JPH0330113B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of the art to which the present invention pertains The present invention relates to a method for transmitting electromagnetic waves generated by moving targets such as aircraft, flying objects, or vehicles, or electromagnetic waves reflected from these targets into a medium. As,
The present invention relates to an improvement of a monopulse receiver used in combination with a monopulse antenna, which is one of the means for detecting the error angle between the target and the antenna reference axis of a continuous wave or pulsed Doppler tracking radar device for tracking a target.

(2) Background of the present invention When tracking targets such as aircraft, flying objects, or vehicles using electromagnetic waves as a medium, it is possible to remove unnecessary clutter signals from fixed targets and efficiently receive Doppler-shifted signals from moving targets. Continuous wave or pulse Doppler monopulse tracking radar devices are often used in place of conical scan tracking radar devices because of their much superior tracking performance. However, monopulse antennas and monopulse receivers used in monopulse tracking radars are very complex, and there are many problems that need to be solved, so various systems have been proposed.

Two types of intermediate frequency amplifiers, which are part of the monopulse receiver used in pulsed Doppler tracking radars, are used depending on the purpose: wideband and narrowband amplifiers. In particular, the bandpass filter of the intermediate frequency amplifier, which is coupled immediately after the mixer following the front end monopulse antenna and amplitude comparison type monopulse comparator, is constructed using a high Q element such as a crystal filter. A monopulse receiver with a narrow band of about 1 kHz is called an inverse receiver, and is attracting attention as the most effective means of removing clutter, which is unnecessary reflected waves from fixed targets such as the ground and sea surface.

In order to extract the target azimuth angle error signal and elevation angle error signal, it is necessary to perform synchronous detection of the difference signal using the sum signal that is the output of the monopulse comparator.
To achieve this, it is necessary to align the phase characteristics of the narrowband crystal filters used in combination, but this has been technically quite difficult, difficult to mass-produce, and economically expensive.

(3) Prior art and its general problems A conventional example of a monopulse receiver will be explained using FIG. The input signal 1 from the target is received by the four multi-beam antennas 30 constituting the monopulse antenna, and the antenna outputs 2, 3, 4, and 5 respectively corresponding to the four multi-beams are obtained, and the monopulse comparator receives the input signal 1 from the target. 31, and the comparator 31 outputs a sum signal 6, a first difference signal 7 containing azimuth angle error information, and a second difference signal 8 containing elevation angle error information.

The sum signal 6 is sent to the local oscillator 4 by the first mixer 33.
Using the output 25 of 1, the first mixed output is 10,
amplified by the first intermediate frequency amplifier 35;
The intermediate frequency amplifier output 12 is obtained, and the synchronous detector 37
becomes the reference signal.

On the other hand, the first difference signal 7 and the second difference signal 8 are
By driving the first switch 32 with the first switch signal 18 which is the output signal of the switch signal generator 40, the first switch output 9 is alternately switched.
becomes. The first switch output 9, which is a signal obtained by time-sharing the first difference signal 7 and the second difference signal 8, is sent to the second mixer 3.
4, the local oscillator output 25 is converted into the second mixer output 11 and the second intermediate frequency amplifier 36
and the second intermediate frequency amplifier output 13
This becomes the input signal of the synchronous detector 37. The synchronous detector output 14 becomes the input signal of the low-pass filter 38, and high frequency components are removed to obtain the low-pass filter output 15.

Since the second switch 39 is switched in synchronization with the first switch 32 by the first switch signal 18, the azimuth error signal 16 and the elevation angle error signal 17 are obtained from the low-pass filter output 15. be able to. That is, by synchronizing and switching the first switch 32 and the second switch 39 using the first switch signal 18 which is the output signal from the first switch signal generator 40, the first difference signal 7 can be generated without crosstalk.
The azimuth angle error signal 16, the second difference signal 8, and the elevation angle error signal 17 can be made to match.

The sum signal 6 is expressed as follows.

X ₆ = cosωt (1) The first difference signal 7 in the azimuth direction is expressed as follows.

X ₇ = dacosωt (2) The second difference signal 8 in the elevation angle direction is expressed as follows.

X ₈ = decosωt ...(3) The sum signal 6 and the difference signals 7 and 8 are sent to the intermediate frequency amplifier 3
After amplification at steps 5 and 36, an azimuth angle error signal 16 and an elevation angle error signal 17 are obtained by a synchronous detector 37.

The azimuth error signal 16 is Az=2·=da (4) where is the average of one cycle. The height angle error signal 17 is similar to equation (4), El=2・=de... (5) Therefore, the phase relationship between the three signals of the sum and difference of the monopulse comparator 31 is the same as that of the intermediate frequency amplifiers 35 and 36.
If the signals are held as they are and synchronously detected, the relationships in equations (4) and (5) will hold and there will be no problem. However, in reality, the intermediate frequency amplifier 3 corresponding to the sum and difference signals
It is not easy to align the phases of 5 and 36.

(4) Specific problems with conventional technology Although input signals from antennas differ depending on the modulation format of electromagnetic waves used, Doppler radar that tracks moving targets uses a wide frequency spectrum, and Since it is necessary to track even small flying objects, and the level difference between the input signals is large, the monopulse receiver aligns the center frequency of the carrier with the center of the intermediate frequency amplifier, and uses the second intermediate frequency that is the input signal of the synchronous detector 37. Frequency amplifier output 1
It is necessary to keep the amplitude of 3 constant, and various additional circuits are required for this purpose, making it increasingly difficult to align the phases of the sum and difference signals. If there is a phase error θ between the sum and difference signals, the synchronous detector output 14 will be as follows.

Az=2(+)・=dacosθ…
...(6) When the phase error θ is close to zero, there are few problems, but
If π is the circumference, if the phase error θ exceeds π/2 radians, the polarity will be reversed and the device will no longer function as a tracking device. It is also difficult to know and correct the phase error θ from equation (6).

(5) Purpose of the present invention The present invention provides a method for amplifying the sum signal and the difference signal obtained as the output of a monopulse comparator using respective intermediate frequency amplifiers. Provided is a monopulse receiver capable of correcting the phase error from a signal obtained by synchronously detecting a difference signal using a sum signal and obtaining accurate azimuth error signals and elevation angle error signals even if there is an error. The purpose is to

(6) Main points of the configuration of the present invention Before explaining the embodiment shown in FIG. 2 in detail,
The principle of the present invention will be explained using the time chart shown in FIG.

As shown in FIG. 3, when the sum signal 6 is modulated via the phase modulator 42 by the second switch signal 19 whose timing is synchronized with the fourth switch signal 21, a phase difference of π/2 radians is obtained. We obtain the following time-divided phase modulator output 22 (X ₂₂ ).

X ₂₂ = cosωt sinωt ...(7) Then, the output 1 obtained by frequency converting this output 22
2 becomes a reference signal for the synchronous detector 37.

The third switch signal 20 synchronized with the fourth switch signal 21 causes the first switch output 9 (X ₉ )
are similarly time-divided, so X ₉ = d ₁ cosωt d ₁ cosωt ...(8). This output 9 is frequency converted and output 13
This becomes the input signal of the synchronous detector 37.

When the respective intermediate frequency amplifiers 35 and 36 have a phase difference of θ radian, the synchronous detector output 1
4 smoothed low-pass filter output 15 (X ₁₅ )
becomes a time series signal as shown below.

X ₁₅ = 2X ₂₂ d ₁ cos (ωt + θ) d ₂ cos (ωt + θ) = d ₁ cos θ d ₁ sin θ d ₂ sin θ d ₂ cos θ The low-pass filter output 15 in equation (9) is the fourth switch signal Digital arithmetic unit 4 at the timing of 21
4, the phase error θ is obtained from the following relationship.
can be calculated.

θ≒tan ^-1 d ₁ sinθ／d ₁ cosθ ≒tan ^-1 d ₂ sinθ／d ₂ cosθ ...(10) The azimuth angle error signal 16 (Az) and the elevation angle error signal 17 (El) are Az＝d ₁ cosθ・cos(tan ^-1 d ₁ sinθ/d ₁ cosθ) + d
₁ sinθ・sin (tan ^-1 d ₁ sinθ／d ₁ cosθ)=d ₁ ...(11)
El＝d ₂ cosθ・cos (tan ^-1 d ₂ sinθ／d ₂ cosθ) + d
₂ sinθ・sin (tan ^-1 d ₂ sinθ／d ₂ cosθ)=d ₂ ......(12)
The phase error θ can be more accurately determined by correcting the phase error θ. In addition,
In FIG. 3, θ is 0.2 radian.

(7) Embodiment of the present invention FIG. 2, which is an embodiment of the present invention, will be explained in more detail.

The input signal 1 from the target is received by the four multi-beam antennas 30 constituting the monopulse antenna, and the antenna outputs 2, 3, 4, and 5 corresponding to the four multi-beams are obtained, and the monopulse comparator receives the input signal 1 from the target. 31, a sum signal 6, a first difference signal 7 containing azimuth angle error information, and a second difference signal 8 containing elevation angle error information are obtained.

The sum signal 6 is a phase modulated signal with a phase difference of π/2 radians that is time-divided by a second switch signal 19 generated by a second switch signal generator 43 using a phase modulator 42. output from the local oscillator 4 by the first mixer 33.
The output 25 of 1 becomes the first mixer output 10. This output 10 is amplified by the first intermediate frequency amplifier 35 and becomes the first intermediate frequency amplifier output 12, which becomes a reference signal for the synchronous detector 37.

On the other hand, the first difference signal 7 and the second difference signal 8
The first switch 32 is driven by the switch signal 20 to alternately switch between the first difference signal 7 and the second difference signal 8, resulting in the first switch output 9. The first switch output 9, which is a time-divided signal of the first signal 7 and the second difference signal 8, is passed through the second mixer 34 to the second mixer output 11 using the local oscillator output 25, and is converted into a second intermediate frequency signal. It is amplified by the amplifier 36 and becomes the second intermediate frequency amplifier output 13, which becomes the input signal of the synchronous detector 37. Synchronous detector output 1
4, high frequency components are removed by a low pass filter 38, resulting in a low pass filter output 15. The digital arithmetic unit 44 executes calculations of equations (10), (11), and (12) to obtain an azimuth error signal 16 and an elevation angle error signal 17. A second switch signal generator 43 generates a second switch signal 1 for driving the phase modulator 42.
9. The third switch signal 20 for driving the first switch 32 and the signal of the low-pass filter output 15 of equation (9) are transferred to the digital calculator 44 without crosstalk.
A fourth switch signal 21, which is a timing pulse necessary for taking in the signals, is generated respectively.

(8) Supplementary explanation of the embodiment (a) Up to now, we have described a two-channel monopulse receiver with two intermediate frequency amplifiers, but an intermediate frequency amplifier with intermediate frequency amplifiers each corresponding to the difference signals 7 and 8 has been described. You can use three 3-channel monopulse receivers, or if you remove the first switch and change the analog input of the digital calculator to 2 channels, you can obtain the azimuth error signal 16 and the elevation angle error signal 17, so it can be made even higher. Possible if sensitivity is required.

(b) In the explanation so far, the sum signal is phase modulated, but even if the difference signal is phase modulated, the azimuth error signal and the elevation angle error signal can be obtained from the relationships in equations (10), (11), and (12). Can be done.

(C) Although the phase modulator 42 and the first switch 32 are connected before the mixers 33 and 34, the phase modulator 4
2 and the first switch 32 may be connected after the mixers 33 and 34.

(9) Effects of the present invention (a) Even if a phase error occurs between the two intermediate frequency amplifiers due to large fluctuations in the amplitude of the input signal or fluctuations in the frequency of the input signal, the effect of the error is canceled out and the correct result is always maintained. An azimuth error signal and an elevation error signal can be obtained.

(b) For amplifiers that use very high Q elements such as crystals in the bandpass filter of intermediate frequency amplifiers, select two paired crystals with well-matched characteristics, and select an amplifier with similarly well-matched characteristics. is technically extremely difficult. Although the device of the present invention has a large number of phase modulators and digital arithmetic units 44, it is still economically advantageous compared to the difficulty of manufacturing two intermediate frequency amplifiers with uniform characteristics.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional example of a monopulse receiver, Fig. 2 is a block diagram showing an embodiment of a monopulse receiver according to the present invention, and Fig. 3 is a timetable for explaining the embodiment of Fig. 2. It's a chat. 1... Input signal, 2, 3, 4, 5... Antenna output, 6... Sum signal, 7... First difference signal, 8...
Second difference signal, 9...first switch output, 10...first mixer output, 11...second mixer output, 12...
...First intermediate frequency amplifier output, 13...Second intermediate frequency amplifier output, 14...Synchronous detector output, 15...
...Reduced pass filter output, 16...Azimuth error signal, 17...Elevation angle error signal, 18...First switch signal, 19...Second switch signal, 20...
3rd switch signal, 21...4th switch signal,
22... Phase modulator output, 25... Local oscillator output, 30... Antenna, 31... Monopulse comparator, 32... First switch, 33... First mixer,
34... Second mixer, 35... First intermediate frequency amplifier, 36... Second intermediate frequency amplifier, 37... Synchronous detector, 38... Low pass filter, 39... Second
Switcher, 40...First switch signal generator, 41
... Local oscillator, 42 ... Phase modulator, 43 ...
Second switch signal generator, 44...Digital arithmetic unit.

Claims (1)

[Claims] 1. In a monopulse receiver having a monopulse antenna and a monopulse comparator, the sum signal of the monopulse antenna, which is one of the outputs of the monopulse comparator, is controlled by a phase modulator using a switching signal. A time series signal having a phase difference of π/2 radians is alternately phase-modulated and used as a reference signal for a synchronous detector, while a difference signal, which is the output of the monopulse comparator, is sent to the synchronous detector using the reference signal. Therefore, each signal obtained in synchronization with the switching signal during synchronous detection is digitized by a digital arithmetic unit in synchronization with the switching signal, calculates the arctangent, and obtains the phase error. A monopulse receiver characterized in that a phase error between the sum signal and the difference signal is corrected to obtain an azimuth error signal and an elevation angle error signal. 2. In a monopulse receiver having a monopulse antenna and a monopulse comparator, the difference signal of the monopulse antenna, which is the output of the monopulse comparator, is alternately modulated by a phase difference of π/2 radians using a switching signal. Each signal obtained in synchronization with the switching signal when a certain time series signal is phase modulated and the phase modulated signal is synchronously detected using the sum signal output from the monopulse comparator as a reference signal of a synchronous detector. is digitized by a digital calculator in synchronization with the switching signal, calculates the arctangent to obtain the phase difference, corrects the phase error between the sum signal and the difference signal, and calculates the azimuth angle. A monopulse receiver characterized in that it obtains an error signal and an elevation angle error signal.