What kind of radar does the aircraft use when carrying out ground attack and its working principle?

Radar was originally the abbreviation of "radio detection and positioning". The basic task of radar is to detect the target of interest and measure the state parameters such as distance, direction and speed of the target. Radar is mainly composed of antenna, transmitter, receiver (including signal processor) and display.

The radar transmitter generates enough electromagnetic energy and transmits it to the antenna through the transceiver switch. The antenna radiates these electromagnetic energies into the atmosphere, concentrates them in a narrow direction to form a beam and propagates forward. After the electromagnetic wave meets the target in the beam, it will reflect in all directions, and part of the electromagnetic energy will reflect back to the direction of the radar and be acquired by the radar antenna. The energy obtained by the antenna is sent to the receiver through the transceiver switch to form a radar echo signal. Because electromagnetic waves will decay with the propagation distance, the radar echo signal is very weak and almost drowned by noise. The weak echo signal is amplified by the receiver, processed by the signal processor, and the information contained in the echo is extracted and sent to the display to show the distance, direction and speed of the target.

In order to measure the distance of the target, the radar accurately measures the delay time from transmitting electromagnetic waves to receiving echoes. This delay time is the propagation time of electromagnetic wave from transmitter to target and then from target to radar receiver. According to the propagation speed of electromagnetic wave, the distance of the target can be determined as S=CT/2.

Where s: target distance

T: the round-trip propagation time of electromagnetic wave from radar to target.

speed of light

Radar uses the directivity of the antenna to determine the direction of the target. Through the combination of mechanical and electrical functions, radar points antenna small things in the direction that radar wants to detect. Once the target is found, the pointing angle of the antenna is the direction angle of the target when the radar reads it. Two-coordinate radar can only measure the azimuth of the target, while three-coordinate radar can measure azimuth and pitch angle.

Measuring the moving speed of a target is an important function of radar. Radar velocity measurement uses Doppler principle in physics. When there is relative position movement between the target and the radar, the frequency of the target echo will change. The change of frequency is called Doppler frequency shift, which is used to determine the relative radial velocity of the target. Radar with speed measurement capability, such as pulse Doppler radar, is much more complicated than ordinary radar.

The tactical indicators of radar mainly include range, power range, ranging resolution and accuracy, angle resolution and accuracy, speed resolution and accuracy, system maneuverability and so on.

Among them, the operating distance refers to the distance at which the radar can reliably find the target. It depends on the product of radar transmission power and antenna aperture, and is related to the ability of the target itself to reflect radar electromagnetic waves (the size of radar cross-sectional area) and other factors. Power range refers to the area determined by the maximum operating distance, minimum operating distance, maximum elevation angle, minimum elevation angle and azimuth range.

There are many technical indexes and parameters of radar, which are related to radar system. Only the main parameters closely related to electronic countermeasures are discussed here.

According to the waveform, radar can be divided into two categories: pulse radar and continuous wave radar. At present, the most commonly used radar is pulse radar. Conventional pulse radar periodically emits high-frequency pulses. Relevant parameters are pulse repetition period (pulse repetition frequency), pulse width and carrier frequency. The carrier frequency is the high-frequency oscillation frequency of the signal in a pulse, which is also called the working frequency of the radar.

The ability of radar antenna to concentrate electromagnetic energy in this direction is described by beam width. The narrower the beam, the better the directivity of the antenna. However, in the process of design and manufacture, it is impossible for radar antenna to concentrate all energy on the ideal beam, and there is the problem of energy leakage in other directions. The energy is concentrated on the main beam, which is often called the main lobe visually, and the leakage in other directions forms side lobes. In order to cover a wide space, it is necessary to scan the radar beam in the detection area by mechanical rotation or electronic control of the antenna.

To sum up, the technical parameters of radar mainly include working frequency (wavelength), pulse repetition frequency, pulse width, transmission power, antenna beam width, antenna beam scanning mode, receiver sensitivity and so on. The technical parameters are selected and designed according to the tactical performance and index requirements of the radar, so their values reflect the functions of the radar to some extent. For example, in order to improve the detection ability of long-range targets, the early warning radar adopts relatively low working frequency and pulse repetition frequency, while the airborne radar adopts relatively high working frequency and pulse repetition frequency for the purpose of reducing volume and weight. This shows that if we know the technical parameters of radar, we can identify the type of radar to some extent.

Radar is widely used and its classification method is very complicated. Generally speaking, radars can be classified according to their uses, such as early warning radar, search and early warning radar, radio altimetry radar, weather radar, air traffic control radar, guidance radar, artillery aiming radar, radar fuze, battlefield surveillance radar, airborne interception radar, navigation radar, anti-collision and identification radar, etc. In addition to its purpose, radar can also be distinguished from the working system. Here are some new radar systems. (warii.net Military Watch)

Bistatic/multistatic radar

The transmitter and receiver of ordinary radar are installed in the same place, while the transmitter and receiver of bistatic/multistatic radar are installed in two or more places far apart, which can be located on the ground, air platform or space platform. Because the shape design of stealth aircraft is mainly to prevent the incident radar wave from directly reflecting back to the radar, it is very effective for monostatic radar. However, the incident radar waves will be reflected in all directions. In bistatic/multistatic radar, some reflected waves are always received by one receiver. Since 1970s, the US Department of Defense has been developing and testing bistatic/multistatic radars. The famous "Temple" project was specially formulated for the study of bistatic radar. The experiments of installing the receiver and transmitter on the ground, the transmitter on the plane, the receiver on the ground and the transmitter and receiver on the aerial platform were completed. Russian air defense forces have applied bistatic radar to detect aircraft with certain stealth capability. Britain began to develop bistatic radar in the late 1970s and early 1980s, which was mainly used for early warning system.

phased-array radar

As we know, every eye of a dragonfly is made up of many small eyes, and each small eye can form a complete image, which makes the dragonfly see a much larger range than the human eye. Similarly, the antenna array of phased array radar is also composed of many radiating elements and receiving elements (called array elements), and the number of elements is related to the function of radar, ranging from hundreds to tens of thousands. These elements are regularly arranged on a plane to form an array antenna. Based on the principle of electromagnetic wave coherence, the direction of the beam can be changed by controlling the phase of the current fed into each radiation unit by computer, so it is called electrical scanning. The radiation unit sends the received echo signal to the host computer to complete the radar's search, tracking and measurement of the target. In addition to the antenna elements, each antenna element also has necessary equipment, such as a phase shifter. Different oscillators can be fed with currents of different phases through phase shifters, so that beams with different directionality can be radiated in space. The more elements of the antenna, the more possible directions of the beam in space. This kind of radar is based on phased array antenna, hence the name "phased array".

Advantages of phased array radar

(1) beam pointing is flexible, which can realize fast scanning without inertia and high data rate; (2) A radar can form multiple independent beams at the same time, and realize multiple functions such as search, identification, tracking, guidance and passive detection. (3) The target capacity is large, and hundreds of targets can be monitored and tracked simultaneously in the airspace; (4) Strong adaptability to complex target environment; (5) Good anti-interference performance. All-solid-state phased array radar has high reliability, and it can still work normally even if a few components fail. However, the equipment of phased array radar is complex and expensive, and the beam scanning range is limited, and the maximum scanning angle is 90 ~ 120. When omni-directional monitoring is needed, 3 ~ 4 antenna arrays should be configured.

Compared with mechanical scanning radar, phased array radar has more flexible scanning, more reliable performance and stronger anti-interference ability, and can quickly adapt to the changes of battlefield conditions. Multifunctional phased array radar has been widely used in ground long-range early warning system, airborne and shipborne air defense system, airborne and shipborne system, gun position measurement, shooting range measurement and other fields. The An /MPQ-53 radar of American Patriot air defense system, the radar of ship-borne Aegis command and control system, the APQ- 164 radar of B- 1B bomber and the multifunctional radar of Russian C-300 air defense weapon system are all typical phased array radars. With the development of microelectronics technology, solid active phased array radar has been widely used as a new generation of tactical air defense, surveillance and fire control radar.

Broadband/UWB radar

A radar with a wide working frequency band is called wideband/ultra-wideband radar. Stealth weapons are usually effective for radars working in a certain band, but they are powerless for radars with wider coverage bands. It is likely to be detected by electromagnetic waves of a certain frequency in ultra-wideband radar waves. On the other hand, UWB radar can detect small targets because of its extremely narrow pulse and high range resolution. At present, the United States is developing and testing ultra-wideband radar, has completed the research of moving target display technology, and will conduct radar waveform test.

synthetic aperture radar

Synthetic aperture radar (SAR) is usually installed on a moving antenna or space platform. Using the relative motion between the radar and the target, the echo signals of the target received by the radar at different positions are processed coherently, which is equivalent to installing a "big" radar in the air, so that the small-aperture antenna can obtain the detection effect of the large-aperture antenna, which has high target azimuth resolution, and the pulse compression technology can obtain high range resolution, so that the stealth target can be detected. Synthetic aperture radar is widely used in military and civilian fields, such as battlefield reconnaissance, fire control, guidance, navigation, resource investigation, map mapping, ocean surveillance, environmental remote sensing and so on. An A /APY 3 X band multifunctional synthetic aperture radar has been newly installed on the aircraft of the United States joint surveillance and target attack radar system, and the cyclone attack aircraft jointly developed by Britain, Germany and Italy is testing the synthetic aperture radar.

millimeter-wave radar

A radar operating in millimeter-wave frequency band is called millimeter-wave radar. It has the characteristics of narrow antenna beam, high resolution, wide frequency band and strong anti-interference ability. At the same time, it works outside the band that stealth technology can fight at present, so it can detect stealth targets. Millimeter-wave radar is also capable, especially suitable for air defense, ground combat and smart weapons, and has been paid attention to by all countries in debugging. For example, the Patriot air defense missile in the United States has installed a millimeter-wave radar seeker, and is currently developing a more advanced millimeter-wave seeker; Russia has millimeter wave radar with continuous wave output power 10 kW. Some air defense systems in Britain, France and other countries will also use millimeter-wave radar.

laser radar

Radar working in infrared and visible light bands is called lidar. It consists of laser transmitter, optical receiver, turntable and information processing system. The laser converts electrical pulses into optical pulses and emits them, and the optical receiver converts the optical pulses reflected by the target into electrical pulses and sends them to the display. Stealth weapons are usually aimed at microwave radar, so lidar can easily "see through" the "tricks" played by stealth targets; Coupled with the narrow beam, good directivity, high measurement accuracy and high resolution, lidar can effectively detect stealth targets. Militarily, lidar is mainly used in shooting range measurement, space target intersection measurement, target precise tracking and aiming, target imaging recognition, navigation, precise guidance, integrated fire control, helicopter collision avoidance, chemical warfare agent monitoring, local wind field measurement, underwater target detection and so on. The U.S. Department of Defense is developing lidar technology for target detection and recognition, and has carried out forward-looking and downward-looking lidar experiments, which are mainly used to detect targets in camouflage trees. France and Germany are actively carrying out joint research on using lidar to detect and identify helicopters.