JP5059717B2 - Monopulse radar device - Google Patents

Description

  The present invention relates to a monopulse radar device that radiates radio waves from a transmitter and receives reflected waves by a plurality of receivers.

  Radar devices that use radio waves such as millimeter waves have a low attenuation of radio wave beams even in bad weather such as rain and fog, and reach far distances. It is widely used as a sensor for measuring the relative position and relative speed.

  The radar device radiates radio waves from the transmission unit, receives reflected waves from targets such as obstacles and vehicles traveling ahead, and performs signal processing on the received signals, so that the distance from the target and the relative speed The azimuth angle is detected.

  There are several methods for measuring the azimuth angle with the target, but a typical one is a monopulse method. In the monopulse method, a reflected wave from a target is simultaneously received by a plurality of antennas, and a phase difference between signals is detected to detect an azimuth angle of the target. The monopulse method can detect the azimuth angle of the target without having a mechanical movable part, and is thus effective for downsizing and high reliability of the radar.

  Patent Document 1 below calculates an imaginary part of the monopulse ratio from a monopulse sum channel and a monopulse difference channel in a situation where a plurality of objects having the same distance and relative velocity exist in the antenna beam. A method for determining whether or not there are a plurality of objects in the antenna beam is shown.

JP-A-7-113862

  However, in a situation where the relative velocities of a plurality of objects existing in the antenna beam are the same, the Doppler frequency of the received signal has the same value, so that reflected waves from the plurality of objects are combined. This state is called a multipath interference state. In the multipath interference state, the phases of the reflected waves from a plurality of objects cannot be individually measured, and thus the azimuth angle of each object cannot be obtained.

  A synthesized wave obtained by synthesizing a plurality of reflected waves may be indistinguishable from a reflected wave when a single object is present in the antenna beam, and accurately determines whether or not multipath interference occurs. I can't. On the other hand, if it is possible to accurately determine that multipath interference is occurring, signal processing according to the characteristics at the time of interference can be used, and more appropriate treatment can be performed.

  The present invention has been made in view of the above points, and an object of the present invention is to accurately determine whether or not multipath interference is occurring so that appropriate signal processing can be executed in a multipath interference state. To provide a monopulse radar device capable of determination.

  An invention of a monopulse radar device made to solve the above-mentioned problem is to determine whether multipath interference is occurring based on a plurality of detection results detected at predetermined time intervals. It is a feature.

  According to the monopulse radar apparatus of the present invention, it is determined whether multipath interference has occurred based on a plurality of detection results detected at predetermined time intervals. Compared with the case where it is determined whether or not multipath interference is occurring based on this, the determination can be made with higher accuracy. Therefore, when multipath interference occurs, signal processing according to the characteristics at the time of interference can be used, and more appropriate treatment can be performed.

Next, embodiments of the present invention will be described below with reference to the drawings.
[First Embodiment]
FIG. 1 is a block diagram illustrating the configuration of the monopulse radar apparatus 101 according to the present embodiment. The monopulse radar apparatus 101 employs, for example, a two-frequency CW system as a radar radio wave transmission system, and is mounted on the host vehicle 201 (see FIG. 5 ). As shown in FIG. 1, the transmission system includes a modulation circuit 102, an oscillator 103, and a transmission antenna (transmission unit) 104. The reception system includes reception antennas (reception units) 105 (a) and 105 (b), and a power amplifier. 106, a mixer circuit 107, a demodulation circuit 108, an A / D converter 109, and a signal processor 110.

  The modulation circuit 102 outputs a modulation signal to the oscillator 103, and the oscillator 103 oscillates based on the modulation signal from the modulation circuit 102 and transmits a radio wave from the transmission antenna 104 serving as a transmission unit. The transmitting antenna 104 is directed to radiate radio waves toward the front of the vehicle body, which is the monitoring area direction.

  The radio wave transmitted from the transmission antenna 104 is reflected by an object (target) that exists within the radiation range of the radio wave, such as a vehicle 306 ahead as shown in FIG. 5, for example, and a pair of reception antennas 105 (a ), 105 (b).

  The reception signals received by these reception antennas 105 (a) and 105 (b) are respectively amplified by the power amplifier 106, mixed with the transmission signal by the mixer circuit 107, and a beat signal is generated.

  The beat signal is demodulated by the demodulation circuit 108, converted to a digital signal by the A / D converter 109, sent to the signal processor 110, and predetermined arithmetic processing is executed by the signal processor 110.

  FIG. 2 is a flowchart for explaining the contents of the arithmetic processing executed by the signal processor 110. First, in step S401, multipath interference determination processing is performed to determine whether multipath interference has occurred (multipath interference determination means). The contents of this multipath interference determination process will be described later.

  If it is determined that the state is not a multipath interference state (NO in step S402), physical quantity conversion is performed in step S403 in the same manner as normal data processing, and prediction is performed from past detected object measurement physical quantities in step S404. Based on the current measured physical quantity, the physical quantity actually calculated is corrected. As this correction means, a Kalman filter, an α-β filter, or the like conventionally used in the field of radar technology is used. Thus, for example, when it is determined that a single object exists within the radio wave irradiation range, the distance, relative speed, and azimuth angle with the host vehicle are calculated.

  On the other hand, if it is determined that the state is the multipath interference state (YES in step S402), physical quantity conversion using the characteristics in the multipath interference state is performed in step S405 instead of normal physical value conversion, and in step S407. Performs filtering using the characteristics of the multipath interference state.

  Next, the multipath interference determination process in step S401, which is a characteristic part of the present invention, will be described in detail with reference to FIG. FIG. 3 is a flowchart for explaining the contents of the multipath interference determination process executed in the signal processor 110.

  First, A / D data (t = t1) acquired in each modulation section is subjected to fast Fourier transform (FFT) in step S501 to obtain a frequency spectrum obtained by decomposing the beat signal in the frequency domain.

  When a pair of receiving antennas 105 (a) and 105 (b) receive a reflected wave from an object, the beat signal has a peak with a large signal-to-noise power ratio (S / N), for example, as shown in FIG. The frequency peak 111 is observed. The frequency peak 111 observed in this way is detected in step S502.

  In step S503, processing for calculating the signal strength of the reception signal of each reception antenna 105 (a) and 105 (b) is performed based on the peak information of the frequency peak detected in step S502.

  Here, for example, as shown in FIG. 5, in the case of a non-multipath interference state where only one vehicle 306 is traveling in front of the host vehicle 201 on which the radar 101 is mounted, the vehicle as shown in FIG. The reflected waves 307 (a) and 307 (b) from 306 are received by the receiving antennas 105 (a) and 105 (b).

  The frequency peaks of the beat signals extracted from these received signals are the same as shown in FIG. 7, for example, in a polar coordinate format in which the vector length represents the magnitude of the signal intensity and the vector direction represents the phase. The received signals 112 (a) and 112 (b) have signal strength. (However, the gain between receiving antennas is assumed to be equal.)

  For example, as shown in FIG. 8, in the case of a multipath interference state in which two vehicles 303 and 304 (target) are running in parallel at the same relative speed in front of the host vehicle 201, as shown in FIG. Thus, the reflected wave 308 (a) from the vehicle 303 and the reflected wave 309 (a) from the vehicle 304 are received by one receiving antenna 105 (a), and the vehicle 303 is received by the other receiving antenna 105 (b). The reflected wave 308 (b) from the vehicle and the reflected wave 309 (b) from the vehicle 304 are received.

  At this time, the Doppler frequencies of the received signals reflected back from the vehicles 303 and 304 are equal. Therefore, when the frequency spectrum of the beat signal is observed, the frequency peaks of the respective reception signals overlap, and the signal received by the reception antenna 105 (a) is, for example, as shown in FIG. a) and the reflected wave 114 (a) from the vehicle 304 are combined into a received signal 115 (a) of a combined wave, and the signal received by the receiving antenna 105 (b) is a reflected wave 113 (b) from the vehicle 303. And the reflected wave 114 (b) from the vehicle 304 is combined into a received signal 115 (b) of a combined wave.

  The reception signals 115 (a) and 115 (b) received by the reception antennas 105 (a) and 105 (b) are different signals even if the gains between the reception antennas 105 (a) and 105 (b) are equal. You can see that it has strength.

  As described above, the signal strengths of the received signals received by the respective receiving antennas 105 (a) and 105 (b) are equal in the case of non-multipath interference (see FIG. 9). It can be seen that the received signals received at (a) and 105 (b) have different signal strengths (see FIG. 10). Therefore, by utilizing this property, it is possible to determine whether multipath interference is occurring.

  In step S504, the signal strengths of the reception signals of the reception antennas 105 (a) and 105 (b) calculated in step S503 are compared with each other to determine whether or not these signal strengths are equal.

  However, for example, a reflected wave from the target may be received with a phase as shown in FIG. 11 despite the multipath interference state. In this case, the reflected wave 113 (a) from the vehicle 303 and the vehicle The composite wave reception signal 116 (a) in which the reflected wave 114 (a) from 304 is combined, and the composite wave in which the reflected wave 113 (b) from the vehicle 303 and the reflected wave 114 (b) from the vehicle 304 are combined. The signal strength of the wave reception signal 116 (b) is equal.

  Thus, even in the multipath interference state, depending on the phase of the reflected wave from the target, the signal strengths of the two received signals may be equal to each other as in the non-multipath interference state. Therefore, it may not be possible to correctly determine whether or not the multipath interference state is obtained only by comparing the signal strengths of the received signals received by the receiving antennas 105 (a) and 105 (b).

  In order to solve this problem, the monopulse radar apparatus 101 of the present invention uses a plurality of detection results (two in the present embodiment) obtained from the A / D converter 109 at predetermined time intervals. Whether or not the signal strength of the received signal is different when the reflected wave is received by the receiving antennas 105 (a) and 105 (b) using a certain A / D data (time t = t1, t2). If the signal strengths differ from each other at least once, it is determined as a multipath interference state. If the signal strengths are equal in both cases, it is determined as a non-multipath interference state.

  That is, when the determination result of a plurality of times includes a determination result that the signal strength is different between the receiving antennas 105 (a) and 105 (b), it is determined as a multipath interference state and is not included. In this case, it is determined as a non-multipath interference state.

  The positional relationship between the host vehicle 201 and the vehicles 303 and 304 changes from moment to moment according to the respective driving conditions. Further, in the case of a 76 GHz band radar, the phase changes by 360 ° due to a change in the positional relationship of 4 mm. Thus, by using the determination results at the two times (t1, t2), it is possible to accurately determine whether multipath interference is occurring.

  For example, as shown in FIG. 8, when both the relative speeds of the vehicles 303 and 304 with respect to the host vehicle 201 are in the same multipath interference state, multipath interference occurs using only a single comparison result at that time. If it is determined whether or not the two signal intensities are accidentally the same due to the phase relationship, there is a possibility that an erroneous determination is made that multipath interference does not occur.

  On the other hand, in the monopulse radar apparatus 101 of the present invention, it is determined whether or not multipath interference has occurred by using a plurality of comparison results based on A / D data obtained with a predetermined time interval. In a situation where multipath interference actually occurs, even if the comparison result at a certain time coincides with the two signal strengths by chance, due to a change in the positional relationship with the target and a change in the relative velocity, It is very unlikely that the two signal strengths will be the same again in the comparison result, and will differ with high probability.

  Therefore, according to the monopulse radar apparatus 101 of the present invention that determines whether or not multipath interference is occurring using the comparison result of the plurality of signal strengths, it is accurately determined whether or not multipath interference is occurring. be able to.

  As a specific process, as shown in FIG. 3, a pair of receiving antennas 105 (a), 105 (105) (105 (a), 105 (a), 105 (a), 105 (a), 105 (a), (t = t1) It is determined whether the received signal strengths received in b) are equal to each other.

  Then, the A / D data (t = t2) after a predetermined time interval from the A / D data (t = t1) is subjected to the processing from step S511 to step S514, and a pair of receiving antennas is received. Processing is performed to determine whether the received signal strengths received at 105 (a) and 105 (b) are equal to each other.

  Then, in the multipath interference determination processing in step S521, reception is performed in at least one of the two A / D data (t1, t2) based on the processing results from step S501 to step S504 and the processing results from step S511 to step S514. Processing is performed to determine whether or not the signal strengths of the received signals received by the antennas 105 (a) and 105 (b) are different.

  Here, when the signal strength of the received signal is different at least once or more, it is determined as a multipath interference state, and when there is no signal strength, it is determined as a non-multipath interference state. The multipath interference determination result in step S521 is output by the determination result output process in step S522, and the process proceeds to step S402 shown in FIG.

  According to the monopulse radar apparatus 101 having the above-described configuration, since it is determined whether multipath interference is occurring based on a plurality of signal intensity comparison results acquired at predetermined time intervals, Compared with the case where it is determined whether or not multipath interference is occurring based on the signal intensity comparison result, the determination can be made with higher accuracy.

  In the above-described embodiment, the case where multipath interference determination is performed based on two signal strength comparison results has been described as an example. However, a plurality of signal strength comparison results obtained at predetermined time intervals are used. Any multi-path interference determination (step S251) may be performed based on, for example, three or more signal intensity comparison results.

  As shown in FIG. 12, in the case of a non-multipath interference state in which two vehicles 301 and 302 are traveling at different traveling speeds (the length of the arrow represents the speed) in front of the host vehicle 201, The frequency of the reception signal that is reflected from the vehicles 301 and 302 when the radio wave irradiated forward from the monopulse radar apparatus 101 is returned causes a Doppler shift corresponding to the relative speed between the vehicle 201 and the vehicles 301 and 302. So, at this time, if you observe the frequency spectrum of the beat signal obtained by mixing the received signal and the transmitted signal, you can obtain the peak corresponding to each Doppler frequency, and analyze the phase information of that peak Thus, the azimuth angles of the front vehicles 301 and 302 with respect to the host vehicle 201 can be correctly measured.

[Second Embodiment]
Next, a second embodiment will be described.
The present embodiment shows a specific example of the signal intensity comparison process in step S504 of FIG.

From the received signal by the receiving antenna 105 (a), detected in step S502 of FIG. 3 the frequency peak information of the target detected in step S502 of FIG. 3 _{S 1,} from the received signal by the receiving antenna 105 (b) the frequency peak information of a target is described as S _2.

Here, the two detected frequency peak information S ₁ and S ₂ are complex numbers, and have phase information in addition to amplitude information corresponding to signal intensity.

In the present embodiment, by examining the orthogonality T of the sum / difference signals of these two frequency peak information S ₁ and S ₂ , the degree of coincidence of S ₁ and S ₂ , that is, the coincidence, is determined. Processing to measure. In particular,

により求まる。

It is obtained by.

The closer the value of the orthogonality T is to zero, the higher the orthogonality is, that is, the higher the coincidence of the sizes of S ₁ and S ₂ , and conversely, the lower the orthogonality T is, the lower the orthogonality is. That is, it can be determined that the coincidence of the sizes of S ₁ and S ₂ is low.

  The signal strength of the received signal received by the receiving antennas 105 (a) and 105 (b) is determined by comparing the orthogonality T with a threshold obtained experimentally in advance to determine whether the orthogonality T is smaller than the threshold. Can be determined whether or not they are the same.

[Third Embodiment]
Next, a third embodiment will be described.

  This embodiment shows another specific example of the signal intensity comparison processing in step S504 in FIG.

From the received signal received by the receiving antenna 105 (a), the target frequency peak information detected in step S502 of FIG. 3 is S _{1. From} the received signal received by the receiving antenna 105 (b), in step S502 of FIG. the frequency peak information of the detected target is described as S _2.

Here, the two detected frequency peak information S ₁ and S ₂ are complex numbers, and have phase information in addition to amplitude information corresponding to signal intensity.

により、一致度Ｕを表す値が求まる。 In this embodiment, the degree of coincidence U of whether or not the magnitudes of S ₁ and S ₂ are equal is determined by examining the normalized difference between the magnitudes of these two frequency peak information S ₁ and S _2. Processing to measure. In particular,

Thus, a value representing the degree of coincidence U is obtained.

Here, the denominator of Equation 3 that normalizes the size cannot be normalized strictly, but in the non-interference state,

Therefore, normalization can be performed correctly. Even in the interference state, by dividing by the smallest possible value, the value of U can be increased, and the determination can be performed correctly.

The closer the value of the coincidence U is to zero, the higher the coincidence of the magnitudes of S ₁ and S _2. Conversely, the closer the value of the coincidence U is from zero, the more coincident the magnitudes of S ₁ and S ₂ are. It can be judged that the nature is low.

  The degree of coincidence U is compared with a threshold obtained experimentally in advance, and it is determined whether or not it is smaller than the threshold, whereby the signal strength of the received signal received by the receiving antennas 105 (a) and 105 (b) is increased. It can be determined whether or not they are the same.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the second embodiment and the third embodiment described above, a method for determining whether or not the signal strengths of the received signals received by the receiving antennas 105 (a) and 105 (b) are the same is described. However, it may be determined by other methods.

The block diagram explaining the structure of a monopulse radar apparatus. The flowchart explaining the processing content performed with a signal processor. The flowchart explaining the content of the multipath interference determination process. The figure which shows that the Doppler frequency which arises when an electromagnetic wave reflects with an object is observed as a peak in a frequency spectrum. The figure which shows the non-multipath interference state where one vehicle is drive | working ahead of the own vehicle. The figure which shows a mode that the reflected wave is received with two receiving antennas in the state of FIG. The figure which showed the received signal received in the state of FIG. 6 with the vector of the polar coordinate form. The figure which shows the multipath interference state which two vehicles with equal relative speed drive | work ahead of the own vehicle. The figure which shows a mode that the reflected wave is received with two receiving antennas in the state of FIG. The figure which represented the received signal received in the state of FIG. 8 with the vector of the polar coordinate form. The figure which represented the received signal received with the phase timing different from FIG. 10 in the state of FIG. 8 with the vector of the polar coordinate form. The figure which shows the multipath interference state which the two vehicles from which relative speed differs drive | work ahead of the own vehicle.

Explanation of symbols

101 Monopulse Radar Device 104 Transmitting Antenna 105 (a), 105 (b) Receiving Antenna 110 Signal Processor 111 Frequency Peak 201 Own Vehicle 301-306 Target Vehicle (Object)

Claims (2)

A monopulse radar device that radiates radio waves from a transmitter and receives reflected waves by two receiving antennas to detect an object,
Multipath interference determination means for determining whether or not multipath interference has occurred based on a plurality of detection results detected at predetermined time intervals ,
The multipath interference determination means includes
Signal strength calculating means for calculating signal strengths of two received signals received by the two receiving antennas;
When the degree of coincidence of each signal intensity is calculated based on a value obtained by normalizing the difference in signal intensity between the two received signals calculated by the signal intensity calculating means, and the degree of coincidence is smaller than a preset threshold value Comprises signal strength comparison means for determining that the signal strengths of the two received signals are equal to each other, and determining that the signal strengths of the two received signals are different from each other when the degree of coincidence is equal to or greater than the threshold value,
The signal strength comparison means determines whether or not a plurality of determination results determined with a predetermined time interval include a determination result that the signal strengths of the two received signals are different from each other. When it is included, it is determined as a multipath interference state, and when it is not included, it is determined as a non-multipath interference state . The normalization of the difference between the signal strengths of the two received signals is performed by dividing the difference by the smaller signal strength of the signal strengths of the two received signals. Monopulse radar device.

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