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59-528: PBR may refer to: Science and technology [ edit ] Passive bistatic radar Partition boot record Pebble bed reactor , a type of nuclear reactor Peripheral benzodiazepine receptor, another name for translocator protein Phosphorus bromide Photobioreactor Physically based rendering , a method used in computer graphics Policy-based routing Precariously balanced rock, another name for

118-486: A balancing rock Pusey-Barrett-Rudolph theorem about the reality of quantum states Commerce [ edit ] Petrobras , Brazilian oil company, NYSE code Payment by Results Pre-Budget Report , one of the two economic forecasts that HM Treasury is required to deliver to the UK Parliament each year Military [ edit ] Patrol Boat, River , a US Navy designation Plastic baton round ,

177-439: A digitized , sampled signal. Most passive radar systems use simple antenna arrays with several antenna elements and element-level digitisation . This allows the direction of arrival of echoes to be calculated using standard radar beamforming techniques, such as amplitude monopulse using a series of fixed, overlapping beams or more sophisticated adaptive beamforming . Alternatively, some research systems have used only

236-431: A forward scatter radar , after the mechanism by which the transmitted energy is scattered by the target. In forward scatter , the scattering can be modeled using Babinet's principle and is a potential countermeasure to stealth aircraft as the radar cross section (RCS) is determined solely by the silhouette of the aircraft seen by the transmitter, and is unaffected by stealth coatings or shapings. The RCS in this mode

295-674: A "fence" (or "barrier") system; the Soviet Union deployed a bistatic CW system called the RUS-1, and the Japanese developed a bistatic CW radar called "Type A". The Germans used a passive bistatic system during World War II . This system, called the Klein Heidelberg Parasit or Heidelberg-Gerät , was deployed at seven sites (Limmen, Oostvoorne, Ostend, Boulogne, Abbeville, Cap d'Antifer and Cherbourg) and operated as bistatic receivers, using

354-494: A distributed passive radar exploiting FM broadcasts to study ionospheric turbulence at altitudes of 100  km and ranges out to 1200  km. Meyer and Sahr have demonstrated interferometric images of ionospheric turbulence with an angular resolution of 0.1 degrees, while also resolving the full, unaliased Doppler Power Spectrum of the turbulence. Silentium Defence has launched the first operational ground passive radar specifically designed to track LEO. The Oculus Observatory

413-416: A low-cost ground station. In a conventional radar system, the time of transmission of the pulse and the transmitted waveform is exactly known. This allows the object range to be easily calculated and for a matched filter to be used to achieve an optimal signal-to-noise ratio in the receiver. A passive radar does not have this information directly and hence must use a dedicated receiver channel (known as

472-439: A pair of antenna elements and the phase-difference of arrival to calculate the direction of arrival of the echoes (known as phase interferometry and similar in concept to Very Long Baseline Interferometry used in astronomy). With some transmitter types, it is necessary to perform some transmitter-specific conditioning of the signal before cross-correlation processing. This may include high-quality analogue bandpass filtering of

531-434: A passive radar system, there is no dedicated transmitter. Instead, the receiver uses third-party transmitters in the environment and measures the time difference of arrival between the signal arriving directly from the transmitter and the signal arriving via reflection from the object. This allows the bistatic range of the object to be determined. In addition to the bistatic range, a passive radar will typically also measure

590-737: A passive radar using FM radio stations to achieve detection ranges of up to 150 km, for high-power analogue TV and US HDTV stations to achieve detection ranges of over 300 km and for lower power digital signals (such as cell phone and DAB or DVB-T) to achieve detection ranges of a few tens of kilometres. Passive radar accuracy is a strong function of the deployment geometry and the number of receivers and transmitters being used. Systems using only one transmitter and one receiver will tend to be much less accurate than conventional surveillance radars, whilst multistatic radars are capable of achieving somewhat greater accuracies. Most passive radars are two-dimensional, but height measurements are possible when

649-425: A radar or sonar system with a separated transmitter and receiver. The Doppler shift is due to the component of motion of the object in the direction of the transmitter, plus the component of motion of the object in the direction of the receiver. Equivalently, it can be considered as proportional to the bistatic range rate . In a bistatic radar with wavelength λ , where the distance between transmitter and target

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708-571: A strong carrier tone , then it is possible to detect and track targets in an alternative way. Over time, moving targets will impose a changing Doppler shift and direction of arrival on the CW tone that is characteristic of the location, speed and heading of the target. It is therefore possible to use a non-linear estimator to estimate the state of the target from the time history of the Doppler and bearing measurements. Work has been published that has demonstrated

767-409: A target can be potentially detected by every transmitter. The return from this target will appear at a different bistatic range and Doppler shift with each transmitter and so it is necessary to determine which target returns from one transmitter correspond with those on the other transmitters. Having associated these returns, the point at which the bistatic range ellipses from each transmitter intersect

826-712: A type of non-lethal projectile Transport [ edit ] Potters Bar railway station , Hertfordshire, England, National Rail station code Puffing Billy Railway , tourist railway in Melbourne, Australia Other [ edit ] Pabst Blue Ribbon , an American beer brand Parti Burkinabè pour la Refondation Pelita Bandung Raya , a football club based in Bandung, Indonesia Performance-based regulation of utilities Plant breeders' rights over new varieties Professional Bull Riders , an international professional bull riding organization Topics referred to by

885-629: A variety of broadcast signals and to use cross-correlation techniques to achieve sufficient signal processing gain to detect targets and estimate their bistatic range and Doppler shift. Classified programmes existed in several nations, but the first announcement of a commercial system was by Lockheed-Martin Mission Systems in 1998, with the commercial launch of the Silent Sentry system, that exploited FM radio and analogue television transmitters. Passive radar systems have been developed that exploit

944-473: Is R tx and distance between receiver and target is R rx , the received bistatic Doppler frequency shift is calculated as: Note that objects moving along the line connecting the transmitter and receiver will always have 0 Hz Doppler shift, as will objects moving around an ellipse of constant bistatic range. Bistatic imaging is a radar imaging technique using bistatic radar (two radar instruments, with one emitting and one receiving). The result

1003-511: Is a radar system comprising a transmitter and receiver that are separated by a distance comparable to the expected target distance. Conversely, a conventional radar in which the transmitter and receiver are co-located is called a monostatic radar . A system containing multiple spatially diverse monostatic or bistatic radar components with a shared area of coverage is called multistatic radar . Many long-range air-to-air and surface-to-air missile systems use semi-active radar homing , which

1062-451: Is a form of bistatic radar. Some radar systems may have separate transmit and receive antennas, but if the angle subtended between transmitter, target and receiver (the bistatic angle ) is close to zero, then they would still be regarded as monostatic or pseudo-monostatic . For example, some very long range HF radar systems may have a transmitter and receiver which are separated by a few tens of kilometres for electrical isolation, but as

1121-480: Is based in Swan Reach, South Australia with plans to scale the technology globally. Silentium has a range of products that support both tactical and strategic applications ranging from drone detection, maritime surveillance to long-range air and space search. The University of Strathclyde is developing an in-orbit system to detect and track space debris from small fragments to inactive satellites. The work, supported by

1180-415: Is calculated as σ=4πA²/λ², where A is the silhouette area and λ is the radar wavelength. However, target may vary from place to place location and tracking is very challenging in forward scatter radars, as the information content in measurements of range, bearing and Doppler becomes very low (all these parameters tend to zero, regardless of the location of the target in the fence). A multistatic radar system

1239-427: Is different from Wikidata All article disambiguation pages All disambiguation pages Passive bistatic radar Conventional radar systems comprise a colocated transmitter and receiver , which usually share a common antenna to transmit and receive. A pulsed signal is transmitted and the time taken for the pulse to travel to the object and back allows the range of the object to be determined. In

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1298-429: Is one in which there are at least three components - for example, one receiver and two transmitters, or two receivers and one transmitter, or multiple receivers and multiple transmitters. It is a generalisation of the bistatic radar system, with one or more receivers processing returns from one or more geographically separated transmitter. A bistatic or multistatic radar that exploits non-radar transmitters of opportunity

1357-510: Is termed a passive coherent location system or passive covert radar . Any radar which does not send active electro-magnetic pulse is known as passive radar. Passive coherent location also known as PCL is a special type of passive radar, which exploits the transmitters of opportunity especially the commercial signals in the environment. The principal advantages of bistatic and multistatic radar include: The principal disadvantages of bistatic and multistatic radar include: The bistatic angle

1416-399: Is the angle subtended between the transmitter, target and receiver in a bistatic radar. When it is exactly zero the radar is a monostatic radar , when it is close to zero the radar is pseudo-monostatic, and when it is close to 180 degrees the radar is a forward scatter radar. Elsewhere, the radar is simply described as a bistatic radar. The bistatic angle is an important factor in determining

1475-455: Is the length of the signal sequence being integrated. A gain of 50  dB is not uncommon. Extended integration times are limited by the motion of the target and its smearing in range and Doppler during the integration period. Targets are detected on the cross-correlation surface by applying an adaptive threshold and declaring all returns above this surface to be targeted. A standard cell-averaging constant false alarm rate (CFAR) algorithm

1534-406: Is the location of the target. The target can be located much more accurately in this way, than by relying on the intersection of the (inaccurate) bearing measurement with a single range ellipse. Again the optimum approach is to combine the measurements from each transmitter using a non-linear filter, such as the extended or unscented Kalman filter. The above description assumes that the waveform of

1593-409: Is typically used. The line-tracking step refers to the tracking of target returns from individual targets, over time, in the range-Doppler space produced by the cross-correlation processing. A standard Kalman filter is typically used. Most false alarms are rejected during this stage of the processing. In a simple bistatic configuration (one transmitter and one receiver) it is possible to determine

1652-606: The BBC shortwave transmitter at Daventry . Early radars were all bistatic because the technology to enable an antenna to be switched from transmit to receive mode had not been developed. Thus many countries were using bistatic systems in air defence networks during the early 1930s. For example, the British deployed the CHAIN HOME system; the French used a bistatic Continuous Wave (CW) radar in

1711-577: The Czech TAMARA and VERA systems and the Ukrainian Kolchuga system. The concept of passive radar detection using reflected ambient radio signals emanating from a distant transmitter is not new. The first radar experiments in the United Kingdom in 1935 by Robert Watson-Watt demonstrated the principle of radar by detecting a Handley Page Heyford bomber at a distance of 12  km using

1770-804: The University of Illinois ), in the NATO C3 Agency in The Netherlands, in the United Kingdom (at Roke Manor Research , QinetiQ , University of Birmingham, University College London and BAE Systems ), France (including the government labs of ONERA ), Germany (including the labs at Fraunhofer-FHR ), Poland (including Warsaw University of Technology ). There is also active research on this technology in several governments or university laboratories in China , Iran , Russia and South Africa . The low-cost nature of

1829-752: The bistatic Doppler shift of the echo and also its direction of arrival. These allow the location, heading and speed of the object to be calculated. In some cases, multiple transmitters and/or receivers can be employed to make several independent measurements of bistatic range, Doppler and bearing and hence significantly improve the final track accuracy. The term "passive radar" is sometimes used incorrectly to describe those passive sensors that detect and track aircraft by their RF emissions (such as radar, communications, or transponder emissions). However, these systems do not exploit reflected energy and hence are more accurately described as Electronic Support Measure or anti-radiation systems. Well known examples include

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1888-467: The carcinotron , a radar jammer that was so powerful it appeared to render long-distance radars useless. Winkle was able to home in on carcinotron broadcasts with the same accuracy as conventional radar, allowing the jammer aircraft to be tracked and attacked at hundreds of miles range. Additionally, by indicating the location of the jammer, other radars in the Linesman/Mediator network could reduce

1947-406: The radar cross section of the target. Bistatic range refers to the basic measurement of range made by a radar or sonar system with separated transmitter and receiver. The receiver measures the time difference of arrival of the signal from the transmitter directly, and via reflection from the target. This defines an ellipse of constant bistatic range, called an iso-range contour, on which

2006-445: The "reference channel") to monitor each transmitter being exploited, and dynamically sample the transmitted waveform. A passive radar typically employs the following processing steps: These are described in greater detail in the sections below. A passive radar system must detect very small target returns in the presence of very strong, continuous interference. This contrasts with a conventional radar, which listens for echoes during

2065-611: The British Chain Home radars as non-cooperative illuminators, to detect aircraft over the southern part of the North Sea. Bistatic radar systems gave way to monostatic systems with the development of the duplexer in 1936. The monostatic systems were much easier to implement since they eliminated the geometric complexities introduced by the separate transmitter and receiver sites. In addition, aircraft and shipborne applications became possible as smaller components were developed. In

2124-670: The UK and European Space Agencies, is a collaboration between the Aerospace Centre of Excellence and the Centre for Signal & Image Processing at the University of Strathclyde. Clemente and Vasile have demonstrated the technical feasibility of the detection of small pieces of debris using a range of existing illuminators and a receiver in Low Earth Orbit. Bistatic range Bistatic radar

2183-406: The cross-correlation processing must implement a bank of matched filters, each matched to a different target Doppler shift. Efficient implementations of the cross-correlation processing based on the discrete Fourier transform are usually used, in particular for OFDM waveforms. The signal processing gain is typically equal to the time-bandwidth product, BT, where B is the waveform bandwidth and T

2242-415: The deployment is such that there is significant variation in the altitudes of the transmitters, receiver and target, reducing the effects of geometrical dilution of precision ( GDOP ). Advocates of the technology cite the following advantages: Opponents of the technology cite the following disadvantages: Passive radar systems are currently under development in several commercial organizations. Of these,

2301-404: The early 1950s, bistatic systems were considered again when some interesting properties of the scattered radar energy were discovered, indeed the term "bistatic" was first used by Siegel in 1955 in his report describing these properties. One of the largest and most complex passive radar systems was the UK's RX12874 , or "Winkle". Winkle was deployed in the 1960s in response to the introduction of

2360-451: The estimates of the bistatic range and bistatic Doppler shift of each target echo. Most analogue and digital broadcast signals are noise-like in nature, and as a consequence, they tend to only correlate with themselves. This presents a problem with moving targets, as the Doppler shift imposed on the echo means that it will not correlate with the direct signal from the transmitter. As a result,

2419-408: The expected target range is of the order 1000–3500 km, they are not considered to be truly bistatic and are referred to as pseudo-monostatic. In some configurations, bistatic radars may be designed to operate in a fence-like configuration, detecting targets which pass between the transmitter and receiver, with the bistatic angle near 180 degrees. This is a special case of bistatic radar, known as

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2478-442: The feasibility of this approach for tracking aircraft using the vision carrier of analogue television signals. However, track initiation is slow and difficult, and so the use of narrowband signals is probably best considered as an adjunct to the use of illuminators with better ambiguity surfaces. Passive radar performance is comparable to conventional short and medium-range radar systems. The detection range can be determined using

2537-592: The following sources of illumination: Satellite signals have generally been found more difficult for passive radar use, either because the powers are too low or because the orbits of the satellites are such that illumination is too infrequent. However, there have been significant developments in the area over the past years. The possible exception to this is the exploitation of satellite-based radar and satellite radio systems. In 2011, researchers Barott and Butka from Embry-Riddle Aeronautical University announced results claiming success using XM Radio to detect aircraft with

2596-539: The horizon or obscured by terrain (such as with the Manastash Ridge Radar Archived 2002-12-05 at the Wayback Machine ), but this is the exception rather than the rule, as the transmitter must normally be within line-of-sight of the receiver to ensure good low-level coverage. The key processing step in a passive radar is cross-correlation . This step acts as the matched filter and also provides

2655-477: The location of the target by simply calculating the point of intersection of the bearing with the bistatic-range ellipse . However, errors in bearing and range tend to make this approach fairly inaccurate. A better approach is to estimate the target state (location, heading and speed) from the full measurement set of bistatic range, bearing and Doppler using a non-linear filter , such as the extended or unscented Kalman filter . When multiple transmitters are used,

2714-461: The periods of silence in between each pulse transmission. As a result, the receiver must have a low noise figure , high dynamic range and high linearity . Despite this, the received echoes are normally well below the noise floor and the system tends to be externally noise limited (due to reception of the transmitted signal itself, plus reception of other distant in-band transmitters). Passive radar systems use digital receiver systems which output

2773-455: The power received to estimate the RCS of the target. The RCS estimate at various aspect angles as the target traverses the multistatic system are compared to a library of RCS models of likely targets to determine target classification. In the latest work, Ehrman and Lanterman implemented a coordinated flight model to further refine the RCS estimate. Researchers at the University of Washington operate

2832-421: The rest of the world is more challenging— transmitter powers are lower, and many networks are set up in a "single frequency network" mode, in which all transmitters are synchronised in time and frequency. Without careful processing, the net result for passive radar is like multiple repeaters jammers . Researchers at the University of Illinois at Urbana–Champaign and Georgia Institute of Technology , with

2891-403: The same term [REDACTED] This disambiguation page lists articles associated with the title PBR . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=PBR&oldid=1188345215 " Category : Disambiguation pages Hidden categories: Short description

2950-401: The sensitivity of their receivers when pointed in that direction, thereby reducing the amount of jamming received when pointed near the jammer's location. The rise of cheap computing power and digital receiver technology in the 1980s led to a resurgence of interest in passive radar technology. For the first time, these allowed designers to apply digital signal processing techniques to exploit

3009-434: The signal, channel equalization to improve the quality of the reference signal, removal of unwanted structures in digital signals to improve the radar ambiguity function or even complete reconstruction of the reference signal from the received digital signal. The principal limitation in detection range for most passive radar systems is the signal-to-interference ratio, due to the large and constant direct signal received from

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3068-421: The standard radar equation , but ensuring proper account of the processing gain and external noise limitations is taken. Furthermore, unlike conventional radar, the detection range is also a function of the deployment geometry, as the distance of the receiver from the transmitter determines the level of external noise against which the targets must be detected. However, as a rule of thumb, it is reasonable to expect

3127-748: The support of DARPA and NATO C3 Agency , have shown that it is possible to build a synthetic aperture image of an aircraft target using passive multistatic radar . Using multiple transmitters at different frequencies and locations, a dense data set in Fourier space can be built for a given target. Reconstructing the image of the target can be accomplished through an inverse fast Fourier transform (IFFT). Herman, Moulin, Ehrman and Lanterman have published reports based on simulated data, which suggest that low-frequency passive radars (using FM radio transmissions) could provide target classification in addition to tracking information. These Automatic Target Recognition systems use

3186-566: The system makes the technology particularly attractive to university laboratories and other agencies with limited budgets, as the key requirements are less hardware and more algorithmic sophistication and computational power. Much current research is currently focusing on the exploitation of modern digital broadcast signals. The US HDTV standard is particularly good for passive radar, having an excellent ambiguity function and very high power transmitters. The DVB-T digital TV standard (and related DAB digital audio standard) used throughout most of

3245-586: The systems that have been publicly announced include: Several academic passive radar systems exist as well: Research on passive radar systems is of growing interest throughout the world, with various open-source publications showing active research and development in the United States (including work at the Air Force Research Labs, Lockheed-Martin Mission Systems, Raytheon , University of Washington , Georgia Tech / Georgia Tech Research Institute and

3304-462: The target lies, with foci centred on the transmitter and receiver. If the target is at range R rx from the receiver and range R tx from the transmitter, and the receiver and transmitter are a distance L apart, then the bistatic range is R rx + R tx - L . Motion of the target causes a rate of change of bistatic range, which results in bistatic Doppler shift . Generally speaking, constant bistatic range points draw an ellipsoid with

3363-406: The transmitter and receiver positions as the focal points. The bistatic iso-range contours are where the ground slices the ellipsoid. When the ground is flat, this intercept forms an ellipse. Note that except when the two platforms have equal altitude, these ellipses are not centered on the specular point. Bistatic Doppler shift is a specific example of the Doppler effect that is observed by

3422-438: The transmitter being exploited possesses a usable radar ambiguity function and hence cross-correlation yields a useful result. Some broadcast signals, such as analogue television, contain a structure in the time domain that yields a highly ambiguous or inaccurate result when cross-correlated. In this case, the processing described above is ineffective. If the signal contains a continuous wave (CW) component, however, such as

3481-417: The transmitter. To remove this, an adaptive filter can be used to remove the direct signal in a process similar to active noise control . This step is essential to ensure that the range/Doppler sidelobes of the direct signal do not mask the smaller echoes in the subsequent cross-correlation stage. In a few specific cases, the direct interference is not a limiting factor, due to the transmitter being beyond

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