Development of passive radar technology
Radar mentioned by people in general refers to active radar. This is a traditional radar that radiates electromagnetic pulses to the target by itself to detect, locate and track. The electromagnetic signals emitted by the active radar will be discovered, located and exposed by the enemy. Introducing the "scourge of death" is the new system radar where people began to study their own electromagnetic radiation. This passive radar, which uses non-cooperative external radiation sources for detection and positioning, is a passive radar.
The characteristics and evolution of passive radar. Passive radar itself does not emit energy, but passively receives the electromagnetic signal of the non-cooperative radiation source reflected by the target to track and locate the target. The so-called non-cooperative external radiation source means that the radiation source and the radar "do not overlap" and there is no direct cooperative combat relationship. This prevents detection equipment and anti-radiation missiles from using electromagnetic signals to capture, track, and attack passive radar.
The passive radar system is simple, small in size, can be installed on a mobile platform, is easy to deploy, and has low order and maintenance costs. Passive radar does not emit signals that illuminate the target, so it is not easy to be perceived by the other party, and there is generally no problem of interference. It can work around the clock and around the clock: it can continuously detect targets, generally once per second, and the signal source is low-frequency electromagnetic waves of 40-400 MHz, which is conducive to the detection of stealth targets and low-altitude targets: no frequency allocation is required, so it can be deployed in the conventional Radar area.
Passive radar itself does not emit signals, which brings both advantages and disadvantages. Due to the dependence on the third-party transmitter, the operator cannot actively control the illuminator. When the detected target remains radio silent and the illuminator does not work, the passive radar becomes passive water and cannot play a role. In addition, some transmitters have low effective radiated power, are susceptible to interference and airborne decoys, and require unobstructed signals between the transmitter and the target, the target and the receiver, and the receiver and the transmitter, which limits passive radar. usage of.
In fact, passive radar is not a new concept, its history is almost as long as the radar technology itself. In 1935, Robert Watson Watt used the short-wave radio frequency emitted by the BBC in a single-base passive system to irradiate the "Hyford" bomber 10 kilometers away. In World War II, early warning passive radar was also tested, such as the German "Kleine Heidelberg" system. But the system at the time lacked sufficient processing power to calculate the precise coordinates of the target.
Currently, many countries are keen on the application research of passive technology. Lockheed Martin of the United States is one of the first companies to get involved in this field. It is said that the detection range of its passive system reaches more than 220 kilometers by relying on televisions and wireless transmitters. The Defense Advanced Research Projects Agency of the US Department of Defense, universities such as the University of Washington and Georgia Tech, and companies such as Thunder have conducted research in this area. In Europe, France has also carried out corresponding technical research work, Italy has demonstrated the prototype system, the United Kingdom is working on passive coherent radar and "cellular" radar (Celldar), Russia and the Czech Republic are also conducting similar research.
Passive radar classification Passive radar systems can be classified according to the detection object or configuration. According to the configuration method, passive radar is divided into two types: fixed (ground-based) and mobile (installed on platforms such as submarines, ships, aircraft, and ground vehicles). The detection object of passive radar can be radar, communication station or other wireless radiation source, or it can be a target that only reflects radio signals. Passive radars can be divided into two categories: detecting and tracking using the self-radiation of the detected target, and using electromagnetic waves emitted by external sources for detection and tracking.
Utilizing the self-radiation of the detected target In the case that the detected target itself is a radiation source or carries a radiation source, passive radar uses the electromagnetic waves radiated by the detection target to detect and track. Possible sources of radiation include electronic equipment such as radars, communication stations, transponders, active jammers, and navigators. The "Vila" series of passive radars developed by the Czech Republic belong to this type of passive radars.
Targets detected by passive radar such as electromagnetic waves emitted from external sources do not directly radiate electromagnetic energy. When the passive radar is working, it receives the direct wave from the external non-cooperative radiation source (third party) through the antenna, and the reflected wave or scattered wave formed after the external radiation source illuminates the target, and uses the Doppler frequency shift carried by it 3. The information such as the time difference and angle of arrival of signals received by multiple stations, after processing, the target information is extracted and the useless information and interference are eliminated, thereby completing the detection, positioning and tracking of the target.
Possible non-cooperative parties include radio stations, radio stations, communication stations, direct broadcast systems (DBS), global positioning systems (GPS), and original radars on various platforms. The Silent Sentry radar developed by the United States is such a radar. The range of use of the Global System for Mobile Communications (GSM) transmitter is only 20 kilometers, the range of using FM wireless base stations can reach 100-150 kilometers, and the range of high-power TV transmitters is farther. The range of passive systems using other radar transmitters is comparable to the radar used.
Several typical passive radars, the United States "silent sentinel", the United States, Lockheed Martin, United States began to study non-cooperative bistatic passive radar in 1983, in 1998 developed a new "silent sentinel" passive detection system . This passive radar uses 50-80 MHz continuous wave signals transmitted by commercial FM radio and television stations to detect, track, and monitor moving targets in the area. The system is composed of a large dynamic range digital receiver, a phased array receiving antenna, a high-performance parallel processor with giga floating-point operations per second, and its software. The test proves that it can track a target with a radar reflection area of ​​10 meters 2 up to 180 kilometers, and it can be improved to 220 kilometers. It can track more than 200 targets at the same time with a resolution interval of 15 meters.
The "Silent Sentinel" can be installed on buildings and fixed structures, as well as on aircraft, trucks and shelters for rapid deployment. Lockheed Martin has also tested two systems installed on surface ships and submarines, which generally use the broadcasting system in coastal areas as the source of illumination. The system on the submarine is installed on the periscope and uses omnidirectional antennas to provide helicopter or coastal reconnaissance aircraft warnings.
The fixed "silent sentinel" system can achieve full airspace coverage, real-time three-dimensional tracking and monitoring of the target, the data is updated 8 times per second, not affected by climatic conditions, the system cost and maintenance costs are low. The phased array antenna uses commercial components and is installed on a building with an antenna size of 2.3 × 2.5 meters. The system has an observation range of 120 °, uses digital beamforming technology to achieve the entire sector coverage, and can track fixed-wing aircraft, rotorcraft, cruise missiles and ballistic missiles.
The rapid deployment system is used for real-time data collection and processing, and is currently deployed on trailers with power self-sufficiency. The trailer is placed in the canopy, the phased array antenna is installed on the side of the canopy, and the reference antenna is installed on the top of the canopy. This special material canopy acts like a Faraday tube, preventing electromagnetic radiation from the processor in the car from interfering with the normal operation of the receiving antenna. In the trailer, the ruggedized receiver, processor and control station occupy half of the space, and the air conditioning system and generator are placed in the other half.
UK's "Honeycomb" Xiaoda UK's "Honeycomb" radar system can detect, track and identify moving targets on land, sea and air, including vehicles moving in the bushes. It can theoretically detect 10 to 15 thousand in the wild environment Meters of ground targets and large aircraft of 100 kilometers. When the target enters the detection area, it causes reflections of cellular phone radiated waves, and these reflections are detected by one or more cellular phone radars. The detection data is transmitted to the central control system in real time through the communication network, where the data is processed to determine the position and speed of the target. In addition to reflecting the radiation signal of the cell phone base station, the radar system can also use the acoustic sensor to detect the noise radiated from the target, which helps to determine the target location.
When the "cellular" radar is used for ground air defense, its phased array receiver can adopt an expanded structure or be integrated in a camouflage network: when used for passive early warning, it can be integrated in a tank or an early warning aircraft. The system can also be used for coastal surveillance, battlefield reconnaissance, special intelligence collection (such as secret unmanned surveillance of airport activities), border security, and offshore operations. The "cellular" radar deployed along the coastline can be used for ship detection, auxiliary search and rescue, piloting, warning and other tasks. It can also be installed on an early warning aircraft to form a passive early warning capability, covertly monitor the airspace, and detect aircraft 100 kilometers away.
"Vila-E" Radar "Vila" series passive radar was developed by the Czech Republic. "Vila-E" is the latest model of the series, which can detect, locate, identify and track air, ground and sea targets. The maximum distance for air detection is 450 kilometers, and it can identify targets and generate images of air targets.
The "Vila-E" system consists of four parts: the analysis and processing center is centered, and the three signal receiving stations are distributed in a circular arc around the station, and the distance between the stations is more than 50 kilometers. The analysis and processing center is deployed in the shelter cabin and has a complete computer system and communication, command and control system. The signal receiving station is carried by heavy vehicles and can be deployed flexibly. When the receiving antenna stand is erected, it is 17 meters high and covers an area of ​​9 × 12 meters. Three people can erect the antenna and enter the monitoring state within 1 hour. The shape of the antenna is a cylindrical structure, with low power consumption and high reliability. The average time between failures is up to 2000 hours, and it can withstand a wind of 30 meters / second.
The future development of passive radar Passive radar systems (especially passive radars using external non-cooperative radiation sources) may be an important development direction for the next 10 to 20 years. With the implementation of several major international communication satellite programs, there will be more than 1,000 communication satellites in orbit in the future. Many of them will emit high enough RF energy, and most locations on the ground will be exposed to several spaceborne radiation sources at the same time. Passive radar systems can make full use of these sources for target detection and tracking. In general, passive radar will be developed in the following aspects:
(1) Expand the types of available external radiation sources. External non-cooperative radiation sources range from the earliest television signals and FM signals to current mobile communication signals, global positioning system satellite signals, and future types of satellite signals and various other possible radiation sources. The variety of sources will increase day by day.
(2) Fourier imaging of radar targets. Researchers at the University of Illinois have confirmed that passive multi-base radar can be used to generate synthetic aperture images of aircraft targets. By using multiple transmitters with different frequencies and different positions, a dense data set in the Fourier domain can be established for a target, and the image of the target can be reconstructed by inverse Fourier transform.
(3) Networking of passive radars on different platforms. Due to the wide variety of external radiation source signals available, different radiation source signals occupy different frequency bands, and the same target will have different radar characteristics in different frequency bands. Therefore, in order to improve the detection capability of the target as much as possible, passive radars of different platforms can be networked.
(4) The combination of passive radar and active radar. When the external electromagnetic radiation equipment is turned off or unavailable, passive radar cannot detect and locate the target. Therefore, consider using passive radar in combination with active radar. If the passive and active radars are reasonably arranged in a bi / multi-base mode, when external electromagnetic radiation does not exist or is unavailable, the passive radar is used to receive the direct signal of the active radar and the reflected signal of the target to detect the target. This not only improves the utilization rate of passive radar, but also enhances the concealment and survivability of active radar.
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