JP2018105769A - Rader system and radar signal processing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To observe a target speed and distance while ensuring LPI property. A radar apparatus according to an embodiment uses a pulse train modulated by an encoded or random signal, divides an observation time axis into a CW period and a ranging period, and converts an Mcw (Mcw ≧ 1) chip into Mcwall (Mcwall) in the CW period. ≧ 2) Transmits a pulse train signal modulated by a signal repeated repeatedly, transmits a pulse train signal modulated by a Mrng (Mrng ≧ 2) chip in the ranging period, and reflects from the target in the CW period and the ranging period, respectively. The pulse train signal to be received is received. The target speed is calculated using the received signal of the CW period, the reference signal is corrected based on the calculated target speed, the range of the received signal of the ranging period is compressed using the corrected reference signal, and the reference signal is corrected. Calculate the target distance. [Selection] Figure 1

Description

  The present embodiment relates to a radar apparatus that calculates a target distance and velocity and a radar signal processing method thereof.

  As an LPI (Low Probability of Intercept) radar apparatus that lowers the detectability, there is a radar system that performs encoding for each pulse and performs range compression using a reference signal (see Non-Patent Document 1). However, this method is not correctly compressed unless the Doppler component due to the target speed is corrected, and a compression loss occurs when the target speed is unknown. For this reason, it is necessary to correct the reference signal by the speed search method, and there is a problem that the processing scale increases. A method of observing the target velocity with a single pulse train without using encoding and correcting the reference signal of the transmission / reception signal by the coding code using the observation result is also conceivable, but the LPI property is low with a single pulse train. There was a problem.

Encoding radar, Yoshida, 'Revised radar technology', IEICE, pp.278-280 (1996) Code code (M-sequence) generation method, M.I.Skolnik, Introduction to radar systems, pp.429-430, McGRAW-HILL (1980) BPSK, QPSK, Nishimura, Communication system design by digital signal processing, CQ Publisher, pp.222-226 (2006) SS (Spread Spectrum) modulation, Marubayashi, spread spectrum communication and its applications, IEICE, pp.1-18 (1998) CFAR (Constant False Alarm Rate) processing, Yoshida, "Revised Radar Technology", IEICE, pp.87-89 (1996) MIMO (Multiple-Input and Multiple-Output), JIAN LI, PETER STOICA, ‘MIMO RADAR SIGNAL PROCESSING’, WILEY, pp.1-5 (2009) Pattern shaping by phase, Robert C. Voges, ‘Phase Optimization of Antenna Array Gain with Constrained Amplitude Excitation’, IEEE Trans. Antennas & Propagation, AP-20, No.4, pp.432-436, (1972)

  As described above, in a radar apparatus that employs an encoding method to obtain LPI characteristics, if range compression is performed when the target speed is unknown, a compression loss occurs. Therefore, the reference signal based on the target speed search method is used. There is a problem that the processing scale increases. The technique of correcting the reference signal of the transmission / reception signal by the coding code from the observation result of the target speed by the single pulse train has a problem that the LPI property is low.

  The present embodiment has been made in view of the above problems, and an object thereof is to provide a radar apparatus and a radar signal processing method thereof capable of observing a target speed and distance while ensuring LPI performance.

  In order to solve the above-described problem, according to the present embodiment, in a radar apparatus using a pulse train that is encoded or modulated by a random signal, an observation time axis is divided into a CW (Continuous Wave) period and a ranging period, and the CW A pulse train signal modulated by a signal that repeats Mcw (Mcw ≧ 1) chips for Mcwall (Mcwall ≧ 2) times in the period, and a pulse train signal modulated by the Mr chip in the ranging period, and the CW period and Receiving a pulse train signal reflected from the target in each ranging period, calculating the target speed using the received signal in the CW period, correcting a reference signal according to the calculated target speed, and the ranging period The target distance is calculated by subjecting the received signal to range compression using the corrected reference signal. That is, since the CW period and the ranging period are encoded and used to calculate the speed, the reference signal is corrected by the speed and the range is compressed, so that the target speed and distance can be set while ensuring the LPI property. It can be observed.

1 is a block diagram showing a schematic configuration of a radar apparatus according to a first embodiment. FIG. 3 is a timing diagram illustrating transmission pulse timings and modulation code examples of the transmission pulses in the first embodiment. The timing diagram which shows the received signal after a correlation process in 1st Embodiment. The conceptual diagram which shows a mode that the range-Doppler data at the time of performing FFT between PRI for every range cell in PRI in 1st Embodiment. The block diagram which shows schematic structure of the radar apparatus which concerns on 2nd Embodiment. The figure which shows an example of the modulation pulse of a transmission signal, and a spreading code in 2nd Embodiment. The figure which shows a transmission signal, a received signal, and a Doppler extraction result in 2nd Embodiment. The block diagram which shows schematic structure of the radar apparatus which concerns on 3rd Embodiment. The figure which shows an example of the modulation pulse of a transmission signal, and a spreading code in 3rd Embodiment. The figure which shows a transmission signal, a received signal, and a Doppler extraction result in 3rd Embodiment. The block diagram which shows schematic structure of the radar apparatus which concerns on 4th Embodiment. The figure which shows the coordinate system in the case of the radar for mounting in 4th Embodiment. The figure which shows a mode that a clutter is suppressed with a speed filter in 4th Embodiment. The block diagram which shows the structure of a transmission system in 5th Embodiment. The block diagram which shows the structure of a receiving system in 5th Embodiment. The figure which shows the conceptual system of MIMO in 5th Embodiment. The figure which shows the coordinate system in the case of the radar for mounting in 5th Embodiment. The figure which shows the outline | summary of the system which makes the transmission phase between subarrays pseudorandom, and does not form a transmission beam in a specific direction in 5th Embodiment. The figure which shows the outline | summary of the system which orient | assigns a transmission beam to predetermined directions, such as a target direction, in 5th Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. In the description of each embodiment, the same portions are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
The radar apparatus according to the first embodiment will be described with reference to FIGS. 1 to 4.

  FIG. 1 is a block diagram showing a schematic configuration of a radar apparatus according to the first embodiment, FIG. 2 is a timing diagram showing transmission pulse timings and modulation code examples of each transmission pulse, and FIG. 3 is the same embodiment. FIG. 4 is a conceptual diagram showing how range-Doppler data is obtained when FFT between PRIs is performed for each range cell in the PRI.

  As shown in FIG. 1, a radar apparatus according to this embodiment includes an antenna 1 that forms a transmission / reception beam by a plurality of antenna elements, and a transmitter / receiver 2 that transmits a transmission signal through the antenna 1 and receives a reflection signal from a target. And a signal processor 3 for observing the target speed and distance from the received signal obtained by the transceiver 2.

  The transmitter / receiver 2 includes a transmitter / receiver 21, a frequency converter 22, an AD converter 23, a modulator 24, and a controller 25. The modulation unit 24 modulates the transmission pulse train with the encoded code generated by the control unit 25. The transmission / reception unit 21 transmits a modulated transmission pulse toward a target through a transmission beam formed by a plurality of antenna elements of the antenna 1, and synthesizes a reflected signal from the target captured by each antenna element of the antenna 1. And receive detection. The frequency conversion unit 22 converts the reception signal of the transmission / reception unit 21 into baseband. The AD conversion unit 23 converts the baseband received signal into a digital signal and outputs it as received data to the signal processor 3.

  The signal processor 3 includes a CW period speed output unit 31, a range compression processing unit 32, a reference signal generation unit 33, a CFAR processing unit 34, and a distance extraction unit 35. The CW period speed output unit 31 divides the pulse train processing period into a CW period and a ranging period, and calculates a target speed in the CW period. The range compression processing unit 32 performs range compression using the reference signal generated by the reference signal generation unit 33. The CFAR processing unit 34 performs threshold detection for the range compressed signal. The distance extracting unit 35 extracts the target distance by converting the time axis of the threshold-detected signal to the distance axis.

  In the above configuration, the radar apparatus according to the present embodiment divides the pulse train processing period into a CW period and a ranging period, and calculates a target speed in the CW period. On the other hand, after performing range compression using the reference signal and performing threshold detection, the target distance is extracted by converting the time axis to the distance axis. At this time, the reference signal for compression is corrected using the target speed in the ranging period.

  2A shows an example of the timing of transmission pulses generated by the transceiver 2, and FIG. 2B shows an example of a modulation code (spread code in the figure) of each transmission pulse. Here, the pulse train is divided into a CW period and a ranging period, a target speed is calculated in the CW period, and a distance is measured by correcting a reference signal for compression using the target speed in the ranging period. Although FIG. 2 shows the case of single pulse transmission as an example, other methods may be used.

  In the case of a single pulse train, code modulation is performed for each pulse. First, it is necessary to observe Doppler in the CW period. As shown in FIG. 2, Mcw × Mall pulses are modulated with the same code for each Mcw chip using the Mcw chip code, and repeated Mcwall times. In the ranging period in the case of HPRF, Mrng pulses are code-modulated using the code of the Mrng chip.

As an encoding method, SS modulation (Non-patent Document 4) is conceivable. Specifically, for example, there is an M-sequence code (Non-Patent Document 2) (other codes may be used). This encoding includes a random signal (noise) including a decimal number within ± 1. Further, the random signal is to make the phase random, and includes a method of modulating (frequency hopping) by changing the frequency, for example. In this case, if the local signal is the same and the frequency from the local signal is changed, the frequency can be changed while ensuring coherency. Using this signal code string, as shown in the following equation, the signal phase is changed to generate a transmission signal.

The above is the case of BPSK (Binary Phase Shift Keying, see Non-Patent Document 3), but other phase modulation methods may be used.

In the transmitter / receiver 2, the control unit 25 performs pulse modulation on the pulse train with a code code, frequency-converts the signal transmitted / received through the transmitter / receiver 21 and the antenna 1, and converts the signal into a digital signal by AD conversion. The state of this received signal is shown in FIG. In FIG. 3, (a) shows the transmission timing of the transmission pulse train, (b) shows the Doppler observation result of the received signal, and (c) shows the range observation result. Here, the reception signal of each reception pulse is given by the following equation.

This reception pulse train is a pulse train in which the Mcw chip signal is repeated Mcwall times as described above. In order to extract this Mcw chip signal, correlation processing is performed in the CW period. A reference signal for correlation processing is given by the following equation.

In order to match the reference signal with the received signal length, zero padding is performed.

Thus, the frequency axis signal of the reference signal is expressed by the following equation.

On the other hand, when the received signal is subjected to FFT processing, the following equation is obtained.

In the correlation processing, the frequency axis multiplication is inverse FFTed to obtain the following equation.

The received signal after this correlation processing corresponds to the result of integration for each Mcw chip, as shown in FIG. 3, and Mcwall peaks in the PRI (Mcw times the pulse repetition period of single pulse unit) period by the Mcw chip. Appears. Doppler signals can be detected by performing FFT processing on the Mall signals. For this purpose, as shown in FIG. 4A, for each range cell (P cell) in the PRI, an FFT between the PRIs (slow-time axis) is performed, and as shown in FIG. Get Doppler data. The target signal can be extracted from CFAR (see Non-Patent Document 5) or the like, and the speed can be output. When there are a plurality of targets, the speed of the plurality of targets can be obtained.

Next, a reference reference signal for performing correlation processing using the signal in the ranging period is generated. As the reference reference signal, the target speed output in the CW period is used.

The set standard reference signal length is Mrng. In order to make the code length (Mrng) the ranging period (FIG. 2) for the range compression process (correlation process), the reference signal is zero-padded.

In order to calculate the correlation between the reference signal and the input signal, the reference signal is subjected to FFT processing.

On the other hand, the received signal during the ranging period can be expressed by the following equation.

The received signal is subjected to FFT processing according to the following equation.

In the range compression process (correlation process), the result of multiplication on the frequency axis is subjected to inverse FFT processing as shown in the following equation.

This is shown in FIG. The target distance can be calculated by detecting the threshold of srng (t) by CFAR or the like and converting the time axis to the distance axis in the distance extraction. As for the speed, the result calculated from the data of the CW period is output.

  As described above, the radar apparatus according to the present embodiment performs observation using a single pulse signal using coding of a chip length of 1 or modulation by a random signal as a modulation pulse by coding or random signal (noise). The time axis is divided into a CW period and a ranging period, a transmission signal is transmitted by a pulse train modulated by a signal that repeats Mcw (Mcw ≧ 1) chips Mcwall times in the CW period, and the speed is received using the signal that has received the reflection from the target In the ranging period, a signal modulated by the Mrng chip is transmitted, and the range is compressed using the signal that has received reflection from the target and the reference signal corrected by the observation speed, and the distance is output. That is, since encoding is used for both the CW period and the ranging period and the speed is calculated and the reference signal is corrected by the speed and the range is compressed, the target speed and distance can be observed while ensuring the LPI property.

(Second Embodiment)
The radar apparatus according to the second embodiment will be described with reference to FIGS. FIG. 5 shows the entire system, FIGS. 6 (a) and 6 (b) show examples of modulation pulses and spreading codes of transmission signals, and FIGS. 7 (a), (b) and (c) show transmission signals, The received signal and Doppler extraction result are shown.
In the first embodiment, the observation time is divided into a CW period and a ranging period, a target speed is calculated in the CW period, and the target distance is output in the ranging period using a reference signal corrected by the target speed. The method of using a single pulse has been described. In this case, since the ranging period also becomes a transmission signal having a relatively high repetition period (PRF), target non-detection due to transmission blinds may occur even at a long distance. As a countermeasure, in this embodiment, as shown in FIG. 5, a case where a mixed pulse of a single pulse and a long pulse is used in the modulation unit 24a and the control unit 25a will be described.

  The CW period is the same as in the first embodiment. In the ranging period, a plurality of pulses having a predetermined pulse width are transmitted. If the chip length of the divided pulse in this case is Mrng, a Mrng M-sequence signal of the entire pulse train is generated, divided by the pulse length, and sequentially modulated. For this reason, each pulse has a different sign.

  As shown in FIG. 7, the correlation process over the entire pulse train is performed using the reference signal corrected by the speed of the CW period. Since this method only replaces the single pulse train of the first embodiment with a long pulse train, the same method as that of the first embodiment can be applied. The correlation processing result is detected by CFAR as shown in FIG. 7C, and the target distance can be output by converting time into distance. As for the speed, the result calculated from the data of the CW period is output. In particular, by increasing the PRI (pulse repetition period) of the ranging period, it is possible to suppress target non-detection due to a long-distance transmission blind.

  As described above, the radar apparatus according to the present embodiment uses the single pulse using the coding of the chip length 1 or the modulation by the random signal in the CW period, and encodes Mcw (Mcw ≧ 2) in the ranging period. Alternatively, N (N ≧ 1) pulses are transmitted and received using a pulse modulated by a random signal, and range compression is performed using an encoded signal over the entire pulse train. That is, by using a single pulse encoded in the CW period and using a pulse encoded in the ranging period, the reference signal is corrected by the speed and the range is compressed after the speed is calculated. , Speed and distance can be observed.

(Third embodiment)
A radar apparatus according to the third embodiment will be described with reference to FIGS. FIG. 8 shows the entire system, FIGS. 9 (a) and 9 (b) show examples of transmission signal modulation pulses and spreading codes, and FIGS. 10 (a), (b) and (c) show transmission signals, The received signal and the Doppler extraction result are shown.
In the first and second embodiments, the observation time is divided into a CW period and a ranging period, a target speed is calculated in the CW period, and range compression is performed using a reference signal corrected by the target speed in the ranging period. Then, the method of outputting the target distance was described. In that case, the first embodiment has described the case of a single pulse, and the second embodiment has described the case of a single pulse and a long pulse. Here, in the case of repetition by a single pulse, since there is a gap between pulses, the interval between Mcw chips is widened, and the Doppler velocity range thereby narrows. On the other hand, in the ranging period, if the sum of the pulse widths is not sufficiently long, the code length may be shortened and the range side lobe may not be sufficiently reduced. As a countermeasure, in this embodiment, as shown in FIG. 8, the modulation unit 24b and the control unit 25b use long pulses for both the CW period and the ranging period.

  That is, in this embodiment, the CW period is also a long pulse, and in order to observe Doppler, the long pulse is divided into Mcwall pieces, and each is modulated by a spreading code of a common Mcw chip. The method of extracting the Mcw chip signal is the same as in the CW period of the first embodiment. That is, it is possible to generate a reference signal in units divided into Mcwall, obtain Mcwall peak output using the reference signal, and calculate the target speed by FFT.

  In the ranging period, one long pulse is transmitted. In the pulse modulation, an M-sequence signal having a code length Mrng over the entire pulse train is generated and modulated. As shown in FIG. 10, the received signal performs correlation processing over the entire pulse train in the ranging period using the reference signal corrected by the speed of the CW period, extracts the target signal, and outputs the distance. The speed is output as a result calculated in the CW period.

  Compared with the second embodiment, in this embodiment, the interval of the correlation output result in the CW period is a code length Mcw without a gap between pulses, which is narrower than the repetition of a single pulse, and is determined by the reciprocal of the interval. The observation speed range can be widened. Further, since the pulses in the ranging period are long, a high correlation output can be obtained and the range side lobe can be easily lowered. On the other hand, reception may occur during the pulse transmission period, requiring simultaneous processing of transmission and reception. In the case of a multistatic system in which transmission and reception are separated, this method is particularly easy to apply.

  As described above, the radar apparatus according to the present embodiment is configured to repeat Mcw (Mcwall ≧ 2) times of the pulse using the coding of the chip length Mcw (Mcw ≧ 2) or the modulation by the random signal in the CW period. A Mcwall chip length pulse is transmitted and received, and a pulse having a chip length Mr (Mr ≧ 2) is transmitted and received during the ranging period, and the range is compressed by an encoded signal over the entire pulse train. That is, by using encoded pulses with a long code length in both the CW period and the ranging period, the reference signal is corrected by the speed and the range is compressed after calculating the speed. The target speed and distance can be observed with a wide signal with a low range side lobe.

(Fourth embodiment)
A radar apparatus according to the fourth embodiment will be described with reference to FIGS. 11 to 13. FIG. 11 shows the entire system, FIG. 12 shows a coordinate system in the case of an on-board radar, and FIG. 13 shows how clutter is suppressed by a speed filter.

  In the above embodiment, when calculating the target speed in the CW period, clutter may be included, and when the detection by the CFAR process is performed, a correct target signal may not be extracted. In this embodiment, the countermeasure is described.

  That is, in the radar apparatus of this embodiment, the CW period speed output unit 31a shown in FIG. 11 performs target speed extraction after suppressing clutter by a filter in a predetermined speed range. As the predetermined speed range, for example, in the case of an on-board radar, if the own speed is V, the speed range of the clutter can be calculated by the following equation. Therefore, if a range other than that range is selected, the clutter can be suppressed. Here, the clutter speed is calculated based on the coordinate system shown in FIG.

First, the vector of the clutter reflection point in the directions of the angles θAZ and θEL with the own machine as the origin is expressed by the following equation: (X, Y, Z).

Next, the velocity vector of the clutter when the own aircraft flies along the Y axis is as follows.

The radial velocity vector Vc toward the clutter's own machine is the inner product of the direction cosine of the clutter coordinate and Vf, and is given by the following equation.

  Centering on this speed Vc, as shown in FIG. 13, the Doppler frequency corresponding to the range of Vc ± ΔV is suppressed. After calculating the target speed, it is omitted because it is the same as in the first to third embodiments.

  As described above, in the radar apparatus according to the present embodiment, when calculating the target speed in the CW period, the speed range of the clutter is calculated from the own machine speed, and the target speed is calculated by the filter output that suppresses the speed. . That is, the clutter speed is estimated based on the own machine speed and is suppressed using a speed filter, thereby calculating the speed of the target signal and correcting the reference signal with the speed to compress the range. Speed and distance can be observed.

(Fifth embodiment)
A radar apparatus according to the fifth embodiment will be described with reference to FIGS. 14 and 19. 14 shows the configuration of the transmission system, FIG. 15 shows the configuration of the reception system, FIG. 16 shows the conceptual system of MIMO, FIG. 17 shows the coordinate system, and FIG. 18 shows the transmission phase between the subarrays as pseudo-random. An outline of a system that does not form a transmission beam in a specific direction is shown, and FIG. 19 shows an outline of a system that directs a transmission beam to a predetermined direction such as a target direction.

  In the transmission system shown in FIG. 14, the antenna 1 includes N transmission subarrays (antenna element L systems) 11 to 1N, and the transceiver 2 includes transmission modules 2T1 to 2TN and a controller 25. The transmission module 1T1 (same for other transmission modules) modulates the transmission pulse by the modulator 241, converts the frequency to the RF band by the local signal from the local signal generator 2121 by the frequency converter 2111, and then power divider 2131. Then, power is distributed to the L system, and each distribution output is phase-shifted by the transmission phase shifter 2141 in accordance with the beam forming instruction, power is amplified by the transmission amplifier 2151, and is transmitted from the antenna element 111 to the space. The controller 25 performs modulation control of the modulator 241 of each system, local signal generation control of the local signal generator 2121, and phase shift amount control of the transmission phase shifter 2141 according to the transmission operation instruction.

  In the reception system shown in FIG. 15, signals received by M reception subarrays (antenna element L systems) 11 to 1M are input to M reception modules 2R1 to 2RM. The reception module 2R1 (same for other reception modules) amplifies the L-system antenna element output by the reception amplifier 2161 with low noise, shifts the phase by the phase shift amount based on the reception beam formation by the reception phase shifter 2171, The combiner 218 performs power combining. The synthesized received signal is converted to baseband by the frequency converter 221 based on the local signal generated by the local signal generator 2121 and converted to a digital signal by the AD converter 231 to convert the received signal for each system into data. The data is stored in the data storage unit 311. Here, the CW period processing unit 312 sends N-system received signals in the CW period to the beam former 313 to form a search beam, and the CFAR processing unit 34 acquires a target signal exceeding the threshold. At this time, first, the target speed is calculated by the speed detection unit 351 (1), the reference signal generated by the reference signal generation unit 331 is adjusted based on the calculated speed, and the range period processing unit 321 performs compression processing. A range period is adjusted, a reception beam is formed in a target direction by the beam former 313, a distance is calculated by the range extraction unit 352 for the target detected by the CFAR processing unit 34 (2), and a speed calculated by the speed extraction unit 351 is calculated. And output.

  In other words, the first to fourth embodiments are methods in which the target speed is extracted in the CW period, and then correlation processing is performed in the ranging period using the reference signal corrected by the target speed, thereby performing distance measurement. If this method is applied to MIMO (see Non-Patent Document 6), the LPI property can be further improved.

  In this embodiment, from FIG. 16, MIMO transmits transmission Nch by transmission modulation with isolation, reception is received by Mch, branches to Mch for each ch, and is demodulated by transmission modulation signals. , N × Mch digital signals are obtained and array-synthesized to form a beam. Since the transmission / reception signal is DBF (Digital Beam Forming), an arbitrary transmission / reception beam can be formed within the range of the transmission subarray pattern and the reception subarray pattern.

  In order to realize MIMO, isolation between transmission channels is necessary. For this reason, a different code or random signal is used for each transmission Mch. The CW period and the ranging period are the same as those in the first to fourth embodiments.

  Specifically, as shown in FIG. 15, the reception digital signal is stored (311) for each of the reception subarrays 11 to 1M, and the data of the CW period process (312) is used in the first process (1). The reference signal is generated using the speed by beam forming (313), CFAR processing (34), speed extraction (351), and reference signal generation (331). In the second process (2), the data of the range period process (321) is extracted from the stored data, the range correlation process is performed, the beam is synthesized by the beam forming (313), and the target is detected by the CFAR (34). Then, the distance is extracted and output by range extraction (352).

In order to embody the beam forming technique by MIMO, the following formula is formulated with reference to the coordinate system of FIG. First, regarding transmission and reception, if a sub-array after analog synthesis is generally used, a transmission signal and a reception signal are expressed by the following equations.

From this, each element becomes the following equation.

Next, when each transmission / reception subarray signal is expressed by a matrix element, the following equation is obtained.

The transmission / reception beam output is obtained by multiplying the element of equation (22) by the weight for reducing the side lobe and the weight for reducing the side lobe, and adding the result as follows.

  The above is a general beam forming method by MIMO. The feature of MIMO is that the transmission / reception subarrays can be digitally controlled using the complex weight Wnm as shown in the equation (23), so that the phase between the transmission subarrays can be set arbitrarily if known. In the subarray, in order to cover a predetermined observation range, the transmission phase directed in a predetermined direction is set by the transmission phase shifter 2141, but the phase between the transmission subarrays can be freely set. In the present embodiment, a technique for improving LPI (Low Probability of Intercept) using this characteristic will be described.

First, as shown in FIG. 18, a method in which the transmission phase between subarrays is pseudo-random and a transmission beam is not formed in a specific direction will be described. If the transmission phase is Φ, the complex weight Wnmcal of the equation (23) when forming the MIMO beam in the reception system may be expressed by the following equation.

  By making the transmission phase pseudo-random, it does not have directivity in all directions, and is difficult to be detected by the target. Therefore, for example, a target having a small RCS (radar reflection cross-sectional area) can be easily detected with a high SN (signal to noise power) due to the integration effect by transmitting and receiving for a long time in a state where it is difficult for the other party to detect. become.

As another method for improving the LPI property, as shown in FIG. 19, there is a method in which a transmission beam is directed toward a predetermined direction such as a target direction. The predetermined direction may be the target direction when the radar transmission to the target cannot be detected. As a method for controlling the transmission phase, considering only the phase shifter, for example, the phase of the following equation may be set (see Non-Patent Document 7).

The set transmission phase is corrected as a phase on the transmission side at the time of reception processing using Wnmcal of the equation (23) in the beam former 13.

  As described above, the LPI property by the transmission beam can be further enhanced by the MIMO beam forming using the first to fourth embodiments.

  As described above, the radar apparatus according to the fifth embodiment uses Nt (Nt ≧ 2) encoded sequences or random signal sequences in a radar using encoding or modulation by random signals, and uses Nt elements ( Nr (Nr ≧ 1) elements (subarrays) are received and Nt × Nr elements (subarrays) transmission / reception signals are calculated and processed. That is, the LPI property can be further improved by randomizing the transmission phase or directing null in the observation direction using a transmission / reception DBF by MIMO (Multiple-Input Multiple-Output).

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... Antenna, 2 ... Transmitter / receiver, 3 ... Signal processor, 21 ... Transmitter / receiver, 22 ... Frequency converter, 23 ... AD converter, 24, 24a, 24b ... Modulator, 25, 25b ... Controller, 31, 31a ... CW period speed output unit, 32 ... range compression processing unit, 33 ... reference signal generation unit, 34 ... CFAR processing unit, 35 ... distance extraction unit, 11-1N ... N transmission subarrays, 2T1-2TN ... transmission module 2R1-2RN: reception module, 241 ... modulator, 2111 ... frequency converter, 2121 ... local signal generator, 2131 ... power divider, 2141 ... transmission phase shifter, 2151 ... transmission amplifier, 2161 ... reception amplifier, 2171 ... reception phase shifter, 218 ... power combiner, 2121 ... local signal generator, 221 ... frequency converter, 231 ... AD converter, 311 ... data storage unit, 3 2 ... CW period processing unit, 313 ... beamformer, 352 ... range extraction unit, 351 ... speed extractor.

Claims (7)

A radar apparatus using a pulse train modulated by an encoded or random signal,
The observation time axis is divided into a CW (Continuous Wave) period and a ranging period, and a pulse train signal modulated by a signal that repeats Mcw (Mcw ≧ 1) chips Mcwall (Mcwall ≧ 2) times in the CW period is transmitted. Transmitting and receiving means for transmitting a pulse train signal modulated by a Mrng (Mrng ≧ 2) chip in a period and receiving a pulse train signal reflected from the target in each of the CW period and the ranging period;
The target speed is calculated using the received signal of the CW period, the reference signal is corrected based on the calculated target speed, the range of the received signal of the ranging period is compressed using the corrected reference signal, and the reference signal is corrected. A radar apparatus comprising: signal processing means for calculating a target distance.   2. The radar apparatus according to claim 1, wherein the transmission / reception unit uses a single-pulse signal that uses encoding of a chip length of 1 or modulation by a random signal for the transmission pulse train in the CW period and the ranging period.   In the CW period, the signal processing unit uses a single pulse using coding of a chip length of 1 or modulation by a random signal, and coding of a chip length Mcw (Mcw ≧ 2) or a random signal in the ranging period. The radar apparatus according to claim 1, wherein N (N ≧ 1) pulses are transmitted and received using modulation, and range compression is performed by an encoded signal over the entire pulse train.   The signal processing means transmits and receives a pulse train of Mcw × Mcwall chip length in which a pulse using coding of a chip length Mcw (Mcw ≧ 2) or modulation using a random signal is repeated Mcwall (Mcwall ≧ 2) times during the CW period. The radar apparatus according to claim 1, wherein during the ranging period, a pulse train having a chip length Mrng (Mrng ≧ 2) is transmitted and received, and range compression is performed using an encoded signal over the entire pulse train.   2. The signal processing unit according to claim 1, wherein, when calculating the target speed in the CW period, the speed range of the clutter is calculated from the speed of the mounted machine, and the target speed is calculated by a filter output that suppresses the speed. Radar device.   It is used in a radar apparatus using a pulse train modulated by the encoding or random signal, and transmitted from a sub-array of Nt elements using Nt (Nt ≧ 2) pulse trains, and in a sub-array of Nr (Nr ≧ 1) elements. The radar apparatus according to claim 1, wherein the radar apparatus receives a signal, calculates a transmission / reception signal of a sub-array using Nt × Nr elements, and forms and processes a predetermined antenna beam. Used in radar devices that use pulse trains that are encoded or modulated by random signals,
The observation time axis is divided into a CW (Continuous Wave) period and a ranging period, and a pulse train signal modulated by a signal that repeats Mcw (Mcw ≧ 1) chips Mcwall (Mcwall ≧ 2) times in the CW period is transmitted. In a period, a pulse train signal modulated by a Mrng (Mrng ≧ 2) chip is transmitted, and a pulse train signal reflected from the target in each of the CW period and the ranging period is received,
The target speed is calculated using the received signal of the CW period, the reference signal is corrected based on the calculated target speed, the range of the received signal of the ranging period is compressed using the corrected reference signal, and the reference signal is corrected. A radar signal processing method of a radar apparatus for calculating a target distance.

Images