it has the following characteristics: it is almost unaffected by season, day and night and weather conditions, and can work all day; Using high-power transmitter, high-gain antenna and high-sensitivity receiver can greatly improve radar power and detect targets several meters away from Qian Qian. Modern mechatronics and data processing technology can make radar measure the coordinates of targets with high accuracy, and can automatically search and track targets. Modulation and coding in the reflected signal of active radar can automatically identify the enemy and us; Radar countermeasure can be realized by using countermeasure technology, which can not only detect enemy targets, but also hide itself. Combined with computer technology, multiple targets can be detected at the same time, and the "synthetic aperture" antenna can shoot images of ground targets from the air (compared with optical detection, it is not affected by visibility).

There are many kinds of radars. As an important equipment of modern military weapon system, radar can be divided into long-range early warning radar, warning radar, navigation radar, gun aiming radar, missile guidance radar, airborne interception radar, fire control radar, reconnaissance radar and so on. According to its technical characteristics, radar can be divided into beam scanning radar, monopulse radar, phased array radar, continuous wave radar, pulsed Doppler radar, electronically controlled phase scanning radar and radar.

Battlefield reconnaissance radar: Battlefield reconnaissance radar is a ground moving target reconnaissance radar used by the army to detect and monitor enemy ground weapons, vehicles, personnel and low-altitude aircraft activities. Its technical feature is to increase the display of moving targets and cancel the fixed targets. Using centimeter band, it can be divided into three types: long-range, medium-range and short-range The long-range battlefield reconnaissance radar is installed on vehicles, which can detect the movement of enemy troops, vehicles and artillery within 20 ~ 30 kilometers, as well as the activities of individual soldiers within 7 kilometers. The medium-range battlefield reconnaissance radar can detect the activities of tanks and vehicles within 8 ~ 10 km, as well as people within 5 km. Short-range battlefield reconnaissance radar can detect enemy activities within the range of 0.5 ~ 3 km, with a mass of less than 2.5 kg, which can be installed on a tripod and is easy to carry. Battlefield reconnaissance radar is characterized by small volume and mass, simple structure, rapid erection, good maneuverability and convenient operation. But at this time, due to the great influence of wind or plants, it is difficult to distinguish the target, and it is necessary to cooperate with other reconnaissance means to have a better resolution.

Warning radar: Warning radar is deployed in coastal areas, border areas and deep areas of the country to detect long-distance enemy planes, missiles and ships. Its characteristic is long detection distance, but the detection accuracy is not very high. According to the detection distance, there are: short-range warning radar, the detection distance is 200 ~ 300 kilometers; Medium-range warning radar with detection distance of 300 ~ 500 kilometers; Long-range warning radar, the detection distance is 500 ~ 4000 kilometers; Ultra-long-range early warning radar, the detection distance is more than 4000 kilometers.

Over-the-horizon radar: Over-the-horizon radar uses the characteristics that short-wave electromagnetic waves can't penetrate the ionosphere and reflect back to the ground to generate jumping propagation, and develops equipment that is not limited by the curvature of the earth and can't directly detect the target (line of sight). Over-the-horizon radar can find ballistic missiles and orbital bombing weapons that have just been launched from the ground, providing a longer warning time, but the accuracy of the information needs to be improved.

Side-looking radar: Side-looking radar is a high-resolution device that detects ground targets from the air and draws images. The antenna is installed under the plane, and the beam is very narrow, covering the targets within tens of kilometers on both sides, hence the name "side view". Radar uses synthetic aperture technology to process the received signal, which is equivalent to a huge antenna array (increased by several hundred times) and an extremely narrow beam, so the resolution is very high, and the image clarity is similar to that of optical photography, but it can work all day. Side-looking radar is very convenient and quick to draw battlefield topographic map.

Phased-array radar: Phased-array radar uses computers to control the phases of transmitted and received signals, so as to improve transmission power, antenna gain and receiver sensitivity. It can integrate long-range warning radar, guidance radar, multi-target tracking radar and guidance radar with high efficiency. This is the combination of computer technology and modern radar technology. The antenna array can realize 360-degree omnidirectional detection without rotation. If the problem of long-distance phase control of radar signals is solved, it is possible to spread the radar antenna array all over the country, forming a very huge radar network, making it an indestructible electronic network with comprehensive functions of land early warning, tracking and confrontation.

Radar guidance methods include radio wave guidance and laser guidance, in addition to infrared guidance, in which laser guidance is a guidance method that uses laser to track and guide objects. Because of the superior characteristics of laser, laser guidance has strong anti-interference and good measurement accuracy, but it also has some shortcomings, such as not being used all day and the guidance complexity is relatively high. Different guidance methods have their own advantages and disadvantages, and they can play their respective roles under different conditions. Precision guided weapons, as precise measurement technology and precise control technology, have been applied in the military. Although the cost of a single guided weapon is more expensive than that of ordinary weapons, it is precisely because it greatly exceeds the hit rate of traditional weapons that the operational cost is decreasing, which can reduce unnecessary damage to other targets. Precision guidance technology refers to a military technology that controls the flight direction, attitude, altitude and speed of weapons according to certain laws, which is referred to as guidance law for guiding its warheads to attack targets accurately. In this way, precision guided weapons have become the focus of military investment in various countries and will play an increasingly important role in future modern wars.