Note: Descriptions are shown in the official language in which they were submitted.
- C~ 1 3352 1 2 73850-1
This invention relates to tar~et ldentlflcation
system6 and in particular to systems for ldentifylng to a
weapon delivery system a target selected by a target marker.
Frequently in modern warfare a target ~elected by an
observer is requlred to be attacked by an independent weapon
delivery system, this being of special importance when the
observer is not in a posltlon to dellver the most suitable type
of weapon. One typical example of such a requlrement ls the
calling of air strlkes by ground troops. In an instance such
as this a saturation attack may be delivered, but lnstances
wlll arlse where lt is posslble to select a single target whlch
may be attacked by a single weapon. For example, an alrcraft
may be called upon to destroy a slnqle tank which may not be
vlslble to the pllot due to camouflage or other factors.
Slmple use of a radio link to describe the location of the
target to the pilot of a fast-moving, possibly supersonic,
aircraft is far from satisfactory.
With any such target identification system it is to
be expected that a selected target will attempt to employ
countermeasures, both electronic and physical. An effective
system has therefore to be able to combat any such
countermeasures to ensure correct identification of the target.
It is an ob~ect of the invention to provide a target
identification system for uniquely and accurately identifying
to a weapon delivery system a target selected by a target
marker.
According to the present invention there is provided
a target identification sy6tem which includes a target marker
adapted to direct radiation at a target, a weapon delivery
system to which the target i8 to be identified, means for
establishing between the target marker and the weapon dellvery
system a two-way communication channel over which pulsed
~ s
- 1 3352 1 2
73850-1
radiation may be transmitted from one to the other by
reflectlon from the selected target, and means carried by the
target marker and the weapon delivery system for so encodlng
the radiation transmitted over the communication channel as to
identify uniguely the selected target to the weapon delivery
system.
The expression "weapon delivery system" as used in
this specification is intended to cover all means of delivering
a weapon to its target. It includes, for example, aircraft
delivering guided or ballistic missiles, guns, and guided
missiles themselves. The expression ~target marker" is used to
indicate apparatus for selecting a target. 5uch apparatus may
be vehicle-mounted.
An embodiment of the invention will now be described,
by way of example, with reference to the accompanying drawings,
in which.-
Eigure 1 is a schematic diagram illustrating anapplication of the invention;
Figure 2 is a part-schematic diagram of apparatus
carried by the target marker; and
Figures 3 and 4 are part-schematic diagrams of
apparatus carried by the weapon delivery system.
Referring now to Figure 1, this shows a target 10,
target marker 11 and weapon delivery system (e.g. an aircraft)
12. The target marker 11 carries an infra-red laser which is
arranged to emit pulses of radiation at the selected target 10.
The radlation is scattered from the target, and some of it
returns to the target marker at time 2t2 to indicate the range
of the target. Similarly, some of the radiation is detected by
the aircraft 12. When the aircraft detects the radiation from
the target it transmits an interrogating pulse towards the
target. Since radiation from the target marker 11 reached the
.
3~ 1 3~52 1 2
73850-1
aircraft by reflection from the target it may be asæumed that
radiation from the aircraft will reach the target marker by the
æame path. If the aircraft emitæ a pulse at a time to, then it
will reach the target maker at a time (to + t1 + t2) where t
and t2 are
,_~,,A~ CA~33~ 7
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the times taken for radiation to cover the two legs o~ the path
shown in ~igure 1, The equipment in the target marker is
arranged to respond to the interrogating pulse by transmitting a
further pulse after a delay time (tc - 2t2), where tc is a
predetermined delay interval and t2 is already known from the
target range, Hence the aircra~t will receive a response to
its interrogating pulse after a time interval of
(to + tl ~ t2) ~ (tC - 2t2) + tl + t2-
or (to + 2t1 + tc)'
The aircraft will also receive a pulse reflected
directly from the target a~ter a time (to ~ 2t1), which indicates
the range of the target ~rom the aircraft. The equipment
carried by the aircra~t is thus able to extract the time tc and
confirm that this equals the predetermined delay interval. This
then confirms that the target marker and aircraft are looking at
the same target.
I~ the target 10 attempts to con~use the aircra~t
equipment by itself illuminating a false target 13, then any
radiation emitted from the aircraft will not result in the
necessary coded response including the time interval tc, and it
will thus be apparent that the target selector and the aircraft
are not looking at the same target,
The above description sets out the principle of
operation of the invention, Figure 2 shows the equipment
carried by the target marker 11, The equipment may be divided
into two sections, one comprising the radiation-transmitting or
receiving section, and the other comprising the controlling
electronics, The radiation source shown in ~igure 2 is a
laser 20, preferably having a solid active medium and emitting
in~ra-red radiation. The laser active medium is excited by a
flash-tube 21 controlled by a triggered power supply 22,
Included in the optical cavity of the laser is an electro-optic
ED,283/DNB _ 4 _
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`
device 23, which, when pulsed electrically, allows the optical
cavity to resonate and emit infra-red radiation through a
telescope optical system shown schematically at 24. A
photo-sensitive device 25 i5 located so as to receive some of
the radiated energy to provide an accurate indication of the
time of emission of the laser pulse. A receiving optical
telescope, illustrated schematically at 26, has its optical
axis fixed parallel to that of the transmitting tele cope 24,
and directs any received radiation on to a photo-sensitive
device 27.
The output of device 27 is fed through an amplifier 28
to an input of each of two AND gates 29 and 30. Gate 29 has
as its other input the "reset" output of a bistable circuit 31,
and the output of gate 29 is connected to one input of an OR
15 gate 32. The other input of gate 32 is provided by a pulse
generator 33 which generates a continuous train of pulses.
The output of OR gate 32 forms the "set" input to the bistable
circuit, and the corresponding "set" output is connected to the
other input of AND gate 30. The output of gate 30 is
20 connected to the "reset" input of the bistable circuit 31 The
"set" output of the bistable circuit is also connected to one
input of a two-input AND gate 34, and to the other input is
connected a source of clock pulses CP. The output of this
gate 34 i8 connected to the input of a counter 35. The
25 outputs from the counter are connected to a comparator 36
which also receives the inputs from a register 37 The
output from the comparator 36 triggers the electro-optic device
23 in the laser cavity. The outputs from the counter 35 are
also connected to a second comparator 38 which also receives
30 inputs from a second register 39 The output from
comparator 38 triggers the power supply 22 of the laser flash-
tube 21. The output from the photo-sensitive device 25 is fed
.~
i ED.283/DNB - 5 -
1 3 3 5 2 ~ 2
~,
through an ampli~ier 40 to the "reset" input of the counter 35.
The operation of the equipment shown in Figure 2 is as
follows:-
The pulse generator 33 is arranged to operate at a
predetermined rate, say ten pulses per second, which i8 knownat least approximately to the equipment in the aircraft. A
pulse from the pulse generator 33 passes through OR gate 32 and
sets the bistable circuit 31. The set output from the bistable
circuit primes the AND gate 34 so that each subsequent clock
pulse i8 fed into the counter 35, the clock pulse frequency
b~ing very much higher than that of the pulse generator 33.
When the oount stored in the counter reaches the value
representing a time (tc - td) set into register 39, the
comparator 38 causes the flash-tube 21 to be fired. The inputs
to the counter continue, and at a later time tc, represented by
the value stored in register 37, the comparator 36 triggers
the electro-optic device 23 so that a laser pulse is transmitted
towards the target. The time tc is a predetermined delay time,
whilst the time td is the time taken by the laser to build up
maximum energy storage in the laser active medium after the
~lash-tube has been fired. The time tc represents the coding
feature of the particular target marker.
When a laser pulse is emitted the photo-sensitive
device 25 detects this and causes the counter 35 to be reset
to zero. Further clock pulses are still applied to the
counter which is now concerned with the measurement o~ target
range. On receipt o~ a signal reflected from the target and
received by photo-electric device 27, the output of amplifier 28
is applied to AND gates 29 and 30. Gate 30 already has applied
to it the "set" output of the bistable circuit, and so the
application o~ the signal from amplifier 28 causes the bistable
circuit to change to its "reset" state. The gate 34 is
ED.283/DNB - 6 -
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$ c , 1 3 3 5 2 1 2
;. .~
therefore closed and the counter 35 stopped. The count stored
in counter 35 represents the time between emission of the laser
pulse and receipt of the reflected signal, that is 2t2, and
hence indicates the range to the,target.
The "reset" output applied to gate 29 has no effect
since the other input has now ceased. The counter remains
~ixed until the pulse generator 33 produces its next pulse to
"set" the bistable circuit via gate 32 and restart the procedure.
Hence the equipment in the *arget marker will continue to
transmit laser pulses under the control of the pulse generator,
and will monitor the range to the target.
The weapon delivery system, such as an aircraft, is
ready to detect any radiation scattered from a target in its
field of view having the predetermined repetition rate, When
such radiation is received the aircra~t emits an interrogating
pulse which is reflected by the target towards the target marker,
This pulse is arranged to reach the target marker shortly be~ore
the next pulse is due from the pulse generator 33. This is
possible because the transmission time (t1 + t2) will be
measured in microseconds whereas the interval between pulses
~rom the pulse generator is o~ the order o~ a hundred milliseconds,
The interrogating pulse is thus received at the target
marker whilst the counter 35 is static and holding the count 2t2,
The output from the detector 27 ~inds gate 30 blocked because
bistable circuit 31 is in its "reset" state, but passes through
gate 29 to "set" the bistable circuit via gate 32 and open
gate 34 to further clock pulses, The counter thus advances
~rom the count 2t2 to the count tc a~ter an interval (tc - 2t2)
after which the laser 20 is fired as described above, The
target marker has thus replied to an interrogating pulse ~rom
the aircraft by itself transmitting a pulse after the time delay
(tc ~ 2tc) microseconds,
~D.283/DNB - 7 -
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1 3352 1 2
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Subsequently the target marker equipment i9 controlled
by successive interrogating pulses from the aircraft.
~ igures 3 and 4 show the equipment carried by the
weapon delivery system (e.g. the aircraft). This equipment is
more complex than that carried by the target marker, and may be
divided into three sections. These are the radiation trans-
mïtting and receiving section, the steering and stabilising
arrangements for the optical system, and the controlling
electronics.
As in the case of the target marker equipment, the
radiation source shown is an infra-red laser 50 excited by a
flash-tube 51 which is controlled by a triggered power supply 52.
Included in the optical cavity o~ the laser is an electro-optic
device 53 which when pulsed electronically allows the optical
cavity to resonate and emit infra-red radiation through an
optical system shown at 54. A receiving optical telescope,
preferably of the reflecting type, has an optical system
represented by a lens 55 which directs the received radiation
onto a beam-splitting element 56. Some o~ the received
radiation passes through the beam-splitter on to a photo-
sensitive device 57 whilst some is reflected back onto a
photo-sensitive device 58. The device 58 is made in four
sectors so that the relative magnitudes of the outputs from
the sectors indicates the direction of the incident radiation,
relative to the optical axis of receiving telescope 55.
The outputs of the photo-sensitive device 58 are used
to control a servo system which steers the optical systems o~
the two telescopes in elevation and azimuth so as effectively
to point the two telescopes in the direction of the radiation
source, that is the target. The servo system comprises a
signal processor 59 which controls an associated servo unit 60.
The signal processor takes the signals from the ~our sectors of
`~ ~D.283/DNB - 8 -
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- 1 33521 2
detector 58, say signals A, B, C, and D,and delivers three
outputs. One o~ these (~ ) represents the sum (A + B + C + D)
of the four signRl~, whilst the other two represent the
elevation signal (A + B) - (C+D) and the azimuth signal (A + D)
- (B + C) for the se~vo unit 60, The servo unit, as well as
moving the two telescopes mechanically also produces an error
signal output which is applied to an inhibit gate 61 which
controls the firing of the laser, and delivers a "fire laser"
~ æignal to Figure 4, As with the target marker, the flash-
tube 51 of the laser i9 fired through its power unit 52 before
the device 53 in the laser optical cavity is activated via the
delay device 62. A photo-electric device 63 i9 provided
to detect the instant of firing of the laser, This detector
is ¢onnected to an amplifier 64, the output of which is used
to strobe an amplifier 65 having applied to it the output of
the photo-electric device 57. The strobing is performed by
a range gate generator 66,
The output of the amplifier 64 i8 connected to the
"set" input of the bistable device 67, The "set" output of
the bistable device is connected to one input of each of two
AND gate9 68 and 69. Each of these two last-mon-bioned gates
has a clock pulse input CP, and gate 69 also has an inhibit f_.~, . .
input from a counter as described below, The output gate 68
forms the stepping input of a master counter 70, The final
stage of this counter, shown as a separate stage 70A, has its
output connected to the inhibit input of gate 69. The output .
of gate 69 forms the input of a second counter 71, the range
counter, The reset input of the range counter 71 is
connected to the output of amplifier 65, The outputs of the
various stages of the range counter are connected to a
comparator 72 and to a display register 73. A coding register
74 also has its outputs connected to the comparator 72, The
~D,283/DN13 _ 9 _
.
1 3352 1 2
output of the comparator is connected to the "set" input of a
monostable device 75, the output of which is a "transponding
gate" signal ~G. The transponding gate signal may conveniently
be used to reset bistable device 67 and counters 70 and 71 in
preparation for the next r~n~i ng shot,
The master counter has one more stage than is
necessary to register the maximum possible value of the time
interval 2t1 (see Figure 1) between the emission by the aircraft
of an interrogating pulse and the returning primary echo from
the target. Such ~;ml~m time interval will be denoted as 2t1m.
The controlling electronics carried by the aircraft
also includes means for authenticating the received signals~
and this i8 shown in ~igure 4.
The sum signal output from the servo signal
processor 59 is applied through an AND gate 100 to a signal
selector 101. As shown this comprises an arrangement of gates
in two parallel paths. One path has a gate primed by a signal
P, whilst the other path comprises a divide-by-two circuit and
a gate primed by a signal Q. The outputs from the two paths
pass to a monostable circuit and through a pulse-shaper 102 to
a decoding register 103. The decoding register is basically
a shift register through which the input pulses are shifted by
the clock pulses ~P, emerging ~rom the register at some later
time. The output from the decoding register is applied to a
coincidence gate generator 104. This is basically a monostable
circuit arranged to produce a 300 microsecond gating pulse when
triggered by an output from the decoding register. The output
of the coincidence gate generator forms one input of a two-
input AND gate 105, the other input being the output from signal
selector 101. The output of the coincidence gate generator 104
also forms one input of an inhibit gate 106, the inhibit input
being provided by the output from the monostable device in the
ED.283/DNB - 10 -
1 3352 1 2
~signal selector 101. The output of gate 106 forms one input
of AND gate 107.
The output o~ AND gate 105 is connected to the "set"
input of a bistable device 108. The output of the decoding
register 103 is also connected via a pulse shaper 109 to the
"reset" input of this bistable device. The set and reset
outputs of the bistable device are connected to a three-stage
shift register 110. The shift clock input is applied from
the pulse shaper 109. The various stages of the shift
register 110 are applied to a 9ystem of gates 111, forming a
"signal lock condition" generator such that when all three
stages of the shift register are in a predetermined state a
bistable 112 is "set" to produce a "signal lock" output SL.
Bistable cir¢uits 108 and 112, shift register 110
and gating circuit 111 together form a three-coincidence
detector shown within a broken line.
The signal lock output SB forms another input o~
gate 107 and one input of an AND gate 113, the other input of
the latter being the output of the signal selector 101. The
output of gate 113 is used to set a monostable device 114 which
provides a signal SS which strobes the outputs of the servo
signal processor 59 (~igure 3). The signal lock output S~
also form9 one input of AND gate 115, together with signals
from the pulse shaper 109 and the reset output of bistable
device 108. The output of gate 115 is connected to the
decoding register 103,
The sum output ~ ~rom the signal processor 59
(~igure 3) is applied to two gates 116 and 117, to the latter
as an inhibit input. To the other input of each of these
gate~ is applied the TG output of monostable device 75. The
output of gate 116 is applied to the "set" input of bistable
device 118, the set output of which is applied to the inhibit
ED.283/DNB
1 3 3 5 2 1 2
,,
input of AND gate 107 and to an inhibit input of gate 119.
~istable device 118 has its "reset" input connected to the F~
output of gate 61 (~igure 3). The other input of gate 119 is
the output of gate 117, which also provides a system reset
signal RS connected to various units shown on Figures 3 and 4.
The output of gate 119 is connected to the shift input of a
JE flip-flop 120. The outputs of this are the control signals
P and Q for the gates in the signal selector 101.
The output of gate 116 i~ also connected to the input
of OR gate 121, the other input being connected to the output
o~ gate 105. The output of gate 121, together with the "reset"
output of bistable device 112, form the inputs of AND gate 122
and the reset input for auxiliary counter 123, clocked by
clock pulses CP. The output of gate 122 forms the "set"
input of a bistable device 124, the reset input of which is the
output of the pl~i 1 iary counter 123. ~he "set" output of the
bistable device 124 is connected to the decoding register 103.
The output of the auxiliary counter 123 forms the "Laser Fire"
(~F) input of gate 61 (Figure 3). The output of AND gate 107,
together with the ~ output from bistable device 112 and the TG
output from monostable device 75 form the inputs of OR gate 125,
the output of which forms the second input of A~D gate 100.
As already indicated, the function of the equipment
shown in Figures 3 and 4 is to detect radiation reflected from
a designated target, interrogate the target marker and at the
same time measure the target range, and finally detect a
response from the target marker and check its authenticity.
Whilst the aircraft is awaiting receipt of a train
of laser pulses from the target the equipment of Figureq 3
and 4 is set to its initial conditions. Bistable device 67
is reset and the master counter 70 and range counter 71 are
~et to zero. The required coding delay is set into the
ED.283/DN~ - 12 -
CA 1 33521 2
.coding register 74, and the display register 73 is cleared.
The decoding register 103 is cleared and the shift register 110
in the coincidence detector is reset. The JK flip-flop 120
is set to the desired state, say to give the output P for the
signal selector 101.
The receiving telescope carried by the aircraft is
arranged such that the sectored detector 58 has a wide-angle
of view, whilst detector 57 has only a narrow angle. Hence,
supposing that a target is detected whilst the telescope is
out of ~ nment~ only detector 58 will receive the incoming
pulse train. Even in the rare case of perfect telescope
alignment, amplifier 65 is blocked by the absence of a strobe
pulse from range gate generator 66.
Incoming pulses detected by detector 58 are applied
as the output ~ via the signal processor 59 through gate 100
to the signal selector 101. Gate 100 is opened by the
presence of the ~ output from bistable 112anda signal is
passed through stage 101 via the path containing the gate
primed by the signal P from flip-flop 120. The output from
the signal selector 101 passes through the pulse shaper 102
to the decoding register 103. This is arranged to detect
pulses occurring at the preset pulse rate, and such pulses
passing through the decoding register 103 are applied to the
coincidence gate generator 104. This generates a 300 micro-
second gating pulse for each received pulse, these gating
pulses being applied to AND gate 105. The other input to
AND gate 105 is the signal selector output, Hence if the
pulses emerging from the coincidence gate generator are
produced by a genuine received pulse from the target marker,
they will coincide with later received pulses passing through
the signal selector. The resultant output from gate 105 is
applied to bistable device 108 and hence to the shift register 110.
'~ ED.283/DNB - 13 -
1 3352 1 2
The output from gate 105 also passes through OR gate
121 to trigger the auxiliary counter 123 and, together with
signal from bistable device 112 applied to gate 112 "set"
bistable device 124. The output of this bistable device
blanks off the decoding register 103 for a time determined by
the auxiliary counter 123, which then resets bistable device 124.
The blRnking signal applied to the decoding register prevents
pulses emerging from the decoding register other than at the
expected time determined by the preset pulse rate.
The above process is repeated until three coincidences
between coincidence gate pulses from generator 104 and pulses
from signal selector 101 have been detected. It is then
assumed that the received pulse train is genuine, and the
gating circuit 111 causes bistable device 112 to be "set" to
give the signal lock signal S~.
The removal of the ~ signal from gate 125 closes
gate 100 but the new SL signal applied to gate 107 allows the
output of the coincidence gate to be applied via gate 106 and 107
to open gate 100 only during a coincidence gate pulse. All
extraneous received pulses are excluded from the decoding
register 103 by the operation of the monostable device in the
signal selector 101. The removal of the S~ signal also prevents
the generation of further bl~nking pulses by bistable device 124,
since gate 122 is now closed.
The SL signal is also applied to gate 113, together
with the selected outputs from the signal selector 101. This
allows monostable device 114 to be set for a short time to
provide the SS signal to sample the signals from the detector 58
and apply control signals to the servo 60. ~ach incoming
pulse is now sampled and the servo drives until the telescope
is pointing directly at the apparent source of pulses, in this
case the target from which the marker's pulses are being reflected.
- 1~ 1335212
When the servo error is reduced to zero, gate 61
responds to the next ~ output of the auxiliary counter 123 and
initiates firing of the aircraft's own laser. The laser power
unit 52 and flash-tube 51 are triggered by the output from
gate 61, followed after a short delay determined by delay unit 62
by the activation of the electro-optical device 53. This
allows the emission of a laser pulse of maximum intensity through
the telescope 54.
The emission of the transmitted laser pulse is
detected by the detector 63. This operates the range gate
generator 66 to enable amplifier 65 to pass an expected echo
return, and also sets the bistable device 67. The "set" output
of this device primes gates 68 and 69, and hence allows clock
pulses CP to be applied to the master counter 70 and range
counter 71.
The primary echo from the target is detected by
detector 57, passed by amplifier 65, and resets the range
counter 71. If there are several primary echos, such as from
cloud, the range counter is reset by each one. This is
necessary since, in such conditions it is the last-received
primary echo that is from the target. Hence, after the
receipt of the last primary echo the range counter will lag on
the master counter by a count representing the time interval
2t1 (~igure 1). The output of range counter 71 is also
applied to the display register 73.
When the master counter 70 has counted up to its
maximum, which is after a period of 80 microseconds, the output
of the extra stage 70A changes, whilst the counter counts for a
further 80 microseconds. The appearance of the output from
stage 70A inhibits gate 69 and prevents the application of
further clock pulses to the range counter 71. At the same
time the display register 73 is caused to accept the count
r .t.
~ ^ 1 3352 1 2
~, ...
stored in the range counter to be used as an indication of
target range (in complementary form) When the master counter
has counted up to (to + 160) microseconds, it returns to zero,
thus removing the inhibit input from gate 69 and allowing
range counter 71 to restart. The range counter thus restarts
from a value representing a time (80 - 2t1) microseconds up to
the value set into the coding register 74. This value
represents (tc - 80) microseconds since the range counter is
held static to allow for transfer of its contents to the
display register 73.
When the count in the range counter 71 equals that set
into the coding register 74, the comparator 72`delivers an
output which "sets" the monostable devioe 75 to deliver a
transponding gate pulse TG of 100 nanoseconds duration. The TG
signal opens gate 100 via OR gate 125 at a time when a response
would be expected. If a response is received during the TG pulse
then gate 116 operates to inhibit any change of state of JK flip-
flop 120 and to start counter 123 via gate 121. This initiates
the firing of the aircraft laser for a second time, and the
above procedure is repeated. Gate 116 also inhibits gate 107
so that gate 100 is only opened during the narrow TG pulse
applied via gate 125.
The ~ove description has assumed that all the required
conditions ~or the apparatus to ~unction are satisfied. There
are, however, several stages at which alternative situations
may exist.
One of these concerns the signal lock condition
resulting from the detection of three successive coincidences
between signals from the signal selector 101 and the coincidence
gate signals from gate generator 104. The bistable device 108
is continu~11y being reset by pulses from decoding register 103
via pulse shaper 109, and the required count will only be
ED.283/DN~ - 16 -
; 1 3 3 5 2 1 2
achieved if the required coincidences occur. The coincidence
detector has to be continl~11y set, and if two expected
coincidences do not occur the bistable device 112 is reset to
produce the output ~. A missed coincidence also means that
gate 100 is closed and no input pulse can enter the decoding
register. This stops the clock input to the coincidence shift
register 110 since there is no input to the pulse shaper 109.
~o maintain the SL output during one missed coincidence to
prevent the above situation, the last output from the
coincidence gate is gated with the SL signal and the shift
register clock in gate 115, and applied to the decoding register
as a "synthetic" input pulse.
Another possible situation which may occur is that no
pulse is received by the detector during the short transponding
gate signal TG from monostable device 75. ~his may occur if,
in addition to the desired signal representing the true target,
spurious signals of the correct repetition rate occur during
the period of the coincidence gate 104 due to scatter from cloud
or from features of the terrain, or due to target countermeasureS-
In the event that the first signal to which the signalselector 101 is designed to respond is a spurious one, arriving
perhaps from a direction different from that in which the
target lies, slgnal lock may be achieved but no corresponding
re~ponse is received during the gating period TC. In this
case gate 117 operates instead of gate 116. ~his results in
the state of JK flip-flop 120 ch~ngi ng to alter the signal
selecting log1c of the signal selector 101. In the example
shown the removal of the signal P and its replacement by signal
Q introduces "second pulse" logic, in that the first pulse is
removed by the divide-by-two circuit in the signal selector and
the second signal present during the coincidence gate period is
selected instead. Since acquisition of the new signal usually
ED.283/DNB - 17 -
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1~ 1 3352 t 2
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requires re-alignment of the laser telescope in a new direction
and the relinquishing of all range data derived from the former
signal it is desirable to reset the system to the initial
conditions listed above. Resetting is achieved by applying
the output of gate G117 as a resetting signal RS to all re-
settable elements not already reset by the transponding gate
signal TG. ~he sequence of signal acquisition is then repeated
as above, except that a new signal selection mode is established
by signal Q being present instead of signal P. ~he system
will alternate between the two signal selection modes in the
hope of picking up a train of genùine pulses.
~ he use of first and second pulse logic is only one
way in which the signal selection mode may be changed. The
system may be designed to respond to any required signal
characteristic, and to alternate between two or more of these.
~ he above description relates to one way in which the
invention may be put into effect. It will be apparent that
the logic may be varied, and that other refinements may be
added to counteract various countermeasures applied by the
target. ~he final output of the system described is a range
measurement and a direction, since the aircraft laser must
finally be pointing directly at the marked target. Hence these
outputs may be used to control the weapon system directly.
