JP3779282B2 - Radio wave radar apparatus and beat signal frequency detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radio wave radar apparatus and a beat signal frequency detection method for detecting a distance of an object and a relative speed with respect to the object.
[0002]
[Prior art]
In a conventional radio wave radar apparatus, an apparatus that detects the distance and relative speed of an object using an FM-CW radar is disclosed (for example, see Patent Document 1). A conventional method for detecting the distance of the object and the relative speed with the object will be described below.
[0003]
[Patent Document 1]
JP 2000-214250 A (2nd page, FIG. 2)
[0004]
A transmission wave having a frequency modulated by a modulation signal using a triangular wave is transmitted toward the object, and a reflected wave reflected from the object is received as a reception wave. Also, a part of the transmission wave is distributed by a distributor and mixed with the reception wave, thereby obtaining a beat signal having a frequency difference between the transmission wave and the reception wave.
[0005]
The beat signal includes information on the distance to the object and the relative speed with the object, and performs frequency analysis. The beat signal is sampled at every sampling period using an A / D converter and becomes discrete value data. Further, discrete spectrum data of the beat signal is obtained by performing a discrete Fourier transform on the beat signal that has become discrete value data. By obtaining the frequency of the beat signal from the discrete spectrum data, the distance to the object and the relative speed with the object can be calculated.
[0006]
In the case of a discrete Fourier transform in a radar, since it is usually performed after a beat function is multiplied by a window function, a discrete Fourier transform and a continuous Fourier transform are performed on the beat signal multiplied by the window function in the following description, and the result is shown. Shall.
[0007]
[Problems to be solved by the invention]
However, the prior art has the following problems. When the beat signal is subjected to frequency analysis, the continuous Fourier transform is applied when the beat signal, which is a continuous amount, is directly Fourier transformed. The continuous Fourier transform can be analyzed for any angular frequency, that is, any frequency, and the beat signal frequency can be uniquely determined by detecting the maximum spectral level from the result of the continuous Fourier transform. . However, since the beat signal sampled by the A / D converter is discrete value data, it is necessary to apply the discrete Fourier transform when performing the Fourier transform.
[0008]
In the discrete Fourier transform, Fourier expansion is performed for each value obtained by dividing the sampling frequency fs by the number of sampling points N (N is an integer equal to or greater than 1). There is a restriction that it cannot be done. Therefore, the maximum spectrum level obtained from the result of continuous Fourier transform does not necessarily match the maximum spectrum level obtained from the result of discrete Fourier transform. When the two results are different, the frequency of the beat signal detected based on the discrete Fourier transform is different from the frequency of the beat signal uniquely detected based on the continuous Fourier transform. As a result, there is a problem that the distance to the object and the relative speed with the object cannot be accurately calculated using the discrete Fourier transform.
[0009]
The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a radio wave radar apparatus that can improve the detection accuracy of the distance to an object and the relative speed with the object using discrete Fourier transform. To do.
[0010]
[Means for Solving the Problems]
The radio wave radar device according to the present invention transmits a transmission wave toward an object, receives a reflected wave reflected from the object as a reception wave, and obtains a beat signal obtained from a frequency difference between the transmission wave and the reception wave The radio wave radar apparatus calculates the distance to the object and the relative speed with respect to the object by obtaining the frequency of the beat signal based on the frequency analysis means, wherein the frequency analysis means includes the beat signal A sampling data of a predetermined number is taken out from the A / D converter that samples the signal and the beat signal sampled by the A / D converter, the discrete Fourier transform is performed, and the maximum level is obtained from the discrete Fourier transform result. A spectrum is detected, the maximum number of data points to be removed from the predetermined number of sampling data is calculated according to the frequency corresponding to the spectrum having the maximum level, and 1 is calculated from the predetermined number of sampling data. By obtaining sampling data with points removed or sampling data with the maximum number of data points removed, sampling data with multiple frequency resolutions is generated, and discrete Fourier transform is performed on the multiple sampling data. Multiple discrete fours Select the spectrum with a maximum level from the conversion result, and a beat signal frequency detection means for detecting the frequency of the beat signal from the selected spectrum Is.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a case where the result of continuous Fourier transform is different from the result of continuous Fourier transform will be described. In the discrete Fourier transform, Fourier expansion is performed for each value obtained by dividing the sampling frequency fs by the number of sampling points N (N is an integer of 1 or more). Therefore, only a spectrum having a frequency that is an integral multiple of fs / N (Hz) is accurately analyzed. Can not. This value is called frequency resolution and is shown in equation (1). Therefore, in the discrete Fourier transform, it is necessary to satisfy the relationship of the following expression (2) in order to accurately obtain the frequency included in the beat signal.
[0012]
fs / N = 1 / (N × ΔTs) (1)
N × ΔTs = M × (beat signal cycle) (2)
Here, M is an integer of 2 or more, ΔTs indicates a sampling period, and N × ΔTs indicates a data time length to be subjected to discrete Fourier transform.
[0013]
A state where the equation (2) is satisfied by the discrete Fourier transform and a case where the equation (2) is not satisfied are shown as a set of FIGS. 1 and 3 and FIGS. 2 and 4. Here, Tx is the data time length of N sampling points, and indicates the data time length to be subjected to discrete Fourier transform. Ta represents the cycle of the beat signal 10a in FIG. 1, and Tb represents the cycle of the beat signal 10b in FIG. Discrete value data obtained by sampling the beat signal of FIGS. 1 and 2 at a certain sampling period is indicated by a sampling point 11.
[0014]
FIG. 1 is an explanatory diagram when the data time length of the discrete Fourier transform is an integral multiple of the cycle of the beat signal. This corresponds to the case where the period Ta of the beat signal 10a and the data time length Tx of the discrete Fourier transform satisfy Expression (2), and the following Expression (3) is established.
Tx = (N × ΔTs) = (L + 1) × Ta (3)
Here, L is an integer of 1 or more.
[0015]
FIG. 3 is a diagram showing the result of the discrete Fourier transform when the data time length of the discrete Fourier transform is an integral multiple of the cycle of the beat signal. FIG. 3 also shows the result 12a of the continuous Fourier transform of the beat signal 10a. Since the relationship of Expression (3) is established, the frequency corresponding to the maximum value of the result 12a of the continuous Fourier transform in FIG. 3 and the frequency of the (L + 1) th spectrum corresponding to the maximum value of the discrete Fourier transform result are the same. In this case, the distance to the object and the relative speed with the object can be accurately detected from the result of the discrete Fourier transform.
[0016]
Next, FIG. 2 is an explanatory diagram when the data time length of the discrete Fourier transform is not an integral multiple of the cycle of the beat signal. This corresponds to the case where the period Tb of the beat signal 10b and the data time length Tx of the discrete Fourier transform do not satisfy the equation (2), and in the case of FIG. 2, the relationship is represented by the following equation (4).
M × Tb <Tx (= (N × ΔTs)) <(M + 1) × Tb (4)
[0017]
FIG. 4 is a diagram showing the result of the discrete Fourier transform when the data time length of the discrete Fourier transform is not an integral multiple of the cycle of the beat signal. FIG. 4A and FIG. 4B show two types of spectral distributions that can be considered when the M-th spectral level is maximized as a result of discrete Fourier transform. FIG. 4 also shows the result 12b of the continuous Fourier transform of the beat signal 10b. Since the relationship of equation (3) is not satisfied and the relationship of equation (4) is satisfied, the frequency corresponding to the maximum value of the result 12b of the continuous Fourier transform in FIG. 4 and the Mth corresponding to the maximum value of the discrete Fourier transform result are shown. The spectrum frequencies do not match. In this case, the result of detecting the distance to the object and the relative speed with the object from the result of the discrete Fourier transform is different from the result obtained from the result of the continuous Fourier transform.
[0018]
Thus, in order to accurately detect the frequency of the beat signal using the discrete Fourier transform, it is necessary to satisfy Expression (2). Therefore, under conditions that do not satisfy Equation (2), the distance to the object and the relative speed with the object cannot be accurately calculated using the discrete Fourier transform. Therefore, a radio radar apparatus capable of improving the detection accuracy of the distance to the object and the relative speed with the object using the discrete Fourier transform will be described in detail below.
[0019]
FIG. 5 is a block diagram showing the radio radar apparatus according to Embodiment 1 of the present invention. The CPU 1 controls the modulation signal generator 2 to generate a triangular wave modulation voltage signal. The voltage control transmitter 3 transmits a transmission wave having a frequency modulated according to the modulation voltage signal, and the transmission wave is transmitted toward the object via the distributor 4 and the transmission antenna 5.
[0020]
The reflected wave reflected by the object is received as a received wave via the receiving antenna 6. Furthermore, the mixer 7 multiplies a part of the transmission wave received from the distributor 4 and generates a beat signal having a frequency difference between the transmission wave and the reception wave. The beat signal is sampled at every sampling period by the A / D converter 8a and becomes discrete value data. The beat signal frequency detection means 9 obtains discrete spectrum data of the beat signal by subjecting the beat signal, which has become discrete value data, to discrete Fourier transform.
[0021]
FIG. 6 is a diagram showing discrete spectrum data of a beat signal obtained by performing a discrete Fourier transform on the beat signal that has become discrete value data. FIG. 7 is a diagram showing the spectrum data of the beat signal obtained by continuous Fourier transform of the beat signal which is a continuous quantity.
[0022]
The beat signal frequency detecting means 9 performs discrete Fourier transform by changing the frequency resolution so that the frequency of the spectrum corresponding to the maximum value of the discrete spectrum data approaches the frequency corresponding to the maximum value of the spectrum data obtained by the continuous Fourier transform. is there.
[0023]
FIG. 8 is a flowchart showing a procedure for performing discrete Fourier transform by changing the frequency resolution according to the first embodiment of the present invention. 9 to 11 are conceptual diagrams of processes performed by the beat signal frequency detecting means 9, and specifically show the processes in the flowchart of FIG. The beat signal frequency detection means 9 performs discrete Fourier transform with varying frequency resolution by acquiring K new sampling data obtained by removing 1 to K point data from N point sampling data. Details of the determination of K and detection of the beat frequency based thereon will be described below with reference to FIGS. The step numbers shown in S801 to S812 indicate the step numbers in the flowchart of FIG.
[0024]
FIG. 9 is a conceptual diagram of a process for determining the numerical value K from the result of the discrete Fourier transform according to Embodiment 1 of the present invention. A beat signal 100 in FIG. 9A indicates a beat signal obtained from the mixer 7. The A / D converter 8a samples the beat signal 100 at a predetermined number N of sampling points, thereby obtaining the sampled beat signal 101 shown in FIG. 9B.
[0025]
Next, a discrete Fourier transform is performed on the sampled beat signal 101 (S801). As a result of the discrete Fourier transform, when the M-th spectrum has the maximum level (S802), the magnitude relationship between the (M-1) -th spectrum and the (M + 1) -th spectrum is as shown in FIGS. There are three patterns as shown in (e). Note that when the Mth spectrum and the (M−1) th spectrum show the same maximum value, or when the Mth spectrum and the (M + 1) th spectrum show the same maximum value, the Mth spectrum is Judging from the maximum level, the following procedure can be adopted.
[0026]
FIG. 9C shows a case where the (M−1) -th spectrum level is higher than the (M + 1) -th spectrum level (S803a), and this is called pattern 1. FIG. 9D shows a case where the (M−1) -th spectrum level is smaller than the (M + 1) -th spectrum level (S803b), and this is called pattern 2. Further, FIG. 9E shows a case where the (M−1) -th spectrum level is equal to the (M + 1) -th spectrum level (S803c), and this is called pattern 3.
[0027]
In the pattern 3 in FIG. 9 (e), the frequency corresponding to the maximum value of the result of continuous Fourier transform and the frequency of the Mth spectrum corresponding to the maximum value of the result of discrete Fourier transform are equal as described with reference to FIG. This is equivalent to what you are doing. Therefore, it is assumed that the frequency of the Mth spectrum accurately indicates the information on the distance to the object and the relative speed with the object, and the frequency of the Mth spectrum is detected as the frequency of the beat signal (S804). A series of processing ends (S812).
[0028]
On the other hand, in the pattern 1 in FIG. 9C and the pattern 2 in FIG. 9D, as described above with reference to FIG. 4, the frequency corresponding to the maximum value of the result of continuous Fourier transform and the discrete Fourier transform result This corresponds to the fact that the frequency of the Mth spectrum corresponding to the maximum value does not match. In this case, the result of detecting the distance to the object and the relative velocity with respect to the object from the result of the discrete Fourier transform is different from that obtained from the result of the continuous Fourier transform, so that accurate detection cannot be performed.
[0029]
Therefore, in the case of pattern 1 and pattern 2, discrete Fourier transform with different frequency resolution is performed by obtaining K new sampling data obtained by removing 1 to K point data from N point sampling data. And the frequency of the beat signal is detected more accurately based on the result.
[0030]
A relational expression for obtaining the numerical value K when the sampling data of 1 to K points is removed from the predetermined sampling data of N points is determined as follows.
[Pattern 1]
If the (M−1) th spectral level is greater than the (M + 1) th spectral level,
K <N / M (5)
The largest integer K that satisfies
[Pattern 2]
When the (M−1) th spectral level is smaller than the (M + 1) th spectral level,
K <N / (M + 1) (6)
The largest integer K that satisfies
[0031]
Next, the relational expressions (5) and (6) will be described. First, in the spectra of FIG. 9C and FIG. 9D, the spectrum detected by the radar as a reflected signal from the object is the Mth spectrum having the maximum level, but the frequency of the actual beat signal is Exists within the following range.
[Pattern 1]
(M-1) The frequency of the actual beat signal exists in a range not less than the frequency of the Mth spectrum and not more than the frequency of the Mth spectrum (Condition 1)
[Pattern 2]
The frequency of the actual beat signal exists in a range not less than the frequency of the Mth spectrum and not more than the frequency of the (M + 1) th spectrum (Condition 2)
[0032]
By removing sampling data from 1 point to K point from sampling data of N points determined in advance, the frequency resolution expressed by the equation (1) is 1 / ((N−1) × ΔTs). ((N−K) × ΔTs), which increases as K increases.
[0033]
Therefore, since the frequency resolution increases as the number of data to be removed increases, the (M-1) th spectrum in FIG. 9C and the Mth spectrum in FIG. Move. Here, since the frequency of the actual beat signal is in the range of the above (condition 1) and (condition 2), the minimum necessary K is selected so as not to exceed the range.
[0034]
First, assuming that the frequency resolution at the sampling point N is Δfs, Δfs is expressed by the following equation (7).
Δfs = 1 / (N × ΔTs) (7)
Further, if the frequency resolution when K points are removed from N sampling points is Δfs ′, Δfs ′ is expressed by the following equation (8).
Δfs ′ = 1 / ((N−K) × ΔTs) (8)
[0035]
Therefore, in order to satisfy the above (Condition 1), the relationship of the following expression (9) may be satisfied.
(M−1) × Δfs ′ <M × Δfs (9)
In order to satisfy the above (Condition 2), the relationship of the following expression (10) may be satisfied.
M × Δfs ′ <(M + 1) × Δfs (10)
[0036]
By substituting the equations (7) and (8) into the equations (9) and (10) and expanding with respect to K, the above equations (5) and (6) are obtained as follows.
[Pattern 1]
If the (M−1) th spectral level is greater than the (M + 1) th spectral level,
K <N / M (5)
The maximum integer K that satisfies the above is determined (S805a).
[Pattern 2]
When the (M−1) th spectral level is smaller than the (M + 1) th spectral level,
K <N / (M + 1) (6)
The maximum integer K that satisfies the above is determined (S805b).
[0037]
As described above, when the frequency resolution is changed, the (M−1) -th spectrum in pattern 1 and the M-th spectrum in pattern 2 are the ranges in which the frequency of the beat signal exists, that is, (condition 1) and (condition 2). ) In a direction that approaches the frequency of the actual beat signal. Therefore, it is not necessary to detect the spectrum having the maximum level from every spectrum level every time discrete Fourier transform is performed. In the case of pattern 1, only the (M−1) th spectrum level is detected. Only the Mth spectral level needs to be detected, and the minimum processing is required.
[0038]
Then, K kinds of data are set by removing sampling data for one point from K points from sampling data for N points given in advance (S806). That is, data for (N−K) points is set from data for (N−1) points (S807). FIG. 10 is a conceptual diagram when the sampling data according to Embodiment 1 of the present invention is reduced. FIG. 10A shows data setting for (N-1) points, and FIG. 10B shows (N- 2) Data setting for points, FIG. 10C shows data setting for (NK) points.
[0039]
As shown in FIGS. 10A to 10C, the data time lengths of the K sampling data are (N−1) × ΔTs, (N−2) × ΔTs,. ) × ΔTs, which differs by K ways. Accordingly, the frequency resolution (= 1 / (data time length)) also changes in K ways (S808).
[0040]
Next, discrete Fourier transform is performed on the obtained K kinds of sampling data (S809). FIG. 11 is a conceptual diagram of a discrete Fourier transform result according to Embodiment 1 of the present invention, and shows a discrete Fourier transform result 102. FIG. 11A shows a discrete Fourier transform result for (N-1) points of sampling data, FIG. 11B shows a discrete Fourier transform result for (N-2) points of sampling data, and FIG. The results of discrete Fourier transform for sampling data of (NK) points are shown.
[0041]
The maximum value K of each level in the K discrete Fourier transform results is compared with the maximum value of one level in the discrete Fourier transform result at a predetermined N point, ie, (K + 1) levels in total ( S810), the spectrum having the maximum value is selected from among them, and the frequency of the finally selected spectrum is detected as the frequency of the beat signal (S811). The distance to the object and the relative speed with the object can be obtained more accurately using the frequency of the detected spectrum, and the beat signal frequency detection is terminated (S812).
[0042]
FIG. 12 is a conceptual diagram of the search for the maximum value of the discrete Fourier transform result according to Embodiment 1 of the present invention. In the case of pattern 1, the maximum value A of the level obtained by using the data for N points in FIG. _N And the maximum values (A) of K levels obtained by reducing the sampling data of FIGS. 12B to 12D by 1 to K points. _N-1 , A _N-2 ... A _NK ) Total (K + 1) levels are compared. In pattern 1, A _N Is the Mth spectral level and A _N-1 ~ A _NK Is the (M-1) th spectral level, and A _N-1 ~ A _NK With respect to, only the (M-1) th spectrum needs to be extracted and compared, and the amount of computation can be reduced.
[0043]
Similarly, in the case of pattern 2, the maximum value A of the level obtained by using the data for N points in FIG. _N And the maximum value (A) of K levels obtained by reducing the sampling data of FIGS. 12 (f) to (h) by 1 to K points. _N-1 , A _N-2 ... A _NK ) Total (K + 1) levels are compared. In pattern 2, A _N Is the Mth spectral level and A _N-1 ~ A _NK Is also the Mth spectral level, A _N-1 ~ A _NK With respect to, only the Mth spectrum needs to be extracted and compared, and the amount of calculation can be reduced.
[0044]
In FIG. 5, the beat signal frequency detection means 9 is independent of the CPU 1, but the processing by the beat signal frequency detection means 9 can be integrated with the CPU 1 to physically eliminate the beat signal frequency detection means 9.
[0045]
According to the first embodiment, the frequency of the beat signal is detected based on the result of performing the discrete Fourier transform with a plurality of frequency resolutions, and compared with the result of performing the discrete Fourier transform with one conventional frequency resolution. Thus, the frequency can be detected with higher accuracy. That is, the distance to the object and the relative speed with the object can be obtained with higher accuracy. Further, the sampling period is fixed and the frequency resolution is changed by reducing the sampling data, so that the A / D converted discrete value data can be used as it is.
[0046]
In addition, when changing the frequency resolution, a relational expression for removing several points of data is provided, so sampling data with multiple frequency resolutions can be easily obtained, and the distance of the object can be obtained with the minimum necessary processing time. And the relative velocity with the object can be detected. Furthermore, when searching for the maximum value from a plurality of discrete Fourier transform results, it is only necessary to extract and compare the spectrum at a specific location, and the amount of calculation can be reduced.
[0047]
Embodiment 2. FIG.
In the second embodiment, a radio wave radar apparatus that acquires sampling data whose frequency resolution is changed by changing the sampling period of the A / D converter will be described. FIG. 13 is a configuration diagram of a radio radar apparatus according to Embodiment 2 of the present invention. Consider a set of A / D converters 8b in which a plurality of A / D converters having different sampling periods are installed. Each A / D converter samples the beat signal obtained from the mixer 7 at different sampling periods. Thereby, sampling data in which the frequency resolution is changed according to the number of installed A / D converters can be obtained.
[0048]
The number of A / D converters installed in the A / D converter 8b is, for example, 5, and A / D converter (1) to A / D converter (5). Each A / D converter simultaneously samples the same beat signal at five different sampling periods ΔTs (1) to ΔTs (5). Then, discrete Fourier transform is applied to the five sampled beat signals. That is, the beat signal is subjected to discrete Fourier transform with five frequency resolutions 1 / (N × ΔTs (1)) to 1 / (N × ΔTs (5)).
[0049]
FIG. 14 is a diagram showing a discrete Fourier transform result using a plurality of A / D converters according to the second embodiment of the present invention. The spectrum having the maximum level is selected from the five discrete Fourier transform results shown in FIGS. 14A to 14E, and the frequency of the selected spectrum is detected as the frequency of the beat signal. By using the frequency of the detected spectrum, the distance to the object and the relative speed with the object can be obtained more accurately.
[0050]
Although the case where a plurality of A / D converters 8b are used has been described, sampling data may be acquired a plurality of times by changing the sampling period with one A / D converter. Furthermore, as a combination of the first and second embodiments, the beat signal frequency detection means 9 can be used to detect a more optimal beat signal frequency for sampling data from a plurality of A / D converters.
[0051]
According to the second embodiment, the frequency of the beat signal is detected based on the result of performing discrete Fourier transform with a plurality of frequency resolutions using a plurality of A / D converters having different sampling periods. The frequency of the beat signal can be detected with higher accuracy. That is, the distance to the object and the relative speed with the object can be obtained with higher accuracy.
[0052]
In the embodiment described above, the radio wave radar apparatus of the present invention is described by taking the FM-CW radar as an example. If it is a radar that measures the distance and relative speed, it operates in the same way and exhibits the same effect.
[0053]
【The invention's effect】
As described above, according to the present invention, a radio wave radar device that can improve the detection accuracy of the distance to an object and the relative speed with the object using discrete Fourier transform by employing sampling data with a plurality of frequency resolutions. Obtainable.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram when a data time length of a discrete Fourier transform is an integral multiple of a cycle of a beat signal.
FIG. 2 is an explanatory diagram when the data time length of the discrete Fourier transform is not an integral multiple of the cycle of the beat signal.
FIG. 3 is a diagram showing the result of discrete Fourier transform when the data time length of discrete Fourier transform is an integral multiple of the cycle of the beat signal.
FIG. 4 is a diagram showing the result of discrete Fourier transform when the data time length of discrete Fourier transform is not an integer multiple of the cycle of the beat signal.
FIG. 5 is a configuration diagram showing the radio wave radar device according to the first embodiment of the present invention.
FIG. 6 is a diagram illustrating discrete spectrum data of a beat signal obtained by performing a discrete Fourier transform on the beat signal that has become discrete value data.
FIG. 7 is a diagram showing spectrum data of a beat signal obtained by performing a continuous Fourier transform on a beat signal that is a continuous quantity.
FIG. 8 is a flowchart showing a procedure for performing discrete Fourier transform by changing the frequency resolution according to the first embodiment of the present invention.
FIG. 9 is a conceptual diagram of a process for determining a numerical value K from the result of discrete Fourier transform according to the first embodiment of the present invention.
FIG. 10 is a conceptual diagram when the sampling data according to Embodiment 1 of the present invention is reduced.
FIG. 11 is a conceptual diagram of a discrete Fourier transform result according to Embodiment 1 of the present invention.
FIG. 12 is a conceptual diagram of maximum value search of a discrete Fourier transform result according to Embodiment 1 of the present invention.
FIG. 13 is a configuration diagram of a radio radar apparatus according to Embodiment 2 of the present invention.
FIG. 14 is a diagram showing a discrete Fourier transform result using a plurality of A / D converters according to the second embodiment of the present invention.
[Explanation of symbols]
1 CPU, 2 modulation signal generator, 3 voltage controlled oscillator, 4 distributor, 5 transmitting antenna, 6 receiving antenna, 7 mixer, 8a A / D converter, 8b A set of A / D converters with different sampling periods 9 beat signal frequency detection means, 10 beat signal, 11 sampling points, 12 continuous Fourier transform result, 100 beat signal, 101 sampled beat signal, 102 discrete Fourier transform result.

Claims (2)

A transmission wave is transmitted toward an object, a reflected wave reflected from the object is received as a reception wave, and a beat signal is obtained by a frequency analysis unit based on a beat signal obtained from a frequency difference between the transmission wave and the reception wave. In the radio wave radar device that calculates the distance to the object and the relative velocity with the object by obtaining the frequency of
The frequency analysis means includes an A / D converter that samples the beat signal ;
From the beat signal sampled by the A / D converter, sampling data of a predetermined number of points is taken out, discrete Fourier transform is performed, a spectrum having the maximum level is detected from the discrete Fourier transform result, and the maximum level is determined. Calculating the maximum number of data points to be removed from the predetermined number of sampling data according to the frequency corresponding to the spectrum possessed, and sampling data obtained by removing one point from the predetermined number of sampling data or the maximum By extracting sampling data from which the number of data points has been removed, sampling data with multiple frequency resolutions is generated, discrete Fourier transform is performed on the multiple sampling data, and the maximum level is obtained from the obtained discrete Fourier transform results. Have Select vector, and the beat signal frequency detection means for detecting the frequency of the beat signal from the selected spectrum
Radio wave radar apparatus characterized by comprising a. Sampling predetermined N points (N is an integer of 1 or more) sampling data from the sampled beat signal, performing discrete Fourier transform, and detecting a spectrum having the maximum level from the discrete Fourier transform result;
When the spectrum having the maximum level is the Mth spectrum (M is an integer of 2 or more) counting from the lowest frequency, the (M−1) th spectrum level is the (M + 1) th spectrum level. Is equal to, the step of detecting the frequency of the beat signal from the Mth spectrum;
When the spectrum having the maximum level is the Mth spectrum counted from the lowest frequency, and the (M−1) th spectrum level is greater than the (M + 1) th spectrum level, K <N Determining a maximum integer K satisfying / M, and determining a maximum integer K satisfying K <N / (M + 1) when the (M−1) th spectral level is smaller than the (M + 1) th spectral level; ,
Based on the integer K determined in the above step, by removing sampling data for 1 point to K points from predetermined N points of sampling data, new K sampling data are created, Performing a discrete Fourier transform of
The spectrum having the maximum level is selected from a total of (K + 1) discrete Fourier transform results obtained by combining each of the K discrete discrete Fourier transform results and the result obtained by performing discrete Fourier transform on predetermined sampling data at N points. Detecting the frequency of the beat signal from the selected spectrum; and
A beat signal frequency detection method comprising:

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