JP4736172B2 - Radar signal processing circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radar signal processing circuit that processes received signals from a plurality of receiving antenna elements.
[0002]
[Prior art]
Conventionally, various radar devices are known, and those that detect a target from a plurality of received signals are also known. For example, Japanese Laid-Open Patent Publication No. 2000-155171 discloses a radar apparatus that provides a plurality of transmission antennas and reception antennas, and obtains a plurality of reception signals by switching between them, and detects a target based on the reception signals.
[0003]
"Related technologies"
In addition, the applicant of the present application, in Japanese Patent Application No. 11-271305, discloses an FM-CW radar that uses a plurality of receiving antennas. In this radar apparatus, a plurality of reception antennas are arranged to obtain reception signals in two phases, an upstream phase and a downstream phase, respectively. Next, frequency analysis is performed on each received signal, and a plurality of obtained analysis results are averaged for each frequency component. Then, an echo generated at the target is detected by a peak search using the discrimination threshold.
[0004]
Thus, by using a plurality of antennas, it is possible to accurately detect a target with a wider field of view.
[0005]
[Problems to be solved by the invention]
Here, the plurality of receiving antennas all have the same directivity, and those having high directivity are adopted so that the target having the maximum detection distance can be detected in each. Further, outside the detection range, the gain is kept low to reduce false detection.
[0006]
For this reason, these receiving antennas have high gain (high detection sensitivity) so that the target can be detected in the front direction, but the gain decreases sharply at the end of the detection range and in the vicinity. Resulting in.
[0007]
Therefore, when a target is present in the front, a strong echo can be obtained. However, if the target orientation reaches the end of the detection range, the echo becomes weak and detection may be difficult due to noise.
[0008]
On the other hand, an antenna that maintains a high gain up to the vicinity of the end of the detection range can be designed. However, in this case, there is a problem in that erroneous detection occurs because the gain outside the detection range cannot be suppressed.
[0009]
Further, when the target is a vehicle, its scattering cross section is greatly reduced as it becomes lateral as compared to when the target is present in the front, and this also weakens the echo. Therefore, there has been a problem that detection of a target (vehicle) becomes increasingly difficult.
[0010]
[Means for Solving the Problems]
The present invention includes a reception signal acquiring means for acquiring a plurality of received signals received by the antenna elements arranged in different positions from each other, for some or all of the plurality of received signals, phase one setting direction performed for a plurality of setting azimuth processing of combining together, and the direction-specific signal calculating means for the orientation-specific signals to a plurality of setting directions for calculating, respectively Re Teso a reception signal having directivity for each setting direction In the signal synthesis means, the plurality of azimuth signals obtained by the azimuth signal calculation means are synthesized by leaving a large amplitude signal in each setting azimuth to form one synthesized signal. an echo detector for detecting an echo based on the resulting combined signal, and wherein the Rukoto to have a. However, the antenna elements need not be actually placed, if it obtains the received signal at different positions, rather it may also be moved one element, by further changing the position of the transmitting antenna, virtually The position of the receiving antenna may be changed.
[0011]
As described above, in the present invention, a direction-specific signal is obtained for each set direction. In this azimuth-specific signal, the echo generated by the target located in front of the set azimuth is large. Accordingly, among the detection range, enabling high-precision target accurate detection in the gain of the antenna element is provided set orientation to the orientation decreases. Further, by performing synthesis in advance, it is sufficient to perform echo detection processing for one synthesized signal, and the amount of calculation can be reduced.
[0012]
Further, it is preferable that the antenna element has a maximum gain capable of detecting a target having a maximum detection distance, and further suppresses a gain in a direction in which a grating lobe generated depending on an antenna element interval is generated. By making the gain of the antenna element sufficiently low outside the detection range, adverse effects of the grating lobe can be prevented.
[0013]
In addition, it is preferable that the direction-specific signal calculation unit changes the number of reception signals to be combined in accordance with a change in gain based on the directivity of the antenna element. By doing so, it is possible to compensate for the amount of decrease in gain and obtain a substantially uniform gain as a whole.
[0014]
In addition, the direction-specific signal means has means for separating the received signals into a plurality of groups according to the distance of the target on which the reflected wave is generated for each received signal. In the group corresponding to the proximity area, the set number of the predetermined azimuth is increased and extended to the side part in a group corresponding to the proximity area by reducing the set azimuth setting number and limiting the azimuth in the vicinity of the front. It is preferable to combine the received signals.
[0015]
Generally, only a relatively narrow area of target information is required in the far area, and a wide area of target information is required in the vicinity. This requirement is particularly strong in vehicles traveling on roads. Thus, by determining the set azimuth number according to this requirement, the amount of calculation can be made appropriate.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, an example in which the present invention is applied to FM-CW radar will be described, but the present invention can also be applied to pulse radar and SS (spread spectrum) radar.
[0018]
FIG. 2 shows the overall configuration of the radar apparatus. In this example, three receiving antenna elements 10-1 to 10-3 and one transmitting antenna 12 are provided. A high-frequency signal from the transmitter 14 is supplied to the transmission antenna 12 from which a transmission wave is transmitted. This transmission wave is an FM-CW wave, for example, a radio wave whose frequency repeatedly rises and falls like a triangular wave as time passes.
[0019]
Then, the transmission wave transmitted from the transmission antenna 12 is reflected by the target 1, and the reflected wave is received by the reception antenna elements 10-1 to 10-3. The reflected waves from the target 1 obtained by the receiving antenna elements 10-1 to 10-3 are subjected to reception processing such as demodulation in the receivers 16-1 to 16-3, respectively. Then, the reception signals obtained by the receivers 16-1 to 16-3 are supplied to the signal processing circuit 18, where predetermined signal processing is performed, and the position and distance of the target 1 are detected.
[0020]
Here, in the present embodiment, three azimuths are set as setting azimuths, and sufficient gain is maintained even at the end of the detection range by using the set azimuths. This will be described below. In the following example, the number of receiving antenna elements and the number of set azimuths are the same, but the number of receiving antenna elements and the number of set azimuths do not have to be the same, and may be more or less than 3, respectively.
[0021]
FIG. 4 shows the in-azimuth directivity pattern of the receiving antenna 10 in this example, the positions of the targets 1a and 1b, and the set orientation.
[0022]
In this example, it is assumed that there are two targets 1a and 1b having the same scattering cross section, and the target 1a exists in a substantially front direction (a direction with high directivity) and the target 1b exists in a side (a direction with low directivity). Is assumed. Here, as shown in the figure, the directivity of each of the receiving antenna elements 10-1 to 10-3 has a high gain in the front direction, and the gain decreases toward the end of the detection range. This is because it has a gain capable of detecting the target having the maximum detection distance set in the front direction, and suppresses the gain outside the detection range so that unnecessary false detection does not occur.
[0023]
Next, FIG. 3 shows the configuration of the signal processing circuit 18. Three reception signals (signals by reflected waves from the targets 1 a and 1 b) obtained by the receivers 16-1 to 16-3 are input to the reception signal acquisition unit 20. The reception signal acquisition means 20 is composed of an A / D converter or the like, A / D converts an analog reception signal, and takes it in as digital data. In the case of FM-CW radar, the reception signal acquisition unit takes in a beat signal obtained by mixing a transmission wave with a received reflected wave as a reception signal of each reception antenna element 10-1 to 10-3.
[0024]
The digital data of the reception signal acquired by the reception signal acquisition unit 20 is supplied to the frequency analysis unit 22. The frequency analysis means 22 performs frequency analysis such as complex FFT (Fast Fourier Transform) on each received signal to obtain three complex amplitude information for each of the receiving antenna elements 10-1 to 10-3. When the operation of changing the number of received signals to be synthesized according to the target distance is not performed, the frequency analyzing means 22 is arranged immediately before an echo detecting means 26 described later as shown in FIG. Frequency analysis may be performed. In this case, if the received signal can be obtained only by amplitude, the propagation delay time is corrected. If the received signal is obtained by a complex number including the phase, the received signal is synthesized after correcting the phase delay.
[0025]
This complex amplitude information indicates the amplitude of the reflected wave received at a frequency corresponding to the distance between the targets 1a and 1b. A plot of the complex amplitude information in this example is shown in FIG. Thus, since the target 1a is located in front of the receiving antenna elements 10-1 to 10-3 and has a short distance, the reflected waves of the target 1a are low in frequency at all the receiving antenna elements 10-1 to 10-3. , Will have a large amplitude. On the other hand, since the target 1b is located in an oblique direction and has a long distance, all the receiving antennas 10-1 to 10-3 become reflected waves with high frequencies and small amplitudes.
[0026]
Thus, since all the receiving antenna elements 10-1 to 10-3 have the same directivity, they have substantially the same waveform, and the echo of the target 1a appears strongly, but the echo of the target 1b is weak. Therefore, the echo from the target 1b may not be detected depending on noise. Furthermore, when the targets 1a and 1b are vehicles, the scattering cross-section area is generally large in the front direction and decreases when it becomes lateral. For this reason, the difference in echo intensity is further increased.
[0027]
Here, in this embodiment, it has the signal calculation means 24-1 to 24-3 according to direction. The azimuth-specific signal calculation means 24-1 to 24-3 synthesize the complex amplitude information from the three receiving antenna elements 10-1 to 10-3 in accordance with the set azimuth for each frequency component. That is, when the distance between the receiving antenna elements 10-1 to 10-3 is L and the angle from the front direction is θ, the incoming wave is only Lsinθ between the receiving antenna elements 10-1 to 10-3. The distances to the receiving antenna elements are different, and the received signals are synthesized with a phase difference of (2πL / λ) sin θ, respectively, so that the phases can be synthesized in accordance with the set direction. Note that λ is the frequency of the transmission wave, and this calculation is performed for each frequency.
[0028]
In this way, in this embodiment, since the signals are combined for each of the three set directions, three signals for each direction are obtained. Since the signals obtained in this way have different set orientations, a strong echo can be obtained with an orientation-specific signal with the vicinity where the target is present as the set orientation.
[0029]
That is, as shown in FIG. 6, in the azimuth-specific signal (i), since the azimuth is directed to the target 1b, the amplitude of the signal due to the reflected wave from the target 1b is increased. In the azimuth-specific signal (ii), the target 1a hits the front of the azimuth, and the amplitude of the signal due to the reflected wave from the target 1a is large. In the azimuth-specific signal (iii), there is no target in front of the set azimuth, only the target 1a is located at the end thereof, and a signal having a small amplitude is obtained as a signal by the reflected wave of the target 1a. The signal due to the reflected wave does not have a significant amplitude.
[0030]
As shown in FIG. 12, in the setting directions (i) and (iii), a gain higher than the gain of each of the receiving antenna elements 10-1 to 10-3 was obtained in each setting direction. Is equivalent.
[0031]
In this way, the three azimuth-specific signal calculation means 24-1 to 24-3 obtain the azimuth-specific signals (i) to (iii), which are supplied to the echo detection means 26. The echo detection unit 26 performs echo detection on each of the directional signals (i) to (iii) sent from the directional signal calculation units 24-1 to 24-3. For the echo detection in the echo detection means 26, a conventional technique such as peak search can be used.
[0032]
Further, the direction detection may be performed on the obtained echo. For this azimuth detection method, echo detection results for each receiving antenna element are used, but DBF (Digitai Beam Forming) may be used, and it is represented by MUSIC (Multiple Signal Classification) and ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques). A high resolution estimation method may be used.
[0033]
Thus, in this embodiment, the complex amplitude signal about the received signal from the several receiving antenna element 10-1 to 10-3 is synthesize | combined for every setting azimuth | direction, and the several signal sequence according to azimuth | direction is obtained. Thereby, the echo of the target existing in the direction where the gain of the antenna element decreases can be easily detected, and the target can be accurately detected over a wide range.
[0034]
In addition, when synthesizing signals by direction, it is not necessary to synthesize the same number of received signals in all. Rather, the more the set direction is sideways, the greater the number of combinations according to the amount of decrease in element directivity gain. It is desirable. As a result, as shown in FIG. 12, a decrease in gain in the end region of the detection range is compensated so that the gain is almost the same in all directions, and an echo having almost the same intensity in any direction in a target having the same scattering cross section. Can be obtained.
[0035]
When combining signals, depending on the element spacing of the receiving antenna elements, a grating lobe is generated outside the detection range when the side is set as the set direction. However, there is no problem if the directivity of the receiving antenna element is suppressed outside the detection range. That is, by suppressing the gain outside the detection range sufficiently low in each receiving antenna element, the grating lobe is not substantially detected, and problems can be prevented from occurring.
[0036]
Next, FIG. 8 shows another configuration example of the radar signal processing circuit. In this example, a signal synthesis unit 30 is provided between the azimuth-specific signal calculation units 24-1 to 24-3 and the echo detection unit 26. Then, in this signal synthesis means 30, a plurality of azimuth signals sent from the azimuth signal calculation means 24-1 to 24-3 are synthesized to obtain one synthesized signal. That is, the directional signals shown in FIG. 6 are combined to obtain the combined signal shown in FIG. Thus, as shown in FIG. 7, this is equivalent to obtaining a combined directivity having a similar gain in all directions. The echo detection means 26 only needs to detect echo for one composite signal, and the amount of calculation can be reduced.
[0037]
Here, as a synthesizing method in the signal synthesizing means 30, there are the following methods.
[0038]
That is, for the same frequency component of each orientation signal,
(I) The signal having the maximum amplitude is the frequency component of the synthesized signal.
(Ii) selecting a plurality of signals having a strong amplitude and averaging them to obtain a frequency component of the synthesized signal;
(Iii) selecting a plurality of signals having a strong amplitude, performing weighting according to the strength of the amplitude, and averaging them to obtain a frequency component of the synthesized signal;
There are methods such as. In any case, a composite signal is obtained by combining a plurality of azimuth signals so as to leave a signal having a large amplitude in each set azimuth.
[0039]
“Second Embodiment”
In the first embodiment, by setting a large number of setting azimuths, the probability that the target azimuth and the setting azimuth are the same increases, and the echo detection accuracy increases. However, as the number of received signals to be combined increases, the azimuth-specific signal sequence also increases, increasing the amount of computation.
[0040]
Therefore, in a radar such as FM-CW radar that can roughly estimate the position of the target from the echo frequency, when it is determined that the target is in the vicinity region, the set direction is increased to widen the detection range, and the target region is in the far region. If it is determined, the set direction is reduced to narrow the detection range. Thereby, it is possible to detect a wide range in the vicinity while suppressing an increase in signal processing.
[0041]
For example, in this embodiment, as shown in FIG. 10, the result of the frequency analysis means 22 is supplied to the azimuth number determination means 32. The azimuth number determination means 32 detects the frequency of the echo generated by the target from the frequency analysis result, and determines the azimuth number based on the detected echo frequency.
[0042]
On the other hand, the result of the frequency analysis means 22 is supplied to the direction-specific signal calculation means 24-1 to 24-5, and whether or not the direction-specific signal calculation means 24-1 to 24-5 perform the direction-specific signal calculation. Is determined by a signal from the azimuth number determining means 32. For example, in this example, when the azimuth number determination means 32 determines that the target is far, only the three azimuth signal calculation means 24-2, 24-3, and 24-4 are directional signal calculation means. Perform the operation. On the other hand, when the azimuth number determination means 32 determines that the target is close, the five directional signal calculation means 24-1 to 24-5 perform calculation.
[0043]
In the pulse radar and SS (spread spectrum) radar, the distance to the target can be known by detecting the propagation delay of the reflected wave. For this reason, it is preferable that the number of setting azimuths is similarly determined according to the distance to the target.
[0044]
In the above description, the processing by each means in the signal processing circuit has been described as being performed by separate circuits. However, any part or all of the processing can be performed as microcomputer software. For example, in the case where one microcomputer performs all the computations of the azimuth-specific signal string calculation units 24-1 to 24-5, the computation amount is reduced by reducing the number of set orientations according to the target distance. An effect is obtained.
[0045]
【The invention's effect】
As described above, according to the present invention, a direction-specific signal is obtained for each set direction. In this azimuth-specific signal, an echo generated at a target located in front of the set azimuth is strong. In view of this, the target can be detected by providing a set azimuth in the azimuth where the gain of the antenna element is reduced in the detection range.
[0046]
In addition, by making the gain of the receiving antenna element sufficiently low outside the detection range, adverse effects of the grating lobe can be prevented.
[0047]
Also, by increasing the number of complex amplitude information to be combined according to the gain reduction amount of the receiving antenna element, the gain reduction amount can be compensated and the gain can be obtained almost uniformly as a whole.
[0048]
In addition, by reducing the number of set azimuths in the far region and increasing the number of set azimuths in the vicinity, necessary information can be obtained with an appropriate amount of computation.
[0049]
In addition, by combining the plurality of azimuth signals into one composite signal, echo detection processing may be performed on one composite signal, and the amount of calculation can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a receiving antenna element of a conventional radar and its directivity.
FIG. 2 is a diagram illustrating a configuration of a radar according to the present embodiment.
FIG. 3 is a diagram illustrating a configuration of a signal processing circuit.
FIG. 4 is a diagram for explaining a setting direction.
FIG. 5 is a diagram illustrating a frequency analysis result of a reception signal for each reception antenna element.
FIG. 6 is a diagram showing signals according to directions.
FIG. 7 is a diagram showing a synthesis directivity obtained by a signal synthesis unit.
FIG. 8 is a diagram showing another configuration of the signal processing circuit.
FIG. 9 is a diagram illustrating a combined signal.
FIG. 10 is a diagram illustrating still another configuration example of the signal processing circuit.
FIG. 11 is a diagram illustrating still another configuration example of the signal processing circuit.
FIG. 12 is a diagram showing signals according to directions.
[Explanation of symbols]
10-1 to 10-3 Receiving antenna element, 12 Transmitting antenna, 14 Transmitter, 16 Receiver, 18 Signal processing circuit, 20 Received signal acquisition means, 22 Frequency analysis means, 24-1 to 24-3 Signal calculation according to direction Means, 26 Echo detection means.

Claims (5)

Received signal acquisition means for acquiring a plurality of received signals received by antenna elements arranged at different positions from each other;
For some or all of the plurality of received signals, the processing to synthesize together the phase in one set direction is performed to a plurality of setting directions, the orientation-specific signal is a received signal having a directivity for each setting direction and the direction-specific signal calculating means for calculating, respectively Re Teso for a plurality of setting directions,
A signal combining means that combines the plurality of signals obtained by the direction-specific signal calculation means, leaving a signal having a large amplitude in each setting direction to be one combined signal;
Echo detecting means for detecting echo based on the synthesized signal obtained in the signal synthesizing means ;
The signal processing circuit of the radar, characterized in Rukoto to have a. The circuit of claim 1, wherein
The antenna element is
It has the maximum gain that can detect the target of the maximum detection distance,
Further , a radar signal processing circuit characterized in that a gain of an azimuth in which a grating lobe generated depending on an antenna element interval is suppressed is suppressed by suppressing a gain of each antenna element outside a detection range . The circuit according to claim 1 or 2,
The radar signal processing circuit, wherein the direction-specific signal calculating means changes the number of received signals to be combined in accordance with a change in gain based on the directivity of the antenna element. The circuit according to any one of claims 1 to 3,
The direction-specific signal calculating means has means for separating the received signals into a plurality of groups according to the distance of the target on which the reflected wave is generated for each received signal,
In the group corresponding to the far field, the set number of the setting azimuth is small, and the reception signal is synthesized only in the azimuth near the front,
A radar signal processing circuit characterized in that, in a group corresponding to a proximity region, a set number of the predetermined azimuths is increased and the reception signals are synthesized by extending to a side portion. In the circuit according to any one of claims 1 to 4,
  The signal synthesis means includes
  For the same frequency component of each azimuth signal, (i) the signal with the maximum amplitude is used as the frequency component of the combined signal, and (ii) a plurality of signals having strong amplitude are selected and averaged to be the frequency component of the combined signal. , (Iii) selecting a plurality of signals having a strong amplitude, performing weighting according to the strength of the amplitude, and averaging them to obtain a frequency component of the synthesized signal;
  A radar signal processing circuit characterized in that a combined signal is obtained by combining a plurality of azimuth signals so as to leave a signal having a large amplitude in each set azimuth.

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