JP4378265B2 - FM-CW radar equipment - Google Patents

Description

  The present invention detects a target by transmitting and receiving a frequency-modulated (FM) continuous wave (CW) signal, and measures the distance to the target, the speed of the target, etc., navigation, search, monitoring, etc. The present invention relates to an FM-CW radar device that enables the above.

  The FM-CW radar is a type of radar that adds frequency modulation to a continuous wave and transmits it as a transmission wave. If a part of the transmission wave is mixed with the reception wave reflected from the target, a beat wave proportional to the delay time in which the radio wave reciprocates is generated. When this beat signal is subjected to frequency analysis, the frequency corresponds to the distance to the target, and the amplitude (intensity) corresponds to the scattering intensity of the target. Such an FM-CW radar system is advantageous in that it uses a continuous wave and requires less power than a pulse radar, and does not require high-frequency components that amplify nanosecond pulses.

  FIG. 16 shows a configuration of a general FM-CW radar apparatus 2 (see Patent Document 1).

  FIG. 17 is a characteristic diagram of the time-frequency change of the transmission / reception wave used for explaining the operation of the general FM-CW radar apparatus 2 shown in FIG.

  As can be seen from FIG. 16, the FM-CW radar apparatus 2 basically includes a sensor unit 4, a signal processing unit 6, and a PPI (Plan Position Indicator) display 8.

  In the sensor unit 4, the transmission signal St modulated by the modulation signal generator 10 that generates a repetitive sawtooth wave and output from the high-frequency oscillator 12 is transmitted in the directional coupler 14, the power amplifier (PA) 16, and the horizontal direction. A transmitted wave Wt is radiated to the space via the antenna 18.

  A reflected wave Wr from a target to be observed is received by the receiving antenna 20 and supplied as one input signal of a mixer (MIX) 24 as a received signal Sr through a low noise amplifier (LNA) 22.

  On the other hand, as the other input signal of the mixer 24, a part of the transmission signal St from the high-frequency oscillator 12 is supplied from the directional coupler 14 as a local signal.

  The mixer 24 mixes the transmission signal St and the reception signal Sr as local signals, and outputs a beat signal Sb corresponding to the time difference between the transmission signal St and the reception signal Sr. The beat signal Sb is amplified by the intermediate frequency amplifier (IFAMP) 26 and supplied to the signal processing unit 6 as the amplified beat signal Sb.

  In FIG. 17, the frequency difference between the frequency change characteristic (transmission frequency change characteristic) Ct of the transmission signal St and the frequency change characteristic (reception frequency change characteristic) Cr of the reception signal Sr is the frequency difference between the transmission signal St and the reception signal Sr. It becomes the frequency fb (beat frequency fb) of Sb.

  Here, the beat frequency fb according to the round-trip propagation delay time τ is created by the frequency shift ΔF and the modulation period T. These relationships are given by the following equation (1).

                fb / τ = ΔF / T (1)

  Further, the round-trip propagation delay time τ and the distance R to the target are given by the following equation (2), where c is the speed at which the radio wave travels (the speed of light).

                τ = 2R / c (2)

  Therefore, the relationship between the distance R to the target and the beat frequency fb is given by the following equation (3) in which the round trip propagation delay time τ is eliminated from the equations (1) and (2).

                fb = ΔF · 2R / T · c (3)

  Therefore, in the FM-CW radar apparatus 2, the beat frequency fb of the beat signal Sb obtained from the near target is relatively low, and the beat frequency fb of the beat signal Sb obtained from the far target is observed to be relatively high. Therefore, if the obtained beat signal Sb is subjected to frequency analysis by means such as FFT (Fast Fourier Transform) constituting the signal processing unit 6, the distance to the target can be obtained. Further, the intensity of scattering of the target is obtained from the amplitude (intensity).

  A radar image is displayed on the PPI display 8 based on the video signal generated by the signal processing unit 6 and the direction signal of the transmission antenna 18 supplied from the encoder 28.

  FIG. 18 shows a display example on the PPI display 8.

Japanese Patent Laying-Open No. 2004-3893 (FIGS. 6 and 12)

  As described in Patent Document 1, in the distance measurement in the FM-CW radar apparatus 2, the distance resolution ΔR is expressed by the following equation (4).

                ΔR = c / 2ΔF (4)

  Therefore, in order to achieve very high distance resolution ΔR, for example, on the order of several centimeters, it is necessary to expand the frequency shift ΔF to an ultra-wide band on the order of several GHz, but this is not always possible due to hardware restrictions, radio wave laws, etc. Can not do it.

  Further, in the FW-CW radar apparatus 2 according to the prior art, since a relatively large side lobe is also generated during the FFT processing in the signal processing unit 6, even if the window function is applied, the side lobe is generated. As the value of the lobe increases, it becomes difficult to distinguish the true target from the side rope when there are many targets in the same azimuth direction.

  In the display example of FIG. 18, the intensity level in the azimuth direction indicated by the dotted line is shown in FIG. There are clear true targets Ta and Tb at positions near a distance of about 1.4 [km] and a distance of about 2.8 [km], and it is difficult to distinguish them from real targets in other portions. It can be seen that a sidelobe appears. In FIG. 18, the display brightness is changed by raising and lowering the PPI display level for 45 [dB].

  A technique for realizing a very high distance resolution ΔR is described in Patent Document 1 described above.

  By the way, in the technique according to Patent Document 1, a transmission signal that is a frequency-modulated continuous wave signal is transmitted as a transmission wave from a transmission antenna, and a reflected wave from a target is received as a reception signal via a reception antenna. . Next, after digitizing the beat signal generated by the time difference between the transmission signal and the reception signal to create a normal beat signal in the time domain, a half-phase beat signal with the first half or the second half of the normal beat signal in reverse phase create. Further, the normal beat signal and the half anti-phase beat signal are each subjected to Fourier transform to create a normal spectrum signal and a half anti-phase spectrum signal in the frequency domain. In this case, since a null point (valley peak) in which the amplitude suddenly decreases appears at the beat frequency position in the half-phase spectrum signal, the null point is obtained by dividing the normal spectrum signal by the half-phase spectrum signal. A quotient signal resulting from the division is obtained, which is a signal having a high peak at the beat frequency position corresponding to. Therefore, by detecting the peak of the quotient signal, the distance to the target can be easily obtained with high resolution.

  The present invention has been made in connection with such a technique, and can maintain and detect information on the intensity of a target while maintaining high resolution in distance measurement. An object is to provide an FM-CW radar apparatus.

  In addition, the present invention makes it possible to reduce the side lobe generated when the beat signal is subjected to Fourier transform, maintain high resolution in distance measurement, and maintain and detect information on the intensity of the target. It is an object of the present invention to provide an FM-CW radar apparatus that can be used.

  The FM-CW radar apparatus according to the present invention transmits a transmission signal, which is a frequency-modulated continuous wave signal, as a transmission wave, receives a reflected wave from a target as a reception signal, and transmits the transmission signal and the reception signal. After the beat signal generated by the time difference between the two is digitized and a normal beat signal is created, a half-phase beat signal in which the first half or the second half of the normal beat signal is in reverse phase is created, and the normal beat signal and the half are An FM-CW radar device that determines the frequency of the beat signal based on a normal spectrum signal and a half-phase spectrum signal in a frequency domain obtained by performing Fourier transform on each of the opposite phase beat signals, In order to determine the frequency, a subtractor for obtaining a subtraction result by taking the difference between the normal spectrum signal and the half-phase spectrum signal is provided. And wherein the Rukoto.

  According to the present invention, the subtractor generates a normal spectrum signal having a relatively large value near the beat frequency and a half-phase spectrum signal in which a valley peak whose amplitude suddenly decreases appears at the beat frequency position. The difference is taken to obtain the subtraction result. This difference signal is a steep signal with improved distance resolution, but since it is not divided as in Patent Document 1, the peak value of the steep signal with improved distance resolution is approximately the peak value of the normal spectrum signal. Corresponds to the strength of the target. Therefore, according to the present invention, by detecting the peak frequency of the difference signal, high resolution in distance measurement is maintained, and information regarding the intensity of the target is retained and detected by the peak value. Then, the strength of the target can be detected with higher accuracy than the technique according to Patent Document 1.

  In addition, according to the present invention, a zero data addition circuit is provided in front of the Fourier transform circuit, and zero data is added to the normal beat signal and the half-phase beat signal in the time domain by the zero data addition circuit, respectively, for a predetermined period. A zero-data-added normal beat signal and a zero-data-added half-phase beat signal with a pseudo sampling period are created and then Fourier transformed by a Fourier transform circuit to add a zero-data-added normal spectrum signal and zero data. Create half-phase spectrum signal. In order to determine the frequency of the beat signal, the difference between the zero-data-added normal spectrum signal and the zero-data-added half-phase spectrum signal is taken by a subtractor. If configured in this way, the sampling period by the Fourier transform circuit can be increased in a pseudo manner, so that the peak value of the spectrum intensity at the beat frequency is more faithfully expressed in the zero data added normal spectrum signal, and the peak value is It changes smoothly as you leave. Further, the half-phase spectrum signal with zero data added is close to the zero value at the beat frequency, and the valley characteristics are more symmetrical with respect to the valley peak value. As a result, the magnitude of the amplitude of the difference signal resulting from the subtraction by the subtracter becomes a value closer to the intensity of the beat signal, and corresponds to the strength of the target. High resolution in distance measurement is retained.

  According to the present invention, it is possible to maintain and detect information on the strength of the target while maintaining high resolution in distance measurement.

  In addition, according to the present invention, it is possible to reduce the side lobe generated when the beat signal is subjected to Fourier transform, maintain high resolution in distance measurement, and retain information on the strength of the target. Can be detected.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings to be referred to below, components corresponding to those shown in FIGS. 16 to 19 are denoted by the same reference numerals, and detailed description thereof is omitted. Moreover, it demonstrates with reference to these figures as needed.

  FIG. 1 shows the configuration of an FM-CW radar apparatus 30 according to an embodiment of the present invention.

  The FM-CW radar apparatus 30 basically includes a sensor unit 4, a signal processing unit 32, and a PPI display 8.

  The configurations of the sensor unit 4 and the PPI display 8 are the same as those shown in FIG. 16, and the sensor unit 4 uses the transmission signal St, which is a frequency-modulated continuous wave signal, as the transmission wave Wt. , The reflected wave Wr from the target is received by the reception antenna 20 as the reception signal Sr, and the beat signal Sb generated by the time difference τ between the transmission signal St and the reception signal Sr is supplied to the signal processing unit 32.

  The signal processing unit 32 digitizes the beat signal Sb and creates a normal beat signal in the time domain, and a time obtained by weighting the normal beat signal in the time domain using a window function such as a Hanning window. A weighting circuit 36 for creating a normal beat signal Sbt in the region is provided.

  The signal processing unit 32 further performs a Fourier transform (FFT) on the weighted normal beat signal Sbt to generate a complex signal IQ, and a normal spectrum signal Ssf in the frequency domain as an amplitude signal that is an absolute value of the complex signal IQ. A Fourier transform / amplitude calculation circuit 44 for generating a half-phase beat signal Sbti with the first half or the latter half of the normal beat signal Sbt output from the weighting circuit 36 in reverse phase, A Fourier transform / amplitude calculation circuit 46 for generating a complex signal IQ by performing a Fourier transform (FFT) on the half antiphase beat signal Sbti and creating a half antiphase spectrum signal Ssfi as an amplitude signal that is an absolute value of the complex signal IQ; In order to determine the beat frequency fb and the level adjuster 48 that adjusts the level of the half-phase spectrum signal Ssfi The subtractor 50 for subtracting the half-phase spectrum signal Ssfi × α after the level adjustment of the valley peak value from the normal spectrum signal Ssf to obtain the difference signal Sub that is a steep signal in the frequency domain of the subtraction result, and the difference signal Sub And a video signal processing unit 52 for generating a video signal from the video signal.

  The PPI display 8 displays a radar image based on this video signal and the azimuth signal of the transmission antenna 18 obtained from the encoder 28 (see FIG. 16) constituting the sensor unit 4.

  The FM-CW radar apparatus 30 according to this embodiment is basically configured as described above. Next, this operation will be described.

  Here, in order to facilitate understanding of the present invention, calculation of distance and intensity for a single target will be described.

  Based on the received signal Sr from the single target, the sine wave beat signal Sb having a beat frequency fb of fb = 50 [kHz] is output from the sensor unit 4 during a time interval of 1.25 [ms]. Shall be output.

  FIG. 2A shows a normal beat signal Sbt that is waveform data that is output from the sensor unit 4 and A / D converted by the A / D converter 34 and weighted by the Hanning window by the weighting circuit 36. Show. The horizontal axis is time, and the vertical axis is amplitude. The normal beat signal Sbt is waveform data obtained by dividing the time interval 1.25 [ms] into 256 (sampling frequency 205 [kHz]).

  By performing FFT on the normal beat signal Sbt by the Fourier transform / amplitude calculation circuit 44 and performing amplitude calculation, in a frequency region having a peak value at a beat frequency fb = 50 [kHz] shown by a solid line in FIG. 3A. A normal spectrum signal Ssf is obtained. The horizontal axis is frequency and the vertical axis is power. The FFT point N is N = 256.

  FIG. 2B shows a half-phase beat signal Sbti, which is created by performing phase processing by the anti-phase processing circuit 38, with the latter half of the normal beat signal Sbt shown in FIG.

  In FIG. 3A, a signal indicated by a dotted line is obtained by applying an FFT to the half-phase beat signal Sbti by the Fourier transform / amplitude calculation circuit 46 and performing an amplitude calculation. The beat frequency fb is 50 [kHz]. A half-phase spectrum signal Ssfi having a peak value, so-called null point, is shown. The horizontal axis is frequency and the vertical axis is power. The FFT point N is N = 256.

  FIG. 3B shows a difference between subtraction results obtained by subtracting the half-phase spectrum signal Ssfi from the normal spectrum signal Ssf without performing level adjustment processing by the level adjuster 48 on the half-phase spectrum signal Ssfi (α = 1). The signal Sub (Sub = Ssf−Ssfi) is shown. In this difference signal Sub, the peak value corresponding to the beat frequency fb appears sharper than the normal spectrum signal Ssf shown in FIG. 3A, and the peak corresponding to the side rope present in the normal spectrum signal Ssf. The power at the skirt (near frequency 48.5 [kHz] and near frequency 51.5 [kHz]) does not exist. The distance from the frequency corresponding to the peak value of the difference signal Sub to the target can be accurately obtained.

  In this embodiment, the subtractor 50 performs a calculation of Sub = Ssf−Ssfil, but performs a process of setting a zero value when the difference becomes a negative value. Here, the operation of the level adjuster 48 will be described in relation to the subtractor 50.

  The level adjuster 48 can be considered as a wideband DC amplifier with a variable gain (amplification degree). That is, it has the effect of multiplying the level at each frequency by the amplification factor. For example, when the amplification degree α is α = 0.5, the half-phase spectrum signal Ssfi × 0.5 after the level adjustment is expressed as indicated by a dotted line in FIG. 4A. The solid line in FIG. 4A reproduces the normal spectrum signal Ssf depicted in FIG. 3A.

  FIG. 4B shows the difference signal Sub = Ssf−Ssfi × 0.5.

  Similarly, FIG. 5A shows a half-phase spectrum signal Ssfi × 2 after level adjustment and an ordinary spectrum signal Ssf with the amplification degree α set to α = 2.

  FIG. 5B shows the difference signal Sub = Ssf−Ssfi × 2.

  Comparing FIG. 3B, FIG. 4B, and FIG. 5B, in this case, the spectrum of the difference signal Sub = Ssf−Ssfi × 0.5 in which the amplification degree α is α = 0.5 has a relatively wide frequency width. And the intensity (power, signal level) is the closest to the intensity of the normal spectrum signal Ssf, so that it retains high resolution in distance measurement and also holds information about the intensity of the target. can do.

  FIG. 6 shows the configuration of an FM-CW radar apparatus 30A according to another embodiment of the present invention.

  Compared with the FM-CW radar apparatus 30 shown in FIG. 1, the FM-CW radar apparatus 30A is provided between the weighting circuit 36 and the Fourier transform / amplitude calculation circuit 44 and in reverse phase processing. The difference is that zero data addition circuits 40 and 42 are inserted between the circuit 38 and the Fourier transform / amplitude calculation circuit 46, respectively.

  Next, the operation of the FM-CW radar apparatus 30A shown in the example of FIG. 6 will be described.

  Here, in order to facilitate understanding of the present invention, calculation of distance and intensity for a single target will be described.

  Based on the received signal Sr from the single target, a sine wave beat signal Sb having a beat frequency fb of fb = 50 [kHz] is output from the sensor unit 4 for 1.25 [ms]. Shall.

  FIG. 7A shows 256-point waveform data obtained by weighting the beat signal Sb output from the sensor unit 4 and A / D converted by the A / D converter 34 using the Hanning window by the weighting circuit 36. Zero data of 768 points (pieces) corresponding to a predetermined period of 3.75 [ms] is added to the normal beat signal Sbt shown in Fig. 4, and the total number of data is 1024 points which is four times the original data. The additional normal beat signal Sbt0 is shown. The horizontal axis is time, and the vertical axis is amplitude. This zero data added normal beat signal Sbt0 is waveform data obtained by dividing the time interval 5.00 [ms] by 1024 (sampling frequency 205 [kHz]).

  By applying FFT to the zero data added normal beat signal Sbt0 by the Fourier transform / amplitude calculation circuit 44 and performing amplitude calculation, the beat frequency fb = 50 [kHz] indicated by the solid line in FIG. As a result, a zero-data-added normal spectrum signal Ssf0 in a smooth and substantially symmetrical frequency range in which the points between the points are complemented is obtained. The horizontal axis is frequency and the vertical axis is power. The FFT point N is N = 1024.

  Similarly, FIG. 7B shows a predetermined period of time for a half-phase beat signal Sbti created by phase processing by the phase-phase processing circuit 38 and having the latter half of the normal beat signal Sbt shown in FIG. 768 points (pieces) of zero data corresponding to 3.75 [ms] is added, and the total number of data is 1024 points, which is four times the original data, and the zero data added half-phase beat signal Sbti0 is shown. ing. The horizontal axis is time, and the vertical axis is amplitude. The zero-data-added half-phase beat signal Sbti0 is waveform data obtained by dividing the time interval 5.00 [ms] by 1024 (sampling frequency 205 [kHz]).

  A signal indicated by a dotted line in FIG. 8A is obtained by performing FFT on the zero-data-added half-phase beat signal Sbti0 by performing FFT on the Fourier transform / amplitude calculation circuit 46, and obtaining a beat frequency fb = 50 [kHz]. 2 shows a substantially symmetrical zero data addition half-phase spectrum signal Ssfi0 having a valley peak value, a so-called null point. The horizontal axis is frequency and the vertical axis is power. The FFT point N is N = 1024.

  It should be noted that the waveform data shown in FIGS. 8A and 8B are only supplemented basically, so that the signal level cannot be lowered.

As an FFT condition, the number of data must be a power of 2 (2 ⁿ : n = 2, 4, 8, 16, 32, 64...). For example, when sampling is performed at about 4 times the maximum frequency of interest, zero data is added to make the length of the original data 4 times, so that a longer length (8 times, 16 times,... ), It is confirmed that almost the same result as the waveform data (Ssf0, Ssfi0) can be obtained. However, it has been confirmed that a substantially satisfactory effect can be obtained even when the number of data is doubled, and in the above case, 512 points. That is, the predetermined period for adding zero data is at least 1 time (n = 2), preferably 3 times (n = 4) the number of points of input data.

  As described above, in the FM-CW radar apparatus 30A in the example of FIG. 6, the number of FFT points N is increased and supplemented by adding zero data, so the zero data added normal spectrum signal Ssf0 shown in FIG. The peak peak value of the power corresponds to the amplitude of the zero data added normal beat signal Sbt0 shown in FIG. 7B and is closer to the true peak peak value (in the normal spectrum signal Ssf of FIG. 4A, the peak peak (The power of the value is about “55”, but in the zero data-added normal spectrum signal Ssf0 of FIG. 8A, the power of the peak peak value is a value near “65”, which is a higher value.)

  Further, since the number of FFT points N is increased and complemented, as can be seen from FIG. 8A, the power of the null point of the half-phase spectrum signal Ssfi0 with zero data addition becomes closer to the zero level (half-reversed in FIG. 3A). The power at the null point of the phase spectrum signal Ssfi is about “25”.)

  FIG. 8B shows a subtraction result difference signal Sub0 (Sub0 = Ssf0−Ssfi0) obtained by subtracting the half-phase spectrum signal Ssfi × α before the level adjustment (α = 1) from the zero data added normal spectrum signal Ssf0 by the subtractor 50. Is shown.

  Here, the operation of the level adjuster 48 in the FM-CW radar apparatus 30A of FIG. 6 will be described in relation to the subtractor 50.

  Assuming that the amplification degree α is α = 0.5, the zero-data-added half-phase spectrum signal Ssfi0 × 0.5 after the level adjustment is expressed as indicated by a dotted line in FIG. 9A. The solid line in FIG. 9A shows the zero data added normal spectrum signal Ssf0 depicted in FIG. 8A again.

  FIG. 9B shows the difference signal Sub0 = Ssf0−Ssfi0 × 0.5.

  Similarly, FIG. 10A shows a zero-data-added half-phase spectrum signal Ssfi0 × 2 and a zero-data-added normal spectrum signal Ssf0 after level adjustment with an amplification degree α set to α = 2.

  FIG. 10B shows the difference signal Sub0 = Ssf0−Ssfi × 2.

  Since the null point of the zero-data-added half-phase spectrum signal Ssfi0 shown in FIG. 8A is accurately offset instead of the zero value, the subtraction result difference signal Sub0 shown in FIG. Decreases by offset.

  On the other hand, as can be seen from FIGS. 9A and 9B, the null point of the zero-data-added half reverse-phase spectrum signal Ssfi0 × 0.5 having the amplification degree α = 0.5 is closer to the zero value. The peak of the signal Sub0 can hold the target level more faithfully. However, since the zero data added half-phase spectrum signal Ssfi0 × 0.5 also halves the level other than the null point, the difference signal Sub0 shown in FIG. 9B, that is, the bandwidth of the beat signal (for example, the half-value bandwidth) Becomes wider, and the resolution decreases accordingly.

  Further, in the zero-data-added half-reversed-phase spectrum signal Ssfi0 × 2 with the amplification degree α = 2 shown in FIG. 10A, the level of the null point becomes large, so that the peak of the difference signal Sub0 in FIG. It becomes smaller than the level. However, as apparent from a comparison between FIG. 10B and FIG. 8B, it can be seen that the bandwidth of the difference signal Sub0 shown in FIG. 10B, that is, the beat signal is extremely narrow, and the resolution is improved accordingly. .

  In this way, the level adjuster 48 allows the radar operator to adjust the degree of resolution improvement and sidelobe suppression in accordance with the situation, while maintaining the target level intensity, and the amplification degree α between 0 and 2, for example. It can be set to amplify linearly. Here, the amplification degree α = 0 is a process equivalent to a conventional FFT that does not use the subtracter 50.

  As can be understood by comparing FIGS. 3A, 3B, 4A, 4B, 5A, and 5B with FIGS. 8A, 8B, 9A, 9B, 10A, and 10B, the level adjuster 48 is more effective when the number of data sampling points is sufficient. In other words, when the number of sampling points is not enough, zero data is added and the number of sampling points is artificially increased to process the effect of the level adjuster 48 (the trade-off between distance resolution and level intensity maintenance). The effect that the relationship can be changed) can be obtained.

  For example, in the difference signal Sub0 shown in FIG. 10B, the peak value corresponding to the beat frequency fb appears sharper than the difference signal Sub shown in FIG. 4B, that is, has a narrow band. The waveform is more symmetrical, and the distance from the frequency corresponding to the peak value to the target can be obtained accurately. In the difference signal Sub0 shown in FIG. 10B, the peak peak power (power peak level) is substantially equal to the power peak level of the zero data-added normal spectrum signal Ssf0 shown in FIG. 10A. Strength can be calculated more faithfully.

  FIG. 11 shows a display example on the PPI display 8 at the same position as FIG. 18 when a plurality of targets are actually present.

  FIG. 12 shows the intensity level in the azimuth direction of the dotted line in the display example of FIG. In FIG. 18, the intensity level 100 of the normal process in which the side lobe appears is the intensity level shown in FIG. 19 again, and on the other hand, the intensity level 102 where the target level is steeply generated. Indicates the intensity level of the phase inversion / zero data interpolation processing.

  As can be seen from the intensity level 102 of the phase inversion / zero data interpolation processing, the true targets Ta and Tb clearly exist at positions near the distance 1.4 [km] and the distance 2.8 [km]. It can be seen that, for example, the target Tc appears in the vicinity of 0.63 [km] in the part confused with the side lobe, and the target also appears near the ship (the center of the display). I understand. The PPI display example in FIG. 11 is understood to be much easier to see than the PPI display example in FIG.

  For reference, FIGS. 13 and 14 show gray scale inversion display examples of FIGS. 18 and 11, respectively. FIGS. 15A and 15B show squares in the display examples of FIGS. The enlarged view of the part enclosed with the dotted line is shown. Although it is difficult to distinguish from the enlarged view of FIG. 15A, it can be easily estimated from the enlarged view of FIG. 15B that the target Ta is a large ship such as a tanker because the distance resolution has improved.

  As described above in detail, the FM-CW radar apparatus 30 in FIG. 1 transmits the transmission signal St, which is a frequency-modulated continuous wave signal, as the transmission wave Wt and receives the reflected wave Wr from the target. After receiving the signal Sr and digitizing and weighting the beat signal Sb generated by the time difference between the transmission signal St and the reception signal Sr to create the normal beat signal Sbt, the latter half (the first half of the normal beat signal Sbt may be used). ) In half-phase beat signal Sbti and half-phase spectrum in the frequency domain obtained by Fourier transforming the normal beat signal Sbt and half-phase beat signal Sbti respectively. In order to determine the frequency of the beat signal Sb based on the signal Ssfi, the spectrum signal half-phase with the normal spectrum signal Ssf is obtained. Comprises a subtractor 50 for obtaining a difference signal Sub subtraction result takes a difference between Ssfi.

  That is, according to the FM-CW radar apparatus 30 of FIG. 1 example, the subtractor 50 causes the normal spectrum signal Ssf (FIG. 3A) in which the vicinity of the beat frequency is a relatively large value and the beat frequency position to abruptly. The subtraction result is obtained by taking the difference from the half-phase spectrum signal Ssfi in which the valley peak whose amplitude decreases appears. As shown in FIG. 3B, the difference signal Sub is a steep signal with improved distance resolution. However, since it is not divided as in Patent Document 1, the peak value of the steep signal with improved distance resolution is In general, the peak value of the normal spectrum signal is held, which corresponds to the intensity of the target. Therefore, by detecting the peak frequency of the difference signal Sub, high resolution in distance measurement is maintained, and the intensity of the target can be detected more faithfully by the peak value.

  Further, according to the FM-CW radar apparatus 30A of FIG. 6 example, zero data addition circuits 40 and 42 are provided in front of the Fourier transform / amplitude calculation circuits 44 and 46, respectively. A zero-data-added normal beat signal Sbt0 and a zero-data-added half-reciprocal beat signal in which zero data is added to the normal beat signal Sbt and the half-reciprocal beat signal Sbti in the time domain, respectively, for a predetermined period, and the sampling period is increased. After creating Sbti0, Fourier transform / amplitude calculation circuits 44 and 46 respectively perform Fourier transform to create a zero-data-added normal spectrum signal Ssf0 and a zero-data-added half-phase spectrum signal Ssfi0. In order to determine the frequency of the beat signal Sb, the subtracter 50 takes the difference between the zero data-added normal spectrum signal Ssf0 and the zero data-added half-phase spectrum signal Ssfi0. With this configuration, the sampling period by the Fourier transform / amplitude calculation circuits 44 and 46 can be increased in a pseudo manner, so that the zero data added normal spectrum signal Ssf0 more faithfully represents the spectrum intensity at the beat frequency fb. Thus, the signal changes smoothly with increasing distance from the peak value, and the side lobe is reduced. In addition, the zero-data-added half-phase spectrum signal Ssfi0 approaches a zero value at the beat frequency fb, and the characteristics of the valley are more symmetrical with respect to the valley peak value, that is, the null point. As a result, the magnitude of the amplitude of the difference signal Sub0 as a result of subtraction by the subtracter 50 becomes closer to the intensity of the beat signal Sb, and corresponds to the strength of the target. Of course, the high resolution in the distance measurement is maintained.

  In the FM-CW radar apparatuses 30 and 30A of FIG. 1 and FIG. 6, the level of the half-phase spectrum signal Ssfi or the half-phase with zero data addition is provided between the Fourier transform / amplitude calculation circuit 46 and the subtractor 50. Since the level adjuster 48 for adjusting the level of the spectrum signal Ssfi0 is provided, the effect of improving the resolution and suppressing the side lobe can be adjusted by the operator in accordance with the situation while maintaining the target level intensity. .

  Note that the present invention is not limited to the above-described embodiment, and various configurations can be adopted without departing from the gist of the present invention.

It is a block diagram which shows the structure of one embodiment of this invention. 2A is a waveform diagram of a normal beat signal after weighting processing, and FIG. 2B is a waveform diagram of a beat signal after half-phase processing. FIG. 3A is a waveform diagram of a normal spectrum signal after Fourier transformation of a normal beat signal and a half-phase spectrum signal after Fourier transformation of a half-phase beat signal, and FIG. 3B is a subtraction of a half-phase spectrum signal from the normal spectrum signal. It is the spectrum figure of the difference signal which was made. FIG. 4A is a waveform diagram in which the half anti-phase spectrum signal in FIG. 3A is replaced with a half anti-phase spectrum signal after adjusting the level to 0.5 times, and FIG. 4B is a diagram showing 0.5 times the level from the normal spectrum signal. FIG. 6 is a spectrum diagram of a difference signal obtained by subtracting a half-phase spectrum signal after adjustment. FIG. 5A is a waveform diagram in which the half anti-phase spectrum signal in FIG. 3A is replaced with the half anti-phase spectrum signal after the level is adjusted to double, and FIG. 5B is the waveform after the level is adjusted to double from the normal spectrum signal. It is a spectrum figure of the difference signal which subtracted the half reverse phase spectrum signal. It is a block diagram which shows the structure of other embodiment of this invention. 7A is a waveform diagram of a normal beat signal to which zero data is added after weighting processing, and FIG. 7B is a waveform diagram of a beat signal after zero data addition and half-phase processing. FIG. 8A is a waveform diagram of a normal spectrum signal after Fourier transformation of a zero-data-added normal beat signal and a half-phase spectrum signal after Fourier transformation of a zero-data addition / half-phase beat signal, and FIG. 8B is a zero-data addition waveform. It is a spectrum figure of the difference signal which subtracted zero data addition and half reverse phase spectrum signal from the usual spectrum signal. FIG. 9A is a waveform diagram in which the zero-data-added half-reversed spectrum signal in FIG. 8A is replaced with a zero-data-added half-reverse spectrum signal after adjusting the level to 0.5 times, and FIG. It is a spectrum figure of the difference signal which subtracted the zero data addition half reverse phase spectrum signal after adjusting a level to 0.5 time from a spectrum signal. 10A is a waveform diagram in which the zero-data-added half-reversed spectrum signal in FIG. 8A is replaced with a zero-data-added half-reverse spectrum signal after the level is adjusted to double, and FIG. 10B is a zero-data-added normal spectrum signal. FIG. 6 is a spectrum diagram of a difference signal obtained by subtracting a half-phase spectrum signal with zero data added after adjusting the level to twice. It is a figure which shows the example of PPI display by the FM-CW radar apparatus of the example of FIG. It is a figure which shows the level of the direction shown with a dotted line in FIG. It is a gradation inversion figure of the PPI display example which concerns on a prior art. FIG. 12 is a gradation inversion diagram of the PPI display example of FIG. 11 example. 15A is a partially enlarged view of a PPI display example according to the prior art, and FIG. 15B is a partially enlarged view of the PPI display example of FIG. It is a block diagram which shows the structure of a general FM-CW radar apparatus. It is explanatory drawing with which the principle of the distance measurement of FM-CW radar apparatus is provided. It is explanatory drawing of the example of PPI display which concerns on a prior art. It is explanatory drawing which shows the level of the direction shown with a dotted line in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 ... Sensor part 6, 32 ... Signal processing part 8 ... PPI display 30, 30A ... FM-CW radar apparatus 34 ... A / D converter 38 ... Reverse phase processing circuit 40, 42 ... Zero data addition circuit 44, 46 ... Fourier transform / amplitude calculation circuit 48 ... level adjuster 50 ... subtractor Ct ... transmission frequency change characteristic Cr ... reception frequency change characteristic fb ... beat frequency Sb ... beat signal Sbt ... normal beat signal Sbt0 ... zero data added normal beat signal Sbti ... Half anti-phase beat signal Sbti0 ... Zero data added half anti-phase beat signal Sr ... Received signal Ssf ... Normal spectrum signal Ssf0 ... Zero data added normal spectrum signal Ssfi ... Half anti-phase spectrum signal Ssfi0 ... Zero data added half anti-phase spectrum signal Ssfil ... Half-phase spectrum signal St after level adjustment ... Transmission signal Sub Sub0 ... the difference signal Wr ... reflected wave Wt ... transmission wave

Claims (2)

Transmitting a transmission signal that is a frequency-modulated continuous wave signal as a transmission wave, receiving a reflected wave from a target as a reception signal, digitizing a beat signal generated by a time difference between the transmission signal and the reception signal, After creating the normal beat signal, create a half-phase beat signal with the first half or the second half of the normal beat signal in reverse phase, and Fourier transform the normal beat signal and half half-phase beat signal respectively. An FM-CW radar apparatus that determines the frequency of the beat signal based on the obtained normal spectrum signal and half-phase spectrum signal in the frequency domain,
An FM-CW radar apparatus comprising: a subtractor that obtains a subtraction result by taking a difference between the normal spectrum signal and the half-phase spectrum signal to determine a frequency of the beat signal. A transmission signal that is a frequency-modulated continuous wave signal is transmitted as a transmission wave, a reflected wave from a target is received as a reception signal, and the object is calculated from the frequency of the beat signal generated by the time difference between the transmission signal and the reception signal. In the FM-CW radar device that detects the distance to the target,
An A / D converter that digitizes the beat signal and creates a normal beat signal;
A reverse phase processing circuit for creating a half-phase beat signal in which the first half or the second half of the normal beat signal is in reverse phase;
Zero to create a zero-data-added normal beat signal and a zero-data-added half-phase beat signal by adding zero data to the normal beat signal and the half-phase beat signal, respectively, for a predetermined period and artificially extending the sampling period. A data addition circuit;
A Fourier transform circuit that Fourier-transforms the zero-data-added normal beat signal and the zero-data-added half-phase beat signal, respectively, to create a zero-data-added normal spectrum signal and a zero-data-added half-phase spectrum signal;
In order to determine the frequency of the beat signal, a subtractor that obtains a subtraction result by taking a difference between the zero data-added normal spectrum signal and the zero data-added half-phase spectrum signal;
FM-CW radar device according to feature in that it comprises.

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