CA2035811C - Polystatic correlating radar - Google Patents
Polystatic correlating radarInfo
- Publication number
- CA2035811C CA2035811C CA002035811A CA2035811A CA2035811C CA 2035811 C CA2035811 C CA 2035811C CA 002035811 A CA002035811 A CA 002035811A CA 2035811 A CA2035811 A CA 2035811A CA 2035811 C CA2035811 C CA 2035811C
- Authority
- CA
- Canada
- Prior art keywords
- signal
- radar
- receivers
- received
- correlating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/003—Bistatic radar systems; Multistatic radar systems
Abstract
ABSTRACT OF THE DISCLOSURE
The polystatic correlating radar includes a plurality of radar receivers which receive a signal reflected from an object from one or more radar signal transmitters. Signals received from the plurality of receivers are cross correlated to provide high resolution of the angular location, range, and radial velocity measurements, as well as tangential velocity measurements for close targets.
The polystatic correlating radar includes a plurality of radar receivers which receive a signal reflected from an object from one or more radar signal transmitters. Signals received from the plurality of receivers are cross correlated to provide high resolution of the angular location, range, and radial velocity measurements, as well as tangential velocity measurements for close targets.
Description
POLYSTATIC CORRELATING RADAR ~-~
BAC~GROUND OF THE INVENTION
Field of the Invention: `
This invention relates generally to correlating radiometer techniques, in combination with standard radar techniques for providing hlgh resolution angular location and range gating measurements, and more particularly relates to polystatic cross correlating `~
radar techniques useful for object angular location, ranging, and radial velocity and tangential valocity measurements for close targets, useful for automotive `
collision avoidance radar, cruise control radar, and -~
self-mobile robotic systems.
Description of Related ~rt In general, conventional radar devices include a transmitting antenna emitting electromagnetic radiation generated by an oscillator, a receiving antenna, and an energy detecting receiver. The receiver provides a received radar signal to a signal processing unit where the radar signals are processed ko detect and identify the presence of a target, and to determine its location and radial velocity with re~pect to the receiver. Distance can be determined by measuring the time taken for the radar signal to travel to ths target and to return. ~he direction, or anqular location of the target may be determined by the direction of arrival of the received radar signal. Directional information is usually obtained with narrow antenna beams, and the radial velocity of the target with rsference to the --receiver can be measured by detecting shifts in the carrier frequency of the radar signal reflected from the target, commonly known as the Doppler e~fect. Continuous ~ ~-waveforms can be used to take advantage of the Doppler ~requency shift, and frequency or phase modulation of the continuous waveform permits range measurements from the received radar signals. ~i ~,-.,,. -.
:., . . - - . :
~, ~, . - . :
' ~ ' ` ' .~ ::: - :, ~3~
Modern radar typically use6 a common antenna for both transmitting and receiving, known as monostatic radar. A bistatic radar is one in which the transmitting and receiving antennae are separated by a given distance.
In early experimental radar systems this was known as CW
wave-interference radar. Such early ~xperimental radar systems utilized continuous wave~orm (CW) radar signals, and depended for detection upon interference produced between the signal receivQd directly from the transmitter and the Doppler frequency shifted signal rePle~ted by a target.
When several separate receivers are employed with a signal transmitter, the radar system is known as multistatic, or polystatic radar. An essential ~eature o~ the bi~tatic or polystatic radar is that the radiated 6ignal from the transmitter arrives at the receiver~ Erom the æcattered path which includes the target, and is also directly correlated with the receiver in a direct path from the transmitter. Information ~rom the transmitted signal allows extraction of in~ormation from the scattered signal. Thus, from the transmitted frequency, the Doppler frequency shi~t, and the phase or tim~ shift may also be determined. Although a bistatic radar can be operated with either pulse modulation or continuous waveform energy, continuous wave radar requires considerable isolation between the transmitter and .....
receiver, which is obtainable in a bistatic or polystatic radar because of inherent separation between the transmitter and receivers.
Continuous wave radar also may be used for determining range if a timing mark is applied to the CW
carrier, permitting the time of transmission and time of return to be recognized. Such a timing mark is applied to the CW carrier, permitting the time of transmission and time o~ retuxn to be recognized. Such a timing mark can be used for identifying the transmitted carrier as ~.- ~..
~ ~ ' . . . ~
. ~' :;: : ~' ~ ' - ' `, '- '; :-............ , .- : : -' :
well. A widely used technique to allow a broad spectrum of radar an~ timing informakion is frequency modulation of the carrier ~FM-CW).
Another convantional radar technigue for obtaining information from a received radar eignal is the process of range gating. Each range gate opens sequentially ju6t long enough to sample the received signal corresponding to a different range of time corresponding to a distance of travel of the signal in space.
If the bandwidth of the receiver pass bank is wide compared with that of the received signal energy, extraneous noise is introduced, reducing the signal to noise ratio of the received signal. If the receiver bandwidth is narrower than the bandwidth of the received signal, noise energy i~ reduced, along with a considerable portion of the received signal energy. This also reduces the signal to noise ratio. A matched filter functions to maximize the output peak signal to mean noise ratio. A matchad filter receiver can be replaced by a cross correlation receiver that performs the same operation. In a cross correlation receiver, an input signal is multiplied by a delayed replica of the transmitted signal, and the product is passed through a low pass filter to perform integration of the signal. It would be desirable to combine such radar techniques to permit high re~olution location and range and radial velocity measurements, as well as tangential ve}ocity measurements of a close target The present invention addresses this need.
SUMMARY OF THE INVENTION
The present invention provides for a polystatic correlating radar for detecting and locating an object at close ranges. A plurali~y of radar receivers receive a signal reflected from the object from ,,, . " , .... .. . . . . . . .
:~
; .. -:, ~:::: ,~:
, 20358~1 one or more radar signal transmitters. Signals received .
from the plurality of receivers are cross correlated to provide high resolution of the angular location, range, and radial velocity measurements, as well as tangential velocity measurements for close targets. The polystatic correlating radar of the invention can, for example, be used to implement a full performance collision avoidance/mitigation radar system. The slyst~m utilizes a polystatic radar front end to achieve high range and rate resolution, and to mini~ize false alarms.
Briafly, and in general terms, a polystatic -~
correlating radar according to the invention includes at :~
least one means for transmitting a radar signal, a 15 plurality of radar receivers including means for range ~-~
gating the received signal, means for cross correlating :~:
the radar signal received by the r~ceivers, and signal processing means for determining the angular location and the radial range of the object. In a preferred 20 embodiment, the receivers also include Doppler processing .- .~. -means, and the signal processing means includes means for ~ `
determining the tangential velocity o~ the target.
Other aspects of this invention are as follows~
A polystatic correlating radar apparatus for detecting and locating an object, comprising at least means for transmitting a radar signal; a plurality of radar signal receivers, including means for correlating said transmitted radar signal with a received signal for range gating said received radar signal for determining the range of said object from said receiver; means for crossing correlating the radar signal received by each o~
said plurality of said receivers with each said receiver .. ,,.. , . ... . - , , ~ ..
' . , 2035~
4a ~--. .
to provide corrected received radar signals from all of said receivsrs; signal processing means in electrical ~ ~-communication with said means for cross correlating said radar signals, for determing the angular location and the radial range of said object from said receivers;
wherein said signal processing includes means for determining the tangential velocity of said object relative to said receivers.
A method for correlating polystatic radar for detecting and locating an object, comprising the steps `~
of: transmitting a radar signal; receiving said radar signal reflected from said object at a plurality of receivers, and range gating said received radar signal from each of said receivers; cross correlating the receiver signal output between each of said receivers;
and processing said cross correlated receiver outputs to determine the angular location and range of said object: further including the step o~ determining the tangential velocity of said object responsive to said cross correlated receiver output.
Other aspects and advantages of the invention will become apparent from the following detailed description, and the accompanying drawings illustrating by way of example the features.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic block diagram of a polystatic correlating radar system; and FIGURE 2 is a block diagram illustrating the steps of cross correlating the received radar signals.
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.: .. . .
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As is shown in the drawings for purposes of illustration, the invention is embodied in an apparatus and a method ~or detecting and locating an object by polystatic correlating radar. The ob~ect to be detected is illuminated with wave radiation which is reflected from the object to a plurality of receivler6 which include means for determining the range of the ob~ect from the receivers. Means are provided ~or correlation beam forming the radar signal received by the receivers to provide corrected signals be~ween all of the receivers to obtain the angular location with a narrow beam response.
A signal processing unit receives the corrected beam output to determine the angular location and radial range of the target, and in a preferred embodlment also to determine the tangential velocity of the target. Doppler processing i8 also provided in the preferred embodiment for determining the radial velocity~ In a preferred embodiment, the correlation beam forming iB performed by correcting the phase of the signal received from each of the receivers, determining the cross correlation products of the corrected signals between all of the elements, and summing of the cross correlation products to provide the corrected, cross correlated beam output. Further signal processing techniques may be optionally utilized in transmitting the radar signal, and on the cross correlated beam output for impr~vement of the detection and location o~ the target.
In accordance with the invention, there is therefore provided a poly tatic correlating radar apparatus for detecting and locating an object, comprising at least one means for transmitting a radar signal: a plurality of radar signal receivers, including means synchronized with the transmitted radar signal for range gating a received radar signal for deter~ining the range of the object from the receivers, means for cross , ' :`~','` ~. ' ~ . ' 2 ~
correlating the radar signal received by each of the plurality o~ the receivers betw~en each of the receivers to provide corrected received radar signals from all of the receivers; and signal processing means ln alectrical communication with the means for cross correlating the radar signals, for determining the angular location and the radial range of the object from the receivers.
The invention also provi~es for a method for correlating polystatic radar for detecting and locating an object, comprising the steps of transmitting a radar signal; receiving a radar signal reflected ~rom said object at a plurality of receivers, and synchronizing with the transmitted radar signal for range gating each of said received radar signals; cross correlating the receiver signal output between each of said receivers;
and signal outputs to determine the angular location and range of said object.
As is shown in the drawings, a polystatic correlating radar 10 includes one or more transmitters including a transmitter antenna 12, and a transmitter amplifier 14 for amplifying a radar signal received from a master oscillator and clock 16 for kransmission by the transmitter antenna. Although conventional radar transmission fre~uencies may be used, one preferred radar carrier wave is electromagnetic energy having wavelengths from one centimeter to one millimeter, and frequencies from 30 GHz to 300 G~z. ~illimeter wav~s are advantageous in having a large bandwidth, and in having a short characteristic wavelength, allowing a small antenna size. In addition, this region of the spectrum is not widely used. This reduces the likelihood of mutual interference between radar systems. Attenuation of millimeter waves in the atmosphere can also be advantageous in minimizing the probability of mutual interference between radar systems. Alternati~ely, other .
. . . ~ . .
,:
r forms and spectxa of electromagnetic energy may aleo be used, much as acoustic waves for sonar, which i8 useful in limited ran~e operation.
The wave enargy reflected ~rom a target i~
recaived by a plurality o~ radar receivers 18a, 18b, 18c, ~ach including a recelver antenna 20a, 20b, 20CI an ampli~ier 22a, 22b, 22c, and range gating circuitry 24a, 24b, 24c. Doppler signal processing circuitry 26a, 26b, 26c, may also be provided for determining radial velocity with respect to the receivers. In order to compare the transmission signals with the received signal for range gating, the master clock and o~cillator is in electrical communication with the range gating circui~ry via line 28 and in communication with the Doppler processiny circuitry via line 30.
A cross correlation beam forming circuit: 32 receives the output of the receivers for focusing the received radar 6ignals and generating a map of obiects in the field of the view, and i5 typically provided for in a digital processing unit. The function of the cross correlation beam forming circuitry 32 is further illustrated in Fig. 2, as will be explained further below. The map defined by cross correlated beam outputs from the cross correlation unit 32 is received by the signal processing unit 34, for general tracking, identification and determination of false alarms concerning the object. The signal processing unit is capable of generating a co~plete two or three dimensional map of objects in the field of view, including range, angular location, radial velocity, tangential velocity, and radar cross section information. A signal code may be utilized by the transmitter ~or identification purposes, which can be recognized by the signal processing unit as well.
Referring to Fig. 2, the target 36 scatters the wave energy in the form of re~lected radar beams 38a, 38b, 38c, to be received by the radar signal receiver `'' units. In the preferred mode of the invention, the outputs o* the multiple radar receivers are cross correlated to obtain a narrow beam response. This correlation beam forming process is per~ormed for each angle at which resolu~ion is desired. The cross correlation beam forming process consists of the steps of correcting the phase of tha signal received from ~ach receiver, based upon the desired focal point, either two or three dimensional. Additionally, the amplitude o~ the received signal may be corrected. The phase and amplitude of the received signals are corrected in the phase correction units 40a, 40b, 40c. The output from the phase correction units i8 cros~ correlated among all of the receiver phaae correction units, a~ illustrated by the lines 42, and is directed to a summer 44 to sum all of the cross correlation products between each of the phase correction units.
As a result of the initial correction of the data of the focal point, this process ls completely general, and is applicable to both far field and near field operation. If the radar system performs Doppler processing to determine range rate, the cross correlation beam forming process must be performed after the Doppler processing. The use of multiple receivers will generate multiple range rate measurements from various angles for any given target. Applicakion of vector algebra in the signal processing unit will then yield an estimate of the tangential velocity, and thus of the total velocity vector, for that object. The accuracy of the tangential velocity estimate degrades with increa~ing range, since the angle between the several radial velocity measurements decreases with range. Thus, this determination is most accurate wlth close targets.
Similarly, improved radial velocity resolution with respect to each receiver will improve the overall tangential velocity estimate.
'J,'.~:
.. : .
: . :
~ ' , It should be understood that the transmitter of the radar system can also provide additional scan capabilities. The correlation beam forming process typically generates significant grating lobes. The directional transmit beam is then ussdl to cut off or eliminate all but one lobe (typically tha center lobe) which is then scanned, by the cross-c:orrelation beam forming unit, within the transmit coverage. However, if ```~
the transmit beam is then used to sele-ct an alternate correlation lobe, this alternate coverage will be scanned in place of the center lobe. Thus, a side total coverage is possible, at the expense of a small increase in transmitter complexity. -The transmit beam scanning may be accomplished by any of several means. Scanning may involve frequency scanning, and Butler-matrix beam ~ `
forming, although other forms of scanning may also be used. Frequency scanning would require only a simple travelling wave antenna and a voltage controlled local oscillator, which would be shared by the transmit and receive portions of the radar system. The Butler-matrix approach involves a complexity of hardware, but involves simply changing feed ports to select alternate transmit coverage.
In view of the foregoing, it has been - ~-demonstrated that the polystatic correlating radar of the invention is advantageous in providing improved resolution to obtain narrow beam response, and for providing a close range radar system, which can provide 30 not only angular location, range, and radial rate -~
information, but also tangential velocity information about the target.
Although a specific embodiment of the invention has been described and illustrated, it is clear ~`
that it is susceptible to numerous modifications and adaptations within the ability of those skilled in the art and without the exercise of the inventive faculty.
' ` ~ `' : ~ -.
. ., ~ .: :
8~
1 0 ~ '. ,`
Thus, it ehould be under~tood that variou6 changes in form, detail and u~a of the present ~nvention may be made without departin~ from the ~pirit and 8COpQ of this ;~
invention. ~-:
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. ~ .
. ~ .. . . .
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.. .: ~:, ~: : :
':`., ~ ` ' ' : '
BAC~GROUND OF THE INVENTION
Field of the Invention: `
This invention relates generally to correlating radiometer techniques, in combination with standard radar techniques for providing hlgh resolution angular location and range gating measurements, and more particularly relates to polystatic cross correlating `~
radar techniques useful for object angular location, ranging, and radial velocity and tangential valocity measurements for close targets, useful for automotive `
collision avoidance radar, cruise control radar, and -~
self-mobile robotic systems.
Description of Related ~rt In general, conventional radar devices include a transmitting antenna emitting electromagnetic radiation generated by an oscillator, a receiving antenna, and an energy detecting receiver. The receiver provides a received radar signal to a signal processing unit where the radar signals are processed ko detect and identify the presence of a target, and to determine its location and radial velocity with re~pect to the receiver. Distance can be determined by measuring the time taken for the radar signal to travel to ths target and to return. ~he direction, or anqular location of the target may be determined by the direction of arrival of the received radar signal. Directional information is usually obtained with narrow antenna beams, and the radial velocity of the target with rsference to the --receiver can be measured by detecting shifts in the carrier frequency of the radar signal reflected from the target, commonly known as the Doppler e~fect. Continuous ~ ~-waveforms can be used to take advantage of the Doppler ~requency shift, and frequency or phase modulation of the continuous waveform permits range measurements from the received radar signals. ~i ~,-.,,. -.
:., . . - - . :
~, ~, . - . :
' ~ ' ` ' .~ ::: - :, ~3~
Modern radar typically use6 a common antenna for both transmitting and receiving, known as monostatic radar. A bistatic radar is one in which the transmitting and receiving antennae are separated by a given distance.
In early experimental radar systems this was known as CW
wave-interference radar. Such early ~xperimental radar systems utilized continuous wave~orm (CW) radar signals, and depended for detection upon interference produced between the signal receivQd directly from the transmitter and the Doppler frequency shifted signal rePle~ted by a target.
When several separate receivers are employed with a signal transmitter, the radar system is known as multistatic, or polystatic radar. An essential ~eature o~ the bi~tatic or polystatic radar is that the radiated 6ignal from the transmitter arrives at the receiver~ Erom the æcattered path which includes the target, and is also directly correlated with the receiver in a direct path from the transmitter. Information ~rom the transmitted signal allows extraction of in~ormation from the scattered signal. Thus, from the transmitted frequency, the Doppler frequency shi~t, and the phase or tim~ shift may also be determined. Although a bistatic radar can be operated with either pulse modulation or continuous waveform energy, continuous wave radar requires considerable isolation between the transmitter and .....
receiver, which is obtainable in a bistatic or polystatic radar because of inherent separation between the transmitter and receivers.
Continuous wave radar also may be used for determining range if a timing mark is applied to the CW
carrier, permitting the time of transmission and time of return to be recognized. Such a timing mark is applied to the CW carrier, permitting the time of transmission and time o~ retuxn to be recognized. Such a timing mark can be used for identifying the transmitted carrier as ~.- ~..
~ ~ ' . . . ~
. ~' :;: : ~' ~ ' - ' `, '- '; :-............ , .- : : -' :
well. A widely used technique to allow a broad spectrum of radar an~ timing informakion is frequency modulation of the carrier ~FM-CW).
Another convantional radar technigue for obtaining information from a received radar eignal is the process of range gating. Each range gate opens sequentially ju6t long enough to sample the received signal corresponding to a different range of time corresponding to a distance of travel of the signal in space.
If the bandwidth of the receiver pass bank is wide compared with that of the received signal energy, extraneous noise is introduced, reducing the signal to noise ratio of the received signal. If the receiver bandwidth is narrower than the bandwidth of the received signal, noise energy i~ reduced, along with a considerable portion of the received signal energy. This also reduces the signal to noise ratio. A matched filter functions to maximize the output peak signal to mean noise ratio. A matchad filter receiver can be replaced by a cross correlation receiver that performs the same operation. In a cross correlation receiver, an input signal is multiplied by a delayed replica of the transmitted signal, and the product is passed through a low pass filter to perform integration of the signal. It would be desirable to combine such radar techniques to permit high re~olution location and range and radial velocity measurements, as well as tangential ve}ocity measurements of a close target The present invention addresses this need.
SUMMARY OF THE INVENTION
The present invention provides for a polystatic correlating radar for detecting and locating an object at close ranges. A plurali~y of radar receivers receive a signal reflected from the object from ,,, . " , .... .. . . . . . . .
:~
; .. -:, ~:::: ,~:
, 20358~1 one or more radar signal transmitters. Signals received .
from the plurality of receivers are cross correlated to provide high resolution of the angular location, range, and radial velocity measurements, as well as tangential velocity measurements for close targets. The polystatic correlating radar of the invention can, for example, be used to implement a full performance collision avoidance/mitigation radar system. The slyst~m utilizes a polystatic radar front end to achieve high range and rate resolution, and to mini~ize false alarms.
Briafly, and in general terms, a polystatic -~
correlating radar according to the invention includes at :~
least one means for transmitting a radar signal, a 15 plurality of radar receivers including means for range ~-~
gating the received signal, means for cross correlating :~:
the radar signal received by the r~ceivers, and signal processing means for determining the angular location and the radial range of the object. In a preferred 20 embodiment, the receivers also include Doppler processing .- .~. -means, and the signal processing means includes means for ~ `
determining the tangential velocity o~ the target.
Other aspects of this invention are as follows~
A polystatic correlating radar apparatus for detecting and locating an object, comprising at least means for transmitting a radar signal; a plurality of radar signal receivers, including means for correlating said transmitted radar signal with a received signal for range gating said received radar signal for determining the range of said object from said receiver; means for crossing correlating the radar signal received by each o~
said plurality of said receivers with each said receiver .. ,,.. , . ... . - , , ~ ..
' . , 2035~
4a ~--. .
to provide corrected received radar signals from all of said receivsrs; signal processing means in electrical ~ ~-communication with said means for cross correlating said radar signals, for determing the angular location and the radial range of said object from said receivers;
wherein said signal processing includes means for determining the tangential velocity of said object relative to said receivers.
A method for correlating polystatic radar for detecting and locating an object, comprising the steps `~
of: transmitting a radar signal; receiving said radar signal reflected from said object at a plurality of receivers, and range gating said received radar signal from each of said receivers; cross correlating the receiver signal output between each of said receivers;
and processing said cross correlated receiver outputs to determine the angular location and range of said object: further including the step o~ determining the tangential velocity of said object responsive to said cross correlated receiver output.
Other aspects and advantages of the invention will become apparent from the following detailed description, and the accompanying drawings illustrating by way of example the features.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic block diagram of a polystatic correlating radar system; and FIGURE 2 is a block diagram illustrating the steps of cross correlating the received radar signals.
:'' ~
-:~
~..
,, ,.~,, .' ~ ~ ' :
.: .. . .
' .~ ;~ :'~ .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As is shown in the drawings for purposes of illustration, the invention is embodied in an apparatus and a method ~or detecting and locating an object by polystatic correlating radar. The ob~ect to be detected is illuminated with wave radiation which is reflected from the object to a plurality of receivler6 which include means for determining the range of the ob~ect from the receivers. Means are provided ~or correlation beam forming the radar signal received by the receivers to provide corrected signals be~ween all of the receivers to obtain the angular location with a narrow beam response.
A signal processing unit receives the corrected beam output to determine the angular location and radial range of the target, and in a preferred embodlment also to determine the tangential velocity of the target. Doppler processing i8 also provided in the preferred embodiment for determining the radial velocity~ In a preferred embodiment, the correlation beam forming iB performed by correcting the phase of the signal received from each of the receivers, determining the cross correlation products of the corrected signals between all of the elements, and summing of the cross correlation products to provide the corrected, cross correlated beam output. Further signal processing techniques may be optionally utilized in transmitting the radar signal, and on the cross correlated beam output for impr~vement of the detection and location o~ the target.
In accordance with the invention, there is therefore provided a poly tatic correlating radar apparatus for detecting and locating an object, comprising at least one means for transmitting a radar signal: a plurality of radar signal receivers, including means synchronized with the transmitted radar signal for range gating a received radar signal for deter~ining the range of the object from the receivers, means for cross , ' :`~','` ~. ' ~ . ' 2 ~
correlating the radar signal received by each of the plurality o~ the receivers betw~en each of the receivers to provide corrected received radar signals from all of the receivers; and signal processing means ln alectrical communication with the means for cross correlating the radar signals, for determining the angular location and the radial range of the object from the receivers.
The invention also provi~es for a method for correlating polystatic radar for detecting and locating an object, comprising the steps of transmitting a radar signal; receiving a radar signal reflected ~rom said object at a plurality of receivers, and synchronizing with the transmitted radar signal for range gating each of said received radar signals; cross correlating the receiver signal output between each of said receivers;
and signal outputs to determine the angular location and range of said object.
As is shown in the drawings, a polystatic correlating radar 10 includes one or more transmitters including a transmitter antenna 12, and a transmitter amplifier 14 for amplifying a radar signal received from a master oscillator and clock 16 for kransmission by the transmitter antenna. Although conventional radar transmission fre~uencies may be used, one preferred radar carrier wave is electromagnetic energy having wavelengths from one centimeter to one millimeter, and frequencies from 30 GHz to 300 G~z. ~illimeter wav~s are advantageous in having a large bandwidth, and in having a short characteristic wavelength, allowing a small antenna size. In addition, this region of the spectrum is not widely used. This reduces the likelihood of mutual interference between radar systems. Attenuation of millimeter waves in the atmosphere can also be advantageous in minimizing the probability of mutual interference between radar systems. Alternati~ely, other .
. . . ~ . .
,:
r forms and spectxa of electromagnetic energy may aleo be used, much as acoustic waves for sonar, which i8 useful in limited ran~e operation.
The wave enargy reflected ~rom a target i~
recaived by a plurality o~ radar receivers 18a, 18b, 18c, ~ach including a recelver antenna 20a, 20b, 20CI an ampli~ier 22a, 22b, 22c, and range gating circuitry 24a, 24b, 24c. Doppler signal processing circuitry 26a, 26b, 26c, may also be provided for determining radial velocity with respect to the receivers. In order to compare the transmission signals with the received signal for range gating, the master clock and o~cillator is in electrical communication with the range gating circui~ry via line 28 and in communication with the Doppler processiny circuitry via line 30.
A cross correlation beam forming circuit: 32 receives the output of the receivers for focusing the received radar 6ignals and generating a map of obiects in the field of the view, and i5 typically provided for in a digital processing unit. The function of the cross correlation beam forming circuitry 32 is further illustrated in Fig. 2, as will be explained further below. The map defined by cross correlated beam outputs from the cross correlation unit 32 is received by the signal processing unit 34, for general tracking, identification and determination of false alarms concerning the object. The signal processing unit is capable of generating a co~plete two or three dimensional map of objects in the field of view, including range, angular location, radial velocity, tangential velocity, and radar cross section information. A signal code may be utilized by the transmitter ~or identification purposes, which can be recognized by the signal processing unit as well.
Referring to Fig. 2, the target 36 scatters the wave energy in the form of re~lected radar beams 38a, 38b, 38c, to be received by the radar signal receiver `'' units. In the preferred mode of the invention, the outputs o* the multiple radar receivers are cross correlated to obtain a narrow beam response. This correlation beam forming process is per~ormed for each angle at which resolu~ion is desired. The cross correlation beam forming process consists of the steps of correcting the phase of tha signal received from ~ach receiver, based upon the desired focal point, either two or three dimensional. Additionally, the amplitude o~ the received signal may be corrected. The phase and amplitude of the received signals are corrected in the phase correction units 40a, 40b, 40c. The output from the phase correction units i8 cros~ correlated among all of the receiver phaae correction units, a~ illustrated by the lines 42, and is directed to a summer 44 to sum all of the cross correlation products between each of the phase correction units.
As a result of the initial correction of the data of the focal point, this process ls completely general, and is applicable to both far field and near field operation. If the radar system performs Doppler processing to determine range rate, the cross correlation beam forming process must be performed after the Doppler processing. The use of multiple receivers will generate multiple range rate measurements from various angles for any given target. Applicakion of vector algebra in the signal processing unit will then yield an estimate of the tangential velocity, and thus of the total velocity vector, for that object. The accuracy of the tangential velocity estimate degrades with increa~ing range, since the angle between the several radial velocity measurements decreases with range. Thus, this determination is most accurate wlth close targets.
Similarly, improved radial velocity resolution with respect to each receiver will improve the overall tangential velocity estimate.
'J,'.~:
.. : .
: . :
~ ' , It should be understood that the transmitter of the radar system can also provide additional scan capabilities. The correlation beam forming process typically generates significant grating lobes. The directional transmit beam is then ussdl to cut off or eliminate all but one lobe (typically tha center lobe) which is then scanned, by the cross-c:orrelation beam forming unit, within the transmit coverage. However, if ```~
the transmit beam is then used to sele-ct an alternate correlation lobe, this alternate coverage will be scanned in place of the center lobe. Thus, a side total coverage is possible, at the expense of a small increase in transmitter complexity. -The transmit beam scanning may be accomplished by any of several means. Scanning may involve frequency scanning, and Butler-matrix beam ~ `
forming, although other forms of scanning may also be used. Frequency scanning would require only a simple travelling wave antenna and a voltage controlled local oscillator, which would be shared by the transmit and receive portions of the radar system. The Butler-matrix approach involves a complexity of hardware, but involves simply changing feed ports to select alternate transmit coverage.
In view of the foregoing, it has been - ~-demonstrated that the polystatic correlating radar of the invention is advantageous in providing improved resolution to obtain narrow beam response, and for providing a close range radar system, which can provide 30 not only angular location, range, and radial rate -~
information, but also tangential velocity information about the target.
Although a specific embodiment of the invention has been described and illustrated, it is clear ~`
that it is susceptible to numerous modifications and adaptations within the ability of those skilled in the art and without the exercise of the inventive faculty.
' ` ~ `' : ~ -.
. ., ~ .: :
8~
1 0 ~ '. ,`
Thus, it ehould be under~tood that variou6 changes in form, detail and u~a of the present ~nvention may be made without departin~ from the ~pirit and 8COpQ of this ;~
invention. ~-:
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Claims (14)
1. A polystatic correlating radar apparatus for detecting and locating an object, comprising at least means for transmitting a radar signal;
a plurality of radar signal receivers, including means for correlating said transmitted radar signal with a received signal for range gating said received radar signal for determining the range of said object from said receiver;
means for crossing correlating the radar signal received by each of said plurality of said receivers with each said receiver to provide corrected received radar signals from all of said receivers;
signal processing means in electrical communication with said means for cross correlating said radar signals, for determining the angular location and the radial range of said object from said receivers;
wherein said signal processing includes means for determining the tangential velocity of said object relative to said receivers.
a plurality of radar signal receivers, including means for correlating said transmitted radar signal with a received signal for range gating said received radar signal for determining the range of said object from said receiver;
means for crossing correlating the radar signal received by each of said plurality of said receivers with each said receiver to provide corrected received radar signals from all of said receivers;
signal processing means in electrical communication with said means for cross correlating said radar signals, for determining the angular location and the radial range of said object from said receivers;
wherein said signal processing includes means for determining the tangential velocity of said object relative to said receivers.
2. The apparatus of claim 1, wherein said means for cross correlating includes means for correcting the phase of the signal received from each of said receivers, means for determining the cross correlation product of the corrected signals between all of the receivers, and means for summing said cross correlation products to provide a corrected receiver signal, whereby said polystatic correlating radar apparatus is enabled to determine the angular location with a narrow beam response.
3. The apparatus of claim 1, wherein each of said radar receivers includes means for determining a Doppler frequency shift of said receiver signal.
4. The apparatus of claim 1, wherein said means for transmitting a radar signal includes means for scanning the frequency of said transmitted radar signal.
5. A method for correlating polystatic radar for detecting and locating an object, comprising the steps of:
transmitting a radar signal;
receiving said radar signal reflected from said object at a plurality of receivers, and range gating said received radar signal from each of said receivers;
cross correlating the receiver signal output between each of said receivers; and processing said cross correlated receiver outputs to determine the angular location and range of said object:;
further including the step of determining the tangential velocity of said object responsive to said cross correlated receiver output.
transmitting a radar signal;
receiving said radar signal reflected from said object at a plurality of receivers, and range gating said received radar signal from each of said receivers;
cross correlating the receiver signal output between each of said receivers; and processing said cross correlated receiver outputs to determine the angular location and range of said object:;
further including the step of determining the tangential velocity of said object responsive to said cross correlated receiver output.
6. The method of claim 5, wherein said step of cross correlating said receiver signal outputs comprises cor-recting the phase of said signals received from each of receivers to focus said received signals, determining the cross correlation product of the corrected signals between each of said receivers, and summing said cross correlation products to determine the angular location with a narrow beam response.
7. The method of claim 5, further including the step of determining the Doppler frequency shift of said received radar signal from each of said receivers.
8. The method of claim 5, wherein said step of transmitting includes scanning said transmitted radar signal.
9. The method of claim 5, wherein said step of transmitting further includes the step of beam shaping said transmitted radar signal.
10. The method of claim 5, wherein said step of transmitting a radar signal comprises illuminating said object with millimeter wave radiation.
11. The method of claim 5, wherein said step of transmitting comprises identifying said transmitted radar signal with a signal code.
12. The method of claim 11, wherein said step of receiving further includes identifying a transmitted signal from characteristics of said signal code.
13. The method of claim 5, wherein said step of cross correlating said receiver outputs includes the step of processing said received signals with said transmitted radar signal to select a lobe of said received radar signals and to substantially eliminate other lobes of the signal.
14. The method of claim 5, wherein said step of deter-mining the tangential velocity of said object comprises sequentially determining the location of said object and determining tangential velocity by vector algebra.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/490,032 US4994809A (en) | 1990-03-07 | 1990-03-07 | Polystatic correlating radar |
| US490,032 | 1990-03-07 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2035811A1 CA2035811A1 (en) | 1991-09-08 |
| CA2035811C true CA2035811C (en) | 1994-10-04 |
Family
ID=23946333
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002035811A Expired - Lifetime CA2035811C (en) | 1990-03-07 | 1991-02-06 | Polystatic correlating radar |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4994809A (en) |
| EP (1) | EP0446678B1 (en) |
| JP (1) | JP2651054B2 (en) |
| CA (1) | CA2035811C (en) |
| DE (1) | DE69128734T2 (en) |
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-
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- 1991-02-20 EP EP91102466A patent/EP0446678B1/en not_active Expired - Lifetime
- 1991-02-20 DE DE69128734T patent/DE69128734T2/en not_active Expired - Fee Related
- 1991-03-06 JP JP3065622A patent/JP2651054B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE69128734D1 (en) | 1998-02-26 |
| JP2651054B2 (en) | 1997-09-10 |
| DE69128734T2 (en) | 1998-04-30 |
| JPH04220582A (en) | 1992-08-11 |
| EP0446678A2 (en) | 1991-09-18 |
| EP0446678B1 (en) | 1998-01-21 |
| EP0446678A3 (en) | 1993-04-07 |
| US4994809A (en) | 1991-02-19 |
| CA2035811A1 (en) | 1991-09-08 |
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