JPH0130431B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical field to which the present invention pertains The present invention relates to a rosette scan method used in a tracking device that tracks electromagnetic waves or light with short wavelengths generated by a target itself or reflected from the target. The present invention relates to a rosette scan demodulator that detects error signals for extracting error signals of the elevation angle and azimuth angle of a target that can be used in a receiver.

(2) 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 directed in that direction, or the target is detected and tracked by searching the vicinity of the target. Follow the steps to enter. In order to improve target tracking accuracy, tracking devices with narrow antenna beam widths using high frequencies such as millimeter waves are used.
Since the beam width is narrow, the width of pull-in for pulling from the search state to the tracking state is naturally narrow. For this reason, the rosette scan tracking method with a wide pull-in width is attracting attention, but demodulators have been made digitally so far, so the equipment is still expensive and low-noise devices are difficult to manufacture. Therefore, there is still a demand for a simple, low-noise analog system.

(3) Prior art and its general problems Figure 1 shows an example of a rosette pattern produced by a rosette scan antenna or optical system.
19 in FIG. 1 is a 12-valve rosette pattern.
The circled area 20 is the search angle. When a target is located at point P on the rosette pattern, the target is detected at time t in the video signal 23 of the rosette scan modulator as shown in FIG. The vertical axis of FIG. 2 is the target intensity 21, and the horizontal axis is the time 22. This is the basic function of a rosette scan modulator. This will be explained in more detail.

A rosette scan modulator, for example, creates a rosette pattern by rotating two antennas for millimeter waves and two lenses, prisms, concave mirrors, etc. for light at different angular velocities ω ₁ and ω ₂ . The principle meaning of the rosette pattern being created by rotating two lenses, prisms, or concave mirrors will be explained. Coordinates of point P on the rosette pattern (x,
y) can be expressed as follows.

x=-φsinω ₁ +ω ₂ /2t・cosω ₁ −ω ₂ /2t =φ/2(sinω ₂ t+sinω ₁ t) …(1) y=−φsinω ₁ +ω ₂ /2t・sinω ₁ −ω ₂ /2t = φ/2(cosω ₂ t−cosω ₁ t) …(2) In Figure 1, φ=1, ω ₂ =5, ω ₁ =7, and the formula
It was drawn by computer using (1) and (2). A target on the pattern of FIG. 1 will produce a video signal 23 as shown in FIG. In order to accurately determine time t from the video signal 23, it is necessary to determine time t from a pulse signal with a sharp rise, and the demodulation circuit becomes wideband, resulting in a poor signal-to-noise ratio. The time t thus obtained is substituted into equations (1) and (2) to obtain the position (x, y) of the target P. Thus, rosette scan tracking devices are significantly more complex than conventional tracking devices, monopulse tracking devices, or reticle tracking devices.

(4) Specific problems with the prior art Figure 3 shows a conventional example of a rosette scan receiver for millimeter waves. The rosette scan antenna 31 creates a rosette pattern as shown in FIG. 1 to search the vicinity of the target. Input signal 30 to the antenna
If there is, the output of the antenna 31 is the local oscillator 3
6. The signal is converted into an intermediate frequency by the mixer 32, amplified by the intermediate frequency amplifier 33, and converted into a video signal by the amplitude detector 34. Then, the video amplifier 35 outputs the video signal 23 shown in FIG.
to the digital demodulator 38. On the other hand, signals 41 and 42 synchronized with the rotation of the rosette scan antenna 31 are obtained from the two rotating axes, and a synchronization signal 39 necessary for demodulation is extracted by the reference signal generator 37. 1) and (2) are calculated to take out the azimuth angle error signal 25 and the elevation angle error signal 26.

FIG. 4 shows a conventional example of an optical rosette scan receiver. The difference from FIG. 3 is that the rosette scan antenna 31 is replaced by a rosette scan optical system 45, and the mixer 32 is replaced by a photodetector 46, but otherwise there is basically no difference from FIG.

By the way, in a rosette scan receiver, the formula
In order to solve x and y by substituting time t into (1) and (2), it is difficult to perform high-speed calculation of sin ( ) and cos ( ) using the analog method, so equations (1) and (2) The calculations are often performed digitally. Therefore, it is necessary to accurately measure the time t, but if the target is small and the pulse width of the video signal 23 when the target in Figure 2 is detected is very narrow, the time t in Figure 2 may be Although it can be measured accurately, when the target is large and the pulse width is wide, it is necessary to measure the time t near the center of the pulse, so the specific device becomes complicated. Further, with the digital method, noise due to quantization errors cannot be removed.

(5) Purpose of the present invention The present invention provides a simple signal pairing method for demodulating a target azimuth error signal and an elevation angle error signal from a video signal obtained as an output signal of a millimeter wave and optical rosette scan modulator. The purpose is to obtain a rosette scan demodulator with excellent noise ratio.

(6) Main points of the configuration of the present invention In the configuration of the embodiment of the present invention shown in FIGS. 8 and 9, the rosette scan antenna 31 or the rosette scan optical system 45 has two angular velocities ω ₁ ,
Since it is rotating at ω ₂ , the next reference signals 41 and 42 can be extracted by generators attached to the two rotating shafts.

S ₁ = sinω ₁ t…(3) S ₂ = cosω ₂ t…(4) However, ω ₁ and ω ₂ are assumed to be positive. From formulas (3) and (4), the multiplication circuit 87 calculates the reference signals 61, 62 of S ₃ =sin(ω ₁ +ω ₂ )t...(5) _S4 = sin(ω ₁ -ω ₂ )t...(6) can be made. Moreover, when the signals of equations (5) and (6) are passed through the 1/2 frequency divider 88, S ₅ = sinω ₁ +ω ₂ /2t …(7) S ₆ = sinω ₁ −ω ₂ /2t …(8) Reference signals 63, 81 are obtained. Furthermore, by passing the signal of equation (8) through the π/2 phase shifter 96, the third reference signal 82 of S ₇ =cosω ₁ −ω ₂ /2t (9) can be generated. Equation (7) is a signal that creates the first reference signal 72 of the first synchronous detection circuit 85 of this demodulator, and Equations (8) and (9) are the signal that creates the second reference signal 81 and the second reference signal 72 of the second synchronous detection circuit 97. 3 reference signal 8
It becomes 2.

The principle of this demodulator will be explained using a model of a circular target 51 having a small radius γ. Consider the case where the vicinity of the center of FIG. 1 is approximated by a straight line and the beam crosses the target as shown in FIG. The arrow numbers 1 to 12 in FIG. 5 indicate the direction and order of passing the target. Further, in this case, the position of the target 51 and the reference axis coincide, and both the azimuth angle error signal 25 and the elevation angle error signal 26 are zero.

FIG. 6 is a further enlarged version of FIG.
However, a case is shown in which the target position A (a, b) and the reference axis O do not match. The physical meaning of FIG. 6 will be explained. O is the reference axis of the tracking system and is the origin of its coordinates. A is the center position (a, b) of the circular target. C and D are the points where the beam crosses the circular target. B is the leg of the perpendicular drawn from A to CD. Therefore, △ABC and △ABD are congruent. This is an example in which the scan signal rotates by θ from the x-axis and passes from the second quadrant to the fourth quadrant. In Figure 6, =m, =l, ==
Let r,=h. As the video output of the modulator, a binary signal such as 1 in between and 0 in other areas is detected. This demodulator performs the operation -. =, so when the origin O of the coordinates is on the target, -=2l...(10), and equation (10) has no relation to the target size r, cutting edge 2m, etc., and we only need to pay attention to l. I understand that. From FIG. 6, a straight line passing through the reference axis O can be determined as follows.

y=cx...(11) However, c=tanθ...(12). The straight line passing through AB is perpendicular to y=cx and passes through the point (a, b), so y=-x/c+cb+a/c...(13).

The coordinates (bx, by) of the intersection point B of the two straight lines are given by formula (11),
Solve (13) (bx, by) = {cb+a/c ² +1, c(bc+a)
/c ² +1} ...(14). Therefore, the distance l of BO is l=|cb+a|/(c ² +1) ^1/2 (15).

If cb+a>0...(16) and using equation (12), l=btanθ+a/(tan ² θ+1) ^1/2 =√ ² + ² cos(
θ−tan ⁻¹ b/a) …(17) Equation (17) is a function only of the position (a, b) of target A. The signal obtained by equation (17) is the same as the signal obtained by a conical scan modulator or a reticle modulator often used in optical systems.

Furthermore, in order to explain this demodulator in an easy-to-understand manner, the center position of target A (a,
The case where b) is deviated from the reference axis O will be schematically explained using the time chart of FIG. As shown in FIG. 5, in the rosette scan modulator, the locus toward the center crosses alternately, so the center position of the pulse of the output video signal 71 of the rosette scan modulator alternates back and forth. The arrow in the video signal 71 in FIG. 7 indicates the direction in which the target has moved due to the misalignment. Video signal 71 and reference signal 72 to first synchronous detection circuit 85 {angular frequency (ω ₁ +
The product of ω ₂ )/2 signal} corresponds to the calculation of equation (10),
By removing harmonic components of the signal, an error signal 75 corresponding to equation (17) is obtained. 6th
The relative position of the target and the signal waveform will be explained in relation to each other using the diagram and the explanatory diagram of FIG. The signal corresponding to that in FIG. 6 corresponds to the pulse width of the video signal 71 in FIG. If the positive side pulse width of the first synchronous detector output 84, which is a bipolar pulse, is the negative side pulse width. Therefore, performing synchronous detection and filtering high frequency components is the same as performing the calculation of equation (10). As shown by the error signal 75 in FIG. 7, θ in equation (17) can be replaced by θ=ω ₁ −ω ₂ /2t (18).

When the second synchronous detection circuit 97 performs synchronous detection using the two orthogonal signals 81 and 82 of equations (8) and (9), Next, equation (19) shows that the azimuth error signal 25 (Az) and the elevation angle error signal 26 (El) are the reference axis O in Fig. 6.
It can be seen that it shows the position (a, b) of target A from . However, represents the average of one cycle. From the above explanation of the principles of the present invention, it can be seen that the present demodulator is completely different from the conical scan method and the reticle method.

When point O in the coordinates in Figure 6 is outside the target, = + ...(20), but in that case, the pulse width of the video signal 71 is not , so =2m ...(21), and it is at the target position. Although a proportional signal can no longer be obtained and the linearity of the input/output relationship deteriorates, when the rosette scan demodulator of the present invention is used in a tracking device equipped with a servo device 92 as shown in FIG. With the passage of time, it draws in near the center and becomes the relationship shown in Fig. 6, so it is sufficiently practical.

(7) Embodiment of the present invention FIG. 8 shows a rosette scan demodulator for millimeter waves, which is a first embodiment of the present invention. Input signal 3
0 is modulated by a rosette scan antenna 31, dropped to an intermediate frequency by a local oscillator 36 and mixer 32, amplified by an intermediate frequency amplifier 33, and detected by an amplitude detector 34. The video signal obtained by the detection is amplified by a video amplifier 35. The video signal 71
is synchronously detected by the first synchronous detector 85 using the first reference signal 72 or 74 as shown in FIG. 7, and becomes the first synchronous detector output 84. A low-pass filter 86 removes harmonic components from the detected signal to obtain an error signal 75, which is then subjected to synchronous detection by a second synchronous detection circuit 97 using the second reference signal 81 and third reference signal 82. This produces an azimuth angle error signal 25 and an elevation angle error signal 26.

Various reference signals will be explained. Two signals 41 and 42 corresponding to equations (3) and (4) synchronized with the rotation are extracted from the generators attached to the two rotating shafts of the rosette scan antenna 31, and are processed by the multiplier 87. Two signals 61 and 6 of equations (5) and (6)
Get 2. Furthermore, the signal 61 is converted into a signal corresponding to equation (7) by a 1/2 frequency divider 88, and is converted into a first reference signal 72 shown in FIG. 7 by a waveform shaping circuit 95.
Or get 74. Note that the reference signal 74 has a waveform in which the polarity of the bipolar pulse signal 76 having an angular frequency of (ω ₁ +ω ₂ ) shown in FIG. In the circuit 95, a process corresponding to the product operation of the first reference signal ₇₂ and the gate signal ₇₃ shown in FIG. (ω ₁ +ω ₂ /2
)t] may be performed. however,
sign(x) is a signal that is 1 when x>0 and -1 when x<0. A second reference signal 81 corresponding to equation (8) is obtained by dividing the low frequency reference signal 62 obtained by the multiplication circuit 87 by a 1/2 frequency divider 88, and a second reference signal 81 corresponding to equation (8) is obtained. The reference signal 81 is π/2
A third reference signal 82 corresponding to equation (9) can be obtained by the phase shifter 96.

According to the first embodiment, as described as the main points of the configuration of the present invention, the video signal 71 obtained by receiving and detecting the electromagnetic waves from the target by the rosette scan antenna 31 and the rosette scan antenna 31 A signal 72 with a frequency of 1/2 of the sum of the two frequencies obtained from the two axes rotating the , or a bipolar pulse signal with a frequency of the sum of the two frequencies, with positive and negative polarities alternated every cycle. By switching, as shown in FIG. 7, an error signal 75 can be obtained by multiplying the signal 74 with a signal 74 whose repetition angular frequency has become (ω ₁ +ω ₂ )/2 (synchronous detection). Can be done. From this error signal 75, the azimuth error signal 25 and the elevation angle error signal 26 can be determined.

FIG. 9 shows an optical rosette scan demodulator according to a second embodiment of the present invention. The fourth example is the conventional example.
Since it is sufficient to explain only the differences from the figure and FIG. 8 which is the first embodiment, only the differences will be described. In FIG. 9, the reference signal 61, which is the output signal of the multiplier 87, is input to a second waveform shaping circuit 98, and in order to remove unnecessary noise or interference signals, a gate signal 73 is generated and applied to the gate circuit 99.
A video signal 71 is obtained as the output of the gate circuit 99. Furthermore, if the signal 72 is used as the first reference signal to the first synchronous detection circuit 85, an error signal 75 is obtained at the output of the low-pass filter 86. The synchronous detection using the gate circuit 99 using the gate signal 73 and the signal 72 is completely the same in operation as the case where the signal 74 is used as the first reference signal of the first synchronous detection circuit shown in FIG. FIG. 10 will be explained. 1st
FIG. 0 is an example of a tracking device using a demodulator according to the present invention. Rosette scan antenna 31 (for optical use, rosette scan optical system 4 in Fig. 9)
5) and the servo device 92 have a mechanically rotated structure. The servo device 92 directs the rosette scan antenna 31 (or the rosette scan optical system 45) toward the target so as to make the azimuth error signal 25 and the elevation angle error signal 26 zero. Note that the other configurations are the same as in FIG. 8.

(8) Supplementary Explanation of Examples (a) So far, we have described the case where the target is wide and the lines of the rosette pattern are very thin.
On the other hand, if the beam width of the rosette scan antenna or the viewing angle of the rosette scan optical system is sufficiently wide compared to the target size, and the target is a point radio source or a point light source,
This will be explained using Figure 1. The field of view of the optical system (the beam of the antenna) shown by the circle in the figure scans. A1 is a point light source (point radio wave source). If the center of the field of view of the optical system (beam of the antenna) moves from C1 to D1, and the signal is received from the state of the circle α indicating the field of view, and the signal disappears in the state of β, the result will be as shown in Figure 6. The corresponding signal is obtained, below:
The explanation is the same as in FIG.

(b) In order to explain the principle of demodulation, the target model was explained as a circle in Figure 6, but when the shape of the target is as shown in Figure 12 and the viewing angle of the optical system is sufficiently narrow relative to the target, m ₁ = _{1 1} = _{1 1} …(22) m ₂ = _{2 2} = _{2 2} …(23) l ₁ = _{1 1} …(24) l ₂ = _{2 1} …(25) r ₁ = _{1 1} = _{1 1} …( 26) r ₂ = _{1 2} = _{1 2} … (27) h ₁ = _{1 1} … (28) h ₂ = _{1 2} … (29) _{1 1} − _{1 1} = 2l ₁ … (30) _{2 1} − _{1 2} = 2l ₁ ...(31) Then, as explained in Fig. 6, the azimuth error signal 25 is as if the center of tracking was _A1 .
and the height angle error signal 26 are obtained, so A ₁
may not be at the center of the target, but the target can still be tracked.

(c) Since the size of the target changes and the pulse width of the video signal 71 also changes depending on the distance between the target and the tracking device, a circuit that adapts the pulse width of 73 in FIG. 7 to the size of the target is provided. In combination with , the signal-to-noise ratio of this demodulator becomes even better.

(d) The rosette pattern in FIG. 1 is an example in which the two rotating axes of the rosette scan modulator rotate synchronously at a ratio of 7:5. As shown in equations (1) to (17) used to explain the demodulation principle, the two rotating axes do not need to be synchronized. In the embodiments shown in FIGS. 8 and 9, an asynchronous case was explained, but in a synchronous example, reference signals such as 63 and 81 can be easily created from one signal of 41 or 42, and the demodulator is even simpler. become.

(e) We have explained that the two rotating angular velocities ω ₁ and ω 2 of the rosette antenna or rosette optical system are positive, but since clockwise and counterclockwise rotations are naturally allowed, ω ₁ and ω ₂ take positive and negative _values . . Of course, this demodulator will work even in that case.

(f) The signals used in the explanation so far, such as the azimuth error signal and the elevation angle error signal, have the same meaning as voltage on actual hardware. Therefore, the meaning of "signal" has a wide meaning, including a normalized amount or a digitized amount of voltage or current.

(e) The gate circuit extracts only the target and removes unnecessary noise or interfering signals, resulting in an excellent signal-to-noise ratio.

(9) Effects of the present invention (a) In order to extract the azimuth angle error signal and the elevation angle error signal, it is necessary to measure the time to detect the target signal.
Compared to the conventional method of calculating sin( ) and cos( ), the present invention is a narrowband analog method and has no quantization error, so it has an excellent signal-to-noise ratio.

(b) The size of the spread of the target in FIG. 6 is not related to the azimuth angle error signal and the elevation angle error signal of the target, as shown by equation (10). Therefore, the input video signal to the demodulator is independent of the target signal strength.
It is an extremely simple demodulator, as it only needs to be binary and does not require an automatic gain control circuit even though it is an analog system.

(c) The demodulation circuit of the present invention includes two synchronous detection circuits. Therefore, even if there is a source of interference near the target, the reception bandwidth is narrowed by the two synchronous detection circuits, so it will not easily be interfered with by electromagnetic waves or light. Note that if the pulse width of the bipolar pulse reference signal of the first synchronous detection circuit is approximated to the target size, interference will be further reduced.

(d) Currently, it is much cheaper than digital methods.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of a rosette pattern created by a rosette scan antenna or optical system, and FIG. 2 is an explanatory diagram showing an example of a video signal obtained when a rosette scan modulator detects a target. Fig. 3 is a block diagram showing a conventional example of a rosette scan receiver for millimeter waves, Fig. 4 is a block diagram showing a conventional example of a rosette scan receiver for optical use, and Fig. 5 shows a rosette pattern with a spread in the center. An explanatory diagram showing the order in which the tip of a narrow beam of a rosette scan antenna or an optical system passes when there is a circular target. FIG. 6 is an explanatory diagram used to explain the principle of the demodulator of the present invention. and the target is from the reference axis of the antenna or optical system (a, b)
Fig. 7 is a time chart used to show that the error signal can be extracted from the video signal output from the rosette scan modulator by synchronous detection, and Fig. 8 is for millimeter waves. FIG. 9 is a block diagram showing a rosette scan demodulator according to a first embodiment of the present invention, and FIG.
FIG. 10 is a block diagram showing an example of a tracking device equipped with a rosette scan demodulator of the present invention, and FIG. 11 is a block diagram showing an example of a tracking device equipped with a rosette scan demodulator of the present invention. A diagram explaining the principle when the target is sufficiently spread compared to the size, and FIG. 12 is a diagram explaining the principle when the target is other than a circle. 1 to 12...Order, 19...Rosette pattern,
20...Search angle, 21...Target intensity, 22...
Time, 23... Video signal, 25... Azimuth error signal, 26... Elevation angle error signal, 30... Input signal, 31... Rosette scan antenna, 32...
... mixer, 33 ... intermediate frequency amplifier, 34 ... amplitude detector, 35 ... video amplifier, 36 ... local oscillator, 37 ... reference signal generator, 38 ... digital demodulator, 39 ... synchronization signal, 41, 42...
... Reference signal, 45 ... Rosette scan optical system,
46...Photodetector, 51...Circular target, 61,6
2, 63...Reference signal, 71...Video signal, 7
2, 74...first reference signal, 73...gate signal, 75...error signal, 81...second reference signal,
82... Third reference signal, 84... First synchronous detector output, 85... First synchronous detection circuit, 86... Low pass filter, 87... Multiplication circuit, 88... 1/2 minute Frequency generator, 92... Servo device, 95... Waveform shaping circuit, 96... π/2 phase shifter, 97... Second synchronous detection circuit, 98... Second waveform shaping circuit, 99... Gate circuit.

Claims (1)

[Claims] 1. A video signal obtained by receiving and detecting electromagnetic waves from a target with a rosette scan antenna, or a video signal obtained by receiving and detecting light from the target with a rosette scan optical system; A bipolar pulse signal having a frequency equal to the sum of two frequencies obtained synchronously from two axes rotating the rosette scan antenna or the rosette scan optical system is alternately switched between positive and negative polarity every cycle. A rosette scan demodulator characterized in that the error signal is extracted by multiplying the reference signal obtained by the above-mentioned reference signal or a reference signal having a frequency of 1/2 of the sum of the two frequencies.