And detecting the work of a police radar (speed indicator) and warning the driver that the traffic police inspector instrumentally monitors compliance with the Rules of the Road (SDA).

The rules of the road set speed limits on highways, for violating traffic rules, a driver may be fined or administratively punished (for example, deprivation of a driver's license). Car drivers, wishing to be informed about the work of the traffic police and / or in an effort to avoid punishment for intentional or unintentional traffic violations, install a radar detector on their cars. The radar detector is a passive device that detects police radar exposure and alerts the driver (exposure warning system).

Design features

The simplest radar detectors and radar detectors are installed behind the windshield, on the interior rear-view mirror or in the passenger compartment, connected to the on-board network (12 volts) through the cigarette lighter. More complex non-removable models for installation require the involvement of specialists. These devices are classified:

• By execution: built-in and non-built-in;
• According to the controlled frequency bands on which police radars operate: X, Ku, K,, Laser;
• By radar mode: OEM , Ultra-X, Ultra-K (K-Pulse)/(Smartscan™), Instant-On, POP™, HYPER-X™, HYPER-K™;
• By coverage angle (in degrees): all directions, oncoming, passing.

(Instruments with a 360° response width can detect speed-monitoring radars at an angle to the direction of travel and on receding vehicles.)

• If possible, binding to GPS, Glonass coordinates.

Radar detectors can respond to interference generated by power lines, electric transport (tram, trolley bus, electric locomotives), so protection against false alarms is built into many models.

The "radar jamming" design feature, or distorting the intruder's speed determined by the police radar, which actually makes it a "radar suppressor" is prohibited in all countries. In addition, some radar detectors can detect laser speed meters (lidars) as well as VG-2 systems (devices that detect radar detectors).

In 2010-2012, the STRELKA-ST complex of video recording of offenses, popular with the Russian traffic police, was not detected by most radar detectors. In 2012, there were only a few models on sale (this functionality was announced by all manufacturers). Today there is not a single radar detector that would not be able to warn in advance about "STRELKA-ST" and "STRELKA-M".

At the end of the summer of 2017, the newest mobile speed meter on a wheelbase appeared in the vastness of the Russian Federation, called "OSCON-SM", which is still confidently determined by literally a few devices costing from 40 thousand rubles.

Features of the use of radar detectors and radar detectors

The use of radar detectors and radar detectors is regulated by law.

In some states and federal associations, local laws prohibit the use of laser/radar detectors. Before using the device, make sure that its use is permitted in your area. Throughout the territory Russian Federation, Ukraine and Belarus, the use of radar detectors is not prohibited.

Laws of other countries

• Austria : Use prohibited. Violators are subject to a monetary fine, and the device is confiscated.
• Azerbaijan: Radar detectors are banned, there is no ban on the use of a radar detector.
• Albania: There is no prohibition on transport and use.
• Belarus: Radar detectors are illegal in Belarus. But the traffic police has nothing against radar detectors, considering them even to some extent useful for road safety.
• Belgium: Prohibited the manufacture, importation, possession, offer for sale, sale and distribution free of charge of equipment that indicates the presence of traffic control devices and interferes with their functioning. Violation threatens imprisonment from 15 days to 3 months, or a monetary fine is charged. In the event of a repeated violation, the fine is doubled. In any case, the device is removed and destroyed.
• Bulgaria: There is no general ban. Use is permitted as long as it does not interfere with the speed measurement
• Hungary: Possession, use while driving, and advertising of radar detectors is prohibited. Failure to comply will result in a fine and the removal of the device.
• Denmark: It is forbidden to equip a vehicle with equipment or separate parts configured to receive electromagnetic waves from police devices configured to control speed or interfere with the operation of these devices. Violation is subject to a monetary fine.
• Spain : prohibited.
• Latvia : Use prohibited. When selling, there are no restrictions. However, upon detection, a fine is imposed, the equipment is confiscated.
• Lithuania: Use prohibited. It is possible to levy a fine and confiscate equipment.
• Luxembourg: Imprisonment from 3 days to 8 years is possible, as well as the collection of a monetary fine and the seizure of equipment.
• Netherlands: no ban on use.
• Norway: No ban on use, but some minor restrictions.
• Poland : Not allowed to be used or transported in operational condition. Transportation is allowed only when the device is declared unfit for use (for example, packed). In case of violation, a monetary fine will be charged.
• Romania: There is no ban on use. This position is being discussed.
• Turkey: There is no ban on use.
• Finland: police use on regular and freelance vehicles for catching violators. 95% of radars are based on the Ka-band, but sometimes the K-band is used, and very rarely laser. There are no radars based on the X and Ku bands. Also in Finland, Gatso type traps are sometimes used on new roads, but these are not radars using radio waves, but GPS direction finders using sensors installed on the median strip of the road. To track such devices, other types of detectors are needed.
• France
• Czech Republic: no ban on use. This position is still under discussion.
• Switzerland: Offering for sale, importation, purchase, sale, installation, use and transportation of instruments that indicate the presence of radars are subject to a monetary penalty. Then the device and the car in which it is located are removed.
• Sweden: There is a ban on production, transfer, possession and use. Violation threatens with the removal of the device, a fine or imprisonment for up to 6 months.
• Germany: in this respect one of the most loyal countries. The police repeatedly carried out special actions, as a result of which radar detectors were given to motorists. For safety reasons, road services have installed so-called "false radars" on the most dangerous sections of roads - devices that imitate the signal of a traffic radar. When the radar detector is triggered, the driver reduces the speed, which accordingly reduces the accident rate. Since 2002, use has been banned. When selling or owning there are no restrictions. However, if the device is found to be installed and ready for use, a monetary fine (75 Euro) and one point in the penalty register will be imposed, and the equipment will be confiscated.
• Estonia: Radar detectors and radar detectors are prohibited. The fine reaches 400 euros, and the device is confiscated. Almost all police crews are equipped with radar detectors and radar detectors. So in 2012 a record was set recent years: then 628 radar detectors were detected in Estonia, mostly from visiting foreigners

The presence of a radar detector in a car sometimes avoids unpleasant contacts with traffic inspectors and can positively influence the self-discipline of drivers, thereby increasing traffic safety.

Traffic police inspectors, knowing that drivers often carry a radar detector in their car, use a different tactic of “hunting” for traffic offenders. The policeman hides in an "ambush" and turns on his radar only for a very short time, "in the forehead" of an approaching car. The violating driver has no chance to slow down in advance in order to avoid punishment. But the driver can stop (the range of the radar is 300 meters) and stand for 10 minutes: after this interval, the readings of the device are automatically reset to zero. Also, a traffic police officer is unlikely to be able to prove that it is your speed on the device. We can say that this method of avoiding punishment is not effective. Recently, all traffic police radars must be equipped with photo or video recording devices, and therefore, no matter how much you stand, waiting for the radar to reset, nothing will come of it. Your photo or even video will be on the computer in the police car

What is a radar?

Radar is an object detection system that uses radio waves to determine the distance, angle, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, vehicles, weather formations and terrain. A radar system consists of a transmitter emitting electromagnetic waves in the radio or microwave range, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver with a processor to determine the properties of the object (s). Radio waves (pulsed or continuous action) of the transmitter are reflected from the object and returning to the receiver, they bring information about the location and speed of the object.

The radar was developed in secrecy for military use by several countries during, before and during World War II. The term RADAR was coined in 1940 by the United States Navy as an acronym for radar or radio direction finding and has since entered English and other languages ​​as a common noun.

Modern views the use of radars (radar stations, radars) is very diverse. This includes air and ground traffic control, radar astronomy, air defense systems, anti-missile systems, maritime positioning and vessel radars, aircraft collision avoidance systems, ocean surveillance systems, space surveillance and rendezvous and docking systems, weather precipitation monitoring, altimetry flight control systems and systems, missile guidance systems, georadar for geological observations, as well as radar for medical research and observations. High-tech radar systems are associated with digital signal processing, machine learning and are able to extract useful information from signals with very high levels of noise.

Other radar-like systems use other regions of the electromagnetic spectrum. One example is "lidar", which uses ultraviolet, visible, or near-infrared laser light rather than radio waves.

History of the invention of radar

As early as 1886, the German physicist Heinrich Hertz showed that radio waves could bounce off solid objects. In 1895, Alexander Popov, a physics teacher at the Imperial School of the Russian Navy in Kronstadt, developed an apparatus using a coherer tube to detect distant lightning strikes. The following year, he added a spark transmitter to the device. In 1897, while testing this equipment to communicate between two ships in the Baltic Sea, he discovered interference beats caused by the passage of a third ship. In his report, Popov wrote that this phenomenon could be used to detect objects, but he practically did not use this observation in any other way.

The German inventor Christian Hulsmeier was the first to use radio waves to detect "the presence of distant metallic objects". In 1904, he demonstrated the ability to detect a ship in dense fog, but not the distance from the transmitter. He received a patent for his detection device in April 1904, and then a patent for an improvement to estimate the distance to a ship. In addition, he received a British patent on 23 September 1904 for a complete radar system, which he called the telemobiloscope. It worked at a wavelength of 50 cm and the pulsed radar signal was created using a spark gap (spark-gap). His system already used the classic parabolic reflector horn antenna design and was introduced by German military officials in practical trials in Cologne and Rotterdam Harbour, but was rejected.

In 1922, A. Hoyt Taylor and Leo C. Young, researchers working with the US Navy, tested a transmitter and receiver located on opposite sides of the Potomac River and found that a ship crossing the radio path caused the signal to disappear and reappear. Taylor presented a paper suggesting that this phenomenon could be used to detect the presence of ships in conditions of poor visibility, but the Navy did not immediately decide to continue research. Eight years later, Lawrence A. Hyland at the Naval Research Laboratory (NRL) observed similar fading effects from an overflying aircraft, applying for a patent, and also receiving a proposal for serious research at NRL (Taylor and Young had already worked in this laboratory) in the field of echo-radio signals of moving targets.

During the 1920s, British research institutions made many advances using radio communications, including sounding the ionosphere and detecting lightning at great distances. Watson-Watt became an expert on the use of radio direction finding, part of his series of lightning detection experiments. As part of his ongoing experimentation, he asked a "newcomer", Arnold Frederick Wilkins, to find a receiver suitable for use with shortwave transmitters. Wilkins did extensive research on available devices before choosing the Department of Communications (GPO) receiver model. His instruction manual noted that "fading" (a common term at the time for interference) occurred when the aircraft was in flight.

Before the outbreak of World War II, researchers in France, Germany, Italy, Japan, the Netherlands, the Soviet Union, the United Kingdom, and the United States, independently and in great secrecy, developed technologies that led to the modern version of the radar. Australia, Canada, New Zealand and South Africa followed the pre-war developments of Great Britain, and in Hungary similar developments were carried out during the war.

In 1934 in France, after systematic studies of the magnetron with a split anode, the research branch of the Leading Wireless Telegraphy Company (CSF - La Compagnie Generate de Telegraph Sans Fil), headed by Maurice Ponte and with the participation of Henri Hutton, Sylvain Berlinet and M. Hugon , began developing radio equipment for detecting obstacles, part of which was installed on the Normandy liner in 1935.

At the same time, the Soviet military engineer P.K. Oshchepkov, in collaboration with the Leningrad Electrophysical Institute, developed the Rapid experimental apparatus capable of detecting an aircraft within 3 km from the receiver. The Soviet Union created its first mass production of radar stations RUS-1 "Rhubarb" and RUS-2 "Redut" in 1939, but further development slowed down due to the arrest of the NKVD Oshchepkov and his sending to the Gulag. In total, only 607 examples of the Redoubt station were produced during the war. Russia's first airborne radar equipment, Gneiss-2, put into service in June 1943 on Pe-2 fighters. More than 230 models of Gneiss-2 stations were produced at the end of 1944. The French and Soviet systems, however, were designed around continuous wave operation and could not achieve the performance eventually achieved by modern radars.

When did the first radars appear?

A full-fledged radar developed as a pulse system, and the first such elementary apparatus was demonstrated in December 1934 by an American, Robert M. Page, who worked at the Naval Research Laboratory. The following year, the United States Army successfully tested a primitive surface-to-water radar to target coastal battery searchlights at night. This was followed by a pulse system demonstrated in May 1935 by Rudolf Künhold and GEMA in Germany, and another demonstrated in June 1935 by an Air Ministry team led by Robert A. Watson-Watt. In Great Britain. Radar development expanded considerably from 1 September 1936, when Watson-Watt became Superintendent of a new establishment under the British Air Ministry, the Budsey Research Station, located on Budsey Manor, near Felixstowe, Suffolk. The work here resulted in the design and installation of aircraft detection systems and a tracking station called "Chain Home" along the coasts of East and South England during the outbreak of World War II in 1939. This system provided vital advance information that helped the Royal Air Force win the Battle of Britain.

In 1935, Watt was asked to make an opinion on the latest reports of Germany's possession of a "death ray" based on radio emission, he passed this request to Wilkins. Wilkins made many calculations demonstrating the impossibility of creating such a system in principle. When Watt asked what they could have done then, Wilkins recalled an earlier report of radio interference caused by aircraft flying nearby. This led to the Deventry experiment on February 26, 1935. Using a powerful BBC shortwave transmitter as source and a Ministry of Communications (GPO) receiver located in the field as the bomber flew around the site. When the benefits of the development became apparent, funds were immediately allocated to the development of a working system. Watt's team received a patent for this device, number GB593017.

Having received all the necessary financial and technical support, the team developed radar systems in 1935 and began to deploy them. By 1936, the first five Chain Home (CH) systems were operational, and by 1940 they were deployed throughout the UK, including Northern Ireland. Even by the standards of that era, CH was crude; instead of emitting and receiving a signal with a directional antenna, the CH system transmitted a signal covering the entire area in front of it and then used one of Watt's own radio direction finders to determine the direction of the returned echoes. This meant that CH transmitters had to be much more powerful and have better antennas than competing systems, but this made it possible to quickly implement it using existing technology.

The April 1940 issue of Popular Science featured an example of a radar device based on the Watson-Watt patent in an article on air defense. In addition, there was an article in Popular Mechanics at the end of 1941 in which an American scientist reflected on the British early warning system deployed on the English east coast, and approached in reasoning how it works and works. Alfred Lee Loomis set up the Radio Emissions Laboratory in Cambridge, Massachusetts, which developed these technologies from 1941-45. Later, in 1943, Page greatly improved the monopulse radar, which was used for many years in most radars.

The war accelerated research into better resolution, greater mobility and more radar capabilities, including additional navigational systems such as the Oboe used by RAF Pathfinder Squadron.

What is radar used for?

The information provided by the radar includes the azimuth and range (and therefore position) of the object relative to the radar scanner. As such, it is used in many different areas where the need for such positioning is critical. Initially, the radar was used for military purposes: to detect air, ground and sea targets. This application has evolved into civilian applications in aviation, shipping and land transport.

In aviation, aircraft are equipped with radar devices that warn of aircraft or other obstacles on or approaching the aircraft's course, display weather information, and provide accurate altitude data. The first commercial device to be installed on board an aircraft was a 1938 Bell Lab design fitted to some United Air Lines aircraft. Such aircraft may land in fog at airports equipped with a GAS radar assistant, in which the flight of the aircraft is observed on radar screens while radio operators transmit landing directions to the pilot.

Marine radars are used to measure the bearing and distance of ships to avoid collisions with other ships, for navigation, and to fix their position at sea when they are within range of the coast or other fixed landmarks such as islands, buoys and lightships. In a port or harbour, ship traffic radar systems are used to monitor and control ship traffic in busy waters.

Meteorologists use radar to monitor precipitation and wind. It has become the main tool for short-term weather forecasting and observing severe weather events such as thunderstorms, tornadoes, winter storms, precipitation patterns, etc. Geologists use specialized, deep-seated radars to map the composition of the earth's crust. Police officers use radar to monitor the speed of vehicles on the roads. Smaller radar systems used to detect human movement. For example, breath pattern detection for sleep monitoring and hand and finger gesture detection for computer interaction.

The principle of operation of the radar

radar transmitter

The radar system has a transmitter that emits radio waves called radar signals in given directions. When they come into contact with an object, they tend to be reflected or scattered in many directions. Radar signals reflect particularly well on highly conductive materials, especially most metals, sea water, and wet ground. Some of them make it possible to use radar altimeters. The radar signals that bounce back to the transmitter are useful (informative) and they do the radar work. If an object moves towards or away from the transmitter, there is a slight corresponding change in the frequency of the radio waves reflected by this object, caused by the Doppler effect.

Radar receivers are usually, but not always, located in the same location as the transmitter. Although the reflected signals picked up by the receiving antenna are generally very weak, they can be amplified with electronic amplifiers. More sophisticated signal processing techniques are also used to recover useful radar signals.

The weak absorption of radio waves by the medium they pass through allows radar to detect objects at relatively long distances - ranges where other electromagnetic waves, such as visible light, infrared light, and ultraviolet light, are attenuated too much. Weather phenomena such as fog, clouds, rain, falling and sleet that block visible light are generally transparent to radio waves. Some radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are tried to be avoided in radar design, unless the radar is designed to detect them.

Radio wave illumination

Radar relies on its own radio emission, not on light from the sun or moon, and not on electromagnetic waves emitted by objects themselves, such as infrared waves (heat). This process of directing artificial radio waves towards objects is called illumination, although the radio waves are invisible to the human eye or optical cameras.

Reflection of radio waves

If electromagnetic waves passing through one material encounter another material having a different dielectric constant or magnetic permeability than the first, then the waves will be reflected or scattered from the interface between the materials. This means that a solid body in air or in a vacuum, or with a significant difference in atomic density between the body and the environment around it, as a rule, scatters radar radio waves from its surface. This is especially true for electrically conductive materials such as metal and carbon fiber, making radar suitable for detecting aircraft and ships. Radar absorbing material containing resistive and sometimes magnetic substances is used in military vehicles to reduce radar reflections. This ability is the radio equivalent of the inability in painting to see with the eyes of something that has dark color at night time.

Radar waves scatter in different directions, depending on the size (wavelength) of the radio wave and the shape of the target. If the wavelength is significantly smaller than the size of the target, the wave will be reflected in the same way that light is reflected by a mirror. If the wavelength is much larger than the size of the target, the target cannot be detected due to poor reflection. Low frequency radar technologies use resonances to detect rather than identify targets. This process is explained by Rayleigh scattering, an effect that creates blue sky Lands and red sunsets. When two wavelengths are comparable, resonances can occur. Early radars used very long wavelengths that were larger than targets and thus received a vague signal, while some modern systems use shorter wavelengths (a few centimeters or less) that can image objects so small. like a loaf of bread.

Short radio waves bounce off curves and corners like glare off the rounded part of a glass. Most reflective targets for short wavelengths have right angles between reflective surfaces. The corner reflector consists of three flat surfaces converging like the inside corner of the box. This structure will reflect waves entering its open portion directly back to the source. It is commonly used as radar reflectors to make hard-to-find objects easier to detect. Corner reflectors on boats, for example, allow them to be detected in order to avoid a collision or during a rescue operation. For the same reasons, objects that are supposed to avoid detection will not have interior corners or surfaces and edges perpendicular to possible detection directions, so they look "unusual" like a stealth aircraft. These precautions do not completely eliminate reflections due to diffraction, especially at longer wavelengths. Pieces of wire or strips of conductive material that are half a wavelength in size, such as chaffs, readily reflect but do not direct the energy they dissipate back to the source. The degree of reflection or scattering by an object of radio waves is called its effective scattering area (EPR - from the English. Radar cross-section (RCS).

Radar range equation

The power of the received response of the radio signal Pr is given by the equation:

Pt - transmitter power

Gt - transmitting antenna gain

Ar is the effective area (aperture) of the receiving antenna; It can also be expressed as , where

λ - wavelength

Gr - receiving antenna gain

σ - effective target scattering area in a given angle

F - propagation loss factor

Rt - distance from transmitter to target

Rr is the distance from the target to the receiver.

In general, when the transmitter and receiver are located at the same location, Rt = Rr and the Rt² Rr² expression can be replaced by R^4, where R is the distance to the target. This gives:

This shows that the power of the received signal decreases with the fourth power of the distance to the target, which means that the power of the signal reflected from distant objects is relatively weak.

Additional filtering and pulse integration slightly modifies the radar equation for pulse-Doppler characteristics, which can be used to increase detection range and reduce transmitter power.

The above equation with F = 1 is a simplification for vacuum free transmission. The propagation factor takes into account the effects of multipath and shadowing and depends on the details of the environment. In a real situation, propagation attenuation effects must also be taken into account.

Doppler effect in radar

Frequency shift is caused by movement that changes the number of wavelengths between the reflector and the radar. This may degrade or improve the performance of the radar depending on the impact on the detection process. As an example, the indication of target movement may be affected by the Doppler effect, which can produce signal blanking at certain radial velocities, degrading radar performance.

Maritime radar systems, semi-active radar guidance systems, active radar guidance systems, weather radar, military aircraft radar, and radar astronomy use the Doppler effect to improve performance. This allows you to get information about the speed of the target during the detection process. It also makes it possible to detect small objects in an environment containing much larger but slow moving objects nearby.

The Doppler shift depends on whether the radar configuration is active or passive. An active radar transmits a signal that is reflected back to the receiver. Passive radar depends on the object sending a signal to the receiver.

The Doppler frequency shift for an active radar is as follows:

Fd - Doppler frequency,

Ft is the frequency of the transmitted signal,

Vr - radial speed,

C is the speed of light

Passive radar is used in electronic jamming and radio astronomy systems as follows:

Only the radial velocity component is relevant. When a reflecting target is moving at right angles to the locator beam, it has no radial velocity relative to the receiver. Vehicles and weather moving parallel to the radar beam produce maximum Doppler frequency shift.

When a signal is transmitted with frequency (Ft) pulses repeating at frequency (Fr), the resulting frequency spectrum will contain harmonics with frequencies above and below (Ft) by the value (Fr).

As a result, the measurement of the Doppler frequency shift is only unambiguous if the Doppler frequency shift is less than half the frequency (Fr) called the Nyquist frequency, since otherwise the frequency of the returned signal cannot be distinguished from the shift caused by the signal sample rate, thus requiring , to:

Or when replacing (Fd):

As an example, a 2 kHz Doppler weather radar with a 1 GHz carrier frequency can reliably measure weather events up to a maximum of 150 m/s (340 mph), so it cannot reliably determine the radial velocity of an aircraft flying at a speed of 1000 m/s (2200 mph).

Polarization of radio waves

In any electromagnetic wave, the electric field is perpendicular to the direction of wave propagation and the direction of oscillation of the electric field vector is called the polarization of the wave. By controlling the polarization of the transmitted radar signal, various effects can be obtained. Radars use horizontal, vertical, linear, and circular polarization to detect various types of reflective objects. For example, circular polarization is used to minimize interference caused by rain. The linear polarization of the reflected signal usually indicates its reflection from metal surfaces. Polarization of the random nature of the reflected signal usually indicates fractal surfaces such as rocks or soils, this is used in navigational radars.

Radio waves and their propagation

Radio wave range

Radar radiation should follow a linear path in a vacuum, but in the atmosphere it travels along a somewhat curved path due to the change in the refractive index of the air, and this defines the radar horizon. Even when a wave is radiated parallel to the earth, it will rise above its surface beyond the horizon due to the curvature of the earth. In addition, the signal is attenuated by the medium through which it passes, and the radiation is scattered.

The maximum detection range of conventional radar can be limited by a number of factors:

• Line of sight, which depends on the height above ground level. This means that in the absence of a line of sight, the propagation of the beam is blocked.

• The maximum uniquely defined distance is determined by the pulse repetition rate. The maximum uniquely defined distance is the distance that a pulse can travel to an object and return to the receiver before the start of the next transmitted pulse.

• Radar sensitivity and reflected signal power are calculated by the radar equation. It includes factors such as environmental conditions and the size (effective scattering area) of the target.

The noise signal is internal source random changes in the signal that are generated by all electronic components.

The reflected signals decay rapidly as the distance increases, so that the noise imposes a limitation on the operating range of the radar. Noise floor and signal-to-noise ratio are two different indicators that affect the operating range. Signals from objects that are too far away are so weak that they do not exceed the noise level and therefore these distant objects cannot be detected. Detection requires a signal that exceeds the noise floor by at least the signal-to-noise ratio.

Noise is usually random variations superimposed on the wanted echo received by the radar receiver. The lower the power of the useful signal, the more difficult it is to distinguish it from noise. Noise figure is a measure of the noise produced by a receiver compared to an ideal receiver and should be kept to a minimum.

Shot noise is caused by the discreteness of charge carriers (electrons) and their transition through the inhomogeneities of the conducting medium, which take place in all detectors. Shot noise is the dominant noise in most receivers. They also have flicker noise caused by the transit of electrons through amplifying devices, which can be reduced with heterodyne amplification. Another reason to use a local oscillator is that for a fixed relative bandwidth, the instantaneous bandwidth increases linearly with frequency. This improves the range resolution. The only notable exception to heterodyne processing (conversion) in radar systems is ultra-wideband radar. It uses a single pulse or transient wave process similar to that used in UWB communications, see List of UWB channels.

Noise is also generated by external sources, the most basic of which is the natural thermal background radiation surrounding the target of interest. In modern radar systems, the internal noise level is usually approximately equal to or lower than the external noise level. An exception is the case of pointing the radar up into a clear sky, where the "picture" is so "cold" that it produces very little thermal noise. Thermal noise is defined as kTB, where T is temperature, B is bandwidth (after the signal has passed through the matching filter), and k is Boltzmann's constant. There is an attractive intuitive interpretation of this relationship in radar. The matching filter allows all the energy received from the target to be compressed into a single receiver (whether it be a band, Doppler, altitude or azimuth receiver). Superficially, it would seem that then, within a fixed time interval, it would be possible to obtain a perfect, error-free detection. To do this, you just need to compress all the energy in an infinitely small time interval. The factor limiting this approach in the real world is that while time can be arbitrarily divided, electric current is not. An electric current quantum is an electron, and therefore the most that can be done is to concentrate all the energy in a single electron by a matched filter. Since the movement of an electron corresponds to a certain temperature (the Planck spectrum of radiation), and this source of noise cannot be further weakened. So, we see that the radar, like all objects of the macrocosm, is subject to the profound influence of quantum theory.

Noise is a random signal, but target signals are not. Signal processing can use this difference to reduce noise using two strategies. Different signal integration methods used in moving target indication can reduce the noise level in each stage. The signal can also be divided among multiple filters for processing pulsed Doppler signals, while reducing the noise level due to the number of filters used. These improvements depend on consistency.

Wave interference

Radar systems must suppress unwanted signals in order to focus on targets of interest. These unwanted signals can come from internal and external sources, both passive and active. The ability of a radar system to suppress these unwanted signals determines its signal-to-noise ratio (SNR). SNR is defined as the ratio of signal power to noise power within the expected signal; it compares the level of the desired target signal with the level of background noise (atmospheric noise and noise generated in the receiver). The higher the system's SNR, the better it distinguishes between actual targets and noise interference.

Radar interference refers to a radio frequency (RF) signal reflected from targets that are of no interest to radar operators. Such targets include natural features such as land, sea, precipitation (rain, snow, or hail), sandstorms, animals (especially birds), atmospheric turbulence, and other atmospheric effects such as ionospheric reflections, meteors, and hail spikes. Interference can also be returned from man-made objects such as buildings and from intentional anti-radar objects such as chaff.

Some form of interference, clutter, can also be caused by a long radar waveguide between the radar transceiver and the antenna. On a typical PPI radar with a rotating antenna, this type of interference will typically be seen as a "sun" or "sunburst" in the center of the display, as the receiver reacts to signal reflections from dust particles and erroneous radio signals in the waveguide. Adjusting the time between the moment the transmitter sends a pulse and the moment the receiver is turned on tends to reduce the "sun" effect without affecting ranging accuracy, since most "sunshine" is caused by scattering of the transmitted radio pulse, reflected earlier than it leaves. antenna. Clutter is considered a passive source of interference as it only appears in response to radar signals sent by the radar.

Detection and neutralization of interference is carried out in several ways. Heaps tend to freeze between radar scans; on subsequent scan echoes, the desired targets will move and all stationary echoes can be eliminated. Sea clutter can be reduced by using horizontal polarization, while rain is reduced by using circular polarization (note that weather radars are expected to have the opposite effect and therefore use linear polarization to detect precipitation). An increase in the signal-to-noise ratio is achieved by other methods.

The interference may move with the wind or be stationary. Two general strategies are used to improve measures or performance in an interfering environment:

• Moving target indication that integrates successive pulses and

• Doppler processing, which uses filters to separate noise from desired signals.

The most effective method of interference reduction is the use of pulse-Doppler radar. Doppler radar separates clutter from aircraft and spacecraft using the properties of the frequency spectrum so that individual signals can be separated from multiple reflectors located in the same area using speed differences. This requires a coherent transmitter. Another method uses a moving target indicator that subtracts the signal received from two successive pulses using phase processing to attenuate signals from slow moving objects. This method can be adapted for systems that do not have a coherent transmitter, such as time-domain pulse-amplitude radar.

Constant false alarm rate, a form of automatic gain control (AGC), is a technique that relies on the clutter returning more echoes than the targets of interest. The receiver gain is automatically adjusted to maintain a constant overall level of visible noise. While this does not help detect targets camouflaged as more visible ambient clutter, it does help to distinguish between visible targets. In the past, electronically controlled AGC was used in radars and it affected the gain of the entire radar receiver. As radar evolved, AGC became controlled by computer software, and began to affect gain with greater graininess in specific detection cells.

Interference can also come from multipath reflections from actual targets caused by ground reflections, atmospheric currents, or ionospheric reflection/refractions (eg anomalous propagation). This type of interference is of particular concern because the signal from it moves and behaves like other normal (points of) targets of interest. In a typical scenario, the ground echo from the aircraft appears at the receiver as an identical target below the actual target. The radar may attempt to unify targets by reporting a target at the wrong height, or eliminate it based on jitter or physical unreality. Jamming systems based on landscape reflections take advantage of this property by amplifying the radar signal and directing it downward. These problems can be overcome by including a ground map of the radar's surroundings and eliminating all echoes that appear to occur underground or above a certain height. The monopulse can be improved by changing the relief algorithm used at low altitude. The latest air traffic control radar equipment uses decoy detection algorithms by comparing current return pulses with adjacent ones and calculating return improbability.

Electronic jamming

Radar electronic jamming refers to radio frequency signals originating from sources outside the radar, transmitted at the frequency of the radar and thus masking a target of interest. Interference can be intentional, created in accordance with electronic warfare tactics, or unintentional, created by active friendly forces equipment that uses the same frequency range. Electronic jamming is considered to be an active source of interference, since it is initiated by elements outside the radar and is not related to the signal of the jammed radar at all.

Electronic jamming is problematic for radars, since the jamming signal only needs to travel part of the path in one direction (from the jammer to the radar receiver), while the radar signal makes a double path (radar-target-radar) and, therefore, its power is significantly reduced to by the time it returns to the radar receiver. Therefore, electronic jamming systems can be much less powerful than the radars they suppress, and at the same time continue to effectively mask targets in the line of sight from the jamming system to the radar (main lobe jamming). Jamming systems have the additional effect of affecting radars along other lines of sight through the side lobes of the radar receiver antenna (side lobe jamming).

Main-lobe suppression can usually only be reduced by narrowing the main-lobe solid angle and cannot be completely eliminated by pointing the receiver antenna directly at a jamming system using the same frequency and polarization as the radar. Sidelobe suppression can be overcome by reducing the sidelobes of the radar antenna pattern and using an omnidirectional antenna to detect and ignore non-main direction signals. Another method of protection against electronic jamming is frequency hopping and polarization directions.

Radar Signal Processing

signal distance measurement method

One way to measure distance is based on measuring the time of flight: a short radio pulse (electromagnetic radiation) is transmitted and the time is measured after which the reflected signal returns to the receiver. The distance is half the product of the travel time (because the signal must first reach the target and then return back to the receiver) and the speed of the signal. Because radio waves travel at the speed of light, accurate distance measurement requires high-speed electronic equipment. In most cases, the receiver does not receive reflected pulses while the signal is being transmitted. Through the use of an antenna switch, the radar switches between transmitting and receiving at a predetermined rate. A similar effect also imposes a limitation on the maximum detection range. In order to maximize the range, it is required to use a longer time between pulses, called the pulse repetition time, or pulse repetition rate.

These two effects tend to conflict with each other, and therefore it is not easy to combine both good short-range and good long-range radars in the same structure. This is because the short pulses needed for good close-range detection have less total energy, which makes the reflected signal much weaker and therefore harder to detect. This disadvantage can be compensated by increasing the number of pulses, but this will reduce the maximum range. Thus, each radar uses a specific type of signal. Long-range radars tend to use long pulses with long delays between them, while short-range radars use short pulses with shorter time intervals between them. With advances in electronics, many radars can now change their pulse repetition rate, thereby changing their ranging range. The latest radars emit two pulses from the same element, one for short range (about 10 km (6.2 miles)) and another for long range (about 100 km (62 miles)).

Distance resolution and received signal level relative to noise depend on the pulse shape. The pulse is often modulated for better performance using a technique known as pulse compression.

Distance can also be measured in units of time. A radar mile is the amount of time it takes for a radio pulse to travel one nautical mile, bounce off the target, and return back to the radar antenna. Since a nautical mile is defined as 1.852 m, dividing this distance by the speed of light (299792458 m/s) and then multiplying the result by 2 results in a duration of 12.36 µs.

FM signal

Another form of radar distance measurement is based on frequency modulation. Comparing the frequency between two signals is a much more accurate method, even with older electronics, than measuring the transit time. By measuring the frequency of the reflected signal and comparing it with the original frequency, you can easily measure the difference between them.

This technique can be used in continuous wave radar and is often used in aircraft radar altimeters. In these systems, the "carrier" radar signal is modulated in a predictable manner, typically varying up and down the audio frequency in a sinusoidal or sawtooth pattern. The signal is then sent from one antenna and received on another, usually located at the bottom of the aircraft, and the signal can be continuously compared using a simple frequency modulator that outputs a signal at a frequency that is the difference between the frequencies of the returned signal and the portion of the transmitted signal.

Since the frequency of the signal changes, by the time the signal returns to the aircraft, the frequency of the transmitted signal is already different. The frequency offset value is used to measure the distance.

The modulation depth of the received signal is proportional to the time delay between the radar and the reflector. The amount of this frequency offset becomes larger with a longer time delay. The measure of the amount of frequency shift is directly proportional to the distance. This distance can be displayed on the instrument and information about it can also be accessed via a transponder. This signal processing is similar to that used to determine the speed of a Doppler radar. Examples of systems using this approach are Azusa, MISTRAM and UDOP.

Another advantage is that the radar can operate effectively at relatively low frequencies. This was important in the early development of this type, when generating a high frequency signal was difficult or costly.

Ground based radars use frequency modulated (FM) signals with low power consumption, which cover a wider range of frequencies. Multiple reflections are analyzed mathematically to change the pattern with multiple passes, creating a computerized synthetic image. The use of the Doppler effect makes it possible to detect slow moving objects, as well as to largely eliminate the "noise" that occurs when reflected from the surfaces of water bodies.

Signal speed measurement method

Velocity is the change in distance to an object over time. Thus, the currently existing systems for measuring distance are equipped with memory elements for remembering the previous position of the target, which is quite sufficient for measuring speed. At one time, the pencil marks made by the operator on the radar screen served as a memory, from which the speed was then calculated using a slide rule. Modern radar systems perform equivalent operations faster and more accurately with the help of computers.

If the transmitter output is coherent (phase locked), then another effect is used to make near-instantaneous velocity measurements (requiring no memory), known as the Doppler effect. Most modern radar systems use this principle in Doppler radars and pulse-Doppler radar systems (weather radars, military radars). The Doppler effect can only determine the target's relative velocity along the line-of-sight from the radar to the target. Any component of the target's velocity that is perpendicular to the line of sight cannot be determined using Doppler effect alone, but it can be determined by tracking the target's azimuth over time.

It is possible to make a Doppler radar without any ripple, known as continuous wave radar (CW radar), which propagates a very clean signal of known frequency. Continuous wave radar is ideal for determining the radial component of a target's velocity. CW radar is typically used in traffic enforcement to quickly and accurately measure vehicle speed where range is not important.

When using pulsed radar, the change in phase of successive returns gives the distance the target has moved between pulses, and thus its speed can be calculated. Other mathematical advances in radar signal processing include time-frequency analysis (Heisenberg's Weyl or wavelet) and the chirplet transform, which exploits the change in the frequency of returns from moving targets ("chirps").

Pulse Doppler signal processing

Pulse Doppler signal processing includes frequency filtering during the detection process. The space between each transmitted pulse is divided into range elements or range selector pulses. Each element is filtered independently in the same way as the process used by a spectrum analyzer to obtain a display of different frequencies. Each different distance produces a different spectrum. These spectra are used to perform the detection process. This is necessary to achieve acceptable performance in adverse weather, terrain, and electronic countermeasures environments.

The main task is to measure the amplitude and frequency of the aggregate reflected signal at several distances. This is used in weather radar to measure the radial wind speed and precipitation speed in every different part of the atmosphere and is linked to computing systems to produce an electronic weather map in real time. The safety of aircraft operations depends on continued access to accurate weather radar information, which is used to prevent injury and accidents. The weather radar uses a low pulse repetition frequency (PRF). The coherence requirements here are not as stringent as those for military systems, since individual signals usually do not need to be separated. Weather radars typically require less complex filtering and range ambiguity handling than military radars designed to track aircraft.

The alternative task "detect and destroy targets in the lower hemisphere" is an ability necessary to improve air combat survivability. Pulse Doppler systems are also used for radar ground surveillance required to protect personnel and vehicles. Pulse Doppler signal processing increases the maximum detection range by using less radiation power in close proximity to aircraft, pilots, maintenance personnel, infantry and artillery. Terrain, water, and weather reflections produce more signals than planes and missiles, allowing fast-moving vehicles to covertly fly at extremely low altitudes, using stealth technology to avoid detection until the attack aircraft reaches the target of destruction . Pulse Doppler signal processing includes more sophisticated electronic filtering that reliably eliminates this kind of vulnerability. This requires the use of a moderate pulse repetition rate using phase coherent hardware that has a large dynamic range. Military applications require an average pulse repetition rate (PRF) which prevents direct definition range, and range resolution ambiguity processing is required to determine the true range of all echoes. Radial motion is typically coupled to the Doppler frequency to capture signals that cannot be produced by jamming systems. Pulse Doppler signal processing also produces audio signals that can be used to identify threats.

Elimination of passive interference

Signal processing is used in radar systems to reduce the effects of radar interference. Signal processing techniques include moving target indication, pulse Doppler signal processing, moving target detection processors, correlation with secondary surveillance radar targets, space-time adaptive processing, and the track-before-detect algorithm. Constant false signal rate and digital terrain model processing are also used in noisy environments.

Target tracking systems

The tracking algorithm is a strategy for improving the performance of a radar. Tracking algorithms predict the future position of multiple moving objects based on the history of individual positions reported by sensor systems.

The scan history is accumulated and used to predict future positions for use in air traffic control, threat assessments, combat system doctrine, weapon aiming and missile guidance. Location data is accumulated by radar sensors over several minutes.

There are four general tracking algorithms.

• Nearest Neighbor Algorithm

• Probabilistic Data Combination Algorithm

• Algorithm for Tracking Many Hypotheses

• Interactive multi-model (IMM) algorithm

Non-real-time reflections can be removed from the displayed information so that only the actual target is shown on the display. In some radar systems, or alternatively in a command and control system to which the radar is connected, and radar tracking is used to link sequences of marks related to individual targets and to estimate target courses and speeds.

Radar station device

The components of the radar station are:

• A transmitter that generates a radio signal with a klystron or magnetron and controls its duration with a modulator.
• Waveguide that connects the transmitter to the antenna.
• A duplexer that serves as a switch between antenna and transmitter or antenna and receiver, depending on the mode of operation of the radar.
• Receiver. Knowing the shape of the desired receiving signal (pulse), it is possible to design an optimal receiver using a matching filter.
• Display processor for receiving signals for output devices adapted to human perception.
• An electronic unit that controls all of these devices and the antenna to perform a radar scan according to a given program.
• Link to end user devices and displays.

Antenna design

Radio signals transmitted from a simple antenna will propagate in all directions, and such an antenna will receive signals equally from all directions. Such an antenna makes it difficult for the radar to locate the target.

Early systems typically used omnidirectional transmit antennas and directional receive antennas that were oriented in different directions. For example, the first system to be deployed, Chain Home, used two rod antennas crossed at right angles to receive signals from each on a different indicator. The maximum reflected signal was to be detected by an antenna located perpendicular to the target, and the minimum - by an antenna directed with its end to the target. The operator could determine the direction to the target by rotating the antenna in such a way that one indicator showed the maximum signal, while the other showed its minimum. One serious disadvantage of this type of design was that the signal was transmitted in all directions, so that only a small part of the total energy generated was transmitted in the desired direction. In order to transmit an adequate amount of power in the direction of the "target", the transmitting antenna must also be directional.

satellite dish

More modern systems use a steerable parabolic "dish" to create a dense "target illumination" beam, usually using the same dish as the receiver. Such systems often combine two radar frequencies into the same antenna to provide automatic heading or target tracking by the radar.

Parabolic reflectors can be either symmetrical parabolas or distorted parabolas. Symmetrical parabolic antennas produce a narrow "pencil" beam in both X and Y dimensions and therefore have higher gain. The NEXRAD pulse-Doppler weather radar uses a symmetrical antenna to perform detailed volumetric scans of the atmosphere. Distorted parabolic antennas produce a narrow beam in one dimension and a relatively wide beam in another. This feature is useful when target detection over a wide range of angles is more important than its location in three dimensions. Most 2D radars use a distorted parabolic antenna with a narrow azimuth lobe and a wide vertical lobe. This beam configuration allows the radar operator to detect an aircraft at a certain azimuth but at an undefined height. On the other hand, so-called "nodding" altitude detection radars use a dish with a narrow vertical width and a wide azimuth beam to detect an aircraft at a certain height, but with low azimuth accuracy.

Scanning in radar

• Primary scan: a scanning technique where the main antenna is moved to acquire the scan beam, examples include circle scan, sector scan, etc.

• Secondary scan: a scanning technique where the antenna power is moved to obtain a scan beam, examples include cone scanning, sector unidirectional scanning, beam switching, etc.

• Palmer Scan: A scanning method that produces a scanning beam by moving the main antenna and its power. The Palmer scan is a combination of a primary scan and a secondary scan.

• Conical Scan: The radar beam rotates in a tight circle around the "aiming" axis, which is pointed at the target.

Slotted waveguide antennas

Applied similarly to a parabolic reflector, the slotted waveguide is moved mechanically for scanning and is particularly suitable for a non-tracking surface scanning system where the vertical pattern can remain constant. Due to lower cost and less wind exposure, surveillance radars on ships, airport surfaces and harbors now use this approach in preference to the parabolic antenna.

Phased array antenna

Another control method is used in phased array radar.

Phased array antennas (PAA) consist of evenly spaced similar radiating elements such as conventional antennas or rows of slotted waveguides. Each antenna element or group of radiating elements contains a discrete phase shift that creates a phase gradient across the grating. For example, grating elements producing a phase shift of 5 degrees for each wavelength along the face of the grating will produce a beam directed 5 degrees away from the center line perpendicular to the grating plane. Signals traveling along this beam will be amplified. Signals that are offset from the beam will be attenuated. The number of radiating elements is the gain of the antenna. The value of the grating period determines the degree of suppression of the side lobes of the radiation pattern.

PAR radars were used at the dawn of radars during the Second World War (Mammut radar, Germany), but the limited capabilities of electronic devices of those years were the reason for their low efficiency. PAR radars were originally used for missile defense (see, for example, the Safeguard Program). They are the heart of the Aegis ship systems and the Patriot missile system. The massive redundancy associated with the presence of a large number of phased array elements improves reliability in the event of a gradual decrease in performance that occurs due to the failure of individual phase elements. To a lesser extent, PAR radars are used in the weather observation system. As of 2017, the US National Oceanic and Atmospheric Administration plans to implement a national network of multifunctional phased array radars throughout the US within 10 years, for meteorological research and flight monitoring.

Phased array antennas can be built in accordance with a specific configuration, both for missiles, ships and aircraft, and for infantry support.

As the price of electronic components declined, PAR radars became more common. Almost all modern military radar systems are based on phased array antennas, where the small additional cost is offset by increased system reliability without any moving parts. Traditional moving antenna designs are still widely used in services where cost is an important factor (air traffic surveillance and similar systems).

PAR radars are invaluable for aircraft use as they can track multiple targets. The first aircraft to use PAR radar was the B-1B Lancer. The first fighter aircraft to use the FAR radar was the MiG-31. The BRLS-8B "Barrier" (NATO classification - "SBI-16"), installed on the MiG-31M, has a passive electronically scanned PAR radar, which was considered the most powerful fighter radar in the world, while the AN / APG-77 system with active An electronically scanned antenna array was not installed on Lockheed Martin's F-22 Raptor.

Phased interferometry, or aperture synthesis techniques using an array of individual parabolic antennas that are phased into a single effective aperture, is not a typical application for radar, although it is widely used in radio astronomy. Due to the curse of sparse antenna arrays, such multiple aperture arrays, when used in transmitters, result in a narrowing of the beam beam by reducing the total power delivered to the target. In principle, such methods can improve spatial resolution, but the power reduction means that this is generally not efficient.

Aperture synthesis with data processing from a separately moving source, on the other hand, is widely used in space and airborne radar systems.

Antenna frequency range

Traditional band names originated as code names during World War II and are still used throughout the world in military and aviation applications. They have been adopted in the United States by the Institute of Electrical and Electronics Engineers and internationally by the International Telecommunication Union. Most countries have additional rules for controlling which areas of the radio bands are reserved for civil or military use.

Other users of the radio spectrum, such as the broadcasting and electronic countermeasures industries, have replaced traditional military designations with their own designation systems.

Antenna signal modulator

The modulators form a wave packet of the RF pulse. There are two different designs of radar modulators:

Non-coherent power generators connected by high-voltage switches. These modulators consist of a high voltage pulse generator generated by a high voltage source generating a network pulse and a high voltage switch such as a thyratron. They generate short pulses of power to power, for example, a magnetron, a special type of vacuum tube that converts direct current (usually pulsating) into microwaves. This technology is known as pulsed power technology. The transmitted RF pulse thus has a defined and generally very short duration.

Hybrid mixers powered by a signal generator and a complex but coherent waveform exciter. This waveform can be produced by low power/low voltage input signals. In this case, the radar transmitter must be a power amplifier, such as a klystron tube or a semiconductor transmitter. Thus, the transmitted pulse is intra-pulse modulated and the radar receiver must use pulse compression techniques.

radar coolant

Coherent microwave amplifiers delivering microwave signals above 1000 W, such as traveling wave tubes and klystrons, require the use of a liquid coolant. The electron beam must contain 5 or even 10 times more energy than the output microwave signal, and therefore it can generate enough heat to generate plasma. This plasma flows from the collector to the cathode. The same magnetic focusing that directs the electron beam forces the plasma to focus into the line of the electron beam, but flow in the opposite direction. In this case, frequency modulation occurs, which degrades the performance of the Doppler radar. To prevent this, coolants with minimal pressure and flow rate are used, as deionized water is commonly used in the most high power Doppler radar systems.

Kulanol (silicate ether) was used in some military radars in the 1970s. However, due to its hygroscopicity, hydrolysis and the formation of flammable alcohols occur. The loss of a US Navy aircraft in 1978 was caused by silica ether ignition. Kulanol is also expensive and toxic. The US Navy has developed a program called Pollution Prevention (PP) to eliminate or reduce the volume and toxicity of waste, air and wastewater emissions, which involves reducing the use of culanol.

Radar law

Radar (also: RADAR) is defined in Article 1.100 of the Radio Regulations (RR) of the International Telecommunication Union (ITU) as:

A radio determination system based on the comparison of reference signals with radio signals reflected or retransmitted from the location to be determined. Each radiodetermination system must be classified by the radiocommunication service with which it interoperates temporarily or permanently. Typical applications of radar are primary and secondary radars. They may be used in the radiolocation or satellite-based radiolocation services.

The general principle of radar operation is to emit a pulse of energy (an electromagnetic wave), wait for the reflected signal to arrive and process it, extracting the necessary information.
The reflected signal can give us information about the location of the object i.e. its azimuth, altitude, range, as well as its speed and direction of movement.
The tasks of the traffic police radar are much narrower - the object is in direct line of sight, the direction of movement is known. It remains only to calculate its speed.

At the same time, the methods of working with it determine some features:
The radar should be light and compact so that the operator can use it while holding it in his hand.
The radar must have built-in power supplies, consume energy economically.
The radar must be safe to use, i.e. the radiated power must be as low as possible.

It is known from radiophysics that the physical dimensions of transmitting and receiving antennas are commensurate with wavelengths. This means that the radar must operate at very short waves (high frequencies), so that its antenna device, together with the transmitter, receiver, decisive and display device, fits in the hand.
In addition, shorter wavelengths improve measurement accuracy. Indeed, at a frequency of 100 kHz, the wavelength will be 3 km. It's like trying to determine the thickness of a hair with a meter rod.
Another limitation is imposed by the small distances over which you have to work.
Most radars used in aviation in the Navy calculate the distance to the target by recalculating it from the time delay of the reflected signal from the emitted one. Then several distance measurements can be converted into speed.
The transmitters of such radars send a short and powerful pulse (duration 1 microsecond, power 600-1000 kW), at a propagation speed of 300,000 km / s, it will reach the target at a distance of 27 km in 90 microseconds, and it will take the same amount to return back. Total - 180 microseconds correspond to 27 kilometers.

The DPS radar does not need such wild powers, but it is short distances that make it impossible to build a radar according to the above scheme.
After all, if the impulse is even only 1 μS, this means that its length in space is 300 meters! That is, the first crests of an electromagnetic wave will reach the target at a distance of 140 meters, they will reflect it, return to the antenna, and then there are the last (and very powerful!) crests of the same impulse. Such a small distance cannot be measured by this method. Moreover, the receiving circuits of such radars are turned off for a short time immediately after the emission of the transmitting pulse, so as not to burn themselves out! It is very problematic to generate radio range pulses shorter than 1 microsecond, so how then to measure short distances and speeds at a short distance?

The physics of the process underlying the construction of the radar was described by the Austrian scientist Christian Doppler back in 1842.
Devices that use the Doppler Effect in their work, allow you to measure the speed of objects at a distance from a few meters to hundreds and thousands of light years.
Traffic police radars operate at frequencies:
10.500 - 10.550 GHz (X-band),
24.050 - 24.250 GHz (K-band),
33.400 - 36.000 GHz (Ka - wide band)
which corresponds to wavelengths of 28, 12 and 9 centimeters, respectively.
At such high frequencies, the resonant circuits are no longer coils and capacitors, as in broadcast receivers, but segments of waveguides (round or rectangular tubes).
The first condition - small size - is already easily met. Even at the lowest frequency, a quarter-wavelength is only 7 cm, and a quarter-wavelength waveguide shorted (baffled) at one end is the equivalent of a tuned parallel oscillatory circuit.
Like any other radar, a traffic police radar consists of a receiver and a transmitter.
The most commonly used transmitter is a Gunn diode oscillator.
Thus, two more conditions are met - a small (minimum sufficient) radiation power and low power consumption.
The receiving part consists of a mixer, an amplifier, a processing unit (computer) and a display device.
Please note that there are no “superheterodynes” in the radar itself, the received reflected signal is immediately mixed with the reference signal, the difference frequency is selected (which is the function of speed, the “Doppler frequency”), then it is amplified and processed. The measured speed is output to the output device.
Traffic police radar transmitters can emit long bursts, short pulses, short pulses in a certain sequence, but since they all emit, it means that everyone can be intercepted (direction finding), you only need the appropriate device - a radar detector.
On the other hand, methods of working with radar can nullify all the tricks of radar detector manufacturers and undisciplined drivers. Indeed, if the “silent” for the time being PR suddenly “shoots” directly at the offender, the signal heard from the warning device will no longer save you from a fine.
In addition to wearable, there are stationary radars. Their signals are confidently detected by all radar detectors, but this is not always required. If in Russia, where the use of radar detectors is allowed, the location of stationary radars is encrypted in every possible way (not officially announced), then, for example, in Lithuania (where the use of radar detectors is prohibited), all stationary posts are indicated on the website of the traffic police, their coordinates are constantly updated in navigator maps , and on the roads in front of them (200-300 meters) there are special warning signs.
Sometimes radar imitators are permanently placed along the roads to intimidate the hurried. These are the simplest devices, radar range signal generators. The simplest because they do not have a complex system for determining speed, their task is to make the radar detector work and cool the ardor of the “racer” at least for a short time. Three or four such noisemakers in a row will dull your vigilance, and the fifth may turn out to be real.
In addition to radars operating in the radio wave bands, laser speed meters are now increasingly used, the so-called. LIDARs (from English - LIght Distance And Ranging).
These devices emit a focused infrared beam (oh, that's the buzzword "nano", the wavelength is nanometers, the pulse duration is nanoseconds) in short pulses and measure the distance, like "large" radars, by the time difference between the transmitted and received pulse. Several distance measurements in a row make it possible to calculate the speed.
The operation of LIDAR is even easier to find than PR of the radio wave range, detection receivers are no more complicated than those that are in all TVs for receiving remote control signals and are now built into almost all radar detectors.
But there is no point in defining the work of a police LIDAR. If your device has signaled, then your speed has already been measured, or you just drove past the automatic doors of a supermarket or gas station.

In some countries, on roads with heavy traffic, speeding violators are even easier to fight - modern technology allows you to fix all cars when entering and leaving the highway. "Champions" who skipped the measured area faster than the allotted time receive a notification by mail about the need to pay a fine.

The most common radar models of the Russian traffic police

RADIS, manufactured by Simikon, St. Petersburg.

Range of measured speeds 10 - 300 km/h
Speed ​​measurement time< 0.3 сек

Iskra-1, manufactured by Simicon, St. Petersburg.
Operating frequency 24.15 + 0.1 GHz (K-band)
Measurement range, not less than 300, 500, 800 m (three levels)
Range of measured speeds 30 - 210 km/h
Speed ​​measurement time 0.3 - 1.0 sec

Radar(from English. RA dio D etection A nd R anging (RADAR) - radio detection and ranging , (synonyms: radar, radar station, radar) - a device used to detect and monitor various objects using radio waves and determine the range, speed, direction of movement and geometric parameters of the detected objects.

Invention history

Anti-aircraft radio detector B-2 "Storm", USSR 1935.

The reflection effect of radio waves was discovered in 1886 by the German physicist Heinrich Hertz. Heinrich Rudolf Hertz). In 1897, while working with his radio transmitter, Alexander Popov discovered that radio waves were reflected from the metal parts of ships.
Patents for the invention of radio detection devices were issued in 1905 in Germany, in 1922 in the USA, in 1934 in Great Britain.
In 1934, an experiment was successfully carried out in the USSR to detect an aircraft using the effect of reflection of radio waves - an aircraft flying at an altitude of 150 meters was detected at a distance of 600 meters from the installation. In the same year, prototypes of the Vega and Konus radars for the Elektrovizor aircraft radio detection system were produced at the Leningrad Radio Plant. In the USSR at that time the term "radar" was not used, the first radar stations were called radio traps or radio detectors. Radars were put into service in the USSR in 1939.
The greatest successes in radar before the start of World War II were achieved by the British, who began to massively install radars on warships, and in 1937 created a radar detection network Chain Home along the English Channel and the east coast of England, consisting of 20 stations capable of detecting an aircraft at a distance of up to 350 km.

Operating principle

The principle of radar

Radar is based on the ability of radio waves to be reflected from various objects. In classic pulse radar, the transmitter generates a radio frequency pulse that is emitted by a directional antenna. In the event that an object is encountered along the propagation path of a radio frequency wave, part of the energy is reflected from this object, including in the direction of the antenna. The reflected radio signal is received by the antenna and converted by the receiver for further processing.
Since radio waves propagate at a constant speed, it is possible to determine the distance to the object by the time the signal travels from the station to the object and back: D km \u003d (300,000 km / s * t s) / 2.
In addition to the slant range to the target, radar can also determine the speed and direction of movement, as well as estimate its size.
For radar, VHF and microwave bands are used; the first radar stations, as a rule, operated at frequencies from 100 to 1000 MHz.

Classification

Radars are classified according to many principles, below are the most common parameters for their classification.
On the signal path:

• active (with active response)
• passive

By waveband:

• meter
• decimeter
• centimeter
• millimeter

According to the separation of the receiving and transmitting parts:

• combined
• separate

By location:

• ground
• aviation
• shipborne

By the type of probing signal:

• continuous action
• impulse

By appointment: By appointment:

• early detection and warning
• review
• target designation
• counter-battery combat

By measured coordinates:

• one-coordinate
• two-coordinate
• three-coordinate

By way of scanning space:

• without scanning
• with scanning in the horizontal plane
• horizontal scanning with V-beam
• with vertical scanning
• with helical scanning
• with beam switching

By way of displaying information

• with range indicator
• with separate range and azimuth (altitude) indicators
• with round view indicator
• with azimuth-range indicator

Chronology

• 1886 Heinrich Hertz discovers the effect of reflection of radio waves.
• 1897 Alexander Popov fixes the influence of a passing ship on the operation of a radio communication channel.
• 1904 Christian Hülsmeyer creates a telemobiloscope - a device that captures the reflection of radio waves.
• 1906 Lee de Forest creates the first radio tube.
• 1921 Albert Hull develops a magnetron - a device for generating microwave radio waves.
• 1930 Lawrence E. Highland detects distortion in the passage of radio waves when an aircraft flies between antennas.
• 1931 The US Navy Aviation Radio Laboratory is starting to design a device for detecting enemy ships and aircraft using radio.
• 1934 An experimental American radar detects an aircraft at a distance of 1 mile.
• 1934 In Leningrad, successful experiments were carried out on the radio detection of aircraft.
• 1935 The German company GEMA creates the first radio detection device for the Kriegsmarine.
• 1935 During the experiment at the British military base Orford Ness, it was possible to detect an aircraft at a distance of 17 km.
• 1936 In the UK, the first Chain Home early warning radars were built in.
• 1936 The UK has successfully tested the Type 79X radar installed on the minesweeper HMS Saltburn.
• 1937 The Kriegsmarine adopts Seetakt and Flakleit type radars.
• 1939 An experimental XAF device was built in the United States, for the first time the word radar was used for its name.
• 1939 In Germany, an early warning system based on Freya and Würzburg radars is being put into operation.
• 1939 In the USSR, the aircraft detection station RUS-1 "Rhubarb" was adopted.
• 1939 In the UK, the ASV Mk.I radar was successfully tested on an Avro Anson K6260 aircraft.
• 1940 In the United States, the first SCR-270 early warning radars enter service.
• 1940 The first CXAM radars enter service with the US Navy.
• 1941 GEMA starts installing Seetakt radars on German submarines.
• 1941 The Luftwaffe adopts the first aviation radars FuG 25a "Erstling" and FuG 200 "Hohentwiel".
• 1941 Radar "Redut-K" installed on the cruiser "Molotov".
• 1941 Japan introduced the first Type 11 early warning radar.
• 1942 Radar "Gneiss-2" entered service with Pe-2 aircraft.
• 1942 The US Navy is entering the SCR-584 automatic anti-aircraft gun guidance system.
• 1943 The German Jagdschloss radar is equipped with a POV indicator for the first time.

Operating principle

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Police radar classification

Main technical characteristics

Types and ranges of traffic police radars

Radar operating modes

Fundamental radar technologies: - OEM, Ultra-X, Ultra-K (K-Pulse)/(Smartscan™), Instant-On, POP™, HYPER-X™, HYPER-K™.

Radars can combine these technologies to achieve the goals of hiding the signal from the radar detector. For example, "ISKRA 1" simultaneously uses Instant-ON as a switching mode and a combination of PULSE + POP in the form of a pack of 5 short pulses. .

Instant-ON is the mode of turning on the radar, when the radar is initially turned on and in standby mode, but does not emit any signal. After pressing the radar button, it instantly starts emitting a signal and measures the speed of the target it is aimed at. This allows you to remain invisible to radar detectors, which significantly increases the efficiency of the radar, as well as saves battery power of the radar.

POP - registered trademark, owned by MPH Technologies. This technology, unlike Instant-ON, is responsible for the structure of the signal itself. The essence of the technology lies in the fact that the radar, after switching on, emits a very short pulse and with its help measures the speed of the target. The use of this technology complicates the detection of the radar signal by radar detectors, since many models perceive such an impulse as interference and do not issue any warning to the driver. Also, due to the too short pulse, the detection distance is significantly reduced. In order for a radar detector to be able to recognize POP radar signals, it must be equipped with the appropriate protection technology.

PULSE - in addition to POP, there is also a pulse signal technology. It differs from POP in that the pulsed signal is continuously emitted. The duration of the pulses can be different. If it is very short, this can also create a problem for the radar detector, but most modern radar detector models are equipped with pulsed radar protection.

Comparative table of police radars, photographic recorders

Model	TYPE Speedcam	Range	Frequency	Protocol	Speed ​​range	Video range	Calibration interval
Avtodoria	4	Video	*	GPS/Glonass	10 km	*	2 years
Vocord Traffic	4	Video	*	GPS	Not ogre.	140 m	2 years
Autohurricane RS/VSM/RM	1/3/5	Video	*	*	*	*	1 year
Amata	1	Laser	800-1100 nm	-	700 m	250 m	1 year
Arena	1	K	24.125 GHz	-	1500 m	-	1 year
Barrier-2M	5	X	10.525 GHz	-	-	-	1 year
Golden eagle	5	K	24.125 GHz	K-Pulse	-	-	1 year
Binar	5	K	24.125 GHz	K-Pulse	-	-	2 years
Vizir	5	K	24.125 GHz	-	400 m	-	1 year
Iskra-1	5	K	24.125 GHz	Instant ON/PULSE/POP	400 m	-	1 year
Chris-S/P	1/5	K	24.125 GHz	-	150 m	50 m	2 years
LISD-2F	1	Laser	800-1100 nm	-	1000 m	250 m	1 year
PKS-4	1	K	24.125 GHz	-	1000 m	-	1 year
Radis	1	K	24.125 GHz	-	800 m	-	2 years
Rapier-1	1	K	24.125 GHz	-	-	20 m	2 years
Jenoptik Robot	1	K	24.125 GHz	-	-	-	-
Sokol-M	5	X	10.525 GHz	K-Pulse	-	-	1 year
Arrow ST/STM	1/5	K	24.125 GHz	K-Pulse	500 m	50 m	1 year

TYPE Speedcam determines the type of radar in Navitel navigation charts. .

"APK "AvtoUragan" can be equipped with radar speed meters "Rapira" or "Iskra-1" when it is stationary and radar "Berkut" in the cabin of a patrol car. .

"The Avtodoria registrar only works in video recorder mode.

"VOCORD Traffic can be equipped with speed meters "Iskra-1"DA/130(Chris), "Iskra"DA/210, "Iskra-1"DA/60

Also, the performance of Vocord Traffic is provided in the form of radarless systems in two versions:

1 - as single blocks, where the speed measurement is based on a precise measurement of the time of each frame;

2 - in the form of several cameras for monitoring the average speed on straight sections of roads.

Both Avtodoria, Avtohuragan and Vocord Traffic systems can measure the excess of the average speed on a road section.

Radar simulators

On the roads, they began to install a Lira-1 radar simulator operating in the X band.

Radar simulators work as false video recorders. The principle of operation is to create a radio signal similar to that emitted by road speed meters, while these devices do not have measuring devices.

SWS warning system

The SWS (Safety warning system) warning system is a messaging system for warning of approaching an emergency or accident site. The system is intended for reception with the help of radar detectors (radar detectors). The signal is transmitted at a frequency of 24.060 ... 24.140 GHz. SWS is not used in the CIS.

Dummy video recorders

Models can be converted into active video recorders by inserting the appropriate radar unit and connecting the camera.

Antiradar

For many drivers, fast driving is a common occurrence. Even special electronic equipment has appeared that helps the driver avoid fines. First