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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to radar systems for detecting threats in
accordance with stored beam parameters of signal emitters associated with
the threats and, more particularly, to a radar system for detecting
threats in accordance with adaptively redefined stored beam parameters
associated with the threats. In other aspects the present invention
relates to radar systems for tracking signals, and more particularly, to
radar systems which verify that tracking has not been transferred to a
second signal having parameters which are similar to the original signal.
2. Description of the Prior Art
As is known in the radar art, devices which employ active radar systems
necessarily contain signal emitters whose emitted signals, commonly known
as beams and so referred to herein, may be used to identify the device
after the characteristic parameters of the emitted signals, or beams, have
been established and associated with the device. That is, devices which
employ active radar systems contain at least one signal emitter which can
be used to identify the device after the characteristic beam parameters
for the emitter are determined and have been associated with the
particular device. In the military sciences, devices which employ active
radar systems include offensive and defensive weapons as well as their
delivery vehicles. Although such weapons and their delivery vehicles are
often used in a defensive posture, the presence of a weapon or a delivery
vehicle is considered to be a threat to the successful mission and/or
survival of the opposing military force so that all such military devices
employing active radar systems are, quite properly, designated as threats
by the opposing force. Therefore, according to the general experience of
the radar art as applied to use in the military sciences, it is well known
in the prior art that military threats containing active radar systems may
be detected in accordance with at least one beam which has a known
association with the threat.
In the prior art, threat detection systems have detected threats by
detecting the presence of beams which have characteristic parameters and
comparing these detected beams to stored beams having similar
characteristic parameters and which are known to be associated in various
combinations with particular threats. The associations of the stored beams
with a particular threat are cataloged as a stored threat so that when the
comparison of the detected beams and the stored beams indicates the
presence of one or more detected beams substantially similar to one or
more stored beams that are cataloged as a stored threat the threat
detection system indicates the presence of a detected threat. Although
these prior art systems are adequate to detect threats whose actual beam
parameters correspond to the stored beam parameters associated with the
threat, the prior art systems are unable to adaptively redefine their
stored beam parameters in response to detected beams which exhibit
parameters that are different than those of the stored beams previously
associated with the threat. Therefore, it has been possible for a threat
to confuse prior art threat detection systems, or to avoid detection
altogether by causing the emitters of its radar system to exhibit beam
parameters deviating from the predetermined, or stored, beam parameters
previously associated with the and cataloged as a stored threat. Although
some prior art threat detection systems afford the flexibility that their
stored beam parameters and stored threat signals may be altered so that
their stored beams may be redefined and associated with new stored threats
once the deviations of the actual beam parameters and their respective
threat associations have become known, it remains for some external
intelligence gathering operation to ascertain the appropriate stored beam
parameters and associate these different stored beams with the appropriate
stored threats. For any radar system which detects devices employing
active radars, the time necessary to perform this intelligence gathering
operation is inconvenient and, for threat detection systems engaged in
military conflicts, this delay could be fatal to the success of the
mission. Moreover, it is unlikely that every combination of actual beam
parameters for each particular threat that will be encountered will be
available as a stored beam parameter of a stored threat. Therefore, there
was a need in prior art threat detection systems for a capability to
adaptively redefine the parameters of stored beams which are associated
with a particular stored threat, and adapt the system's stored threats in
accordance therewith.
Prior art radar systems have been developed for tracking the incidence of
threat signals upon an antenna that is sensitive to microwave energy. Some
of these systems are capable of detecting a situation in which the radar
system has lost track of a threat signal. However, for the situation in
which a second signal having similar paramters is substituted for the
signal which was originally being tracked, these prior art radar sytems
could confuse the second signal with the original signal and begin to
track the second signal as though it were the original. There was,
therefore, a need for a radar system which would not only track signals
but would also be able to detect a situation in which a signal having
parameters similar to the parameters of the originally tracked signal had
been substituted for the original signal in the course of operation of the
radar system.
SUMMARY OF THE INVENTION
In accordance with the presently disclosed apparatus for detecting threats
which are associated with at least one beam having parameters which are
controllably varied, a receiver detects beams having selected parameters
of predetermined values. These detected beams are provided to a central
processing unit in which they are compared with parameters of stored beams
to detect a particular threat in accordance with the known association of
the stored beams with that threat. When the comparison of the selected
parameters of the detected beams with the stored beam parameters indicates
the prsence of a predetermined number of detected threats and the detected
beams associated with the different detected threats differ in a selected
number of parameters but are otherwise identical, the radar system
determines that the threat is actively varying those parameters of the
detected beams and expands the respective parameters of the corresponding
stored beams, thereby limiting threat detection errors due to the active
variation of the detected beam parameters by the threat.
In accordance with the present invention, a radar system includes a
receiver for detecting signals, a tracker for predicting the occurrence of
the signals detected by the receiver, and a central processing unit which
cooperates with the receiver and the tracker to verify that the radar
system has continuously maintained track of a particular signal over its
course of operation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the apparatus employed in the preferred
embodiment of the present invention.
FIG. 2 illustrates the waveforms of two threat signals which have single
and multiple beams respectively, and also shows various parameters of the
threat signals.
FIG. 3 is a more detailed block diagram of the multiplexed tracker of FIG.
1 which predicts the time of arrival of pulses of a beam at the receiver.
FIG. 4 is a more detailed block diagram of the There generator shown in
FIG. 3.
FIG. 5 is a more detailed block diagram of the window generator shown in
FIG. 3.
FIG. 6 is a more detailed block diagram of the error correction control
shown in FIG. 3.
FIG. 7 is a more detailed block diagram of the pointer hold register shown
in FIG. 3.
FIG. 8 illustrates the operation of the signal tracker of FIG. 1 and FIGS.
3 through 7 while tracking a pulse train of a single beam.
FIG. 9 illustrates the operation of the signal tracker of FIG. 1 and FIGS.
3 through 7 while tracking a pulse train having multiple beams.
FIG. 10 represents typical waveforms which illustrate the operation of the
disclosed radar system for adaptively redefining stored beam parameters
associated with particular threats in response to detected beam
parameters.
FIG. 11 is a flow chart illustrating the entrance of the operation of the
central processing unit to an adaptive mode and the operation of the
central processing unit in collecting all the detected threats which
correspond to a single stored threat.
FIG. 12 is a flow chart describing the operation of the central processing
unit in making an investigation of the detected beams associated with
detected threats corresponding to a single stored threat to determine if
the radio frequency excursion of any of the stored beams of the stored
threat can be redefined to more nearly match the radio frequency excursion
of the detected beams.
FIG. 13 is a flow chart illustrating the operation of the central
processing unit in making a list of the various stored beams that are
associated with a particular stored threat.
FIG. 14 is a flow chart illustrating the operation of determining the
detected threat associated with the highest number of detected beams.
FIG. 15 is a flow chart describing the compilation of the identification
numbers of the detected threat having the highest number of detected
beams.
FIG. 16 is a flow chart which describes the comparison of the detected
beams of the detected threat having the most beams with the detected beams
of the other detected threats.
FIG. 17 is a flow chart illustrating the deletion of a detected beam of a
detected threat from the detected threats which correspond to a single
stored threat in accordance with FIG. 12.
FIG. 18 shows typical waveforms which illustrate a typical example for
which the present invention determines whether the radar system has
continuously maintained track of a particular signal.
FIG. 19 is a flow chart describing the operaion of the central processing
unit in determining whether the radar system has continuously maintained
track of a particular signal.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As was explained previously, threat detectors of the prior art detected
threats by comparing certain parameters of detected beams with stored beam
parameters that were previously known to be associated with particular
threats. However, in the prior art, threats could confuse or avoid
detection by these threat detectors by actively varying the parameters of
their beams. This was because the prior art threat detectors were unable
to adaptively redefine their stored beam parameters in response to
variations in the parameters of detected beams when such variations
indicated that the detected beam parameters were being actively controlled
by the threat. In contrast to this, the preferred embodiment of the
present invention maintains the detection of a threat by adaptively
redefining stored beam parameters in accordance with variations in the
parameters of detected beams when such variations are indicative of the
active control of those parameters by the threat.
The preferred embodiment of the disclosed apparatus for detecting a threat
which actively varies the parameters of its beams is described in relation
to FIG. 1. In the operation of the disclosed apparatus, a processing
device which, in the example of the preferred embodiment, is a multiplexed
tracker 10 which is further described in relation to FIGS. 3-7, but which
could equivalently be a signal intercept system as well known to those
skilled in the pertinent art, cooperates with a central processing unit 12
to predict the incidence of a threat signal on an antenna 14 which is
coupled to a receiver 15. The threat signal is comprised of phase coherent
beams whose parameters are characteristic of the threat. Initially,
predetermined parameters of beams are stored in the central processing
unit 12 with these predetermined parameters hereafter referred to as
stored beams. The associations of these stored beams with various
particular threats in accordance with predetermined information is also
stored in the memory of the central processing unit 12, with the
association of one or more of those stored beams with a threat hereafter
referred to as a stored threat. The central processing unit 12 may be
comprised of a general purpose digital computer such as the Westinghouse
Millicomputer CP-1138 which has been in public use for more than one year
and which is more fully described in a publication entitled "CP-1138
Millicomputer", copyright 1972 by Westinghouse Electric Corporation, and
published by Westinghouse Electric Corporation, Defense and Electronic
Systems Center, Systems Development Division, Baltimore, Maryland.
According to the operation of the disclosed apparatus, the central
processing unit 12 provides the information of the stored threats and
their respective stored beams to the receiver 15 through the receiver
control 20. Specifically the central processing unit 12 causes the
receiver 15 to detect beams having parameters substantially similar to the
parameters of the stored beams by providing signals in lines 16, 18 and 22
to a receiver control 20. The signals provided to the receiver control 20
substantially correspond to the radio frequency (hereafter referred to as
RF) and amplitude parameters of the stored beams. The receiver control 20
includes a threshold register 24 and a radio frequency register (hereafter
referred to as RF register) 26 and an enable signal generator 28 which
includes a dwell counter 30, an AND gate 32 and a clock 34. The threshold
register 24 and the RF register 26 respectively operate in response to the
signals provided by the central processing unit 12 on lines 16 and 18 to
provide an amplitude threshold control signal on line 36 and an RF control
signal on line 38 to the receiver 15. The enable signal generator 28
provides an enable signal on line 40 to the receiver 15 in response to the
timing signal provided by the processing unit 12 on line 22 to the dwell
counter 30. This timing signal establishes a value in the dwell counter 30
which is counted down by the rate at which pulses are provided from the
clock 34 to the dwell counter 30. The dwell counter 30 provides an output
signal to the AND gate 32 such that the AND gate 32 provides an enable
signal on line 40 to the receiver 15 as long as the value of the dwell
counter 30 is positive. Therefore, if the clock 34 operates at a fixed
rate, the duration of the enable signal on line 40 will be determined by
the magnitude of the value established by the timing signal provided to
the dwell counter 30 by the central processing unit 12.
The antenna 14 collects microwave or radio frequency (RF) signals which are
propagating in a line which coincides with the antenna position and
provides these signals to the receiver 15. In response to the control
signals provided to the receiver control 20, the receiver 15 detects
signals that are collected by the antenna 14 which substantially
correspond to the RF frequency control signal on line 38 and to the
amplitude threshold control signal on line 36. The receiver 15 may be
comprised of any such well-known device which, for example, may be a
Varian receiver, Part No. VZZ-3017 or, alternatively, Varian receiver,
Part. No. VZX-3017.
Typical signals which are detected by the receiver 15 are illustrated in
waveforms 2A and 2B of FIG. 2. The time of arrival (TOA), radio frequency
(RF), and amplitude of the pulses of signals detected by the receiver 15
are respectively provided on lines 46, 48 and 50 to a buffer memory 52
which is comprised of a time of arrival memory (TOA memory) 54, a radio
frequency memory (RF memory) 56, and an amplitude memory 58. For each
pulse detected by the receiver 15, the TOA memory 54 stores the time of
arrival (TOA) of the pulse, the RF memory 56 stores the RF of the signal
whose envelope determines the pulse, and the amplitude memory 58 records
the amplitude of each detected pulse in response to address and write
signals provided by a buffer memory control 66.
The buffer memory control 66 provides the appropriate address and write
signals to the buffer memory 52 to provide for the storage of the
information detected by the receiver 15 in the TOA memory 54, the RF
memory 56 and the amplitude memory 58. The buffer memory control 66 also
provides the appropriate address and read signals to provide for the
delivery of the pulse information stored in the buffer memory 52 to the
central processing unit 12. The buffer memory control 66 may be comprised
of any suitable combination of logic elements which perform the
above-described functions as is well known to those skilled in the
pertinent art. The example of the preferred embodiment of FIG. 1 includes
an AND gate 73 which is responsive to a TOA receiver strobe signal on line
74 and which supplies an enable signal on lines 75 and 76 to a one-shot
generator 77 and a counter 78 respectively. The one-shot generator 77
provides a TOA write signal on line 80 and a second one-shot generator 82,
which is responsive to a receiver conversion signal on line 84, provides
an amplitude and an RF write signal on line 86. The counter 78 provides
the TOA, RF and amplitude memory address signals on lines 88 and 90 in
response to an enable signal from the AND gate 73 on line 76, or in
response to the combination of read and address signals on lines 94 and 96
respectively from the processing unit 12. The address signals of the
counter 78 are also provided to a comparator 98 on lines 100 and 102. The
comparator 98 is hard wired to provide a maximum count signal on line 104
to the AND gate 73 unless the comparator 98 determines that the capacity
of the buffer memory 52 has been exceeded.
In the operation of the buffer memory control 66 to store signals detected
by the receiver 15 in the buffer memory 52, the AND gate 73 receives the
TOA receiver strobe signal on line 74 which is provided by the receiver 15
whenever a pulse is detected by the receiver provided a verify command
network 105 is conductive. If the maximum count signal is simultaneously
present on line 104 when the receiver strobe signal is received, the AND
gate 73 provides an enable signal to the counter 78 which provides a pulse
address on lines 88 and 90 to the TOA memory 54, the RF frequency memory
56, and the amplitude memory 58. At the same time, the AND gate 73
provides an enable signal to the one-shot generator 77 which, as well
known in the art, provides a short TOA write pulse on line 80 in response
to an increase in the amplitude level of the signal on line 75 to permit
the receiver 15 to write the time of arrival (TOA) of the detected pulse
into the TOA memory 54 at the address designated by the counter 78. If the
receiver 15 determines that the detected pulse which arrived at the
receiver 15 at one-shot no 75 the time stored at the address of the TOA
memory 54 contained the requisite RF and amplitude called for by the
amplitude and RF control signal on lines 36 and 38 respectively, the
receiver 15 provides a receiver conversion on line signal to the one-shot
generator 82 on line 84. In a manner similar to the one-shoot generator
77, the one-shot generator 82 provides an RF and amplitude write pulse on
line 86 in response to an increase in the amplitude level of the signal on
line 84 to permit the receiver 15 to write the RF and amplitude of the
detected signal pulse into the RF memory 56 and the amplitude memory 58
respectively at addresses determined by the counter 78 and corresponding
to the address at which the TOA of the pulse was stored in the TOA memory
54. The comparator 98 is hard wired such that, when all the addresses of
the TOA memory 54 have been filled, the maximum count signal is not longer
provided on line 104. Without the presence of the maximum count signal on
line 104, the AND gate 73 no longer provides an enable signal on line 75,
or 76 and, therefore, no more TOA's are stored in the memory buffer 52.
The maximum count signal provided on line 104 is extinguished so that the
receiver 15 cannot write over received signal pulse parameters which have
already been stored in the memory buffer 52 thereby resulting in
unreliable received signal pulse data.
When the receiver 15 detects the TOA of a detected signal pulse but the
detected pulse does not have the requisite RF and amplitude required by
the threshold and RF control signals on lines 36 and 38, the one-shot
generator 82 receives no receiver conversion signal on line 84
corresponding to the TOA receiver strobe signal on line 74 so that no RF
and amplitude write pulse is generated by the one-shot generator 82.
Therefore, no RF or amplitude information corresponding to the detected
pulse is stored in the RF memory 56 or the amplitude memory 58 at the
address corresponding to the address of the TOA memory 54 at which the TOA
of that pulse is stored. Subsequently, when the central processing unit 12
addresses the TOA memory 54 to obtain this TOA value, it is also given the
information that no suitable RF or amplitude information corresponding to
this TOA was obtained by the receiver 15.
The central processing unit 12 obtains the TOA, RF and amplitude of the
detected signals from the buffer memory 52 by providing a read signal on
line 94 and an address signal on line 96 to the counter 78. The read and
address signals from the central processing unit 12 cause the counter 78
to provide address and read signals on lines 88 and 90 which cause the TOA
memory 54, the RF memory 56 and the amplitude memory 58 to provide the
TOA, RF and amplitude of the particular detected signal pulse which is
addressed on lines 68, 70 and 72 respectively. The receiver control 20,
the receiver 15, the buffer memory 52, and the buffer memory control 66
thus far described in relation to FIG. 1 thus provide a means for
detecting signals having selected TOA, RF and amplitude parameters that
are within a predetermined range of values.
The detected signals which are detected by the receiver 15 and delivered
through the memory buffer 52 to the central processing unit are sorted
into detected threat signals comprised of phase coherent detected beams by
comparison of the detected signals with the stored threats and stored
beams in accordance with conventional threat signal acquistion techniques.
These detected threat signals and detected beams may be established by any
of several well-known signal acquisition methods such as appropriately
programming the central processing unit 12 with a sort routine. In general
the TOA, RF and amplitude for each pulse of a detected signal, as stored
is the buffer memory 52, is made available on lines 68, 70 and 72 to the
central processing unit 12 which compares selected parameters of the
signals detected by the receiver 15 and stored in the buffer memory 52
with the parameters of the stored beams which are considered to be
exhibited by particular threats based on predetermined information to
establish detected beams from the detected signals. The central processing
unit 12 then detects threats by associating these detected beams with the
stored threats that catalog the stored beams corresponding to the detected
beams. Accordingly, the central processing unit 12 provides a means for
detecting threat signals from the signals detected by the receiver 15 by
comparing the detected signals with stored beams that are associated with
stored threats to detect beams transmitted by the threat, and by detecting
threat signals comprised of the detected beams where said detected threat
signals correspond to the stored threat signals associated with the stored
beams that are comparable to the detected beams.
The detected threat signals of phase coherent detected beams are provided
by the central processing unit 12 to the multiplexed tracker 10 whbich is
hereafter more fully described in relation to FIGS. 3 through 7. The
multiplexed tracker 10 tracks the detected threat signals by making
predictions as to the RF and PRI of the detected threat signals and
providing an RF control signal to the receiver control 20 on line 18 and a
window signal on line 40 to cause the receiver 15 to detect this threat
signal as it is collected by the antenna 14. The TOA and RF of signals
detected by the receiver 15 in response to the control signal are provided
to the multiplexed tracker 10 which then corrects errors in its
predictions as hereafter more fully explained in relation to FIGS. 3
through 9.
As previously stated, threats are detected by comparing the detected beams
with stored beams that are considered to be associated with specific
threats, the associations of the stored beams being cataloged as stored
threats. Periodically, the central processing unit 12 examines the
detected beams to determine whether the detected beams indicate that the
threat is actively varying selected parameters of the detected beams as is
more particularly described in relation to the flow charts shown in FIGS.
11 through 17. The central processing unit 12, as appropriately programmed
in accordance with FIGS. 11 through 17 provides a means for comparing
detected threats having detected beams with at least one selected
parameter to determine a range of values for the selected parameter of
said detected beams, and comparing the range of values for the selected
parameter of said detected beams with the range of values for the selected
parameter of said stored beams corresponding to said detected beams to
determine whether the range of values for the selected parameter of said
stored beams should be adaptively redefined in accordance with the ranges
of values of the detected beams of said detected threats. If redefinition
of the parameter of the detected beams is indicated from the comparison
made by the central processing unit 12 between the ranges of the detected
beams and the ranges of the stored beams, the central processing unit
appropriately redefines the limits of the range of the parameters of the
stored beams so that detected beams are thereafter detected from signals
provided to the central processing unit 12 from the detecting means in
relation to these redefined stored beams, consequently eliminating the
redundant indication of threats due to the variation of the detected beams
parameters by the threat. The detected threat signals that are detected in
accordance with the adaptively redefined stored beams are provided to the
multiplexed tracker 10 which predicts the further incidence of the
detected threats. The multiplexed tracker 10 therefore provides a means
for controlling the detecting means in response to the detected threat
signals of the comparing means to cause the detecting means to detect
threat signals in accordance with the adaptively redefined stored beams of
the comparing means.
As was previously explained, the strobe signal of the receiver 15 is
transmitted to the buffer memory control 66 to cause the storage of
detected beam pulses in the buffer memory 52 in accordance with the
foregoing description, provided the verify command network 105 is
conductive. As shown in FIG. 1, the verify command network 105 includes an
inverter 106, an AND gate 107, an AND gate 108, an OR gate 109, an
inverter 110 and an AND gate 111. The inverter 106 is responsive to a
verify command signal of the control processing unit 12 which, as
explained more particularly in relation to FIGS. 18 and 19, provides the
verify command signal when the disclosed tracking system verifies that
tracking has been maintained on a particular threat signal. The AND gate
107 is responsive to the output of the inverter 106 and to the enable
signal generator 28. The AND gate 108 is responsive to the verify command
signal provided by central processing unit 12, and is also responsive to
an inverter 110 which is responsive to a tracker prediction signal
provided by the multiplexed tracker 10. The OR gate 109 is responsive to
the outputs of the AND gates 107 and 108 and the AND gate 111 is
responsive to the output of the OR gate 109 and the strobe signal of the
receiver 15. The verify command network 105 will be conductive to the
strobe signals of the receiver 15 whenever a signal is applied to the AND
gate 111 from the OR gate 109. However, no signal will be applied to the
AND gate 111 from the OR gate 109 unless the OR gate 109 receives an
output signal either from the AND gate 107 or from the AND gate 108. The
AND gate 107, which s responsive to the inverter 106, provides an output
to the OR gate 109 whenever there is no verify command signal provided to
the inverter 106 and there is an enable signal provided on line 40. The
AND gate 108 provides an output to the OR gate 109 whenever there is a
verify command signal from the central processing unit 12 and there is no
tracker prediction signal provided by the multiplexed tracker 10.
Therefore, the conduction of the strobe signal from the receiver 15 to the
buffer memory control 66 is dependent upon the presence of the enable
signal on line 40 in combination with the absence of a verify command
signal from the central processing unit 12, or the presence of a verify
command signal in combination with the absence of a tracker prediction
signal from the multiplexed tracker 10.
In the regular operation of the disclosed tracker system, the central
processing unit 12 operates on the premise that the multiplexed tracker 10
has continuously maintained track of a particular threat signal.
Therefore, in the regular operation of the disclosed tracker system, no
verify command signal will be provided by the central processing unit 12
to verify that the multiplexed tracker 10 has continuously maintained
track of the same threat signal. When there is no verify command signal
provided to the AND gate 108, the AND gate 108 will be non-conductive. In
this normal mode of operation, therefore, the verify command network 105
will be non-conductive to the strobe signal of the receiver 15 unless the
AND gate 107 is conductive. When no verify command signal is provided by
the central processing unit 12, no signal is provided to the inverter 106
and the inverter provides a signal to the AND gate 107. The AND gate 107
then provides an output to the OR gate 109 whenever the enable signal is
present on line 40. In response to an output from the AND gate 107, the OR
gate 109 provides an output to the AND gate 111 which then provides an
output to the buffer memory control 66 in response to a strobe signal from
the receiver 15. Accordingly, whenever there is an enable signal in
combination with the absence of a verify command signal, the verify
command network 105 provides an output to the buffer memory control 66 in
response to a strobe signal from the receiver 15, or, equivalently, the
verify command network 105 is conductive to the strobe signal of the
receiver 15.
When the central processing unit 12 determines that a verification should
be performed as to whether the multiplexed tracker 10 has continuously
maintained track of a particular threat signal, the central processing
unit 12 provides a verify command signal to the inverter 106 so that no
output is provided from the inverter 106 to the AND gate 107. Therefore,
the verify command network 105 will be conductive to the strobe signals of
the receiver 15 only if the verify command signal is provided to the AND
gate 108 in combination with the absence of a tracker prediction signal
from the multiplexed tracker 10. As will be explained more specifically in
relation to FIGS. 3 and 5, the multiplexed tracker 10 will provide a
tracker prediction signal to the AND gate 108 coincident with a verify
command signal from the central processing unit 12 in combination with the
prediction of a pulse in the threat signal by the multiplexed tracker 10.
When the verify command signal is provided to the AND gate 108 in the
absence of a tracker prediction signal from the multiplexed tracker 10 to
the inverter 110, the AND gate 108 provides an output to the OR gate 109.
In response to an output from the AND gate 108, the OR gate 109 provides
an output to the AND gate 111 so that the AND gate 111 provides an output
to the buffer memory control 66 in response to a strobe signal from the
receiver 15. Equivalently, it can be said that the verify command network
105 is made conductive to the strobe signal of the receiver 15 in response
to the verify command signal from the central processing unit 12 in the
absence of a prediction signal from the multiplexed tracker 10.
Waveforms 2A and 2B of FIG. 2 illustrate two waveforms which may be
considered to comprise typical examples of threat signals, each of which
are known to be characteristic of a particular threat. Waveform 2A is
comprised of the envelope of a radio frequency (RF) signal which has RF
excursions at periodic intervals such that the envelope of the RF signal
forms pulses of a predetermined width which occur at predictable times.
The elapsed time between correlative points on successive pulses is
generally referred to as the pulse repetition interval or PRI. Waveform 2B
is also comprised of the envelope of a radio frequency signal (RF signal)
which is similar to the waveform 2A with the exception that the pulse
repetition interval (PRI) between successive pulses of the waveform is not
always the same. However, the pulses of waveform 2B are phase coherent so
that the pulse repetition interval (PRI) values between the successive
pulses remain the same over the duration of the signal. Moreover, the
pattern of the pulses of waveform 2B can be seen to repeat themselves over
predetermined intervals which are generally referred to as cycle times. In
the particular example of waveform 2B, a cycle time includes four
successive, phase coherent pulses of the waveform so that an alternative
way of considering waveform 2B is to consider it to be the linear
combination of four, phase coherent pulse trains whose pulses are
separated by one cycle time and whose phases are staggered by intervals
equivalent to the pulse repetition intervals of the waveform 2B. In
accordance with this description of the threat signal illustrated as the
waveform 2B, the waveform may be referred to as a pulse waveform having
four stagger levels or, equivalently, as a threat signal comprised of four
beams. Referring to the threat signal illustrated as the waveform 2A, it
will now be understood that the threat signal is comprised of a single
stagger level, or equivalently, a single beam. The beam parameters which
are of particular interest for the example of the preferred embodiment
herein described are the PRI and RF of each beam. However, it will become
apparent upon an understanding of the operation of the preferred
embodiment, that the scope of the present invention extends to the control
of any particular threat signal parameter which, for example, could
include the number of beams, scan type, or pulse doppler or continuous
wave identification bits or any combination of such threat signal
parameters.
The threat signals determined from the RF, TOA and amplitude information
provided to the central processing unit 12 from the memory buffer 52 are
tracked by the multiplexed signal tracker 10 described in FIGS. 3-9. The
signal tracker 10 makes predictions as to the RF and PRI of received
threat signals and provides corresponding control signals to the receiver
control 20 to cause the receiver 15 to detect the threat signals if they,
in fact, occur. The signal tracker of FIG. 3 tracks all phase coherent
beams of a single threat signal provided at least one beam of the threat
signal is present by maintaining all PRI values for multiple beam threat
signals in a single memory associated with each threat signal. The order
of access of the memory containing the PRI values is determined by a beam
pointer whose time of access is controlled by a beam monitor which is
operative with a particular address in a TOA memory that is associated
with the threat signal that is being tracked.
FIG. 3 shows a block diagram of the preferred embodiment of the multiplexed
tracker 10, portions of which are further described in FIGS. 4, 5, 6, and
7. The detected threat signal which, for purposes of illustration, may be
considered to be the pulse train shown in waveforms 2A and 2B of FIG. 2,
are detected by the receiver 15 and delivered through the buffer memory 52
to the central processing unit 12 which establishes an initial PRI and
phase condition for each of the phase coherent beams of the threat signal.
For each beam of the threat signal, the central processing unit 12 stores
an initial PRI value at a specified address in a PRI memory 110 and an
initial RF value at a corresponding address in an RF memory 112.
Simultaneously, the central processing unit 12 dedicates a tracker address
in a TOA memory 114 to the threat signal and stores a value representing
the predicted time of arrival (TOA) of the next pulse in the threat signal
at this address. Therefore, the number of independent threat signals that
can be tracked is limited only by the number of tracker addresses in the
TOA memory 114 and the number of beams of a particular threat signal that
can be tracked is limited only by the number of addresses in the PRI
memory 110 and the RF memory 112 which are associated with a particular
tracker address of the TOA memory 114.
The predicted time of arrival stored in the address of the TOA memory 114
is counted down by a means for counting toward the predicted time of
arrival of pulses contained in all beams of a detected threat signal. The
counting means includes the TOA memory 114, a time clock 116, a roll
generator 118, a roll multiplexer 120, a TOA subtracter multiplexer 122, a
TOA subtracter 124, and a TOA register 126. Each time the predicted time
of arrival stored at the address of the TOA memory 114 that is dedicated
to the detected threat signal is accessed by the time clock 116, the roll
generator 118 delivers a signal, whose value is substantially equal to
.DELTA.t, to terminal A of the TOA subtracter 124 through the roll
multiplexer 120 and the subtracter multiplexer 122. The roll generator 118
may, in practice, be a hard wired bit of the roll multiplexer 120. The
initial predicted time of arrival previously stored in the TOA memory 114
in accordance with the initial acquisition of the detected threat signal
is provided to terminal B of the TOA subtracter 124, which then subtracts
the value of the signal provided at terminal A from the value of the
signal provided at terminal B to provide an output whose value is
substantially equal to the value of the predicted time of arrival for the
signal pulse decremented by an amount .DELTA.t. In the design of the roll
generator 118, the value of .DELTA.t is made equal to one roll which is
the real time which elapses between successive accesses of a single
tracker address in the TOA memory 114 by the time clock 116 so that the
predicted time of arrival of the next pulse of the signal is decremented
in real time. The output of the TOA subtracter 124 is provided to the TOA
register 126 which then delivers this value to the tracker address in the
TOA memory 114. The next time the tracker address of the TOA memory 114 is
accessed by the real time clock 116, this decremented value of the initial
predicted TOA is again itself decremented by again subtracting from it a
value equal to one roll in the TOA subtracter 124, as described above.
This decrementing process continues until the value provided to the
tracker address in the TOA memory 114 by the TOA register 126 is less than
or equal to some predetermined value of time which will be identified as
W/2.
When the predicted time of arrival stored in the tracker address of the TOA
memory 114 has been counted down to the value of W/2, the value of the
memory address is provided to a There generator 128 that causes the There
generator 128 to provide a There signal which performs two functions.
First, the There signal is provided as a control input to the roll
multiplexer 120 to cause the roll multiplexer 120 to convey a predicted
pulse repetition interval for the next pulse of the detected threat signal
from the PRI memory 110 to terminal A of the TOA subtracter 124 through
the subtracter multiplexer 122. This function provides for a variation in
the predicted pulse repetition interval of the next pulse one example of
which is illustrated by the waveform 9A which is hereafter discussed in
relation to FIG. 9. Secondly, the There signal provided by There generator
128 is delivered to a window generator 130 that provides a window pulse
which corresponds to the pulse of the detected threat signal which was
predicted to arrive at the receiver 15 at time W/2 subsequent to the
generation of the There signal. The There generator 128 and the window
generator 130 are described later in further detail in FIGS. 4 and 5,
respectively.
The window signal of the window generator 130 is provided to line 40 (FIG.
1) which provides the enable signal to the receiver 15 thereby enabling
the receiver 15 to detect pulses corresponding to the amplitude and RF
determined by the amplitude and RF control signals on the lines 36 and 38.
The window signal is simultaneously provided to the error correction
control 132 along with the signal pulses detected by receiver 15 and count
signals from the time clock 116 to provide phase and pulse repetition
interval error signals. In addition, the error correction control 132
provides flag signals which serve to control the multiplexing of phase
corrections to be made to the predicted time of arrival stored in the TOA
memory 114, pulse repetition interval corrections to be made to the
predicted pulse repetition interval stored in the PRI memory 110, and RF
corrections to be made to the predicted RF stored in the RF memory 112, as
will be explained below.
As will be further described in relation to FIG. 6, the error correction
control 132 provides flag one, flag two, and flag three | | |
