JP4377772B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus that observes a target in a multipath environment, and more particularly to a technique for eliminating a decrease in the level of a received signal due to multipath.

  2. Description of the Related Art Conventionally, a radar apparatus that detects a target by performing Fourier transform on a received signal and using a filter bank having a Doppler frequency is known. In such a radar apparatus, in a multipath environment, a direct wave reflected directly from a target and a multipath wave reflected and reached from the sea surface or the ground in the middle are combined and input to an antenna. Therefore, depending on the distance to the target, the received power decreases rapidly (see Non-Patent Document 1, pages 49-55). As a result, there has been a problem that the target cannot be detected and kept up. This problem is the same even in the case of a beam pattern that is an angular characteristic of an antenna.

As a countermeasure against such a problem, there is known a frequency diversity method using a maximum value of a received signal obtained by shifting a point where the level of abrupt reduction in received power is shifted using a plurality of frequencies (for example, non-frequency (Refer patent document 1, p.269-272).
Supervised by Takashi Yoshida, “Revised Radar Technology”, first edition, The Institute of Electronics, Information and Communication Engineers, February 15, 2003

  However, in the conventional radar apparatus described above, when the frequency diversity method is used, if the frequency is changed, the frequency diversity effect can be obtained even when a direct wave and a multipath wave are mixed in the same filter on the filter bank of the Doppler frequency axis. However, if the frequency selection range is narrow, there is a problem that a large effect cannot be expected.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a radar apparatus capable of improving target detection performance and tracking ability even when the frequency selection range is narrow. There is.

In order to solve the above-described problem, a radar apparatus according to a first aspect of the invention performs target detection processing on a Doppler frequency axis obtained by Fourier-transforming a signal between transmitted and received pulse repetition intervals (PRI: Pulse Repetition Interval). And a radar apparatus that performs radar signal processing including tracking processing, calculating a plurality of complex weights having a predetermined phase gradient in which a predetermined PRI is used as a reference time and different offset amounts are added to the reference time. A plurality of phase patterns indicating the relationship between the Doppler frequency and the phase corresponding to the complex weight of the phase, the phase of each phase pattern changes with respect to the Doppler frequency, and the phase patterns have different slopes from each other. A weight calculation unit in which the slope of each phase pattern changes according to the offset amount, and a complex calculation calculated by the weight calculation unit. A Fourier transform processing unit that obtains filter data by a filter bank by Fourier transform formed by sequentially setting a number of complex weights, and a filter that constitutes the filter bank from a plurality of filter data obtained by the Fourier transform processing unit Each includes a maximum value selection processing unit that detects a maximum value among a plurality of complex weights, and a target detection processing unit that detects a target based on a detection result in the maximum value selection processing unit.

According to a second aspect of the present invention, there is provided a radar apparatus including a target detection process and a tracking process on a Doppler frequency axis obtained by Fourier-transforming a signal between transmitted and received pulse repetition intervals (PRI: Pulse Repetition Interval). In a radar apparatus that performs signal processing, a desired filter having a plurality of phase patterns indicating a relationship between a Doppler frequency and a phase, the phase of each phase pattern changing with respect to the Doppler frequency, and each phase pattern having a different slope Filter by a weight calculation unit that calculates a plurality of complex weights of Fourier transform so that a bank is formed, and a filter bank by Fourier transform formed by sequentially setting a plurality of complex weights calculated by the weight calculation unit Obtained by Fourier transform processing unit to obtain data and Fourier transform processing unit A maximum value selection processing unit that detects a maximum value among a plurality of complex weights for each filter constituting a filter bank, and a target detection that detects a target based on a detection result in the maximum value selection processing unit from a plurality of filter data. And a processing unit.

According to the radar apparatus of the first invention, a plurality of complex weights having a predetermined phase gradient in which a predetermined PRI is used as a reference time and different offset amounts are added to the reference time are calculated, and the plurality of complex weights are calculated. Correspondingly, there are multiple phase patterns indicating the relationship between Doppler frequency and phase, and the phase of each phase pattern changes with respect to the Doppler frequency, and each phase pattern has a different slope and the slope of each phase pattern is offset. Varies with quantity. That is, by changing the slope of the phase pattern of the filter bank output, the phase relationship between the direct wave and the multipath wave is shifted, and the level drop point of the Doppler frequency with respect to the distance is changed. Since the maximum value between the banks is taken as the received signal, the target detection process and the follow-up process can be performed using the received signal with a small level drop due to multipath. As a result, the detection probability and tracking maintenance rate can be improved.

According to the radar apparatus of the second invention, the phase of each phase pattern changes with respect to the Doppler frequency and each phase pattern has a different slope from each other, and a desired filter bank is obtained by inverse Fourier transform to obtain the filter bank output. By changing the slope of the phase pattern, the phase relationship between the direct wave and the multipath wave is shifted, and the level drop point of the Doppler frequency with respect to the distance is changed. It is taken as a received signal. As a result, the target detection process and the tracking process can be performed using a received signal with a small level drop due to multipath, and thus the detection probability and the tracking maintenance ratio can be improved.

  Hereinafter, a radar apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration of a radar apparatus according to Embodiment 1 of the present invention. The radar apparatus includes an antenna 1, a transmitter 2, a receiver 3, and a signal processor 4.

  The antenna 1 includes a plurality of antenna elements and has a phased array configuration. The antenna 1 transmits a transmission signal transmitted from the transmitter 2 toward the air, and also receives a signal from the air, that is, a direct wave and a multipath wave from a target, and transmits the signals to the receiver 3.

  The transmitter 2 generates a transmission signal and sends it to the antenna 1. The receiver 3 converts the frequency of the received signal transmitted from the antenna 1 and further converts it into a digital signal. The digital signal obtained by the receiver 3 is sent to the signal processor 4 as a received digital signal.

  The signal processor 4 includes an MTI (Moving Target Indicator) processing unit 41, a DFT (Discrete Fourier Transformation) processing unit 42, a maximum value selection processing unit 43, a target detection processing unit 44, and a radar control unit. 45.

  The MTI processing unit 41 performs, for example, MTI processing for suppressing clutter on the received digital signal transmitted from the receiver 3 in accordance with the type of radar. The signal subjected to MTI processing in the MTI processing unit 41 is sent to the DFT processing unit 42.

  The DFT processing unit 42 corresponds to the Fourier transform processing unit of the present invention, and sends signals sent from the MTI processing unit 41 to the radar control unit 45 in order to separate and detect targets having different Doppler frequencies. By applying the complex weight, discrete Fourier transform processing that is filter bank processing in units of a pulse repetition period (PRI) is performed. The result of the discrete Fourier transform process in the DFT processing unit 42 is sent to the maximum value selection processing unit 43. The DFT processing unit 42 may be configured to perform FFT (Fast Fourier Transform) processing instead of DFT processing.

  The maximum value selection processing unit 43 detects the maximum value between a plurality of offsets (described later in detail), in other words, between a plurality of complex weights, for each filter constituting the filter bank. The maximum value obtained by the maximum value selection processing unit 43 is sent to the target detection processing unit 44.

  The target detection processing unit 44 executes radar signal processing such as target detection processing or tracking processing based on the maximum value for each filter constituting the filter bank that is sequentially sent from the maximum value selection processing unit 43 for each distance. The detection result in the target detection processing unit 44 is sent to the outside as target information.

  The radar control unit 45 corresponds to the weight calculation unit of the present invention, and performs weight calculation for a plurality of offsets. The complex weight obtained by the weight calculation in the radar control unit 44 is sent to the DFT processing unit 42.

  Next, the operation of the radar apparatus according to Embodiment 1 of the present invention configured as described above will be described. First, an outline of the operation of the radar apparatus will be described with reference to FIGS.

  FIG. 2 is a diagram for explaining a change in the amplitude level of the received signal with respect to the distance in one filter constituting the filter bank. In the conventional radar apparatus, for example, a complex weight that is not offset (for example, a complex weight with an offset of 1) is given to the DFT processing unit 42. In this case, due to the interference between the direct wave and the multipath wave, a portion A having a large drop in amplitude level occurs depending on the distance.

  On the other hand, in the radar apparatus according to Embodiment 1 of the present invention, a drop occurs when a complex weight having a plurality of offsets (offset 1 and offset 2 in the example shown in FIG. 2) is given to the DFT processing unit 42. A plurality of received signals with different distances (in the case of offset 2, the drop in amplitude level becomes large at portion B) are acquired, and the maximum value (indicated by a bold line) at each distance of these received signals is detected and received. Signal. Therefore, it is possible to obtain a reception signal having a substantially flat amplitude level with little drop.

  Here, the offset will be described. FIG. 3A shows a state in which a complex weight having a phase gradient as shown by a thick line is given to a reception signal obtained from each antenna element with a predetermined PRI as a reference time. FIG. 3B shows a state in which an offset L is added to the reference time. In this case, the phase gradient is the same, but the phase of the complex weight given to the received signal from each antenna element changes as indicated by the bold line. Therefore, a larger phase is given to the received signal from each antenna element as compared with the case shown in FIG.

  FIG. 4 shows amplitude characteristics and phase characteristics when a non-offset complex weight is given to the received signal from the antenna 1 as shown in FIG. In this case, since the phase pattern is constant with respect to the Doppler frequency, the phase characteristics of the direct wave and the multipath wave are the same, and due to the difference between the phase of the direct wave and the phase of the multipath wave, As shown by offset 1 in FIG. 2, a portion A in which the amplitude level of the received signal drops at a predetermined distance occurs.

  On the other hand, FIG. 5 shows amplitude characteristics and phase characteristics when a complex weight obtained by adding an offset L to the reference time shown in FIG. In this case, the amplitude characteristic is the same as that when not offset, but the phase pattern has a slope with respect to the Doppler frequency. The inclination of this phase pattern increases as the offset L increases. Therefore, the phase characteristics of the direct wave and the multipath wave differ depending on the offset amount. As a result, as indicated by offset 2 in FIG. 2, the amplitude level of the received signal in one filter constituting the filter bank drops at a portion B at a different distance from that when the filter is not offset. Therefore, if the maximum value of the received signals for each of the plurality of filters obtained for a plurality of offsets is selected as the final received signal for each distance, as shown by the thick line in FIG. It is possible to obtain a received signal for each Doppler frequency having a large amplitude level.

  Next, the detailed operation of the radar apparatus according to Embodiment 1 of the present invention will be described with reference to the flowchart shown in FIG.

  First, weight calculation with a predetermined offset is executed for a predetermined distance (step S10). That is, the radar control unit 45 calculates the complex weight of the received beam. Next, a filter bank is formed (step S11). That is, the complex weight calculated in step S10 is set in the DFT processing unit 42.

Next, filter data acquisition is performed (step S12). That is, the DFT processing unit 42 performs DFT processing, that is, discrete Fourier transform processing, according to the following formula (1).

Here, X (n) is a received signal (n = 1 to N) input from the MTI processing unit 41, n is a PRI number (n = 1 to N), N is the number of PRIs, and np is an offset of the set number p. 2 (see FIG. 2), Wdft (n) is the DFT window function, b (p, m) is the signal after DFT (m = 1 to M, p = 1 to P), P is the number of sets, and m is the filter The number of the filter constituting the bank (m = 1 to M), j is an imaginary unit. The result of the discrete Fourier transform acquired in step S12 is sent to the maximum value selection processing unit 43. Next, it is checked whether or not acquisition of all filter sets has been completed, that is, whether or not acquisition of filter data for all offsets has been completed (step S13). Here, if it is determined that the acquisition of filter data for all offsets has not been completed, the sequence returns to step S10, and the above-described processing is repeated.

On the other hand, when it is determined in step S13 that all filter sets have been acquired, maximum value detection is performed (step S14). That is, the maximum value selection processing unit 43 obtains the maximum value bmax by the following equation between a plurality of filters having different np for each filter constituting the filter bank. The maximum value for each filter obtained by the maximum value selection processing unit 43 is sent to the target detection processing unit 44.

  Here, max [] represents the maximum value.

  Next, it is checked whether or not the data acquisition for all distances has been completed (step S15). Here, if it is determined that data acquisition for all distances has not been completed, the next distance is selected (step S16), and then the sequence returns to step S10 to repeat the above-described operation.

  Then, when it is determined in step S15 that the data acquisition has been completed, the process for acquiring the reception signal ends. Thereafter, although not shown, the target detection processing unit 44 performs target detection processing.

  As described above, according to the radar apparatus according to Embodiment 1 of the present invention, the phase relationship between the direct wave and the multipath wave is obtained by changing the slope of the phase pattern of the filter bank output by offsetting the reference time of PRI. By shifting the level drop point of the Doppler frequency with respect to the distance, the maximum value between the same banks is taken as the received signal in the filter bank using a plurality of complex weights. As a result, the target detection process and the tracking process can be performed using a received signal with a small level drop due to multipath, and thus the detection probability and the tracking maintenance ratio can be improved.

  The radar apparatus according to Embodiment 2 of the present invention is configured to synthesize a desired filter bank having a desired inclination in a phase pattern when forming the filter bank.

  The configuration of the radar apparatus according to the second embodiment of the present invention is the same as that of the radar apparatus according to the first embodiment shown in FIG. 1 except that the processing contents executed by the radar control unit 45 of the signal processor 4 are different. Is the same. Hereinafter, only different parts will be described.

  The radar control unit 45 prepares a desired filter bank having a phase characteristic (phase pattern) having an amplitude characteristic and an inclination as shown in FIG. 5 in advance, for example, and inverse Fourier transforms the prepared desired filter bank. To calculate complex weights.

  Next, the detailed operation of the radar apparatus according to Embodiment 2 of the present invention will be described with reference to the flowchart shown in FIG. The flowchart shown in FIG. 7 is obtained by changing the weight calculation process by the offset in step S10 in the flowchart according to the first embodiment shown in FIG. 6 to the weight calculation process by the inverse Fourier transform of the desired filter bank to be step S20. is there.

  First, in the weight calculation process of step S20, for example, as shown in FIG. 5, a desired filter bank bd in which a phase pattern created in advance has a slope is obtained by inverse Fourier transform, and a plurality of complex weights W (p, n ) Is calculated. That is, the radar control unit 45 calculates the complex weight W (p, n) of the received beam by inverse Fourier transform of the desired filter bank bd according to the following equation (3). The calculated complex weight W (p, n) is sent to the DFT processing unit 42.

Next, a filter bank is formed (step S11). That is, the complex weight calculated in step S10 is set in the DFT processing unit 42. Next, filter data acquisition is performed (step S12). That is, the DFT processing unit 42 performs DFT processing, that is, discrete Fourier transform processing, according to the following equation (4). The following process is the same as the process in the radar apparatus according to the first embodiment described with reference to the flowchart of FIG.

Here, W (p, n) is the complex weight (n = 1 to N, p = 1 to P) of the nth element of the set number p, P is the number of sets, and bd (p, m) is the phase pattern Different desired filter banks (m = 1 to M), m is a frequency number (m = 1 to M) defining a phase pattern, and b (p, m) is a forming filter bank (m = 1 to M).

  As described above, according to the radar apparatus of the second embodiment of the present invention, a desired filter bank having a gradient in the phase pattern is obtained by inverse Fourier transform to change the gradient of the phase pattern of the filter bank output. Thus, the phase relationship between the direct wave and the multipath wave is shifted to change the level drop point of the Doppler frequency with respect to the distance, and the maximum value between the same banks is taken as the received signal in the filter bank using a plurality of complex weights. As a result, the target detection process and the tracking process can be performed using a received signal with a small level drop due to multipath, and thus the detection probability and the tracking maintenance ratio can be improved.

  In the radar apparatus according to the first embodiment and the second embodiment described above, a plurality of filters having different slopes of the phase pattern are used to change the phase relationship between the direct wave and the multipath wave, thereby reducing the level due to the multipath. Since the purpose is to prevent, other filter bank forming methods can be used. Further, not only a phase pattern that can provide a great effect but also a difference in amplitude pattern can be configured to prevent a level drop.

It is a figure which shows the structure of the radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the change of the amplitude level with respect to the distance of the radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the offset used with the radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the amplitude characteristic and phase characteristic when there is no offset of the radar apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the amplitude characteristic and phase characteristic when there exists an offset of the radar apparatus which concerns on Example 1 of this invention. It is a flowchart which shows the flow of a process of the radar apparatus which concerns on Example 1 of this invention. It is a flowchart which shows the flow of a process of the radar apparatus which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 Transmitter 3 Receiver 4 Signal processor 41 MTI processing part 42 DFT processing part 43 Maximum value selection processing part 44 Target detection processing part 45 Radar control part

Claims (2)

In a radar apparatus that performs radar signal processing including target detection processing and tracking processing on a Doppler frequency axis obtained by Fourier-transforming a signal of a transmitted and received pulse repetition period (PRI: Pulse Repetition Interval ) ,
A plurality of complex weights having a predetermined phase gradient in which a predetermined PRI is set as a reference time and different offset amounts are added to the reference time are calculated, and the Doppler frequency and the phase corresponding to the plurality of complex weights are calculated. There are a plurality of phase patterns indicating the relationship, the phase of each phase pattern changes with respect to the Doppler frequency, and each phase pattern has a different slope, and the slope of each phase pattern changes according to the offset amount. A weight calculation unit;
A Fourier transform processing unit for obtaining filter data by a filter bank by Fourier transform formed by sequentially setting a plurality of complex weights calculated by the weight calculation unit;
A maximum value selection processing unit for detecting a maximum value between a plurality of complex weights for each filter constituting a filter bank, from a plurality of filter data obtained by the Fourier transform processing unit;
A target detection processing unit for detecting a target based on a detection result in the maximum value selection processing unit;
A radar apparatus comprising: In a radar apparatus that performs radar signal processing including target detection processing and tracking processing on a Doppler frequency axis obtained by Fourier-transforming a signal of a transmitted and received pulse repetition period (PRI: Pulse Repetition Interval ) ,
A desired filter bank having a plurality of phase patterns indicating the relationship between the Doppler frequency and the phase, the phase of each phase pattern changing with respect to the Doppler frequency, and the phase patterns having different slopes is formed. A weight calculation unit for calculating a plurality of complex weights of Fourier transform,
A Fourier transform processing unit for obtaining filter data by a filter bank by Fourier transform formed by sequentially setting a plurality of complex weights calculated by the weight calculation unit;
A maximum value selection processing unit for detecting a maximum value between a plurality of complex weights for each filter constituting a filter bank, from a plurality of filter data obtained by the Fourier transform processing unit;
A target detection processing unit for detecting a target based on a detection result in the maximum value selection processing unit;
A radar apparatus comprising:

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