JP4377756B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus that detects a target whose amplitude is greatly changed with time and a received signal with a short period of time is obtained, such as a rotor blade of a helicopter.

  Conventionally, a radar device that detects a target by emitting a radio wave toward the target, receiving a reflected wave from the target, and performing signal processing is known. When such a conventional radar apparatus is used to detect a helicopter hovering at a low altitude, the reflected wave from the helicopter includes an unnecessary reflected wave called clutter.

  In the case of a reflected wave from a moving target, the reflected wave from the target can be extracted using the Doppler effect. However, when the target is not moving, for example, in the case of a helicopter in a hovering state, the Doppler effect cannot be used, so that the reflected wave from the helicopter fuselage cannot be extracted.

  In order to detect a helicopter in such a hovering state, a method of detecting a target by extracting a reflected wave from a rotor blade or the like that is rotating even in the hovering state is considered.

  For example, the presence or absence of a hit by a CFAR (Constant False Alarm Rate) device before and after integration in the frequency direction after frequency analysis of the received signal and the change in amplitude of the hit before and after frequency direction integration are extracted, and the presence or absence of the frequency direction integration effect Thus, a radar device that determines helicopter detection is known (see Patent Document 1). This radar apparatus radiates a transmission wave generated by a transmitter from an antenna, sends a received signal to a receiver through a circulator, and converts it into a digital video signal. Clutter suppression of received signal with MTI (Moving Target Indicator) device, coherent integration with frequency analysis device, integration with frequency direction integration device, presence / absence of hit by CFAR device before and after frequency direction integration, and frequency of amplitude with hit The change before and after the direction integration is extracted, and it is determined by the detection determination device whether the target is a helicopter.

  There is also known a radar apparatus that stably detects a hovering helicopter without being affected by a strong ground clutter (Patent Document 2). This radar device is a clutter level calculation device that calculates a clutter level from a digital video signal output from a receiver, and a frequency range setting that sets a Doppler frequency range for detecting a hovering helicopter based on the calculated clutter level. A hovering helicopter detection device including a circuit detects a hovering helicopter based on a Doppler frequency range that varies depending on a set clutter size, a preset detection slicer level, and a hovering helicopter determination reference value.

  However, the reflected wave from the rotor blade is a received signal whose amplitude greatly changes with time and whose amplitude is large. For this reason, the FFT (Fast Fourier Transform), which is often used as an integration and frequency analysis means, cannot expect a large integration effect with respect to a stationary signal whose amplitude is substantially constant over time. Therefore, in a radar device that extends the detection distance due to the integration effect, for a target such as a rotor blade, where the amplitude changes greatly in time and a received signal with a short period of large amplitude is obtained. The detection distance may be shortened.

  The target detection operation by the conventional radar apparatus as described above will be described with reference to the drawings. FIG. 7 is a block diagram showing a configuration of an example of a conventional radar apparatus. The radar apparatus includes an antenna 1, a transmitter 2, a circulator 3, a receiver 4, an MTI apparatus 5, a frequency analysis apparatus 6, a CFAR apparatus 7, and a detection apparatus 8.

  The antenna 1 converts a transmission signal transmitted from the transmitter 2 via the circulator 3 into a radio wave, and transmits the radio wave as a transmission wave to a space in a specified direction, and receives the reflected wave reflected by the target. The received signal is sent to the receiver 4 via the circulator 3.

  The receiver 4 converts a received signal sent from the antenna 1 via the circulator 3 into a digital video signal. The digital video signal obtained by converting the received signal by the receiver 4 is sent to the MTI device 5.

  The MTI device 5 suppresses clutter components included in the digital video signal sent from the receiver 4. The digital video signal whose clutter component is suppressed by the MTI device 5 is sent to the frequency analysis device 6.

  The frequency analysis device 6 performs coherent integration of the digital video signal in which the clutter component is suppressed in the MTI device 5 for the purpose of improving the signal-to-noise ratio (S / N ratio). Note that FFT is often used for coherent integration in the frequency analyzer 6.

When detecting a target from which a received signal having a substantially constant amplitude in time is detected, an integration effect corresponding to the number of integration pulses can be obtained by the FFT used as the integration means. The relationship between the integration pulse number N and the integration gain G (unit: dB) is shown in the following formula (1).

When detecting a target whose amplitude changes greatly with time and a received signal with a short period of large amplitude is obtained, a large integration effect cannot be expected with the FFT used as the integration means. As an example, in the case where the received signal from the target is a rectangular wave having a constant amplitude within the number of pulses M and the amplitude is zero outside the number of pulses M, the number of pulses M and the number of integrated pulses other than zero are the amplitudes. The relationship between N and integral gain G ′ (unit: dB) is shown below.

  When the number M of pulses having an amplitude other than zero is “10”, the integral gain G and the integral gain G ′ are as shown in FIG. As described above, even if the number N of integrated pulses is increased, the integration effect is small when the number of pulses M is not greater than zero, and the integration gain G ′ decreases.

  The CFAR device 7 detects the signal having the amplitude and phase output from the frequency analysis device 6 (converts it into a signal having only amplitude information), calculates the reference amplitude from the signal amplitude around the target range bin, and pays attention to the reference amplitude. An amplitude ratio signal is output as a signal representing the range bin amplitude ratio.

The detection device 8 sets a threshold value for the amplitude ratio signal output from the CFAR device 7 and detects a signal exceeding the threshold value as a target.
Patent No. 2991080 Japanese Patent No. 3359586

  However, in the conventional radar apparatus configured as described above, a predetermined integration effect can be obtained for a target from which a reception signal having a substantially constant amplitude in time is obtained, but the amplitude is large in time. As described above, the desired integration effect cannot be obtained even if the number of integration pulses is increased, and the integration gain decreases. End up. As a result, there is a problem that the signal-to-noise ratio (SN ratio) is lowered and the target detection performance is lowered.

  The present invention provides a radar apparatus capable of improving target detection performance by improving a signal-to-noise ratio (S / N ratio) of a received signal whose amplitude changes greatly with time and whose amplitude period is short. is there.

  According to a first aspect of the present invention, a radar apparatus includes: a receiver that converts a received signal obtained by receiving a reflected wave of a transmitted wave transmitted to space into a digital video signal; and a digital video signal output from the receiver. Unnecessary wave suppression device that suppresses unnecessary wave components and the signal whose unwanted wave components are suppressed by the unnecessary wave suppression device are complex conjugates for each pulse of the received signal from the target to be detected and the integral gain is maximized A convolution operation device that performs a convolution operation with a reference signal having a length in a possible pulse direction, and a detection device that detects a signal of a reflected wave from a target based on a signal output from the convolution operation device It is characterized by.

  According to a second aspect of the present invention, there is provided a radar apparatus for converting a received signal obtained by receiving a reflected wave of a transmitted wave transmitted to space into a digital video signal, and a digital video output from the receiver. An unnecessary wave suppression device that suppresses unnecessary wave components from the signal, a signal obtained by Fourier-transforming the signal whose unnecessary wave components are suppressed by the unnecessary wave suppression device, and a complex conjugate for each pulse of the received signal from the target to be detected. In addition, after multiplying a signal having a length in the pulse direction capable of maximizing an integral gain by a reference signal obtained by Fourier transform, a Fourier transform device that performs inverse Fourier transform, and a signal output from the Fourier transform device And a detection device for detecting a signal of a reflected wave from the target.

  According to the radar apparatus of the first aspect, the target changes based on the signal obtained by the convolution operation of the received signal and the reference signal having a length that can maximize the integral gain, with the amplitude greatly changing over time. Therefore, the signal-to-noise ratio (SN ratio) of the received signal having a short period with a large amplitude can be improved.

  Further, according to the radar apparatus of the second invention, the signal obtained by Fourier transforming the received signal and the Fourier-transformed reference signal having a length capable of maximizing the integral gain are multiplied and integrated and then inverse Fourier transformed. Since the presence / absence of the target is detected based on the obtained large signal, the received signal whose amplitude changes greatly in time and whose period of large amplitude is short, although the amount of calculation is smaller than the convolution calculation. The signal-to-noise ratio (S / N ratio) can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same reference numerals as those used in the column of the conventional technology are used for the parts corresponding to the components described in the column of the conventional technology.

  The radar apparatus according to Embodiment 1 of the present invention improves the SN ratio of the received signal by using a convolution operation between the received signal and the reference signal.

  FIG. 1 is a block diagram showing a configuration of a radar apparatus according to Embodiment 1 of the present invention. This radar device is composed of an antenna 1, a transmitter 2, a circulator 3, a receiver 4, an unnecessary wave suppression device 9, a convolution operation device 10, a CFAR device 7, and a detection device 8.

  The antenna 1 converts a transmission signal transmitted from the transmitter 2 via the circulator 3 into a radio wave, and transmits the radio wave as a transmission wave to a space in a specified direction, and receives the reflected wave reflected by the target. The received signal is sent to the receiver 4 via the circulator 3.

  The receiver 4 converts a received signal sent from the antenna 1 via the circulator 3 into a digital video signal. The digital video signal obtained by converting the received signal by the receiver 4 is sent to the unwanted wave suppressing device 9.

  The unnecessary wave suppressing device 9 suppresses unnecessary wave components included in the digital video signal transmitted from the receiver 4. The unnecessary wave component includes a component of a reflected wave from the body of the clutter and the helicopter. In order to suppress the reflected wave from the clutter, the MTI apparatus 5 described in the section of the prior art is often used. The unnecessary wave suppression device 9 may use the MTI device 5, but a higher effect can be obtained by using a band rejection filter that suppresses signals other than the frequency included in the received signal from the rotor blade. The digital video signal whose unnecessary wave component is suppressed by the unnecessary wave suppression device 9 is sent to the convolution operation device 10.

  FIG. 2 is a block diagram showing a detailed configuration of the convolution operation device 10. The convolution operation device 10 includes a convolution operation unit 12 and a reference signal generation unit 13.

  The reference signal generator 13 generates a reference signal that simulates the amplitude and phase of a received signal from a target to be detected. Here, when the reference signal is represented by h (0) to h (P-1) and the received signal from the target is s (n), the reference signal h (0) to h (P-1) is the signal s. The signal h (n) complex to (−n) is generated by selecting a portion having a length P in the pulse direction that can maximize the integral gain. For example, in the case of a rectangular wave, the integral gain G ′ in the equation (3) is maximized when M = N, and thus the reference signal length P is selected to be M. An example in the case of M = 10 is shown in FIG. The reference signals h (0) to h (P-1) generated by the reference signal generator 13 are sent to the convolution calculator 12.

  The convolution operation unit 12 performs a convolution operation on the signal transmitted from the unnecessary wave suppression device 9 and the reference signal generated by the reference signal generation unit 13. The calculation result in the convolution calculation unit 12 is sent to the CFAR device 7.

  The CFAR device 7 detects the signal having the amplitude and phase output from the convolution operation unit 12 (converts it into a signal having only amplitude information), calculates the reference amplitude from the signal amplitude of the peripheral pulse of the target range bin, An amplitude ratio signal is output as a signal representing the ratio of the target range bin amplitude. The amplitude ratio signal output from the CFAR device 7 is sent to the detection device 8.

  The detection device 8 sets a threshold value for the amplitude ratio signal output from the CFAR device 7 and detects a signal exceeding the threshold value as a target.

  Next, the operation of the radar apparatus according to Embodiment 1 of the present invention configured as described above will be described. First, the reflected wave received by the antenna 1 is sent to the receiver 4 via the circulator 3 as a received signal. The receiver 4 generates a digital video signal based on the received signal from the circulator 3 and sends it to the unwanted wave suppression device 9. The unnecessary wave suppression device 9 suppresses the unnecessary wave component included in the digital video signal from the receiver 4 and sends it to the convolution operation device 10.

The convolution operation device 10 performs a convolution operation on the signal in which the unnecessary wave component transmitted from the unnecessary wave suppression device 9 is suppressed and the reference signal generated by the reference signal generation unit 13. Assuming that the input signal of the convolution operation device 10 is x (n), the reference signals are h (0) to h (P-1), and the output signal of the convolution operation device 10 is y (n), the convolution operation device 10 The output signal y (n) is obtained by the following equation (4).

  For this reason, in the convolution period, the relationship between the input signals x (n) to x (n−P + 1) and the reference signals h (0) to h (P−1) of the convolution operation device 10 is complex conjugate (amplitude). , The output y (n) from the convolution operation device 10 becomes large. As a result, the SN ratio of the input signal can be improved.

  The calculation result in the convolution calculation unit 12 is sent to the CFAR device 7. The CFAR device 7 generates the amplitude ratio signal described above and sends it to the detection device. The detection device 8 detects a signal exceeding the threshold value among the amplitude ratio signals from the CFAR device 7 as a target.

  As described above, according to the radar apparatus according to the first embodiment of the present invention, the presence / absence of the target is determined based on the signal obtained by the convolution operation between the received signal and the reference signal having a length that can maximize the integral gain. Therefore, the signal-to-noise ratio (S / N ratio) of a received signal whose amplitude changes greatly with time and whose amplitude is short can be improved.

  The radar apparatus according to Embodiment 2 of the present invention is configured to improve the SN ratio of a received signal by using a convolution operation between the received signal and a plurality of types of reference signals.

  FIG. 3 is a block diagram showing the configuration of the radar apparatus according to Embodiment 2 of the present invention. In the following, the same components as those of the radar apparatus according to the first embodiment are denoted by the same reference numerals as those of the radar apparatus according to the first embodiment, and the description thereof is omitted.

  The radar apparatus includes an antenna 1, a transmitter 2, a circulator 3, a receiver 4, an unnecessary wave suppression apparatus 9, a convolution operation apparatus 10-1 to 10-n, a CFAR apparatus 7-1 to 7-n, and a detection apparatus 8-. 1 to 8-n.

  The configuration and operation of each of the convolution operation devices 10-1 to 10-n are the same as the configuration and operation of the convolution operation device 10 in the radar apparatus according to the first embodiment except for the following points. That is, the convolution operation devices 10-1 to 10-n respectively generate a plurality of types of reference signals corresponding to n types of helicopters. The calculation results in the convolution operation devices 10-1 to 10-n are sent to the CFAR devices 7-1 to 7-n, respectively.

  The configuration and operation of each of the CFAR devices 7-1 to 7-n are the same as the configuration and operation of the CFAR device 7 in the radar apparatus according to the first embodiment. The amplitude ratio signals generated by the CFAR devices 7-1 to 7-n are sent to the detection devices 8-1 to 8-n, respectively.

  The configuration and operation of each of the detection devices 8-1 to 8-n are the same as the configuration and operation of the detection device 8 in the radar apparatus according to the first embodiment. The detection devices 8-1 to 8-n detect signals that exceed the threshold among the amplitude ratio signals from the CFAR devices 7-1 to 7-n, respectively. Here, when the target helicopter is the type m (1 ≦ m ≦ n), the SN ratio of the output signal from the convolution operation device 10-m is maximized.

  As described above, according to the radar apparatus according to the second embodiment of the present invention, it is possible to maximize the SN ratio of received signals from a plurality of types of helicopters. The target detection performance can be improved.

  The radar apparatus according to the third embodiment of the present invention detects a target based on a signal obtained by performing inverse Fourier transform after multiplying a received signal by Fourier transform and a Fourier-transformed reference signal. It is a thing.

  FIG. 4 is a block diagram showing the configuration of the radar apparatus according to Embodiment 3 of the present invention. In the following description, parts corresponding to the constituent parts of the radar apparatus according to the first embodiment are denoted by the same reference numerals as those used in the radar apparatus according to the first embodiment, and description thereof is omitted.

  The radar apparatus according to the third embodiment includes an antenna 1, a transmitter 2, a circulator 3, a receiver 4, an unnecessary wave suppression apparatus 9, a Fourier transform apparatus 11, a CFAR apparatus 7, and a detection apparatus 8.

  FIG. 5 is a block diagram showing a detailed configuration of the Fourier transform apparatus 11. The Fourier transform device 11 includes a Fourier transform unit 14, a Fourier transform reference signal generation unit 15, a multiplication unit 16, and an inverse Fourier transform unit 17.

  The Fourier transform unit 14 performs Fourier transform on the signal sent from the unwanted wave suppression device 9 by FFT. The output of the Fourier transform unit 14 is sent to the multiplication unit 16.

  The Fourier transform reference signal generator 15 generates a signal obtained by Fourier transforming the reference signal in the first embodiment. The Fourier-transformed reference signal generated by the Fourier-transform reference signal generator 15 is sent to the multiplier 16.

  The multiplication unit 16 multiplies the Fourier-transformed signal sent from the Fourier transform unit 14 and the Fourier-transformed reference signal sent from the Fourier transform reference signal generation unit 15. The multiplication result in the multiplication unit 16 is sent to the inverse Fourier transform unit 17.

  The inverse Fourier transform unit 17 performs an inverse Fourier transform on the signal transmitted from the multiplication unit 16 by IFFT (Inverse Fast Fourier Transform). The output of the inverse Fourier transform unit 17 is sent to the CFAR device 7.

  The operation of the radar apparatus according to the third embodiment is the same as the operation of the radar apparatus according to the first embodiment except that Fourier transform is performed instead of the convolution calculation.

  As described above, according to the radar apparatus according to Embodiment 3 of the present invention, processing equivalent to the convolution operation is performed by using the FFT and IFFT, but the convolution is performed when the data length of the reference signal is long. The amount of calculation can be reduced compared to the calculation.

  The radar apparatus according to Embodiment 4 of the present invention detects a target based on a signal obtained by performing inverse Fourier transform after multiplying a received signal by Fourier transform and a plurality of types of reference signals subjected to Fourier transform. It is what you do.

  FIG. 6 is a block diagram showing a configuration of a radar apparatus according to Embodiment 4 of the present invention. In the following, the same components as those of the radar apparatus according to the third embodiment are denoted by the same reference numerals as those of the radar apparatus according to the third embodiment, and the description thereof is omitted.

  The radar apparatus includes an antenna 1, a transmitter 2, a circulator 3, a receiver 4, an unnecessary wave suppression apparatus 9, Fourier transform apparatuses 11-1 to 11-n, CFAR apparatuses 7-1 to 7-n, and a detection apparatus 8-. 1 to 8-n.

  The configuration and operation of each of the Fourier transform devices 11-1 to 11-n are the same as the configuration and operation of the Fourier transform device 11 in the radar apparatus according to the third embodiment except for the following points. That is, the Fourier transform devices 11-1 to 11-n respectively generate signals obtained by Fourier transforming the reference signals corresponding to the n types of helicopters, and multiplying the output signal of the unwanted wave suppression device 9 by the signal obtained by Fourier transform. Inverse Fourier transform is performed. The outputs of the Fourier transform devices 11-1 to 11-n are sent to the CFAR devices 7-1 to 7-n, respectively.

  The configuration and operation of each of the CFAR devices 7-1 to 7-n are the same as the configuration and operation of the CFAR device 7 in the radar apparatus according to the first embodiment. The amplitude ratio signals generated by the CFAR devices 7-1 to 7-n are sent to the detection devices 8-1 to 8-n, respectively.

  The configuration and operation of each of the detection devices 8-1 to 8-n are the same as the configuration and operation of the detection device 8 in the radar apparatus according to the first embodiment. The detection devices 8-1 to 8-n detect signals that exceed the threshold among the amplitude ratio signals from the CFAR devices 7-1 to 7-n, respectively. Here, when the target helicopter is the type m (here, 1 ≦ m ≦ n), the SN ratio of the output signal from the Fourier transform device 11-m is maximized.

  As described above, according to the radar apparatus according to Embodiment 4 of the present invention, it is possible to maximize the S / N ratio of received signals from a plurality of types of helicopters. The target detection performance can be improved.

  In the radar apparatus according to the fourth embodiment described above, each of the Fourier transform apparatuses 11-1 to 11-n is configured to Fourier-transform the output signal of the unwanted wave suppression apparatus 9, but the Fourier transform apparatus 11- 1 to 11-n, the output signal of the unwanted wave suppression device can be Fourier transformed, and the other Fourier transform device can be configured to input the output signal. According to this configuration, the calculation load of Fourier transform can be reduced.

  The present invention can be applied not only to a radar apparatus but also to a sonar apparatus that detects a target from which a reception signal whose amplitude greatly changes with time and whose amplitude is short can be obtained.

1 is a block diagram illustrating a configuration of a radar apparatus according to Embodiment 1 of the present invention. It is a block diagram which shows the detailed structure of the convolution operation apparatus used with the radar apparatus which concerns on Example 1 of this invention. It is a block diagram which shows the structure of the radar apparatus which concerns on Example 2 of this invention. It is a block diagram which shows the structure of the radar apparatus which concerns on Example 3 of this invention. It is a block diagram which shows the detailed structure of the Fourier-transform apparatus used with the radar apparatus which concerns on Example 3 of this invention. It is a block diagram which shows the structure of the radar apparatus which concerns on Example 4 of this invention. It is a block diagram which shows the structure of the conventional radar apparatus. It is a figure which shows the example of calculation of integral gain G and integral gain G '.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 Transmitter 3 Circulator 4 Receiver 5 MTI apparatus 6 Frequency analysis apparatus 7 CFAR apparatus 8 Detection apparatus 9 Unwanted wave suppression apparatus 10 Convolution operation apparatus 11 Fourier transform apparatus 12 Convolution operation section 13 Reference signal generation section 14 Fourier transform section 15 Fourier transform reference signal generator 16 Multiplier 17 Inverse Fourier transform

Claims (4)

A receiver that converts a received signal obtained by receiving a reflected wave of a transmitted wave transmitted to space into a digital video signal;
An unnecessary wave suppressing device for suppressing unnecessary wave components from the digital video signal output from the receiver;
A reference signal having a length in a pulse direction that is a complex conjugate for each pulse of a received signal from a target to be detected and has a maximum integral gain with respect to a signal in which an unnecessary wave component is suppressed by the unnecessary wave suppressing device. A convolution operation device that performs a convolution operation between
A detection device for detecting a signal of a reflected wave from a target based on a signal output from the convolution operation device;
A radar apparatus comprising: The convolution operation device is:
The radar apparatus according to claim 1, wherein a convolution operation is performed on a signal whose unnecessary wave component is suppressed by the unnecessary wave suppression apparatus with a plurality of types of reference signals. A receiver that converts a received signal obtained by receiving a reflected wave of a transmitted wave transmitted to space into a digital video signal;
An unnecessary wave suppressing device for suppressing unnecessary wave components from the digital video signal output from the receiver;
The signal in which the unwanted wave component is suppressed by the unwanted wave suppression device is Fourier-transformed, and the length of the pulse direction that is a complex conjugate for each pulse of the received signal from the target to be detected and that can maximize the integral gain. A Fourier transform device that performs an inverse Fourier transform after multiplying a signal having the signal obtained by performing a Fourier transform on the signal,
A detection device for detecting a signal of a reflected wave from a target based on a signal output from the Fourier transform device;
A radar apparatus comprising: The Fourier transform device
The signal in which the unwanted wave component is suppressed by the unwanted wave suppression device is Fourier-transformed, and the length of the pulse direction that is a complex conjugate for each pulse of the received signal from the target to be detected and that can maximize the integral gain. 4. The radar apparatus according to claim 3, wherein each of the plurality of types of reference signals obtained by performing Fourier transform on the received signal is multiplied, and then inverse Fourier transform is performed.

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