JPH0727857A - Radar equipment - Google Patents

Abstract

PURPOSE:To obtain a radar equipment which finds the Doppler frequency of a traveling target in an observation time longer than a sub-pulse width irrespective of the carrier frequency when the radar equipment uses FH(frequency hopping) signals. CONSTITUTION:In the radar equipment using FH signals, M pieces of band-pass filters 13a-13c and phase shifters 14a-14c discriminate received FH signals at a frequency near an intermediate frequency and M pieces of phase detectors 6a-6c convert the FH signals into complex sub-pulse video signals the phase of which is detected at intermediate frequency of sub-pulses. Frequency spectrum analyzers 15a-15c find the frequency spectra of the complex sub-pulse video signals. Since the condition for eliminating the unnecessary phase shifting amount of the frequency spectra is set and adders 16a-16c add the spectra to each other in the form of a discrete Fourier transformation, the Doppler frequency of a traveling target can be found in an observation time longer than a sub-pulse width.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar device for improving a detection capability of a moving target such as an aircraft by obtaining a Doppler frequency from a reception signal of a radar using an FH signal as a transmission signal for an observation time longer than a subpulse. Is.

[0002]

2. Description of the Related Art FIG. 9 shows, for example, "Guy V. Morri".
s; AIRBONE PULSEDDOPPLER R
ADAR, Artech House (1988) ”is a basic configuration diagram of a pulse Doppler radar device, in which 1 is an antenna, 2 is a local oscillator that supplies a stable oscillation output, and 3 is a radio frequency band received signal from the antenna. A mixer for converting the frequency to an intermediate frequency band by the local oscillator 2, 4 an amplifier for amplifying the output of the mixer 3, and 5 a coherent oscillator oscillating on the basis of the phase of the transmission signal,
6 is a phase detector that performs phase detection from the output of the amplifier 4 by the coherent oscillator 5, and 7 is A /
The A / D converters 8a to 8c for D conversion use A / D as a unit measurement distance based on a distance resolution determined by a transmission signal to be used.
N distance gates for separating the output of the D converter 7 into N distance resolutions, 9a to 9c are N frequency component analyzers for obtaining Doppler frequency components of the outputs of the distance gates 8a to 8c, and 10a to 10c are Square-law detectors that perform square-law detection for each output of each frequency component analyzer 9a-9c, and 11a-11c are N detecting target signals of a certain threshold level or more for each output of the square-law detectors 10a-10c. The individual target detectors 12 are indicators for displaying information output from the target detectors 11a to 11c.

Next, the operation will be described. A pulse of a single carrier frequency that is coherently repeated is emitted as a transmission signal, and the radio wave reflected by the target and other objects is received by the antenna 1. The received pulse is for mixer 3
Then, the local oscillator 2 converts the radio frequency band to an intermediate frequency, the amplifier 4 amplifies the signal, and the phase detector 6 phase-detects it using the coherent oscillator 5 to obtain a complex video signal. The output of the phase detector 6 is converted into a digital complex video signal by the A / D converter 7.

The distance gates 8a to 8c distribute the distance resolution determined by the transmission signal using this digital complex video signal as a unit measurement distance for each of N distance resolutions, and the frequency component analyzers 9a to 9c respectively. ~
FFT (FastFourier Tra) every 8c output
nsform) and DFT (Discrete Four)
The target Doppler frequency observed in the pulse repetition period is obtained by performing the iier Transform) to convert the observed signal from the time domain to the frequency domain, and the moving target signal of the aircraft and other unnecessary signals are separated. Two
In the multi-detectors 10a-10c, frequency component analyzers 9a-9
c Each output is square-law detected, and the target detectors 11a to 11c detect a signal having a certain threshold level or higher for each output of the square-law detectors 10a to 10c as a target, and the indicator 1
1 displays information such as the target distance and speed.

[0005]

In a radar, the transmission wave is frequency-modulated to spread the spectrum to reduce the peak transmission power and the transmission power per unit band. The FH signal is used because it can reduce interference. In that case, since the carrier frequency changes depending on the time, it is difficult to obtain the target Doppler frequency in the observation time longer than the sub-pulse width, and there is a problem that cross-terms such as interference between multiple target signals and interference between signals and clutter occur. There was a point.

The present invention has been made to solve the above problems, and pays attention to the frequency spectrum of each sub-pulse complex video signal, and sets measurement conditions to remove or compensate for unnecessary phase amounts. By doing so, the target Doppler frequency is obtained with an observation time of at least the sub-pulse width,
An object of the present invention is to obtain a radar device that improves the detection ability of a moving target.

[0007]

According to a first aspect of the present invention, there is provided a radar apparatus in which the number of carrier frequencies to be used is M, and the received FH signals converted into intermediate frequencies are input, and respective pass center frequencies are received. Where M is the sub-pulse intermediate frequency, M number of first phase shifters for compensating the delay phase shift amount for each output of the band pass filter, and each of the first phase shifters. M phase detectors that phase-detect each sub-pulse at each sub-pulse intermediate frequency and output a sub-pulse complex video signal, and M A / D converters that perform A / D conversion for each output of the phase detector And the distance resolution determined by the transmission signal to be used as the unit measurement distance,
For each output of the A / D converter, N distance gates are separated for each N distance resolutions, and M × N number of frequency spectrums are calculated for each sub-pulse complex video signal from each output of the distance gates. A frequency spectrum analyzer, N adders for adding the M frequency spectrum analyzer outputs that have passed through the same distance gate, and N square detectors for square-detecting each output of the adder. When the frequency sequence of M carrier waves to be used is f _i (i = 1 to M), the observation distance is R, and the velocity of the electromagnetic wave is C, the setting condition of 2f _i R = nC (n is an integer) It is used.

A radar apparatus according to the invention of claim 2 is
M × N second phase shifters for compensating the phase for each output of the frequency spectrum analyzer are provided at the output end of the frequency spectrum analyzer, and the output of the adder is provided at the adder output end. It is provided with N phase controllers for inputting and controlling the second phase shifter.

A radar device according to a third aspect of the invention is
At the output end of the square-law detector, N integrators for integrating the number of observations for each output of the square-law detector are provided.

A radar apparatus according to the invention of claim 4 is
At the output end of the integrator, N target detectors that compare with a certain threshold level for each output of the integrator and detect signals higher than that as a target are provided.

A radar device according to the invention of claim 5 is
Instead of the M × N frequency spectrum analyzers at the output of the distance gate, N memories for temporarily recording the output of the distance gate, and a high-speed frequency spectrum of the data recorded in the memory The required number of FFT calculators is provided.

A radar device according to the invention of claim 6 is
The phase shifter at the output end of the bandpass filter is removed, and M digital phase shifters for compensating the delay phase shift amount of the bandpass filter from the output of the A / D converter are provided at the output end of the A / D converter. Is provided.

A radar device according to a seventh aspect of the invention is
The frequency sequence used in the above setting conditions is f _i (i = 1 to M)
To f _ij (i = 1 to M, j = 1 to J) and the observation distance R is changed to an observation distance sequence R _j (j = 1 to J), 2f _ij R _j = nC (n is Integer) setting conditions are used.

[0014]

In the radar apparatus according to the first aspect of the present invention, the number of carrier frequencies to be used is M, and there are M band pass filters each having an intermediate frequency of each sub-pulse as a pass center frequency, and each output of the band pass filter. The M first phase shifters for compensating for the delay phase shift amount discriminate the received FH signal converted to the intermediate frequency into a received signal for each sub-pulse intermediate frequency vicinity. The received signals in the vicinity of each sub-pulse intermediate frequency are phase-detected by M phase detectors at each sub-pulse intermediate frequency to form sub-pulse complex video signals,
The M A / D converters perform A / D conversion for each output of the phase detector to obtain digital sub-pulse complex video signals.
The N distance gates divide the distance resolution determined by the transmission signal to be used as a unit measurement distance into N distance resolutions for each output of the A / D converter, and M × N frequency spectrum analyzers measure distances. Obtain the frequency spectrum of each gate output. The frequency sequence of M carrier waves used at this time is f
_{When i} (i = 1 to M), the observation distance is R, and the electromagnetic wave velocity is C, the frequency spectrum of each digital complex video signal is set by setting the setting condition of 2f _i R = nC (n is an integer). A part of the phase amount of
The N adders add M frequency spectrum analyzer outputs that have passed through the same distance gate, and the N square detectors square detect each adder output, thereby observing a sub-pulse width or more. Find the Doppler frequency component in time.

In the radar apparatus of the second aspect, N
A plurality of phase controllers each input the output of the adder and control M second phase shifters, and M × N second phase shifters compensate each output phase of the frequency spectrum analyzer. , Observe the target at a distance from the observation distance. Other functions are similar to those of the radar device according to claim 1.

In the radar apparatus of the third aspect, N
Each of the integrators integrates the output of the square wave detector by the number of observations. Other functions are similar to those of the radar device according to claim 2.

In the radar apparatus of the fourth aspect, N
Each of the target detectors compares the output of the integrator with a certain threshold level and detects a signal higher than that as a target. Other functions are similar to those of the radar device according to claim 3.

In the radar apparatus of the fifth aspect, N
The number of memories temporarily records the output of the range gate, and the number of FFT calculators determines the frequency spectrum of the data recorded in each memory at high speed. Other functions are similar to those of the radar device according to claim 4.

In the radar apparatus according to claim 6, M
The digital phase shifters compensate the delay phase shift amount of the bandpass filter from the output of the A / D converter. Other functions are similar to those of the radar device according to claim 5.

In the radar apparatus according to the seventh aspect, the frequency sequence used under the above setting conditions is f _ij (i = 1 to M, j).
= 1 to J), the observation distance sequence R _j (j = 1 to 1)
J) and the observation distance will be J times larger. Other functions are similar to those of the radar device according to claim 6.

[0021]

【Example】

Embodiment 1 An embodiment of the present invention will be described below with reference to the drawings. Figure 1
In the above, 1 to 4 are the same as those in the conventional example. 1
3a to 13c are input to the received FH signal converted to the intermediate frequency, and M band pass filters whose pass center frequencies are the sub-pulse intermediate frequencies, and 14a to 14c.
Are M first phase shifters for compensating the delay phase shift amount for each output of the band pass filters 13a to 13c, and 6a to 6c are sub pulse intermediates for each output of the first phase shifters 14a to 14c. Coherent oscillators 5a to 5c oscillating at frequencies
M phase detectors for phase-detecting and outputting sub-pulse complex video signals, 7a-7c are M A / D converters for performing A / D conversion for each output of the phase detectors 6a-6c, 8a-
Reference numeral 8c designates a distance resolution determined by a transmission signal to be used as a unit measurement distance, and N distance gates for separating each N distance resolution for each output of the A / D converters 7a to 7c.
5a to 15i are M × N frequency spectrum analyzers for obtaining a frequency spectrum for each sub-pulse complex video signal from each output of the distance gates 8a to 8c, and 16a to 16c are M number of frequency spectrum analyzers that have passed through the same distance gates 8a to 8c. N number of adders for adding the outputs of the frequency spectrum analyzers 15a to 15i, 10a to 10c are 2 outputs of each output of the adders 16a to 16c.
N square-law detectors for multi-detection, 12 is a square-law detector 10a
It is an indicator which displays each output of 10c.

Next, the operation will be described. FIG. 2 shows an example of a transmission signal using the FH signal. This FH signal has a sub-pulse width τ and M carrier frequencies f expressed by the equation (1).
₁ , f ₂ , ..., f _M are repeated at a constant cycle T,
It is assumed that the observation time T ₀ is represented by the equation (2). However, the M carriers for each cycle T are coherent.

[0023]

[Equation 1]

When the velocity is v (the direction toward the radar side is positive), the reflection characteristics for M carrier waves are constant, and when the transmission signal is irradiated to the moving target existing at the observation distance R, it is reflected by the moving target. The received radio waves are received by the antenna 1,
The local oscillator 2 converts the radio frequency band to the intermediate frequency by the mixer 3, and the amplified FH signal is amplified by the amplifier 4.

The received FH signal has a bandpass filter 10a whose pass center frequency is the intermediate frequency of each sub-pulse.
10c to 10c, the received signals are discriminated in the vicinity of each sub-pulse intermediate frequency. This band pass filter is composed of an analog or digital filter, and the pass band width is Δf or less.

The first phase shifters 14a to 14c compensate the output of the bandpass filters 13a to 13c for the specific delay phase amount generated in the bandpass filters 13a to 13c.

Next, the phase detectors 6a to 6c phase-detect the outputs of the first phase shifters 14a to 14c by the coherent oscillators 5a to 5c oscillating at the respective sub-pulse intermediate frequencies, and generate sub-pulse complex video signals. Output as.

Each of the sub-pulse complex video signals output from the phase detectors 6a to 6c is A / A like the above-mentioned conventional example.
A / D conversion is performed by the D converters 7a to 7c, and the distance gate 8a
.About.8c, the distance resolution is used as a unit measurement distance, and each of the outputs of the A / D converters 7a to 7c is separated into N distance resolutions.

The frequency spectrum analyzers 15a to 15i determine the frequency spectrum of each of the M × N outputs of the distance gates 8a to 8c. At this time, if the Doppler frequency of each carrier is given by equation (3), the frequency spectrum S _i (f) of each sub-pulse complex video signal (i = 1, 2,
..., M) is expressed by the equation (4).

[0030]

[Equation 2]

If the carrier frequency and the observation distance are given the setting conditions of equation (5), the frequency spectrum S _i (f) of each sub-pulse complex video signal (i = 1, 2,
..., M) is expressed by the equation (6).

[0032]

[Equation 3]

The adders 16a to 16c add the outputs of the M frequency spectrum analyzers 15a to 15i which have passed through the same distance gates 8a to 8c. This calculation is represented by the equation (7) and is in the form of performing a discrete Fourier transform with respect to the frequency of the carrier wave, and the Doppler frequency spectrum is obtained from a plurality of carrier waves, that is, in the observation time of the subpulse width or more.

[0034]

[Equation 4]

The square-law detectors 10a to 10c are composed of an adder 16
The absolute value of the Doppler frequency spectrum is obtained by square-law detection of each output of a to 16c, and the indicator 12 outputs the result.

Second Embodiment Another embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, 1 to 8, 10 and 12 to 16 are the same as those in the first embodiment.
Is the same as 17a to 17i are M for compensating the phase for each output of the frequency spectrum analyzers 15a to 15i.
× N second phase shifters, 18a to 18c are adders 16a
It is an N phase controller which inputs the output of 16c and controls the second phase shifters 17a to 17c.

Next, the operation will be described. Example 1 above
If the moving target exists at a distance R + ΔR slightly deviated from the observation distance R in the same operation as the above, the frequency spectrum analyzers 15a to 15a represented by the equation (4) are obtained.
The frequency spectrum of each sub-pulse complex video signal which is each output of 5i is given by equation (9). Given the setting condition of Expression (5), the frequency spectrum is expressed by Expression (10).
Becomes

[0038]

[Equation 5]

The phase controllers 18a to 18c control the phases of the second phase shifters 17a to 17i to remove the phase term for ΔR in the equation (10). This phase controller 18
An operation example of a to 18c will be described with reference to the flowchart of FIG. First, in ST1, the phase controller increases the phase amount of the phase shifter. Next, in ST2, the output of the adder is observed, and the phase at the Doppler frequency, which is the peak value, is compared with the phase term of equation (6). If the phase difference is small, the process proceeds to ST1, and if it is large, the process proceeds to ST3. In ST3, the phase controller reduces the phase amount of the phase shifter. Then, in ST4, the output of the adder is observed again as in ST2, and if the phase difference becomes small, ST3
If it becomes larger, the operation ends. In the above operation, the step of the change in the phase amount of the phase shifter is determined by the capability of the phase shifter and the measurement accuracy.

Third Embodiment Another embodiment of the present invention will be described below with reference to the drawings. In FIG. 5, 1 to 8, 10, 12 to 18 represent the second embodiment.
Is the same as 19a to 19c are square-law detectors 10
These are N integrators that integrate the number of observations for each output a to 10c.

Next, the operation will be described. Example 2 above
When the same operation as the above is performed over a plurality of observations, the integrators 19a to 19c reduce noise variations by integrating the outputs of the square wave detectors 10a to 10c obtained by the number of observations. To improve the signal-to-noise power ratio.

Fourth Embodiment Another embodiment of the present invention will be described below with reference to the drawings. In FIG. 6, 1 to 8, 10, 12 to 19 are the same as those in the third embodiment.
Is the same as 11a to 11c are integrators 19a to
It is N target detectors that compare with a certain threshold level for each output of 19c and detect signals higher than that as a target.

Next, the operation will be described. Example 3 above
When the same operation as the above is performed, the target detectors 11a to 11
c is a constant threshold level for each output of the integrators 19a to 19c, for example, by comparing with an average value around the target point and detecting a point of output higher than that as a target, a false alarm is made constant. To do.

Embodiment 5 Another embodiment of the present invention will be described below with reference to the drawings. In FIG. 7, 1 to 8 and 10 to 19 are the same as those in the fourth embodiment. 20a to 20c are distance gates 8a to 8c
N memories 21a to 21 for temporarily recording the output of
Reference numeral c denotes N FFT calculators for obtaining the frequency spectrum of the data recorded in the memories 20a to 20c at high speed.

Next, the operation will be described. Example 4 above
When the operation similar to the above is performed, the memories 20a to 20c temporarily record the outputs of the distance gates 8a to 8c. This memory has M systems in parallel, and each records data of each sub-pulse complex video signal.

The FFT calculators 21a to 21c are composed of dedicated processors, and obtain the frequency spectrum of the data recorded in the memories 20a to 20c at high speed by FFT.

Sixth Embodiment Another embodiment of the present invention will be described below with reference to the drawings. In FIG. 8, 1 to 8 and 10 to 21 are the same as those in the fifth embodiment. 22a to 22c are A / D converters 7a to 7
These are M digital phase shifters for compensating the delay phase shift amounts of the bandpass filters 13a to 13c from the c output.

Next, the operation will be described. Example 5 above
Similarly to the received FH signal, the band pass filter 13a-
13c performs discrimination in the vicinity of each sub-pulse intermediate frequency, phase detection is performed at each sub-pulse intermediate frequency by the phase detectors 6a to 6c, and A / D conversion is performed by the A / D converters 7a to 7c.
After conversion, digital phase shifters 22a-22c
Compensates the delay phase shift amount of the bandpass filters 13a to 13c.

Embodiment 7 The operation of another embodiment of the present invention will be described below.
When the above-described embodiments 6 and similar operation is being performed, f _ij (i = 1~ frequency sequence from f _{i (i} = 1~M) used
M, j = 1 to J), the observation distance satisfying the equation (5) becomes the observation distance sequence R _j (j = 1 to J) from R, and the observable distance becomes J times.

[0050]

According to the first aspect of the present invention, in the radar device using the FH signal, a setting condition for removing an unnecessary phase shift amount of the radar reception signal is provided, and the frequency spectrum of each sub-pulse complex video signal is provided. Since it is configured so as to be in the form of the discrete Fourier transform, the Doppler frequency of the moving target can be obtained in the observation time longer than the subpulse width.

According to the second aspect of the present invention, in the radar device using the FH signal, the unnecessary phase term generated in the moving target existing at a distance slightly deviated from the observation distance is compensated. It is possible to obtain the Doppler frequency of the moving target existing at a distance slightly deviated from the observation distance.

According to the third aspect of the invention, in the radar device using the FH signal, the output signal is integrated for the number of times of observation, so that the variation of noise is reduced and the signal-to-noise power ratio is improved. it can.

According to the fourth aspect of the invention, in the radar device using the FH signal, the output signal is compared with a certain threshold level, and a signal higher than that is detected as a target. Can be constant.

According to the fifth aspect of the present invention, in the radar device using the FH signal, the frequency spectrum analysis is performed by using the memory and the FFT calculator, so that the configuration is simplified.

According to the sixth aspect of the present invention, in the radar device using the FH signal, the delay phase shift amount of the bandpass filter is configured to be compensated after A / D conversion. It is kept within the quantization error.

According to the seventh aspect of the invention, in the radar device using the FH signal, the condition is set so as to be compatible with a plurality of observation distances, so that the observable distance increases.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a radar device showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of an FH transmission signal.

FIG. 3 is a configuration diagram of a radar device showing a second embodiment of the present invention.

FIG. 4 is a flowchart showing the operation of the phase controller used in the second embodiment of the present invention.

FIG. 5 is a configuration diagram of a radar device showing a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a radar device showing a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram of a radar device showing a fifth embodiment of the present invention.

FIG. 8 is a configuration diagram of a radar device showing a sixth embodiment of the present invention.

FIG. 9 is a basic configuration diagram of a conventional pulse Doppler radar device.

[Explanation of symbols]

 1 Antenna 2 Local Oscillator 3 Mixer 4 Amplifier 5 Coherent Oscillator 6 Phase Detector 7 A / D Converter 8 Distance Gate 9 Frequency Component Analyzer 10 2 Square Detector 11 Target Detector 12 Indicator 13 Bandpass Filter 14 First Phase shifter 15 Frequency spectrum analyzer 16 Adder 17 Second phase shifter 18 Phase controller 19 Integrator 20 Memory 21 FFT calculator 22 Digital phase shifter

Claims (7)

[Claims] 1. A FH (Frequen) in which the frequency of a carrier wave changes within a single pulse for each sub-pulse width of a constant time.
In a radar device that transmits a cy-hopping signal to space and receives the reflected signal, the number of carrier frequencies used is M, and the sub-pulse intermediate frequency that is each intermediate frequency converted from each carrier of the sub-pulse width is the pass center. M number of band-pass filters that receive the received FH signal converted into the sub-pulse intermediate frequency, and M first phase shifters that compensate the delay phase shift amount for each output of the band-pass filters And M phase detectors for phase-detecting at each sub-pulse intermediate frequency for each output of the first phase shifter and outputting a sub-pulse complex video signal which is a complex video signal of each carrier having a sub-pulse width, The unit resolution is the distance resolution determined by the M A / D converters that perform analog / digital conversion for each output of the detector and the transmission signal used. Then, for each output of the A / D converter, N distance gates are separated for each N distance resolution, and a frequency spectrum is calculated for each sub-pulse complex video signal from each output of the distance gate M × N. Frequency spectrum analyzers, N adders that add the M frequency spectrum analyzer outputs that have passed through the same distance gate, and N square detections that square-detect each output of the adder. The frequency sequence of M carriers to be used is f _i (i = 1 to 1).
M), the observation distance is R, and the velocity of the electromagnetic wave is C, a setting condition of 2f _i R = nC (n is an integer) is used. 2. The output terminal of the frequency spectrum analyzer, M × N second phase shifters for compensating the phase for each output of the frequency spectrum analyzer, and the output terminal of the adder, 2. The radar apparatus according to claim 1, further comprising N phase controllers for inputting the output of the adder and controlling the second phase shifter. 3. An N integrator for integrating each output of the square wave detector by the number of observations is added to the output end of the adder. The described radar device. 4. The output terminal of the integrator is provided with N target detectors that compare with a certain threshold level for each output of the integrator and detect signals higher than that as a target. The radar device according to any one of claims 1 to 3. 5. N memory for temporarily recording the output of the distance gate, the M × N frequency spectrum analyzers at the output terminal of the distance gate, and a frequency spectrum of the data recorded in the memory. 5. The radar device according to any one of claims 1 to 4, characterized in that N is replaced with N FFT arithmetic units for high speed calculation. 6. The first phase shifter at the output end of the bandpass filter is removed, and the A / D converter output end is provided with the A / D converter.
The radar according to any one of claims 1 to 5, wherein M digital phase shifters for compensating the delay phase shift amount of the bandpass filter from the output of the D converter are added. apparatus. 7. The frequency sequence used in the above setting conditions is f _i
When (i = 1 to M) is changed to f _ij (i = 1 to M, j = 1 to J) and the observation distance R is changed to an observation distance sequence R _j (j = 1 to J), 2f _ij The radar device according to any one of claims 1 to 6, wherein a setting condition of R _j = nC (n is an integer) is used.