Signal Processing in Noise Waveform Radar
Click on the cover image above to read some pages of this book! Formatting may be different depending on your device and eBook type. This book is devoted to the emerging technology of noise waveform radar and its signal processing aspects. It is a new kind of radar, which use noise-like waveform to illuminate the target.
The book includes an introduction to basic radar theory, starting from classical pulse radar, signal compression, and wave radar. Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the United Kingdom , which allowed the creation of relatively small systems with sub-meter resolution.
The modern uses of radar are highly diverse, including air and terrestrial traffic control, radar astronomy , air-defense systems , antimissile systems , marine radars to locate landmarks and other ships, aircraft anticollision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring, altimetry and flight control systems , guided missile target locating systems, and ground-penetrating radar for geological observations.
High tech radar systems are associated with digital signal processing , machine learning and are capable of extracting useful information from very high noise levels. Radar is a key technology that the self-driving systems are mainly designed to use, along with sonar and other sensors. Other systems similar to radar make use of other parts of the electromagnetic spectrum. With the emergence of driverless vehicles, radar is expected to assist the automated platform to monitor its environment, thus preventing unwanted incidents.
As early as , German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In , Alexander Popov , a physics instructor at the Imperial Russian Navy school in Kronstadt , developed an apparatus using a coherer tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter. In , while testing this equipment for communicating between two ships in the Baltic Sea , he took note of an interference beat caused by the passage of a third vessel.
In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation. In , he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter. He also obtained a British patent on September 23,  for a full radar system, that he called a telemobiloscope. His system already used the classic antenna setup of horn antenna with parabolic reflector and was presented to German military officials in practical tests in Cologne and Rotterdam harbour but was rejected.
In , Robert Watson-Watt used radio technology to provide advance warning to airmen  and during the s went on to lead the U. Through his lightning experiments, Watson-Watt became an expert on the use of radio direction finding before turning his inquiry to shortwave transmission. Requiring a suitable receiver for such studies, he told the "new boy" Arnold Frederic Wilkins to conduct an extensive review of available shortwave units.
Wilkins would select a General Post Office model after noting its manual's description of a "fading" effect the common term for interference at the time when aircraft flew overhead. Across the Atlantic in , after placing a transmitter and receiver on opposite sides of the Potomac River , U. Navy researchers A. Hoyt Taylor and Leo C.
Young discovered that ships passing through the beam path caused the received signal to fade in and out. Taylor submitted a report, suggesting that this phenomenon might be used to detect the presence of ships in low visibility, but the Navy did not immediately continue the work. Eight years later, Lawrence A.
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Hyland at the Naval Research Laboratory NRL observed similar fading effects from passing aircraft; this revelation led to a patent application  as well as a proposal for further intensive research on radio-echo signals from moving targets to take place at NRL, where Taylor and Young were based at the time.
Before the Second World War , researchers in the United Kingdom , France , Germany , Italy , Japan , the Netherlands , the Soviet Union , and the United States , independently and in great secrecy, developed technologies that led to the modern version of radar.
Australia , Canada , New Zealand , and South Africa followed prewar Great Britain's radar development, and Hungary generated its radar technology during the war. Hugon, began developing an obstacle-locating radio apparatus, aspects of which were installed on the ocean liner Normandie in During the same period, Soviet military engineer P. In total, only Redut stations were produced during the war. The first Russian airborne radar, Gneiss-2 , entered into service in June on Pe-2 dive bombers. More than Gneiss-2 stations were produced by the end of Full radar evolved as a pulsed system, and the first such elementary apparatus was demonstrated in December by the American Robert M.
Page , working at the Naval Research Laboratory. In , Watson-Watt was asked to judge recent reports of a German radio-based death ray and turned the request over to Wilkins. Wilkins returned a set of calculations demonstrating the system was basically impossible. When Watson-Watt then asked what such a system might do, Wilkins recalled the earlier report about aircraft causing radio interference. This revelation led to the Daventry Experiment of 26 February , using a powerful BBC shortwave transmitter as the source and their GPO receiver setup in a field while a bomber flew around the site.
When the plane was clearly detected, Hugh Dowding , the Air Member for Supply and Research was very impressed with their system's potential and funds were immediately provided for further operational development. Work there resulted in the design and installation of aircraft detection and tracking stations called " Chain Home " along the East and South coasts of England in time for the outbreak of World War II in This system provided the vital advance information that helped the Royal Air Force win the Battle of Britain ; without it, significant numbers of fighter aircraft, which Great Britain didn't have available, would always need to be in the air to respond quickly.
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If enemy aircraft detection relied solely on the observations of ground-based individuals, Great Britain may have lost the Battle of Britain. Also vital was the " Dowding system " of reporting and coordination to provide the best use of radar information during the tests of early radar deployment during and Given all required funding and development support, the team produced working radar systems in and began deployment.
Even by standards of the era, CH was crude; instead of broadcasting and receiving from an aimed antenna, CH broadcast a signal floodlighting the entire area in front of it, and then used one of Watson-Watt's own radio direction finders to determine the direction of the returned echoes. This fact meant CH transmitters had to be much more powerful and have better antennas than competing systems but allowed its rapid introduction using existing technologies. A key development was the cavity magnetron in the UK, which allowed the creation of relatively small systems with sub-meter resolution.
Britain shared the technology with the U. In April , Popular Science showed an example of a radar unit using the Watson-Watt patent in an article on air defence. Later, in , Page greatly improved radar with the monopulse technique that was used for many years in most radar applications. The war precipitated research to find better resolution, more portability, and more features for radar, including complementary navigation systems like Oboe used by the RAF's Pathfinder. The information provided by radar includes the bearing and range and therefore position of the object from the radar scanner.
It is thus used in many different fields where the need for such positioning is crucial. The first use of radar was for military purposes: to locate air, ground and sea targets. This evolved in the civilian field into applications for aircraft, ships, and roads. In aviation , aircraft can be equipped with radar devices that warn of aircraft or other obstacles in or approaching their path, display weather information, and give accurate altitude readings. The first commercial device fitted to aircraft was a Bell Lab unit on some United Air Lines aircraft.
Military fighter aircraft are usually fitted with air-to-air targeting radars, to detect and target enemy aircraft. In addition, larger specialized military aircraft carry powerful airborne radars to observe air traffic over a wide region and direct fighter aircraft towards targets. Marine radars are used to measure the bearing and distance of ships to prevent collision with other ships, to navigate, and to fix their position at sea when within range of shore or other fixed references such as islands, buoys, and lightships.
In port or in harbour, vessel traffic service radar systems are used to monitor and regulate ship movements in busy waters. Meteorologists use radar to monitor precipitation and wind. It has become the primary tool for short-term weather forecasting and watching for severe weather such as thunderstorms , tornadoes , winter storms , precipitation types, etc. Geologists use specialized ground-penetrating radars to map the composition of Earth's crust. Police forces use radar guns to monitor vehicle speeds on the roads.
Smaller radar systems are used to detect human movement. Examples are breathing pattern detection for sleep monitoring  and hand and finger gesture detection for computer interaction. A radar system has a transmitter that emits radio waves called radar signals in predetermined directions.
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When these come into contact with an object they are usually reflected or scattered in many directions. But some of them absorb and penetrate into the target to some degree.
Signal Processing in Noise Waveform Radar - Krzysztof Kulpa - Google книги
Radar signals are reflected especially well by materials of considerable electrical conductivity —especially by most metals, by seawater and by wet ground. Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either toward or away from the transmitter, there is a slight equivalent change in the frequency of the radio waves, caused by the Doppler effect.
Radar receivers are usually, but not always, in the same location as the transmitter.
Filter-Based Design of Noise Radar Waveform With Reduced Sidelobes
Although the reflected radar signals captured by the receiving antenna are usually very weak, they can be strengthened by electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light , infrared light , and ultraviolet light , are too strongly attenuated.
Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves.
Signal Processing in Noise Waveform Radar
Certain radio frequencies that are absorbed or scattered by water vapour, raindrops, or atmospheric gases especially oxygen are avoided in designing radars, except when their detection is intended. Radar relies on its own transmissions rather than light from the Sun or the Moon , or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths heat. This process of directing artificial radio waves towards objects is called illumination , although radio waves are invisible to the human eye or optical cameras. If electromagnetic waves travelling through one material meet another material, having a different dielectric constant or diamagnetic constant from the first, the waves will reflect or scatter from the boundary between the materials.
This means that a solid object in air or in a vacuum , or a significant change in atomic density between the object and what is surrounding it, will usually scatter radar radio waves from its surface. This is particularly true for electrically conductive materials such as metal and carbon fibre, making radar well-suited to the detection of aircraft and ships.
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Radar absorbing material , containing resistive and sometimes magnetic substances, is used on military vehicles to reduce radar reflection. This is the radio equivalent of painting something a dark colour so that it cannot be seen by the eye at night. Radar waves scatter in a variety of ways depending on the size wavelength of the radio wave and the shape of the target. If the wavelength is much shorter than the target's size, the wave will bounce off in a way similar to the way light is reflected by a mirror.
If the wavelength is much longer than the size of the target, the target may not be visible because of poor reflection. Low-frequency radar technology is dependent on resonances for detection, but not identification, of targets. This is described by Rayleigh scattering , an effect that creates Earth's blue sky and red sunsets. When the two length scales are comparable, there may be resonances. Early radars used very long wavelengths that were larger than the targets and thus received a vague signal, whereas many modern systems use shorter wavelengths a few centimetres or less that can image objects as small as a loaf of bread.
Short radio waves reflect from curves and corners in a way similar to glint from a rounded piece of glass. A corner reflector consists of three flat surfaces meeting like the inside corner of a box.