A tracking-rader system measures the coordinates of a target and provides data which may be used to determine the target path and o predict its future position.All or only part of the available rader data - range,elevation,angle,azimuth angle and doppler frequency shift may be used in predicting future position;that is,a rader might track in range,in angle,in dopple,or with any cobination.Almost any rader can be considered a tracking reder provided its output information is processed properly.But,in general,it is the method by which angle tracking is accomplished that distinguishes what is normally considered a tracking rader and a track-while-scan (TWS) rader.The former supplies continuous tracking data on a particular target,while the track-while-scan supplies sampled data on one or more targets.In generalthe continuous tracking rader and the TWS rader employ different types of equipment.
The antenna beam in the continuous tracking rader is positioned anle y a aservomechanism actuated by an reeor signal.The various methods for generating the error signal may be classified as sequential lobing,conical scan and simultaneous lobing or monopulse.The range and doppler frequency shift can also be continuously tracked,if desired by a servo-control loop actuated by an error signal generated in the rader receiver.The informatio available from a tracking reder may be presented on a
cathode-ray-tube(CRT) display for action by an operator,or may be supplied to an automatic computer which determines th target path and calculates its probable future course.
The tracking rader must first find its target before it can track.Some raders operate in a search,or acquisition,mode in order to find the target before switching to a tracking mode.Although it is possible to use a single rader for both the search and the tracking functions,such a procedure usually results in certain operational limitations.Obviously,when the rader is used in its tracking mode,it has no knowledge of other potential targets.Also,if the antenna pattern is a narrow pencil beam and if the search volume is large,a relatively long time might be required to find the target.Therefore many rader tracking systems employ a separate search rader to provide the information necessary to position the tracker on the target .A search rader,when used for this purpose,it called an acquistion rader.The acquisition rader designates targets to the tracking rader by providing the coordinates where the targets are to be found.The tracking rader acquires a target by performing a limited search in the area of the designated target coordinates.
The scanning fan-beam search rader can also provide tracking information to determine the path of the target and predict its future position.Each time the rader beam scans path the target,its coordinates are obtained.If the change in target coordinates from scan to scan is not too large,it is possible to reconstruct the track of the target from the sampled data.this may be accomplished by providing the PPI-scope operator with a grease pencil to mark the target pips on the face of the scope.A line joining those pips that correspond to the same target provides the target track.When the trafffic is so dense that operators cannot maintain pace with the information available from the rader,the target trajectory data may be processed automatically in a digital computer.The availability of small,inexpensive minicomputers has made it practical to obtain target tracks,not just target detections,from a surveillance rader.Such processing is usually called ADT(automatic detection and track).When the outputs from more than one rader are automatically combined to provide target tracks,the processing is called ADIT(automatic detection and integrated track) or IADT (integrated ADT).
A surveillance rader that provides target tracks in sometimes called a track-while-scan rader.This terminology is also applied to raders that scan a limited angular sector to provide tracking information at a high data rate on one or more targets within its field of view.Landing raders used for GCA (ground control of approach) and some missile control raders are of this type.
When the term tracking rader is used in this book,it generally refers to the continuous tracker,unless otherwise specified.
The antenna beam in the continuous tracking rader is positioned anle y a aservomechanism actuated by an reeor signal.The various methods for generating the error signal may be classified as sequential lobing,conical scan and simultaneous lobing or monopulse.The range and doppler frequency shift can also be continuously tracked,if desired by a servo-control loop actuated by an error signal generated in the rader receiver.The informatio available from a tracking reder may be presented on a
cathode-ray-tube(CRT) display for action by an operator,or may be supplied to an automatic computer which determines th target path and calculates its probable future course.
The tracking rader must first find its target before it can track.Some raders operate in a search,or acquisition,mode in order to find the target before switching to a tracking mode.Although it is possible to use a single rader for both the search and the tracking functions,such a procedure usually results in certain operational limitations.Obviously,when the rader is used in its tracking mode,it has no knowledge of other potential targets.Also,if the antenna pattern is a narrow pencil beam and if the search volume is large,a relatively long time might be required to find the target.Therefore many rader tracking systems employ a separate search rader to provide the information necessary to position the tracker on the target .A search rader,when used for this purpose,it called an acquistion rader.The acquisition rader designates targets to the tracking rader by providing the coordinates where the targets are to be found.The tracking rader acquires a target by performing a limited search in the area of the designated target coordinates.
The scanning fan-beam search rader can also provide tracking information to determine the path of the target and predict its future position.Each time the rader beam scans path the target,its coordinates are obtained.If the change in target coordinates from scan to scan is not too large,it is possible to reconstruct the track of the target from the sampled data.this may be accomplished by providing the PPI-scope operator with a grease pencil to mark the target pips on the face of the scope.A line joining those pips that correspond to the same target provides the target track.When the trafffic is so dense that operators cannot maintain pace with the information available from the rader,the target trajectory data may be processed automatically in a digital computer.The availability of small,inexpensive minicomputers has made it practical to obtain target tracks,not just target detections,from a surveillance rader.Such processing is usually called ADT(automatic detection and track).When the outputs from more than one rader are automatically combined to provide target tracks,the processing is called ADIT(automatic detection and integrated track) or IADT (integrated ADT).
A surveillance rader that provides target tracks in sometimes called a track-while-scan rader.This terminology is also applied to raders that scan a limited angular sector to provide tracking information at a high data rate on one or more targets within its field of view.Landing raders used for GCA (ground control of approach) and some missile control raders are of this type.
When the term tracking rader is used in this book,it generally refers to the continuous tracker,unless otherwise specified.
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