When was radar invented?

Everyone knows that bats can emit ultrasonic waves from their throats when flying at night, and they can reflect them when they meet obstacles such as mosquitoes or moths, and then receive echo signals with their ears. Bats have this ability, but people don't, but people can find targets and measure distances more accurately by skillfully using electromagnetic waves, and the device to accomplish this task is radar.

The use of electromagnetic waves to detect targets appeared in the 1930s. 1930 65438+ 10, Rudolf Kuno of German Gamma Company was inspired by the biological phenomenon that bats generate ultrasonic waves to obtain information. After several years of hard work, he finally developed the early radar. In fact, this kind of radar is a special kind of radio equipment. It can emit electromagnetic waves into space and will be reflected when it meets the target. Radar can quickly calculate the distance and position of the target according to the round-trip time of electromagnetic waves and the azimuth and elevation angle when transmitting, and display the characteristics of the target on the monitor. 1934, when a British scientist was studying the radio echo signal of the earth's atmosphere, he came across a string of bright spots on the screen. After repeated experiments and research, he confirmed that it was an echo signal reflected by electromagnetic waves from a nearby building. This unexpected discovery gave him the idea of using radio echoes to detect moving targets. 1935, Watson watt and other British electrical engineers developed the first radar to detect aircraft. At that time, although the detection distance was only a few tens of kilometers, it was of great significance and opened up the development path of electromagnetic wave detection and positioning.

Early radar can only find the distance between the target and the measured target, so it is called "radio discovery and ranging". People take the first few letters of this English word to form a new word "radar", which is transliterated as "radar" in Chinese.

In World War II, radar technology was widely used and developed rapidly. At the beginning of the war, both sides used radar to predict the invasion of the other plane. For example, in August of 1940, Nazi Germany was ready to occupy Britain after conquering the European continent. To this end, Hitler personally formulated a battle plan codenamed "Sea Lion" and dispatched nearly a thousand planes to Britain. However, what he didn't expect was that the first German sneak attack was intercepted by the British Air Force, and the Germans lost more than 600 planes in just two weeks. Hitler's plan to occupy Britain failed. Why can the British accurately attack the Germans? It turned out that the British army built many radar stations in the coastal areas, and used them to predict the number, course and distance of the invading German planes, so as to take defensive measures in time, which made the Germans suffer a fiasco. This is the first time to use radar in actual combat. For another example, before the "Pearl Harbor Incident", the US military also set up a radar station and found the invading Japanese aircraft. However, the US military commander was too careless and delayed the time, which made the invading Japanese aircraft attack Pearl Harbor successfully and dealt a heavy blow to the main force of the US Pacific Fleet stationed in Pearl Harbor. At this time. Americans who despise the role of radar suddenly wake up from their dreams, but it is too late.

Shortly after radar was used in air defense, it was also installed on warships, which had a great impact on naval tactics. British warships can find and chase German warships even in the night when the wind is high and the clouds are light, taking advantage of their radar to search for targets. So in the late World War II, the number of ships and submarines sunk by the Germans increased rapidly. By 1943, radar was widely used in Britain, and 64 German submarines were destroyed in September alone, which caused great trauma to the Germans.

In the late World War II, the combination of radar and weapon control system made radar also aggressive. After using this radar, artillery units can not only automatically search and track targets, but also attack targets, thus greatly improving the artillery's hit rate and combat effectiveness.

Also in the late World War II, a new IFF system was used in the radar, which enabled the radar to identify IFF again. Some radars can also automatically adjust their working status with the changes of environment and targets, making the radar more powerful.

After World War II, radar began to be widely used in economic construction.

On land, electromagnetic waves emitted by radar are used to measure the moving speed of objects; Measure wind speed and direction; Forecast typhoons and rainstorms; Using radar to realize the modern management and scheduling of airport.

At high altitude, use electromagnetic waves emitted by radar to help high-speed flying objects fly over mountains; The combination of radar and TV technology enables pilots to visually see the shape of the target and the image of the environment on their own screens; The combination of radar and astronomy formed "radio astronomy". Using the electromagnetic wave emitted by radar, we can detect the meteor trail and calculate the atmospheric temperature, density and wind direction within the range of 120km. 1964, the electromagnetic wave emitted by the radar selected a suitable landing site for the spacecraft to land on the moon.

Underground, electromagnetic waves emitted by ground penetrating radar can accurately detect faults, voids, collapses and other crustal structural defects of the earth. It can detect the strata within 20 meters below the ground by analyzing electromagnetic waves and reflected echoes, so as to prevent catastrophic events such as collapse, landslide and dam collapse, and can also be used to explore underground antiquities or metal deposits.

With the continuous progress of science and technology and the rapid development of economic construction, the application field of radar is still expanding. Now people have generally realized that radar is an indispensable tool to help people understand the world and observe the mysteries of the universe, and radar also plays an important role in the field of economic construction. Therefore, people vividly call radar a "senior detective" and a good friend of mankind.

Having said so much about the benefits of radar, you may be anxious to think: How does radar work? How can you have such a great ability? Now briefly talk about this.

The basic components of radar include three parts: transmitter, receiver and antenna. At the beginning, the receiver is turned off and the transmitter is turned on. Some form of high-frequency electromagnetic wave (ultrashort wave or microwave) is generated by a transmitter and radiated in a specific direction through a transmitting antenna. Then turn off the transmitter and turn on the receiver, and the original transmitting antenna becomes the receiving antenna. When electromagnetic waves encounter a target in the process of space propagation, some high-frequency electromagnetic waves will be reflected back, and the receiving antenna will receive this signal and input it into the receiver. The observer can judge whether there is a target and its nature at the output of the receiver. The time it takes for electromagnetic waves to receive reflected electromagnetic signals from transmitter to receiver, multiplied by the speed of electromagnetic waves (that is, the speed of light: 300,000 km/s), is the round-trip distance from radar to target. Then divided by 2, the result is the distance of the measured target. The angular position of the target can be measured by using the directivity of the antenna or using a dual-beam antenna system.

Doppler effect is a natural phenomenon that people often encounter. For example, when you are standing next to the railway, a high-speed train flies head-on with a whistle, and then you will hear the whistle become louder; As the train goes away, you will hear the tone become lower again; When you hear the whistle of a stationary train, the tone remains the same. This shows that the frequency (tone) of sound waves will change due to the relative motion between the wave source and the observer, which is called Doppler effect. The UHF electromagnetic wave emitted by radar also has this property. Using the Doppler effect of electromagnetic waves, people can measure whether the target is moving towards or away from the radar station and calculate its speed.

According to the different types and functions of radiated electromagnetic waves, radars can be divided into many types, and different types of radars have different uses. We briefly introduce this as follows: conical scanning radar. The antenna of this radar has a special shape, which forms a conical coverage area in the radiation space when rotating. The overall structure of this radar is simple; It is mainly used for measuring the angular position of targets and automatic tracking, and has been widely used in anti-aircraft gun fire control. Its disadvantage is that it can only track slow targets, and there are some errors.

Monopulse radar. It only needs to emit an electromagnetic pulse signal, and it can realize the target angle positioning and automatic tracking. Its advantages are high precision and strong anti-interference ability. Disadvantages are complicated structure and inconvenient use.

Three-coordinate radar. It can determine the position of the target in several aspects at the same time, which is mainly used for air warning. This kind of radar has strict requirements on the beam shape of electromagnetic waves, and it must have multi-channel receiving devices, so its structure is naturally more complicated.

Synthetic aperture radar. It uses the regular movement of vehicles to emit coherent electromagnetic pulse signals at different positions in turn, and then processes and synthesizes a series of echo signals. The obtained results have high resolution and are suitable for high-altitude aircraft and satellites. Its disadvantages are low transmitting power and high signal-to-noise ratio.

Phased array radar. It is made up of many radiation units arranged in space, and after special technical treatment, it can realize the spatial scanning of radiation electromagnetic beam. Multiple batches and targets can be searched and tracked flexibly at the same time, which is mainly used for vigilance and tracking. Its advantages are high detection speed, strong anti-interference ability, multiple functions and long measuring distance, which can reach 3700 kilometers. Therefore, it has a wide range of uses and is called the "darling" of the radar family. Its disadvantages are complex structure, high cost, huge equipment and difficult to conceal. Even so, because of its outstanding advantages, it is still an important direction of radar technology development.

According to the position of the radar. There is ground air defense radar to alert the enemy to attack; Airborne radar can search for targets invisible to ground air defense radar and is not easy to be attacked by the enemy; Ship-borne radar is called "special radar" because of its small size but strong "capability". In addition, there are weather radars that specialize in weather forecasting and so on.

The performance and characteristics of these radars are obtained by controlling the spatial scanning motion of the antenna electromagnetic beam. Therefore, mastering the radiation characteristics and related laws of electromagnetic waves is the key to understand the specific functions of radar, and then use radar to serve mankind.