U.S. patent number 3,844,506 [Application Number 04/087,491] was granted by the patent office on 1974-10-29 for missile guidance system.
This patent grant is currently assigned to The Singer Company. Invention is credited to Thomas W. Odell, Gus Stavis.
United States Patent |
3,844,506 |
Stavis , et al. |
October 29, 1974 |
MISSILE GUIDANCE SYSTEM
Abstract
1. A missile guidance system comprising, a missile carrying a
microwave receiver and beam antenna, means adapted to fire said
missile in the general direction of a target, a stationary
microwave transmitter irradiating said target and its vicinity by a
single beam, means conically rotating said beam at a first rate
about a line joining said transmitter and said target, the conical
angle thereof being substantially equal to the beam angular width,
means conically rotating the beam direction of said receiver
antenna at a second rate whereby at a selected first range said
receiver perceives and receives said irradiation reflection
modulated at said second rate, means demodulating the received
modulation to secure a signal having a frequency determined by said
second rate and a phase relative to a datum line on said missile,
means steering said missile coarsely toward said target in
accordance with the phase of said signal, means in said receiver
operative at a selected second range less than said first range for
receiving said irradiation reflection and demodulating said first
rate modulation thereof to form a second signal having a
determinable phase, and means steering said missile in fine
guidance mode toward said target in accordance with the phase of
said second signal.
Inventors: |
Stavis; Gus (Briarcliff Manor,
NY), Odell; Thomas W. (Pearl River, NY) |
Assignee: |
The Singer Company (New York,
NY)
|
Family
ID: |
22205507 |
Appl.
No.: |
04/087,491 |
Filed: |
February 6, 1961 |
Current U.S.
Class: |
244/3.15;
244/3.19 |
Current CPC
Class: |
F41G
7/2286 (20130101); F41G 7/2213 (20130101); F41G
3/145 (20130101); F41G 7/226 (20130101) |
Current International
Class: |
F41G
7/22 (20060101); F41G 7/20 (20060101); F42b
015/02 (); F42b 015/00 (); F42b 015/10 () |
Field of
Search: |
;244/14,14.3,14.55,3.15
;250/83.3UV ;102/50 ;343/7,7.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Webb; Thomas H.
Attorney, Agent or Firm: Kennedy; T. W.
Claims
What is claimed is:
1. A missile guidance system comprising, a missile carrying a
microwave receiver and beam antenna, means adapted to fire said
missile in the general direction of a target, a stationary
microwave transmitter irradiating said target and its vicinity by a
single beam, means conically rotating said beam at a first rate
about a line joining said transmitter and said target, the conical
angle thereof being substantially equal to the beam angular width,
means conically rotating the beam direction of said receiver
antenna at a second rate whereby at a selected first range said
receiver perceives and receives said irradiation reflection
modulated at said second rate, means demodulating the received
modulation to secure a signal having a frequency determined by said
second rate and a phase relative to a datum line on said missile,
means steering said missile coarsely toward said target in
accordance with the phase of said signal, means in said receiver
operative at a selected second range less than said first range for
receiving said irradiation reflection and demodulating said first
rate modulation thereof to form a second signal having a
determinable phase, and means steering said missile in fine
guidance mode toward said target in accordance with the phase of
said second signal.
2. A missile guidance system comprising, a missile carrying a
microwave receiver and beam antenna, means adapted to fire said
missile toward a target with a polar error of less than 15.degree.
measured at a selected first range during flight, a stationary
microwave transmitter irradiating said target and its vicinity by a
single narrow beam, means conically rotating said narrow beam at a
first rate about a line joining said transmitter and target, the
conical rotation angle being substantially equal to said narrow
beam width, means conically rotating said receiver antenna beam at
a second rate about a line joining said missile and a point at or
near said target, said receiver antenna beam conical rotation angle
being approximately 30.degree. at said selected first range, means
reducing said receiver antenna beam conical rotation angle to an
angle approximately equal to the receiver antenna beam width, said
reduction occurring during a search and acquisition phase of
operation, said receiver during the search and acquisition phase
acquiring and receiving the reflection of said target irradiation
to form a signal modulated at said second rate, means demodulating
said signal to form a second signal having a phase relative to a
datum line on said missile, means for generating a course
correction signal the value of which is dependent on said relative
phase, means steering said missile coarsely toward said target in
accordance with said course correction signal, means in said
receiver operative at a selected second range less than said first
range for receiving said irradiation reflection and demodulating
said first rate modulation thereof to form a third signal having a
frequency determined by said first rate and a phase which is
determined by its relation to a datum phase, and means steering
said missile in a fine guidance phase toward the target in
accordance with the third signal phase.
3. A missile guidance system comprising, a missile carrying a
microwave receiver and beam antenna, means adapted to fire said
missile toward a target with a polar error of less than 15.degree.
measured at a selected first range during flight, a stationary
microwave transmitter irradiating said target and its vicinity by a
single narrow beam amplitude modulated at a selected rate, means
conically rotating said narrow beam at a first rotation rate about
a line joining said transmitter and target, the conical rotation
angle being substantially equal to said narrow beam width, means
frequency modulating said selected rate at said first rotation rate
at a selected phase, means conically rotating said receiver antenna
beam at a second rotation rate about a line joining said missile
and a point at or near said target, said receiver antenna beam
conical rotation angle being initially of the order of 30.degree.
at said selected first range, means starting at said selected first
range spirally scanning said receiver beam inward to reduce the
cone of rotation angle to substantial equality with the receiver
antenna beam width and substantially greater than said transmitter
narrow beam width, said spiral scan constituting the search mode of
operation, whereby said receiver during the search mode acquires
and locks to a signal derived from the target echo of said
transmitter radiations terminating the search mode and commencing
the lock-on mode, means adapted to secure a coarse signal having
said second rate for coarse guidance of said missile, and means
operative at a selected second range less than said first range
adapted to secure a fine signal having said first rate for fine
guidance of said missile.
4. A missile guidance system comprising, a missile carrying a
receiver and antenna, means adapted to fire said missile in the
general direction of a target, a stationary transmitter for
irradiating said target by a single amplitude modulated microwave
beam, said amplitude modulation being frequency modulated, means
for conically rotating said microwave beam about a rotation axis at
a first rate, the conical angle being substantially equal to the
beam angular width, means conically rotating the receiving axis of
said antenna at a second rate, the conical angle thereof being
approximately equal to the received beam angular width, means for
acquiring a signal by said receiver from the reflections at said
target of said irradiating microwave beam, a demodulator in said
receiver deriving a signal having the rate of said amplitude
modulation, a second demodulator operative at a first range
demodulating said last named signal to secure a coarse steering
signal having a frequency equal to said second rate and a phase
representing the direction of steering error relative to a datum
point on said missile, gate and switch means adapted to apply the
amplitude and phase of said coarse steering signal to generate a
coarse correction signal the amplitude and phase of which are
dependent on the amplitude and phase of said coarse steering
signal, a vertical reference in said receiving means operative at a
second selected range less than said first range for receiving said
irradiation reflection and demodulating said frequency modulation
at said first rate to form a fine steering signal having phase
representing direction of steering error and amplitude representing
amount of steering error, said gate and switch means being adapted
to apply said fine steering signal to generate a fine correction
signal the amplitude and phase of which are dependent on said
vertical reference signal and on the amplitude and phase of said
fine steering signal.
5. A missile guidance system comprising, a missile carrying a
microwave receiver and beam antenna, means adapted to fire said
missile toward a target with a polar error of less than 15.degree.
measured at a selected first range during flight, a stationary
microwave transmitter irradiating said target and its vicinity by a
single narrow beam amplitude modulated at a selected rate, means
conically rotating said narrow beam at a first rotation rate about
a line joining said transmitter and target, the conical rotation
angle being substantially equal to said narrow beam width, means
frequency modulating said transmitter beam at said first rotation
rate and at a selected phase, means conically rotating said
receiver antenna beam at a second rotation rate about a line
joining said missile and a point at or near said target, said
receiver antenna beam conical rotation angle being initially of the
order of 30.degree. at said selected first range, means starting at
said selected first range spirally scanning said receiver antenna
beam inward to reduce the cone of rotation angle to substantial
equality with the receiver antenna beam width and substantially
greater than said transmitter narrow beam width, said spiral scan
constituting the search mode of operation, whereby said receiver
during the search mode acquires a signal derived from the target
echo of said transmitter radiations, a demodulator in said receiver
deriving a signal having said selected rate of amplitude
modulation, a second demodulator demodulating said last-named
signal to secure a coarse steering signal having a frequency equal
to said second rotation rate and a phase representing the direction
of steering error relative to a datum point on said missile, gate
and switch means adapted to apply the amplitude and phase of said
coarse steering signal to generate a coarse correction signal the
amplitude and phase of which are dependent on the amplitude and
phase of said coarse steering signal, a vertical reference in said
receiver, and means in said receiver operative at a selected second
range less than said first range for receiving said irradiation
reflection and demodulating said frequency modulation at the first
rotation rate to form a fine steering signal having phase
representing direction of steering error and amplitude representing
amount of steering error, said gate and switch means being adapted
to apply said fine steering signal to generate a fine correction
signal the amplitude and phase of which are dependent on said
vertical reference signal and on the amplitude and phase of said
fine steering signal.
Description
The invention herein described was made in the course of or under a
contract, or subcontract thereunder, with the Department of the
Army.
This invention relates to radar guidance systems and particularly
to semi-active radar systems applied to the guidance of
missiles.
The problem of accurate ground-to-ground missile guidance involves
more than mere aiming at launch when no target misses are
permitted. In this case, terminal guidance is required and a
target-seeking principle is desirable. When a radio or radar target
seeker is employed it should be proof against countermeasures
which, for example, would make the radar reflectivity of the target
indistinguishable from that of its background. For tactical use
against mobile targets it is practically necessary for the guidance
system to have pinpoint accuracy and to have such reliability as to
hit its target on the first shot in every case.
The present invention meets these requirements and, in addition, is
insensitive to ground clutter and other interfering effects
reducing the effectiveness of low altitude radars. The invention
employs a radar transmitter on the ground at the missile firing
point or at an advanced post. It also employs a radar receiver in
the missile. Both the transmitter and receiver employ single-beam
antennas, and both antenna beams are conically rotated or scanned,
but at different rates.
In a typical situation, a target tank is dug into the forward slope
of a hillside and is so concealed that its radar reflectivity is
indistinguishable from that of its background. A missile firing
battery faces the target at a range of 5,000 yards. An observation
post at 2,500-yard range has a clear view of the target and is
connected by a channel of signal communication with the firing
battery. The observation post radar transmitter is connected to a
sighting device, which may be an optical or infrared telescopic
sight, so that the radar transmitting pointing direction is at all
times that of the sighting device.
In operation, the sighting device is aimed at a selected vulnerable
point of the target and the transmitter is turned on. Its beam
irradiates the target and surroundings with a beam having 1.degree.
angle and turning conically at a rate, P, so that its axis
describes a circle at the target, which is centered at the aiming
point. At a signal the missile is fired toward the target. Its
radar receiver receives the radar energy reflected from the target
and its background, but at long ranges perceives this reflecting
area as a point source. The rotated receiving antenna scans the
target vicinity at a rate, Q, and, perceiving the radar reflections
during a part of each antenna revolution, observes the received
phase and from it the deflection of the line of sight, from missile
to target, from the missile axis, and generates a signal
representing the deflection. At a selected range, say 1,800 yards,
missile control elements including a gyroscope are activated. The
received deflection signal is then employed to guide the missile
toward its target. This is termed coarse guidance operation.
Upon closer approach, for example, at a range of 500 yards, the
receiving system of the missile, now aimed generally at the
reflecting area, perceives the ring pattern caused by the
transmitter beam rotation at P revolutions per second. This
actuates suitable circuits in the missile to cause it to seek the
center of the ring pattern. It thus homes on a target spot which
may be as small as 1 yard in diameter. This is termed fine guidance
operation.
An object of this invention is to provide a semi-active radar
system for terminal guidance of a missile to a target.
Another object of this invention is to provide a ground radar
transmitter and a receiver carried on a missile for homing the
missile on a target which cannot be distinguished by radar from its
background.
Another object of this invention is to provide an extremely
accurate missile guidance system for complete reliability in
causing a hit by the first missile fired.
A further understanding of this invention may be secured from the
detailed description and drawings, in which:
FIG. 1 depicts a terrain profile showing a typical situation
employing this invention.
FIG. 2 is a block schematic drawing of the microwave transmitter at
the observation post.
FIG. 3 is a graph showing the distribution of transmitted
irradiation at the target.
FIG. 4 is a block schematic drawing of the microwave receiver in
the missile.
FIG. 5 is a schematic diagram of the diode switch.
FIG. 6 is an oblique drawing showing the pattern in the vicinity of
the target as scanned by the receiver at a range of 1,500
yards.
FIG. 7 is an oblique drawing showing the target pattern as scanned
by the receiver at a range of 200 yards.
Referring now to FIG. 1, a target 11 consists of an enemy
installation such as a tank which, by camouflage, has a radar
reflectivity indistinguishable from its hillside background. The
target is, however, perceivable from an observation post 12 by a
sighting device which may be, for example, either an ocular
telescope or infrared telescope 13. The sighting device is secured
to a microwave narrow-beam transmitting antenna 14 so that both are
adjusted together to point in the target direction. A communication
channel is set up between the observation post and a missile
launcher 16.
The missile launcher 16 is positioned at a range of 5,000 yards
from target so that the missile can be fired toward the target. The
accuracy need be only enough to insure that at a distance of 1,800
yards between missile and target a cone of 30.degree. angle
generated at the missile will include the target.
The construction of the missile includes means to maintain its axis
approximately parallel to its line of flight and means, such as
movable vanes or adjustable steering jets, to steer it toward the
target under control of electrical signals. These elements are
outside of the scope of this invention.
A microwave transmitter, FIG. 2, is positioned at the observation
post. It contains a microwave continuous-wave generator, 17, which,
through a ferrite isolator 18 and ferrite amplitude modulator 19
feeds the transmitting antenna 14.
The antenna 14 emits a narrow beam of radiation having an angular
width between 3 db points of 1.degree.. This beam is rotated or
scanned so that its axis sweeps a cone with an included angle of
1.degree. having its apex at the transmitter. Thus the axial center
line of this 1.degree. cone, accurately aimed at a vulnerable point
of the target, continuously transmits microwave energy which is 3
db below the beam axis energy. The beam is rotated at a rate of 498
revolutions per second by a motor 21 but any other of several
methods of beam scanning may be used instead.
Associated with the rotating beam is generator 22 emitting a 498
cps alternating waveform in which the phase progressively changes
throughout one cycle of the beam rotation. This alternating
waveform is sawtooth, but alternatively may be sinusoidal or of any
other form satisfying the above requirement. This waveform is
applied through a frequency modulator 24 to modulate the frequency
of a 10 kcps oscillator 26. The frequency excursion of the
modulation may be whatever is desired. As an example, it is here
chosen to be 255 cps, so that the oscillator 26 is modulated to
emit a signal having a frequency varying between 9,745 cps and
10,255 cps.
This modulated 10 kcps signal is applied as modulating frequency to
the modulator 19, where it amplitude modulates the microwave energy
before its application to the antenna.
In the operation of the microwave transmitter, a beam of microwave
energy is rotated around the center of the target to form an
irradiation pattern, as shown in FIG. 3. The pattern laid on the
target has a diameter of 44 yards at this range, and the accuracy
of application is limited only by the accuracy of aiming. The
center of the pattern can easily be positioned within a 3-foot
circle on the target.
The microwave receiver carried by the missile is shown
schematically in FIG. 4. A gyroscope 27 is carried in two gimbal
rings borne by the missile frame, so that when these rings are
unlocked, the gyroscope rotor axis 28 has freedom to depart from
alignment with the missle axis 29 by any amount up to 8.degree..
This gimbal angle is shown as angle 31 in FIG. 4. A microwave dish
antenna 32 is fixed to the gyroscope rotor so that as the rotor
rotates, the antenna must rotate at the same speed. The identity of
the antenna rotational axis 33 with the rotor axis 28 is indicated
by the dashed line 34. Thus the gyroscope has two distinct
funtions: its gyroscopic inertia serves as an important part of the
missile steering function, and the rotor, in rotating, rotates the
antenna.
The antenna is fixed to the rotor by means of a hinge joint, so
that although they always rotate together, the antenna dish axis
can depart from the rotor axis by an angle having a minimum fixed
at 1.4.degree. and a maximum limited to 71/2.degree.. This angle is
shown as angle 35 in FIG. 4. Thus, as the rotor rotates, the
antenna axis sweeps out a cone having an angle which is between
2.8.degree. and 15.degree., with the cone axis coincident with the
rotor axis.
The microwave antenna 32 is tuned to receive the frequency of
transmission of the transmitter shown in FIG. 2. The receiving
energy pattern of antenna 32 constitutes a single beam having a
width between 3 db points of 4.degree.. Since the microwave feed
component is fixed to the rotor and in line with its axis and the
antenna dish reflector is hinged relative to the rotor axis, the
beam axis angle relative to the rotor axis is double the antenna
hinge angle, with limits 2.8.degree. and 15.degree., as shown in
FIG. 4 at 36.
The electrical signal received from the antenna 32 is applied to a
mixer 37, where it is mixed with the output of a local oscillator
38 differing in frequency from the microwave carrier frequency by
30 mcps, the amount of the intermediate amplification frequency.
The mixer output is applied to an intermediate frequency amplifier
39 having a 10 mcps transmission band centered at 30 mcps. The
width of this transmission band permits some variations in the
frequency of the local oscillator 38 and of the generator 17, FIG.
2.
The IF output is amplitude detected by detector 41, recovering the
10 kcps average amplitude modulation, which is amplified in the
amplifier 42.
The 10 kcps average amplitude modulation is again amplitude
detected by detector 43. The outputs are amplified and separated by
two bandpass amplifiers 44 and 45 having transmission band centers
of 498 cps and 150 cps respectively. The outputs are added in an
adding circuit 47, the output of which is applied through conductor
48 to a diode switch 49.
The output of 10 kcps amplifier 42 is also amplitude limited in a
limiter 51, then frequency demodulated in FM detector 52. The
resulting 498 cps frequency is applied to a trigger circuit 53,
where a pulse is generated at each cycle at a selected phase. This
pulse train is applied to a gate circuit 54. An independently
oscillating generator 56 oscillates at 1 mcps. Its output is also
applied to gate 54, with the gate output imposed on conductor
57.
The output of amplifier 44 is additionally applied to a trigger
circuit 58 which emits a trigger pulse once each cycle at a
selected phase. The output of trigger circuit 58 is applied to the
gate circuit 54. The output of amplifier 46 is additionally applied
to a trigger circuit 59 which emits a trigger pulse once each cycle
at a selected phase. The output of trigger circuit 59 is applied to
gate circuit 61.
Gate circuit 61 is similar to gate 54, and imposes its output on
condutor 62. These gates are of the digital type, allowing
transmission of the signal of oscillator 56 to the output between
start and stop trigger pulse inputs. A design for such a gate is
given in Pulse and Digital Techniques, by Millman and Taub, FIG.
14.21, Page 445.
The outputs of gates 61 and 54 imposed on conductors 62 and 57 are
applied to an adding circuit 63, and their sum is applied to a
storage counter 64. This counter is described in the Millman and
Taub Publication, supra, on Page 351, and its circuit is shown in
FIG. 11.28.
In the operation of this counter, an input at 1 mcps is started and
stopped, for example, by gate 54, at two selected phases within one
cycle of the 498 cps input, and a direct-current output is emitted
by the storage counter on conductor 66 representing by its
magnitude the angular difference between the two selected phases.
At the end of each cycle of the 498 cps input, the counter is
restored to begin a new output amplitude in the next cycle. When
the input is from the 150 cps filter through gate 61, the output of
the storage counter 64 is at conductor 67.
The storage counter output is applied through conductor 66 to a
summing circuit 68, where the output is added to the output of a
vertical reference 69, its relation to the missile attitude being
indicated by the symbol 71. The summing circuit 68 performs
algebraic addition of direct-current components, the algebraic sum
being imposed on conductor 72. This sum is added in adding circuit
73 to the signal in conductor 67.
The sum output of adding circuit 73 in conductor 74 is applied to
diode switch 49. This switch emits a signal in cable 76 at a time
during each revolution of the gyroscope 27 controlled by the signal
in conductor 74 and having an amplitude controlled by the signal in
conductor 48. Cable 76 is also connected to the missile steering
mechanism.
A circuit for the diode switch 49 is shown in FIG. 5. The conductor
74 is connected through four resistors 77, 78, 79 and 81 and four
capacitors 82, 83, 84 and 86 to the cable 76 containing the four
conductors 87, 88, 89 and 91. This cable 76 containing four
conductors is connected to the gyroscope 27. In the gyroscope four
precessing coils 92, 93, 94 and 96 are distributed at 90.degree.
intervals around its gimbal suspension, and each coil is connected
for excitation from a respective one of the four conductors 87, 88,
89 and 91.
The four junctions 97, 98, 99 and 101 between the resistors and
capacitors are connected to limiting diodes and limiting potentials
of 4, 8, 12 and 16 volts so arranged that coil 92 is excited only
when the potential applied from conductor 74 is between 0 and +4
volts, coil 93 is excited only when the potential is between 4 and
8 volts, coil 94 only when potential is between 8 and 12 volts and
coil 96 only when potential is between 12 and 16 volts. Conductor
48 is connected through four resistors 102, 103, 104 and 106 to the
four coils respectively.
The diode switch operates as follows. When the signal on conductor
74 is between 0 and +4 volts, diode 107 is nonconducting but diodes
108, 109 and 111 are conducting, shorting conductors 88, 89 and 91
to ground for alternating inputs. Meanwhile, alternating potential
at either 498 cps or 150 cps is applied from conductor 48, its
potential amplitude representing the amount of pointing error and
hence the amount of correction of gyroscope pointing direction
needed. This signal is applied only to coil 92, precessing the
gyroscope in the quadrant controlled by that coil with a force
proportional to the amount of existing pointing error. Similarly,
voltages between 4 and 8 volts impress the amplitude signal on coil
93 only, the other coils being grounded, each through its capacitor
and diodes, for alternating current.
It is to be noted that the signals on conductor 74 are
unidirectional pulse signals having the coarse guidance operation
rate of 150 cps or the fine guidance operation rate of 498 cps, and
are always at the same rate as the alternating signals in conductor
48.
A pulse signal is taken from the gyroscope 27 at the same selected
phase in each revolution thereof and applied to gate 61 through
conductor 112.
The gyroscope 27 output conductor 113 carries a signal emitted by
the gyroscope components representing the angular rate of movement
of the gyroscope axis 28 toward the line of sight, which is the
line between the missile and the target. The gyroscope output
conductor 114 carries yaw and pitch damping signals. The conductors
76, 113 and 114 control the missile direction of flight through
vanes or direction jets on the missile but these control devices
are outside of the scope of this invention. They are employed in
proportional navigation of the missile as described in the book
Guidance, by Arthur S. Locke, on Pages 475-478.
The operation of the missile is divided into the ballistic phase
and the guided or homing phase. The ballistic phase refers to the
missile flight between launch and range of 1,800 yards from the
target. The guided or homing phase refers to the last 1,800 yards
of its flight terminated by impact on the target. The missile is
preset at firing so that, during the ballistic phase, its gyroscope
does not rotate and its gimbal rings are locked. Thus the antenna
cone rotational axis 33 and rotor axis 28 are coincident with the
missile axis 29.
The antenna hinge bearings which hinge it to the gyroscope rotor
are locked at their maximum angle, so that the antenna is canted or
hinged with its reflector dish axis at the maximum mechanical angle
35 of 71/2.degree. to the rotor axis.
The operation of the receiver during the guided or homing phase, in
the last 1,800 yards of its flight, can be divided into two modes
or kinds of operation, the search mode and the locked-on mode. When
locked on to the target echo signals and electrical signals are
consequently being received, these signals are of two kinds or
degrees of fineness, resulting in coarse guidance operation and
fine guidance operation. These modes and operations merge into one
another to some extent but for clarity they are described in the
above order.
At 1,800 yards, operation is converted from the ballistic phase to
the guided or homing phase by several actions which may be nearly
or quite simultaneous, or partly overlapping, but which are
described in the closely consecutive order in which they may
occur.
First, a spring in the missile is released by a timing mechanism.
This spring now spins the gyroscope rotor and accelerates it to a
speed of 150 rps in one-half second, when the spring frees itself
from the rotor, which thereafter coasts, spinning itself and the
antenna at or near this speed. Since the gimbal rings are locked at
0.degree., the antenna axis, canted at 71/2.degree., describes a
cone of 15.degree. angle. The microwave path as reflected by the
antenna reflector is such that the mechanical angle is doubled as
before stated, and the lobe of antenna microwave reception
therefore describes a cone of 30.degree.. The antenna has been held
at the maximum 71/2.degree. axis cant angle by a latch, which next
is released and a spring urging the antenna axis toward the rotor
axis is thereby permitted to move the antenna. Since the antenna is
now rotating with the rotor while the antenna axis is moving toward
the rotor axis, the combination causes the lobe of antenna
reception to spiral inward from a diameter of 30.degree. to a
diameter of 5.6.degree., which is four times the minimum cant angle
of 1.4.degree., at which angle further antenna hinge motion is
stopped by a pin.
The third and last timed action is to release the gyroscope gimbal
rings, permitting precession to occur and permitting the corrective
action of the gyroscopic momentum to be applied through circuits
and mechanisms to the missile steering vanes or jets, so that the
missile axis is thereby brought into line with the rotor axis and
so maintained. These circuits and mechanisms are outside of the
scope of this invention.
In operation in the search mode, coincident with the inwardly
spiralling scan which begins at 1,800-yard range, the irradiated
area at and near the target with a diameter of about 44 yards is
perceived by the missile receiver as a mere point of reradiation
somewhere within its 30.degree. diameter field. The transmitter
scan modulation at 498 cps is not perceived. FIG. 6 illustrates
this situation at a selected instant. The scanning area 116 has a
diameter of 30.degree., equal to 770 yards at 1,500 yards range.
The 4.degree. receiving beam area is indicated at 117, and is
spiralling inward from the circle 116 at 150 cps. Let it be assumed
that the reradiation area is at 118. As the received beam area 117
sweeps past 118 the receiver receives a pulse of microwave energy
having an average modulation frequency of 10 kcps. After
demodulation this 10 kcps signal is found in conductor 119, FIG. 4.
After demodulation in detector 43 and amplification by the bandpass
amplifier 46, the signal is converted to a signal having a
frequency of 150 cps in conductor 121.
The gyroscope 27 emits a pulse at a reference angle of rotation
relative to the missile frame which is, for example, termed
0.degree. in FIG. 6. This pulse is applied through conductor 112 to
gate 61, opening it and causing 1 mcps energy from oscillator 56 to
flow into counter 64. The energy in conductor 121 is applied to the
trigger generator 59 to generate a trigger which is representative
of the angular position .theta. of the irradiated target area 118,
FIG. 6, in the circle 116 swept by the received beam. This trigger
is applied to close gate 61, stopping the flow of 1 mcps energy to
the storage counter. The output, then, of the storage counter in
conductor 67 is a direct voltage pulse having an amplitude
proportional to the angle, .theta., FIG. 6, representing the angle
of the target in the received field relative to a datum line on the
missile.
The voltage proportional to .theta. in conductor 67, FIG. 4, is
applied through the summing circuit 73 and conductor 74 to the
diode switch 49, where is produces a signal in conductor 76
determining, through gyroscope 27, which one of the four quadrant
steering elements is energized, the amplitude signal in conductor
48 determining the amplitude of the steering effort.
Thus the missile is steered toward the target. In FIG. 6, the
center 122 of the circle is thereby moved toward the target area
118 while the 15.degree. radius of the circle 116 is reduced toward
2.8.degree.. By the time the spiralling-in of the antenna lobe has
been completed the target has been acquired, the target spot 118
remains within the received are 117 and the receiver is in the
locked-on mode, with coarse guidance operation.
As the missile approaches a range of 500 yards from the target, the
detail of the pattern laid down by the transmitter begins to be
perceived. The transmitted pattern modulated at 498 cps and the
received pattern modulated at 150 cps are about the same size at
the target. At closer approach the 150 cps modulation decreases
toward zero while the 498 cps modulation begins to dominate. This
498 cps modulation of the 10 kcps carrier has an amplitude nature
for a reason similar to that which was shown by the scanning
diagram of FIG. 6 for 150 cps. The 498 cps signal also has a
frequency modulation nature since the 10 kcps average frequency is
moved between 9,945 cps and 10,255 cps at a rate of 498 cps.
Accordingly, energy at 498 cps is amplitude detected at 43, FIG. 4,
and amplified at 44 to generate a trigger each cycle in trigger
circuit 58. This trigger has a phase representing the phase of the
transmitted signal relative to a datum direction, such as directly
upward, when perceived most strongly by the narrow received beam.
This is shown in FIG. 7, in which the received beam 117 is scanned
in a tight circle 116 and the transmitted beam 123, rotating at a
rate of 498 cps in a large circle 118, is perceived at maximum
strength once in each of its revolutions. The trigger signal from
circuit 58 is used to close gate 54.
The frequency-modulated signal in conductor 119 is limited at 51
and demodulated at 52 to produce a 498 cps signal in conductor 124.
This generates a pulse in trigger circuit 53 at a phase marking a
selected datum direction in the transmitter scanning circle, here
selected as the "up" direction. This trigger is used to open gate
54.
Thus gate 54 is conductive for the angle of transmitter rotation
from directly upward to the direction of the receiving pattern, or
.theta.' in FIG. 7.
The signal is transmitted to the storage counter 64, producing a
direct current output signal representative thereof in conductor
66.
Since the missile will generally be rotating, a signal must be
produced representing the angle between the datum line on the
missile, previously referred to, and the upward direction. This
signal is generated by employing the vertical reference 69 and
generating a signal in component 71 representing at any instant the
changing angle between the vertical direction and the missile datum
line direction. This signal, .theta.", is added in the adding
circuit 68 to .theta.' to form .theta. in conductor 72. This signal
is applied to adding circuit 73, where it is used as before
described.
* * * * *