The Stanford Dish , known locally as the Dish , is a radio antenna in the Stanford foothills. The 150-foot-diameter (46 m) dish was built in 1961 by the Stanford Research Institute (now SRI International). The cost to construct the antenna was $ 4.5 million, and was funded by the United States Air Force . In the 1960s the Dish was used to provide information on Soviet radar installations by detecting radio signals bounced off the moon.
30-523: Later on, the Dish was used to communicate with satellites and spacecraft. With its unique bistatic range radio communications, where the transmitter and receiver are separate units, the powerful radar antenna was well-suited for communicating with spacecraft in regions where conventional radio signals may be disrupted. At one point, the Dish transmitted signals to each of the Voyager craft that NASA dispatched into
60-431: 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
90-425: 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
120-425: 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
150-507: 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 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
180-427: A transmitter and receiver which are separated by a few tens of kilometres for electrical isolation, but as 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
210-473: 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
240-473: 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
270-511: 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
300-451: 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
330-470: Is a more detailed image than would have been rendered with just one radar instrument. Bistatic imaging can be useful in differentiating between ice and rock on the surface of a remote target, such as the moon , due to the different ways that radar reflects off these objects—with ice, the radar instruments would detect "volume scattering", and with rock, the more traditional surface scattering would be detected. Monostatic radar Bistatic radar
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#1732855872184360-415: 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
390-429: 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
420-510: 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
450-510: 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
480-399: 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
510-399: 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
540-406: 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
570-406: 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
600-455: The aircraft seen by the transmitter, and is unaffected by stealth coatings or shapings. The RCS in this mode 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
630-409: The bistatic angle near 180 degrees. This is a special case of bistatic radar, known as 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
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#1732855872184660-534: The dish is known for its rolling hills and beautiful views, which on a clear day extend to San Jose, San Francisco, and the East Bay. The Stanford Running Club hosts an annual Dish Race and fun run that forms a 3.25 mile loop around the Dish trail. While hikers, walkers, and runners are welcome, biking and dogs at the dish are not allowed on the trail. The opening hours are as per the schedule below, roughly matching daylight hours: As of June 2018, 360 cows were grazing on
690-408: 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
720-536: The grounds of the Stanford Dish. Stanford leases the land to farmers who own the cows. Bistatic range Bistatic radar 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
750-500: The location of the target in the fence). A multistatic radar system 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
780-487: The outer reaches of the solar system. In 1982 it was used to rescue the amateur radio satellite UoSAT-1 . The dish is still actively used today for academic and research purposes. It is owned by the U.S. Government and operated by SRI International. It is used for commanding and calibrating spacecraft and for radio astronomy measurements. The area around the Dish offers a popular 3.5 mile recreational trail, visited by an average of 1,500–1,800 people daily. The trail around
810-462: 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
840-462: 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
870-455: 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
900-406: 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
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