Development History and Trends of Passive Radar
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1. Discussion on the name of passive radar
Passive radar refers to a radar that has no radiation source. It detects targets by using the echoes formed by existing radio waves in space and irradiating them.
From the basic principles of radar, from the classic type of radar, to the passive radar that is widely concerned today, the difference between the two lies in their components. Classic radars are all generated by transmitters. The radio waves of the required frequency band are radiated into space through antennas to illuminate the target to be measured. The latter has no transmitter, and the radio waves that illuminate the target are made with the help of the radio waves already in space, which is called the radiation source outside the radar. This type of radar is called passive radar, also known as external radiation source radar (external sources). Since the radar itself does not radiate radio waves, this leads to changes in related issues such as radar positioning methods and information processing.
Phased Array Radar
Working principle of passive location radar system
From the radar itself, it is a non-radiation source, but in fact it is active, and the source is an external radiation source. In addition, this radar is a stealth radar, and the nemesis of radar, anti-radiation missiles, tracks radar radiation waves and attacks them. Passive radar does not radiate radio waves into space, which will make it impossible for anti-radiation missiles to find the location of the radar. Therefore, passive radar is a real stealth radar, without the need to use stealth materials and reduce the scattering, reflection and diffraction waves of the radar device itself.
In addition, this type of radar can be regarded as a passive radar because it does not actively transmit but passively receives.
Passive radar is also called passive concealed radar and passive coherent radar. This is based on the fact that it uses an opportunity radiation source or a cooperative radiation source to work. This is to associate the direct wave from the radiation source with the reflected wave from the moving target, and use the known receiving and transmitting positions as the two foci of the ellipse to form an ellipse. Then, by using multiple radiation sources and multiple receivers, the intersection points of multiple ellipses are determined. And the target direction is determined. Finally, the target position information is obtained.
In short, it is more accurate to name it as passive radar, which is better to distinguish it from active radar. Other names are not unique. There can be multiple external radiation sources, unlike the previous one that only used a single external radiation source.
2. The Origin of Passive Radar
1. How did the concept of passive radar come about?
As early as 1922, two researchers at the U.S. Naval Research Laboratory (NRI): Taylor and Young
While conducting radio wave propagation experiments, they used two electronic devices to transmit 60MHz continuous wave signals and accidentally discovered a wooden boat sailing in the river. This discovery became a by-product of their experiment.
In 1930, Hyndland and others from the U.S. Naval Research Laboratory accidentally captured a flying airplane 3.2 kilometers away while experimenting with a direction finder. The frequency used was 33MHz.
In 1932, Taylor, Young and Hyndland used two electronic devices, similar to the simple configuration of today's bistatic radar, to detect aircraft 80 kilometers away.
2. The birth of passive radar
Based on these works, they applied for a patent titled "System for Detecting Moving Objects by Radio Waves" in June 1933. The key points of the patent are: using a radio transmitter to transmit continuous wave signals, and configuring two receiving devices, which are placed in two places respectively, to measure the Doppler frequency shift of the echo signal of the moving object, thereby determining the position of the object.
It should be pointed out that the academic community believes that the founder of radar was Robert Watson-Watt in 1917, who successfully designed a thunderstorm locating device, announcing the birth of radar.
In 1922, MG Marconi of the United Kingdom proposed the angle measurement of ship anti-collision radar when he received an award from the Institute of Radio Engineers (IRE). The title of his speech was "Plane angle measurement radar that can prevent ship collisions." The ship radar he proposed was also in 1922, and it was related to the work of the US Naval Research Laboratory, but they were all working independently.
In 1935, Arnold Wilkins of the United Kingdom conducted the first radar detection research with the help of external radiation sources. This is the famous Daventry experiment. This is a real test of passive radar. The test was conducted in Daventry, Northamptonshire, central England. The radiation sources used were Daventry and BBC (1.8-30MHz) transmitters. The frequency band was shortwave. The receiving devices were set on two transport vehicles. The detection distance was 12 kilometers away. The target was the Heyford heavy bomber of the Royal Air Force (RAF). The distance between the receiver and the transmitter was 10 kilometers.
After the test was completed, a new radar research institute was established the following year, named Bowdsey, with Robert Watson as director. After that, Britain deployed a series of radars on the southeast coast, including passive radars along the coast of Channel 1.
3. Practical application of passive radar
During World War II, radar developed rapidly and passive radar became practical. In 1943, the first dual-base external radiation source radar used in a war environment was the "Klein Keidelberg" radar developed by Germany. It used the transmitter of the British coastal warning radar Chain Home as the radiation source and searched for the target's reflected signal through a receiver installed in Denmark. This receiver has good anti-interference performance. It can detect and locate fighters taking off from the UK, and can detect fighters 450 kilometers away. The accuracy is poor, about 10km, but it completed the early warning mission of Allied bombers at that time.
3. The “dormant” period of passive radar
After World War II, large-scale wars around the world had completely ended, and the United States and the Soviet Union were in the Cold War. From the founding of the People's Republic of my country to the reform and opening up, China experienced the Korean War, and in the 1960s, it experienced the Cultural Revolution. During this period, the country mainly focused on the development of "two bombs and one satellite", which did not stop even during the Cultural Revolution.
After the reform and opening up, domestic industry associations resumed work one after another, and academic exchanges at home and abroad were fully launched. From this perspective, my country's radar academic community paid little attention to passive radar. However, from the perspective of the international environment, the power of war to promote weapons development has weakened, and major countries have turned to space development.
In the mid-1950s, practical shipborne phased array radars were developed. In the late 1950s, the United States developed active phased array radars. In 1964, the United States installed the first space orbit surveillance radar to monitor artificial earth satellites or space vehicles. In the 1970s, Britain, France, Japan, Italy, Germany, Sweden and other countries were also equipped with phased array radars.
Satellites are launched, missile ranges are constantly updated, and there are more and more varieties. The development of radar is also accompanied by the development and innovation of these research and development work. Active radar is the general trend of development. In addition, radar itself does not feel threatened. The problem of its own safety is not prominent. But after the 1980s, there were the Iraq War, the Kosovo War, the Afghanistan War, etc., the emergence of stealth aircraft, electronic jamming, and anti-radiation missiles, radars were threatened, and the problem of radar stealth became more prominent. The introduction of radar mobility, multi-station deployment, and radar startup restrictions, coupled with the rapid development of digital technology, imaging technology, network technology, computer technology, miniaturization, integration, and modularization of electronic devices, laid the foundation for the development of passive radars and provided important conditions.
Why is passive radar so popular?
Since World War II, Germany, the United States, the former Soviet Union, Britain, France, Japan, Sweden, Canada and other countries have been developing and developing their own stealth technology. As for the United States, there are more than 20 types of stealth aircraft and stealth drones. Typical stealth aircraft include F-117A, B-2A, F-22, F-35, etc. There are also stealth missiles and stealth ships.
In the previous Panama War, Gulf War, and Kosovo War, the F-117A and B-2A demonstrated strong stealth capabilities, appearing and disappearing like ghosts, and achieved brilliant results. It shows that stealth fighters have unprecedented penetration and attack capabilities, and the cost-effectiveness is greatly improved. It also indicates that high technology has greatly enhanced combat effectiveness, and puts forward new and higher requirements for future air defense systems.
In February 2014, the British Ministry of Defense and BEA Systems Group jointly announced the first stealth unmanned fighter "Thor". This aircraft can be compared with the US X-47B and the French "Neuron" drone. This development trend shows that drones are armed with stealth technology, coupled with the increase in flight speed, which greatly increases their penetration capabilities and will become the main force on the battlefield in the future. UAV systems may become an effective tool for global strikes. In addition, the accelerated development of hypersonic aircraft has brought new and huge challenges to the air defense system.
Modern active radars face the following threats: stealth aircraft, electronic jamming, ultra-low altitude penetration, anti-radiation missiles, and hypersonic aircraft in near space. In fact, stealth technology, hypersonic technology, and electronic jamming are used in combination on various aircraft, and then they are flexible and maneuverable in strategy and tactics, such as missile trajectory change, submunitions, autonomous flight of hypersonic aircraft, "sensing" of drones, and low-altitude penetration of drones. This has brought huge impacts and challenges to ground air defense systems, especially radars, and their response strategies must undergo major changes.
The warnings of local wars in the past and the huge threats of modern missiles, unmanned aircraft, hypersonic aircraft and other penetration capabilities have forced radars to change and adapt to the needs of future wars. In response to these threats, passive radars came into being. Although it is not a new radar, it is rich in new elements and new achievements of modern science and technology, and is also a product of multidisciplinary integration.
5. Development of Passive Radar
In 1974, Marko et al. in the United States used an FM radio station as an external radiation source and a passive radar with a dual-base receiving setting to determine the position of the target. The system uses cross-correlation technology to measure the delay time of the target's reflected signal relative to the direct wave signal of the external radiation source, and obtains the equidistant ellipse where the target is located. Combined with the arrival angle measurement of the reflected signal, the target can be located.
In the 1970s, Czech Tesla conducted research on passive detection systems and launched the "TAMARA" system in 1987. It is said that in the 1995 Bosnian War, the Serbs used this system to detect and shoot down the US F-16 fighter jets. It was also reported that an F-117 stealth fighter jet that participated in the Kosovo War in 1999 was shot down by the Yugoslav Army with a SAM-3 missile, and it was the "Tamara" radar that discovered the stealth fighter jet. The external radiation source of this system is the radiation of the detection target itself. Its updated mobile version is the "VERA" system launched in 1998, which can track 200 batches of air targets at the same time.
In 1986, Griffiths et al. from University College London (UCL) in the UK first used TV station signals as external radiation sources to receive passive radars set up as dual bases. They analyzed several problems in signal detection and pointed out that the ambiguity function of the external radiation source waveform is the key to the research, which determines the range resolution, range ambiguity interval, range sidelobe level and Doppler resolution.
In 1989, the IEEE International Radar Conference documents revealed that an article by E. G. Thompson pointed out: Use the AWACS system and joint surveillance target attack radar system of the early warning aircraft E-3A as non-cooperative radiation sources, and use passive detection methods to detect flying targets.
In 1992, Griffiths et al. proposed to use satellite-relayed TV signals as the radiation source of passive radar. The receiving end consists of a direct wave channel for receiving satellite TV signals and an echo channel for receiving target reflected waves. The two signals are correlated and then incoherent accumulation is used to improve the processing gain. Studies have shown that for a target with RCS=20 at a distance of 100km, an 80dB processing gain is required to achieve a false alarm rate and a 90% detection probability. However, since the time intervals of coherent accumulation and incoherent accumulation are limited by the target Doppler frequency shift and the moving target distance offset, respectively, only 45dB of processing gain can be achieved for civil aircraft with a speed of 200m/s. This experiment failed to detect the real target at the possible distance.
In 1994, at the International Radar Conference held in France, three papers on passive radar based on television signals as external radiation sources were published, marking a new stage in the research of passive radar. After that, with the update of signal processing methods and devices, and the introduction of mature signal processing technology, several typical external radiation source radar systems appeared in the world.
In 1994, the French National Aeronautics Research Agency developed a multi-base radar test system with a TV station as an external radiation source. The radiation source is a TV station located near Paris, and the receiving station is located in Palaiseau, using two Yagi directional antennas. The system uses 5 transmitters and only uses Doppler information for positioning and tracking. Since the system tracking algorithm requires a high signal-to-noise ratio, it can only detect targets 5 km away from the receiving station.
In 1994, Howland of the British Defense Research Agency developed a passive radar system that uses a TV station as an external radiation source. The system uses the TV audio amplitude modulation carrier in Rennes, France as the radiation source. The receiving equipment includes a pair of Yagi antennas and a digital receiver. The target is located by measuring Doppler frequency shift and angle of arrival (DOA) information. The test results show that the system can detect and track aerial targets within 260km by using modern signal processing technology and tracking algorithms.
The passive radar system developed by Germany uses the US global positioning satellite and the Russian global navigation satellite as external radiation sources. Since the navigation system consists of multiple satellites and can provide multiple external radiation sources, the system can use a flexible phased array receiving antenna. The research results show that to detect a target with RCS=10 1 km away from the receiving station, the receiver needs a signal processing gain of 70dB.
The Manastash Ridge radar developed by the University of Washington is a passive detection radar used for meteorological detection and imaging of the atmosphere and ionosphere. The radar uses the FM radio station in Seattle as the radiation source and uses two receiving stations: the reference receiving station located in the University of Washington is used to receive the direct signal of the radio station. This receiving station uses a logarithmic periodic antenna with a pointing gain of 5dB; the receiving station located on Manastash Mountain 115km away captures the target scattered signal. This receiving station uses a simple overlapping dipole antenna. The system uses GPS to complete the time and frequency synchronization between the two receiving stations and has successfully detected targets 240km away.
The Silent Sentry, developed by Lockheed Martin in the United States in 1998, is a passive detection radar that has reached practical application. It uses commercial FM radio and television signals as external radiation sources. The receiving station of the system consists of a phased array antenna, a digital receiver with a large dynamic range, a high-performance parallel processor with a gigabit floating-point operation per second, and a three-dimensional tactical display. By measuring the target's arrival angle, Doppler frequency shift, and the time difference between the target signal and the direct wave signal arriving at the receiving station, the passive coherent positioning (PCL) technology is used to locate and track the target. The signal source database of the Silent Sentry system stores the location and frequency information of 55,000 commercial radio and television stations around the world, so the system can be used in most areas of the world. The system can detect targets with an RCS of 10 at a distance of up to 220km, and the positioning accuracy meets the requirements of warning radars, but it cannot meet the requirements of tracking radars.
In recent years, the United States has developed the third-generation "Silent Sentinel" system. The phased array antenna of the new system adopts the principle of bionics, imitating the 360° "compound eye" structure of flies. The four-sided antenna with a size of about 2.5m×2.5m is installed on the base of a fixed radar station, which can realize all-round and all-weather monitoring of the target. "Silent Sentinel" is divided into a fixed station system and a rapid deployment system. In addition, the radar can also be installed on aircraft and ships, and can realize high-precision detection of aerial targets such as aircraft and missiles in real time. It can simultaneously track more than 200 targets and distinguish between two targets 15m apart. The system has also captured the US Air Force's B-2 stealth bomber 250km away.
In addition, in 1999, the University of Illinois measured the echoes of FM radio and television signals reflected by the target through a sensor array, and used the Bayesian method to achieve joint tracking and identification of the target. In addition, the university also studied the imaging algorithm of passive dual (multi) base radar, using direct Fourier reconstruction (DFT) and wigner-ville distribution (WVD) algorithm to image moving targets, and selected 22 TV stations and FM radio stations as radiation sources. Using simulation data, the imaging algorithm and the influence of the location of the transmitter and the selection of system configuration on the imaging quality were studied.
Entering the 21st century, exo-radiation radar has developed rapidly. Scientific research institutions in many countries have made exo-radiation radar a research focus, and the forms of exo-radiation signals used are becoming increasingly extensive.
In 2001, Poullin proposed using COFDM modulated DAB and DVB television signals as external radiated signals, and he later confirmed that the passive radar was detectable to the target;
Saini et al. studied the ambiguity function of digital television signals and proposed a mismatch filtering method to eliminate the interference sidelobes in the ambiguity function.
Capria et al. used passive radar based on DVB television signals to conduct detection tests on moving ships close to the coast, further confirming the feasibility of passive radar based on DVB-T.
Conti et al. proposed a method to improve the distance resolution of DVB-T passive radar, making it feasible for DVB-T passive radar to image and identify targets. In 2001, Siemens of Germany developed a passive radar system that uses GSM cellular base stations to transmit signals. The system can successfully detect airplanes and cars, and can also be installed on early warning aircraft. The detection distance for large air targets exceeds 100km.
In addition, Singapore, Italy and other countries are also researching GSM-based passive radars. Due to the limitation of GSM signal bandwidth, the distance resolution of this passive radar is poor, about 1.8km, while the bandwidth of the third generation (3G) cellular mobile communication standard CDMA is about 1.2MHz, and the corresponding distance resolution can reach 122m. Therefore, research on passive radars based on CDMA signals has also appeared one after another.
In 2007, Guo et al. proposed a passive radar based on WiFi beacon signals, which used WiFi signals to detect targets in outdoor low-noise environments. They then studied target detection in indoor strong-noise environments.
Mojarrabi et al. studied a passive radar using GPS as the illumination source and theoretically calculated that the maximum detection range of the radar is about 214 km.
In addition, NAVSYS uses a phased array receiving antenna with 109 elements and digital beam control to detect weak GPS signals by increasing signal gain. The gain of this antenna is increased by 20dB compared to a single antenna, and it can detect signals that a single antenna cannot detect.
In addition to studying various external radiation signals, some scholars have also proposed new concepts based on external radiation source radars. For example, Inggs from South Africa proposed the concept of passive coherent cognitive radar, which consists of multiple receiving stations and multiple radiation sources (including FM, mobile cellular base stations, WiFi, other radars, etc.), which can improve radar performance in interference and complex terrain environments. Various passive radars that use different external radiation signals can use perception methods to check the occupancy of the spectrum and perceive the location information of the external radiation source to improve the coverage performance of the system;
Kulpa of Poland proposed the concept of MIMO passive coherent positioning radar, introducing the concept of MIMO and signal processing technology into passive radar, which can increase the monitoring range of radar and reduce the detection blind area of passive radar.
In the late 1970s, China conducted research on using AM broadcast energy to detect targets. However, due to the limitations of the development level of software and hardware at the time, only some related experiments were conducted and no practical system was formed.
Since 2000, Xidian University, Beijing Institute of Technology, National University of Defense Technology, University of Electronic Science and Technology of China, Nanjing University of Science and Technology and 38th Institute of China Electronics Technology Group Corporation have successively conducted research on external radiation source radar based on FM radio, television and GSM mobile phone signals, and have made phased progress. Among them, Xidian University used FM radio signals to achieve real-time track observation and tracking of targets over 240km in China for the first time.
6. Development Trend of Passive Radar
In summary, the technical development of passive radar can be summarized into the following aspects to explore its development trend:
(1) External radiation sources of passive radar
There are two and three types of external radiation source signals for passive radars, namely, the radiation sources such as radar, communication, navigation, and transponders carried by the detection targets such as aircraft and missiles; the other type is the existing and long-term used radio wave radiation sources in free space, such as television, FM radio, etc. The latter includes both one's own radiation sources and the enemy's non-cooperative radiation sources.
The common external radiation source signals of passive radar are:
FM radio signals and TV signals; in the early days, radio was analog, but now it is digital.
The same is true for television signals, which are now digital terrestrial television broadcast signals. At present, passive radars based on terrestrial television and digital FM broadcasting as external radiation sources have attracted widespread attention in some countries around the world.
The updates on external radiation source types are mainly mobile communication, navigation and positioning satellite, and satellite communication signals. For example, mobile cellular base stations, WiFi, and GSM cellular base stations.
Singapore, Italy and other countries are researching passive radars based on GSM. Research on passive radars based on CDMA signals has also emerged.
In 2001, Poullin proposed using COFDM modulated DAB and DVB television signals as external radiation source signals, and then he confirmed that the passive radar was detectable to the target. Saini et al. studied the ambiguity function of digital television signals and proposed a mismatch filtering method to eliminate the interference sidelobes in the ambiguity function.
The ambiguity function is the key to signal research, which determines the range resolution, range ambiguity interval, range sidelobe level and Doppler resolution.
In 2007, Guo et al. proposed a passive radar based on WiFi beacon signals, which used WiFi signals to detect targets in outdoor low-noise environments. They then studied target detection in indoor strong-noise environments.
Navigation satellite signals; Mojarrabi et al. studied passive radars with GPS signals as external radiation sources, wireless communication signals (including low-orbit satellite signals and high-orbit satellite signals), etc.
It should be pointed out that the types of external radiation sources have expanded to various types. The space that these sources can illuminate has developed from low altitude to medium altitude and high altitude, and may develop towards near space in the near future. In addition, the use of passive radars has expanded from fixed to mobile, and mobile has included vehicle-mounted, ship-mounted and aircraft-mounted. This means that the passive radar system must consider establishing a database of external radiation sources and storing the main parameters and waveform characteristics of existing external radiation sources in the database in case of emergency. For example, the passive radar "Silent Sentinel" system developed by Lockheed Martin in the United States has an external radiation source database that stores the location and frequency information of 55,000 commercial radio and television stations around the world, so the system can be used in most areas of the world.
(2) Operating frequency band of passive radar;
There are mainly the following types:
1. The working frequency band of passive radar is from 30MHz to 3GHz. Such radiation sources include
2. Digital audio broadcasting (DAB, 174~240MHz);
3. FM broadcasting (FM, 88~108MHz); the passive detection radar developed by the University of Washington in the United States, the FM radio station is the external radiation source;
4. Digital video terrestrial broadcasting (DVB-T, 30~300MHz and 300~3GHz);
5. Satellite communication;
6. Satellite TV DBS;
7. Global positioning navigation GPS. GPS signals have the advantages of high security and all-weather operation. Passive radar of GPS signals is still in the exploratory stage.
(3) Type of receiving antenna for passive radar;
The receiving antenna type of passive radar is closely related to the type of external radiation source, operating frequency band, detection distance, and target characteristics.
In 1994, the French National Aeronautics Research Agency and the British Defense Research Agency adopted the Yagi directional receiving antenna.
In 1994, the British Defense Research Agency adopted the Yagi directional receiving antenna, which is a good choice for receiving antennas with television signals as external radiation sources.
The passive radar system developed in Germany uses a phased array receiving antenna.
The University of Washington in the United States developed log-periodic receiving antennas and overlapping dipole antennas for passive radars.
The passive radar developed by Lockheed Martin of the United States uses a phased array receiving antenna.
The third-generation "Silent Sentinel" passive radar system developed by Lockheed Martin of the United States uses a phased array receiving antenna that adopts the principle of bionics and imitates the 360° "compound eye" structure of a fly. The four-sided antenna with a size of about 2.5m×2.5m is installed on the base of a fixed radar station, which can realize all-round and all-weather monitoring of the target.
(4) Passive radar information processing and its algorithm
The passive radar developed by Lockheed Martin in the United States uses a high-performance parallel processor with a gigaflop of floating-point operations per second.
The University of Illinois at Urbana-Champaign uses the Bayesian method to achieve joint tracking and identification of targets. In addition, the university also studies the imaging algorithm of passive dual (multi) base radars, using direct Fourier reconstruction (DFT) and wigner-ville distribution (WVD) algorithms to image moving targets.
It should be pointed out that the use of modern signal processing technology and tracking algorithms is related to the detection and tracking distance of aerial targets, as well as the display and imaging of targets.
(5) Display and imaging of passive radar;
The passive radar developed by Lockheed Martin in the United States uses a digital receiver with a large dynamic range and a three-dimensional tactical display.
The University of Illinois at Urbana-Champaign used simulation data to study the effects of imaging algorithms, launch pad location, and system configuration on imaging quality.
(6) Main detection targets of passive radar (including aircraft and missiles)
It should be pointed out that passive radar detection targets should include drones, and the development and application of drones have made them large, medium and small; high-speed and ultra-high-speed, and even hypersonic aircraft should be considered; low altitude, high altitude and near space, as well as ships, etc.
(7) Main performance of passive radar
In 1994, the British Defense Research Agency detected and tracked aerial targets within 260km.
In 1994, the French National Aeronautics Research Agency detected a target 5 km away from the receiving station.
In 1998, the Czech Tesla company launched the "VERA" system, which can track 200 batches of air targets at the same time. It is the "Klein Keidelberg" radar developed by Germany during World War II, which can detect fighter planes 450 kilometers away, with a poor accuracy of about 10km.
In 1994, the system tracking algorithm developed by the French National Aeronautics Research Agency required a higher signal-to-noise ratio and could only detect targets 5 km away from the receiving station.
The University of Washington in the United States developed a passive radar that detected a target 240 km away. GPS was used to synchronize the time and frequency between the two receiving stations.
The passive radar developed by Lockheed Martin in the United States uses passive coherent positioning (PCL) technology to locate and track targets by measuring the target's arrival angle, Doppler frequency shift, and the time difference between the target signal and the direct wave signal arriving at the receiving station. The detection range for targets with an RCS of 10 can reach 220km.
In recent years, the third-generation "Silent Sentinel" passive radar system developed by Lockheed Martin of the United States uses a phased array receiving antenna that adopts the principle of bionics and imitates the 360° "compound eye" structure of a fly. The four-sided antenna with a size of about 2.5m×2.5m is installed on the base of a fixed radar station, which can realize all-round and all-weather monitoring of the target.
Silent Sentinel is divided into fixed station system and rapid deployment system. In addition, the radar can be installed on aircraft and ships, and can achieve high-precision detection of aircraft, missiles and other air targets in real time, can track more than 200 targets simultaneously, and can distinguish between two targets 15 meters apart. The system has also captured a US Air Force B-2 stealth bomber 250km away.
In short, the main technical indicators of passive radar are: long detection distance, high precision, real-time detection of multiple targets (including aircraft, missiles), all-round, all-weather monitoring, coexistence of fixed and fast-moving types, and can be installed on the ground, aircraft and ships.
(8) Research hotspots of passive radar
Passive radar cannot accurately control the waveform and emission direction of the external radiation signal. The target echo signal is subject to strong ground clutter and multipath interference. Passive radar systems have certain difficulties in detecting weak targets. Effective interference suppression technology has become a key issue that needs to be solved in the process of passive radar weak target detection. At present, the methods to suppress these interferences are to reasonably configure the system, optimize the antenna design, the terrain selection of the receiving station and the signal processing method.
The suppression of electromagnetic interference is the research scope of electromagnetic compatibility, which can be handled comprehensively by various methods such as grounding, filtering, and shielding.
In multi-platform and single-platform situations, the study of methods, positioning algorithms, positioning accuracy and performance for passive positioning of targets using multiple parameters such as arrival direction, arrival time difference, Doppler frequency difference, phase change rate, etc. has also become a hot research topic today.
Multi-station data fusion, multi-parameter data fusion of multi-sensor detection, simultaneous irradiation of targets in multiple frequency bands, detection optimization and data fusion, ultra-wideband reception data fusion and other technical updates are used to improve the detection and tracking accuracy and resolution of passive radars.
The electronic scanning speed and data acquisition rate of radar systems have become bottlenecks in many application fields, and it is still difficult to overcome this problem.
(9) Application of Passive Radar
Passive radar can be used for both military and civilian purposes. It mainly includes:
Monitoring ports, airports, power plants, water plants and other key departments;
air traffic control;
militarily, it can counter stealth aircraft;
counter stealth cruise missiles;
counter anti-radiation missiles;
counter enemy reconnaissance;
counter interference;
counter low-altitude penetration;
In short, passive radar has the characteristics of good concealment, strong mobility, low cost, and resistance to enemy reconnaissance and anti-stealth. Passive radar has many advantages such as anti-reconnaissance, anti-interference, anti-stealth aircraft and cruise missiles, anti-anti-radiation missiles, and anti-low-altitude penetration. It is an important field of modern radar research. Therefore, it has been valued by various countries. It can survive in extremely harsh war environments, which has attracted widespread attention from industry experts and military experts.
Passive positioning of radiation source targets plays a very important role in the fields of navigation, aviation, aerospace, electronic warfare, etc.
This article comes from Du Shimin Science Network Blog.
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