JPS6336473B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a monopulse receiver of a monopulse tracking device using light or electromagnetic waves.

Tracking receivers have different formats depending on the frequency of the electromagnetic waves and wavelength of the light used, and they can also be used to direct strong light or electromagnetic waves from a tracking device to the reflected light or electromagnetic waves. There are various other types, such as active tracking devices that track the target and passive tracking devices that track based on the brightness and darkness between the target and the background. The monopulse receiver of the present invention is of the type used in passive tracking devices.

First, we will discuss the problems with conventional monopulse receivers for passive radars that do not use an illuminator, which is one of the most difficult tracking receivers to manufacture.

It is known that each object has its own brightness temperature, which varies depending on its shape and surrounding conditions. A radiometer is used to measure this brightness temperature, but if you try to use this radiometer to track tanks, cars, etc. on the ground,
Since a tracking receiver is constructed using the radiometer, a conical scan tracking device that is easy to manufacture is often used. The reason why a conical scan tracking device, which has lower tracking accuracy than a monopulse tracking device, is used is due to the difficulty in manufacturing a monopulse receiver. conical scan tracking device,
Both monopulse tracking devices use a radiometer to form a passive tracking receiver. The sensitivity ΔT min of this radiometer is calculated using the following formula:
It can be expressed by (1).

K varies depending on the type of radiometer and ranges from 1 to
Takes a value between 3. Ts is the sum of antenna noise temperature and receiver noise temperature, n is the number of receivers, B is the receiver bandwidth, and τ is the integration time after detection.

FIG. 1 shows a conventional example of a monopulse receiver used in a receiving section of an amplitude comparison type monopulse tracking radar. In this figure, signals 11, 12, 13, and 14 entering a monopulse antenna 8 are processed by a monopulse comparator 9 into a sum signal 15, a difference signal 16,
17 and added to mixer 5. A signal from a local oscillator 6 is also applied to each mixer 5, and the sum signal 15 and difference signals 16 and 17 are reduced to an intermediate frequency and applied to an intermediate frequency amplifier 7, respectively. The output of each intermediate frequency amplifier 7 is applied to a phase detector 10, and an azimuth angle error signal 18 and an elevation angle error signal 19 are extracted from each phase detector 10. From these two signals 18 and 19, the error angle of the target from the central axis of the monopulse antenna 8 is known.

In the configuration shown in FIG. 1, the intermediate frequency amplifier 7 is
Since there are a number of units, n in equation (1) is 3. However, in order to reduce the sensitivity ΔT min, we would like to widen the bandwidth B in equation (1) to about several hundred megahertz, but with the current technology, the Since the incoming signal is added to the phase detector 10, the sum signal 15
It is extremely difficult to align the phases of the carriers between the signal and the difference signals 16 and 17 and perform phase detection, which prevents the practical use of monopulse receivers.

FIG. 2 shows a conventional example of an optical monopulse receiver.
The photodetector 21 is placed on the focal plane of the lens or concave mirror of the optical system 20, and is placed on the focal plane of the lens or concave mirror of the optical system 20.
It has three detection elements 31, 32, 33, and 34. The four outputs of the photodetector 21 are each amplified by an amplifier 22, and the difference between these outputs is calculated by a subtraction circuit 26.
The azimuth angle error signal 18 and the elevation angle error signal 19 are output.

In the configuration shown in FIG. 2, the target is tracked so that the line 35 resulting from the optical signal 28 is centered on the four detection elements 31 to 34 of the photodetector 21 as shown in FIG. When the optical axis of the optical system 20 is shifted, the image on the focal plane is naturally shifted in the opposite direction. Therefore, if there is no variation between the channels of the photodetector 21 and the amplifier 22, the angle of the target from the optical axis can be known from the outputs 18 and 19. However, the outputs 18 and 19 in FIG.
2, the zero points of the outputs 18 and 19 do not coincide with the optical axis due to variations in the gain of the amplifier 22, and the target angle measurement error increases. Of course, this is a drawback.

In a tracking device for such a purpose, the key to making the tracking receiver successful is to reduce ΔT min in equation (1) and increase tracking angle accuracy.

Therefore, the present invention aims to provide a monopulse receiver that has high sensitivity, good angle tracking accuracy, and is easy to manufacture.

Embodiments of the monopulse receiver according to the present invention will be described below with reference to the drawings.

FIG. 4 is a first embodiment of the present invention, and shows a monopulse receiver for tracking a weak target signal (weak electromagnetic wave noise signal). Input signals 11, 12, 13, and 14 entering the monopulse antenna 8 are reduced to an intermediate frequency by a local oscillator 6 and a mixer 5, and then sent to four intermediate frequency amplifiers 7 in sequence at a constant cycle by a switch 41. Can be sorted. The signal that has passed through the intermediate frequency amplifier 7 is square-law detected by the detector 42 and sent to the second switch 43.
Here, the first switch 41, the second switch 43
As shown in FIG. 5, this is a 4-input, 4-output switch, and performs a switching operation so that each of the four input signals passes through the same intermediate frequency amplifier 7 the same number of times. This purpose can be achieved by using a rotary switch as shown in FIG. 5 and synchronizing the first switch 41 and the second switch 43. In other words, the signal from the antenna output end 8a is sent to the output end 43a of the second switch 43, the signal from the antenna output end 8b is sent to the output end 43b of the second switch 43, and the signal from the antenna output end 8c is sent to the output end 43b of the second switch 43.
The first and second switches 41 and 43 are switched so that the signal from the antenna output end 8d is output to the output end 43c of the second switch 43, and the signal from the antenna output end 8d is output to the output end 43d of the second switch 43. The output signals of the four output terminals of the second switch 43 pass through a low-pass filter 44 and enter a combination circuit 45, respectively, and a subtraction circuit 26 calculates the difference between the two output signals. Alternatively, the difference between multiple sums is created.
The output of one subtraction circuit 26 becomes the azimuth angle error signal 18, and the output of the other subtraction circuit 26 becomes the elevation angle error signal 19. The coupling circuit 45 is
The outputs of each filter 44 are added two by two as necessary and outputted to the subtraction circuit 26.

Next, the operation of this first embodiment will be explained. Compared to the conventional example shown in FIG. This will be shown and the role of a pair of synchronized switches 41 and 43 will be explained. 6th
The figure shows the mathematical model of Fig. 4. Input signal 1
Let 1, 12, 13, and 14 be x ₁ , x ₂ , x ₃ , and x ₄ .
It is assumed that the input-referred receiver noise corresponding to each of the four inputs is n ₁ , n ₂ , n ₃ , and n ₄ and is added to the input end of the first switch 41 via the adder 65, respectively. The outputs of the four detectors 42 are y ₁ , y ₂ , y ₃ ,
Let y be ₄ . It is sufficient to explain the switching operation of the switches 41 and 43 for one cycle, so considering one cycle, becomes. a ₁ , a ₂ , a ₃ , and a ₄ are the amplification degrees of the four intermediate frequency amplifiers 7, the subscript of the symbol in equation (2) represents the channel number, and the number inside the bracket represents the output order. Further, ² ₁ , ² ₂ , ² ₃ , and ² ₄ represent the averaged output after square detection. Next, if the second switch 43 is synchronized with the first switch 41, the outputs z ₁ , z ₂ , z ₃ and z ₄ of the second switch 43 are respectively expressed as follows.

Equation (3) corresponds to the case where two switches as shown in FIG. 5 are rotated in opposite directions. Next, low pass filter 4
4, calculate the sum of z ₁ (1), z ₁ (2), z ₁ (3), and z ₁ (4). similarly
z ₂ (1), z ₂ (2), z ₂ (3), z ₂ (4), ..., z ₄ (1), z ₄ (2), z ₄ (3
),
Also take the sum for z ₄ (4). Alternatively, the four sums may be literally calculated digitally. That is, the output of each low-pass filter 44 is s ₁ , s ₂ , s ₃ ,
If s ₄ , becomes. In equation (4), n ₁ , n ₂ , n ₃ , and n ₄ are input conversion noises connected to the four receiving systems, and are determined by the loss in the high frequency section and the noise figure of the mixer, preamplifier, etc. Therefore, it is possible to adjust ² ₁ , ² ₂ , ² ₃ , and ² ₄ equally.

² ₁ = ² ₂ = ² ₃ = ² ₄ ...(5) The outputs 18 (azimuth angle error signal: Az) and 19 (elevation angle error signal: El) of the subtraction circuit 26 are expressed by the formula
From (4) and (5) or becomes. Equations (6) and (7) show that the error angle outputs Az and El are proportional to the input power difference, which indicates that they are desirable as outputs of a monopulse receiver. Note that the coupling circuit 45 has s ₁ +s ₂ and s ₃ + in equation (7).
This circuit executes the operations of s ₄ , s ₁ +s ₄ , and s ₂ +s ₃ if necessary.

According to the first embodiment, the following effects can be achieved.

(1) The output of the monopulse antenna 8 is
The switches 41 and 43 distribute the amplification equally to the four intermediate frequency amplifiers 7, and the sum of the outputs of all the amplifiers 7 is calculated. The angle error signal 18 and the elevation angle error signal 19 do not fluctuate. Therefore, highly accurate tracking is possible.

(2) If the input conversion noise of the four receiving systems (mixer, intermediate frequency amplifier, etc.) is made equal so that the above equation (5) holds, then the signals 18 and 19 will have substantially no noise due to the receiving system. You can prevent it from appearing. Moreover, the intermediate frequency amplifier 7 has 4
Since it is a stand, n in equation (1) is 4. Highly sensitive tracking is possible from these points.

In the first embodiment, the mixer 5 is used to reduce the signal to an intermediate frequency and amplify it, but if the signal can be directly amplified, the mixer 5 may be omitted. Furthermore, although the second switch 43 is located after the detector 42, it may also be located after the amplifier 7. The low-pass filter 44 is located between the second switch 43 and the combination circuit 45, but the combination circuit 45 and the subtraction circuit 26
It may be during the subtraction circuit 26 or after the subtraction circuit 26.

FIG. 7 shows a mathematical model of a second embodiment of the invention in which the first switch is placed immediately after the monopulse antenna. In this case, the same components are given the same reference numerals. In this configuration, the outputs y ₁ of the four detectors 42,
y ₂ , y ₃ , and y ₄ are expressed by the following formulas.

Similarly, the outputs of the second switch 43 z ₁ , z ₂ , z ₃ , z ₄
teeth becomes. Therefore, the outputs s ₁ , s ₂ , s ₃ , s ₄ after passing through the low-pass filter 44 of z ₁ , z ₂ , z ₃ , z ₄ are The outputs of the subtraction circuit 26 are 18 (azimuth angle error signal: Az) and 19 (elevation angle error signal: El).
becomes as follows.

or It is. Since Equation (12) does not include the condition of Equation (5), the input-referred noise of the four mixers and amplifiers ^{is 2} ₁ ,
n ² ₂ , ² ₃ and ² ₄ may be different.

Up to now, the monopalace receiver for electromagnetic waves has been described in the first and second embodiments, but the same can be done in the case of optical signal source tracking. FIG. 8 shows a monopalace receiver for tracking an optical signal source as a target as a third embodiment of the present invention. The optical system 20 receiving the optical signal 28 is configured by a lens, a concave mirror, or a combination of a lens and a concave mirror.
Four detection elements 31 as shown in Fig. 3 are placed on the focal plane of
The output of each detector is sent to four amplifiers 2 by a first switch 41.
2 and synchronized with the first switch 41.
The switch 43 makes the relationship between the input signal and the output signal match again. That is, the signal at the output end 21a of the photodetector 21 is transmitted to the output end 4 of the second switch 43.
3a, the signal at the output end 21b is sent to the output end 43b,
The signal at the output end 21c is sent to the output end 43c,
The signal 1d is output to the first output terminal 43d.
And the switching operation of the second switches 41 and 43 is performed.
Below, the azimuth angle error signal 1 is calculated by the subtraction circuit 26.
8 and the principle of obtaining the elevation angle angle error signal 19 is the fourth
This is similar to the case of the first embodiment shown in the figure. A mathematical model of the signal processing method after the photodetector 21 of this third embodiment can be expressed as shown in FIG.

FIG. 9 shows a fourth embodiment of the present invention, in which a rotating photodetector is used in place of the first switch. In this case, the rotary detector 91 is considered to have the functions of both a switch and a detector, and a mathematical model of the signal processing method can be expressed as shown in FIG.

The first switch may be located after the monopulse antenna, after the mixer, or after the output of a preamplifier placed after the mixer. In addition, the position of the first switch as shown in Fig. 7 is
It is good when the high frequency loss of the first switch is small, but when the high frequency loss is large, the configuration shown in FIGS. 4 and 6 will be adopted. Furthermore, the difference between the two signals is expressed as shown in equations (6), (7), (11), and (12).
We compared s ₁ , s ₂ , s ₃ and s ₄ , but instead of s ₁ −s ₃ , z ₁ (i)
Delay the signal by two synchronization intervals to obtain Az= _∞ 〓 ⁱ⁼¹ {z ₁ (i)−z ₃ (i+2)} ...(13) and obtain outputs 18 and 19 from this. Good too. However, i in equation (13) is modulo 4. It is clear that this Az can be created from the output of the second switch 43 by a combination of a delay circuit and a subtraction circuit.

Furthermore, in order to obtain the outputs of equations (6) and (7) or equations (11) and (12) in the monopulse receiver that tracks the optical signal source shown in FIGS. 4), an arithmetic circuit that executes (10) or an arithmetic circuit that includes a delay circuit that executes equation (13) is required, but the specific configuration is exactly the same as that of the first embodiment shown in FIG. be.

Each example so far has two axes (azimuth angle, elevation angle)
The case of a four-channel amplifier has been described in order to obtain the output for the tracking system, but in the case of one-axis (either azimuth angle or elevation angle) tracking, two channels are sufficient. Therefore, in that case, the four-input, four-output switches 41 and 43 become two-input, two-output switches.

Furthermore, the amplification method described so far is a total power type radiometer method according to the classification of radiometers. Many other radiometers have been announced, including the Deitske type and phase relationship.
Instead of the total power type amplification method used here, a radiometer method such as the Deitske type can be used.

As explained above, when the input signal from the target is light or very weak noise input, it is extremely difficult to create a low-noise monopulse receiver with good angular accuracy using conventional technology. According to Equations (6), (7), (11), and (12) used in the previous explanation, a radiometer can be used to obtain B of Equation (1) with good angular accuracy. It is possible to increase ΔT
A high-sensitivity monopulse receiver with a small min can be realized with a configuration that is completely different from conventional technology. Also,
It is technically easy to manufacture and has extremely large practical effects.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a conventional monopulse receiver that tracks an electromagnetic wave signal source, Figure 2 is a block diagram showing a conventional monopulse receiver that tracks an optical signal source, and Figure 3 shows the configuration of a photodetector. 4 is a block diagram showing a first embodiment of a monopulse receiver according to the present invention, FIG. 5 is a circuit diagram showing an example of a switch used in the first embodiment, and FIG. 6 is a block diagram showing an example of a switch used in the first embodiment. FIG. 7 is a block diagram showing a mathematical model of signal processing in a second embodiment of the present invention, and FIG. 8 is a block diagram showing a mathematical model of signal processing in a third embodiment of the present invention. 9 are block diagrams showing a fourth embodiment of the present invention. 5...Mixer, 6...Local oscillator, 7...Intermediate frequency amplifier, 8...Monopulse antenna, 11 to 14...Input signal, 18...Azimuth angle error signal, 19...Height angle angle error signal, 20...Optical system, 21...Photodetector, 22...Amplifier, 26...
...Subtraction circuit, 41, 43...Switch, 42...
Detector, 44...Low pass filter, 45...Coupling circuit, 91...Rotating photodetector.

Claims (1)

[Claims] 1. A monopulse receiver for tracking a weak target signal includes a monopulse antenna having multiple outputs, multiple amplifiers that amplify the output of the monopulse antenna, and detecting the output of the amplifier. a plurality of detectors, a plurality of low-pass filters or a plurality of delay circuits that receive the outputs of the detectors, and a subtraction circuit that subtracts the plurality of outputs of the low-pass filters or delay circuits; comprising first and second switches with multiple inputs and multiple outputs synchronized with each other, the antenna output or the signal from the stage before the amplifier is switched by the first switch, inputted to the plurality of amplifiers, and passed through each amplifier. A second switch inserted before or after the detection of the signal outputs the signal from the antenna output end 1 to the output end 1 of the second switch, and the signal from the antenna output end 2 to the output end 2 of the second switch.
The signal at the antenna output terminal 3 is outputted to the output terminal 3 of the second switch, and the signal at the antenna output terminal 4 is outputted to the output terminal 4 of the second switch. A monopulse receiver characterized in that an error angle signal from the central axis of the antenna is extracted based on the difference between the sums of the antennas. 2. A monopulse receiver for tracking an optical signal source includes an optical system that includes an objective lens, a concave mirror, or a combination of both, a photodetector that receives the optical signal that has passed through the optical system, and multiple outputs of the photodetector. a plurality of amplifiers for amplification, first and second switches having multiple inputs and multiple outputs synchronized with each other, a plurality of low-pass filters or a plurality of delay circuits receiving the outputs of the plurality of amplifiers; a subtraction circuit for subtracting a plurality of outputs of a filter or a delay circuit, the photodetector is placed on the focal plane of the optical system, and the signal of the photodetector is switched by the first switch. and input the amplified signal to the plurality of amplifiers, and the amplified signal is sent to the second switch, so that the signal at the detection output terminal 1 is input to the second switch output terminal 1, and the signal at the detector output terminal 2 is input to the second switch output terminal 2. The signal at the detector output end 3 is outputted to the second switch output end 3, and the signal at the detector output end 4 is outputted to the second switch output end 4, respectively.
A monopulse receiver characterized in that an error angle signal from the optical axis of the optical system is extracted based on the difference between two of these output signals or the difference between the sum of a plurality of output signals. 3. In a monopulse receiver for tracking an optical signal source, an optical system comprising an objective lens, a concave mirror, or a combination of both, a rotating photodetector that receives the optical signal that has passed through the optical system, and the rotating photodetector a plurality of amplifiers that amplify a plurality of outputs, a plurality of low-pass filters or a plurality of delay circuits that receive the outputs of the plurality of amplifiers, and a plurality of outputs of the low-pass filters or delay circuits that are subtracted; a subtracting circuit that performs a subtraction circuit, and a multiple input multiple output switch that is synchronized with the rotary photodetector, the rotary photodetector is placed on the focal plane of the optical system, and the output of the amplifier is connected to the switch. Therefore, the first input signal in the optical system is sent to the switch output end 1, and the second input signal is sent to the switch output end 2.
Then, the third input signal is outputted to the switch output terminal 3, and the fourth input signal is outputted to the switch output terminal 4. A monopulse receiver characterized by extracting an error angle signal from the optical axis of an optical system.