Pulse compression radar device and radar signal processing method

Abstract

To make it possible to observe a target with high resolution and high accuracy even in a blind range caused by a transmission pulse.SOLUTION: According to an embodiment, a pulse compression radar device modulates inside a transmission pulse with a reference signal when transmitting and receiving the transmission pulse. Within a blind range determined by a transmission pulse width, the pulse compression radar device performs conjugate-multiplication of a range frequency reception signal which is obtained by padding a reception signal with zeros and converting it to a range frequency axis and a range frequency reference signal which is obtained by converting the reference signal to a range frequency, performs range high-resolution processing such as a range axis KR product using a result of the conjugate-multiplication, and detects targets within the blind range from a result of the processing. Outside the blind range, the pulse compression radar device detects targets using the result of conjugate multiplication without range high-resolution processing, and applies range high-resolution processing such as KR product processing to the result of conjugate multiplication at the range frequency of the reception signal and the reference signal, thereby reducing an impact of reduced range resolution in the blind range.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This embodiment relates to a pulse compression radar device and a radar signal processing method thereof.

Background Art

[0002] In a pulse compression radar device, when transmitting and receiving a transmission pulse, since the inside of the transmission pulse is modulated by a predetermined modulation signal, a transmission blind spot occurs where the reception system saturates within a distance (range) determined by the transmission pulse width from the transmission position. For this reason, in a conventional pulse compression radar device, pulse compression processing is performed except for the range where the transmission blind spot occurs (hereinafter, the blind range). However, when the transmission pulse width is long, the blind range becomes wide, and there is a problem that a short-range target cannot be observed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, in the conventional pulse compression radar apparatus, since the pulse compression process is performed except for the blind range, when the transmission pulse width is long, the blind range becomes wide and there is a problem that a short-range target cannot be observed.

[0006] The problem of the present embodiment is to provide a pulse compression radar apparatus and a radar signal processing method thereof that can observe a target with high resolution and high accuracy even in the blind range regardless of the length of the transmission pulse width.

Means for Solving the Problems

[0007] In order to solve the above problems, a first embodiment is a pulse compression radar device that modulates the inside of a transmission pulse with a reference signal when transmitting and receiving the transmission pulse. Within a blind range determined by the transmission pulse width, a range frequency reception signal obtained by padding zeros to a reception signal and converting it to a range frequency axis and a range frequency reference signal obtained by converting the reference signal to a range frequency are conjugate multiplied, and using the conjugate multiplication result, range high-resolution processing such as a range axis KR product is performed, a target within the blind range is detected from the processing result, and outside the blind range, a target is detected using a conjugate multiplication result without performing range high-resolution processing.

[0008] That is, according to the first embodiment, by applying range high-resolution processing such as a KR product process to the conjugate multiplication result in the range frequency of the reception signal and the reference signal, the influence of the reduction in the range resolution of the blind range is reduced.

[0009] Further, a second embodiment is a pulse compression radar device that modulates the inside of a transmission pulse with a reference signal when transmitting and receiving the transmission pulse. Within a blind range determined by the transmission pulse width, a range frequency reception signal obtained by padding zeros to a reception signal and converting it to a range frequency axis and a range frequency reference signal obtained by converting the reference signal to a range frequency are conjugate multiplied, and using the conjugate multiplication result, a target is temporarily detected within the blind range by CFAR or the like. Based on the range of the temporarily detected target cell, a pulse width τ other than zero padding of the reception signal is calculated, and by restricting the pulse width of the reference signal to the calculated pulse width τ, after restricting the pulse width and the band of the range frequency axis, range high-resolution processing such as a range axis KR product is performed, a target within the blind range is detected from the processing result, and outside the blind range, a target is detected using a conjugate multiplication result without performing range high-resolution processing.

[0010] That is, according to the second embodiment, after restricting the frequency band using the temporary detection result for the conjugate multiplication result in the range frequency of the reception signal and the reference signal, by applying range high-resolution processing such as a KR product process, the influence of the reduction in the range resolution of the blind range is reduced, and further, the range side lobe is reduced.

[0011] Further, in the third embodiment, in a pulse compression radar device that modulates a transmission pulse with a reference signal when transmitting and receiving the transmission pulse, within a blind range determined by the transmission pulse width, a range frequency received signal obtained by zero-padding a received signal and converting it to the range frequency axis and a range frequency reference signal obtained by converting the reference signal to the range frequency are conjugate multiplied, and using the conjugate multiplication result, among the received signals, a range frequency received signal obtained by zero-padding a signal within the blind range and converting it to the range frequency axis, and P (P ≧ 1) observation range ranges are set, pulse widths τ other than zero-padding of the received signals for P cases are calculated, and by restricting the pulse width of the reference signal to the calculated pulse width τ, range high-resolution processing such as range axis KR product is performed using a reference signal on the range frequency axis with restricted pulse width and range frequency axis band, a target within the blind range is detected from the processing result, and outside the blind range, a target is detected using a conjugate multiplication result without performing range high-resolution processing.

[0012] That is, according to the third embodiment, after eliminating the need for preliminary detection by setting a target distance within a predetermined observation range and selecting the target distance that is the maximum value of the conjugate multiplication result at the range frequency obtained by controlling the pulse width of the reference signal, by applying range high-resolution processing such as KR product processing, the influence of the reduction in the range resolution of the blind range is reduced, and further, the range side lobe is reduced.

[0013] Further, in the fourth embodiment, in any of the first to third embodiments, within the blind range, after detecting a target based on the result of performing range high-resolution processing such as range axis KR product, the range is output for the detected target using range axis monopulse processing, and outside the blind range, a target is detected using a processing result without performing range high-resolution processing.

[0014] That is, according to the fourth embodiment, after frequency band limiting the conjugate multiplication result at the range frequency of the received signal and the reference signal using the preliminary detection result, range high-resolution processing such as KR product processing is applied, thereby reducing the influence of the degradation of the range resolution in the blind range and the increase of the range side lobe. Further, range axis monopulse processing is used to reduce the degradation of range accuracy due to the spread of range cells.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

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Figure 12

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[0016] Hereinafter, embodiments will be described with reference to the drawings.

[0017] (First Embodiment) The first embodiment will be described with reference to FIGS. 1 to 6.

[0018] FIG. 1 is a block diagram showing the configurations of the transmission system and the reception system of the pulse compression radar apparatus according to the first embodiment.

[0019] In FIG. 1, in the transmission system, a reference signal generator 11 generates a reference signal for pulse compression (for example, a linear chirp signal), a signal generator 12 generates a transmission type signal, a modulator 13 modulates the transmission type signal with the reference signal, and the modulated signal is converted into a high-frequency signal in the radio frequency (RF) band (hereinafter, an RF signal) by a frequency converter 14. The RF signal is pulse-modulated by a pulse modulator 15 to generate a transmission pulse train at intervals of a pulse repetition interval (PRI), and is transmitted as a pulse signal from a transmission antenna 16.

[0020] On one hand, in the receiving system, the receiving antenna 17 receives the reflected wave of the pulse signal transmitted from the transmitting antenna 16, frequency-converts the received signal into an intermediate-frequency signal by the frequency converter 18, and converts it into a digital signal by the AD converter 19 to acquire data in units of range cells within the PRI. Subsequently, for the signal (data) output from the AD converter 19, after the zero-padding processor 20 pads the signal in the blind range of the fast-time axis with zeros, it is converted into a signal on the frequency axis by the fast-time axis FFT (Fast Fourier Transform) processor 21. Also, in the receiving system, after the reference signal generated by the reference signal generator 11 is converted into a signal on the frequency axis by the fast-time axis FFT processor 22, it is conjugate-multiplied by the conjugate multiplier 23 with the signal whose blind range has been zero-padded.

[0021] Here, the conjugate multiplication result is converted into a signal on the range axis by the fast-time axis inverse FFT processor 24, the signal outside the blind range is extracted by the out-of-blind-range extractor 25, and the target is detected by the target detector 26 using CFAR (see Non-Patent Document 3) or the like. Also, the conjugate multiplication result is input to the KR product processor 27 to apply range-axis KR product processing. After performing operations of square root of amplitude and Σ weight multiplication on the processing result by the square root of amplitude processor 28 and the Σ weight multiplier 29, it is converted into a signal on the range axis by the fast-time axis inverse FFT processor 30, the signal within the blind range is extracted by the in-of-blind-range extractor 31, and the target is detected by the target detector 32 using CFAR (see Non-Patent Document 3) or the like.

[0022] In the radar apparatus with the above configuration, with reference to FIGS. 2 to 6, the respective target detection processes within and outside the blind range will be described.

[0023] Figure 2 is a waveform diagram showing the target detection processing operation within the blind range in the first embodiment, Figure 3 is a waveform diagram showing the normal (outside the blind range) range compression processing operation in the first embodiment, and Figure 4 is a waveform diagram showing the range compression processing operation within the blind range in the first embodiment. Further, Figure 5 is a diagram showing the content of range high-resolution processing when range axis KR product processing is applied in the first embodiment, and Figure 6 is a waveform diagram showing the state of obtaining high-resolution range data by applying range axis KR product processing as extended array processing in the first embodiment.

[0024] First, regarding target detection within the blind range, it will be described with reference to Figure 2. Since it becomes blind within the transmission pulse as shown in Figure 2(a), normally, the signal on the fast-time axis at a distance beyond the blind range is extracted and pulse compression processing is performed. On the other hand, in this embodiment, even within the blind range, as long as the target distance is not 0, a part of the pulse width of the received pulse is outside the blind range as shown in Figure 2(b), so it is considered to detect that signal. Therefore, among the signals on the fast-time axis, for the blind range, since it is reception-saturated, zero-padding processing is performed as shown in Figure 2(c) to process the entire fast-time range. This will be formulated and described with reference to Figures 3 and 4.

[0025] Next, regarding the normal (outside the blind range) range compression processing (see Non-Patent Document 1), it will be described with reference to Figure 3. In Figure 3, (a1) is the received pulse on the fast-time axis (range time domain), (a2) is the reference signal on the fast-time axis, (b1) is the received pulse in the range frequency domain after fast-time axis FFT processing, (b2) is the reference signal in the range frequency domain after fast-time axis FFT processing, (c) is the conjugate multiplication result of the received signal and the reference signal in the range frequency domain, and (d) is the range compression signal obtained by performing inverse FFT processing on the conjugate multiplication result on the fast-time axis.

[0026] Range compression is the correlation process between the input signal and the reference signal for range compression. The input signal (Fig. 3(a1)) and the reference signal (Fig. 3(a2)) on the fast-time axis are each subjected to fast-time axis FFT processing and converted into the range frequency domain. When formulating the correlation process (conjugate multiplication of the input signal and the reference signal, Fig. 3(c)) between the input signal (Fig. 3(b1)) and the reference signal (Fig. 3(b2)), it is as follows.

[0027] [Number]

[0028] Also, the reference signal sref (linear chirp signal) can be expressed by the following equation.

[0029] [Number] If the inverse FFT is performed on equation (3), the range compression signal shown in Fig. 3(d) can be obtained.

[0030] [Number]

[0031] Next, the range compression process within the blind range will be described with reference to Fig. 4. In Fig. 4, (a1) is the received pulse on the fast-time axis (range time domain), (a2) is the reference signal on the fast-time axis, (b1) is the received pulse in the range frequency domain after fast-time axis FFT processing, (b2) is the reference signal in the range frequency domain after fast-time axis FFT processing, (c) is the conjugate multiplication result of the received signal and the reference signal in the range frequency domain, and (d) is the range compression signal obtained by performing inverse FFT processing of the conjugate multiplication result on the fast-time axis.

[0032] In the blind range, a part of the received pulse on the fast-time axis falls within the blind range as shown in Fig. 4(a1), becoming a region of received saturation. Since this range cannot be used for processing, after zero-padding, it is subjected to fast-time axis FFT processing and converted into the signal in the range frequency domain shown in Fig. 4(b).

[0033]

Number

[0034] The subsequent processing is the same as that in equations (2) to (5), and a range-compressed signal can be obtained. The state of this processing is shown in Fig. 4. Depending on the target distance within the blind range, the range to be zero-padded changes, and the closer the target distance, the wider the range to be zero-padded. In the case of modulation by the linear chirp signal shown in equation (4), when the target distance is close and the zero-padding range is large, as shown in Fig. 4(c), the chirp bandwidth also becomes narrow, so the range resolution deteriorates as shown in Fig. 4(d).

[0035] For this countermeasure, it is considered to apply the range axis KR product processing shown in Fig. 5 (see Patent Document 1). Fig. 5(a) illustrates the virtual array, the actual array, and the conjugate of the actual array in the KR product array, and Fig. 5(b) illustrates the correlation matrix in the conjugate multiplication of the virtual array and the actual array. As the input signal, on the range frequency axis, it is the signal represented by equation (3) which is the result of conjugate multiplication of the received signal and the reference signal. This signal contains a phase gradient corresponding to the target distance with respect to the range frequency.

[0036]

Number

[0037] Next, using this signal X, as an extended array processing, the KR product array processing (see Patent Document 1) is performed. First, the correlation matrix can be expressed by the following equation.

[0038]

Number

[0039] When vectorizing the elements at the left end and the upper end, the following equation is obtained.

[0040]

Number

[0041] Taking this Xkr as the signal of the extended array, the state of the range-axis inverse FFT processing is shown in Fig. 6. In Fig. 6, (a1) is the received pulse on the fast-time axis (range time domain), (a2) is the reference signal on the fast-time axis, (b1) is the received pulse in the range frequency domain after the fast-time axis FFT processing, (b2) is the reference signal in the range frequency domain after the fast-time axis FFT processing, (c) is the conjugate multiplication result of the received signal and the reference signal in the range frequency domain, (d) is the signal obtained by performing the KR product processing on the conjugate multiplication result, and (e) is the range compression signal obtained by performing the fast-time axis inverse FFT processing on the KR product processing result.

[0042] As shown in Fig. 6(e), by performing the range-axis inverse FFT processing with Xkr as the signal of the extended array, high-resolution range data can be obtained. Using this processing result, the range signal within the blind range is extracted and detected by CFAR or the like.

[0043] The above extended array processing is the processing within the blind range where the range resolution deteriorates due to the influence of zero-padding. Outside the blind range, since there is no deterioration of the range resolution due to the influence of zero-padding, the extended array processing is not applied. For this reason, after performing the inverse FFT14 processing after the conjugate multiplication of the receiving system in Fig. 1, the range outside the blind range is extracted and the target detection processing is performed by CFAR or the like.

[0044] As described above, the pulse compression radar device according to the first embodiment conjugates and multiplies a range frequency reception signal obtained by zero-padding a reception signal and converting it to the range frequency axis within a blind range determined by the transmission pulse width, and a range frequency reference signal obtained by converting a reference signal to the range frequency, and performs range high-resolution processing by the range axis KR product using the conjugate multiplication result, detects a target within the blind range from the processing result, and detects a target using a conjugate multiplication result without performing range high-resolution processing outside the blind range.

[0045] Therefore, according to the first embodiment, even within the blind range, since range high-resolution processing by the KR product process is applied to the conjugate multiplication result in the range frequency of the reception signal and the reference signal, it is possible to reduce the influence of the reduction in the range resolution of the blind range, and it is possible to observe the target in the blind range with high resolution and high accuracy.

[0046] (Second Embodiment) The second embodiment will be described with reference to FIGS. 7 to 9.

[0047] In the first embodiment, as a countermeasure against the reduction in range resolution when observing a target in the blind range by zero-padding the blind range and performing range compression processing, a method of performing the KR product process on the range frequency axis has been described. In this KR product process, as shown in FIG. 6, since there is a region that becomes zero on the range frequency axis, when inverse FFT is performed on the range frequency axis and converted to the range axis, the range side lobe deteriorates. In this embodiment, this countermeasure will be described.

[0048] FIG. 7 is a block diagram showing the configuration of the transmission system and the reception system of the pulse compression radar device according to the second embodiment. In FIG. 7, the same parts as those in FIG. 1 are denoted by the same reference numerals, and redundant descriptions are omitted here.

[0049] In the receiving system shown in FIG. 7, the range-axis signal of the conjugate multiplication result converted by the fast-time axis inverse FFT processor 24 is output to the blind range outside extractor 25 and also output to the blind range inside extractor 33 to extract the signal within the blind range, and a rough target is temporarily detected by the temporary detector 34 by CFAR or the like, and its distance is obtained. On the other hand, the conjugate multiplication result is input to the band extractor 35, and based on the distance of the target detected by the temporary detection, the band to be filled with zeros within the blind range is calculated and extracted, and output to the KR product processor 27.

[0050] In the above configuration, the processing operation of this embodiment will be described with reference to FIGS. 8 and 9.

[0051] FIG. 8 is a waveform diagram showing the target detection processing operation within the blind range when linear chirp modulation is performed on the transmission pulse in the second embodiment. (a) is the blind range by the transmission pulse, (b) is the temporarily detected target distance of the received pulse within the blind range, (c) is the zero-filling range for performing the range compression process, and (d) shows the extracted frequency band and the entire frequency band in the extraction cell.

[0052] FIG. 9 is a diagram showing the content of the range high-resolution processing when the range-axis KR product process is applied after band limiting in the second embodiment. (a1) is the received pulse in the fast-time axis (range time domain), (a2) is the reference signal in the fast-time axis, (b1) is the received pulse in the range frequency domain after the fast-time axis FFT process, (b2) is the reference signal in the range frequency domain after the fast-time axis FFT process, (c) is the conjugate multiplication result of the received signal and the reference signal in the range frequency domain, (d) is the signal obtained by band-limiting the conjugate multiplication result, (e) is the KR product process result after band limiting, and (f) shows the range compression signal obtained by the fast-time axis inverse FFT process.

[0053] That is, in the signal after conjugate multiplication of the received signal and the reference signal on the range frequency axis, if the target distance within the blind zone is known, the range to be zero-filled can be calculated. Therefore, in this embodiment, in order to perform preliminary detection of the target before the KR product process, the conjugate-multiplied signal is subjected to inverse FFT processing on the fast-time axis, the range within the blind zone is extracted, preliminary detection is performed by means of CFAR or the like, and an approximate target distance is output.

[0054] When the approximate target distance is known, the pulse width other than zero filling of the received signal is known, so the pulse width of the reference signal can be corrected to match that of the received signal. This reference signal can be expressed by the following formula.

[0055]

Equation

[0056] Using this reference signal with the corrected pulse width, conversion to range frequency is performed. In the case of linear chirp modulation, as shown in Fig. 8(d), within the pulse, the frequency changes linearly with respect to the fast-time axis. For this reason, when the target distance is known, the zero-filled range is known, and the frequency range Bsel outside zero filling is known.

[0057]

Equation

[0058] If the signal of the Nallsel samples of the fast-time axis (total Nall samples) corresponding to this band Bsel is substituted into Equation (7) in Equation (13), the KR product process can be performed in the same manner as in Equations (8) and (9).

[0059]

Equation

[0060] This signal has no gap region of 0 at the range frequency, like the band-limited signal shown in Fig. 9(d). Therefore, according to this embodiment, the range resolution can be improved without degrading the range side lobe.

[0061] As described above, the pulse compression radar device of the second embodiment conjugates and multiplies the range frequency received signal obtained by zero-padding the received signal and converting it to the range frequency axis within the blind range determined by the transmission pulse width, and the range frequency reference signal obtained by converting the reference signal to the range frequency. Using the result of the conjugate multiplication, the pulse width τ other than the zero-padding of the received signal is calculated based on the range temporarily detected within the blind range, and the pulse width of the reference signal is restricted to the calculated pulse width τ. After restricting the pulse width and the band of the range frequency axis, range high-resolution processing of the range axis KR product is performed, and the target within the blind range is detected from the processing result. Outside the blind range, the target is detected using the conjugate multiplication result without performing range high-resolution processing.

[0062] Therefore, according to the second embodiment, by applying range high-resolution processing by KR product processing after restricting the frequency band using the temporary detection result to the conjugate multiplication result of the received signal and the reference signal at the range frequency, the influence of the reduction in the range resolution of the blind range can be reduced, and furthermore, the range side lobe can be reduced.

[0063] (Third Embodiment) The third embodiment will be described with reference to FIGS. 10 to 11.

[0064] In the second embodiment, the method of correcting the pulse width and frequency band of the reference signal and performing pulse compression after temporarily detecting the target was described. In this case, during the temporary detection, the range side lobe is degraded and false detection may occur. This embodiment describes countermeasures for this.

[0065] FIG. 10 is a block diagram showing the configuration of a transmission system and a reception system of a pulse compression radar apparatus according to a third embodiment. In FIG. 10, the same parts as those in FIGS. 1 and 7 are denoted by the same reference numerals, and redundant descriptions are omitted here.

[0066] In the reception system shown in FIG. 10, a reference signal is input to a reference signal pulse width setter 36 to set the pulse width of the reference signal according to the observation distance, and then output to a fast-time axis FFT processor 22. Further, the range axis signal of the conjugate multiplication result converted by the fast-time axis inverse FFT processor 24 is output to a blind range outside extractor 25, the maximum value for each observation distance is stored by a maximum value storage 37, and the distance of the maximum value is extracted by a distance extractor 38. On the other hand, the conjugate multiplication result is input to a band extractor 35, and based on the distance of the maximum value extracted by the distance extractor 38, the band to be filled with zeros within the blind range is calculated and extracted, and output to a KR product processor 27.

[0067] In the above configuration, the processing operation of this embodiment will be described with reference to FIG. 11. In FIG. 11, (a1) is a received pulse (filled with zeros within the blind range) in the fast-time axis (range time domain), (a2) is a reference signal in the fast-time axis (pulse width control (P cases)), (b1) is the received pulse in the range frequency domain after fast-time axis FFT processing (frequency band limited), (b2) is the reference signal in the range frequency domain after fast-time axis FFT processing, (c) is the conjugate multiplication result of the received signal and the reference signal in the range frequency domain (with Nallsel points), (d) is the signal obtained by band-limiting the conjugate multiplication result, (e) is the KR product processing result after band-limiting, and (f) is the range compression signal obtained by performing fast-time axis inverse FFT processing (extracting the result of the reference signal that becomes the maximum value among the P cases).

[0068] In the signal (Fig. 11(c)) after conjugate multiplication of the received signal and the reference signal on the range frequency axis, the range where it becomes zero can be calculated if the target distance within the blind area is known. However, since the target distance is unknown, a search method is used. In the search method, the reference signal pulse width setter 36 calculates the pulse compression results when the target distance is changed in P (P≥1) ways within the target distance observation range. When each of the P target distances is set, since the pulse width of the part other than the zero-padding of the received signal is known, the pulse width of the reference signal can be corrected to match the pulse width of the received signal. The reference signal with the corrected pulse width can be converted to the range frequency. Using this corrected reference signal, conjugate multiplication of equations (2) and (3) is performed for pulse compression, the maximum value of the pulse compression results for each observation distance is stored in the maximum value storage 37, and the result of the reference signal that becomes the maximum value among the P maximum values is extracted as the target distance by the distance extractor 38. Thus, the target distance can be extracted.

[0069] If the target distance can be calculated, by the method of equations (10) to (13) of the second embodiment, range frequency KR product processing without a zero gap region at the range frequency is performed, and the range resolution can be improved without degrading the range side lobe.

[0070] As described above, the pulse compression radar device according to the third embodiment conjugates and multiplies the range frequency received signal obtained by zero-padding the received signal and converting it to the range frequency axis and the range frequency reference signal obtained by converting the reference signal to the range frequency within the blind range determined by the transmission pulse width, and uses the conjugate multiplication result to zero-pad the signal within the blind range of the received signal and convert it to the range frequency axis for the range frequency received signal, sets the observation range in P (P≥1) ways, calculates the pulse width τ other than zero-padding of the P received signals, and restricts the pulse width of the reference signal to the calculated pulse width τ, thereby performing range high-resolution processing of the range-axis KR product using the reference signal on the range frequency axis with restricted pulse width and range frequency axis bandwidth, detecting the target within the blind range from the processing result, and detecting the target using the conjugate multiplication result without performing range high-resolution processing outside the blind range.

[0071] Therefore, according to the third embodiment, after eliminating the need for preliminary detection by setting a target distance within a predetermined observation range and selecting the target distance that gives the maximum value of the conjugate multiplication result at the range frequency obtained by controlling the pulse width of the reference signal, by applying range high-resolution processing using the KR product process, it is possible to reduce the influence of the reduction in range resolution in the blind range, and further reduce the range side lobe.

[0072] (Fourth Embodiment) Referring to FIGS. 12 to 14, the fourth embodiment will be described.

[0073] In the first and second embodiments, a method for improving the range resolution in the blind range has been described. However, since the bandwidth of pulse compression becomes narrow within the blind range, it is difficult to obtain a range resolution equal to or better than that outside the blind range. When the range resolution is low, there is a problem that the range accuracy deteriorates. Therefore, in this embodiment, countermeasures for this will be described.

[0074] FIG. 12 is a block diagram showing the configuration of the transmission system and the reception system of the pulse compression radar device according to the fourth embodiment. In FIG. 12, the same parts as those in FIGS. 1 and 7 are denoted by the same reference numerals, and redundant descriptions are omitted here.

[0075] In the receiving system shown in FIG. 12, the range-axis signal of the conjugate multiplication result converted by the fast-time axis inverse FFT processor 24 is output to the blind range out extractor 25 and also output to the blind range in extractor 33 to extract the signal within the blind range. A rough target is temporarily detected by a temporary detector 34 using CFAR or the like, and its distance is obtained. On the other hand, the conjugate multiplication result is input to the band extractor 35, and based on the distance of the target detected by the temporary detection, the band to be zero-filled within the blind range is calculated and extracted, and input to the KR product processor 27 to apply range-axis KR product processing. For the processing result, the amplitude square root is obtained by the amplitude square root processor 28, the Σ signal is obtained by the Σ weight multiplier 29, converted into a range-axis signal by the fast-time axis inverse FFT processor 30, the signal within the blind range is extracted by the blind range in extractor 31, and the target is detected by the target detector 32 using CFAR (see Non-Patent Document 3) or the like. Further, the calculation result of the amplitude square root processor 28 is input to the Δ weight multiplier 39 to obtain a Δ signal, converted into a range-axis signal by the fast-time axis inverse FFT processor 40, and output to the range monopulse processor 41. The range monopulse processor 41 performs range monopulse processing using the Σ signal and the Δ signal of the range cell where the target is detected by the target detector 32, and outputs it as target information within the blind range.

[0076] In the above configuration, the processing operation of this embodiment will be described with reference to FIGS. 13 and 14. FIG. 13 shows the phase monopulse processing applied as the range monopulse processing of this embodiment, and FIG. 14 shows the squint monopulse processing applied as the range monopulse processing of this embodiment.

[0077] Range accuracy is usually calculated by a detection range cell. However, when the range resolution deteriorates, the range cell width expands, resulting in deteriorated range accuracy. As a countermeasure, range axis monopulse processing (see Patent Document 2) is used for the signal on the range frequency axis after the KR product processing. This uses the KR product array ((7) or (10) formula) of the conjugate multiplication result of the received signal and the reference signal on the range frequency axis to perform Σ weight calculation and Δ weight calculation (29, 39), and perform fast-time axis inverse FFT processing (30, 40) respectively to calculate the Σ signal and the Δ signal. For the Σ signal, the range within the blind is extracted, and target detection is performed by CFAR, etc. (32). Using the Σ signal and the Δ signal of the detection cell shown in Fig. 13(a), range monopulse processing is performed by phase monopulse. This calculates the error voltage by the following formula and outputs on the fast-time axis by comparing with the table of the error voltage calculated in advance as shown in Fig. 13(b), and converts it to the range.

[0078]

Number

[0079] By this method, the range within the range cell can be calculated with high accuracy.

[0080] Also, as shown in Figs. 14(a) and (b), instead of the Δ signal, the range can also be calculated by squint monopulse using the signal Σ2 of the adjacent range cell.

[0081]

Number

[0082] As described above, the pulse compression radar apparatus according to the fourth embodiment detects a target based on the result of performing range high-resolution processing such as range axis KR product within the blind range, and then outputs the range using range axis monopulse processing for the detected target. Outside the blind range, the target is detected using the processing result without performing range high-resolution processing.

[0083] Therefore, according to the fourth embodiment, after frequency band limiting the conjugate multiplication result at the range frequencies of the received signal and the reference signal using the preliminary detection result, by applying range high-resolution processing using the KR product process, the influence of the degradation of the range resolution in the blind range and the increase of the range side lobe can be reduced, and further, by range-axis monopulse processing, the degradation of the range accuracy due to the spread of the range cell can be reduced.

[0084] Note that in the above embodiment, the method of performing the KR product on the range frequency axis during the pulse compression process has been described. However, when the range resolution can be tolerated, as a method for observing the short-distance blind range, it can be applied as a process that does not perform the KR product process.

[0085] Also, in the fourth embodiment, the target cell detection before the KR product is described in the case of the preliminary detection method described in the second embodiment of FIG. 7, but it is also applicable to the search method based on the reference signal pulse width in FIG. 10.

[0086] In addition, the present invention is not limited to the above embodiments as they are, and at the implementation stage, the components can be modified and embodied without departing from the gist thereof. Also, various inventions can be formed by appropriately combining a plurality of components disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined.

Explanation of Reference Numerals

[0087] 11…Reference signal generator, 12…Signal generator, 13…Modulator, 14…Frequency converter, 15…Pulse modulator, 16…Transmitting antenna, 17…Receiving antenna, 18…Frequency converter, 19…AD converter, 20…Zero-padding processor, 21…Fast-time axis FFT processor, 22…Fast-time axis FFT processor, 23…Conjugate multiplier, 24…Fast-time axis inverse FFT processor, 25…Extractor outside blind range, 26…Target detector, 27…KR product processor, 28…Square root of amplitude processor, 29…Σ weight multiplier, 30…Fast-time axis inverse FFT processor, 31…Extractor within blind range, 32…Target detector, 33…Extractor within blind range, 34…Tentative detector, 35…Band extractor, 36…Reference signal pulse width setter, 37…Maximum value saver, 38…Range extractor, 39…Δ weight multiplier, 40…Fast-time axis inverse FFT processor, 41…Range monopulse processor.

Claims

1. In a pulse compression radar device that modulates the inside of a transmission pulse with a reference signal when transmitting and receiving the transmission pulse, a conjugate multiplication unit that conjugate multiplies a range frequency reception signal obtained by zero-padding a reception signal and converting it to the range frequency axis within a blind range determined by the pulse width of the transmission pulse, and a range frequency reference signal obtained by converting the reference signal to the range frequency; a target detection unit that performs high-range-resolution processing using the conjugate multiplication result of the conjugate multiplication unit, detects a target within the blind range from the processing result, and detects a target using the conjugate multiplication result before performing the high-range-resolution processing outside the blind range A pulse compression radar device comprising:

2. In a pulse compression radar device that modulates the inside of a transmission pulse with a reference signal when transmitting and receiving the transmission pulse, a conjugate multiplication unit that conjugate multiplies a range frequency reception signal obtained by zero-padding a reception signal and converting it to the range frequency axis within a blind range determined by the pulse width of the transmission pulse, and a range frequency reference signal obtained by converting the reference signal to the range frequency; using the conjugate multiplication result of the conjugate multiplication unit, a target is temporarily detected within the blind range, the pulse width other than zero-padding of the reception signal is calculated based on the range of the temporarily detected target cell, and the pulse width of the reference signal is restricted by the calculated pulse width other than zero-padding, thereby restricting the pulse width and the bandwidth of the range frequency axis to perform high-range-resolution processing, detecting a target within the blind range from the processing result, and outside the blind range, a target detection unit that detects a target using the conjugate multiplication result before performing the processing A pulse compression radar device comprising:

3. In a pulse compression radar device that modulates the inside of a transmission pulse with a reference signal when transmitting and receiving the transmission pulse, a conjugate multiplication unit that conjugate multiplies a range frequency reception signal obtained by zero-padding a reception signal and converting it to the range frequency axis within a blind range determined by the pulse width of the transmission pulse, and a range frequency reference signal obtained by converting the reference signal to the range frequency; Using the conjugate multiplication result of the conjugate multiplication unit, among the received signals, the range frequency received signal obtained by zero-padding the signals within the blind range and converting them to the range frequency axis, and setting the observation range in P (P≥1) ways, calculating the pulse widths other than zero-padding of the received signals in P ways, and restricting the pulse width of the reference signal to the pulse widths other than zero-padding calculated, range high-resolution processing is performed using the range frequency reference signal with the pulse width and the bandwidth of the range frequency axis restricted, a target within the blind range is detected from the processing result, and outside the blind range, a target is detected using the conjugate multiplication result before performing the range high-resolution processing, and a target detection unit A pulse compression radar device comprising the same.

4. The target detection unit according to any one of claims 1 to 3, wherein within the blind range, after detecting a target based on the result of performing the range high-resolution processing, a range is output using range-axis monopulse processing on the detected target.

5. When transmitting and receiving a transmission pulse, it is used in a pulse compression radar device that modulates the inside of the transmission pulse with a reference signal. Within the blind range determined by the pulse width of the transmission pulse, the range frequency received signal obtained by zero-padding the received signal and converting it to the range frequency axis is conjugate-multiplied with the range frequency reference signal obtained by converting the reference signal to the range frequency. Using the conjugate multiplication result of the conjugate multiplication, range high-resolution processing is performed, a target within the blind range is detected from the processing result, and outside the blind range, a target is detected using the conjugate multiplication result before performing the range high-resolution processing. A radar signal processing method for a pulse compression radar device.

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