Radar

Radar stands for Radio Detection and R was concerned (freely translated: “radio detection and distance measurement”), originally Radio Aircraft Detection and R was concerned (loosely translated as “radio-based aircraft radiolocation and distance measurement”) and is the name for various detection and location PROCEDURE OF and equipment on the basis of electromagnetic waves in the radio frequency range (radio wave n).

The term radar has in the past, the original German name “of radar” replaced.

General

A radar device is a device that a so-called electromagnetic wave bundles n emits primary signal, the “Echo s” receives light reflected from objects as the secondary signal, and analyzes on various criteria. Thus, information can be gained about the objects. Usually it is a location (determination of distance and angle). There are different depending on the purpose radar principles like the weather radar, the harmonic radar and over the horizon radar.

From the received reflected waves from the object, information may be obtained include:

•the angle or direction of the object

•the distance to the object (from the time delay between transmission and reception, see the speed of light)

•the relative movement between transmitter and object – they can be calculated by the Doppler effect of the shift of the frequency of the reflected signal

•the juxtaposition of individual measurements provides the distance and the absolute velocity of the object

•with good resolution of the radar can be detected contours of the object (eg Are obtained as the type of aircraft) or even pictures (Earth and Planetary Exploration).

The Germans coming from the original name Funkmeßtechnik (short of radar) after the Second World War in the Federal Republic of Germany replaced by the term radar. In the GDR was still spoken in the jargon of Funkmeßtechnik.

History

Discovery

1886 Heinrich Hertz introduced the experimental evidence

electromagnetic waves determines that radio wave n

be reflected by metal objects.

The first attempts to locate with the help of radio waves led the German

RF engineer Christian Hülsmeyer 1904 by. He found that by

Electric wave reflected back metal surfaces can be used to

distant metallic objects to be detected. His telemobiloscope detection

Ships is considered the forerunner of today’s radar systems and was completed on 30 April 1904

patent pending. However, the use of radar technology was not initially

recognized and so the invention came provisionally into oblivion.

Development of advanced radar systems in World War II

The Scottish physicist Sir Robert Alexander Watson-Watt, FRS milling (1892-1973) is considered one of the inventors of the radar.

Watson-Watt was an assistant at the Department of Natural Philosophy, University College, Dundee, then part of the University of St Andrews. From 1936 he was Director at the British Air Ministry.

He worked on the reflection of radio waves in meteorology. 1919 he patented a method for tracking of objects using radio waves (radar) patent, which after further developments (development of sight-or short-term direction finder; Watson-Watt direction finder) could be in 1935 for the first time used for radar tracking of aircraft in the meter wavelength range. On 26 February 1935 succeeded the scientists attempt to discover the test as the place Daventry approaching bombers of the type Handley Page HP50 using radar.

Watson-Watt was instrumental in the development of British radar systems during World War II.

The breakthrough of radar technology followed only shortly before and during the

Second World War. The military build-up in this

Time meant that from the mid-1930s in several countries in parallel intensive

research has been done on the development of radar. In particular, the Germans and

The British contributed in the episode a real race in the development

of radar systems. But even in the United States, the Soviet Union and in France, Japan,

Italy and the Netherlands, at the start of the war in 1939 radar systems for

instruction/writ/provision/decree/directive/instruction/mandate

On the German side Rudolf Kühnhold had as scientific director of the

News attempt Department of the Navy decisive role in the

Development: He developed a radar device that DeTe to camouflage device

(Decimeter-telegraphy) was named in 1934 for the first time in Kiel, he harbor

tested for the detection of vessels. The British introduced on 26 February 1935 a

first field trial carried in the aircraft up to a distance of 13 km,

could be traced. In September 1935, the GEMA presented from

Berlin as a first fully functional radio meter.

In addition to the GEMA, the systems such as Freya, Mammut,

Aquarius and Seetakt developed, was

Telefunken also with the systems of Würzburg and

Würzburg-Riese instrumental in the German radar technology. On 18

December 1939 was the first radar-guided Abfangeinsatz than 24 British

Bombers flew a raid on Wilhelmshaven, which could be blocked.

The German defense system against bomber squadron Kammhuber line led,

over a length of more than 1000 km from Denmark to northern France.

The British established in 1936 with Chain Home is also a chain of

Radar stations on the east coast of the on a different wavelength than the

Germans worked and was therefore initially not recognized by them. A milestone in the development of radar in early 1940 was the invention of the magnetron s at the University of Birmingham, which should be the core unit for all subsequent radar applications.

End of January 1943, the British put in an attack on Hamburg for the first time a mobile radar system in an aircraft that was used for navigation (H2S). Both sides developed called chaff, simple metal foil strips to disrupt enemy radar systems. Quickly, however, improved systems have been developed that could filter out these interferers.

Research after the Second World War

In Germany, the research was in the area after the war, radar completely for

Halt. The Allies banned this until 1950. Significant progress was made in

Research in the following years, particularly in the U.S., where a number of new theoretical approaches and innovative components such as semiconductors and microprocessors were developed. As a

Example is called from the year 1951, the Synthetic Aperture Radar.

Also on board civilian aircraft and ships are airborne radars standard equipment.

One of the first and still most civil applications is monitoring the

Aviation by Air Traffic Control (ATC).

In the late 1970s, the first systems of distance warning radars developed for

the automotive sector. In the space radar technology is mainly used for surveying since the mid-1990s

Earth and other planets used. For recording weather data is also

Weather radar s used.

Fields of Application

Radars have been developed for different uses:

•Surveillance radar, monitoring of sea and air transport (including early warning stations, for As the Freya radar), either as solid as the air traffic control radar station or in shipping traffic safety, or mobile on vehicles and aircraft (AWACS) as well as on ships (ARPA) plant.

Boats can be equipped for better visibility with a radar reflector.

•For target tracking radars (Ground Control Intercept) and position of the air defense radar, ground-based (eg Of Würzburg, Würzburg-Riese) or on board vehicles and aircraft, ships and missiles

•Aircraft on board radar (radome) to discover to discover weather fronts (Radar) or other aircraft and missiles (anti-collision systems, radar homing)

•Ground-penetrating radar (airfield surveillance radar) to monitor the position of aircraft and vehicles on the taxiways of an airport

•Radar remote sensing and military reconnaissance to identify details on the ground in poor visibility can

•Weather radar detection and location of bad weather fronts, measuring wind speed

Artillery radar, to correct their own artillery fire and missiles as well as the location of enemy artillery positions

•Radar motion sensor for monitoring of buildings and grounds, for As a door opener or light switch

•Radar to measure the speed on the road.

•Automotive technology: radar-based Spacer ACC (Adaptive Cruise Control) or ADC interfacing with emergency braking in PSS1 to PSS3 (Predictive Safety System), short-range functions such as collision warning and automatic parking (24 GHz short pulse in the range 350-400 ps, ​​and in the 77-79 GHz band).

•Trains also measure distance and speed with Doppler radars (in the ISM band at 24 GHz).

•Radar sensors and motion detectors or level

•Astronomy: mapping of planets (eg B. Venus, Mars), from which earth or from aboard a spacecraft, measuring the orbits of planets, asteroid s and space probes and space debris

•BioRadar for detecting people and the living body movement, such as when buried in avalanches, over distances of a few meters.

•Wind energy: for the detection of aircraft to the considered as a nuisance to reduce nighttime aviation obstruction lighting of the plants. The plan is the use of pulsed L-and X-band radar systems.

After the Second World War came the steering radar controlled anti-aircraft weapons such as rocket n it. In addition, the radar for civilian shipping and aviation was used. Today’s passenger aviation would not be possible without air surveillance by radar. Also, satellites and space debris are now monitored by radar.

When the radars were powerful, this technique also discovered the science. Weather radar to help in meteorology or on board aircraft in the forecast. By means of large stations radar images of the moon, the sun and planet a few are created from the ground. Conversely, the earth from space are measured and explored through satellite-based radars.

Organization and functioning of

rect 94,157,223,177 # radar pulse radar

rect 153 80,305,101 primary radar

rect 312 15 451 40 radar

rect 390 79,563,101 secondary radar

rect 478 221 582 258 continuous wave radar

rect 347 156 568 177 # Unmoduliertes_Dauerstrichradar continuous wave radar (CW radar)

rect 325 221 444 258 # continuous wave frequency-modulated continuous wave radar (FMCW radar)

rect 17,220,107,257 pulse compression method

desc top-left

Active cameras are divided into imaged and not imaged. A further distinction between impulse – and continuous wave radar devices. Such devices are in turn means Peilempfängern identifiable and locatable.

As a primary radar pulse radar devices are referred to, which evaluate only the passive echo reflected the target. It can be determined in addition to the distance and the radial velocity of the objects and their approximate size. Evaluation reflected harmonics allows conclusions on the type of aircraft.

A secondary radar also comprises a pulse radar apparatus but are located on the target object the transponder responsive to the pulses, and in turn returning a signal. This increases the range, the objects are identifiable and can optionally return their ID, and other data increases.

DF receivers, which can locate the source of radio waves (radar and other devices and their noise emission) for military purposes, is also called passive radar. A passive radar is not to discover the basis of its radio wave transmission.

Another type of speed cameras which are difficult to discover that the noise radar is emitting long pulses which look like random interference.

Pulse radar

Distance determination with the pulse method

A pulse radar device transmits pulses having a typical length in the lower range of microseconds and then waits for echoes. The term \Delta t of the pulse is the time between the transmission and reception of the echo. It is used for distance determination. For the distance r, the relationship is:

The group velocity c is approximately equal to the speed of light in vacuum, because the refractive index of air of radio waves is very close to the first Depending on the range of the radar device is received after a transmitted pulse a few microseconds to milliseconds, before the next pulse is emitted.

On the classic radar screen, the deflection starts with the excitation pulse. The velocity of propagation of electromagnetic waves in space is to scale with the display. When an echo is received, then the distance of the echo pulse is a measure on the display device for the removal of the reflecting object (in this case the airplane)

the radar device.

Pulse generating

In order to produce in the pulse radar devices high transmit powers in the megawatt range, which, for the detection As are necessary on some 100 km s magnetron used today. This is such a magnetron Example by Trigatron, a high-voltage switch tube, thyratron s or more recently pulsed semiconductor switches also operate.

Since the frequency of a magnetron can change as a function of temperature and operating mode, wherein measurements of the relative radial velocity, the frequency reference is derived from the reception of the transmission frequency.

Stationary pulse radars achievements to up to 100 MW as peak pulse power. Modern radars require much less energy for distances of more than 100 km and sending partial pulses with a pulse power of one megawatt. Use of many small transmitter can be completely dispensed with radiant interrupters. These transmitters generate the pulse then in combination. Devices with active phased array antenna n use this technique.

Direction determination

If you turn the antenna of a radar pulse, obtained a surveillance radar. The sharp directivity of the antenna affects both the transmitting and receiving. From the dependence of the strength of the echo of the orientation of the antenna can be determined very accurately its direction. The best-known application areas are of such a panoramic view of radar air traffic control and weather radar.

An airport surveillance radar (ASR Airport Surveillance Radar) usually combines a primary radar with a secondary surveillance radar. In addition to general air traffic control has mainly the task to provide the pilot approach an accurate picture of the situation in the air around the airport. The range of an ASR is typically 60 nm.

An approach radar consists of each one horizontally and one vertically moving antenna and allows to determine angle of approach, approach direction and approach altitude country forming aircraft. The pilot receives the correction instructions by radio from the ground staff or has a display instrument on board, indicating that passive deviations from the received radar pulses. Such instrument landings or blind landings are especially in poor visibility or at non-fired or camouflaged military reasons runway of importance. Shortly before touchdown but ground visibility is required.

The ground-based system STCA (Short Term Conflict Alert) used for collision avoidance in airspace surveillance radar. It is calculated from the flight path (track) of aircraft, the probability of a close flyby (near miss) or even crash and warns optically and acoustically the air traffic controllers.

The pivoting of the scanning beam of a pulsed radar can be accomplished by taking the orientation of the antenna also electronically steerable phased array antenna. So that multiple objects can be targeted and pursued almost simultaneously in rapid succession.

The Synthetic Aperture Radar reached a high, distance-independent resolution in azimuth. The required aperture size is calculated from the real composed of a small aperture, the moving antenna. This movement of the antenna must be known relative to that observed (rigid) and the phase of the object accurately transmitted pulses to be coherent each other. Satellites and space probes use such systems for the measurement of surface profiles.

Modules in the radar pulse radar

Radar antennas

The antenna is one of the most striking parts of the radar system. The antenna of the antenna pattern and ensures a necessary rotation of the required distribution of the transmission power in the room. The antenna is usually used in time division multiplexing. During reception time, it then receives the reflected energy.

The antenna pattern must concentrate very hard for a good lateral and vertical resolution is achieved. The distance resolution is however determined by the pulse duration. In case of a mechanical room or scanning the antenna is rotated back and forth. This movement can cause a significant mechanical problem, because the antenna reflectors reach very large dimensions at long wavelengths and high directivity. With radar sensors, the following antenna types are common:

•Phased array antenna n (see antenna array panel antenna)

•Active Electronically Scanned Array, as before, but with electronic control of the individual elements, electronic beam steering, target tracking

•Parabolic antenna n

Modern radars with multifunctional properties always use a phased-array antenna systems usually older devices use a satellite dish that’s different for generating a cosecant squared-diagram of the ideal parabolic shape.

Radar transmitter

A radar used in older devices, but also today transmitter type are self-oscillating pulse oscillators, which consist of a magnetron. The magnetron is energized by a high voltage pulse and generates a high-frequency high-power pulse (0.1 … 10 ms, a few kW to a few MW power). The high-voltage pulse to the magnetron is provided with a modulator (interrupter or today semiconductor switch with MOSFET). This transmission system is also called POT (P ower O szillator T ransmitter). Radars with a pot are either inconsistent or pseudokohärent.

A concept used in modern radars is the PAT (P ower A mplifier T ransmitter). In this system, the finished transmitter transmitting pulse is generated at low power and then brought to the required power with a high power amplifier (Amplitron, klystron, traveling wave tube or semiconductor transmitter modules) in a generator. Radar apparatus having a PAT vollkohärent in most cases, and can therefore be employed particularly well for the detection of moving objects by taking advantage of the Doppler frequency.

Recipient

The receiver usually uses the transmitting antenna and must be protected from the transmit pulse, is done with en circulator, directional couplers n and n Nullode The reception takes place with the superposition principle, was formerly used as a reflex klystron oscillator, were used for mixing and demodulation coaxially designed in waveguide screwed-n diode peak Today’s receivers operate fully with semiconductors and are constructed in stripline technology.

Continuous wave radar (CW radar)

A CW radar (CW for continuous wave eng -. Permanent stations) constant frequency can not measure distances, but the directivity of the antenna’s azimuth to a target. It is used for measuring speed. The radiated by an antenna is frequency from the target (for example, a car), and are received with a certain amount of Doppler shift, that is slightly changed, again. Since only moving objects are detected, missing disturbing influence of fixed targets. By comparing the sent and the received frequency (homodyne detection) the radial velocity component can be determined by a cosine factor is less than the magnitude of the velocity vector.

•On rail vehicles speed sensors are used on this principle, they radiate diagonally onto the track. The transmit powers required are very low and are often produced with Gunn diodes.

•First radar traffic police were also continuous wave radar devices. Since they could not measure distance, they are not working automatically.

•Air defense radars with Doppler radar detection, as the AN/MPQ-55 (CWAR), recognize their target even with heavy chaff disorder.

•Radar motion also work on this principle, but this must also slow changes in the received signal strength can register due to changing interference conditions.

Modulated continuous wave radar (FMCW radar)

A refined style are the FMCW (frequency modulated continuous wave) radar, also called “Modulated CW Radar” or “FM radar”. Send them with a continuously changing frequency. Either the frequency increases linearly to drop abruptly back to the initial value at a certain value (sawtooth), or rises and falls alternately at a constant rate of change. The linear change in the frequency and the continuous transmission, it is possible to determine at the same time in addition to the speed difference between the transmitter and the object whose absolute distance from each other. “Radar traps” the traffic police work this way and solve for speeding at a certain distance to the target from the photo flash.

Radar altimeter of planes and proximity warning devices in cars to work on this principle. Recently, this technology is also used in recreational boating, for example under the name “Broadband Radar”. The use of this “Broadband Radar” at airports is not possible, since the Doppler frequency of aircraft is too large to arise from measurement errors of up to several kilometers.

FMCW radars are also used in industrial applications for distance measurement and the measurement of liquid level in tanks.

Health by radar

The resulting shift in the X-ray tubes military radars until at least the 1980s, often inadequately shielded. In addition, maintenance and adjustment often had to be carried out on the open device. This led to radiation damage in many operating and maintenance soldiers in the NVA and Bundeswehr. A large number of soldiers, mainly former radar technician, diseased by cancer later, many have already died at a relatively young age. The number of victims (victims radar) is several thousand. Basically, the connection was recognized by the German Army and paid a supplementary pension in many cases.

The German HPIR High Power Illuminating Radar of the MIM-23 Hawk weapons system were therefore provided with an additional yellow rotating beacon that shone with an active transmitter.

Literature

•David K. Barton (Ed.): radar evaluation handbook. Artech House, Boston, MA, 1991, ISBN 0-89006-488-1, (Artech House radar library).

•Guy Kouemou (ed.): Radar Technology. InTech, 2010, ISBN 978-953-307-029-2, ( online ).

•JD shield connection: Theoretical foundations of radiolocation. Military Publishing House of the GDR, Berlin 1977.

Links

•Introduction to radar bases. radartutorial.eu on

•Research Institute for High Frequency Physics and Radar Techniques (FHR FGAN) on fhr.fgan.de

•Large Radar System TIRA (Tracking and Imaging Radar) of the FGAN-FHR on fhr.fgan.de

Avionics

Dimensional metrology

Air traffic control

Measuring instrument

Navigation device

Radar

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