JPH0130432B2 - - 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 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.
Naturally, since the beam width is narrow, the pull-in width for pulling from the search state to the tracking state becomes 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, the equipment is still expensive, and low-noise ones are difficult to manufacture. be.
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. Vertical axis 2 in Figure 2
1 is the target intensity, and the horizontal axis 22 is time.
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, or concave mirrors for light in opposite directions 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. The coordinates (x, y) of point P on the rosette pattern 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 produces a video signal 23 as shown in FIG. Video signal 23
In order to accurately determine the time t from the pulse signal, it is necessary to determine the 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 obtained in this way is calculated using equations (1) and (2).
The position (x, y) of the target P is determined by substituting it into . Thus, compared to conventional tracking devices, monopulse tracking devices, or reticle tracking devices, rosette scan tracking devices are significantly more complex.

(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 near 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 signal 35 outputs the video signal 23 in FIG. 2 and is applied to a digital demodulator 38. On the other hand, signals 41 and 42 synchronized with the rotation are obtained from the two axes rotating the rosette scan antenna 31, a reference signal generator 37 extracts a synchronization signal 39 necessary for demodulation, and a digital demodulator 38 converts the By calculating (1) and (2), an azimuth angle error signal 25 and an elevation angle error signal 26 are extracted.

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, as shown in FIGS. 3 and 4, in the conventional rosette scan receiver, equations (1) and (2)
In order to solve the azimuths x and y from time t, it is difficult to perform high-speed calculations of sin ( ) and cos ( ) using an analog method, so calculations (1) and (2) are performed using a digital method. It is often For this purpose, 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, it is necessary to accurately measure the time t in Figure 2. However, if the distance between the target and the receiver is short or the target is relatively large, for example, the pulse width of the video signal 23 in Figure 2 will widen, so the time t near the center of the pulse will be measured. As a result, the specific device is complicated. Further, in 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. 7 and 8, the rosette scan antenna 31 or the rosette scan optical system 45 has two angular velocities ω ₁ ,
Since it is rotating in the opposite direction at ω ₂ , the next reference signals 41 and 42 are generated by the generators attached to the two rotating shafts.
can be taken out.

Reference signal 41...S ₁ = sinω ₁ t (3) Reference signal 42...S ₂ = cosω ₂ t (4) However, ω ₁ and ω ₂ are assumed to be positive. From the signals of equations (3) and (4), the multiplier 87 calculates the reference signal...S ₃ = sin(ω ₁ +ω ₂ )t...(5) The reference signal...S ₄ = sin(ω ₁ -ω ₂ )t...( 6) A reference signal can be created. Also, equations (5) and (6)
When the reference signals 61 and 62 are passed through the 1/2 frequency dividers 88 and 89, the first frequency divider output 90 is S ₅ =sinω ₁ +ω ₂ /2t (7) The second frequency divider output 91 is S ₆ = sinω ₁ −ω ₂ /2t (8) is obtained. Furthermore, the signal of equation (8) is converted to the first (π/2)
When passed through the phase shifter 96, a reference signal _S7 of _S7 = _cosω1 - _ω2 /2t (9) can be generated. Equations (7) and (8) become the signals that create the second reference signal 81 of the synchronous detection circuit 97 of this demodulator, and equations (7) and (9) create the third reference signal 82 of the synchronous detection circuit 97. It becomes a signal.

The principle of the present demodulator will be explained using a model of a circular target 51 having a small radius r as the target size. Consider the case where 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, ΔABC and ΔABD are congruent.
The scan signal is rotated by θ from the x-axis, and
This is an example of passing from the quadrant to the 24th quadrant. In Figure 6, =m, =l, ==r, =
Let it be 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 −=2l (10), and it can be seen that equation (10) has no relation to the target size r, the cutting edge 2m, etc., and it is sufficient to pay attention only to l. 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 becomes 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, and is a reference signal with an angular frequency of (ω ₁ +ω ₂ )/2. Corresponds to synchronous detection of the signal. θ in equation (17) can be replaced by θ=ω ₁ −ω ₂ /2 (18).

When the two orthogonal signals S ₆ and S ₇ of equations (8) and (9) are used for synchronous detection in the synchronous detection circuit 97, 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. In the explanation so far, the angular frequency of the fundamental wave of the reference signal is (ω ₁ + ω ₂ )/2 and the synchronous detection using the reference signal is (ω ₁ − ω ₂ )/2.
Although the synchronous detection using the reference signal has been explained separately, it is also possible to perform synchronous detection all at once. When the video signal 71 is expressed by V(t), the azimuth error signal 25 (Az) and the elevation angle error signal 26 (El) can be written as follows.

However, Sign(x)=1 x>0 0 x=0 −1 x<0 (21). 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.

(7) Embodiment of the present invention FIG. 7 shows a rosette scan demodulator for millimeter waves, which is a first embodiment of the present invention. Input signal 3
0 is demodulated 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 to obtain a video signal 71.

On the other hand, two reference signals 41 corresponding to equations (3) and (4) synchronized with the rotation are generated from generators attached to the two rotating shafts of the rosette scan antenna 31,
42, and by the first multiplier 87, the formula
Two reference signals 61 and 62 of (5) and (6) are obtained. Further, from the reference signal 61, a first (1/2) frequency divider 88 produces a first frequency divider output 90 corresponding to equation (7). By dividing the low frequency reference signal 62 obtained by the multiplier 87 by the second (1/2) frequency divider 89, a second frequency divided output signal 91 corresponding to equation (8) is obtained.
is obtained. When the first frequency divider output 90 and the second frequency divider output 91 are input to the third multiplier 102, the following signal can be obtained as the third multiplier output.

S ₁₀ = sin (ω ₁ +ω ₂ /2t)·sin (ω ₁ −ω ₂ /2t) (22) The following signal is obtained as the output of the first (π/2) phase shifter 96.

S ₇ = cosω ₁ −ω ₂ /2t (23) When the first frequency divider output 90 (S ₅ ) and the output S ₇ of the first (π/2) phase shifter 96 are input to the fourth multiplier 103, , we get the following signal as the output of the fourth multiplier:

S ₁₁ = sin(ω ₁ +ω ₂ /2t)・cos(ω ₁ −ω ₂ /2t) (24) The output S ₁₀ of the third multiplier 102 is the waveform shaping circuit 9
5 and becomes the second reference signal 81. This signal 81 can be written as follows.

S ₁₂ =Sign{sin(ω ₁ +ω ₂ /2t)・sin(ω ₁ −ω ₂ /
2t)}...(25) The fourth multiplier output _S11 passes through the waveform shaping circuit 95 and becomes the third reference signal 82. This signal 82 can be written as follows.

S ₁₃ =Sign{sin(ω ₁ +ω ₂ /2t)・cos(ω ₁ −ω ₂ /
2t)} ...(26) When the video signal 71 is synchronously detected by the synchronous detection circuit 97 using the second reference signal 81 and third reference signal 82 obtained in this way, the azimuth error signal 25 and the height are An angular error signal 26 is generated.

As explained above, according to the first embodiment,
As stated in the main points of the configuration of the present invention, the video signal 71 obtained by receiving and detecting electromagnetic waves from the target by the rosette scan antenna 31 and the two axes on which the rosette scan antenna 31 is rotated are transmitted. Two angular frequencies obtained synchronously (ω ₁ ,
ω ₂ ), the angular frequency of the fundamental wave is 2 in the form of the product of two reference signals, (ω ₁ +ω ₂ )/2 and (ω ₁ −ω ₂ )/2.
An azimuth angle error signal 25 and an elevation angle error signal 26 can be extracted by synchronous detection using two orthogonal reference signals.

FIG. 8 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 parts that are different from the figures and FIG. 7 which is the first embodiment, only the differences will be described. In the configuration shown in FIG. 8, the input signal 30 is input to the rosette scan optical system 45,
After being modulated here and detected by the photodetector 46,
It is amplified by a video amplifier 35. The obtained video signal is applied to a synchronous detection circuit 97. On the other hand, Equation (3) synchronized with the rotation from the generator attached to the two rotating shafts of the rosette scan optical system 45,
The two reference signals 41 and 42 corresponding to (4) are taken out, and the second (π/2) phase shifter 115 and the third (π/2) phase shifter 115 and the third (π/2)
2) Add to phase shifter 116. This causes signal 4
1 and 42 are respectively as follows.

S ₈ = sinω ₂ t … (27) S ₉ = −cosω ₁ t … (28) The first adder output S ₁₄ connects the second (π/2) phase shifter output and the reference signal 41 to the first adder 110, so it can be written as follows.

S ₁₄ = sinω ₁ t + sinω ₂ t (29) Since the second adder output S ₁₅ is the result of adding the third (π/2) phase shifter output and the reference signal 42 by the second adder 111, It can be written as follows.

S ₁₅ = cosω ₂ t−cosω ₁ t (30) The first adder output S ₁₄ is waveform-shaped by the waveform shaping circuit 101 to obtain the second reference signal 81 (S ₁₂ ).

S ₁₂ =Sign{−sin(ω ₁ +ω ₂ /2t)・sin(ω ₁ −ω ₂
/2t)} (31) The second adder output S ₁₅ is waveform-shaped by the waveform shaping circuit 101 to obtain the second reference signal 82 (S ₁₃ ).

S ₁₃ =Sign{−sin(ω ₁ +ω ₂ /2t)・cos(ω ₁ −ω ₂
/2t)} ...(32) (8) Supplementary explanation of the embodiment (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, the beam width of the antenna or the viewing angle of the optical system is expanding, and even if the target is a point radio source or a point light source, the explanation using the previous formula can be justified as is, so the explanation so far is However, there is no concern about practicality.

(b) In order to explain the principle of demodulation, the target model was described as circular, but actual models, such as aircraft, ships, and vehicles, are of course not circular, but as shown by the calculation of equation (10), the target model is circular. Since it tracks nearby areas, there is no problem with practicality.

(c) 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 has been explained, but in a synchronous case, the reference signals 81 and 82 can be easily created from one reference signal 41 or 42, and the demodulator is even simpler. become.

(d) The two oppositely rotating angular velocities ω ₁ and ω ₂ of the rosette scan antenna or rosette scan optical system have been explained as positive, but clockwise,
Since counterclockwise rotation is naturally allowed, ω ₁ and ω ₂ take positive and negative values. Of course, this demodulator will work even in that case.

(e) 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.

(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 is superior in signal-to-noise ratio.

(b) The size of the spread of the target in FIG. 6 is not related to the target azimuth error and elevation angle error signals, as shown by equation (10). Therefore, the video signal input to the demodulator can be a binary signal regardless of the target signal strength, and although it is an analog system, an automatic gain control circuit is not required, making it an extremely simple demodulator.

(c) 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)
7 is a block diagram showing a millimeter wave rosette scan demodulator according to the first embodiment of the present invention, and FIG. 8 is a block diagram of an optical rosette scan demodulator according to the first embodiment of the present invention. FIG. 2 is a block diagram showing a second embodiment. 1-12...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, 3
2...Mixer, 33...Intermediate frequency amplifier, 34...
...Amplitude detector, 35...Video amplifier, 36...
Local oscillator, 39...Synchronization signal, 41, 42...
Reference signal, 45... Rosette scan optical system, 4
6...Photodetector, 51...Circular target, 61, 62,
63...Reference signal, 71...Video signal, 81...
...Second reference signal, 82...Third reference signal, 87...
...First multiplier, 88...First (1/2) frequency divider, 89
...Second (1/2) frequency divider, 90...First frequency divider output, 91...Second frequency divider output, 95...Waveform shaping circuit, 96...First (π/2) Phase shifter, 97...
Synchronous detection circuit, 101...Waveform shaping circuit, 102
...Third multiplier, 103...Fourth multiplier, 110
...First adder, 111...Second adder, 115
...Second (π/2) phase shifter, 116...Third (π/2) phase shifter, 116...Third (π/2) phase shifter,
2) Phase shifter.

Claims (1)

[Claims] 1 Receive and detect electromagnetic waves from the target with a rosette scan antenna, or receive and detect light from the target with a rosette scan optical system to obtain a video signal, and rotate the rosette scan antenna or the rosette scan optical system. _The angular frequency of _the fundamental wave is (ω ₁ +
Create orthogonal reference signals in the form of the product of two reference signals, ω ₂ )/2 and (ω ₁ −ω ₂ )/2, and perform synchronous detection of each of the video signals using these orthogonal reference signals. A rosette scan demodulator for extracting an error signal at the target position.