JPH0156389B2 - - 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 Invention When tracking a target such as an aircraft, ship, or vehicle, the antenna or optical system of the tracking device is first pointed in that direction to search the vicinity of the target, detect the target, and then begin tracking. Follow the steps. In order to increase the accuracy of target tracking, a tracking device with a narrow antenna beam width using high frequencies such as millimeter waves is used. The retraction width becomes narrower. For this reason, the rosette scan tracking method, which has a wide pull-in width, is attracting attention.
Since demodulators have been manufactured using digital methods, the devices are 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. Axis 21 in Fig. 2
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 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.

Figure 1 shows the formula with φ = 1, ω ₂ = 5, ω ₁ = 7.
It was drawn using (1) and (2).

FIG. 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 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 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 (1) and (2) are calculated to generate an azimuth error signal 25 and an elevation angle error signal 26.
Take out.

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.

As shown in FIGS. 3 and 4, in the conventional rosette scan receiver, time t is determined by equations (1) and (2).
In order to obtain the azimuths x and y from the azimuth angle at high speed, the calculation is performed by a digital demodulator. For this purpose, it is necessary to accurately measure time t, but if the distance between the target and the receiver is short or the target is relatively large, for example, the video signal 23 in Fig. 2
Since the pulse width of t becomes wider, it becomes difficult to measure time t, and a specific device becomes complicated. Further, in the digital method, noise due to quantization errors cannot be removed.

(4) 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.

(5) Principle and Examples of the Present Invention The principle of the present invention will be explained using the embodiments of the present invention shown in FIGS. 6, 7, and 8.

Since the rosette scan antenna 31 or the rosette scan optical system 45 rotates in opposite directions at two angular velocities ω ₁ and ω ₂ , the next reference signals 41 and 42 can be extracted from the two rotation axes.

Reference signal 41...S ₁ = sinω ₁ t...(3) Reference signal 42...S ₂ = cosω ₁ t...(4) Multiplier (mixer) and frequency divider from the signals of equations (3) and (4) By using a filter and a filter, the following signals can be obtained.

Reference signal...S ₃ = sin (ω ₁ + ω ₂ ) t ... (5) Reference signal... S ₄ = sin (ω ₁ - ω ₂ ) t ... (6) As the reference signal 63 S ₅ = sin ω ₁ + ω ₂ /2t ...(7) As the second reference signal 81 S ₆ = sinω ₁ −ω ₂ /2t ...(8) As the sixth reference signal 107 S ₉ = cosω ₁ +ω ₂ /2t ...(9) Added signal As 102, S ₈ = cosω ₁ +ω ₂ /2t...(10) As third reference signal 82, S ₇ = cosω ₁ -ω ₂ /2t...(11) As eighth reference signal 112, S ₁₀ = -cosω ₁ - ω ₂ /2t ...(12) are obtained, respectively.

The principle of the present invention will be explained diagrammatically using the time charts of FIGS. 5A, B, and C. When the center of the rosette pattern in FIG. 1 and the center of the target are deviated from each other, the trajectories toward the center in FIG. The position alternates back and forth. The arrows in the video signal 71 of FIG. 5A indicate the direction in which the target has moved due to the misalignment. The video signal 71 is converted into a fifth reference signal 101 as shown in FIG. 5B.
When synchronous detection is performed with , the third synchronous detection output 103
As shown in Figure 5C, the carrier angular frequency is (ω ₁ +ω ₂ )/2 and the modulation angular frequency is (ω ₁ −ω ₂ )/2.
When this third synchronous detection output 103 is filtered by the first bandpass filter 119, the first bandpass filter output 104 is obtained, which is approximately as follows. I can write.

S ₁₁ =2r ₁ cos(ω ₁ −ω ₂ /2t−φ) cosω ₁ +ω ₂ /2
t = r ₁ cos (ω ₁ t−φ) + r ₁ cos (ω ₂ t + φ)……(13) However , and the center position of the target is (a, b).

The dotted envelope in FIG. 5C is the error signal 75, from which the azimuth error signal 25 and the elevation angle error signal 26 are finally obtained.

The first embodiment shown in FIG. 6 will be described in detail.
The embodiment shown in FIG. 6 is an optical rosette scan demodulator. The optical input signal 30 is modulated by rosette scan optics 45, converted to a video signal by a photodetector 46, and converted to a video signal by a video amplifier 35.
A video signal 71 is obtained. on the other hand,
The fifth reference signal generator 1 obtains signals 41 and 42 synchronized with rotation from the two shafts rotating mechanical parts such as prisms and mirrors of the rosette scan optical system 45.
22, the second reference signal 81 and the third reference signal 8
2. Create a fifth reference signal 101 and a first addition signal 102. Now, when the video signal 71 is synchronously detected with the fifth reference signal 101 by the third synchronous detector 135, the angular frequency of the carrier is (ω ₁ +ω ₂ )/2, and the modulation frequency is (ω ₁ −ω ₂ )/2. A third synchronous detection output 103 that is very close to the balanced modulator output is obtained, and when harmonics are removed by passing this through a first bandpass filter 119, the first bandpass filter output 104 of equation (13) is obtained. When the first bandpass filter output 104 and the addition signal 102 are added together in the adder 120, the following signal is obtained as the adder output 105.

S ₁₂ = [1+r ₁ cos(ω ₁ −ω ₂ /2t−φ)] ×cosω ₁ +ω ₂ /2t ...(15) The amplitude of the addition output 105 is detected by the envelope detector 121, and high frequency components are removed. Then, the error signal 75
get.

S ₁₃ = r ₁ cos (ω ₁ + ω ₂ /2t-φ) ...(16) When the error signal 75 is synchronously detected by the second reference signal 81 and the third reference signal 82 in the second synchronous detection circuit 97, the following is obtained. An azimuth angle error signal 25 (Az) and an elevation angle error signal 26 (El) are obtained.

The second embodiment shown in FIG. 7 will be explained.
Only the differences from the first embodiment shown in the figure will be described. In this second embodiment, an eighth synchronous detection circuit 13 is used instead of the adder 120 and the envelope detector 121.
8, and the sixth reference signal 107 is used instead of the first addition signal 102. That is, when the first band-pass filter output 104 is synchronously detected in the eighth synchronous detection circuit 138 using the sixth reference signal 107 and passed through the low-pass filter 86, the following error signal 75 is obtained.

S ₁₄ = 2 ₁₁・₁ + ₂ 2 = r ₁ cos (ω ₁ − ω ₂ /2t−φ) ...(18) Equation (18) is the same as equation (16), and the following explanation is based on the It is the same as Figure 6.

The third embodiment shown in FIG. 8 will be described in detail.
The input signal 30 undergoes pulse modulation by a rosette scan antenna 31, is converted into an intermediate frequency signal by a first mixer 32 and a local oscillator 36, is amplified by an intermediate frequency amplifier 33, and is further amplified by an amplitude detector. 34 into a video signal and amplified by a video amplifier 35 as shown in FIG.
A video signal 71 is obtained. On the other hand, the reference signal 4 is transmitted from the two rotation axes of the rosette scan antenna 31.
1 and 42, and from these, the sixth reference signal generator 123 generates a reference signal 63, a fifth reference signal 101,
A second reference signal 81, a third reference signal 82, a sixth reference signal 107, and an eighth reference signal 112 are created. When the video signal 71 is synchronously detected using the fifth reference signal 101 shown in FIG. 5B, a third synchronous detection output 103 shown in FIG. 5C is obtained. Since only the signal of angular frequency ω ₁ passes through the second bandpass filter 124, from equation (13), the second bandpass filter output 10
6 can be written as follows.

S ₁₅ = r ₁ cos (ω ₁ t−φ) ...(19) Adding the second bandpass filter output 106 and the reference signal 63 as inputs to the second mixer 126,
(ω ₁ −ω ₂ )/2 of the mixer output spectrum
is selected by the fourth bandpass filter 128 to obtain the fourth bandpass filter output 110. This output 110 can be written as:

S ₁₆ = r ₁ sin (ω ₃ t−φ) ...(20) On the other hand, in the third band pass filter 125, only the signal with the angular frequency ω ₂ of the third synchronous detection output 135 passes through. Therefore, from equation (3), the third bandpass filter output 108 can be written as follows.

_{( ω 1 _} -ω ₂ )/2 is selected by the fifth bandpass filter 129 to obtain the fifth bandpass filter output 111.
This output 111 can be written as follows.

S ₁₈ = r ₁ cos (ω ₃ t−φ) ...(23) The azimuth error signal 25 (Az) is the result when the fourth bandpass filter output 110 and the second reference signal 81 are input. The synchronous detection output from the fourth synchronous detector 130 and the output from the fifth synchronous detector 131 when the fifth bandpass filter output 111 and the third reference signal 82 are input are sent to the second adder 136. Since it is an addition, it can be written as follows.

Az=r sin(ω ₃ t−φ) sinω ₃ t +r cos(ω ₃ t−φ)・cosω ₃ t =r ₃ cosφ=a ……(24) Similarly, the elevation angle error signal 26 (El) is The synchronous detection output by the sixth synchronous detector 132 when the fourth band-pass filter output 110 and the eighth reference signal 112 are input, the fifth band-pass filter output 111 and the second reference signal 81 Since it is the result of adding the seventh synchronous detector output of the seventh synchronous detector 133 when inputted to the third adder 137, it can be written as follows.

El=r sin(ω ₂ t−φ)・(−cosω ₃ t) +r cos(ω ₃ t−φ)・sinω ₃ t=r sinφ=b……(25) Equations (24) and (25) In the product operation, equation (17)
Unlike , one-cycle averaging operation is not required, so
Compared to the first embodiment shown in FIG. 6, the third embodiment shown in FIG. 8 allows a faster response.

(6) 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, even if the antenna beam width or the viewing angle of the optical system is widened and the target is a point radio wave source or a point light source, the explanation using the previous formula can be justified as is.

(b) Although the demodulation principle of the present invention uses a circular target as a model, even in the case of an actual non-circular target, the vicinity of the center is tracked.

(c) The two angular frequencies ω ₁ and ω ₂ can be determined independently, but by synchronizing them,
It is also possible to simplify the extraction of the reference signal.

(d) In the explanation so far, the term "signal" has a wide meaning in an actual device, such as normalized voltage or current.

(7) Effects of the present invention (a) Compared to conventional methods, the band is narrower, there is no quantization error, and the signal-to-noise ratio is superior.

(b) The target size and signal strength are unrelated to the error signal, and although it is an analog system, an automatic gain control circuit is not required in principle, making the demodulator extremely simple.

(c) Narrowing the band makes it more resistant to interference.

[Brief explanation of drawings]

Figure 1 is a graph showing an example of a rosette pattern, Figure 2 is an explanatory diagram of a video signal obtained when a rosette scan modulator detects a point target, and Figure 3 is a conventional example of a rosette scan receiver for millimeter waves. 4 is a block diagram of a conventional example of an optical rosette scan receiver, and FIG. 5 is a block diagram of a conventional example of an optical rosette scan receiver.
C is a waveform diagram showing that an error signal can be extracted from a video signal according to the principle of the present invention, and FIG. 6 is a first embodiment of a rosette scan demodulator according to the present invention, which is an optical rosette scan demodulator. FIG. 7 is a block diagram showing a rosette scan demodulator for optical use, which is a second embodiment of the present invention, and FIG. 8 is a block diagram showing a rosette scan demodulator for millimeter waves, which is a third embodiment of the present invention. FIG. 19... Rosette pattern, 20... Search angle,
23...Video signal, 25...Azimuth error signal (Az), 26...Elevation angle error signal (El), 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...
...Reference signal (S ₁ ), 42 ...Reference signal (S ₂ ), 45
... Rosette scan optical system, 46 ... Photodetector, 63 ... Reference signal (S ₅ ), 71 ... Video signal, 75 ... Error signal (S ₁₃ ), 81 ... Second reference signal (S ₆ ) , 82...Third reference signal ( _S7 ), 86...
...Low pass filter, 97...Second synchronous detection circuit,
101...Fifth reference signal, 102...First addition signal ( _S8 ), 103...Third synchronous detection output, 104
...First bandpass filter output (S ₁₁ ), 105...
Adder output (S ₁₂ ), 106... Second band pass filter (S ₁₅ ), 107... Sixth reference signal (S ₉ ), 10
8... Third band pass filter output (S ₁₇ ), 110...
...Fourth band pass filter output ( _S16 ), 111...Fifth band pass filter output ( _S18 ), 112...Eighth reference signal ( _S10 ), 119...First band pass filter wave equipment,
120... Adder, 121... Envelope detector, 1
22...Fifth reference signal generator, 123...Sixth reference signal generator, 124...Second band pass filter,
125...Third band pass filter, 126...Second
Mixer, 127...Third mixer, 128...Fourth
Bandpass filter, 129...Fifth bandpass filter, 130...Fourth synchronous detector, 131...Fifth
Synchronous detector, 132...Sixth synchronous detector, 133
...Seventh synchronous detector, 135... Third synchronous detector, 136... Second adder, 137... Third adder, 138... Eighth synchronous detector.

Claims (1)

[Scope of 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, as described above. Synchronized by a reference signal with an angular frequency (ω ₁ +ω ₂ ) that is the sum of two angular frequencies (ω ₁ , ω ₂ ) obtained synchronously from the two axes rotating the rosette scan antenna or the rosette scan optical system. A rosette scan characterized in that an amplitude modulated signal is created by adding a reference signal of angular frequency (ω ₁ +ω ₂ )/2 to the signal obtained by detection, and an error signal is extracted by amplitude-detecting the signal. Demodulator. 2. A video signal obtained by receiving and detecting electromagnetic waves from the target by the rosette scan antenna or a video signal obtained by receiving and detecting light from the target by the rosette scan optical system is transmitted to the rosette scan antenna or the A signal obtained by synchronous detection using a reference signal with an angular frequency (ω ₁ +ω ₂ ) that is the sum of two angular frequencies (ω ₁ , ω ₂ ) obtained synchronously from the two axes rotating the rosette scan optical system. A rosette scan demodulator is characterized in that an error signal is extracted by performing synchronous detection using a reference signal of angular frequency (ω ₁ +ω ₂ )/2. 3. A video signal obtained by receiving and detecting electromagnetic waves from the target by the rosette scan antenna or a video signal obtained by receiving and detecting light from the target by the rosette scan optical system is transmitted to the rosette scan antenna or the The angle obtained when synchronously detecting the angular frequency (ω ₁ +ω ₂ ) of the sum of the two angular frequencies (ω ₁ , ω ₂ ) obtained synchronously from the two rotating axes of the rosette scan optical system. Two signals with frequencies ω ₁ and ω ₂ are mixed with two orthogonal reference signals with an angular frequency (ω ₁ +ω ₂ )/2, and the resulting angular frequency (ω ₁ −
The _two signals with angular frequency (ω ₁ −
The azimuth error signal and the elevation angle error signal are obtained by summing two signals obtained by synchronous detection using two orthogonal reference signals of ω ₂ )/2. Rosette scan demodulator.