JP2024009334A - radar system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radar system capable of reducing an arithmetic processing load and effectively suppressing a false image caused by a factor other than disturbing waves.

SOLUTION: If a plurality of intensity peaks occur on an azimuth spectrum of every distance, selection is performed as to whether an intensity value to a group of the intensity peaks exceeds a threshold as a necessary condition, and information of a distance and an azimuth shown by a main peak satisfying a selection condition is outputted as target detection information. Thus, arithmetic processing having a high load of a conventional method required for side lobe reduction by a weight arithmetic can be replaced with simple selection processing of the intensity peak, and a radar system having a small arithmetic processing load can be achieved. Also, an intensity peak derived from a false image generated by a factor other than disturbing waves can effectively suppressed by selection processing.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a radar system that measures the distance and direction to a target.

Many radar systems have been proposed that use antenna arrays to measure the distance and direction to a target. In these radar systems, the arriving wave from the target becomes the desired signal, but interference waves are superimposed on it due to various factors, causing false images to be detected. In a radar system using an antenna array, by using a phase shifter to align the phase of the output waveform of each element antenna to the desired receiving beam direction, the combined output (response characteristics) of the antenna array to the desired direction can be maximized. (so-called beamforming method).

Mathematically, the composite output E of the antenna array is obtained by multiplying the output waveform function of each element antenna by a weighting coefficient w (complex number) that gives the amount of phase shift, and adding the resultant weight coefficient w to the azimuth θ. By giving it as a function w(θ) of θ, the composite output E of the antenna array can also be expressed as a function E(θ) of θ. The composite output E(θ) is a complex function, and the mapping of the absolute ||E(θ)|| for various angle values θ is called the directivity pattern of the antenna array, and the area around its maximum value is the main It is called the lobe (main beam). On the other hand, it is said that the weighting coefficient w should ideally be selected to be close to zero so that the response characteristics at angular positions other than the main lobe are as small as possible, but In principle, maximum values of the response characteristics also occur at the other angular positions. This is called a side lobe.

If interference waves arrive from the direction of the sidelobes, radar artifacts are produced, so various sidelobe cancellers have been proposed for suppressing these sidelobes. In the sidelobe canceller, the weighting coefficient of the function E that provides the combined output of the antenna array is determined by calculation so that the antenna gain with respect to the arrival direction of the interfering wave is small. As a method of determining this weighting coefficient w, a method is often adopted in which the value of the weighting coefficient w is successively updated for each sample of the received signal so that it converges to an optimal value (for example, Patent Document 1, Reference 1).

Japanese Patent Application Publication No. 2006-162397

"Adaptive Sidelobe Suppression Method for High Gain Arrays", IEICE Transactions B Vol. J86-B No.5 pp.790-797 May 2003

However, the conventional sidelobe canceller described above has the following problems.
(1) In order to converge the output value of the array antenna to the optimum value, the processing load for repeatedly calculating the weighting coefficient w increases, and the processing time also increases.
(2) If an attempt is made to significantly reduce the sidelobe level, the mainlobe level will also be pulled down by this, which may easily lead to a decrease in sensitivity.
(3) It is difficult to remove false images caused by factors other than interference waves.

An object of the present invention is to provide a radar system that requires a small calculation processing load and that can effectively suppress false images caused by factors other than interference waves.

In order to solve the above problems, the radar system of the present invention includes a transmitter that transmits a search radio wave as a transmission wave for searching for a target object, and a receiving antenna array consisting of a plurality of element antennas. The receiving section receives the reflected waves of the radio waves as received waves via the receiving antenna array, and the receiving beam direction of the receiving antenna array is sequentially changed and controlled within a predetermined azimuth angle range. Based on the scanning section that performs beam scanning, the transmitted waveform signal from the transmitting section, and the received waveform signals of various receiving beam directions obtained by beam scanning, a distance spectrum indicating the relationship between distance and reception intensity in the receiving beam direction is calculated. By extracting received wave intensity points at the same distance from a distance spectrum generator that generates each direction and a plurality of distance spectra generated for each direction, the direction spectrum that shows the relationship between the received beam direction and the received intensity is calculated based on the distance spectrum. Intensity values are predetermined for the azimuth spectrum generation section that generates separately, the peak extraction section that extracts intensity peaks in each of the azimuth spectra generated for each distance, and the set of intensity peaks extracted for each azimuth spectrum. A peak selection process that sets a selection condition that includes as a necessary condition that the intensity exceeds a specified threshold value, and selects an intensity peak that satisfies the selection condition in the set of intensity peaks as a main peak for target identification. The present invention is characterized by comprising a target detection output unit that outputs distance and azimuth information indicated by the selected main peaks as target detection information.

In the configuration of the present invention, when a plurality of intensity peaks occur on the azimuth spectrum for each distance, the set of intensity peaks is selected based on whether or not the intensity value exceeds a threshold, Information on the distance and direction indicated by the main peak that satisfies the selection conditions is output as target object detection information. As a result, when it is desired to sufficiently reduce sidelobes through weight calculation, the heavy calculation processing that is conventionally required can be replaced with simple intensity peak selection processing, making it possible to realize a radar system with a small calculation processing load. In addition, intensity peaks originating from false images caused by factors other than interference waves can also be effectively suppressed by the screening process.

FIG. 1 is a functional block diagram of a radar system that is an embodiment of the present invention. FIG. 2 is a circuit diagram showing an example of a specific configuration of a transmitter. FIG. 2 is a block diagram showing a more specific electrical configuration of the signal processing device of the radar system shown in FIG. 1; FIG. 3 is a schematic diagram showing an example of a frequency modulation pattern of a transmitted wave. FIG. 3 is a diagram explaining the concept of analyzing the frequency spectrum of a beat waveform signal. FIG. 3 is a diagram conceptually showing the contents of a target list memory. 5 is a flowchart showing the overall processing flow of the measurement control program. 5 is a flowchart showing the flow of the direction analysis process in FIG. 4. FIG. 5 is a flowchart showing the flow of the peak analysis process in FIG. 4. FIG. 5 is a flowchart showing the flow of the false image filtering process in FIG. 4. 11 is a flowchart showing main parts of a modification of the process in FIG. 10. FIG. 3 is a schematic diagram showing an example of an azimuth spectrum together with an example of setting a false image search section. FIG. 13 is a schematic diagram showing a state in which a suppression process is applied to the azimuth spectrum of FIG. 12 in such a way that the intensities of the false image peaks are aligned to a certain level. FIG. 13 is a schematic diagram showing the concept of effective false image peak intensity in the orientation spectrum of FIG. 12. FIG. 15 is a schematic diagram illustrating a state in which suppression processing is performed to reduce the ratio between the azimuth reference level and the effective false image peak intensity of the azimuth spectrum in FIG. 14; The mapping diagram which shows an example of a target object detection result before performing a false image filter process. FIG. 14 is a mapping diagram showing an example of a result when false image filtering is performed using the method shown in FIG. 13; FIG. 16 is a mapping diagram showing an example of the result when false image filtering is performed using the method shown in FIG. 15; The mapping diagram which shows an example of the result when a reduction coefficient is set larger than FIG. 18. FIG. 3 is a schematic diagram showing an example of a frequency modulation pattern of a transmitted wave when speed detection is performed. FIG. 7 is a diagram conceptually showing the contents of a target object list memory when speed is identified and target object detection output is performed. Flowchart showing the processing flow of the measurement control program when performing false image filtering processing after peak detection processing FIG. 23 is an explanatory diagram showing the concept of implementing the false image filtering process of FIG. 22 on a target object list memory. FIG. 6 is a diagram illustrating the concept of correcting the reference level of the azimuth spectrum according to the background waviness level.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a block diagram showing the electrical configuration of a radar system 1 that is an embodiment of the present invention. The radar system 1 is configured as a device that measures the distance and direction to a target based on the principle of Frequency Modulated Continuous Wave (FMCW) radar. It has a front end section 3 for transmission and reception.

The front end section 3 includes a master IC 50M and a slave IC 50S connected in cascade to the master IC 50M via a wiring section SCL. In this embodiment, these master IC 50M and slave IC 50S are both configured as radar front-end ICs of the same type, and can function as a master IC and as a slave IC by switching setting inputs to predetermined switching terminals (not shown). Functions can be selected as appropriate. An example of a commercially available radar front-end IC is AWR1243P (manufactured by Texas Instruments, USA).

The master IC 50M includes an oscillation circuit 54, a transmission amplifier 41, and a transmission antenna 51 that serve as a transmitter (they are also incorporated in the slave IC 50S, but are not used). The oscillation circuit 54 generates a transmission waveform signal whose frequency is continuously modulated based on the frequency instruction value input from the control circuit 56. The transmission waveform signal is amplified by the transmission amplifier 41 and then outputted from the transmission antenna 51 as a transmission wave (target search radio wave). As shown in FIG. 2, the transmitting antenna 51 is configured as a transmitting antenna array consisting of a plurality of element antennas 51(A) to 51(C). The transmission waveform signals from the oscillation circuit 54 are phase-shifted by the phase shifter 42 for each element antenna 51 (A) to 51 (C), and are superimposed on each other as a directional transmission beam in a desired direction (θ). Sent out. By receiving a phase shift control signal from a control circuit 56 in the IC, the phase shifter 42, together with the control circuit 56, plays the role of scanning the directional transmission beam within each angle range in a predetermined direction.

On the other hand, a plurality of element antennas (receiving antennas) 52 constituting a reception antenna array are installed in a distributed manner in the master IC 50M and slave IC 50S, and a low-noise amplifier 43 that amplifies the waveform signal of the wave received by the element antennas 52 is installed in the reception section. It is established as. The waveform signal output from the low noise amplifier 43 is mixed in the mixer 53 with the waveform signal of the transmission wave distributed from the master IC 50M via the wiring section SCL. The beat waveform signal outputted by the mixing unit 53 is digitally converted by the A/D converter 55 to become beat waveform data X1(t) to Xn(t), which are serially output from the waveform output ports WO1 to WOn. be done. In the A/D converter 55, the waveform frame capture start timing and the output timing of each waveform bit are controlled by a clock signal inputted from the clock circuit 59 via the control circuit 56.

As for the transmission wave, one that follows a linear modulation pattern in which the frequency shift width (occupied frequency band) Δf and period T are fixed is used. The frequency of the transmitted wave changes depending on the distance to the target during the period from when the transmitted wave is issued until the reflected wave returns. As a result, when a transmitted wave sent at a certain time returns as a reflected wave, if the received wave and the transmitted wave at the time of reception are mixed, the standing wave corresponding to the difference frequency between the two becomes a beat. (beat) occurs. Specifically, if the distance to the target is d, the frequency of the beat signal (=the difference frequency between the transmission frequency f1 and the reception frequency f2) is δf, and the speed of light is c,
δf=2・d・Δf/(c・T)
becomes. Since c, T, and Δf are constant, it can be seen that the frequency δf of the standing wave beat signal is simply proportional to the distance d. Therefore, the distance d to the target can be directly determined from the measurement of δf. FIG. 4 shows an example of a sawtooth linear modulation pattern, in which the frequency change rate for each cycle T is always constant. The fundamental frequency of the transmitted wave is appropriately set in the range of 75 GHz or more and 80 GHz or less, the frequency deviation width Δf of the transmitted wave is 300 MHz or more and 1.5 GHz or less (preferably 300 MHz or more and 1 GHz or less), and the period T is 0.5 msec or more and 10 msec. It is appropriately set within the range of the following (preferably 1 msec or more and 5 msec or less).

Although only one set of the element antenna 52, low noise amplifier 43, mixer 53, and A/D converter 55 on the receiving side is depicted for each master IC 50M and slave IC 50S in FIG. 1, in reality, each IC 50M, 50S A plurality of these sets are provided (for example, 4 sets in AWR1243P).

The master IC 50M and each slave IC 50S are cascade-connected by a wiring section SCL connecting a synchronous output port SYNO and a synchronous input port SYNI provided in each IC. The wiring section SCL forms a waveform distribution line WVL and a control signal line SCL together with the IC internal wiring. The transmission waveform signal from the oscillation circuit 54 of the master IC 50M is input to each mixer 53 in the slave IC 50S via the buffer amplifier 57 via the waveform distribution line WVL.

On the other hand, the control circuit 56 of each slave IC 50S receives the synchronization signal from the master IC 50M via the signal line SCL, and adjusts the timing of the clock signal input from the clock circuit 59 based on the synchronization signal. The signal is input to the D converter 55. As a result, each slave IC 50S (and master IC 50M) outputs beat waveform data from the waveform output ports WO1 to WOn in a form in which the waveform frame capture start timing and the output timing of each waveform bit are synchronized. Therefore, the control circuit 56 functions as a synchronization control section.

Next, the signal processing device 2 includes each functional block of a distance spectrum generation section 60A, an azimuth spectrum generation section 60B, a peak extraction section 60C, and a false image filter section 60D (functioning as a peak selection processing section and a target object detection output section). has. Each functional block is characterized as follows.
- Distance spectrum generation unit 60A: Provided in one-to-one correspondence with the master IC 50M and slave IC 50S, and converts beat waveform data (signals) output from the waveform output ports WO1 to WOn of each IC into a frequency spectrum that is a distance spectrum. Convert. In this embodiment, the entire scanning angle range related to the receiving beam direction is divided and covered by the master IC 50M and the slave IC 50S into sub-scanning angle ranges each having a different central direction. Each distance spectrum generation unit 60A determines a weighting coefficient w(θ) for each azimuth θ by sequentially changing the reception beam azimuth θ in the sub-scanning angle range assigned to each, and then determines a weighting coefficient w(θ) for each azimuth θ according to a well-known beamforming algorithm , 50S is multiplied by the weighting coefficient w(θ) and added. As a result, the beat waveform data for each receiving beam azimuth θ is synthesized (that is, the beam scanning of the received wave is controlled by sequentially changing the receiving beam direction of the receiving antenna array within a predetermined azimuth angle range). (It functions as a scanning unit). Then, by performing fast Fourier transform processing on the beat waveform data obtained for each azimuth θ within the sub-scanning angle range (that is, the transmitted waveform signal by the transmitter and the received waveform signal of various receive beam directions obtained by beam scanning) ), a distance spectrum indicating the relationship between distance and reception intensity in the reception beam orientation θ is generated for each orientation within the sub-scanning angle range.

- Azimuth spectrum generation section 60B: extracts received wave intensity points at the same distance from a plurality of distance spectra generated for each direction in each distance spectrum generation section 60A, thereby determining the relationship between the received beam direction and reception intensity. A direction spectrum shown is generated for each distance d.
- Peak extraction unit 60C: extracts intensity peaks in each of the azimuth spectra generated for each distance.
- False image filter section 60D: serves as a false image peak suppression section. Specifically, for the set of intensity peaks extracted for each azimuth spectrum, we set screening conditions that include as a necessary condition that the intensity value exceeds a predetermined threshold, and also A process is performed to select an intensity peak that satisfies the selection conditions in the group as a main peak for target identification (peak selection processing unit). Then, information on the distance and direction indicated by the selected main peak is output as target object detection information from the output port DO (target object detection output section).

FIG. 3 is a block diagram showing details of the electrical configuration of the signal processing section 2. As shown in FIG. The signal processing section 2 has a CPU 31, a RAM 32, a ROM 33, an input/output section 34, and a bus 30 that connects them. The following programs are stored in the ROM 33. Both are executed by the CPU 31 using the RAM 32 as an execution area, and embody individual function implementation units.
- Measurement control program 33a: This is a basic program for realizing each function of the above-described distance spectrum generation section 60A, azimuth spectrum generation section 60B, peak extraction section 60C, and false image filter section 60D.
Digital filter 33b: Loads the beat signal waveform data into the waveform filter memory 32a of the RAM 32, and performs digital filtering processing to remove noise derived from harmonics and the like. It is configured as a low-pass filter or a band-pass filter.

- Reception beam scanning program 33c: This is a program that implements a part of the function of the azimuth spectrum generation section 60B. The beat waveform data output from the waveform output ports WO1 to WOn is received at each input port WI1 to WIn of the input/output section 34, and is taken into the waveform memories w1 to wn of the RAM 32. Then, the weighting coefficient w(θ) for each azimuth θ is determined by sequentially changing the reception beam azimuth θ in the above-mentioned sub-scanning angle range (for example, by reading it from the azimuth-specific weighting coefficient table stored in the ROM 33). In the waveform synthesis/scanning memory 32b, the beat waveform data received from the corresponding ICs 50M and 50S is multiplied by the weighting coefficient w(θ) and summed, thereby synthesizing the beat waveform data for each direction θ.
-FFT module 33d: Converts the beat waveform data for each direction shown in FIG. 5 into a frequency spectrum Spm using the FFT processing memory 32h in the RAM 32, and generates a distance spectrum indicating the relationship between distance and reception intensity in the reception beam direction θ. is generated for each direction.
- Orientation analysis program 33e: This is a program that implements part of the functions of the orientation spectrum generation section 60B. In the azimuth analysis memory 32c, by extracting received wave intensity points at the same distance from a plurality of distance spectra generated for each azimuth, an azimuth spectrum indicating the relationship between the received beam azimuth and reception intensity is generated for each distance d. .

- Intensity peak extraction program 33f: This is a function realization program of the peak extraction section 60C. In the intensity peak analysis memory 32d of the RAM 32, the intensity level and peak position (angle) of the intensity peak is specified in each of the azimuth spectra generated for each distance. The peak position can be determined from the apex position by, for example, finding three adjacent bins that form a spectral maximum point, and approximating them to a quadratic curve.
・False image filter processing program 33g: This is a function realization program of the false image filter unit 60D, and uses the false image filter processing memory 32f of the RAM 32 to satisfy the above-mentioned selection conditions in the set of intensity peaks extracted on the azimuth spectrum. A process is performed to select the intensity peaks that are detected as main peaks for target identification. Then, the information on the distance and direction indicated by the selected main peak is outputted as target object detection information from the output port DO of the input/output unit 34 in FIG.

The processing flow of each program will be explained below.
FIG. 7 shows the flow of processing of the measurement control program 33a.
S1 and S2 are steps carried out by the receiving beam scanning program 33c. First, in S1, beat waveform data X1(t) to Xn(t) from each IC 50M and 50S is taken in, and in S2, fast Fourier transform (FFT) processing is performed to obtain a frequency spectrum, that is, a distance spectrum σ1 to σn. Next, in S3, the weighting coefficient w(θ) of the azimuth θ is determined, and in S4, the beat waveform data X1(t) to Xn(t) are multiplied by the weighting coefficient w(θ) and added. Beat waveform data corresponding to the received beam of θ is synthesized. The above processing is performed for all quantized azimuth angle positions in the sub-scanning angle range of each IC 50M, 50S.

Next, the process proceeds to direction analysis processing in S5. FIG. 8 shows the details. In S501, the distance d is set to an initial value d0. In S502, the spectrum intensity value I(d) of the frequency corresponding to the distance d is extracted from the distance spectrum of each direction θ. Then, in S503, the set of (θ, I(d)) is saved as azimuth spectrum data. In S504, the distance d is incremented by Δd (1 bin), and in S505, the process returns to S502 and repeats the following process until the value of d exceeds the upper limit value dmax.

Returning to FIG. 7, the peak detection process of S6 follows. FIG. 9 shows the details thereof, and will be explained with reference to FIG. 12 as well. The peak detection process is performed on all azimuth spectrum data obtained for each value of distance d. First, in S601, azimuth spectrum data is read. Next, a reference level y' of the orientation spectrum is set. As the reference level y', an average value or a median value of the intensity values indicated by each data point of the azimuth spectrum can be adopted. Next, in S603, spectral points whose intensity exceeds the threshold value y'+α are extracted as search target points. Next, in S604, spectral points in three adjacent bins forming the maximum point of the spectrum are searched. Then, in S605, quadratic curve approximation is performed on the spectrum points forming the maximum points, and in S606, the apex coordinates are specified as the intensity ym and azimuth angle position of the main peak.

Next, the false image filtering process of S7 in FIG. 7 is executed. The details will be explained using the flowchart of FIG. 10 and FIG. 13. Here, artifact peak suppression processing is performed by replacing artifact peaks with lower-level intensity peaks in the orientation spectrum. First, in S701 of FIG. 10, as shown in FIG. 13, a false image search interval Ik is set to [y'+α, ym-β] on the intensity axis. Next, in S702, a false image peak is searched for in the azimuth spectrum by finding three bins that have maximum values within the false image search section Ik. The false image peak to be suppressed is not subject to target detection output, and quadratic curve approximation, etc., as performed for the main peak, is not performed. Then, the intensity value at the center of the three bins is read as the peak value ys of the false image peak. In S703, ys is uniformly replaced with a fixed correction intensity level ysc (eg, y'+α, which is the lower limit of the false image search section Ik, or a value lower than that).

In FIGS. 12 and 13, the intensity axis is expressed logarithmically (unit: dB), and the false image peak intensity level Y after reduction is the intensity level before reduction as y.
Y=α・(y−y') +y'
It is expressed as If this is expressed as a true value rather than a logarithm, the false image peak intensity level Η after reduction is given by η, the intensity level before reduction, and η', the reference level.
Η=η ^α・η' ^(1-α)
It can be expressed as

Returning to FIG. 7, in S8, the apex coordinates of each peak are read for each azimuth spectrum for each distance d on which the false image filtering process has been performed, and compared with a predetermined threshold for noise removal. Then, in S9, the peak exceeding the threshold value is associated with the azimuth angle θ indicated by the vertex coordinates and the distance d, as shown in FIG. It is registered in the target list memory 32g. The target object detection information registered in this way is output from the output port DO in FIG. 1 or 3 as a detection result in S10 (if the process is not completed in S11, the process returns to S1 and the following process is repeated). FIG. 17 is an example in which the target object detection information is mapped and output on a plane defined by the azimuth angle θ and the distance d. Further, FIG. 16 is a comparative example in which false image peak suppression is not performed. It can be seen that the large number of false images that occurred in the comparative example (FIG. 16) can be significantly reduced in the example (FIG. 17).

Further, in this embodiment, as shown in FIG. 1 or 3, the front end section 2 for transmitting and receiving radio waves is constituted by a set of a master IC 50M and a slave IC 50S connected by a wiring section SCL. , frame sampling of the beat waveform signal and data output in the slave IC 50S are synchronously controlled. According to the inventor's study, this type of control can cause synchronization between ICs due to internal factors such as variations in characteristic impedance due to the line length of the wiring section SCL, and disturbances in clock signals due to external noise. It is clear that This synchronization shift is directly reflected in the phase difference between the beat signals output by each IC, and becomes a factor in the generation of false images, regardless of side lobes occurring in the response characteristics of the receiving antenna array. Although such artifacts cannot be removed in principle by conventional sidelobe suppression methods, they can be suppressed without problems by employing the present invention.

Note that under the selection conditions in the above algorithm, intensity peaks that fall outside the upper limit of the false image search interval [y'+α, ym-β] are not regarded as false images and are left as main peaks. In the examples shown in FIGS. 12 and 13, there is only one intensity peak larger than ym-β in one azimuth spectrum, and as a result, there is only one target at a certain distance d from the radio wave transmission source. Only those are detected. However, as a matter of course, in this method, if there are multiple intensity peaks that fall outside the upper limit of the false image search interval [y' + α, ym - β] in one azimuth spectrum, multiple main peaks will also be selected. remain. The number of main peaks left after the selection changes depending on the setting value of the upper limit side adjustment coefficient β set for the intensity value ym of the maximum intensity peak. It is desirable to set the value of β as appropriate through calibration measurements using various target models, etc., so that the rejection rate of true targets is as small as possible and the rejection rate of false images is as high as possible. It can be said.

In this case, by setting the adjustment coefficient α on the lower limit side to zero in the setting of the false image search section, it is possible to set ysc to zero, that is, to completely delete the false image peak from the azimuth spectrum. On the other hand, by setting the adjustment coefficient β on the upper limit side as small as possible, only the intensity peak with the maximum intensity can be regarded as the main peak, and all other intensity peaks can be rejected as false image peaks. It is also possible to perform processing such that only one target is considered to be equidistant from the transmission source, and other targets are rejected as false images regardless of the cause of their occurrence.

Note that the method for reducing (suppressing) the peak value ys of the false image peak is not limited to the method shown in FIGS. 12 and 13 above, and other methods may also be adopted. An example thereof is shown in FIGS. 14 and 15. In this method, as shown in FIG. 14, in logarithmic intensity display, the protruding difference ys-y' of the false image peak intensity ys from the reference level y' is determined as the effective false image peak intensity. Then, as shown in FIG. 15, the value of the effective artifact peak intensity (ys-y')/y' standardized by the reference level y' is multiplied by the reduction coefficient γ (0<γ<1). Aiming to reduce the false image peak intensity ys. According to this method, even if the intensity level of the false image is reduced, the intensity ratio between different false images is preserved, so in the calibration when setting the reduction coefficient γ, the true target is treated as a false image. The probability of rejection may be reduced. As explained above, the false image filtering process using this algorithm is the same as replacing S703 in the flowchart of FIG. 10 with S703' and S704' of FIG. 11.

FIGS. 18 and 19 show examples in which target object detection information is mapped and output by changing the value of γ. FIG. 18 shows the case when γ=0.5, and FIG. 19 shows the case when γ=0.8, and it can be seen that the number of artifacts removed varies greatly depending on the value of γ.

Hereinafter, modified embodiments of the present invention will be further described.
First, in the radar system of the present invention, the velocity of a target candidate indicated by the intensity peak extracted by the peak extractor in each of the azimuth spectra generated for each distance is converted into received waveform signals of various azimuths obtained by beam scanning. A speed identification unit may be provided that identifies the speed based on the speed. In this case, the peak selection processing unit selects, as main peaks, the maximum peak and intensity peaks for which a speed different from the maximum peak has been specified, among the intensity peaks exceeding the threshold value extracted for each azimuth spectrum. It can be configured to screen. For targets with different moving speeds, for example, by allowing them to be detected as different targets even if they are at the same distance, it is possible to reduce the probability that a true target is erroneously determined as a forgery.

In this case, by modulating the transmitted wave for target object search into a triangular wave as shown in FIG. 20, it becomes possible to detect the speed of the target object using Doppler shift. This method is well known, and Δf: frequency shift width, c: speed of light, d: distance, V: velocity, T: period of frequency shift, β _U : beat frequency difference (during upward sweep of modulation), β _D : As the beat frequency difference (during downward sweep of modulation),
d=c・(β _U +β _D )・T/4Δf
V=c・(β _U −β _D )/4Δf
Each can be determined by As shown in FIG. 21, the speed V is added to the items registered in the target object list memory 32g, and even if the distances are the same (d3=d4) like targets B3 and B4, the former has a speed of V3. In both cases, the intensity peak is selected as the main peak and output as target object detection information.

Further, the measurement control program shown in FIG. 7 can also be modified as shown in FIG. In this method, the intensity peaks extracted by the peak extractor for each azimuth spectrum are compared with the aforementioned threshold value, and for each set of intensity peaks that are equal to or greater than the threshold value, the distance d, the azimuth θ, and the intensity value indicated by each intensity peak are compared. All information of I is once registered as target candidate information in the target candidate registration section (target list memory 32g). Further, the peak selection processing section is provided with a function of an invalidation processing section that performs invalidation processing on the registered target candidate information that corresponds to an intensity peak that does not satisfy the selection conditions. Then, the target object detection output unit reads the information on the distance d and the direction θ included in the remaining target candidate information that has not been invalidated in the target object candidate registration unit, and uses it as the main peak target object detection information. Output.

Specifically, in FIG. 22, after the peak detection processing in S6 is completed, each intensity peak detected in S7' is compared with the above-mentioned threshold value, and the false image filter processing is performed on the intensity peaks that are equal to or higher than the threshold value. As shown on the left side of FIG. 23, the value of peak intensity I is further incorporated into the target object detection information (distance d and direction θ) for all intensity peaks, and a peak ID is added to the target object list memory. 32g (FIG. 22: S8'). Then, forgery filter processing is performed on this target list memory 32g (FIG. 22: S9'). In the processing at S9' in FIG. 22, the data for the intensity peak determined to be a false image is invalidated (for example, deleted as shown on the right in FIG. 23) to prevent it from being output as a target object. This is a difference from the forgery filter processing shown in FIG. In FIG. 23, among the target object candidates detected at the same distance, those with smaller peak intensities (B1 and B2) are invalidated. With this method, information on all intensity peaks, including false images, is stored in the target list memory 32g as target candidate information, so, for example, reviewing the intensity peak selection conditions with respect to past measurement data, This has the advantage that processing becomes easier when it is desired to output the data again.

In addition, in FIGS. 12 to 15, the reference level y' set for the azimuth spectrum is set constant based on the average value of the spectrum waveform, for example, but the reference level y' is corrected according to the background undulation level. You may also do so. Specifically, the azimuth spectrum is divided into cells (sections) on the azimuth angle axis, the undulation level yud is calculated for the average level y0 for each cell, and the reference level y' of each cell is calculated as y' = y0 + yud
Set it so that According to this method, it becomes possible to accurately evaluate the peak level of false images and, in turn, perform selection while reducing the influence of waviness. Note that the peak correction on the spectrum based on the waviness level can be similarly performed on the distance spectrum and the speed spectrum. FIG. 24 shows an example of undulations occurring in the velocity spectrum (beat frequency spectrum).

The details of the action and effects of the present invention are summarized as follows. As described in detail above, in the present invention, a plurality of intensity peaks appearing on the azimuth spectrum classified by distance are selected based on whether the intensity value exceeds a threshold value or not. Then, information on the distance and direction indicated by the main peak that satisfies the selection conditions is output as target object detection information. As a result, the heavy-load calculation processing conventionally required to suppress the appearance of false images can be replaced with simple intensity peak selection processing. In addition, intensity peaks originating from false images caused by factors other than interference waves can also be effectively suppressed by the screening process.

The peak selection processing unit identifies an intensity peak that does not satisfy the selection condition in the set of intensity peaks as a false image peak, and deletes the false image peak in the azimuth spectrum or replaces it with a lower level intensity peak. It can be configured to include a false image peak suppression section that performs peak suppression processing. In this case, the target object detection output unit identifies an intensity peak exceeding a predetermined threshold as a main peak in the azimuth spectrum that has been subjected to the false image peak suppression process, and outputs distance and azimuth information corresponding to the intensity peak. It is assumed to be output as target object detection information. By lowering or deleting intensity peaks that fail to meet the selection conditions on the azimuth spectrum in advance, the target detection output unit can identify the intensity peak as the main peak by simply searching for the intensity peak that exceeds the threshold. , it is possible to further simplify the processing algorithm.

On the other hand, a target candidate registration unit may be provided that registers information on the distance, direction, and intensity value indicated by each intensity peak as target candidate information for the set of intensity peaks extracted by the peak extraction unit for each azimuth spectrum. can. In this case, the peak selection processing section can be configured to include an invalidation processing section that performs invalidation processing on the registered target candidate information that corresponds to intensity peaks that do not satisfy the selection conditions. The target object detection output unit reads the distance and direction information included in the remaining target candidate information that has not been invalidated by the target candidate registration unit, and outputs it as main peak target object detection information. Can be configured. According to this configuration, information on all intensity peaks including false images is registered as target candidate information, so it is possible to improve the flexibility of intensity peak data when it is desired to respond to changes in screening conditions, etc. This has the advantage of facilitating processing when it is desired to review the intensity peak selection conditions for the measurement data and output it again.

The peak selection processing unit selects the maximum peak having the maximum intensity as the main peak from among the intensity peaks exceeding the threshold value extracted for each distance-based azimuth spectrum. In this method, by assuming that there is only one target existing at the same distance, it is possible to easily identify only the maximum peak as the target (main peak) in the azimuth spectrum for each distance. In particular, in the case of stationary objects that exist in different directions, it is considered to be an extremely accidental event that their detection distances match, and even if processing is performed to treat objects other than those with the maximum peak as false images, It can be said that there is a low possibility that this will lead to an erroneous determination.

On the other hand, it includes a speed identification section that identifies the speed of the target candidate indicated by the intensity peak extracted by the peak extraction section in each of the azimuth spectra generated for each distance based on received waveform signals of various directions obtained by beam scanning. It can be made into The peak selection processing unit is configured to select, as main peaks, the maximum peak and the intensity peak for which a speed different from the maximum peak has been specified, among the intensity peaks exceeding the threshold value extracted for each azimuth spectrum. It can be configured as follows. If multiple targets in different directions include moving targets, the distances may be temporarily the same between the different targets, so as mentioned above Furthermore, by selecting targets with different speeds as the main peak, it is possible to avoid the problem of erroneously rejecting the latter as a false image.

The transmitter used in the radar system of the present invention can be configured to transmit a transmission wave whose frequency is continuously modulated in a predetermined modulation pattern as a search radio wave. In this case, a mixing section is provided that mixes the waveform signal of the transmitted wave and the waveform signal of the received wave and outputs a beat waveform signal based on the frequency difference between the transmitted wave and the received wave, and the distance spectrum generation section is configured to generate a beat waveform signal. can be configured to generate a frequency spectrum as a distance spectrum. With this method, it is possible to specify the distance to the target with high accuracy based on the frequency spectrum of the beat waveform signal.

In this case, the radio wave transmission/reception front end section of the radar system can be configured to include a master IC and a slave IC that is cascade-connected to the master IC via a wiring section. A transmitter is incorporated in the master IC, and a plurality of element antennas constituting a receiving antenna array are installed in a distributed manner in the master IC and slave IC. Furthermore, a mixing section mixes the waveform signal of the received wave by the element antenna and the waveform signal of the transmission wave distributed from the master IC via the wiring section, and the beat waveform signal outputted by the mixing section is digitally converted and serialized. It is possible to provide an output A/D conversion section and a signal processing device functioning as a target object detection output section. The signal processing device is provided with an input section to which the beat waveform signals from the A/D converters of the master IC and slave IC are individually serially input, and the slave IC receives the beat waveform signals from the master IC via the wiring section. A synchronization control section can be provided that receives a synchronization signal and causes the A/D conversion section to output a beat waveform signal in synchronization with the master IC. The inventors' studies have revealed that in the above configuration, internal factors such as variations in characteristic impedance due to the wire length of the wiring section, and clock signal disturbances caused by external noise tend to cause synchronization between the ICs. are doing. This synchronization shift is directly reflected in the phase difference between the beat signals output by each IC, and becomes a factor for generating artifacts regardless of side lobes occurring in the response characteristics of the receiving antenna array. Although such artifacts cannot be removed in principle by conventional sidelobe suppression methods, the present invention makes it possible to suppress them without any problem.

1 Radar system 2 Signal processing device 3 Front end section 31 CPU
32 RAM
33 ROM
33a Measurement control program 33b Digital filter 33c Reception beam scanning program 33d FFT module 33e Direction analysis program 33f Intensity peak extraction program 33g False image filtering program 34 Input/output section DO Output port 30 Bus 41 Transmission amplifier 42 Phase shifter 43 Low noise amplifier 50M Master IC
50S slave IC
SYN0 Synchronous output port SYNI Synchronous input port SCL Wiring section WVL Waveform distribution line 51 Transmitting antenna 52 Element antenna 53 Mixing section 54 Oscillation circuit 56 Control circuit (synchronous control section)
55 A/D conversion section 57 Buffer amplifier 59 Clock circuit WO1 to WOn Waveform output port 60A Distance spectrum generation section 60B Direction spectrum generation section 60C Peak extraction section 60D False image filter section

Claims (5)

a transmitter that transmits a search radio wave as a transmission wave for searching for a target;
a receiving unit having a receiving antenna array including a plurality of element antennas and receiving reflected waves of the search radio waves as received waves via the receiving antenna array;
a scanning unit that performs beam scanning of the received waves by sequentially changing and controlling the receiving beam azimuth of the receiving antenna array in a predetermined azimuth angle range;
Based on the transmission waveform signal by the transmitter and the reception waveform signals of various reception beam directions obtained by the beam scanning, a distance spectrum indicating a relationship between distance and reception intensity in the reception beam direction is generated for each direction. a distance spectrum generator;
an azimuth spectrum generation unit that generates an azimuth spectrum indicating the relationship between the received beam direction and the received intensity for each distance by extracting received wave intensity points at the same distance from the plurality of distance spectra generated for each azimuth; ,
a peak extraction unit that extracts an intensity peak in each of the azimuth spectra generated for each distance;
For the intensity peak set consisting of the intensity peaks extracted for each of the azimuth spectra, a selection condition including as a necessary condition that the intensity value exceeds a predetermined threshold is set, and the intensity peak set is a peak selection processing unit that performs a process of selecting an intensity peak that satisfies the selection conditions as a main peak for target identification;
A target object detection output unit that outputs information on the distance and direction indicated by the selected main peak as target object detection information,
The transmitter transmits a transmission wave whose frequency is continuously modulated in a predetermined modulation pattern as the search radio wave,
A mixing unit is provided that mixes the waveform signal of the transmitted wave and the waveform signal of the received wave and outputs a beat waveform signal based on a frequency difference between the transmitted wave and the received wave,
The distance spectrum generation unit generates a frequency spectrum of the beat waveform signal as the distance spectrum,
the mixing section that mixes the waveform signal of the received wave by the element antenna and the waveform signal of the transmission wave via the wiring section; and the beat waveform signal outputted by the mixing section is digitally converted and serially output. An A/D conversion section is provided,
A signal processing device functioning as the distance spectrum generation section, the azimuth spectrum generation section, the peak extraction section, the peak selection processing section, and the target object detection output section is provided, and the signal processing device includes the A/ An input section is provided to which the beat waveform signal from the D conversion section is individually serially input,
A synchronization control unit that outputs the beat waveform signal from the A/D conversion unit is provided,
A radar system comprising: a digital filter that captures beat signal waveform data of the beat waveform signal into a waveform filter memory and removes noise derived from harmonics. The peak selection processing unit identifies an intensity peak that does not satisfy the selection condition in the intensity peak set as a false image peak, and deletes the false image peak in the azimuth spectrum or replaces it with an intensity peak of a lower level. a false image peak suppression unit that performs false image peak suppression processing;
The target object detection output unit specifies an intensity peak exceeding a predetermined threshold as the main peak in the azimuth spectrum subjected to the false image peak suppression process, and outputs distance and azimuth information corresponding to the intensity peak. The radar system according to claim 1, wherein the radar system outputs the detection information of the target object. A target candidate registration unit that registers information on the distance, direction, and intensity value indicated by each intensity peak as target candidate information for the intensity peak set extracted by the peak extraction unit for each of the azimuth spectra,
The peak selection processing unit includes an invalidation processing unit that performs invalidation processing on information corresponding to intensity peaks that do not satisfy the selection conditions among the registered target candidate information,
The target object detection output unit reads distance and direction information included in the remaining target candidate information that has not been subjected to the invalidation process in the target object candidate registration unit, and detects the target object of the main peak. The radar system according to claim 1, wherein the radar system outputs the information as information. 3. The peak selection processing unit selects a maximum peak having the maximum intensity as the main peak from among the intensity peaks exceeding the threshold value extracted for each distance-based azimuth spectrum. The radar system according to any one of the above. A speed at which the speed of the target candidate indicated by the intensity peak extracted by the peak extraction unit in each of the azimuth spectra generated for each distance is specified based on the received waveform signals of various azimuths obtained by the beam scanning. Equipped with a specific part,
The peak selection processing unit selects the maximum peak and an intensity peak for which a speed different from the maximum peak is specified among the intensity peaks exceeding the threshold value extracted for each of the azimuth spectra. The radar system according to claim 4, wherein the radar system selects the main peak.