radar equipment

Abstract

A radar device, which continuously transmits a plurality of transmission pulses into space, sequentially receives reflected signals from a target, and measures a distance and Doppler frequency to the target, comprises: a radar signal generation unit (50) including a code generation unit (1) that generates basic codes; an interval modulation unit (11) that modulates the interval of the codes generated by the code generation unit (1), and generates N code sequences (N is an integer of 2 or greater) that are mutually uncorrelated; and a transmission unit (2) that upconverts and amplifies the code sequences generated by the interval modulation unit (11), and generates a transmission signal for emitting M code-modulated transmission pulses per observation time per pulse repetition period (M is an integer of N or greater).

Description

[Technical Field]

[0001] The present disclosure relates to a radar device that continuously transmits a plurality of transmission pulses into space, sequentially receives reflected signals from a target, and measures the distance to the target and the Doppler frequency. [Background technology]

[0002] Conventionally, pulse Doppler radar devices (hereinafter, for convenience, abbreviated as "coded pulse radar devices" or simply "radar devices") that use coded pulse compression technology for the purpose of increasing transmission power and preventing deterioration of distance resolution have been known (for example, Non-Patent Document 1 below).

[0003] In the coded pulse radar device disclosed in Non-Patent Document 1 below, the following processing is performed. (1) A transmission pulse is generated by performing phase modulation with a code sequence (hereinafter referred to as "code modulation") within the transmission pulse at time intervals shorter than the transmission pulse. (2) The code-modulated transmission pulse is emitted from the antenna into space P times (P is a positive integer) at each pulse repetition interval (hereinafter abbreviated as "PRI" where appropriate). (3) The signal pulse reflected back from the target is received and converted into a digital video signal, and the code sequence (number of codes L, bandwidth per code B) used to generate the transmitted pulse is used as a reference function to perform correlation processing between the digital video signal and the reference function to obtain a pulse hit signal at point P containing distance information for each time delay. This correlation processing, i.e., correlation processing using the code sequence as a reference function, is called "pulse compression (processing)." (4) The pulse hit signal obtained by correlation processing is subjected to a discrete Fourier transform at point P for each time delay to measure the distance to the target, and the Doppler frequency is measured from the phase change in the pulse hit direction. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] "INTRODUCTION TO AIRBORNE RADAR SECOND EDITION" by George W. Stimson, 1998, P169-176, P209-246 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional coded pulse radar device described above, the code sequence applied to the multiple transmitted pulses transmitted consecutively is the same for each PRI, making it impossible to determine which code modulation was applied to the received pulse, which can result in "range ambiguity," in which the distance to the target becomes unclear. Range ambiguity occurs when the time delay is equal to or greater than the PRI, and can lead to erroneous measurements when calculating distance, so there has been a need to suppress range ambiguity.

[0006] The present disclosure has been made in view of the above, and has an object to provide a radar device that can suppress distance ambiguity even under conditions in which distance ambiguity occurs. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, a radar device according to the present disclosure is a radar device that continuously transmits a plurality of transmission pulses into space, sequentially receives reflected signals from a target, and measures the distance to the target and Doppler frequency, and includes a code generation unit that generates a basic code, an interval modulation unit that modulates the intervals of the codes generated by the code generation unit to generate N (N is an integer equal to or greater than 2) code sequences that are uncorrelated with each other, a transmission unit that up-converts and amplifies the code sequences generated by the interval modulation unit, and generates transmission signals for emitting M (M is an integer equal to or greater than N) code-modulated transmission pulses per pulse repetition period per observation time, an antenna that radiates the transmission signals generated by the transmission unit into space, a reception unit that receives reflected waves from the target, detects the received signals, and converts them into analog video signals, and an analog to digital (Analog to Digital) converter that converts the analog video signals converted by the reception unit into digital video signals. and a distance and Doppler frequency measurement unit that generates pulse hit signals containing distance information for each time delay by correlation processing between the digital video signal and the reference function using the code sequence generated by the interval modulation unit as a reference function, and measures the distance to the target and the Doppler frequency based on the generated pulse hit signals, wherein the distance and Doppler frequency measurement unit has a correlation unit that generates pulse hit signals, an ambiguity coupling processing unit that sorts the output of the correlation unit for each distance folding, and a frequency analysis unit that performs frequency analysis on the distance folding pulse hit signals output by the ambiguity coupling processing unit. [Effects of the Invention]

[0008] According to the radar device of the present disclosure, even under conditions where distance ambiguity occurs, it is possible to suppress the distance ambiguity, and transmission blindness can be eliminated. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a radar device according to an embodiment of the present invention. [Figure 2] FIG. 1 shows a sequence of transmission signals according to the present embodiment. [Figure 3] FIG. 1 shows an example of a code sequence according to the present embodiment. [Figure 4] FIG. 10 is a diagram for explaining the detailed operation of the ambiguity combination processor in the radar device of the present embodiment. [Figure 5] FIG. 1 is a diagram for explaining in detail the operation for solving the problem in this embodiment. [Figure 6] FIG. 1 is a diagram for explaining why transmission blindness is eliminated in the radar device of this embodiment. [Figure 7] FIG. 10 is a diagram showing received power in the radar device according to the present embodiment. [Figure 8] A diagram showing the basic configuration of a coded pulse radar device. [Figure 9] FIG. 9 is a diagram showing a sequence of transmission signals in the coded pulse radar device shown in FIG. 8. [Figure 10] FIG. 9 is a diagram for explaining distance ambiguity in the coded pulse radar device shown in FIG. 8. [Figure 11] FIG. 9 is a diagram for explaining why transmission blindness occurs in the coded pulse radar device shown in FIG. 8. [Figure 12] A diagram showing the change in received power when transmission blindness occurs DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, radar devices according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0011] 1 is a block diagram showing an example of the configuration of a radar device according to this embodiment. The radar device according to this embodiment comprises a code generation unit 1 that generates a basic code, an interval modulation unit 11 that modulates the intervals of the codes generated by the code generation unit to generate N code sequences (N is an integer equal to or greater than 2) that are uncorrelated with each other, a transmission unit 2 that up-converts and amplifies the code sequences generated by the interval modulation unit 11 and generates transmission signals for emitting M code-modulated transmission pulses (M is an integer equal to or greater than N) per observation time for each PRI, an antenna 3 that radiates the transmission signals generated by the transmission unit 2 into space, and an antenna 4 that receives reflected waves from a target, detects the received signals, and converts them into analog signals. the signal processing unit 12 sorts the output of the correlation unit 6 for each distance folding; and the frequency analysis unit 7 performs frequency analysis on the distance folding pulse hit signal output from the ambiguity coupling unit 12.

[0012] In the above configuration, the code generating section 1, the interval modulating section 11, and the transmitting section 2 constitute a radar signal generating section 50. The radar signal generating section 50 may be configured as a radar signal generating device.

[0013] The correlation unit 6, the ambiguity combining unit 12, and the frequency analysis unit 7 constitute a distance and Doppler frequency measurement unit 100. The correlation unit 6 includes a code sequence 1 correlation unit 61, a code sequence 2 correlation unit 62, ..., a code sequence N correlation unit 6 N are provided, and each of them is configured to receive the output of the A / D conversion unit 5. In addition, the frequency analysis unit 7 is configured to include a distance wrap 0 frequency analysis unit 71, a distance wrap 1 frequency analysis unit 72, ..., a distance wrap N-1 frequency analysis unit 73, etc., in accordance with the configuration of the correlation unit 6. N The processing in the correlation unit 6, the ambiguity combining unit 12, and the frequency analysis unit 7 will be described in detail later.

[0014] Next, the operation of the main parts of the radar device according to this embodiment will be described with appropriate reference to the drawings of Figures 1 to 5. Figure 2 is a diagram showing a sequence of a transmission signal in this embodiment, Figure 3 is a diagram showing an example of a code sequence in this embodiment, Figure 4 is a diagram explaining the detailed operation of the ambiguity combination processor in the radar device of this embodiment, and Figure 5 is a diagram explaining in detail the operation for solving the problems in this embodiment.

[0015] First, the code generation unit 1 generates a basic code sequence. An example of the code sequence is as shown in Fig. 9, which is a code sequence with L codes and B bandwidth per code.

[0016] The interval modulation unit 11 uses the code sequence generated by the code generation unit 1 to generate N types of code sequences (code sequence 1 to code sequence N) by modulating the intervals between codes in the code sequence. The N types of code sequences (code sequence 1 to code sequence N) shown in Fig. 2 are examples, and are pre-selected as combinations that are uncorrelated with each other. Note that the uncorrelated combinations referred to here are combinations such as those shown in Fig. 3. Fig. 3 shows three types of code sequences as examples: code sequence 1: [11000010-1000], code sequence 2: [1001-10000100], and code sequence 3: [-100010000101].

[0017] In Figure 3, the autocorrelations of code sequence 1, code sequence 2, and code sequence 3 reach a maximum value at a certain time (time "11" on the horizontal axis), as indicated by the cross marks in Figure 3(a), the plus marks in Figure 3(b), and the diamond marks in Figure 3(c). However, the correlation between code sequence 1 and code sequence 2 only takes values ​​in the range of ±1 at all times, as indicated by the plus marks in Figure 3(a) and the cross marks in Figure 3(b). The correlation between code sequence 2 and code sequence 3 only takes values ​​in the range of ±1 at all times, as indicated by the diamond marks in Figure 3(b) and the plus marks in Figure 3(c). The correlation between code sequence 3 and code sequence 1 only takes values ​​in the range of ±1 at all times, as indicated by the diamond marks in Figure 3(a) and the cross marks in Figure 3(c).

[0018] Returning to FIG. 2, the transmitter 2 up-converts and amplifies code sequence 1 to code sequence N generated by the interval modulation unit 11, and emits the interval code modulated pulses N times into space from the antenna 3 for each PRI. After emitting code sequence N into space, the transmitter 2 returns to code sequence 1 and repeats this emission a preset number of times. Note that the example in FIG. 2 is an example in which the total number of PRIs in one observation time period is set to M, which satisfies the relationship M≧N. In FIG. 2, in the time period of (N+1)PRI after transmitting code sequence N, code sequence 1 is transmitted, and in MPRI, which is the last time period of one observation time period, code sequence Z is transmitted. Note that when the order of code sequence 1 to code sequence N is repeated in a fixed manner as in the example of this embodiment, if the code sequence number in the time period of MPRI is Z, Z can be expressed by the following equation.

[0019] Z=(M mod N)+1 Here, "M mod N" in the above equation represents the remainder when integer M is divided by integer N.

[0020] As shown in Fig. 1, the digital video signal converted by the A / D converter 5 is converted into a distance signal and a Doppler frequency signal in the correlation unit 6. In the code sequence 1 correlation unit 61, the code sequence 1 generated by the interval modulator 11 is used as a reference function, and correlation processing is performed between the digital video signal and the reference function. In the code sequence 2 correlation unit 62, the code sequence 2 generated by the interval modulator 11 is used as a reference function, and correlation processing is performed between the digital video signal and the reference function. Similar processing is performed sequentially thereafter, and the code sequence N correlation unit 6 N In the modulation section 11, a correlation process is performed between the digital video signal and the reference function, using the code sequence N generated by the interval modulation section 11 as a reference function. This correlation process is also called "pulse compression process."

[0021] Code sequence 1 correlation unit 61 to code sequence N correlation unit 6 N The correlation results calculated in step (1) are sorted by the ambiguity combining unit 12.

[0022] The details of the sorting process will be explained using Figures 2 and 4. First, as shown in Figure 2, one observation time consists of M intervals from 1PRI to MPRI. Here, each of the M intervals into which one observation time is divided is defined as a PRI signal interval. The width of the PRI signal interval is the generation cycle of the digital video signal generated for each transmission pulse. Furthermore, the correlation result between the pth (p = 1, 2, ..., M) digital video signal (C1, C2, ..., CN, C1, C2, ..., CZ) and the code sequence n (n = 1, 2, ..., N) is denoted as PC(n, p). For example, in Figure 4, the correlation result between the code sequence 1 and the digital video signal C1 is denoted as "PC(1, 1)," and the correlation result between the code sequence 1 and the (N+1)th digital video signal C1 is denoted as "PC(1, N+1)." Note that other correlation results are denoted similarly.

[0023] Here, the notation combining the word "distance wrap" and "number" will be explained with reference to FIG. 5. First, "distance wrap 0" means that the detected target does not cross PRI intervals. For example, in FIG. 5, if target 2 detected in the 2PRI signal interval is due to a signal pulse of code sequence 2, it does not cross multiple PRI intervals, so it corresponds to a case where there is no distance wrap, and is classified as "distance wrap 0." On the other hand, if target 2 detected in the 2PRI signal interval is due to a signal pulse of code sequence 1, it crosses two PRI intervals, so it corresponds to a case where there is distance wrap, and is classified as "distance wrap 1." The classification continues with "distance wrap 2," "distance wrap 3," and so on. For example, if target 3 detected in the NPRI signal interval is due to a signal pulse of code sequence 1, it crosses N PRI intervals, so it is classified as "distance wrap N-1."

[0024] Returning to Figure 4, for example, if the target is located at range wrap 0, the partially hatched PC(1,1), PC(2,2), PC(3,3), ..., PC(N,N), PC(1,N+1), PC(2,N+2), PC(3,N+3), ..., PC(Z,M) have high correlation values, so they are rearranged in the pulse hit direction to obtain a range wrap 0 pulse hit signal. Similarly, if the target is located at range wrap 1, the transmitted signal is delayed by 1 PRI, so PC(N,1), PC(1,2), PC(2,3), ..., PC(N-1,N), PC(N,N+1), PC(1,N+2), PC(2,N+3), ..., PC(Z-1,M) have high correlation values, so they are rearranged in the pulse hit direction to obtain a range wrap 1 pulse hit signal. Similarly, when the target is located at range wrap N-1, the transmitted signal is delayed by (N-1)PRI, so PC(2,1), PC(3,2), PC(4,3), ..., PC(1,N), PC(2,N+1), PC(3,N+2), PC(4,N+3), ..., PC(Z-N+1,M) have high correlation values, so they are rearranged in the pulse hit direction to obtain the range wrap N-1 pulse hit signal.

[0025] The frequency analysis unit 7 includes a distance fold 0 frequency analysis unit 71, a distance fold 1 frequency analysis unit 72, and a distance fold N-1 frequency analysis unit 7. N measures the Doppler frequency by applying an L-point discrete Fourier transform to each pulse hit direction of the distance folded 0 pulse hit signal, the distance folded 1 pulse hit signal, and the distance folded N-1 pulse hit signal obtained by the ambiguity combining processor 12. Note that the L-point discrete Fourier transform is just an example, and other frequency analysis methods may also be used.

[0026] Next, the unique effects of the radar device according to this embodiment will be described with reference to Fig. 5 and Fig. 8 to Fig. 10. Here, Fig. 8 is a diagram showing the basic configuration of a coded pulse radar device, Fig. 9 is a diagram showing the sequence of transmission signals in the coded pulse radar device shown in Fig. 8, and Fig. 10 is a diagram explaining distance ambiguity in the coded pulse radar device shown in Fig. 8.

[0027] First, the basic configuration of the coded pulse radar device is as shown in Figure 8, and does not include the interval modulation unit 11 shown in Figure 1, nor does the distance and Doppler frequency measurement unit 101 include the ambiguity combining unit 12 shown in Figure 1. Furthermore, the correlation unit 6 does not include the code sequence 1 correlation unit 61, code sequence 2 correlation unit 62, ..., code sequence N correlation unit 6 shown in Figure 1. N The frequency analysis unit 7 is not provided with a distance folding 0 frequency analysis unit 71, a distance folding 1 frequency analysis unit 72, ..., a distance folding N-1 frequency analysis unit 7 N is not provided.

[0028] An example of a transmission signal sequence when using the coded pulse radar device shown in FIG. 8 is shown in FIG. 9. In the example of FIG. 9, a code sequence with L codes and a bandwidth B per code (time width of 1 / bandwidth B) is transmitted P times per observation period. In the case of FIG. 9, a "distance ambiguity" occurs, as explained in the background art section. FIG. 10 shows an example of a range ambiguity. As shown in the figure, when target 1 and target 2 exist within a time delay of 1PRI and 2PRI, respectively, the code sequence applied to the transmitted pulse is the same for each PRI, so it may be impossible to identify which code sequence is reflected by target 2. In such a case, the distance R1 can be measured correctly for target 1, but the distance to target 2 is an apparent distance R2-Rpri. In other words, a distance ambiguity occurs in the distance measurement of target 2, resulting in an incorrect measurement.

[0029] In contrast, with the radar device according to this embodiment, as shown in Fig. 5, even when target 1 is located at a point with range wrap 0, target 2 is located at a point with range wrap 1, and target 3 is located at a point with range wrap N-1 (where range ambiguity occurs for both targets 2 and 3), it is possible to suppress the range ambiguity and measure the distances to targets 2 and 3. Note that Fig. 5 illustrates an example in which the target has two range wraps, but the range of the target's range wrap can be identified in the range from 0 to N-1, and is not limited to the range shown in the example of Fig. 5.

[0030] Therefore, in the radar device according to this embodiment, the distance where distance ambiguity does not occur (non-occurrence distance) is extended by several times the number of code sequences (N times in the example of this embodiment) compared to the distance where distance ambiguity does not occur in a conventional coded pulse radar device. If the distance where distance ambiguity does not occur in the radar device according to this embodiment is Rmax, it can be expressed as follows using the speed of light c:

[0031] Rmax=(c / 2)·PRI·N

[0032] Finally, the accompanying effects of the radar device of this embodiment will be described with reference to Figures 6, 7, 11, and 12. Figure 6 is a diagram explaining why transmission blindness is eliminated in the radar device of this embodiment, and schematically shows the timing of sending a transmission signal and the timing of receiving a reception signal. Figure 7 is a diagram showing the received power in the case of Figure 6, showing the relationship between the received power and the distance. Meanwhile, Figure 11 is a diagram explaining why transmission blindness occurs in the coded pulse radar device shown in Figure 8. Figure 12 is a diagram showing the change in received power when transmission blindness occurs.

[0033] First, the coded pulse radar device shown in Figure 8 transmits the same pulse for each PRI, which can lead to a transmission blind situation where the target received power is zero during pulse transmission. In Figure 11, "0 Delay," "1 Delay," "2 Delay," "3 Delay," "4 Delay," "5 Delay," ... "PRI Delay" indicate the reception status corresponding to the target distance from the transmitted pulse. For example, at positions that are integer multiples of the PRI, such as "0 Delay" and "PRI Delay," the position of the transmitted pulse and the position of the received pulse coincide, resulting in a received power of zero. On the other hand, for "4 Delay" and "5 Delay," the position of the transmitted pulse and the position of the received pulse do not overlap, so the received power over the three PRI intervals is 12 (= 4 × 3). Note that the same calculation can be performed for "1 Delay," "2 Delay," and "3 Delay."

[0034] Figure 12 shows a waveform plotting the received power shown on the right side of Figure 11. As indicated by the black circles in the figure, transmission blindness occurs at distances equivalent to integer multiples of PRI (Rpri, 2·Rpri, ..., (N-1)·Rpri, N·Rpri). In other words, with the coded pulse radar device shown in Figure 8, the received power becomes 0 at positions that are integer multiples of PRI, making it impossible to detect targets.

[0035] In contrast, in the radar device according to this embodiment, the interval modulation unit 11 performs interval modulation between codes, thereby eliminating the transmission blindness at each PRI interval. In FIG. 6, for example, at "1 delay," the 10 received pulses shown by hatching do not overlap with the transmitted pulses, making reception possible. Below, for "2 delay," "3 delay," "4 delay," "5 delay," and "PRI delay," received pulses that do not overlap with the transmitted pulses are also shown by hatching, and the received power is the value shown on the right. FIG. 7 is a waveform plotting the received power shown on the right side of FIG. 6. As indicated by the black circles in FIG. 7, the transmission blindness at each PRI interval is eliminated. Therefore, with the radar device according to this embodiment, the received power does not become zero even at intervals that are integer multiples of the PRI, making it possible to detect targets.

[0036] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, and parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0037] 1 code generation unit, 2 transmitter, 3 antenna, 4 receiver, 5 A / D converter, 6 correlation unit, 61 code sequence 1 correlation unit, 62 code sequence 2 correlation unit, 6 N Code sequence N correlation unit, 7 Frequency analysis unit, 71 Distance folding 0 Frequency analysis unit, 72 Distance folding 1 Frequency analysis unit, 7 N Distance folding N-1 frequency analysis unit, 11 interval modulation unit, 12 ambiguity coupling processing unit, 100, 101 distance and Doppler frequency measurement unit.

Claims

1. A radar device that continuously transmits a plurality of transmission pulses into space and sequentially receives reflected signals from a target to measure the distance to the target and the Doppler frequency, a code generator for generating a basic code; an interval modulation unit that modulates the intervals of the codes generated by the code generation unit to generate N code sequences (N is an integer of 2 or more) that are uncorrelated with each other; a transmitter that up-converts and amplifies the code sequence generated by the interval modulation unit and generates a transmission signal for emitting M code-modulated transmission pulses (M is an integer equal to or greater than N) per pulse repetition period per observation time; an antenna that radiates the transmission signal generated by the transmitter into space; a receiving section that receives reflected waves from a target, detects the received signals, and converts them into analog video signals; an analog-to-digital converter that converts the analog video signal converted by the receiver into a digital video signal; a distance and Doppler frequency measurement unit that generates a pulse hit signal containing distance information for each time delay by correlation processing between the digital video signal and the reference function using the code sequence generated by the interval modulation unit as a reference function, and measures the distance to a target and the Doppler frequency based on the generated pulse hit signal; Equipped with The distance and Doppler frequency measurement unit a correlation unit that generates the pulse hit signal; an ambiguity combining processor that rearranges the outputs of the correlation processor for each distance folding; a frequency analysis unit that performs frequency analysis on the distance folded pulse hit signal output from the ambiguity coupling processing unit; A radar device comprising:

2. The correlation unit 2. The radar device according to claim 1, wherein each code sequence from the first pulse to the Nth pulse generated by the interval modulation unit is used as a reference signal, and target detection processing is performed for each pulse by calculating the correlation between the reference signal and the received signal at the corresponding pulse.

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