WO2019073597A1

WO2019073597A1 - Radar device

Info

Publication number: WO2019073597A1
Application number: PCT/JP2017/037196
Authority: WO
Inventors: 隆文永野; 良次澤; 佐藤　貴志; 立範小林; 洋介勝又
Original assignee: 三菱電機株式会社
Priority date: 2017-10-13
Filing date: 2017-10-13
Publication date: 2019-04-18
Also published as: JP6615405B2; JPWO2019073597A1

Abstract

A distance calculation unit (22): creates two sets, each including at least two frequency components among a plurality of frequency components included in a cross-spectrum in a plurality of frequency bands calculated by a cross-spectrum calculation unit (21); and estimates a delay time by employing a correlation between the frequency components corresponding to one another between the two sets.

Description

Radar equipment

The present invention relates to a radar device that calculates a distance to a target.

In recent years, in order to improve the separation performance of a target, a radar device is required to have high distance resolution.
As means of the radar apparatus for achieving high resolution of the distance, means for achieving wide band of the frequency band is effective.
However, since the available frequencies are tight, it is difficult to broaden the frequency band. For this reason, there is a need for a technique for achieving high distance resolution by combining a plurality of distant frequency bands.
The following Patent Document 1 discloses a radar device which realizes high resolution of the distance.

Japanese Patent Application Laid-Open No. 11-133130

Since the conventional radar device is configured as described above, high resolution can be realized. However, when a plurality of distant frequency bands are combined and the combined frequency band is used, there is a problem that a false target may be generated at a distance at which no target actually exists.
As described above, the principle that false targets are generated is that, when an incoming direction of radio waves from a target is estimated using an array antenna, if a plurality of elements constituting the array antenna are widely spaced, This is similar to the principle that false targets are generated as a result of grating lobes being generated due to the periodicity of the phase difference.

The present invention has been made to solve the problems as described above, and it is an object of the present invention to obtain a radar device capable of achieving high distance resolution without causing generation of a false target.

A radar device according to the present invention generates a linear frequency modulation signal in a plurality of distant frequency bands and outputs a combined signal of the generated plurality of frequency modulation signals, and a signal generation unit A signal transmitting unit that transmits the synthesized signal, a signal receiving unit that receives a reflected signal that is a signal that is reflected by the synthesized signal transmitted by the signal transmitting unit to a target, a reflected signal received by the signal receiving unit, A cross spectrum calculation unit that calculates cross spectra in a plurality of frequency bands with the composite signal transmitted by the signal transmission unit, and a time difference between the reception time of the reflected signal received by the signal reception unit and the transmission time of the composite signal And a distance calculation unit that estimates a delay time of a certain reflected signal and calculates a distance to a target from the delay time. Of a plurality of frequency components included in the cross spectrum calculated by the calculation unit, two sets including two or more frequency components are generated, and the relative relationship between the corresponding frequency components is used between the two sets. To estimate the delay time.

According to the present invention, the distance calculation unit generates two sets including two or more frequency components among the plurality of frequency components included in the cross spectrum calculated by the cross spectrum calculation unit, and Since the delay time is estimated using the relative relationship of the corresponding frequency components among the sets, there is an effect that high distance resolution can be realized without causing the generation of a false target.

It is a block diagram which shows the radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the signal processing circuit 19 of the radar apparatus by Embodiment 1 of this invention. FIG. 2 is a hardware configuration diagram showing hardware of a signal processing circuit 19; FIG. 18 is a hardware configuration diagram of a computer when the signal processing circuit 19 is realized by software or firmware. It is a flowchart which shows the process sequence in case the signal processing circuit 19 is implement | achieved by software or a firmware. It is explanatory drawing which shows an example of two sets produced | generated from the several frequency component contained in the cross spectrum. FIG. 16 is an explanatory drawing showing an example of the results of frequency modulation signals in a plurality of frequency bands generated by DDS 4-1 to 4-S and the delay time deviation between the frequency bands being compensated. It is explanatory drawing which shows the example of two shift invariant sub arrays in the estimation problem of DOA equivalent to the estimation problem of delay time when arrangement | positioning of two sets becomes central symmetry. It is an explanatory view showing an example of a shift invariant sub-array in which three element arrays of the same element number (six elements) of sub-array (1) and sub-array (2) are arranged at equal intervals.

Hereinafter, in order to explain the present invention in more detail, a mode for carrying out the present invention will be described according to the attached drawings.

Embodiment 1
FIG. 1 is a block diagram showing a radar apparatus according to Embodiment 1 of the present invention.
In FIG. 1, a signal generation unit 1 includes a reference signal generation circuit 2, a control device 3, a DDS (Direct Digital Synthesizer: digital direct synthesis oscillator) 4-1 to 4-S, a high frequency signal generation circuit 5, and a mixer 6-1 to 6-S, filters 7-1 to 7-S, and synthesizer 8 are provided.
The signal generation unit 1 generates linear frequency modulation signals in a plurality of distant frequency bands, and outputs the generated composite signal of the plurality of frequency modulation signals to the signal transmission unit 9.

The reference signal generation circuit 2 is a circuit that generates a reference signal.
The control device 3 outputs control information indicating transmission start times, start frequencies, chirp rates and signal lengths of frequency modulation signals in a plurality of frequency bands to the DDSs 4-1 to 4-S and the signal processing circuit 19.
The DDSs 4-1 to 4-S generate a frequency modulation signal according to the reference signal generated from the reference signal generation circuit 2 and the control information output from the control device 3, and the generated frequency modulation signal is converted to a mixer 6-1. Output to 6-S.

The high frequency signal generation circuit 5 is a circuit that generates a high frequency signal.
The mixers 6-1 to 6-S mix the high frequency signals generated from the high frequency signal generation circuit 5 with the frequency modulation signals output from the DDS 4-1 to 4-S, and The frequency of the output frequency modulation signal is converted, and the frequency modulation signal after frequency conversion is output to the filters 7-1 to 7-S.
The filters 7-1 to 7-S extract a signal of a desired signal band from the frequency modulation signals output from the mixers 6-1 to 6-S, and output the extracted signal band signal to the synthesizer 8.
The combiner 8 combines the output signals of the filters 7-1 to 7-S and outputs a combined signal of a plurality of output signals to the amplifier 10 as a transmission signal.

The signal transmission unit 9 includes an amplifier 10, a transmission / reception switch 11 and an antenna 12.
The signal transmission unit 9 transmits a transmission signal which is a combined signal output from the signal generation unit 1.
The amplifier 10 amplifies a transmission signal which is a combined signal output from the combiner 8 of the signal generation unit 1, and outputs the amplified transmission signal to the transmission / reception switch 11.
The transmission / reception switch 11 outputs the transmission signal output from the amplifier 10 to the antenna 12.
The transmission / reception switch 11 also outputs the reception signal output from the antenna 12 to the amplifier 14.
The antenna 12 radiates the transmission signal output from the transmission / reception switch 11 toward a target and radiates it into space, while receiving a reflection signal which is a signal reflected by the target, and using the received reflection signal as a reception signal, the transmission / reception switch Output to 11.

The signal receiving unit 13 includes a transmission / reception switch 11, an antenna 12, an amplifier 14, a high frequency signal generation circuit 5, a mixer 15, a filter 16, an amplifier 17 and an analog-to-digital converter (hereinafter referred to as A / D converter) 18. ing.
The signal receiving unit 13 receives a reflection signal which is a signal in which the transmission signal transmitted by the signal transmission unit 9 is reflected to a target.

The amplifier 14 amplifies the received signal output from the transmission / reception switch 11 and outputs the amplified received signal to the mixer 15.
The mixer 15 mixes the high frequency signal generated from the high frequency signal generation circuit 5 with the received signal output from the amplifier 14, converts the frequency of the received signal output from the amplifier 14, and converts the frequency of the received signal Is output to the filter 16.
The filter 16 extracts a signal of a desired signal band from the reception signal output from the mixer 15, and outputs the extracted signal of the signal band to the amplifier 17.
The amplifier 17 amplifies the output signal of the filter 16 and outputs the amplified output signal to the A / D converter 18.
The A / D converter 18 converts the output signal of the amplifier 17 from an analog signal to a digital signal, and outputs the digital signal to the signal processing circuit 19.

The signal processing circuit 19 includes a cross spectrum calculation unit 21 and a distance calculation unit 22 shown in FIG.
FIG. 2 is a block diagram showing a signal processing circuit 19 of the radar device according to the first embodiment of the present invention.
FIG. 3 is a hardware configuration diagram showing the hardware of the signal processing circuit 19.
The cross spectrum calculation unit 21 is realized by, for example, the cross spectrum calculation circuit 31 illustrated in FIG.
The cross spectrum calculation unit 21 calculates cross spectra in a plurality of frequency bands of a reception signal which is a reflected signal received by the signal reception unit 13 and a transmission signal which is a combined signal transmitted by the signal transmission unit 9 Conduct.
The distance calculation unit 22 is realized by, for example, the distance calculation circuit 32 illustrated in FIG.
The distance calculation unit 22 estimates the delay time of the received signal, which is the time difference between the reception time of the reception signal received by the signal reception unit 13 and the transmission time of the transmission signal transmitted by the signal transmission unit 9. A process of calculating the distance to the target from the delay time is performed.
In addition, the distance calculation unit 22 generates two sets including two or more frequency components among the plurality of frequency components included in the cross spectrum calculated by the cross spectrum calculation unit 21, and generates two sets. A process of estimating a delay time is performed using the relative relationship between corresponding frequency components.

In FIG. 2, it is assumed that each of the cross spectrum calculation unit 21 and the distance calculation unit 22 which are components of the signal processing circuit 19 is realized by dedicated hardware as shown in FIG. 3. That is, what is realized by the cross spectrum calculation circuit 31 and the distance calculation circuit 32 is assumed.
Here, the cross spectrum calculation circuit 31 and the distance calculation circuit 32 may be, for example, a single circuit, a complex circuit, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA). Or a combination thereof.

The components of the signal processing circuit 19 are not limited to those realized by dedicated hardware, and the signal processing circuit 19 may be realized by software, firmware, or a combination of software and firmware. Good.
The software or firmware is stored as a program in the memory of the computer. A computer means hardware that executes a program, and for example, a central processing unit (CPU), a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a processor, or a digital signal processor (DSP). Do.
FIG. 4 is a hardware configuration diagram of a computer when the signal processing circuit 19 is realized by software or firmware.
When the signal processing circuit 19 is realized by software or firmware, a program for causing the computer to execute the processing procedure of the cross spectrum calculation circuit 31 and the distance calculation circuit 32 is stored in the memory 41, and the processor 42 of the computer calculates the memory 41. The program stored in may be executed.
FIG. 5 is a flowchart showing the processing procedure when the signal processing circuit 19 is realized by software or firmware.

Before describing the operation of the radar apparatus according to the first embodiment, a method for estimating the delay time of the received signal will be described.
The estimation problem of delay time can be handled as an estimation problem of DOA (Direction of Arrival) using an array antenna.
In a radar device transmitting linear frequency modulation signals in a plurality of spaced frequency bands, the plurality of frequency bands in the estimation problem of delay time corresponds to the array of elements spaced apart in the estimation problem of DOA ing.
The cross spectrum x (τ) for received signals of a plurality of frequency bands in the delay time estimation problem is expressed by the following equation (1), similarly to the received signal in the DOA estimation problem.

In equation (1), A (τ) is a steering matrix defined by the following equations (2) to (4).

τ is the delay time of the received signal of the signal reflected to the K targets, and α is the complex amplitude of the received signal. T is a symbol representing transposition.

Equation (4) shows the steering vector of the s (s = 1, 2,..., S) element array, which corresponds to the s-th frequency band among the S frequency bands .
The s-th element array is composed of m _s elements, and the total number of elements in the entire element array is M.

Δω is the discrete frequency interval of the Fourier transform, and f _s is the center frequency of the s-th frequency band.

As shown in FIG. 6, the radar apparatus according to the first embodiment generates two sets including two or more frequency components among a plurality of frequency components included in the cross spectrum in a plurality of frequency bands. The delay time of the received signal, which is a reflected signal, is estimated using the relative relationship between the corresponding frequency components between the two sets.
FIG. 6 is an explanatory view showing an example of two sets generated from a plurality of frequency components included in the cross spectrum.
The radar apparatus, as shown in FIG. 6, shifts the frequency of the plurality of frequency components included in one of the two sets, and then shifts the frequency on the frequency axis of the plurality of frequency components shifted in frequency. Two sets are generated such that the arrangement is identical to the arrangement on the frequency axis of the plurality of frequency components included in the other set.
In FIG. 6, among the plurality of frequency components included in one set, the frequency component having the lowest frequency and the plurality of frequency components included in the other set, the frequency component having the lowest frequency. And are illustrated as corresponding frequency components between the two sets.
However, this is only an example, and among the plurality of frequency components included in one set, the frequency component having the nth lowest frequency and the plurality of frequency components included in the other set The frequency component with the nth lowest frequency is the corresponding frequency component between the two sets.
The property of the two sets is referred to as "shift invariant", and the predetermined frequency to be shifted is the frequency difference between the two frequency components contained in the same frequency band. The two frequency components are, for example, components of two adjacent frequencies.
When the delay time estimation problem is treated as a DOA estimation problem, in FIG. 8 and FIG. 9 described later, a plurality of elements included in the sub array (1) corresponds to one set, and the sub array (2) The plurality of included elements correspond to the other set.

As a method of estimating the delay time of the received signal from the relative relationship between corresponding frequency components between the two sets, for example, a DOA estimation method of ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) type can be used. When using the standard ESPRIT method, a plurality of frequency bands can be arranged at arbitrary intervals, and the frequency bandwidth can also be set to be different in each frequency band.

In DOA estimation, the covariance matrix R of the measurement matrix X composed of a plurality of received signals is calculated by the following equation (9). H is a symbol representing the complex conjugate transpose of the matrix.

However, when the delay time estimation problem is treated as a DOA estimation problem, since the covariance matrix R is not usually full rank due to signal coherency, a means for recovering the rank is required.

Therefore, the radar apparatus according to the first embodiment applies the spatial averaging method defined by the following equation (11) to the covariance matrix R to calculate the covariance matrix R tilda. Covariance matrix R Tilda is a covariance matrix whose rank is recovered. In the text of the specification, it is written as "R tilda" because the character "-" can not be added above the character because of the electronic application.

In Equation (11), L is the number of sub-arrays used in spatial averaging, and B _{m, L, l} is a selection matrix defined by Equation (12) below.

In equation (13), I _n is an n × n identity matrix, and 0 _{i, j} is an i × j zero matrix.
Incidentally, applying the spatial average, the number of elements m _s tilde each element array corresponding to the frequency band is reduced as follows.

The procedure for estimating the delay time using the standard ESPRIT method is described below.
First, the radar apparatus performs eigenvalue decomposition of the covariance matrix R tilda to which spatial averaging is applied.
Here, the number of received signals as d, the absolute value is the largest d eigenvectors of E _s.

Next, the radar apparatus solves the overdetermined system of simultaneous equations (17) by the total least squares method.

Here, the simultaneous equations (17) are solved by the total least squares method, but the simultaneous equations (17) may be solved by the ordinary least squares method.

Next, the radar apparatus calculates an eigenvalue decomposition γ of the solution solved by the total least squares method, as shown in the following equation (21).

The radar apparatus calculates the delay time τ _k of the received signal as shown in the following equation (23).

In equation (23), argω _k corresponds to the phase difference Δωτ shown in equation (4).
The radar apparatus calculates the distance r _k to the target from the delay time τ _k of the received signal, as shown in the following equation (24).

In equation (24), c is the speed of light.

In the calculation of the distance to the target, an arbitrary interval can be used as an interval of a plurality of frequency bands, but by using unequal intervals, the decrease in distance resolution depending on the distance between targets is suppressed. can do.

So far, the method for estimating the delay time τ _k of the received signal has been described, but when the target is moving, different Doppler frequencies are generated for each frequency band, so the distance r _k to the target is accurate It is necessary to compensate for delay time deviation Δτ between frequency bands in order to estimate in
The delay time shift Δτ between frequency bands is expressed by the following equation (25), where α is the chirp rate of linear frequency modulation.

In equation (25), f _d is the Doppler frequency.

The delay time shift Δτ between the frequency bands is shown in FIG. 7 if the ratio of the chirp rate α _s of each frequency band to the center frequency f _s is equal as shown in the following equation (26). Thus, even if the movement speed of the target changes, it can be made equal. The delay time shift Δτ between frequency bands corresponds to the distance error between frequency bands.
In other words, if the radar apparatus generates a linear frequency modulation signal so that the ratio of the chirp rate α _s to the center frequency f _s in each frequency band becomes equal, the delay time shift Δτ between the frequency bands is compensated. can do.

FIG. 7 is an explanatory drawing showing an example of the result of compensating for the delay time deviation between the frequency bands and the frequency modulation signals in the plurality of frequency bands generated by the DDSs 4-1 to 4-S.

Next, the operation of the radar device will be described.
First, the signal generation unit 1 generates linear frequency modulation signals in a plurality of distant frequency bands, and outputs the generated composite signal of the plurality of frequency modulation signals to the signal transmission unit 9.
Hereinafter, the operation of the signal generation unit 1 will be specifically described.

The reference signal generation circuit 2 of the signal generation unit 1 generates a reference signal.
The control device 3 of the signal generation unit 1 performs control information indicating the transmission start time, the start frequency, the chirp rate, and the signal length of the frequency modulation signal in a plurality of distant frequency bands and the signal processing circuit Output to 19.
The DDSs 4-1 to 4-S of the signal generation unit 1 generate a frequency modulation signal according to the reference signal generated from the reference signal generation circuit 2 and the control information output from the control device 3, and the generated frequency modulation signal Is output to mixers 6-1 to 6-S.
FIG. 7 shows an example in which two frequency modulation signals are generated since S = 2 for simplification of the description.
Each frequency modulation signal generated by DDS 4-1 to 4-S has a chirp rate α _s of each frequency band as shown in equation (26) in order to compensate for delay time deviation between frequency bands. The ratio to the center frequency f _s is generated to be equal.

The high frequency signal generation circuit 5 of the signal generation unit 1 generates a high frequency signal.
The mixers 6-1 to 6-S of the signal generation unit 1 mix the high frequency signal generated from the high frequency signal generation circuit 5 with the frequency modulation signals output from the DDS 4-1 to 4-S, The frequency of the frequency modulation signal output from 4 to 4-S is converted, and the frequency modulation signal after frequency conversion is output to the filters 7-1 to 7-S.
The filters 7-1 to 7-S of the signal generation unit 1 extract a signal of a desired signal band from the frequency modulation signals output from the mixers 6-1 to 6-S, and combine the extracted signal of the signal band Output to
The combiner 8 of the signal generation unit 1 combines the output signals of the filters 7-1 to 7-S, and outputs a combined signal of a plurality of output signals to the amplifier 10 as a transmission signal.

The signal transmission unit 9 transmits a transmission signal which is a combined signal output from the signal generation unit 1.
The operation of the signal transmission unit 9 will be specifically described below.
When the amplifier 10 of the signal transmitter 9 receives the transmission signal from the synthesizer 8 of the signal generator 1, the amplifier 10 amplifies the transmission signal and outputs the amplified transmission signal to the transmission / reception switch 11.
The transmission / reception switch 11 of the signal transmission unit 9 outputs the transmission signal output from the amplifier 10 to the antenna 12.
The antenna 12 radiates the transmission signal output from the transmission / reception switch 11 into space toward a target.

The signal receiving unit 13 receives a reflection signal which is a signal in which the transmission signal transmitted by the signal transmission unit 9 is reflected to a target.
Hereinafter, the operation of the signal receiving unit 13 will be specifically described.
The antenna 12 receives a reflection signal which is a signal reflected to the target, and outputs the received reflection signal to the transmission / reception switch 11 as a reception signal.
The transmission / reception switch 11 of the signal reception unit 13 outputs the reception signal output from the antenna 12 to the amplifier 14.

The amplifier 14 of the signal receiving unit 13 amplifies the received signal output from the transmission / reception switch 11 and outputs the amplified received signal to the mixer 15.
The mixer 15 of the signal receiving unit 13 mixes the high frequency signal generated from the high frequency signal generation circuit 5 with the received signal output from the amplifier 14 to convert the frequency of the received signal output from the amplifier 14 The converted received signal is output to the filter 16.
The filter 16 of the signal reception unit 13 extracts a signal of a desired signal band from the reception signal output from the mixer 15, and outputs the extracted signal of the signal band to the amplifier 17.
The amplifier 17 of the signal reception unit 13 amplifies the output signal of the filter 16 and outputs the amplified output signal to the A / D converter 18.
The A / D converter 18 of the signal receiving unit 13 converts the signal output from the amplifier 17 from an analog signal into a digital signal, and outputs the digital signal to the signal processing circuit 19.

The cross spectrum calculation unit 21 of the signal processing circuit 19 includes a plurality of reception signals, which are reflection signals received by the signal reception unit 13, and a plurality of composite signals transmitted by the signal transmission unit 9, as shown in equation (1). The cross spectrum x (τ) in the frequency band is calculated.
Hereinafter, the processing content of the cross spectrum calculation unit 21 will be specifically described.

The cross spectrum calculation unit 21 performs Fourier transform on the digital signal output from the A / D converter 18 based on the transmission start times of the frequency modulation signals in a plurality of frequency bands indicated by the control signal output from the control device 3 By doing this, frequency components of frequency modulation signals (hereinafter referred to as “reception modulation signals”) in a plurality of frequency bands included in the digital signal are obtained.
Further, the cross spectrum calculation unit 21 is similar to the frequency modulation signal generated by DOS4-1 to 4-S based on the control signal output from the control device 3 and the reference signal output from the reference signal generation circuit 2. A frequency modulation signal (hereinafter referred to as "transmission modulation signal") is generated, and the generated transmission modulation signal is subjected to Fourier transform.
Cross spectrum calculation unit 21 is a cross that is a product of the frequency component of the reception modulation signal in each frequency band and the complex conjugate component of the Fourier transform of the transmission modulation signal in the frequency band corresponding to each reception modulation signal. The spectrum x (τ) is calculated respectively (step ST1 in FIG. 5).

The distance calculation unit 22 of the signal processing circuit 19 calculates the delay time τ _k of the reception modulation signal using the reception modulation signal output from the A / D converter 18 according to Equations (9) to (23). Step ST2 of FIG. 5). The delay time τ _k of the reception modulation signal is a delay time from the transmission start time of the transmission modulation signal.
Next, the distance calculation unit 22 calculates the distance r _k to the target by substituting the delay time τ _k into the equation (24) (step ST3 in FIG. 5).
Hereinafter, the calculation process of the distance r _k by the distance calculation unit 22 will be specifically described.

When the cross spectrum calculation unit 21 calculates the cross spectrum x (τ) in a plurality of frequency bands, the distance calculation unit 22 calculates a plurality of frequency components included in the cross spectrum in a plurality of frequency bands, as shown in FIG. And generate two sets including two or more frequency components.
That is, as shown in FIG. 6, the distance calculation unit 22 shifts the frequency when each of the frequencies of the plurality of frequency components included in one of the two sets is shifted by a predetermined frequency. The arrangement on the frequency axis of the plurality of frequency components generates two sets that are identical to the arrangement on the frequency axis of the plurality of frequency components included in the other set.
K ₁ represented by equation (18) represents a matrix for selecting frequency components included in one set, and K ₂ represented by equation (19) represents frequency components included in the other set. Represents the matrix to select.

Next, the distance calculation unit 22 estimates the delay time τ _k of the received signal using the relative relationship between the corresponding frequency components between the two sets, and substitutes the estimated delay time into equation (24). Then, the distance r _k to the target is calculated.

As apparent from the above, according to the first embodiment, the distance calculating unit 22 determines that two or more frequencies among the plurality of frequency components included in the cross spectrum calculated by the cross spectrum calculating unit 21. Since two sets including components are generated and the delay time is estimated by using the relative relationship between the corresponding frequency components between the two sets, high distance resolution can be achieved without causing generation of false targets. It is possible to realize the effect of
In the DOA estimation problem, the inter-element phase difference when the distance between a plurality of elements constituting the array antenna is wide causes the generation of grating lobes, but in the first embodiment, the inter-element phase difference is large. Since the relative relationship between corresponding frequency components is not used, it is possible to suppress the occurrence of false targets.

Further, according to the first embodiment, in each of the frequency bands, the signal generation unit 1 has a plurality of frequency bands such that the ratio of the chirp rate of the frequency modulation signal to the center frequency of the frequency modulation signal is equal. Since the linear frequency modulation signals in the above are generated respectively, it is possible to suppress the decrease in the calculation accuracy of the distance to the target even if the target moving speed changes.

Second Embodiment
In the second embodiment, a plurality of frequency bands are arranged in central symmetry so that the arrangement of the two sets generated by the distance calculation unit 22 is in central symmetry, and frequency modulation signals in the plurality of frequency bands are respectively arranged. An example of generation will be described.

As in the first embodiment, the signal generation unit 1 generates linear frequency modulation signals in a plurality of distant frequency bands, and generates a composite signal of the plurality of generated frequency modulation signals to the signal transmission unit 9. Output.
However, in the second embodiment, when the signal generation unit 1 generates linear frequency modulation signals in a plurality of frequency bands, two sets generated by the distance calculation unit 22 are different from the first embodiment. The plurality of frequency bands are arranged in central symmetry so that the arrangement of the two in FIG.
FIG. 8 is an explanatory drawing showing an example of two shift invariant sub-arrays in the DOA estimation problem equivalent to the delay time estimation problem when the arrangement of the two sets is centrosymmetric.
In FIG. 8, the arrangement of the sub array (1) and the sub array (2) is centrosymmetrical.
Although FIG. 8 shows an example in which the arrangement of the sub array (1) and the sub array (2) is centrosymmetrical, as shown in FIG. 9, the number of elements of the sub array (1) and the sub array (2) is the same. And the elements of the subarray (1) and the subarray (2) may be shift invariant subarrays arranged at equal intervals.

When the cross spectrum calculation unit 21 calculates the cross spectrum x (τ) in a plurality of frequency bands, the distance calculation unit 22 of the signal processing circuit 19 calculates the received signal that is the target reflected signal as in the first embodiment. The delay time τ _k is estimated.
However, the second embodiment is different from the first embodiment in that the distance calculation unit 22 uses unitary ESPRIT based on real number operation when estimating the delay time τ _k of the received signal.

The estimation process of the delay time τ _k by the distance calculation unit 22 will be specifically described below.
The distance calculation unit 22 calculates the covariance matrix R by the following equation (27) instead of the equation (9). The bar above X is a symbol representing a complex conjugate.
The calculation of the covariance matrix R according to Equation (27) corresponds to doubling the number of received signals and applying an FB (Forward Backward) spatial average.

Similar to the first embodiment, the distance calculating unit 22 applies the spatial averaging method defined by Equation (11) to the covariance matrix R to calculate the covariance matrix R tilda.

Next, the distance calculation unit 22 converts the covariance matrix R tilda into a real-valued matrix Τ (R tilda) as shown in the following equation (28).

In the formula (28), Q _{M -S (L-1)} is represented by the following formula (29) if M-S (L-1) is an even number, and M-S (L-1) is If it is odd, it is expressed by the following equation (30).

In the second embodiment, K ₁ represented by formula (18) is represented by the following formula (31), and K ₂ represented by formula (19) is represented by the following formula (32) Ru.

Thereafter, as in the first embodiment, the distance calculation unit 22 estimates the delay time τ _k of the received signal, and calculates the distance r _k to the target using the estimated delay time τ _k .

As apparent from the above, according to the second embodiment, the signal generation unit 1 performs center symmetry on a plurality of frequency bands so that the arrangement of the two sets generated by the distance calculation unit 22 becomes center symmetry. Because the frequency modulation signals in a plurality of frequency bands are respectively generated, the distance calculation unit 22 can calculate the distance to the target using unitary ESPRIT based on real number operation. As a result, it is possible to improve the calculation accuracy of the distance and reduce the calculation load.

Third Embodiment
In

Embodiments

1 and 2 above, an example is shown in which the distance calculation unit 22 calculates the distance r _k to the target using the reflection signal received by the signal reception unit 13.
In the third embodiment, the distance calculating unit 22 determines, from among the plurality of frequency components included in the reflected signal received by the signal receiving unit 13, a frequency component corresponding to the Doppler frequency generated at the target velocity. , And frequency components corresponding to frequencies adjacent to the Doppler frequency, respectively.
And the distance calculation part 22 demonstrates the example which calculates the distance r _k to a target from the signal containing each extracted frequency component.

First, the signal generation unit 1 outputs a composite signal of a plurality of frequency modulation signals at constant intervals, and the signal transmission unit 9 transmits the composite signal output from the signal generation unit 1.
The signal receiving unit 13 receives a reflection signal which is a signal in which the transmission signal transmitted by the signal transmission unit 9 is reflected to a target.
The distance calculation unit 22 Fourier transforms the measurement matrix X, which is composed of the plurality of reception modulation signals output from the A / D converter 18 of the signal reception unit 13, in the row direction.
Next, the distance calculation unit 22 corresponds to the frequency component corresponding to the Doppler frequency generated at the desired target velocity and the frequency adjacent to the Doppler frequency among the frequency components indicated by the result of the Fourier transform in the row direction. Each frequency component is extracted. Here, the Doppler frequency generated by the desired target velocity is a frequency set in advance.
In the third embodiment, the frequency component corresponding to the frequency adjacent to the Doppler frequency is a frequency component corresponding to a frequency one higher than the Doppler frequency among the frequency components indicated by the result of the Fourier transform in the row direction. And a frequency component corresponding to a frequency one lower than the Doppler frequency. However, this is only an example, and the frequency adjacent to the Doppler frequency is a frequency within 〇 Hz from the Doppler frequency if the difference from the Doppler frequency is defined as the frequency within 〇 Hz. The corresponding frequency component may be extracted.

The distance calculating unit 22 defines the extracted frequency components as a measurement matrix X ′ shown in the following equation (33), and calculates the covariance matrix R of the measurement matrix X ′.

In Equation (33), N ′ is the number of frequency components extracted by the distance calculation unit 22.
The distance calculating unit 22 estimates the delay time τ _{k of the} signal including each extracted frequency component using the calculated covariance matrix R, and uses the estimated delay time τ _k to calculate the distance r _k to the target. calculate.

As apparent from the above, according to the third embodiment, the distance calculating unit 22 generates the target frequency from among the plurality of frequency components included in the reflected signal received by the signal receiving unit 13. The frequency component corresponding to the Doppler frequency to be selected and the frequency component corresponding to the frequency adjacent to the Doppler frequency are respectively extracted, and the delay time of the signal including the extracted frequency components is estimated, so that the target It is possible to suppress the influence of the reflected signal from an object moving at a speed away from the speed of. As a result, the effect of being able to improve the calculation accuracy of the distance can be achieved as compared with the first and second embodiments.

Fourth Embodiment
In the first, second, and third embodiments, the signal generation unit 1 generates linear frequency modulation signals in a plurality of distant frequency bands and outputs a composite signal of the plurality of frequency modulation signals generated, and a signal. A signal transmission unit 9 for transmitting the combined signal output from the generation unit 1, a signal reception unit 13 for receiving a reflected signal which is a signal that is reflected by the combined signal transmitted by the signal transmission unit 9 to a target, and signal reception A cross spectrum calculation unit 21 for calculating cross spectra in a plurality of frequency bands of the reflected signal received by the unit 13 and the composite signal transmitted by the signal transmission unit 9; An example is shown in which the distance to the target is calculated using the cross spectrum in the frequency band of
In the fourth embodiment, instead of the cross spectrum calculation unit 21, beats for calculating beat signals in a plurality of frequency bands of the reflected signal received by the signal reception unit 13 and the composite signal transmitted by the signal transmission unit 9. A signal calculating unit is provided, and the distance calculating unit 22 calculates the distance from a beat signal in a plurality of frequency bands calculated by the beat signal calculating unit to a target instead of the cross spectrum calculated by the cross spectrum calculating unit 21. An example of calculation will be described.

First, sampling data of the beat signal in the s-th frequency band of the reception signal of the signal of delay time τ that is reflected to one target is expressed by equation (34) of the same format as equation (4).

m _s is the number of samples of the s-th frequency band, f _s is the center frequency of the s-th frequency band, and Δω is represented by the following equation (35).

In equation (35), α is the chirp rate, and Δt is the sampling interval of the beat signal.
Since Equations (4) and (34) have the same format, the distance calculation unit 22 treats the extracted beat signals as the measurement matrix X shown in Equation (10), so that the first and second embodiments can be performed. , 3 can be calculated. That is, if the cross spectrum is replaced with the beat signal and the plurality of frequency components included in the cross spectrum are replaced with the plurality of sample points included in the beat signal, as in the first, second, and third embodiments, The distance to the target can be calculated.
In the fourth embodiment, the distance calculation unit 22 generates two sets including two or more sample points among the plurality of sample points included in the beat signal calculated by the beat signal calculation unit, The delay time will be estimated using the relative relationship of the corresponding sample points between the two sets.

As apparent from the above, according to the fourth embodiment, the beat signal calculation unit instead of the cross spectrum calculation unit 21 combines the reflected signal received by the signal reception unit 13 with the signal transmitted by the signal transmission unit 9. Since beat signals in a plurality of frequency bands with the signal are calculated, the distance calculation unit 22 can calculate the distance to the target from the calculated beat signals. As a result, the sampling frequency can be lowered and the distance to the target can be calculated with a small amount of calculation.

In the scope of the invention, the present invention allows free combination of each embodiment, or modification of any component of each embodiment, or omission of any component in each embodiment. .

The present invention is suitable for a radar device that calculates the distance to a target.

Reference Signs List 1 signal generation unit, 2 reference signal generation circuit, 3 control devices, 4-1 to 4-S DDS, 5 high frequency signal generation circuits, 6-1 to 6-S mixer, 7-1 to 7-S filter, 8 synthesis , 9 signal transmitters, 10 amplifiers, 11 duplexers, 12 antennas, 13 signal receivers, 14 amplifiers, 15 mixers, 16 filters, 17 amplifiers, 18 A / D converters, 19 signal processing circuits, 21 cross spectrum Calculation unit, 22 distance calculation unit, 31 cross spectrum calculation circuit, 32 distance calculation circuit, 41 memory, 42 processor.

Claims

A signal generation unit that generates linear frequency modulation signals in a plurality of distant frequency bands and outputs a composite signal of the generated plurality of frequency modulation signals;
A signal transmission unit that transmits the combined signal output from the signal generation unit;
A signal reception unit that receives a reflected signal that is a signal that is a signal that is reflected at the target by the composite signal transmitted by the signal transmission unit;
A cross spectrum calculation unit that calculates cross spectra in a plurality of frequency bands of the reflected signal received by the signal reception unit and the combined signal transmitted by the signal transmission unit;
The distance for calculating the distance from the delay time to the target by estimating the delay time of the reflected signal, which is the time difference between the reception time of the reflected signal received by the signal reception unit and the transmission time of the combined signal And a calculation unit,
The distance calculation unit generates two sets including two or more frequency components among a plurality of frequency components included in the cross spectrum calculated by the cross spectrum calculation unit, and A radar apparatus characterized in that the delay time is estimated using a relative relationship of corresponding frequency components.
When the distance calculation unit shifts the frequency of the plurality of frequency components included in one of the two sets, the arrangement on the frequency axis of the plurality of frequency components shifted in frequency is the other The radar apparatus according to claim 1, wherein two sets are generated to be identical to the arrangement on the frequency axis of the plurality of frequency components included in the set of.
The distance calculation unit selects two frequency components included in the same frequency band, and shifts the frequencies of a plurality of frequency components included in one set by the frequency difference between the two frequency components. The radar apparatus according to claim 2, characterized in that:
The radar apparatus according to claim 1, wherein the signal generation unit generates the frequency modulation signals in the plurality of frequency bands by arranging the plurality of frequency bands at unequal intervals.
The signal generation unit generates linear frequency modulation signals in the plurality of frequency bands such that the ratio of the chirp rate of the frequency modulation signal to the center frequency of the frequency modulation signal is equal in each frequency band. The radar apparatus according to claim 1, characterized in that:
The signal generation unit arranges the plurality of frequency bands in central symmetry so that the arrangement of the two sets generated by the distance calculation unit becomes central symmetrical, and the frequency modulation signals in the plurality of frequency bands are The radar apparatus according to claim 1, wherein each of the radar apparatuses is generated.
The distance calculation unit is configured to, among a plurality of frequency components included in the reflected signal received by the signal reception unit, a frequency component corresponding to a Doppler frequency generated by the velocity of the target and an adjacent to the Doppler frequency The radar apparatus according to claim 1, wherein each of the frequency components corresponding to the frequency being extracted is extracted, and a delay time of a signal including the extracted frequency components is estimated.
A signal generation unit that generates linear frequency modulation signals in a plurality of distant frequency bands and outputs a composite signal of the generated plurality of frequency modulation signals;
A signal transmission unit that transmits the combined signal output from the signal generation unit;
A signal reception unit that receives a reflected signal that is a signal that is a signal that is reflected at the target by the composite signal transmitted by the signal transmission unit;
A beat signal calculation unit that calculates beat signals in a plurality of frequency bands of the reflected signal received by the signal reception unit and the combined signal transmitted by the signal transmission unit;
The distance for calculating the distance from the delay time to the target by estimating the delay time of the reflected signal, which is the time difference between the reception time of the reflected signal received by the signal reception unit and the transmission time of the combined signal And a calculation unit,
The distance calculation unit generates two sets including two or more sample points among a plurality of sample points included in the beat signal calculated by the beat signal calculation unit, and A radar apparatus characterized in that the delay time is estimated using the relative relationship of corresponding sample points.