JP5460290B2 - Radar equipment - Google Patents

Description

  The present invention relates to a radar apparatus that eliminates distance ambiguity and measures a target distance.

  A conventional radar apparatus that eliminates the distance ambiguity and measures the target distance will be described with reference to FIGS. 41 to 43 (for example, see Patent Document 1).

  FIG. 41 is a block diagram showing a configuration of a conventional radar apparatus. FIG. 42 is a flowchart showing the operation of the conventional radar apparatus (a method for calculating the target distance by eliminating the distance ambiguity). FIG. 43 is a timing chart showing code modulation of a conventional radar apparatus.

  41, the conventional radar apparatus mainly includes a code modulation data generation unit 10, a transmission wave generator 30, a transmission unit 40, a circulator 50, a transmission / reception antenna 60, a reception unit 70, and a Doppler shift calculation. Unit 90, signal delay unit 110, frequency shifter 120, correlation processing unit 131, and coarse distance calculation unit 140.

  Next, a method for eliminating the distance ambiguity of the conventional radar apparatus and calculating the target distance will be described with reference to FIG.

  This radar apparatus first transmits a high pulse repetition frequency signal that does not perform code modulation but performs FM ranging, and obtains a frequency including a Doppler shift amount of a reflected wave of an object (target) from the transmission pulse and the reception pulse. At the same time, FM ranging is performed to obtain a rough distance to the object.

  Next, FM ranging is not performed, that is, frequency modulation is not performed. Instead, a high pulse repetition frequency signal with code modulation added is transmitted (see FIG. 43), and correlation processing is performed on the received pulse. The distance ambiguity is eliminated and the distance to the object is obtained using the rough distance obtained in step (b).

  This radar apparatus can be expected to improve the ranging performance by eliminating the distance ambiguity.

JP 2008-101997 A

However, in the conventional radar apparatus as described above, a high pulse repetition frequency signal that does not perform code modulation but performs FM ranging and a high pulse repetition frequency signal that does not perform frequency modulation but adds code modulation are separately transmitted and received. Therefore, there is a problem that the observation time for distance measurement becomes long and the distance measurement accuracy may deteriorate. Further, as shown in FIG. 43, since one code is used for one pulse, there is a problem that high distance resolution of 2T _pri / c or less cannot be achieved.

  The present invention has been made to solve the above-mentioned problems, and its purpose is to shorten the observation time related to distance measurement, to improve distance measurement performance that eliminates distance ambiguity and achieves high distance resolution. A radar apparatus capable of performing the above is obtained.

The radar apparatus according to the present invention has a plurality of distance resolutions after FM ranging that can eliminate the distance ambiguity of distances in the PRI, and a plurality of parameters based on a parameter that makes the distance resolution in the PRI more accurate than the distance resolution after FM ranging. Transmitting means for radiating a transmission signal that is pulse-modulated by PRI with respect to a carrier signal that has been frequency-modulated over PRI, and receiving the transmission signal reflected and returned from the target as a reception signal. Te, downconverts using the carrier signal obtained from said transmitting means, a receiving means for converting the received beat signal sampled through the PRI, FM on the received beat signal obtained by sampling the PRI obtained from said receiving means Distance in PRI to perform ranging and calculate relative distance to target-FM range The distance in the PRI for creating the distance map after the distance-distance map creating means after the FM ranging, and the distance in the PRI-the distance in the PRI obtained from the distance map creating means after the FM ranging-the distance after the FM ranging Using the target candidate detecting means for detecting the target candidate based on the signal strength and the distance after FM ranging of the target candidate obtained from the target candidate detecting means, the distance ambiguity of the distance in the PRI is eliminated. Target relative distance calculating means for calculating a relative distance to the target is provided.

  The radar apparatus according to the present invention has an effect of shortening the observation time related to ranging, eliminating the distance ambiguity, and improving the ranging performance for increasing the distance resolution.

It is a block diagram which shows the structure of the radar apparatus which concerns on Embodiment 1 of this invention. It is a figure for demonstrating the relationship between the transmission signal and reception signal which carried out frequency modulation and the code | symbol modulation in the pulse. It is a figure for demonstrating the relationship of the transmission pulse of FM ranging, a reception pulse, the frequency change of a transmission signal, the frequency change of a received signal, and the frequency change of a local oscillation signal. It is a figure for demonstrating the distance map after the distance-FM ranging in PRI. It is a figure for demonstrating the signal of FM ranging, the signal after a correlation process, the ranging result between PRI, and the ranging result in PRI. It is a figure which shows 4 bit Barker code. It is a block diagram which shows the process with respect to the received beat signal of the signal processor. It is a figure for demonstrating the attention cell, guard cell, and sample cell in connection with a CFAR process. CFAR processing result diagrams for CFAR threshold CFAR_th _(k h, l) is the cell exceed explains a procedure in the case where the aggregate. It is a block diagram which shows the structure of the radar apparatus which concerns on Embodiment 2 of this invention. It is a block diagram which shows the process with respect to the received beat signal of signal processor 200B. It is a figure for demonstrating the signal on the distance map after the distance in FM-FM ranging in case of relative distance v ≠ 0 with a target. It is a figure which shows the influence of the relative speed with the target with respect to the signal of the distance direction in PRI. It is a block diagram which shows the structure of the radar apparatus which concerns on Embodiment 3 of this invention. It is a figure for demonstrating the influence of a clutter. It is a figure which shows the relationship between a radar apparatus, a target, and a clutter. It is a figure which shows the relationship between a radar apparatus, the transmission direction of the main beam of a transmission signal, beam width, and a clutter. It is a figure which shows the range where a target is buried in clutter. It is a block diagram which shows the structure of the radar apparatus concerning Embodiment 4 of this invention. It is a block diagram which shows the process with respect to the received beat signal of signal processor 200D. It is a figure which shows the influence of a ground clutter side lobe. It is a figure which shows the case where a target is buried in a ground clutter side lobe. It is a figure which shows a filter characteristic. It is a figure which shows the effect of a filter process. It is a block diagram which shows the structure of the radar apparatus which concerns on Embodiment 5 of this invention. It is a block diagram which shows the process with respect to the received beat signal of the signal processor 200E. It is a figure which shows the effect of performing a window function process in the case of a correlation process. It is a figure which shows the effect which performs a window function process in the case of FM ranging. It is a block diagram which shows the structure of the radar apparatus based on Embodiment 6 of this invention. It is a block diagram which shows the process with respect to the received beat signal of the signal processor 200F. It is a figure for demonstrating the signal of FM ranging in the case of not carrying out speed compensation, the signal in PRI, the ranging result between PRI, and the ranging result in PRI. It is a figure which shows the ranging result when not speed-compensating (when the target movement between transmission signal frequency sweep time _{TL is} not considered). It is a figure which shows the ranging result when not speed-compensating (when the target movement between transmission signal frequency sweep time _TL is considered). It is a block diagram which shows the structure of the radar apparatus based on Embodiment 7 of this invention. It is a figure which shows the relationship between the transmission signal and reception signal which carried out the stepwise frequency modulation and the intra-pulse code modulation. It is a block diagram which shows the structure of the radar apparatus based on Embodiment 8 of this invention. It is a block diagram which shows the process with respect to the received beat signal of the signal processor 200G. It is a figure for demonstrating the distance map after distance in PRI (before a correlation process) -FM ranging. It is a figure for demonstrating the signal after the integration in PRI. It is a figure which shows the influence of the frequency modulation and the target relative distance with respect to the signal of the distance direction in PRI. It is a block diagram which shows the structure of the conventional radar apparatus. It is a flowchart which shows operation | movement of the conventional radar apparatus (The method of canceling distance ambiguity and calculating a target distance). It is a timing chart which shows the code modulation of the conventional radar apparatus.

Embodiment 1 FIG.
A radar apparatus according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a block diagram showing a configuration of a radar apparatus according to Embodiment 1 of the present invention. In addition, in each figure, the same code | symbol shows the same or equivalent part.

  In FIG. 1, a radar apparatus according to Embodiment 1 of the present invention includes an antenna 1, a transmission means 2, a transmission / reception switch 7, a receiver (reception means) 8, a signal processor 200, and a display 9. And are provided.

  The transmission means 2 includes a transmitter 3, an intra-pulse modulation signal generator 4, a pulse modulator 5, and a local oscillator 6.

  The signal processor 200 is composed of a computer having a CPU, a RAM, a ROM, an interface circuit, and the like, and arithmetic processing is performed by the CPU according to a program stored in the ROM. The processing result of the signal processor 200 is recorded in a memory such as a RAM.

  The signal processor 200 includes a distance map creation unit 201 after distance-FM ranging in the PRI, a target candidate detection unit 220, and a target relative distance calculation unit 221.

  The distance map creating unit 201 includes a correlating unit 202 and an FM ranging unit 203.

  Next, the operation of the radar apparatus according to the first embodiment will be described with reference to the drawings.

  First, an operation until a reception beat signal is generated will be described with reference to FIGS. FIG. 2 is a diagram for explaining the relationship between a transmission signal and a reception signal subjected to frequency modulation and intra-pulse code modulation. FIG. 3 is a diagram for explaining the relationship among FM ranging transmission pulse, reception pulse, frequency change of the transmission signal, frequency change of the reception signal, and frequency change of the local oscillation signal.

2 and 3, f ₀ is a transmission start frequency, T _pri is a pulse repetition period (PRI), _TL is a transmission signal frequency sweep time, B _L is a transmission signal bandwidth, and T ₀ is a beat signal. Observation time, B ₀ is the transmission signal bandwidth in the time interval of T ₀ , T _p is the transmission pulse width, φ ₀ is the initial phase of the transmission signal and the local oscillation signal, and R (t) is relative to the target at time t Distance, R _max is the maximum detection distance, T _offset is the first transmission pulse transmission start time at time 2R _max / c or more, and c is the speed of light.

Also, the first transmission pulse transmission start time T _offset , maximum detection distance R _max , transmission signal frequency sweep time T _L , transmission signal bandwidth B _L , beat signal observation time T ₀ , T ₀ at time 2R _max / c or more The transmission signal bandwidth B ₀ at the time interval has a relationship represented by the following equations (1), (2), and (3). A plurality of pulse repetition periods are set as a transmission signal frequency sweep time _TL . Here, ceil (X) represents an integer obtained by rounding up the variable X. The frequency modulation within the transmission signal frequency sweep time _TL will be described as up-chirp modulation.

  Next, a method for setting parameters related to transmission signals will be described with reference to FIGS. FIG. 4 is a diagram for explaining a distance map in the PRI after distance-FM ranging. FIG. 5 is a diagram for explaining an FM ranging signal, a signal after correlation processing, an inter-PRI distance measurement result, and an intra-PRI distance measurement result.

Equation (4), Equation (5), and Equation (6) are set so that the distance resolution after the correlation processing becomes higher than the distance resolution after the FM ranging and the distance ambiguity of the distance in the PRI is resolved. Parameters for calculating distance resolution ΔR ′ _FM and sampling interval ΔR _FM after FM ranging, distance resolution ΔR ′ _PC after correlation processing, and 1 PRI folding distance R _pri (at beat signal observation times T ₀ and T ₀ ) Transmission signal bandwidth B ₀ , pulse repetition period T _pri , sampling frequency F _samp ).

Further, distance resolution ΔR ′ _FM after FM ranging is expressed by equation (7), sampling interval ΔR _FM after FM ranging is expressed by equation (8), folding distance R _pri within PRI is expressed by equation (9), and distance resolution ΔR after correlation processing is calculated. ' _PC is calculated by equation (10). Here, H represents the number of FFT points for FM ranging. The transmission means 2 operates based on the parameters set as described above.

The local oscillator 6 generates a local oscillation signal L ₀ (t) represented by the following expression (11) that is frequency-modulated with the transmission signal frequency sweep time T _L and the transmission signal bandwidth B _L , and the pulse modulator 5 And output to the receiver 8.

Here, _AL is the amplitude of the local oscillation signal.

The pulse modulator 5 performs pulse modulation on the local oscillation signal L ₀ (t) input from the local oscillator 6, and the pulse-modulated local oscillation signal L ′ ₀ (t) expressed by the following equation (12). ) To the transmitter 3.

Here, n _L represents the pulse number within the transmission signal frequency sweep time _TL , and N _L represents the number of pulses within the transmission signal frequency sweep time _TL .

  The intra-pulse modulation signal generator 4 generates the 4-bit Barker code shown in FIG. 6 as the intra-pulse modulation signal φ (t) and outputs it to the transmitter 3. Another bit Barker code may be used as the intra-pulse modulation signal. Further, other code modulation or frequency modulation may be used as the intra-pulse modulation signal.

The transmitter 3 receives an intra-pulse modulation signal φ (t) input from the intra-pulse modulation signal generator 4 with respect to the pulse-modulated local oscillation signal L ′ ₀ (t) input from the pulse modulator 5. Using this, intra-pulse modulation is performed, and a transmission RF signal Tx (t) represented by the following equation (13) is output to the transmission / reception switch 7.

Here, _AT is the amplitude of the transmission RF signal, rem (X, Y) is the remainder when variable X is divided by variable Y, and φ ₀ indicates the initial phase of the transmission RF signal.

  The transmission / reception switch 7 outputs the transmission RF signal input from the transmitter 3 to the antenna 1. Then, the transmission RF signal is radiated from the antenna 1 into the air.

  The transmission RF signal radiated into the air is reflected by the target and enters the antenna 1 as a reflected RF signal. Therefore, the antenna 1 receives the incident reflected RF signal and outputs it to the transmission / reception switch 7 as a received RF signal.

The transmission / reception switch 7 outputs the reception RF signal input from the antenna 1 to the receiver 8. When the transmission RF signal Tx (t) represented by Expression (13) receives a reflected RF signal from the target at a relative distance R (t) from the target, the received RF signal Rx _tgt (n _L , t) Is represented by the following equation (14).

Here, A _tgt represents the amplitude of the received RF signal. When the relative speed with respect to the target is v, the relative distance R (t) with respect to the target is expressed by the following equation (15). However, R ₀ represents the initial relative distance from the target at time t = 0. In this embodiment, the following description will be made assuming that the relative speed with respect to the target is v = 0.

The received RF signal Rx _tgt (n, t) observed within the beat signal observation time T ₀ is expressed by the following equation (16).

Here, n represents the pulse number within the beat signal observation time T ₀ , and N represents the number of pulses within the beat signal observation time T ₀ .

The receiver 8 down-converts the received RF signal Rx _tgt (n, t) input from the transmission / reception switch 7 using the local oscillation signal L ₀ (t) input from the local oscillator 6 and then amplifies the received RF signal Rx _tgt (n, t). Then, phase detection is performed, and the signal is output to the signal processor 200 as a received beat signal expressed by the following equation (17). Where * the complex conjugate, A _S represents the amplitude of the received beat signal.

  Further, when the expression (17) is expanded, it is expressed as the following expression (18).

  Hereinafter, using m as the sampling number within 1 PRI, M as the number of sampling points within 1 PRI, and Δt as the sampling time within 1 PRI, using the received beat signal S (n, m) represented by the following equation (19), Give an explanation.

  Hereinafter, the processing content of each means for the received beat signal shown in FIG. 7 will be described.

  A distance map creation means 201 after distance-FM ranging in the PRI is composed of a correlation means 202 and an FM ranging means 203, performs correlation processing and FM ranging on the received beat signal, and calculates a relative distance from the target. A distance map in the PRI for distance-FM ranging is created.

The correlation means 202 performs correlation processing between the received beat signal S (n, m) and the reference signal Ex (m _τ ) expressed by the equation (19), that is, pulse compression. Here, correlation processing in the frequency domain will be described.

The reference signal Ex (m _τ ) after A / D conversion which is the same as the intra-pulse modulation component of the transmission RF signal is expressed by Expression (20). Here, m _τ represents the sampling number, M _τ represents the number of sampling points of 1 PRI (Equation (21)), F _samp represents the sampling frequency, and floor (X) represents the maximum integer that does not exceed the variable X.

The correlation means 202 multiplies the received beat signal S (n, m) and the reference signal Ex (m _τ ) by performing fast Fourier transform (FFT) according to the equations (22) and (23), respectively (FFT). Formula (24)). Here, * represents a complex conjugate, l represents a sampling number in PRI, and L ′ represents an FFT score for correlation processing. However, when L ′> M, 0 is substituted for S (n, m), and when L ′> M _τ , 0 is substituted for Ex (m _τ ).

  Correlation means 202 sets 0 according to equation (25) when sampling the signal after correlation processing with higher accuracy than the sampling interval of the received beat signal. Here, L is the inverse fast Fourier transform (IFFT) point of the correlation process, and is expressed by equation (26). However, q is an integer greater than or equal to 0. When q = 0, the sampling interval is the same as the sampling interval of the received beat signal.

Finally, the correlator 202 performs fast Fourier inverse transform (IFFT) on the multiplication result F _{V · Ex} (n, k _r ) according to the equation (27), and results of the correlation processing, that is, the signal after pulse compression. R _{V · Ex} (n, l) is output. Further, the relative distance R _PC (l) in PRI corresponding to the sampling number 1 of the signal R _{V · Ex} (n, l) after the pulse compression is expressed by Expression (28).

The FM ranging means 203 performs the IFFT of the signal R _{V · Ex} (n, l) after pulse compression in the PRI direction at the H point by the equation (29), so that the distance in the PRI—the distance map R _FM R after the FM ranging. _PC (k _h , l) is output. However, when H> N, R _{V · Ex} (n, l) is zero-padded. Here, _{k h} represents a sampling number after FM ranging. Moreover, the relative distance R _FM (k _h ) between PRIs corresponding to the sampling number after FM ranging is expressed by Expression (30).

  As described above, the distance map creation unit 201 after the distance in the PRI-FM ranging calculates the relative distance to the target by performing the pulse compression in the PRI as the correlation processing and the FFT between the PRIs as the FM ranging. The distance map after the distance-FM ranging in the PRI shown in FIG. 4 is output to the target candidate detection means 220.

Processing contents of target candidate detection by CFAR (Constant False Alarm Rate) processing will be described with reference to FIGS. FIG. 8 is a diagram for explaining a cell of interest, a guard cell, and a sample cell related to the CFAR process. FIG. 9 is a result of the CFAR processing are diagrams for CFAR threshold CFAR_th _(k h, l) is the cell exceed explains a procedure in the case where the aggregate.

The target candidate detection unit 220 uses a formula for a distance in the PRI-distance map in the PRI obtained from the distance map creation unit 201 after the FM ranging-distance map R _FM R _PC (k _h , l) in the PRI range. The CFAR process is performed according to 31) to detect a target candidate. _Here, R _{FM R PC,} represents CFAR _(k h, l) is the target candidate detection result by the CFAR process, the target candidate 0 is set.

Also, the CFAR threshold value CFAR_th (k _h , l) is calculated by the equation (32). Here, CFAR_cor the CFAR factor, Samp_cell _(k h, l) is the sample cell, ave (Z (p)) represents the average value of the sequence Z (p). However, if the cell exceeds the CFAR threshold CFAR_th _(k h, l) as shown in FIG. 9 was set to detect a cell that indicates the maximum value of the amplitude among the set as a target candidate.

The target relative distance calculation unit 221 uses a distance ambiguity of the relative distance R _PC (l) within the PRI for the target candidate input from the target candidate detection unit 220 using an inter-PRI relative distance R _FM (k _h ). 33), and the target relative distance R _{FM, PC} (k _h , l) is calculated by equation (34). Here, N _tgt (k _h ) is a received signal start pulse number, and ceil (X) is an integer obtained by rounding up the variable X.

  When there is a distance map in the PRI-distance map after FM ranging and a target candidate, the display 9 displays the target relative distance on the screen as target information.

  As described above, according to this embodiment, the transmission RF signal subjected to the frequency modulation for performing the FM ranging and the intra-pulse modulation for performing the intra-pulse compression is transmitted and received, and the PRI signal is received with respect to the received beat signal. Inside is pulse compression, between PRI is FM ranging to create a distance map in the PRI-distance map after FM ranging, and for the distance map in the PRI-distance map after FM ranging, target candidates are calculated by CFAR processing, The target ambiguity within the PRI of the target candidate is solved using the relative distance between the PRIs, and the target relative distance is calculated.

  As a result, it is possible to obtain a radar apparatus with high distance resolution without distance ambiguity, by solving the relative distance within PRI having high distance resolution but using the relative distance between PRIs by FM ranging. Further, in the above-mentioned Patent Document 1, the frequency modulation and the intra-pulse modulation transmission signal are performed separately, but this embodiment is performed at the same time, the observation time for calculating the distance is shortened, and the distance measurement performance Can be improved. Further, in Patent Document 1, code modulation is performed with one code within one pulse, but in this embodiment, code modulation is performed with a plurality of codes within one pulse (for example, 4-bit barker code within one pulse). This enables high range resolution.

Embodiment 2. FIG.
A radar apparatus according to Embodiment 2 of the present invention will be described with reference to FIGS. FIG. 10 is a block diagram showing a configuration of a radar apparatus according to Embodiment 2 of the present invention.

  In FIG. 10, the radar apparatus according to Embodiment 2 of the present invention is provided with an antenna 1, a transmission means 2, a transmission / reception switch 7, a receiver 8, a signal processor 200B, and a display 9. ing.

  Since the radar apparatus according to the second embodiment is different from the radar apparatus according to the first embodiment except for the signal processor 200B, the same components are denoted by the same reference numerals, and description thereof is omitted. To do.

  That is, as shown in FIG. 10, the signal processor 200 </ b> B may further include a speed compensation unit 204 in the distance map creation unit 201 after distance-FM ranging in the PRI of the signal processor 200 according to Embodiment 1. Since they are different and are otherwise the same, the same reference numerals are given to the same parts, and the description is omitted.

  Next, the operation of the radar apparatus according to the second embodiment will be described with reference to the drawings.

  The signal processor 200B performs the process shown in FIG. 11 on the received beat signal.

  In this embodiment, the case where the relative speed v ≠ 0 with respect to the target will be described. As shown in FIG. 12, when the relative speed with respect to the target is v ≠ 0, the target moves in the distance direction after the FM ranging in the distance map within the PRI-distance map after the FM ranging according to the relative speed with the target. To do. Further, as shown in FIG. 13, the distance direction signal within the PRI in the distance map within the PRI-distance map after the FM ranging has a degradation in distance resolution, disturbance of side lobes (degradation of compression characteristics), and ranging performance. There is a possibility of deterioration.

For the purpose of suppressing the influence of the relative speed with respect to the target and preventing the deterioration of the distance measurement performance, the speed compensation means 204 uses the relative speed v _init obtained in advance to obtain the received beat signal S by the following equation (35). Speed compensation is performed on (n, m), and the received beat signal S _{v, cor} (n, m) after speed compensation is output.

In the equation (35), the target movement in the distance direction after FM ranging, the degradation of the distance resolution of the signal in the distance direction in the PRI, and the disturbance of the side lobe are simultaneously compensated. In the case of speed compensation only for degradation of distance resolution and sidelobe disturbance, speed compensation is performed on the received beat signal S (n, m) by the following equation (36), and after speed compensation in the distance direction in the PRI. The received beat signal S ′ _{v, cor} (n, m) is output. In this case, the target movement in the distance direction after FM ranging is taken into account using the relative velocity v _init obtained in advance when calculating the target relative distance.

  As described above, according to the second embodiment, even when the target relative speed v ≠ 0, the speed compensation means 204 is provided to suppress the influence of the relative speed with the target and prevent the ranging performance from being deteriorated. Therefore, it is possible to obtain a radar apparatus with improved ranging performance. The same effect can be obtained even when the target relative speed v = 0.

Embodiment 3 FIG.
A radar apparatus according to Embodiment 3 of the present invention will be described with reference to FIGS. FIG. 14 is a block diagram showing a configuration of a radar apparatus according to Embodiment 3 of the present invention.

  In FIG. 14, the radar apparatus according to Embodiment 3 of the present invention is provided with an antenna 1, a transmission means 2B, a transmission / reception switch 7, a receiver 8, a signal processor 200B, and a display 9. ing.

  Since the radar apparatus according to this embodiment is different from the radar apparatus according to the above-described embodiment except for the transmission means 2B, the same components are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 15, in the radar apparatus, when there is a clutter having an intensity higher than the target, the target is buried in the clutter, and the target detection performance and the ranging performance deteriorate. For the sake of explanation, a ground clutter main lobe with respect to a transmission signal main beam is assumed as a clutter with a two-dimensional geometry (see FIG. 16), and a method for improving the separation performance of the target and the clutter of the radar apparatus according to the third embodiment is described To do.

In the case of the transmission signal elevation EL, the beam width BW, the transmission signal minimum elevation EL _min , and the transmission signal maximum elevation EL _max (see FIG. 17), the ground clutter of the radar device transmission signal maximum elevation EL _max main The lobe relative distance R _{clt, ELmax} , relative velocity v _{clt, ELmax} , and Doppler frequency fd _{clt, ELmax} are calculated by the following equations (37), (38), and (39). Here, Alt is the altitude of the own aircraft equipped with the radar device, v _R is the velocity of the own device equipped with the radar device, v _T is the target velocity, chirp is the frequency modulation over the transmission signal frequency sweep time _TL. In the case of chirp modulation, 1 is substituted, and in the case of down chirp modulation, -1 is substituted.

In the case of transmission signal elevation EL, beam width BW, transmission signal minimum elevation EL _min , and transmission signal maximum elevation EL _max (see FIG. 17), the ground of the minimum elevation EL _min of the transmission signal of the radar device The relative distance R _{clt, ELmin of} the clutter main lobe, the relative velocity v _{clt, ELmin} , and the Doppler frequency fd _{clt, ELmin} are calculated by the following equations (40), (41), and (42).

  The range in which the target is buried in the ground clutter main lobe can be calculated by the following equation (43).

  The range in which the target calculated by equation (43) is buried in the ground clutter main lobe is as shown in FIG. FIG. 18 shows a case where there is a target within the ground clutter main lobe range when a transmission RF signal subjected to down-chirp modulation is transmitted.

Since the target is out of the ground clutter main lobe range when the up-chirp modulated transmission RF signal is transmitted, the target becomes detectable. Therefore, the transmission means 2B has the distance resolution ΔR ′ _FM and the sampling interval ΔR _FM after FM ranging satisfying the expressions (4) to (6), the distance resolution ΔR ′ _PC after correlation processing, and the folding distance R _pri of 1PRI. In addition to the parameters, the operation is based on the parameters for which the chirp code chirp considering the ground clutter main lobe range is set. As shown in FIG. 18, when detecting a target within the ground clutter main lobe range in the case of down-chirp modulation, the code chirp = 1 for up-chirp modulation is set.

  As described above, according to the third embodiment, the transmission unit 2B that operates based on the parameter set by adding the parameter that the target is not buried in the ground clutter main lobe is provided. An improved radar apparatus can be obtained. In the third embodiment, the case where the speed compensation unit 204 is provided has been described. However, the same effect can be obtained even when the speed compensation unit 204 is not provided.

Embodiment 4 FIG.
A radar apparatus according to Embodiment 4 of the present invention will be described with reference to FIGS. FIG. 19 is a block diagram showing a configuration of a radar apparatus according to Embodiment 4 of the present invention.

  In FIG. 19, a radar apparatus according to Embodiment 4 of the present invention is provided with an antenna 1, a transmission means 2B, a transmission / reception switch 7, a receiver 8, a signal processor 200D, and a display 9. ing.

  Since the radar device according to the fourth embodiment is different from the radar device according to the third embodiment except for the signal processor 200D, the same components are denoted by the same reference numerals, and description thereof is omitted. To do.

  That is, as shown in FIG. 19, the signal processor 200D is different from the signal processor 200B according to the embodiment in that the filter processing unit 205 is included in the distance map creating unit 201B after distance-FM ranging in the PRI. Since the rest is the same, the same reference numerals are attached to the same parts, and the description is omitted.

  The signal processor 200D performs the process shown in FIG. 20 on the received beat signal.

  In this embodiment, ground clutter side lobes are further assumed as clutter, and filtering is performed for the purpose of reducing ground clutter side lobes. When there is a ground clutter having a high strength, the target may be buried in the ground clutter side lobe as shown in FIG. 22 even if the target is at a distance different from the ground clutter main lobe as shown in FIG.

The filter processing unit 205 calculates filter parameters for attenuating the ground clutter main lobe and attenuating the ground clutter side lobe according to the following equations (44), (45), and (46). Here, f _c1 and f _c2 are stop band edge frequencies, f _a1 and f _a2 are cut-off frequencies, α is a bandwidth allowing a preset stop band bandwidth, β is a preset transition bandwidth, a _c is the passband ripple amount set in advance, a _a is the stopband attenuation amount set in advance. Further, min (X, Y) represents the minimum value of variables X and Y, and max (X, Y) represents the maximum value of variables X and Y.

The filter processing means 205 creates an N _flt- order filter flt (p) having parameters calculated by the equations (44) to (46) and preset filter characteristics. In this embodiment, an FIR (Finite Impulse Response) filter will be described as a filter, but the same effect can be obtained when an IIR (Infinite Impulse Response) filter is used.

  As shown in FIG. 23, since the filter characteristic that the ground clutter main lobe attenuates is provided, the ground clutter main lobe and the ground clutter side lobe can be attenuated after the filtering process.

For the purpose of reducing the ground clutter side lobe, the filter processing means 205 performs a filter process in the PRI direction by the following equation (48) on the signal R _{V · Ex} (n, l) after the pulse compression. The processed signal R _flt (n, l) is output.

The FM ranging means 203 performs an IFFT on the input filtered signal R _flt (n, l) at the point H in the PRI direction to obtain a distance map in the PRI-distance map R _FM R _PC (after FM ranging). k _h, l) to output.

  As shown in FIG. 24, by performing the filter processing, the ground clutter main lobe and side lobes in the distance direction after the FM ranging of the distance map in the PRI after the distance-FM ranging are reduced, and the target detection performance is improved. .

  As described above, according to the fourth embodiment, since the filter processing means 205 is provided to perform the filter processing so that the target is not buried in the ground clutter side lobe, the clutter separation performance is improved, that is, the target detection is performed. A radar device with improved performance can be obtained. In the fourth embodiment, the case where the speed compensation unit 204 is provided has been described. However, the same effect can be obtained even when the speed compensation unit 204 is not provided. Further, the same effect can be obtained when the transmission unit 2 is used instead of the transmission unit 2B.

Embodiment 5 FIG.
A radar apparatus according to Embodiment 5 of the present invention will be described with reference to FIGS. FIG. 25 is a block diagram showing a configuration of a radar apparatus according to Embodiment 5 of the present invention.

  In FIG. 25, a radar apparatus according to Embodiment 5 of the present invention is provided with an antenna 1, a transmission means 2B, a transmission / reception switch 7, a receiver 8, a signal processor 200E, and a display 9. ing.

  Since the radar apparatus according to this embodiment is different from the radar apparatus according to the above-described embodiment except for the signal processor 200E, the same parts are denoted by the same reference numerals, and description thereof is omitted.

  That is, as shown in FIG. 25, the signal processor 200E replaces the correlation means 202 and the FM ranging means 203 of the distance map creation means 201B after the distance-FM ranging in the PRI of the signal processor 200B according to the embodiment. The distance map generation means 201D after the distance-FM ranging is different from the correlation means 202B and the FM ranging means 203B, and the other parts are the same. Omitted.

  The signal processor 200E performs the process shown in FIG. 26 on the received beat signal.

Correlation means 202B performs window function processing in order to reduce the influence of clutter after pulse compression. Correlation means 202B calculates a window function wind _PC (m _τ ) for correlation processing by the following equation (49). Here, the window function for correlation processing is described as a Hamming window, but the same effect can be obtained when other window functions are used.

The correlation means 202B multiplies the reference signal Ex (m _τ ) after A / D conversion by the window function wind _PC (m _τ ) for correlation processing by the following equation (50), and the reference signal after the window function processing Ex ′ (m _τ ) is calculated.

Correlation means 202B uses reference signal Ex ′ (m _τ ) after window function processing instead of reference signal Ex (m _τ ) after A / D conversion, according to equations (22) to (28), A signal R ′ _{V · Ex} (n, l) after pulse compression subjected to window function processing is output.

  As shown in FIG. 27, by performing the window function process in the correlation process, the ground clutter side lobe is reduced and the target detection performance is improved.

The FM ranging means 203B calculates the window function wind _FM (n) for FM ranging by the following equation (51). Here, the window function for FM ranging will be described as a Hamming window, but the same effect can be obtained when other window functions are used.

The FM ranging means 203B multiplies the signal R ′ _{V · Ex} (n, l) after the pulse compression subjected to the window function processing by the following equation (52) and the window function wind _FM (n) for FM ranging. , A pulse-compressed signal R ″ _{V · Ex} (n, l) obtained by performing window function processing in the PRI direction is calculated.

The FM ranging means 203B replaces the signal R _{V · Ex} (n, l) after the pulse compression with the signal R ″ _{V · Ex} (n, l) after the pulse compression in which the window function processing is performed in the PRI direction. (29) as the distance map after distance -FM ranging in PRI by IFFT at point H in the PRI direction _{R FM R PC (k h,} l) to output a.

  As shown in FIG. 28, by performing window function processing in the case of FM ranging, ground clutter side lobes are reduced, and target detection performance is improved.

  As described above, according to the fifth embodiment, since the correlating means 202B and the FM ranging means 203B for performing the window function process so that the target is not buried in the ground clutter side lobe are provided, the clutter separation performance is improved. It is possible to obtain a radar apparatus that is improved, that is, improved in target detection performance. In the embodiment, both the correlation process and the FM ranging are performed by adding the window function process. However, when the correlation process or the FM ranging is added to either the correlation process or the FM ranging, the same effect is obtained. In the fifth embodiment, the case where the speed compensation unit 204 is provided has been described. However, the same effect can be obtained even when the speed compensation unit 204 is not provided. Further, the same effect can be obtained when the transmission unit 2 is used instead of the transmission unit 2B.

Embodiment 6 FIG.
A radar apparatus according to Embodiment 6 of the present invention will be described with reference to FIGS. FIG. 29 is a block diagram showing a configuration of a radar apparatus according to Embodiment 6 of the present invention.

  In FIG. 29, the radar apparatus according to Embodiment 6 of the present invention is provided with an antenna 1, a transmission means 2B, a transmission / reception switch 7, a receiver 8, a signal processor 200F, and a display 9. ing.

  Since the radar apparatus according to the sixth embodiment is different from the radar apparatus according to the above-described embodiment except for the signal processor 200F, the same parts are denoted by the same reference numerals, and the description thereof is omitted. .

  That is, as shown in FIG. 29, the signal processor 200F replaces the distance in the PRI of the signal processor 200B according to Embodiment 3 with the speed compensation means 204 of the distance map creation means 201B after FM ranging, instead of the distance. The difference is that the speed compensation means 204B of the distance map creation means 201F after FM ranging is provided and the target relative speed calculation means 222 is different, and the other parts are the same. Additional description will be omitted.

  The signal processor 200F performs the process shown in FIG. 30 on the received beat signal.

In the sixth embodiment, the transmission signal frequency sweep time T _L performs up-chirp modulation will first be described as a case of performing the down-chirp modulation for the next transmission signal frequency sweep time T _L.

The speed compensation means 204B performs speed compensation on the received beat signal S (n, m) by the equation (35) using the target relative speed v ′ input from the target relative speed calculation means 222, and after speed compensation. The reception beat signal S _{v, cor} (n, m) is output. However, when the target relative speed v ′ is not input from the target relative speed calculation unit 222, the speed compensation unit 204B outputs the received beat signal S (n, m) without performing speed compensation.

  The correlation means 202 and the FM ranging means 203 output a distance map in the PRI after the distance-FM ranging. As shown in FIG. 31, when speed compensation is not performed, distance measurement is performed at different distances by up-chirp modulation and down-chirp modulation due to the influence of the target relative speed.

The target relative distance calculation means 221 calculates the target relative distance regardless of whether speed compensation is performed. Here, the target relative distance when speed compensation is not performed by up-chirp modulation is R _u , and the target relative distance when speed compensation is not performed by down-chirp modulation is R _d . Ranging results obtained when up-chirp modulation or down-chirp modulation is performed without speed compensation are measured at different distances as shown in FIG.

The target relative speed calculation means 222 solves the simultaneous equations of Expression (53) and calculates the target relative speed v ′ according to Expression (54). However, K _R and K _v are calculated by the equations (55) and (56).

Further, as shown in FIG. 33, the simultaneous equation of Expression (57) is established in consideration of the target movement during the transmission signal frequency sweep time _TL . When considering the target movement during the transmission signal frequency sweep time _TL , the target relative speed calculation unit 222 solves the simultaneous equation of Expression (57) and calculates the target relative speed v ′ according to Expression (58). By considering the target movement between up-chirp modulation and the down-chirp modulation transmission signal frequency sweep time T _L, it is possible to accurately calculate the target relative speed.

  The target relative speed calculation unit 222 outputs the calculated target relative speed v ′ to the speed compensation unit 204B.

  As described above, according to the sixth embodiment, even when the target relative speed for speed compensation cannot be obtained in advance, speed compensation is not performed, and distance measurement results obtained when up-chirp modulation and down-chirp modulation are performed. By calculating the target relative speed, a radar apparatus capable of calculating the target relative distance can be obtained. Further, in the sixth embodiment, the case where the transmission unit 2B is provided has been described, but the same effect can be obtained when the transmission unit 2 is used instead of the transmission unit 2B.

Embodiment 7 FIG.
A radar apparatus according to Embodiment 7 of the present invention will be described with reference to FIGS. 34 and 35. FIG. FIG. 34 is a block diagram showing the configuration of the radar apparatus according to Embodiment 7 of the present invention.

  In FIG. 34, the radar apparatus according to Embodiment 7 of the present invention is provided with an antenna 1, a transmission means 2C, a transmission / reception switch 7, a receiver 8, a signal processor 200, and a display 9. ing.

  Since the radar apparatus according to this embodiment is different from the radar apparatus according to the above-described first embodiment except for the transmission unit 2C, the other parts are the same.

  That is, as shown in FIG. 34, the transmitting means 2C has a local oscillator 6B instead of the local oscillator 6 of the transmitting means 2 according to the embodiment, and the other parts are the same, and the same parts are the same. Reference numerals are added and description is omitted.

The transmission means 2C has parameters of the distance resolution ΔR ′ _FM after FM ranging and the sampling interval ΔR _FM satisfying the expressions (4) to (6), the distance resolution ΔR ′ _PC after the correlation process, and the folding distance R _pri of 1PRI. Is set.

Hereinafter, the operation of the local oscillator 6B will be described with reference to FIG. The local oscillator 6B generates a local oscillation signal L ₀ (t) represented by the following equation (59), which is stepwise frequency modulated at a PRI interval with a transmission signal frequency sweep time T _L and a transmission signal bandwidth B _L. And output to the pulse modulator 5 and the receiver 8. Here, the frequency modulation width Δf of the PRI interval is calculated by the following equation (60).

The local oscillator 6B performs frequency modulation stepwise, but the processing for the received beat signal performs the same processing, so the signal processor 200 performs the processing shown in FIG. 7 on the received beat signal. However, since frequency modulation is performed in stages, the sampling interval of the distance after FM ranging is the same as the distance resolution ΔR ′ _FM after FM ranging. The need for frequency modulation within the pulse is eliminated, and the hardware scale can be reduced.

  As described above, according to the seventh embodiment, it is not necessary to perform frequency modulation within the pulse, the hardware scale can be reduced, and the target relative distance can be accurately calculated. Can be obtained.

Embodiment 8 FIG.
A radar apparatus according to Embodiment 8 of the present invention will be described with reference to FIGS. FIG. 36 is a block diagram showing a configuration of a radar apparatus according to Embodiment 8 of the present invention.

  In FIG. 36, the radar apparatus according to Embodiment 8 of the present invention includes an antenna 1, a transmission means 2, a transmission / reception switch 7, a receiver 8, a signal processor 200G, and a display 9. ing.

  Since the radar apparatus according to the eighth embodiment is different from the radar apparatus according to the first embodiment except for the signal processor 200G, the same components are denoted by the same reference numerals, and description thereof is omitted. To do.

  That is, as shown in FIG. 36, the signal processor 200G includes the second target candidate detection unit 206 and the distance map creation unit 201 after distance-FM ranging in the PRI of the signal processor 200 according to Embodiment 1. The difference is that the distance compensating means 207 is provided. Further, the distance map creation means 201 after distance-FM ranging in the PRI of the signal processor 200 according to the first embodiment may be in any order of the correlation means 202 and the FM ranging means 203. Since the distance map creation means 201G after distance-FM ranging in the PRI of the signal processor 200G performs distance compensation using the distance measurement result of FM ranging, the difference is that FM ranging is performed before distance compensation. Since other than that is the same, the same code | symbol is attached | subjected to the same part and description is abbreviate | omitted.

The processing contents of each means for the received beat signal shown in FIG. 37 will be described. The FM ranging means 203 replaces the pulse-compressed signal R _{V · Ex} (n, l) according to the equation (29) with the received beat signal S (n, m) represented by the equation (19) in the PRI direction. By performing IFFT at the point H, a distance map R _FM R ′ _PC (k _h , l) within the PRI (before correlation processing) -FM ranging is output to the second target candidate detection means 206. However, the distance in the PRI (before correlation processing) -distance map R _FM R ′ _PC (k _h , l) after FM ranging is a signal in the PRI before performing pulse compression as shown in FIG. .

The second target candidate detection means 206 uses the equations (31) and (32) for the distance map in the PRI (before correlation processing) -distance map R _FM R ′ _PC (k _h , l) after FM ranging. And target candidates are detected by CFAR processing. Further, the relative distance between the PRIs of the detected target candidates is calculated by calculating the relative distance R _FM (k _h ) between the PRIs using the equation (30), and is output to the distance compensation unit 207 as a compensation relative distance. In addition, when improving the detection probability of the target candidate, the second target candidate detection unit 206 integrates in the distance direction in the PRI by the following equation (61). In this case, the target candidate is detected by performing CFAR processing on the signal after integration in PRI shown in FIG. 39, and the relative distance is calculated.

  Here, the purpose of the distance compensation means 207 will be described. The received beat signal S (n, m) represented by Expression (19) is subjected to frequency modulation between a plurality of PRIs and code modulation within a pulse, and is represented by the following Expression (62). When the chirp rate is high or the target is a long distance, the term affects the correlation processing as shown in FIG. 40, and the distance resolution and the side lobe can be degraded.

  Therefore, the distance compensation means 207 uses the inputted compensation relative distance to compensate for a term that affects the correlation process, thereby improving the distance measurement performance.

Next, the operation of the distance compensation unit 207 will be described. The distance compensator 207 uses the relative distance R _FM of the target candidates input from the second target candidate detector 206, and the distance in the PRI (before correlation processing) -after the FM ranging according to the following equation (63) Distance compensation is performed on the distance map R _FM R ′ _PC (k _h , l), and the distance within the PRI subjected to distance compensation (before correlation processing) −distance map R _FM R ′ ′ _PC (k after FM ranging) _h 1 and l) are output to the correlation means 202.

  In the eighth embodiment, the compensation relative distance is obtained from the signal after FM ranging. However, when the compensation relative distance is set in advance, it may be used. In the case of the sixth embodiment, the second target relative distance calculating means (not shown) obtains the relative distance by the following equation (64), and the same effect is obtained by performing distance compensation using the relative distance. can get.

Correlation means 202, wherein the distance of the formula (28) to the used as well distances compensated within PRI from (22) (pre-correlation) -FM distance map after the ranging _{R FM R '''PC (} k h , L) and the reference signal Ex (m _τ ), that is, pulse compression is performed, and a distance map R _FM R _PC (k _h , l) after distance-FM ranging in PRI is output.

As described above, according to the eighth embodiment, the FM ranging means 203, the frequency modulation, and the target relative distance affect the correlation processing before the correlation means 202 in order to perform FM ranging before the correlation processing. In order to compensate the distance in the PRI (before the correlation process) -the second target candidate detecting means for detecting the target candidate from the distance map R _FM R ′ _PC (k _h , l) after the FM ranging and obtaining the relative distance 206. Since the distance compensator 207 performs distance compensation that compensates a term affecting the correlation processing using the relative distance of the target candidate, the frequency modulation over a plurality of PRIs and the influence of the target relative distance are correlated. A radar apparatus with high distance resolution can be obtained without degrading compression characteristics, that is, distance resolution, side lobes, and the like during processing.

  1 Antenna 2, 2, 2B, 2C Transmitting means, 3 Transmitter, 4 In-pulse modulation signal generator, 5 Pulse modulator, 6, 6B Local oscillator, 7 Transmission / reception switch, 8 Receiver, 9 Display, 200, 200B , 200D, 200E, 200F, 200G Signal processor, 201, 201B, 201C, 201D, 201F, 201G Distance map creation means, 202, 202B Correlation means, 203, 203B Ranging means, 204, 204B Speed compensation means, 205 Filter processing Means 206 second target candidate detection means 207 distance compensation means 220 target candidate detection means 221 target relative distance calculation means 222 target relative speed calculation means

Claims (8)

Frequency modulation over multiple PRIs based on distance resolution after FM ranging that can eliminate distance ambiguity of distances in PRI and parameters that make distance resolution in PRI more accurate than distance resolution after FM ranging Transmitting means for emitting a transmission signal pulse-modulated by PRI with respect to the carrier signal;
The transmission signal reflected back from the target is received as a reception signal, and the reception signal is down-converted using the carrier signal obtained from the transmission means, and converted into a reception beat signal sampled in the PRI. Receiving means for
FM ranging is performed on the received beat signal sampled in the PRI obtained from the receiving means, and the distance in the PRI for calculating the relative distance to the target -the distance in the PRI for creating the distance map after the FM ranging- A distance map creation means after FM ranging;
A target candidate detecting means for detecting a target candidate based on a signal strength with respect to a distance map in the PRI-distance map after FM ranging obtained from the distance in the PRI-distance map creating means after the FM ranging;
A target relative distance calculating means for canceling the distance ambiguity of the distance in the PRI and calculating the relative distance to the target using the distance after the FM ranging of the target candidate obtained from the target candidate detecting means. Radar equipment. The radar apparatus according to claim 1, wherein the distance map creating means after distance-FM ranging in the PRI adds speed compensation so as to reduce the influence of the target movement using the input speed. Based on the relationship between the radar device and the clutter, the transmission means embeds the target in the clutter on the distance in the PRI-distance map in the PRI created by the distance map creation means after the FM ranging. The radar apparatus according to claim 1, wherein a parameter is added so as not to be present. The radar apparatus according to claim 1, wherein the distance map creation means after the distance-FM ranging in the PRI performs a filtering process so as to reduce the influence of the clutter based on the relationship between the radar apparatus and the clutter. The radar apparatus according to claim 1, wherein the distance map creation means after distance-FM ranging in the PRI adds window function processing so as to reduce the influence of clutter. 3. A target relative speed calculating means for calculating a relative speed with respect to a target using a target candidate obtained from a received signal in which transmission signals at different times are reflected back from the target. The radar apparatus described. Instead of the transmission means, a plurality of PRIs based on distance resolution after FM ranging that can eliminate the distance ambiguity of distances in PRI, and parameters that make the distance resolution in PRI more accurate than the distance resolution after FM ranging. The radar apparatus according to claim 1, further comprising: a transmission unit that radiates a transmission signal that is pulse-modulated by PRI with respect to a carrier signal that is frequency-modulated step by step. The transmission means applies intra-pulse modulation to the carrier signal with PRI,
The distance map creation means after distance-FM ranging in the PRI adds correlation processing with intra-pulse modulation to the received beat signal. 8. Radar device.

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