JPH0513276B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a rotary modulator for tracking light emitted by a target itself or reflected from the target, and to a rotary modulator for tracking light emitted by the target itself or reflected from the target. Extracting the target signal from among the signals obtained from the demodulator of the rotary modulator that demodulates the azimuth error signal and the elevation angle error signal of the target, which are necessary for tracking the target, from the signals obtained from the modulator, This invention relates to a target extraction receiver for extracting other unnecessary signals.

(Background of the present invention) When tracking a target such as an aircraft, ship, or vehicle, the antenna or optical system of the tracking device is pointed in that direction in advance, or the target is detected by searching the vicinity of the target and tracking begins. Follow these steps. In order to improve target tracking accuracy and target detection sensitivity, the viewing angle of the optical system of the tracking device is narrowed, so naturally the range of pulling in from the search state to the tracking state is narrowed. Therefore, it would be an extremely excellent improvement if an optical tracking device could be created that has a wide pull-in width, high target detection sensitivity, and high ability to remove unnecessary noise signals in the background of the target.

(Prior art and its general problems) When tracking a target using light as a medium, if image-based signal processing is performed by capturing the target as a signal in a certain background, it is possible to distinguish between the target and the background. As his ability improves, the precision with which he guides his body toward his target should also improve.

For this reason, a tracking device using a rosette scan modulator (optical system) as shown in FIG. 5 has been proposed. FIG. 6 shows an example of a rosette pattern, where 3 is a rosette pattern and 2 is a circle target. Specifically, the rosette scan modulator shown in FIG.
A rosette pattern is created by rotating two pieces of 0,51 at different angular velocities ω ₁ and ω ₂ .

Since the coordinates (X _R , Y _R ) of point P on the rosette pattern in FIG. 6 are the sum of two rotating vectors, they can be expressed as follows.

X _R =φsinω ₁ +ω ₂ /2t・cosω ₁ −ω ₂ /2t=
φ/2(sinω ₂ t+sinω ₁ t)…(1) Y _R =φsinω ₁ +ω ₂ /2t・sinω ₁ −ω ₂ /2t=
φ/2(cosω ₂ t−cosω ₁ t)…(2) The rosette pattern in Fig. 6 is φ=1, ω ₂ =5,
It was drawn by a computer using equations (1) and (2) with ω ₁ =7. The rosette pattern in Figure 6 is 1.
In order to draw the image twice (one field), it takes t ₁ = 4π/||ω ₁ |−|ω ₂ || (seconds)...(3). However, | | is a symbol representing an absolute value.

(Specific Problems with the Prior Art) By the way, in the rosette scan optical system shown in FIG. 5, the first prism 50 and the second prism 51 that receive the input signal from the target position 1 rotate at different angular velocities ω ₁ and ω ₂ . The light is focused on a unit type detector 53 by a condensing lens 52, and a unit type detector output 5 is obtained. As shown in FIG. 5, since there are two rotating systems, the device becomes very complicated and is not very economical. Furthermore, compared to the rotational angular velocities ω ₁ and ω ₂ of the two rotation systems, the angular velocity for drawing a pattern of one field is (|ω ₁ |−|ω ₂ |)/2, which is very slow.

(Objective of the present invention) The present invention uses a coaxial rotary array detector to demodulate an azimuth error signal and an elevation angle error signal representing the target position from a video signal obtained from the array detector. The first object is to provide a tracking receiver using a rotating array detector, and further, a target extraction means for eliminating the harmful effects of unnecessary reflected waves, unnecessary light sources, or interference sources mixed in the video signal. The second objective is to obtain a tracking receiver using a coaxial rotating array detector.

(Main points of the configuration of the present invention) In the configurations of the present invention shown in FIGS. The array detector 54 is placed on the focal plane of the system, and the array detector 54 is rotated so that the center of rotation of the array detector 54 coincides with the optical axis of the optical system. The readout angular frequency of the array detector 54 is ω ₁ , and the angular frequency of the rotating array detector 54 is ω ₂ . As an example, array detector 5
If a CCD (charged coupled device) is used as the clock signal 21, the line reference signal 19 synchronized with the clock signal 21 can be obtained since the clock signal 21 is required for reading. The line reference signal 19, S ₁₉ is as follows: S ₁₉ =sinω ₁ t (4). A generator (first reference signal generator 64) attached to the shaft of the rotating array detector 54 generates second reference signals 1 synchronized with the rotation and orthogonal to each other.
7, S ₁₇ and a third reference signal 18, S ₁₈ can be taken out.

S ₁₇ = sinω ₂ t …(5) S ₁₈ = cosω ₂ t …(6) From each reference signal of equations (4), (5), and (6), the fourth reference signal 16, S ₁₆ and fifth reference signal 15,
Can make _S15 .

S ₁₆ = sinω ₁ t sinω ₂ t …(7) S ₁₅ = sinω ₁ t cosω ₂ t …(8) Calculate the size of the target using the model of circular target 2 with a small radius R as shown in Figure 3. The principle of a tracking receiver will be explained. A linearly arranged array detector 54 made of an image CCD or the like is placed on the focal plane of an optical system 56 such as a lens or mirror, and the center of the array detector 54 is aligned with the center of rotation of the array detector 54. Furthermore, the optical axis of the optical system 56 and the center of rotation of the array detector 54 are made to coincide with each other. In this case, the optical system 56 may be fixed. The readout of one line of the array detector 54 is set to an angular frequency ω ₁ , and the angular velocity of the rotating machine 57 of the array detector 54 is set to ω ₂ .

FIG. 3 shows a case where a circular target 2 with a radius R is imaged on the field of view 4 of the array detector 54 located on the focal plane of the optical system 56. The center A of the circular target 2 is shifted from the center of rotation by coordinates a and b, and the array detector 54
Assuming that the array detector output 7 read from S corresponds to the coordinate point (x, y), the following signal is obtained as the array detector output 7, _S7 .

S ₇ = kSign {R ² - [(x-a) ² + (y-b) ² ]} ...(9) However, k is a constant, SignZ=1 0 -1 z>0 z=0 z< 0...(10)x=p( _ω1t ) _cosω2t ...(11)y=p( _ω1t ) _sinω2t ...(12). Furthermore, if we assume the clock frequency of the clock signal 21 to be constant and normalize it, we get p(ω ₁ t)=ω ₁ t(−π<ω ₁ t<π)=2 _∞ 〓 ⁿ⁼¹ (−1) ^{n- 1} sin nω ₁ t/n (13) Therefore, equation (9) can be transformed as follows.

S ₇ = kSign {R ² − [p ² (ω ₁ t) − 2rp (ω ₁ t) × cos
(ω ₂ t-θ) + r ² } …(14) However It is. Here, if we create an approximation of equation (14) using only the fundamental wave of equation (13), we get S ₇ ≒kSign{R ² −[−2cos2ω ₁ t−4r sinω ₁ t・
cos(ω ₂ t−θ)+r ² +2]} …(16). Here, it is sufficient to consider the terms necessary to demodulate the target position in equation (16). Therefore,
Consider the next low-pass amplifier output 12, S ₁₂ , present in the array detector output 7.

S ₁₂ ≒4r sinω ₁ t cos (ω ₂ t-θ) ...(17) The azimuth error signal 13, Az and the elevation angle error signal 14, El are the following fourth reference signal 16, S ₁₆ and the fifth reference It is obtained by multiplying signal 15 and S ₁₅ .

Az El=S ₁₂ sinω ₁ t・sinω ₂ t sinω ₁ t・cosω ₂ t=a b ...(18) From equation (18), if the circular target is near the center of the array detector 54, the target can be approximated. You can know the location of

Therefore, the azimuth error signal 13 is a signal proportional to the X component a of the coordinate A in FIG. 3, and the elevation angle error signal 14 is a signal proportional to the Y component b of the coordinate A in FIG. , these error signals are quantities proportional to the deviation of the target position (angle) from the center of the optical system.

The explanation up to this point is the principle explanation of the array detector output 7 obtained by the receiver using the rotating array detector 54 when there is a circular target 2, and the azimuth error signal 13 and the height and low values from the array detector output 7. Having explained how the angular error signal 14 is obtained, next we will explain the principle of generating the gate signal 22 for extracting the target signal.

Equation (9) is the video signal obtained in the case of circular target 2 with radius R, but conversely, the variables R ² ,
If x, y, a, and b are created electrically, it should be possible to create the gate signal 22 for signal extraction.

Therefore, the gate signal 22, S ₂₂ may be created so that S ₂₂ =Sign[Rg ² −(x−Az) ² −(y−El) ² ] (19). However, Rg ² is the amount that determines the pulse width with the gate width signal 23, x, y are reference signals generated from the line reference signal 19 as shown in equations (11) and (12), and Az is a known value. is the azimuth angle error signal 13, and El is the known elevation angle error signal 14
It is.

Azimuth error signal 13 using gate signal 22
A gate circuit 59 uses the gate signal 22 to extract the target portion of the bandpass amplifier output 10 {V(t)}, and a synchronous detector 61 extracts the respective error signals. As a result, Az El=V(t)S ₂₂ S ₁₆ S ₁₅ =Ccosθ sinθ=Cab (20), and it can be seen that the target position can be correctly demodulated. However, C is a proportionality constant, and -- is the average of one period. In this way, a target extraction receiver using a rotating array detector is constructed.

(Embodiment of the present invention) An embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. The input signal (generated by the difference in brightness between the target and the background) 8 is focused by the objective lens 55 as shown in FIG.
The image is formed on an array detector 54 which is placed on the focal plane of the lens and whose center of rotation coincides with the lens axis, resulting in the array detector output 7.

Here, an example of the array detector 54 will be explained with reference to FIG. The clock signal 21 is sent to the switch drive circuit 82.
is input. Switch SW ₁ , SW ₂ , SW ₃ ,...
SW _o transfers charges accumulated in photodetectors D ₁ , D ₂ , D ₃ , ..., D _o according to the intensity of light to capacitors C ₁ , C ₂ , C ₃ , ..., C _o , respectively. The switch drive circuit 82 changes from the off state to the on state.
By switching to the OFF state, when the movement is completed, the OFF state is restored. Photodetector D ₁ ,
D ₂ , D ₃ , ..., D _o are switches SW ₁ , SW ₂ , SW ₃ ,
..., charges are accumulated when SW _o is off. The switches SW ₁ ′, SW ₂ ′, SW ₃ ′…, SW _o ′ are
Since the switches are switched from off to on in synchronization with the clock signal 21 in the order of SW ₁ ′, SW ₂ ′, SW ₃ ′..., SW _o ′, the photodetector
Array detector outputs 7 proportional to the charges accumulated in D ₁ , D ₂ , D ₃ , . . . , _Do , respectively, are output as time-series signals. This FIG. 7 is an example of the inside called CCD.

In the optical system of the embodiment shown in FIG. 2, the center A of the circular target 2 within the field of view 4 as shown in FIG.
The difference is b). Further, a signal proportional to the intensity of the optical image on the array detector 54 and corresponding to the coordinates (x, y) of a certain point on the array detector 54 is the array detector output 7 in equation (9).

In FIG. 1, the input signal 8 is focused by the optical system 56, forming an optical image of the field of view 4 (optical system output 9) on the focal plane on the array detector 54; Since it is rotated by the rotating machine 57, the output accompanying the rotation is the clock signal 2.
1, obtained as array detector output 7,
It is amplified by the bandpass amplifier 58 to become the bandpass amplifier output 10, and in the gate circuit 59, the target portion is extracted by the gate signal 22 to become the gate circuit output 11, and the gate circuit output 11 is amplified by the low-pass amplifier 60.
Amplified by
and synchronously detected using the fifth reference signal 15,
This results in an azimuth angle error signal 13 and an elevation angle error signal 14.

That is, the synchronous detector 61 has the output 12 and the fourth
The output 12 is multiplied by the reference signal 16 and averaged for each period to obtain the azimuth error signal 13, and the output 12 and the fifth reference signal 15 are multiplied and averaged for each period to obtain the elevation angle error signal 14. [see formula (20)].

The other output of the clock signal generator 66 is input to the line reference signal generator 65 and the array detector 5
The line reference signal 19 is synchronized with the first line of No. 4, and is input to the second reference signal generator 63. The rotating machine output 20 synchronized with the rotation of the rotating machine 57 is the first
The second reference signal 1 is input to the reference signal generator 64.
The reference signal 7 and the third reference signal 18 are branched into two orthogonal signals, and are input to the second reference signal generator 63. A fourth reference signal 16 and a fifth reference signal are output from the second reference signal generator 63 and are two orthogonalized signals.
The reference signal 15 is input to a gate signal generator 62 and a synchronous detector 61. Gate signal generator 62
Then, the gate signal 22 is output using the fourth reference signal 16, the fifth reference signal 15, the known azimuth error signal 13 (used for target tracking until just before), and the elevation angle error signal 14.

FIG. 4 shows a circuit configuration for generating the gate signal 22. In this figure, the fourth reference signal 16
is waveform-shaped by the second waveform shaping circuit 74 into a signal corresponding to equation (11), and together with this second waveform shaping circuit output 30, x, the azimuth error signal 13 is
They are added in the adder 67 to become the fourth adder output 24, squared in the first and second multiplier 69 to become the first and second multiplier output 25, and input to the third adder 71. be done.

On the other hand, the fifth reference signal 15 is waveform-shaped by the third waveform shaping circuit 75 into a signal corresponding to equation (12), and together with this third waveform shaping circuit output 31y,
The height angle error signal 14 is added by the sixth adder 68 to become the sixth adder output 27, and is squared by the second/square multiplier 70 to the second/squared multiplier 70.
The output becomes the squaring multiplier output 28, and is added together with the first and squaring multiplier output 25 in the third adder 71 to become the third adder output 26, which is added together with the gate width signal 23 to the fourth adder 72. and becomes the fourth adder output 29, and the first waveform shaping circuit 73
The waveform is shaped by the gate signal 22 to become the gate signal 22.

Through the above explanation, it has been explained that the position of the target can be known by extracting only the signal of the target part using the coaxial rotation type array detector.

(Supplementary explanation of the embodiment) (A) In Fig. 3, the array detector 54 was explained as a linear array detector in one row, but the array detectors are arranged in two rows, one as an infrared detector and the other You can make it two-color like an ultraviolet detector, or
They may be arranged in a cross pattern instead of in two rows. In this case, a receiver is connected to each row of array detectors. It is also possible to divide and use the array detector.

(b) In the embodiment shown in Fig. 1, when the azimuth angle and elevation angle error signals are demodulated by the synchronous detector 61, synchronous detection is performed once using the signal in the form of the product of equations (7) and (8). Although the processing was performed in the above, synchronous detection may be performed separately using two synchronous detectors.

(c) In order to explain the principle of demodulation, the target mobile was described as circular, but of course actual models, aircraft, ships, vehicles, etc. are not circular, but in that case, the gate width signal 23 is It may be changed depending on the angle.

(D) In FIG. 1, the gate circuit 59 is placed after the bandpass amplifier 58, but the array detector 54
It can be placed behind.

(E) Although the algorithm for generating the gate signal 22 has been explained using equation (19), the gate signal 22 may also be generated using the following equation.

g ₁ (t)=Sign {｜Rg｜ ^z − [(x−Az) ² + (y−El)
² ] ^z } ...(21) where z is a real number excluding 0. Of course, when Rg is positive, the absolute value of equation (21) is unnecessary.

(Effects of the present invention) (a) In order to avoid being tracked, the target on the tracked side may, as a hindrance to the tracked side,
A decoy (decoy interference source device) is often placed at a certain distance from the target, but since the present invention has a gate circuit that extracts only the target signal, there is little interference from the decoy.

(b) Since there is a gate circuit that extracts only the target signal when there is noise in the background of the target, the signal-to-noise ratio of the azimuth error signal 13 and the elevation angle error signal 14 when tracking starts is improved. .

(c) Tracking receivers are equipped with an automatic gain control circuit to prevent target signal saturation, but if there is a large signal interference source, the automatic gain control circuit compresses the target signal to a small size. Gate circuit 5 that extracts only the target even when there are problems such as storage
9, such troubles can be avoided.

(d) Although the array detector 54 has the disadvantage that it is more expensive than a unit-type detector, it is much cheaper and has higher performance than a two-dimensional array detector, and the image processing speed of the rosette scan tracking device is lower than that of a two-dimensional array detector. It is possible to process much faster than .

(E) In order to improve the ability to discriminate between a target and the background or a target and a decoy, two-color detectors for infrared and ultraviolet light are used, but linear array detectors or unit type detectors are used. It is much more difficult to manufacture a two-dimensional array detector for two colors than a conventional detector.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating an embodiment of a tracking receiver using a coaxially rotating array detector according to the present invention, FIG. 2 is an explanatory diagram of an optical system in an embodiment of the present invention, and FIG. An explanatory diagram showing the relationship between the target and the array detector in the example; FIG. 4 is a block diagram for explaining the gate signal generator used in FIG. 1;
FIG. 5 is a block diagram showing a conventional example of a rosette scan optical system, FIG. 6 is an explanatory diagram showing an example of a rosette pattern, and FIG. 7 is a block diagram showing an example of an array detector. 1... Target position, 2... Circle target, 3... Rosette pattern, 4... Field of view, 5... Unit type detector output, 7... Array detector output, 8... Input signal, 9
...Optical system output, 10... Bandpass amplifier output,
11... Gate circuit output, 12... Low pass amplifier output, 13... Azimuth error signal, 14... Elevation angle error signal, 15... Fifth reference signal, 16... Fourth reference signal, 17... ...Second reference signal, 18...Third reference signal, 19...Line reference signal, 20...
Rotating machine output, 21... clock signal, 22... gate signal, 23... gate width signal, 24... fifth
Adder output, 25...First and second multiplier output, 2
6...Third adder output, 27...Sixth adder output, 28...Second/square multiplier output, 29...Fourth adder output, 30...Second waveform shaping circuit output,
31...Third waveform shaping circuit output, 50...First prism, 51...Second prism, 52...Condensing lens, 53...Unit type detector, 54...Array detector, 55...Objective Lens, 56...Optical system, 57
... Rotating machine, 58 ... Bandpass amplifier, 59 ...
Gate circuit, 60...Low pass amplifier, 61...
Synchronous detector, 62... Gate signal generator, 63...
...Second reference signal generator, 64...First reference signal generator, 65...Line reference signal generator, 66...
Clock signal generator, 67...Fifth adder, 68
...Sixth adder, 69...First and second multiplier, 7
0...Second/square multiplier, 71...Third adder,
72... Fourth adder, 73... First waveform shaping circuit, 74... Second waveform shaping circuit, 75... Third waveform shaping circuit, A... Center of circle target 2, R... Center of circle target Radius, a, b... Coordinates of the center of circular target 2,
x, y...Coordinates of the readout position of the array detector 7, 82...Switch drive circuit.

Claims (1)

[Claims] 1. A tracking receiver that detects the position of a target using the difference in brightness between the target and the background, comprising: an optical system that forms an image of the target on a focal plane; and a focal plane of the optical system. an array detector placed on top of the array detector in which optical detection elements are arranged linearly; a rotating machine that rotates the detector; a clock signal generator that generates a clock signal for reading out the output signal of the array detector and applies it to the array detector; and a synchronous detector that receives the output signal of the array detector. a first reference signal having the same period as the readout period of the output signal synchronized with the clock signal; and second and third mutually orthogonal references synchronized with the rotation of the array detector. A fourth and a fifth reference signal which are orthogonal to each other and which are generated using the signals are applied to the synchronous detector, and the synchronous detector uses the fourth and fifth reference signals to detect the array detector. A tracking receiver using a coaxial rotary array detector, characterized in that an error signal proportional to the deviation of a target from the optical axis is detected by synchronously detecting an output signal. 2. A gate signal for extracting a signal of a target portion included in the output signal of the array detector is applied to a gate circuit inserted between the array detector and the synchronous detector. A tracking receiver using the coaxial rotary array detector described in 2.