1.1 Definition of Complex Electromagnetic Environment and Relationship with Informatization Conditions The background of informationized operations mainly refers to the operational environment in a complex electromagnetic interference environment, the so-called complex electromagnetic environment. The strict definition of complex electromagnetic environments is not yet unified, but there are many definitions of complex electromagnetic environments in various non-academic publications. The so-called complex electromagnetic environment, in a nutshell, is the sum of human electromagnetic emissions and various electromagnetic phenomena in a certain combat period. The main factors that constitute the complex electromagnetic environment are the electronic countermeasures of the enemy and ours, the high-density, high-intensity, multi-spectral electromagnetic waves released by various weapons and equipment, the radiation of civilian electromagnetic equipment and the electromagnetic waves generated by nature. Specifically, the so-called complex electromagnetic environment refers to the multi-type, full-spectrum, high-density electromagnetic radiation signals generated by the fierce confrontation of the warring parties on the informationized battlefield, and the mutual influence and interference caused by the extensive use of electronic devices. Thus, it causes sudden changes in the time domain, criss-crossing in the airspace, and crowded overlap in the frequency domain, which seriously affects the invisible battlefield environment of weaponry effectiveness, operational command, and force operations. The complex electromagnetic environment mainly includes electromagnetic radiation and detection environment of military equipment, electromagnetic radiation environment of civil electronic equipment, and natural electromagnetic radiation environment.
1.2 Characteristics of complex electromagnetic environment
The complication of the electromagnetic environment is accompanied by the development of electronic technology and the continuous use of electronic technology in weapons and equipment. The complexity is mainly reflected in the increase of military and civilian electromagnetic use activities; the dependence of the two parties on the electromagnetic spectrum makes the equipment and technical means for interference and anti-interference used by the two parties to compete for electromagnetic rights to increase; the electromagnetic spectrum band increases, almost covering The entire electromagnetic spectrum band and so on. In addition to these artificial electromagnetic activities, there are also natural electromagnetic activities, mainly solar system and interstellar electromagnetic radiation, Earth and atmospheric electromagnetic fields, lightning and electromagnetic pulses. All of these together constitute a complex electromagnetic environment, in which the electromagnetic environment caused by intentional interference is the main part, and it is also the part that has the greatest impact on the operation under informatization conditions. Its main features are:
(1) Extensive
In order to weaken the electronic warfare capability of the other party, reduce or destroy the use efficiency of the other party's electronic equipment, and ensure the normal performance of the equipment of the other party, various measures will be taken to compete for the electromagnetic spectrum in multi-dimensional space such as land, sea, air and even space. The dominance of the struggle involves radio communications, radar, guidance, navigation, sonar and telecommunications, radio, television and other electronic devices, covering the entire electromagnetic spectrum space.
(2) Intensive
In a certain airspace, time domain, and frequency domain, a large number of electronic devices in the military are concentrated at the same time, electromagnetic waves are very dense, and the working frequency is very concentrated, resulting in a complicated electromagnetic environment in the combat area.
(3) Dynamic
In the informationized battlefield, the two sides of the war will continue to use the new system radar, radio and new communication frequencies in order to maintain uninterrupted communication and operational command, resulting in the battlefield electromagnetic spectrum environment
The party’s struggle situation in the field of electromagnetic spectrum is constantly changing and changing.
(4) confrontational
In the future war, in order to accurately grasp the enemy's combat operations, the warring parties will strengthen the reconnaissance and surveillance of electronic equipment, and implement soft and hard strikes on the command, communication, radar and other systems, reconnaissance and anti-reconnaissance, and interference.
The fight against anti-jamming, suppression and counter-repression, destruction and anti-destruction will be fierce, and the electronic information system will work in the electromagnetic environment of fierce confrontation.
1.3 The impact of complex electromagnetic environment on combat operations
In the information battlefield, the electromagnetic environment has penetrated into all aspects of battlefield perception, command and control, and operational coordination. It has produced a wide and profound impact on the correctness of judgment, the effectiveness of combat effectiveness, and even the construction of the battlefield. In summary, these effects are mainly reflected in the following aspects:
(1) The complex electromagnetic environment enhances the difficulty of battlefield perception;
(2) The complex electromagnetic environment restricts the efficiency of command and control;
(3) The complex electromagnetic environment increases the difficulty of operational support;
(4) The complex electromagnetic environment affects the performance of combat effectiveness.
Among them, the most direct and first impact is the constraint of the complex electromagnetic environment on the perception and grasp of the battlefield environment. The enemy's electronic interference will make the radar lose its combat power, which will make us a "scorpion" and unable to command our own targets; we cannot distinguish between the enemy and the enemy.
2.2 Low sidelobe and ultra low sidelobe antenna technology
When the beam is narrow enough and the side lobes are low enough, the radar will only receive the target echo signal, and the various interferences around the target space will be suppressed, which can improve the signal-to-interference ratio of the radar reception. In order for the radar to work effectively in severe object interference and electronic interference environments, antennas with low side lobes must be used whenever possible. Low sidelobe and ultra-low sidelobe antennas are also effective in preventing radar attacks from anti-radiation missiles.
2.3 Sidelobe blanking and sidelobe cancellation techniques
The presence of the side lobes of the radar antenna enables the enemy to implement side-lobe interference, and the strong interference can even form an all-round interference fan. In order to eliminate interference from side lobes, sidelobe blanking and adaptive sidelobe cancellation techniques can be employed.
2.4 Antenna adaptive anti-jamming technology
The antenna adaptive anti-jamming technology automatically controls the shape of the antenna beam according to the specific environment of the signal and the interference, so that the maximum direction of the main lobe of the beam always points to the target and the direction of the zero value points to the interference source, so as to receive the echo energy and the least Receive interference energy to maximize the signal to interference ratio.
2.5 Power Countermeasure Technology
In electronic defense, power countermeasures are an important measure against active interference, especially against main-lobe interference. By increasing the radar transmit power, extending the beam dwell time on the target, or increasing the antenna gain, the echo signal power can be increased, the received signal to interference ratio can be increased, and the target can be found and tracked. The basic methods of power confrontation include: increasing the peak power of a single tube; using a pulse compression system; power synthesis; beam synthesis; and increasing the pulse repetition frequency.
2.6 Frequency selection technology
The frequency selection is to use the difference between the frequency domain characteristics of the radar signal and the interference signal to filter out the interference. When the radar quickly changes the operating frequency and jumps out of the interference frequency range, it can avoid the interference. Commonly used frequency selection methods are: Selecting a frequency close to the enemy radar carrier frequency; opening up a new frequency band; fast frequency modulation; frequency agility; frequency diversity.
2.7 Constant false alarm processing technology
Constant false alarm processing refers to a technical measure to keep the radar false alarm probability constant when the noise and external interference intensity change. In the automatic detection system, the constant false alarm processing technology can make the computer not saturate due to too much interference; in the artificial detection radar, the constant false alarm processing technology can realize the clear and easy observation of the display under strong clutter interference. . At present, the commonly used constant false alarm rate processing methods can be divided into two categories: slow threshold constant false alarm rate processing and shutter limit constant false alarm processing.
Although radar anti-jamming technology has been rapidly developed, the increasingly complex electromagnetic environment interference technology and the anti-jamming capability of radar have put forward higher requirements. It is urgent to study new technologies and new systems to enhance the survivability of radars. Combat capability.
3 New technologies and systems in development to improve radar target recognition
In recent years, China has increased its investment in scientific research on electronic anti-interference technology, which has made some breakthroughs in China's new radar technology. Some new technologies and systems have emerged. These technical systems have been applied and greatly improved. The level of informationization of military equipment and its ability to survive in complex electromagnetic environments. There are:
3.1 Passive radar detection technology
Passive radar is also called passive radar. Passive radar itself does not radiate signals. Instead, it uses the electromagnetic waves radiated by radar, communication, navigation, interference and other equipment on the enemy's target to realize the recognition, location and tracking of the target. Because passive radar does not radiate signals, it can be well concealed, has strong anti-anti-radiation missile capabilities, and has good ability to detect stealth targets.
3.2 Synthetic Aperture Radar Technology
Synthetic Aperture Radar (SAR) is a radar that uses a coherent imaging principle to image a target to detect a target. Synthetic Aperture Radar can image the target and use the shape of the target to directly identify the target, improving the ability to resist fraud.
3.3 Radar networking technology
Because different radars work in different systems, frequencies, polarizations, signal parameters, etc., and occupy a large airspace, it is impossible to be seriously interfered by the enemy at the same time. These radars can be reasonably formed into a radar network. The high and low airspaces and the long-range and short-range can be reasonably matched. The data provided by the radars that are not interfered or only slightly interfered with the network can be used to discover and track the targets, thereby achieving strong interference against the enemy. Identification, tracking and attack of party targets. Obviously, the radar network must be equipped with reliable communication equipment, accurate coordinate conversion system and efficient command and control system.
3.4 Dual (multi) base radar technology
The dual (multi) base radar is divided by the receiving and transmitting bases, and the receiving base transmits the side scatter of the transmitted signal to determine the position of the target. Since the receiving base does not radiate electromagnetic waves, it is in a concealed position and is usually not subject to strong electromagnetic interference. It is also effective against anti-radiation missile attacks and can also identify invisible targets.
4 Conclusion
In summary, the complex electromagnetic environment has a great impact on radar target recognition. Research on complex electromagnetic environment The gap between China and developed countries is still very large. Developed countries have started research on combat, training, equipment, technology, and talents in complex electromagnetic environments earlier. Nowadays, a large number of achievements have been made, most of which have already been applied to actual equipment. In this respect, China is already in a backward situation. Only by mobilizing all positive factors to catch up and narrowing the gap, can we stand in an invincible position in the local war under the conditions of informationization in the future.
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