JP2006105968A - Radar apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the effect of noise induced by antenna switching, in a radar apparatus constructed to perform switching among a plurality of receiving antennas using a switch. <P>SOLUTION: A situation where there is no echo signal from a target is created, for example, by turning off a transmitter amplifier (step 1000), and the Fourier transformed result obtained at this time is taken as the correction value (step 1002) and stored to a memory (step 1004). At radar operation, the effect of noise caused by the antenna switching can be eliminated, by subtracting the correction value from the Fourier transformed result. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to noise removal associated with antenna switching in a radar apparatus configured to switch a plurality of receiving antennas with a switch.

  As one of the methods for determining the azimuth of the target, a DBF (digital beam forming) method using a plurality of receiving antennas, a phase monopulse method, and the like are known. For example, Japanese Patent Laid-Open No. 11-160423 describes that the number of expensive high-frequency components is reduced by sequentially switching and selecting a plurality of receiving antennas.

  In this way, in a radar apparatus having a configuration as shown in FIG. 1 in which a plurality of receiving antennas are sequentially switched and selected, a sneak signal between the transmitting side and the receiving side in the high frequency section becomes a dc value and sneaks. Since it differs between channels, a square wave as shown in the column (A) of FIG. 2 is generated at the output of the mixer 7. This square wave becomes excessive response noise as shown in the column (B) of FIG. When the filtered signal shown in FIG. 2B is Fourier-transformed, a noise peak appears at a frequency position corresponding to the frequency component, and analysis is difficult if the frequency of the peak due to the reflected wave from the target is close to this. There is a problem of making it. For example, if the noise frequency is in the vicinity of the peak frequency of the reflected wave from the target existing at a short distance, it becomes difficult to identify the peak of the short distance target, and the short distance detection performance deteriorates.

JP-A-11-160423

  Accordingly, an object of the present invention is to eliminate the influence of noise caused by antenna switching in a radar apparatus configured to switch a plurality of receiving antennas with a switch.

  According to the present invention, a beat signal is generated by mixing a switch that sequentially switches and selects one of signals received by a plurality of receiving antennas, and a part of the transmission signal selected by the switch. A mixer, a Fourier transform computing means for Fourier transforming the output signal of the mixer, and a Fourier transform result of the Fourier transform computing means when there is no reflected signal from the target, the DC level of the mixer as the switch is switched Radar apparatus comprising: correction value storage means for storing as a correction value for canceling the influence caused by fluctuations, and correction means for correcting the Fourier transform result of the Fourier transform operation means with the correction value stored in the storage means Is provided.

  FIG. 3 shows a schematic configuration of the radar apparatus of the present invention. In FIG. 3, a radar apparatus according to the present invention includes a switch 2 that sequentially switches and selects one of signals received by a plurality of receiving antennas 1, and a received signal selected by the switch 2 and a part of a transmission signal. Mixer 3 that generates a beat signal by mixing, Fourier transform operation means 4 that Fourier-transforms the output signal of mixer 3, and Fourier transform result of Fourier transform operation means 4 when there is no reflected signal from the target, The correction value storage means 5 for storing the correction value for canceling the influence caused by the change in the DC level of the mixer 3 as the switch 2 is switched, and the Fourier transform result of the Fourier transform calculation means 4 are stored in the storage means 5. And a correction means 6 for correcting with the correction value stored in.

  FIG. 4 is a block diagram showing a configuration of a first example of an in-vehicle FM-CW radar apparatus as an example of a radar apparatus to which the present invention is applied. In FIG. 4, a transmission signal which is output from a voltage controlled oscillator (VCO) 10 and is FM-modulated with a triangular wave is amplified by a transmission amplifier 14 and transmitted from a transmission antenna 16. For reception, one selected from the three antennas AT0, AT1, AT2 by the switch 22 is used.

  One of the received signals received by each antenna is selected by the switch 22, amplified by the receiving amplifier 26, and mixed with a part of the transmission wave by the mixer 28 to generate a beat signal. The beat signal generated in the mixer 28 is distributed to one of the upper and lower two processing systems in the figure by the switch 30, converted to a digital signal by the A / D converter 32, and fast Fourier transformed (34) to the CPU 36. Entered.

  FIG. 5 shows a waveform of a triangular wave input to the voltage controlled oscillator 10 of FIG. 4, and columns (A) to (C) in FIG. 6 respectively show control signals SWT, SWR, The waveforms of SW0, SW1, and SW2 are shown, and the (D) column in FIG. 6 shows the waveform of the control signal CH of the switch 30 with the same time scale and the same timing as the (A) to (C) columns. Note that the time scale of the horizontal axis in FIG. 5 is significantly compressed as compared with FIG.

  In the first period of the triangular wave shown in FIG. 5, that is, in section A, transmission → reception by AT0 → transmission → reception by AT1 is repeated as can be seen from FIG. 6D, the beat signal based on the AT0 received signal is distributed to the upper system in the figure by the switch 30 in FIG. 4, and the beat signal based on the AT1 received signal is distributed to the lower system in the figure. And processed in parallel. That is, in the section A, beat signal data in the up and down sections of the triangular wave generated from the reception signals of the receiving antennas AT0 and AT1 are collected. The peak frequency appearing in these Fourier transform results is used for the calculation of the distance to the target and the relative speed, and the peak phase is used for the calculation of the phase monopulse by the antennas AT0 and AT1.

  In the next period of the triangular wave shown in FIG. 5, that is, the section B, transmission → reception by AT1 → transmission → reception by AT2 is repeated as can be seen from FIG. 6 (B). As can be seen from FIG. 6D, the beat signal based on the received signal of AT1 is distributed to the upper system in the figure by the switch 30 of FIG. 4, and the beat signal based on the received signal of AT2 is distributed to the lower system in the figure. And processed in parallel. That is, in the section B, beat signal data in the up and down sections of the triangular wave generated from the reception signals of the receiving antennas AT1 and AT2 are collected. The peak frequency appearing in these Fourier transform results is used for the calculation of the distance to the target and the relative velocity, and the peak phase is used for the calculation of the phase monopulse by the antennas AT1 and AT2.

  In the further next cycle of the triangular wave shown in FIG. 5, that is, in the section C, transmission → reception by AT2 → transmission → reception by AT0 is repeated as can be seen from FIG. As can be seen from FIG. 6D, the beat signal based on the AT2 received signal is distributed to the upper system in the figure by the switch 30 in FIG. 4, and the beat signal based on the AT0 received signal is distributed to the lower system in the figure. And processed in parallel. That is, in section C, beat signal data in the up and down sections of the triangular wave generated from the reception signals of the receiving antennas AT2 and AT0 is collected. The frequency of the peak appearing in these Fourier transform results is used for the calculation of the distance to the target and the relative velocity, and the phase of the peak is used for the calculation of the phase monopulse by the antennas AT2 and AT0.

  FIG. 7 is a block diagram showing a configuration of a second example of an in-vehicle FM-CW radar apparatus as an example of a radar apparatus to which the present invention is applied. In FIG. 7, a transmission signal that is output from a voltage controlled oscillator (VCO) 10 and is FM-modulated with a triangular wave is multiplied to a millimeter wave band by a multiplier 12, amplified by a transmission amplifier 14, and input to an antenna selector switch 13. In the antenna selector switch 13, the signal is transmitted from the antenna AT 0 through the amplifier 15 and the switch 16. In the radar apparatus shown in FIG. 7, only the antenna AT0 is used for transmission among the three antennas AT0, AT1 and AT2, and reception is selected by the switch 22 among the three antennas AT0, AT1 and AT2. Is used. A switch 21 is provided between the antenna AT0 and the amplifier 24 to prevent the transmission signal from wrapping around to the reception side. The switches 16 and 21 are not necessarily required when the sneaking to the receiving side can be prevented by another means.

  The received signal received by each antenna is amplified by the amplifier 24, selected by the switch 22, amplified by the receiving amplifier 26, and mixed with a part of the transmission wave by the mixer 28 to generate a beat signal. The subsequent processing is the same as the first example described with reference to FIG. Signals given to the switches are the same as those in FIG.

  FIG. 8 is a flowchart of an example of the correction value storing process in the present invention. In FIG. 8, first, the transmission amplifier 14 is turned off so that the peak resulting from the reflection from the target does not appear in the Fourier transform result (step 1000). Otherwise, the same operation as described above is performed, and the Fourier transform is performed. The result is fetched (step 1002) and stored in the memory as a correction value (step 1004). During the radar operation, the effect of noise associated with antenna switching can be eliminated by subtracting this correction value from the Fourier transform result. As shown in FIGS. 5 and 6, since the antenna switching order is different for each of the sections A, B, and C, the appearing noise is also different. Therefore, a correction value is stored for each section.

  This process is performed, for example, during product inspection before product shipment, and the correction value is stored in a nonvolatile memory. By rewriting correction values at regular time intervals during radar operation, it is possible to cope with temperature fluctuations and component aging. In this case, the correction value is stored in the RAM.

  Instead of turning off the transmission amplifier 14, a target-free situation may be created by covering the antenna with a radio wave absorber.

The correction value is stored for each of the real number component and the imaginary number component of the Fourier transform result, and correction calculation is performed for each of the real number component and the imaginary number component. That is, when the real component before correction as a function of the frequency f is Re (f) and the correction value of the real component is Re _N (f), the corrected real component Re _t (f) Re _t (f) = Re (f) −Re _N (f)
Similarly, for the imaginary component, the expression Im _t (f) = Im (f) −Im _N (f) for each frequency f
Calculated from

For example, when the direction is detected by mechanical scanning and phase information is not used, the correction value may be stored and corrected for the power after the power (absolute value) calculation.
Further, instead of performing correction values, storage, and correction operations on the Fourier transform results, correction values may be stored and correction operations may be performed on the output values of the AD converter 32 before the Fourier transform.
However, in this case, noise in the time domain before Fourier transform as shown in the column (B) of FIG. 2 is often not stable on the time axis, so that it is difficult to perform appropriate correction. On the other hand, since noise in the frequency domain after Fourier transform is stable on the frequency axis, appropriate correction can be performed.

  In the case of FM-CW radar, the correction value includes FM-AM conversion noise in addition to noise caused by antenna switching. If the FM modulation by the triangular wave is stopped in addition to the no target state, only the noise caused by the antenna switching can be detected.

It is a figure which shows the structure of the radar apparatus which performs antenna switching. It is a figure explaining the noise resulting from antenna switching. It is a block diagram which shows schematic structure of the radar apparatus of this invention. It is a figure which shows the 1st example of a structure of the vehicle-mounted FM-CW radar apparatus to which this invention is applied. It is a wave form diagram which shows the modulation wave by a triangular wave. It is a wave form diagram which shows the waveform of each control signal of FIG. It is a figure which shows the 2nd example of FM-CW radar apparatus. It is a flowchart of an example of the correction value storage process of this invention.

Claims (13)

A switch for sequentially switching and selecting one of signals received by a plurality of receiving antennas;
A mixer that mixes the reception signal selected by the switch and a part of the transmission signal to generate a beat signal;
Fourier transform operation means for Fourier transforming the output signal of the mixer;
Correction value storage means for storing the Fourier transform result of the Fourier transform operation means when there is no reflected signal from the target as a correction value for canceling the influence caused by fluctuation of the DC level of the mixer accompanying the switching of the switch When,
A radar apparatus comprising: correction means for correcting a Fourier transform result of the Fourier transform calculation means with a correction value stored in the correction value storage means. A transmission amplifier for amplifying the transmission signal;
The radar apparatus according to claim 1, wherein the correction value storage means stores a Fourier transform result when the transmission amplifier is turned off as the correction value.   The radar apparatus according to claim 1, wherein the correction value storage unit stores a Fourier transform result when the target does not exist as the correction value.   The radar apparatus according to claim 2, wherein the correction value storage means updates the correction value by periodically turning off the transmission amplifier during operation of the radar. The correction value storage means stores a correction value for each of a real component and an imaginary component of a Fourier transform result,
The radar apparatus according to claim 1, wherein the correction unit corrects each of a real component and an imaginary component of a Fourier transform result. The correction value storage means stores a correction value for the power of the Fourier transform result,
The radar apparatus according to claim 1, wherein the correction unit corrects power of a Fourier transform result.   The radar apparatus according to claim 1, wherein the transmission signal is frequency-modulated with a triangular wave, and the correction value storage means stores a Fourier transform result when the frequency modulation is stopped as a correction value. A switch for sequentially switching and selecting one of signals received by a plurality of receiving antennas;
A mixer that mixes the reception signal selected by the switch and a part of the transmission signal to generate a beat signal;
An AD converter for converting the output signal of the mixer into a digital value;
Correction value storage means for storing the output value of the AD converter when there is no reflected signal from the target, as a correction value for canceling the influence caused by fluctuation of the DC level of the mixer accompanying the switching of the switch;
A radar apparatus comprising: correction means for correcting the output value of the AD converter with a correction value stored in the correction value storage means. A transmission amplifier for amplifying the transmission signal;
The radar apparatus according to claim 8, wherein the correction value storage means stores the output value of the AD converter when the transmission amplifier is turned off as the correction value.   The radar apparatus according to claim 8, wherein the correction value storage unit stores an output value of the AD converter when no target exists as the correction value.   The radar apparatus according to claim 9, wherein the correction value storage means updates the correction value by periodically turning off the transmission amplifier during operation of the radar.   9. The radar apparatus according to claim 8, wherein the transmission signal is frequency-modulated with a triangular wave, and the correction value storage means stores an output value of the AD converter when the frequency modulation is stopped as a correction value.   12. The radar apparatus according to claim 3, 4, 10 or 11, wherein the correction value storage means collects and stores correction values prior to product shipment.

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