JP6630541B2 - Low frequency clutter remover - Google Patents

Description

  The present invention relates to a technique for removing low-frequency clutter in a radar device.

  2. Description of the Related Art In a radar apparatus, FTC (Fast Time Constant) processing for extracting a signal from a target by removing clutter due to rain, snow, or the like is applied. Prior to the disclosure of Patent Literature 1, low-frequency clutter due to rain and snow was removed by applying an analog high-pass filter. After the disclosure of Patent Document 1, instead of applying the FTC processing, a threshold for distinguishing between clutter and a signal is statistically set by applying a CFAR (Constant False Alarm Rate) processing, Noise level clutter due to rain and snow is removed.

JP 2011-002426 A

  However, prior to the disclosure of Patent Literature 1, an analog high-pass filter was applied, so that the circuit design and circuit configuration of the FTC process were complicated. After the disclosure of Patent Document 1, since the CFAR processing is applied instead of the FTC processing, the radar image changes abruptly before and after the CFAR processing, and the target and the topography are overlooked. May occur.

  Therefore, in order to solve the above problems, the present invention provides a radar device that simplifies the circuit design and circuit configuration of low-frequency clutter removal processing and continuously changes radar images in the low-frequency clutter removal process. To eliminate the risk of oversight of targets and terrain.

  In order to achieve the above object, a digital high-pass filter having a continuously variable cutoff frequency is used to remove low frequency components and pass high frequency components. Here, “continuously variable” means not only taking an arbitrary real value, but also taking a discrete real value such that the radar image does not change abruptly.

  Specifically, the present invention uses a radar reception signal input unit that inputs a radar reception signal before clutter is removed, and a digital high-pass filter whose cutoff frequency is continuously variable, so that clutter is removed. A low-frequency clutter removing unit that removes low-frequency components from the received radar signal before passing the high-frequency component and generates a radar-received signal from which clutter has been removed, and a radar after the clutter has been removed. And a radar reception signal output unit that outputs a reception signal.

  According to this configuration, in the radar device, the circuit design and the circuit configuration of the low-frequency clutter removal processing are simplified, and the radar image is continuously changed in the low-frequency clutter removal processing, so that the target device and the terrain are removed. It is possible to eliminate the risk of oversight.

  Further, the present invention, the low-frequency clutter removing device further comprises a cut-off frequency input unit for inputting a user-set value of a cut-off frequency of the digital high-pass filter, wherein the low-frequency clutter removing unit includes the digital high-pass filter. When the user set value of the cut-off frequency of the filter is smaller than a preset threshold value, a FIR (Finite Impulse Response) filter is used as the digital high-pass filter, while the user set value of the cut-off frequency of the digital high-pass filter is A low frequency clutter removing apparatus characterized in that an IIR (Infinite Impulse Response) filter is used as the digital high-pass filter when the digital high-pass filter is equal to or greater than the preset threshold.

  According to this configuration, the FIR filter and the IIR filter can be used in the right place at the right place for continuously changing the radar image in the low frequency clutter removal process.

  Also, in the present invention, the digital high-pass filter is shared by an FIR filter and an IIR filter, and the low-frequency clutter removing unit is configured such that a user-set value of a cut-off frequency of the digital high-pass filter is higher than the preset threshold. When the value is smaller, the filter coefficient value of the feedback loop of the digital high-pass filter is set to 0. On the other hand, when the user-set value of the cut-off frequency of the digital high-pass filter is equal to or more than the preset threshold, the digital high-pass filter is set. A low frequency clutter removing apparatus characterized in that a filter coefficient value of a feedback loop of a filter is set to non-zero.

  According to this configuration, to simplify the circuit design and circuit configuration of the low frequency clutter removal processing, the FIR filter and the IIR filter can be realized by a shared circuit.

  Further, in the present invention, the low-frequency clutter removing apparatus stores in advance a correspondence table indicating a correspondence relationship between a user setting value of a cutoff frequency of the digital high-pass filter and a filter coefficient value of the digital high-pass filter. Further comprising a filter coefficient value storage unit, wherein the low frequency clutter removal unit, the user setting value of the cut-off frequency of the digital high-pass filter, the correspondence table stored in advance in the filter coefficient value storage unit, And a filter coefficient value of the digital high-pass filter is set based on the following equation.

  According to this configuration, the filter coefficient value of the digital high-pass filter is calculated without responding to the user's instruction to continuously change the cut-off frequency of the digital high-pass filter. Only by acquiring from the memory, the cutoff frequency of the digital high-pass filter can be quickly followed.

  As described above, the present invention simplifies the circuit design and circuit configuration of the low-frequency clutter removal processing in the radar apparatus, and continuously changes the radar image in the low-frequency clutter removal processing, thereby reducing the target and terrain. Etc. can be avoided.

It is a figure showing the composition of the radar device of the present invention. FIG. 4 is a diagram illustrating a low frequency clutter removing method according to the present invention. FIG. 6 is a diagram illustrating a low frequency clutter removal method at a low cutoff frequency. FIG. 3 is a diagram illustrating a low frequency clutter removal method at a high cutoff frequency. FIG. 9 is a diagram illustrating a result of removing low-frequency clutter at a low cutoff frequency. FIG. 7 is a diagram illustrating a result of removing low-frequency clutter at a high cutoff frequency.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments.

  FIG. 1 shows the configuration of the radar apparatus of the present invention. The radar device R includes a radar transmitting unit 1, a radar receiving unit 2, a low frequency clutter removing device 3, a radar display unit 4, and an operation volume 5. The low frequency clutter removing device 3 includes a radar reception signal input unit 31, a low frequency clutter removal unit 32, a radar reception signal output unit 33, a cutoff frequency input unit 34, and a filter coefficient value storage unit 35. The low frequency clutter removing unit 32 includes a digital high-pass filter 321 and a filter coefficient value setting unit 322.

  The radar transmitting unit 1 transmits a radar output signal to the target T. The radar receiving unit 2 receives a radar reflected signal from the target T. The low-frequency clutter removing device 3 inputs a radar reception signal before low-frequency clutter is removed, and outputs a radar reception signal after low-frequency clutter is removed. The radar display unit 4 displays an image of the radar reception signal from which low-frequency clutter has been removed. The operation volume 5 is an interface for the user to set the cutoff frequency of the digital high-pass filter 321.

  The radar reception signal input unit 31 inputs from the radar reception unit 2 a radar reception signal before clutter is removed. The digital high-pass filter 321 removes low-frequency components from the radar reception signal before the clutter is removed, passes high-frequency components, and generates a radar reception signal after the clutter is removed. The radar reception signal output unit 33 outputs the radar reception signal from which the clutter has been removed to the radar display unit 4.

  Here, the digital high-pass filter 321 makes the cutoff frequency continuously variable. However, "continuously variable" means not only taking an arbitrary real value, but also taking a discrete real value such that the radar image does not change rapidly.

  As described above, in the radar apparatus R, the circuit design and the circuit configuration of the low-frequency clutter removal processing are simplified, and the radar image is continuously changed in the low-frequency clutter removal processing, so that the target T and the terrain and the like are changed. It is possible to eliminate the risk of oversight.

FIG. 2 shows the low frequency clutter removal method of the present invention. The cutoff frequency input unit 34 inputs a user setting value of the cutoff frequency of the digital high-pass filter 321 from the operation volume 5. Filter coefficient value setting unit 322, when the user setting value f ₁ of the cut-off frequency of the digital high-pass filter 321 is less than the threshold value f _t that is set in advance, while use of the FIR filter as a digital high-pass filter 321, a digital high-pass filter When the user set value f ₂ of the cut-off frequency 321 is _{equal to} or greater than a preset threshold ft, an IIR filter is used as the digital high-pass filter 321.

User setting value f ₁ of the cut-off frequency of the digital high-pass filter 321, when less than the threshold value f _t that is set in advance, the cut-off frequency of the digital high-pass filter 321 for the user to set a low cut-off frequency. Therefore, the filter coefficient value setting unit 322 uses, as the digital high-pass filter 321, an FIR filter that can realize a low cutoff frequency even with a small number of cascade stages. In the FIR filter, there is no waveform disturbance due to the group delay even if the linear phase correction is not performed.

User setting value f ₂ of the cut-off frequency of the digital high-pass filter 321, when the threshold value f _t or more set in advance, the cut-off frequency of the digital high-pass filter 321 for the user to set a high cut-off frequency. Therefore, the filter coefficient value setting unit 322 uses, as the digital high-pass filter 321, an IIR filter that can realize a high cutoff frequency even with a small number of cascade stages. In the IIR filter, if linear phase correction is performed, waveform disturbance due to group delay is eliminated.

When the user set value f ₀ of the cutoff frequency of the digital high-pass filter 321 is near 0 which is the DC frequency, the filter coefficient value setting unit 322 uses an all-pass filter as the digital high-pass filter 321.

  As described above, the FIR filter and the IIR filter can be used in the right place at the right place for continuously changing the radar image in the low frequency clutter removal process.

  FIG. 3 shows a method for removing low frequency clutter at a low cutoff frequency. FIG. 4 shows a method for removing low frequency clutter at a high cutoff frequency.

The digital high-pass filter 321 is shared by the FIR filter and the IIR filter, and has a secondary cascade configuration in which the number of cascade stages is N. When the user set value f ₁ of the cut-off frequency of the digital high-pass filter 321 is smaller than a preset threshold value f _{t, the} filter coefficient value setting unit 322 sets the filter coefficient values a ₁₁ and a ₁₁ of the feedback loop of the digital high-pass filter 321. ₂₁ , a ₁₂ , a ₂₂ ,..., A _1N , a _2N are set to 0, while the user set value f ₂ of the cutoff frequency of the digital high-pass filter 321 is _{equal to} or _larger than a preset threshold ft. In some cases, the filter coefficient values a ₁₁ , a ₂₁ , a ₁₂ , a ₂₂ ,..., A _1N , a _2N of the feedback loop of the digital high-pass filter 321 are set to non-zero.

  As described above, to simplify the circuit design and circuit configuration of the low-frequency clutter removal processing, the FIR filter and the IIR filter can be realized by a shared circuit.

The filter coefficient value storage unit 35 stores the correspondence between the user set value (f ₁ , f _2, etc.) of the cutoff frequency of the digital high-pass filter 321 and the filter coefficient value (a, b, etc.) of the digital high-pass filter 321. Is stored in advance. The filter coefficient value setting unit 322 is based on a user setting value (f ₁ , f _2, etc.) of the cutoff frequency of the digital high-pass filter 321 and a correspondence table stored in the filter coefficient value storage unit 35 in advance. The filter coefficient values (a, b, etc.) of the digital high-pass filter 321 are set.

  As described above, in response to a user's instruction to continuously change the cutoff frequency of the digital high-pass filter 321, the digital high-pass filter 321 does not need to calculate the filter coefficient values (a, b, etc.) each time. Only by acquiring the filter coefficient values (a, b, etc.) of the filter 321 from the filter coefficient value storage unit 35, the cutoff frequency of the digital high-pass filter 321 can be quickly followed.

  In the present embodiment, the digital high-pass filter 321 is shared by the FIR filter and the IIR filter, and has a secondary cascade configuration in which the number of cascade stages is N. As a first modification, the digital high-pass filter 321 may be separated into an FIR filter and an IIR filter. As a second modification, the digital high-pass filter 321 may increase the number of cascade stages as the user-set value of the cutoff frequency increases. As a third modification, the digital high-pass filter 321 may have any configuration as long as it operates as an FIR filter and an IIR filter. In the present embodiment and the first to third modifications, when switching between the FIR filter and the IIR filter is performed, it is desirable that the cutoff frequency of the digital high-pass filter 321 changes smoothly.

  FIG. 5 shows the result of removing the low frequency clutter at the low cutoff frequency. FIG. 6 shows the result of removing the low frequency clutter at the high cutoff frequency.

  5 and 6, a broken line indicates a radar reflection signal from the target T having a large size, and a solid line indicates a radar reception signal after the filtering process is performed. In FIG. 5, in order to realize a low cutoff frequency, an FIR filter having 16 cascade stages is applied, and there is no need to perform linear phase correction. In FIG. 6, in order to realize a high cutoff frequency, an IIR filter having 16 cascade stages is applied, and it is desirable to perform linear phase correction.

  As can be seen from FIG. 5, by applying the FIR filter, a low cutoff frequency (normalized cutoff frequency of 0.4) can be realized even if the number of cascade stages is reduced to 16, and linear phase correction can be performed. Even without this, it is possible to suppress waveform disturbance due to group delay. As can be seen from FIG. 6, by applying the IIR filter, a high cutoff frequency (normalized cutoff frequency 0.01) can be realized even when the number of cascade stages is reduced to 16, and linear phase correction can be performed. By doing so, waveform disturbance due to group delay can be suppressed.

  INDUSTRIAL APPLICABILITY The low-frequency clutter removing apparatus of the present invention can be applied to FTC processing for removing clutter due to rain and snow and extracting a signal from a target in a radar apparatus.

R: radar device T: target 1: radar transmission unit 2: radar reception unit 3: low frequency clutter removal device 4: radar display unit 5: operation volume 31: radar reception signal input unit 32: low frequency clutter removal unit 33: Radar reception signal output unit 34: cutoff frequency input unit 35: filter coefficient value storage unit 321: digital high-pass filter 322: filter coefficient value setting unit

Claims (4)

A radar reception signal input unit for inputting a radar reception signal before clutter is removed;
Using a digital high-pass filter whose cutoff frequency is continuously variable, the low-frequency component is removed from the radar reception signal before clutter is removed, the high-frequency component is passed, and after the clutter is removed. A low-frequency clutter removing unit that generates a radar reception signal;
A radar reception signal output unit that outputs a radar reception signal after clutter has been removed,
A low frequency clutter removing device comprising: The low-frequency clutter removing apparatus further includes a cutoff frequency input unit that inputs a user-set value of a cutoff frequency of the digital high-pass filter,
When the user-set value of the cut-off frequency of the digital high-pass filter is smaller than a preset threshold, the low-frequency clutter removing unit uses a FIR (Finite Impulse Response) filter as the digital high-pass filter, 2. The low-pass filter according to claim 1, wherein when a user setting value of a cut-off frequency of the high-pass filter is equal to or higher than the preset threshold value, an IIR (Infinite Impulse Response) filter is used as the digital high-pass filter. 3. Frequency clutter removal device. The digital high-pass filter is shared by the FIR filter and the IIR filter,
The low frequency clutter removing unit sets a filter coefficient value of a feedback loop of the digital high-pass filter to 0 when a user-set value of a cutoff frequency of the digital high-pass filter is smaller than the preset threshold. When the user-set value of the cut-off frequency of the digital high-pass filter is equal to or higher than the preset threshold value, the filter coefficient value of the feedback loop of the digital high-pass filter is set to non-zero. Item 3. The low frequency clutter removing apparatus according to Item 2. The low-frequency clutter removing device includes a filter coefficient value storage unit that stores in advance a correspondence table indicating a correspondence between a user setting value of a cutoff frequency of the digital high-pass filter and a filter coefficient value of the digital high-pass filter. And further comprising
The low-frequency clutter removing unit is configured to filter a digital high-pass filter based on a user-set value of a cut-off frequency of the digital high-pass filter and the correspondence table stored in the filter coefficient value storage unit in advance. The low frequency clutter removing apparatus according to claim 2, wherein a numerical value is set.

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