Target angle detection device and target angle detection program

Abstract

The purpose of the present disclosure is to reduce erroneous detection of a false image caused by sidelobes and also minimize the deterioration of angular resolution by appropriately using a window function when detecting a target using a radar.　A target angle detection device 2 comprises: an angle spectrum calculation unit 21 that performs digital beamforming on the same reception signal of a radar array antenna by using first and second window functions having different sidelobe suppression levels, and calculates first and second angle spectra, respectively; a differential spectrum calculation unit 22 that calculates a differential-intensity spectrum on the basis of the first and second angle spectra; and a target angle detection unit 23 that detects a target at a spectral angle where the spectral intensity lies within a predetermined range on the basis of the differential-intensity spectrum, and determines that what is detected is a false image rather than the target at spectral angles where the spectral intensity lies outside the predetermined range.

Description

Target angle detection device and target angle detection program

[0001] The present disclosure relates to a technique for detecting a target using a radar while suppressing false images.

[0002] Patent Documents 1 and 2 disclose techniques for detecting targets after suppressing false images using millimeter-wave radar, MIMO (Multiple-Input Multiple-Output) radar and / or KR (Khatri-Rao) product expansion radar, etc.

[0003] In Patent Documents 1 and 2, digital beamforming (multi-beam formation by Fourier transform) is performed on the received signal of a radar array antenna using a window function (Taylor window, Hanning window, Hamming window, or the like) to calculate the angular spectrum. Then, for the angular spectrum, targets are detected at spectral angles where the spectral intensity is equal to or greater than a predetermined threshold, and spectral angles where the spectral intensity is less than the predetermined threshold are determined to be false targets rather than targets.

[0004] Japanese Patent No. 7341372 Japanese Patent Application Laid-Open No. 2019-070558

[0005] The issues with target angle detection processing in the prior art are shown in Figure 1. When detecting targets using radar, it is desirable to reduce false detections caused by side lobes and minimize degradation of angular resolution, but there is no single window function that can meet both of these requirements.

[0006] In the upper part of Figure 1, when digital beamforming is performed on the received signal of the radar array antenna using a first window function (with a large side lobe suppression level) and the first angular spectrum is calculated, it is possible to reduce false detection of artifacts due to side lobes, but it is not possible to minimize the degradation of angular resolution.

[0007] In the lower part of Figure 1, when digital beamforming is performed on the received signal of the radar array antenna using a second window function (with a small side lobe suppression level) and a second angular spectrum is calculated, the deterioration of angular resolution can be minimized, but the false detection of false images due to side lobes cannot be reduced.

[0008] Therefore, in order to solve the above-mentioned problems, an object of the present disclosure is to reduce false detection of artifacts due to side lobes and minimize degradation of angular resolution when detecting targets using radar, by appropriately using a window function.

[0009] To solve the above problem, digital beamforming (multi-beam formation by Fourier transform) is performed on the same received signal of a radar array antenna using multiple window functions with different sidelobe suppression levels, and the angular spectrum of each is calculated.

[0010] Here, by using a window function with a large side lobe suppression level and a window function with a small side lobe suppression level, it is possible to achieve both the advantage of the former window function (reducing erroneous detection of artifacts due to side lobes) and the advantage of the latter window function (reducing degradation of angular resolution).

[0011] At the spectral angle where a target should be detected, the difference in intensity between each angular spectrum is small. On the other hand, at the spectral angle where no target exists, i.e., where a false image is present, the difference in intensity between each angular spectrum is large. In other words, a target is detected at the spectral angle where the difference in intensity between each angular spectrum is small and falls within a predetermined range. On the other hand, at the spectral angle where the difference in intensity between each angular spectrum is large and falls outside the predetermined range, it is determined to be a false image rather than a target.

[0012] Specifically, the present disclosure provides a target angle detection device comprising: an angular spectrum calculation unit that performs digital beamforming on the same received signal of a radar array antenna using a first window function and a second window function with different side lobe suppression levels to calculate a first angular spectrum and a second angular spectrum, respectively; a differential spectrum calculation unit that calculates an intensity difference spectrum for the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit; and a target angle detection unit that (1) detects a target at a spectral angle where the spectral intensity is within a predetermined range for the intensity difference spectrum calculated by the differential spectrum calculation unit, and (2) determines that the target is not a target but a false target at a spectral angle where the spectral intensity is outside the predetermined range.

[0013] According to this configuration, when detecting targets using radar, it is possible to reduce false detections of artifacts caused by side lobes and minimize degradation of angular resolution by using multiple window functions with different side lobe suppression levels.

[0014] The present disclosure also provides a target angle detection device, characterized in that, for the intensity difference spectrum calculated by the difference spectrum calculation unit, (1) the target is detected at a spectrum angle where the spectral intensity is within the predetermined interval and has a peak or a bottom, and (2) the spectral intensity is within the predetermined interval but does not have a peak or a bottom at a spectrum angle where it is determined to be a false target rather than a target.

[0015] At the spectral angle at which a target should be detected, the difference in intensity between each angular spectrum becomes small, and the deviation between the peak angles of each angular spectrum becomes small. With this configuration, a target can be detected at a spectral angle where the difference in intensity between each angular spectrum is small and within a predetermined range, and where the spectral angle forms a peak or bottom.

[0016] At spectral angles where no target is present, i.e., where a false image is present, even if the difference in intensity between each angular spectrum is small, the deviation between the peak angles of each angular spectrum is large. With this configuration, at spectral angles where the difference in intensity between each angular spectrum is small and within a predetermined range but does not form a peak or bottom, it can be determined that the spectrum is a false image rather than a target.

[0017] The present disclosure also provides a target angle detection device, wherein the differential spectrum calculation unit calculates a differential spectrum of the intensities after changing null spectrum intensities that are less than a same threshold value for the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit to different fixed values.

[0018] If the null intensities of the angular spectra are maintained at their original values ​​at the spectral angles where nulls should be removed, the difference in intensity between the angular spectra may be small and may form a peak or trough. On the other hand, if the null intensities of the angular spectra are changed to different fixed values ​​at the spectral angles where nulls should be removed, the difference in intensity between the angular spectra will be large and will not form a peak or trough. This configuration makes it possible to prevent erroneous target detection at spectral angles where nulls should be removed.

[0019] The present disclosure also provides a target angle detection device, wherein the difference spectrum calculation unit calculates the intensity difference spectrum after normalizing the maximum spectral intensities of the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit to equal values, or after compensating for S / N degradation due to the first window function and the second window function, respectively, and the target angle detection unit, with respect to the intensity difference spectrum calculated by the difference spectrum calculation unit, (1) detects a target at a spectral angle where the spectral intensity is within the predetermined range (having equal widths in the positive and negative directions with 0 dB as the center), and (2) determines that the target is not a target but a false target at a spectral angle where the spectral intensity is outside the predetermined range.

[0020] If the maximum intensity of each angular spectrum is maintained at its current value at the spectral angle at which a target object is to be detected, the difference in intensity between the angular spectra may deviate from 0 dB. On the other hand, if the maximum intensity of each angular spectrum is changed to a substantially equal value at the spectral angle at which a target object is to be detected, the difference in intensity between the angular spectra will approach 0 dB. With this configuration, the predetermined interval for detecting targets while suppressing false images can be easily set to an interval having equal widths in the positive and negative directions, centered at 0 dB.

[0021] The present disclosure also provides a target angle detection program for causing a computer to sequentially execute the processing steps executed by the processing units included in the target angle detection device described above.

[0022] According to this configuration, it is possible to provide a program having the above-described effects.

[0023] The above-disclosed inventions can be combined as much as possible.

[0024] In this way, the present disclosure can reduce false detection of artifacts caused by side lobes and minimize degradation of angular resolution when detecting targets using radar, by appropriately using window functions.

[0025] FIG. 1 is a diagram illustrating a problem with target angle detection processing of the prior art; FIG. 2 is a diagram illustrating the configuration of a target angle detection system according to the present disclosure; FIG. 3 is a diagram illustrating the procedure of target angle detection processing according to the present disclosure; FIG. 4 is a diagram illustrating the principle of target angle detection processing according to the present disclosure; FIG. 5 is a diagram illustrating normalization processing of maximum spectral intensity in an angular spectrum according to the present disclosure; FIG. 6 is a diagram illustrating removal processing of null spectral intensity in an angular spectrum according to the present disclosure; FIG. 7 is a diagram illustrating target angle detection processing based on an intensity difference spectrum according to a comparative example;

[0026]

[0023] The following embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of implementation of the present disclosure, and the present disclosure is not limited to the following embodiments.

[0027] (Principle of target angle detection processing of the present disclosure) The configuration of a target angle detection system of the present disclosure is shown in Fig. 2. The procedure of target angle detection processing of the present disclosure is shown in Fig. 3. The target angle detection system S includes a radar transmitter / receiver 1, a target angle detection device 2, and a radar display device 3. The target angle detection device 2 includes an angle spectrum calculation unit 21, a difference spectrum calculation unit 22, and a target angle detection unit 23. The target angle detection device 2 can be realized by installing the target angle detection program shown in Fig. 3 on a computer.

[0028] The radar transceiver 1 is a millimeter-wave radar, a MIMO radar, and / or a KR product expansion radar, and emits radar transmission signals and receives radar reflection signals. The target angle detection device 2 performs digital beamforming (multi-beam formation by Fourier transform) on the received signals of the radar array antenna using a window function (Taylor window, Hanning window, Hamming window, rectangular window, etc.), calculates the angular spectrum, suppresses false images, and detects targets. The radar display device 3 displays the detected targets with false images suppressed.

[0029] The principle of the target angle detection process of the present disclosure is shown in Figure 4. In the present disclosure, digital beamforming is performed on the same received signal of the radar array antenna using a first window function (which has a high side lobe suppression level but a coarse angular resolution) and a second window function (which has a low side lobe suppression level but a fine angular resolution), and a first angular spectrum and a second angular spectrum are calculated, respectively.

[0030] Here, by using a first window function with a large side lobe suppression level and a second window function with a small side lobe suppression level, it is possible to achieve both the advantage of the first window function (reducing erroneous detection of artifacts due to side lobes) and the advantage of the second window function (reducing degradation of angular resolution).

[0031] At the spectral angle where a target should be detected, the difference in intensity between the first and second angular spectra is small, whereas at the spectral angle where no target is present, i.e., where a false image is present, the difference in intensity between the first and second angular spectra is large.

[0032] That is, a target is detected at a spectral angle where the difference in intensity between the first and second angular spectra is small and within a predetermined range (approximately 20° and approximately −15° in FIG. 4 ). On the other hand, at a spectral angle where the difference in intensity between the first and second angular spectra is large and outside the predetermined range (approximately 40° and approximately −35° in FIG. 4 ), the target is determined to be a false image rather than a target.

[0033] Therefore, when detecting a target using a radar, it is possible to reduce false detections of false images due to side lobes and minimize degradation of angular resolution by using a first window function and a second window function with different side lobe suppression levels.

[0034] At a spectral angle where a target should be detected, the deviation between the peak angle of the first angular spectrum and the peak angle of the second angular spectrum is small. On the other hand, at a spectral angle where no target is present, i.e., where a false image is present, the deviation between the peak angle of the first angular spectrum and the peak angle of the second angular spectrum is generally large, but may occasionally be small.

[0035] Therefore, whether or not to detect a target is not determined based on the magnitude of the difference between the peak angle of the first angular spectrum and the peak angle of the second angular spectrum.In fact, it is not obvious which peak angle of the first angular spectrum and which peak angle of the second angular spectrum correspond to the same target or the same false image.

[0036] (Preprocessing of the target angle detection process of the present disclosure) First, the preprocessing of the target angle detection process of the present disclosure will be described. The normalization process of the maximum spectral intensity in the angular spectrum of the present disclosure is shown in Fig. 5. The angular spectrum calculation unit 21 performs digital beamforming (multi-beam formation by Fourier transform) on the same received signal of the radar array antenna using a first window function (with a high side lobe suppression level) and a second window function (with a low side lobe suppression level), and calculates a first angular spectrum and a second angular spectrum, respectively (step S1).

[0037] The differential spectrum calculation unit 22 normalizes the maximum spectral intensities of the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit 21 to the same value, or compensates for the S / N degradation caused by the first window function and the second window function (step S2), and then calculates the differential spectrum of the intensities (step S4).

[0038] Here, if the maximum intensities of the first angular spectrum and the second angular spectrum are maintained at their original values ​​at the spectral angle at which a target is to be detected (see the upper part of FIG. 5 ), the difference in intensity between the first angular spectrum and the second angular spectrum may deviate from 0 dB.

[0039] On the other hand, if the maximum intensity of the first angular spectrum and the maximum intensity of the second angular spectrum are changed to approximately equal values ​​at the spectral angle at which a target should be detected (see the bottom part of Figure 5), the difference in intensity between the first angular spectrum and the second angular spectrum approaches 0 dB.

[0040] Therefore, a predetermined section for detecting a target after suppressing false images can be easily set to a section having equal widths in the positive and negative directions with 0 dB as the center (see FIG. 7).

[0041] The process of removing null spectral intensities in the angular spectrum according to the present disclosure is shown in Fig. 6. The difference spectrum calculation unit 22 changes the null spectral intensities of the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit 21 that are less than the same threshold (-15 dB in Fig. 6) to different fixed values ​​(-50 dB and -100 dB in Fig. 6, respectively) (step S3), and then calculates the difference spectrum of intensities (step S4).

[0042] Here, at the spectral angle where the null should be removed, if the null intensity of the first angular spectrum and the null intensity of the second angular spectrum are maintained at their original values, the difference in intensity between the first angular spectrum and the second angular spectrum may peak or trough and may be small (see approximately 60° and approximately −50° in FIG. 8 ).

[0043] On the other hand, if the null intensity of the first angular spectrum and the null intensity of the second angular spectrum are changed to different fixed values ​​at the spectral angle where the null should be removed, the difference in intensity between the first angular spectrum and the second angular spectrum will not form a peak or bottom and will become large (see approximately 60° and approximately −50° in FIG. 7 ).

[0044] Therefore, it is possible to prevent erroneous detection of targets at spectral angles where nulls should be removed, and of course it is also possible to prevent erroneous detection of false images due to side lobes (see FIG. 7).

[0045] (Specific Example of Target Angle Detection Process of the Present Disclosure) Next, a specific example of the target angle detection process of the present disclosure will be described. The target angle detection process based on the intensity difference spectrum of the present disclosure (where nulls are removed as in FIG. 6 ) is shown in FIG. 7 . The target angle detection process based on the intensity difference spectrum of a comparative example (where nulls are maintained, unlike FIG. 6 ) is shown in FIG.

[0046] First, the target angle detection unit 23 detects a target (step S7) at a spectral angle where the spectral intensity is within a predetermined range (in FIGS. 7 and 8, −1 dB or more and 1 dB or less) for the intensity difference spectrum calculated by the difference spectrum calculation unit 22 (step S5, YES).

[0047] That is, as explained in (Principles of target angle detection processing of the present disclosure), the intensity difference spectrum becomes small at the spectrum angle at which the target should be detected. Therefore, the target can be detected at the spectrum angle where the intensity difference spectrum is small and within the predetermined range.

[0048] On the other hand, when the spectral intensity of the difference spectrum calculated by the difference spectrum calculation unit 22 is outside the predetermined range (in FIGS. 7 and 8 , −1 dB or more and 1 dB or less) (step S5, NO), the target angle detection unit 23 determines that the target is not a target but a false image (step S8).

[0049] That is, as explained in (Principles of target angle detection processing of the present disclosure), the intensity difference spectrum becomes large at spectrum angles where no target exists, i.e., where a false image is present. Therefore, at spectrum angles where the intensity difference spectrum is large and outside the predetermined range, it can be determined that the target is not a false image but a false image.

[0050] Here, the target angle detection unit 23 detects a target (step S7) in principle at a spectral angle where the spectral intensity is within a predetermined range (step S5, YES) and where the spectral intensity reaches a peak or bottom (step S6, YES; in FIGS. 7 and 8, these are approximately 20° and approximately −15°) for the difference spectrum of intensity calculated by the difference spectrum calculation unit 22.

[0051] That is, at the spectral angle at which a target should be detected, the intensity difference spectrum becomes small, and the difference between the peak angle of the first angular spectrum and the peak angle of the second angular spectrum becomes small (in FIG. 4 , the magnitudes of the first and second angular spectra do not change at the boundaries of approximately 20° and approximately −15°). Therefore, a target can be detected at a spectral angle where the intensity difference spectrum is small, within a predetermined range, and forms a peak or bottom.

[0052] On the other hand, for the difference spectrum of intensity calculated by the difference spectrum calculation unit 22, the target angle detection unit 23 determines that the spectral intensity is within a predetermined range (YES in step S5) but does not form a peak or bottom at a spectral angle (NO in step S6; approximately 60° and approximately −50° in FIG. 7; approximately 40°, approximately 0°, and approximately −35° in FIG. 8), as an exceptional case, the target angle detection unit 23 determines that the spectral intensity is not a target but a false image (step S8).

[0053] That is, even if the intensity difference spectrum is small at a spectral angle where no target is present, i.e., where a false image is present, the difference between the peak angle of the first angular spectrum and the peak angle of the second angular spectrum becomes large (in FIG. 4 , the magnitudes of the first and second angular spectra are reversed at the boundaries of approximately 40° and approximately −35°). Therefore, at a spectral angle where the intensity difference spectrum is small and within a predetermined range but does not form a peak or bottom, it can be determined that the spectrum is a false image rather than a target.

[0054] The target angle detection unit 23 sets a predetermined interval for the difference spectrum of intensity calculated by the difference spectrum calculation unit 22 to an interval having equal widths in the positive and negative directions centered on 0 dB. This is because the difference spectrum calculation unit 22 normalizes the maximum spectral intensity of the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit 21 to the same value (see the lower part of FIG. 5).

[0055] On the other hand, the difference spectrum calculation unit 22 may not normalize the maximum spectrum intensities of the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit 21 to the same value (see the upper part of FIG. 5 ). In this case, the target angle detection unit 23 may set the predetermined section for the intensity difference spectrum calculated by the difference spectrum calculation unit 22 to a section having equal widths in the positive and negative directions centered on a non-0 dB point.

[0056] 8, the null intensities of the first and second angular spectra are maintained at their original values, and the difference spectrum of intensities may have peaks or troughs and may be small (see approximately 60° and approximately −50°). Therefore, it is not possible to prevent false detection of targets at the spectral angles where the nulls should be removed.

[0057] On the other hand, in Fig. 7, the null intensities of the first and second angular spectra are changed to different fixed values, and the difference spectrum of the intensities does not form a peak or a bottom and is large (see approximately 60° and approximately -50°). Therefore, it is possible to prevent false detection of targets at the spectral angles where the nulls should be removed.

[0058] The target angle detection device and target angle detection program of the present disclosure can reduce false detection of false images due to side lobes and minimize degradation of angular resolution when detecting targets using millimeter-wave radar, MIMO radar, and / or KR product expansion radar, by using multiple window functions with different side lobe suppression levels.

[0059] S: Target angle detection system 1: Radar transmitter / receiver 2: Target angle detection device 3: Radar display device 21: Angle spectrum calculation unit 22: Difference spectrum calculation unit 23: Target angle detection unit

Claims

1. A target angle detection device comprising: an angular spectrum calculation unit that performs digital beamforming on the same received signal of a radar array antenna using a first window function and a second window function with different side lobe suppression levels to calculate a first angular spectrum and a second angular spectrum, respectively; a differential spectrum calculation unit that calculates an intensity difference spectrum for the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit; and a target angle detection unit that, for the intensity difference spectrum calculated by the differential spectrum calculation unit, (1) detects a target at a spectral angle where the spectral intensity is within a predetermined range, and (2) determines that the target is not a target but a false target at a spectral angle where the spectral intensity is outside the predetermined range.

2. The target angle detection device according to claim 1, characterized in that, for the intensity difference spectrum calculated by the difference spectrum calculation unit, (1) the target is detected at a spectrum angle where the spectral intensity is within the predetermined interval and forms a peak or bottom, and (2) the target is determined to be a false target at a spectrum angle where the spectral intensity is within the predetermined interval but does not form a peak or bottom.

3. The target angle detection device according to claim 1 or 2, characterized in that the differential spectrum calculation unit calculates the differential spectrum of the intensities after changing null spectrum intensities below the same threshold value for the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit to different fixed values.

4. The target angle detection device according to claim 1 or 2, characterized in that the difference spectrum calculation unit calculates the intensity difference spectrum after normalizing the maximum spectral intensity of the first angular spectrum and the second angular spectrum calculated by the angular spectrum calculation unit to the same value, or after compensating for S / N degradation due to the first window function and the second window function, respectively, and the target angle detection unit, for the intensity difference spectrum calculated by the difference spectrum calculation unit, (1) detects a target at a spectral angle where the spectral intensity is within the predetermined interval (having equal widths in the positive and negative directions, centered at 0 dB), and (2) determines that the target is not a target but a false target at a spectral angle where the spectral intensity is outside the predetermined interval.

5. A target angle detection program for causing a computer to sequentially execute the processing steps executed by the processing units of the target angle detection device according to claim 1 or 2.

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