JP2001349941A - Fm-cw radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image faithful to the intensity of a target signal, having a sufficient distance resolution in an FM-CM radar device. SOLUTION: An FFT analyzer 111 and an MEM analyzer 112 are used as frequency analyzing means, a range determined to have a target by a comparator 12 is extracted from the output of the FFT analyzer 111 that is faithful to the intensity of a target signal, result of analysis for the range is extracted from the output of the MEM analyzer 112 that has an excellent resolution using a gate circuit 13. By determining that there is a target when a threshold value is exceeded in a comparator 14, a well-resolved target pulse signal is generated, and an image by this is combined with image display based on output of the FFT analyzer 111 on a display 16 to be displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of an FM-CW radar device, and relates to a technique for improving the resolution of a reception target.

[0002]

2. Description of the Related Art An FM-CW radar apparatus linearly modulates a frequency as a transmission wave with respect to time (Frequency).
Modulation: FM (Continuous Wave: C)
W), and detects the distance to the target and the target speed by taking the difference frequency between the received wave reflected from the target and the transmitted wave.

FIG. 5 is a block diagram showing a configuration of a conventional FM-CW radar device. FIG. 6 is a signal explanatory diagram of each part in the configuration of FIG. The sweep signal generator 5 generates a sawtooth waveform signal, which is sent to a high frequency oscillator 6,
Here, the transmission signal 1 in FIG.
Frequency modulation as shown below. This figure shows an example in which the frequency increases linearly with time during the sweep cycle.

[0004] The transmission signal 1 output from the high-frequency oscillator 6 is radiated from the transmission antenna 8 to the space via the directional coupler 7. The directional coupler 7 is for extracting a part of a transmission signal to be input to the mixer 10.

[0005] The radio wave radiated into the space is reflected by a target object, returns to the receiving antenna 9 and is received.
Is input to the mixer 10. Since this transmission signal is delayed by the transmission time of the transmission signal to and from the target, the transmission signal is shifted by the transmission time to the right in FIG. The received signal is as shown in FIG.

[0006] The received signal 2 is input to a mixer 10. A part of the transmission signal 1 is input from the directional coupler 7 to the mixer 10, and a signal of a frequency fb (referred to as a beat frequency) which is a difference between the frequency of the transmission signal 1 and the frequency of the reception signal 2 is input. 3) is output. FIG.
(B) shows a beat signal.

The beat frequency fb in FIG. 6A is proportional to the shift amount of the received signal 2 to the right from the transmitted signal 1, that is, the round-trip propagation time to the target. Since the round trip propagation time is proportional to the distance R to the target, the beat frequency fb is eventually proportional to the distance R to the target. Therefore, by knowing the beat frequency, the distance to the target can be known.

Then, the output signal 3 of the mixer 10 is sent to the frequency analysis means 11 to perform frequency analysis, and FIG.
The frequency spectrum signal 4 as shown in FIG. Fast Fourier Transform (FFT) as frequency analysis means
Although an analysis means using the maximum entropy method (MEM) is used, FIG. 6 (c) is drawn assuming that a frequency analysis that is close to ideal has been performed. In FIG. 6C, the horizontal axis is the frequency axis and the distance axis proportional thereto, and the vertical axis is the intensity axis of the spectrum. There is a beat frequency at the position where the spectrum that can be identified from noise appears. It is shown that.

In FIG. 6C, on the frequency axis, f1, f2, f3
Since the spectrums 41, 42, and 43 respectively stand at the respective positions, three beat frequencies f1, f2, and f3 are included in this signal, and the distance corresponding to these beat frequencies is R.
Since 1, R2 and R3, it indicates that there are targets at three places with different distances.

In these processes, when the distance is swept in each direction as the antenna rotates, PPI display can be performed.

[0011]

As described above, the FM-C
In the W radar device, the frequency analysis means plays an important role. The fast Fourier transform method (FFT) and the maximum entropy method (MEM) have the following problems, respectively.

First, in the case of FFT, the frequency resolution depends on the number of samples for a beat signal. That is,
The higher the number of samplings, the higher the frequency resolution, but the lower the number, the lower the frequency resolution.

Now, assuming that FIG. 7A is a case where a frequency analysis close to the ideal is performed (same as FIG. 6C), if the number of samplings is not sufficient, the result of the frequency analysis is shown in FIG. (B). That is, in this case, the spectrum 41 of the beat frequency f1 and the spectrum 42 of the beat frequency f2 are not decomposed and are aggregated into a spectrum 411.
This means that two targets that are close to each other are glued together and can only be seen as one target. As described above, the FFT has a problem that there is a restriction in terms of frequency resolution.

On the other hand, regarding the intensity of the spectrum, the intensity of the left shoulder of the spectrum 411 is the same as the intensity of the spectrum 41, the intensity of the right shoulder of the spectrum 411 is the same as the intensity of the spectrum 42, and the intensity of the spectrum 431 is the spectrum. There is an advantage that it is faithfully reproduced, for example, the intensity is the same as 43.

On the other hand, the MEM has a problem that the frequency resolution does not depend on the sampling number and a high resolution can be obtained, but the intensity of the spectrum is not faithfully reproduced. In FIG. 7, the result of the ideal frequency analysis (a) is as shown in (c). Looking at (c), spectrum 442 has no corresponding spectrum in (a). As described above, there is a case in which an actual error does not exist but an arithmetic error appears. The spectrum 412 is the spectrum 41 of FIG.
, The spectrum 422 corresponds to the spectrum 42 of (a), and the spectrum 432 corresponds to the spectrum 43 of (a), but the intensity is very large.

As described above, there is a problem in that the spectrum intensity is infidelity, and in particular, the spectrum stands at a beat frequency which does not originally exist, such as the spectrum 442.

In view of the above-mentioned problems of the prior art, an object of the present invention is to combine the advantage that the spectral intensity of the FFT has fidelity with the advantage that sufficient frequency resolution of the MEM can be obtained, and Strength is faithful, and
An object of the present invention is to provide an FM-CW radar device capable of obtaining a target image having a high distance resolution.

[0018]

In order to achieve the above object, a first FM-CW radar apparatus according to the present invention comprises:
And (g). (A) A mixer that receives a transmission signal and a reception signal at the level necessary for mixing and outputs a signal having a frequency difference between the two signals. (B) A high-speed Fourier that receives the output signal of the mixer and analyzes the frequency. Conversion frequency analysis means (c) Maximum entropy frequency analysis means for receiving the output signal of the mixer and analyzing the frequency thereof (d) comparing the output level from the fast Fourier transform frequency analysis means with a preset threshold value A binary signal (“1”, “1”,
(E) receiving the output signal from the maximum entropy frequency analysis means and the binary signal from the first comparator, and maximizing only when the binary signal is "1" A gate circuit for outputting a signal of the entropy frequency analysis means (f) receiving the output of the gate circuit, comparing the level with a preset threshold value, and when exceeding the threshold value, generating a pulse signal indicating the presence of the target; Second comparator to output (g) A display for displaying an image by superimposing an output signal from the fast Fourier transform frequency analysis means and an output signal from the second comparator

Next, the second FM-CW radar apparatus according to the present invention is characterized by comprising the following means (a) to (h). (A) A mixer that receives a transmission signal and a reception signal at the level necessary for mixing and outputs a signal having a frequency difference between the two signals. (B) A high-speed Fourier that receives the output signal of the mixer and analyzes the frequency. Conversion frequency analysis means (c) Maximum entropy frequency analysis means for receiving the output signal of the mixer and analyzing the frequency thereof (d) comparing the output level from the fast Fourier transform frequency analysis means with a preset threshold value A binary signal (“1”, “1”,
(E) receiving the output signal from the maximum entropy frequency analysis means and the binary signal from the first comparator, and maximizing only when the binary signal is "1" A gate circuit for outputting a signal of the entropy frequency analysis means (f) receiving the output of the gate circuit, comparing the level with a preset threshold value, and when exceeding the threshold value, generating a pulse signal indicating the presence of the target; Second comparator to be output (g) Multiplier for multiplying the output of the second comparator by the output of the fast Fourier transform frequency analysis means (h) Display for displaying the output signal of the multiplier as an image

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of the present invention is based on the fact that one type of frequency analysis means has conventionally been used. It is intended to eliminate the defect by using the analysis means together.

That is, although the FFT frequency analysis means has a problem in the frequency resolution, the presence / absence and intensity of the target are faithful, while the MEM frequency analysis means has a problem in the presence / absence and fidelity of the intensity. , In terms of frequency resolution.

Therefore, the analysis result of the FFT frequency analysis means is used for the presence / absence and strength of the target, and the analysis result of the MEM frequency analysis means is used for the frequency resolution, ie, the distance resolution, and both are superimposed and displayed. Or by displaying the result of multiplication of the two, display information with higher accuracy than before can be obtained.

Accordingly, the configuration is such that, in the receiving system of the conventional FM-CW radar apparatus, the configuration after the mixer is processed by using new frequency analysis means and signals of these two frequency analysis means. Are added.

[0024]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the first embodiment of the FM-CW radar device of the present invention. this house,
Transmission system, transmission antenna 8, reception antenna 9, mixer 1
Up to 0 is the same as FIG. 4 which is a configuration diagram of the conventional apparatus.

The difference from the prior art is that the FFT frequency analyzer 111 and the MEM frequency analyzer 1
12 and subsequent processing means. The FFT frequency analyzer 111 outputs the frequency spectrum signal 40 having high intensity and high fidelity as shown in FIG.
Outputs 1. This signal is sent to the display 16 and to the comparator 12. The comparator 12 converts the frequency spectrum signal 401 into a predetermined threshold value 501 indicated by a horizontal dotted line in FIG.
As shown in (b), the output is zero at a position lower than the threshold value 501 and a binary signal 601 having a constant amplitude is output at a position beyond the threshold value 501. Then, this binary signal 601 is sent to the gate circuit 13.

On the other hand, the gate circuit 13 supplies a frequency spectrum signal 40 having a high frequency resolution (distance resolution) as shown in FIG.
2 has been entered. A signal (partial signal 701) corresponding to a part of the frequency spectrum signal 402 corresponding to a part of the binary signal 601 having a constant amplitude (part separated by a dotted line corresponding to the pulse waveform of (b)). Is only output. This is illustrated in FIG. 3D.

The partial signal 701 is input to the comparator 14, where it is compared with a preset threshold value 801 shown by a horizontal dotted line in FIG. A pulse signal 901 in which a signal having a constant amplitude appears only in the portion (e) of FIG.

Thus, the FFT frequency analyzer 11
In the frequency spectrum signal 401 of FIG. 3 ((a) of FIG. 3), the signal that has not been sufficiently decomposed is clearly decomposed, while the signal of the frequency spectrum signal 402 of the MEM frequency analyzer 112 ((c) of FIG. )) Shows the spectrum 442
3A does not exist if it does not exist in FIG. 3A, thereby avoiding the influence of the presence / absence of the signal and the uncertainty of the intensity in the frequency spectrum signal 402 of the MEM frequency analyzer 112.

FIGS. 4A and 4B are views showing a part of a PPI scope. FIG. 4A is a partial image based on a frequency spectrum signal of a conventional FFT frequency analyzer, and FIG. This is a video in which the video output from the FFT frequency analyzer and the video output from the comparator 14 in FIG. 1 are superimposed. In the case of (a), the target 182 is a single image with a spread, but in the case of (b),
In fact, it can be seen that the target 192 and the target 193 exist.
The target 182 is a lump due to insufficient resolution of the FFT frequency analyzer.

If the resolution is not sufficient, the target image spreads and it is difficult to grasp the true target position. However, by superimposing the image processed from the output of the MEM frequency analyzer, the target 195 and the target 194 are superimposed. The target position becomes clearer, and the position accuracy is improved.

In (b), no superimposed image appears at the target 181. This is because a spectrum appears at the output of the FFT frequency analyzer 111 but no spectrum appears at the output of the MEM frequency analyzer 112. Is the case. However, regarding the presence or absence of a target and the spectrum intensity, the FFT frequency analysis means has higher fidelity, and if it appears here, it is displayed as having a target.

FIG. 2 is a block diagram showing the configuration of a second embodiment of the FM-CW radar device according to the present invention. FIG.
1 is that both the output of the FFT frequency analyzer 111 and the output of the comparator 14 are sent to the display 16 in FIG. 1 and displayed as shown in FIG. Is provided with a multiplier 17, the output of the FFT frequency analyzer 111 and the output of the comparator 14 are sent to the multiplier 17, where the output of the comparator 14 is multiplied by the output of the FFT frequency analyzer 111, and the output Is sent to the display 16.

The output 901 of the comparator 14 is as shown in FIG.
Since the output 401 of FIG. 1 is as shown in FIG. 3A, the waveform resulting from the multiplication has an envelope connecting the peaks of the pulse of FIG. 3E as shown in FIG. It becomes a form. That is, the waveform of FIG. 3E has a shape as if the waveform of FIG. 3A has been subjected to amplitude modulation. Although the waveform of (e) is an output having no intensity information, the waveform is multiplied to have the intensity information of (a).

When this is displayed on the display 16, the target images 192, 193, 194, 1 in the diagram of FIG.
95 is displayed in different shades. Since the density of the image indicates the intensity of the spectrum, and the spectrum intensity indicates the size of the target, an image with high resolution and the size of the target can be obtained on the display screen.

[0035]

As described above, the FM-C of the present invention
In the first configuration of the W radar apparatus, the display based on the analysis result of the FFT frequency analyzer which is superior in the presence / absence of the target and the fidelity of the spectrum intensity is based on the MEM which is superior in the frequency resolution for the part where the target exists.
Based on the analysis result of the frequency analyzer, a target pulse is generated for each frequency-resolved frequency, and this is superimposed on the display based on the analysis result of the FFT frequency analyzer, so that the target can be detected without fail. There is an advantage that the distance resolution and the accuracy of the target position with respect to the detected target can be improved.

Further, in the second configuration, the intensity of each target pulse generated for each frequency that has been frequency-decomposed based on the analysis result of the MEM frequency analyzer having excellent frequency resolution is determined by the presence or absence of a target and the spectral intensity. Since the intensity is modulated by the output from the FFT frequency analyzer, which is superior in the fidelity, and displayed on the display, there is an advantage that an image with high resolution and a target size can be determined on the screen of the display. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the FM-CW radar device of the present invention.

FIG. 2 is a block diagram showing a configuration of a second embodiment of the FM-CW radar device of the present invention.

FIG. 3 is a waveform chart of each part in a signal processing process in the embodiment of FIG. 1;

FIG. 4 is a comparison diagram of a PPI partial display image between the conventional device and the first embodiment.

FIG. 5 is a block diagram illustrating a configuration of a conventional FM-CW radar device.

FIG. 6 is a signal explanatory diagram of each unit in the device of FIG. 5;

FIG. 7 is a comparative explanatory diagram of a frequency spectrum obtained as a result of analysis by a frequency analysis unit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transmission signal 2 reception signal 3 beat signal 4 frequency spectrum signal 5 sweep signal generator 6 high frequency oscillator 7 directional coupler 8 transmission antenna 9 reception antenna 10 mixer 11 frequency analysis means 12 comparator 13 gate circuit 14 comparator 16 display 17 multiplication Instrument 111 FFT frequency analyzer 112 MEM frequency analyzer

Claims (2)

[Claims] 1. An FM-CW radar device comprising the following means (a) to (g). (A) A mixer that receives a transmission signal and a reception signal at the level necessary for mixing and outputs a signal having a frequency difference between the two signals. (B) A high-speed Fourier that receives the output signal of the mixer and analyzes the frequency. Conversion frequency analysis means (c) Maximum entropy frequency analysis means for receiving the output signal of the mixer and analyzing the frequency thereof (d) comparing the output level from the fast Fourier transform frequency analysis means with a preset threshold value A binary signal (“1”, “1”,
(E) receiving the output signal from the maximum entropy frequency analysis means and the binary signal from the first comparator, and maximizing only when the binary signal is "1" A gate circuit for outputting a signal of the entropy frequency analysis means (f) receiving the output of the gate circuit, comparing the level with a preset threshold value, and when exceeding the threshold value, generating a pulse signal indicating the presence of the target; Second comparator to output (g) A display for displaying an image by superimposing an output signal from the fast Fourier transform frequency analysis means and an output signal from the second comparator 2. An FM-CW radar device comprising the following means (a) to (h). (A) A mixer that receives a transmission signal and a reception signal at the level necessary for mixing and outputs a signal having a frequency difference between the two signals. (B) A high-speed Fourier that receives the output signal of the mixer and analyzes the frequency. Conversion frequency analysis means (c) Maximum entropy frequency analysis means for receiving the output signal of the mixer and analyzing the frequency thereof (d) comparing the output level from the fast Fourier transform frequency analysis means with a preset threshold value A binary signal (“1”, “1”,
(E) receiving the output signal from the maximum entropy frequency analysis means and the binary signal from the first comparator, and maximizing only when the binary signal is "1" A gate circuit for outputting a signal of the entropy frequency analysis means (f) receiving the output of the gate circuit, comparing the level with a preset threshold value, and when exceeding the threshold value, generating a pulse signal indicating the presence of the target; Second comparator to be output (g) Multiplier for multiplying the output of the second comparator by the output of the fast Fourier transform frequency analysis means (h) Display for displaying the output signal of the multiplier as an image