JP6523350B2 - Radar apparatus and object recognition method - Google Patents

Description

  The present invention relates to a radar device and an object recognition method for detecting a position (distance and angle) at which a target exists by receiving radio waves (reflected waves) reflected from the target using a plurality of receiving antennas. It is.

There is an angle measurement technology that can calculate with high accuracy the arrival direction (the angle at which a target exists) of a reflected wave from a target using the amplitude and phase information of the reflected wave received by a plurality of antennas (Non-Patent Document 1) reference).
The radar apparatus can measure the angle of arrival of the reflected wave from the target more accurately by increasing the number of antennas and increasing the area where the antennas are present, that is, the antenna aperture (non-patent) Reference 2).

  By the way, in order to accurately measure the arrival angle of the reflected wave from the target with a limited number of antennas, it is necessary to widen the intervals between the plurality of antennas. However, if multiple antenna spacing is set to a half wavelength or more of the used frequency, grating lobes with the same amplitude and phase information as the main beam are generated, and the arrival direction of the reflected wave can not be identified uniquely. There is a problem of erroneous measurement angle (see Non-Patent Document 3 and Patent Document 1).

Patent No. 4143 007

The Institute of Electronics, Information and Communication Engineers "Antenna Engineering Handbook (2nd edition)" Ohmsha July 2008 P492-P515 Steven M. Kay "Fundamentals of Statistical Signal Processing Estimation Theory" P57-P59 The Institute of Electronics, Information and Communication Engineers "Revision Radar Technology" Corona P119-P123

  As described above, in the radar apparatus using a plurality of antennas, it is desirable to arrange the antennas at half the wavelength of the used frequency or less, in order to prevent occurrence of erroneous measurement angles, but in practice, with a limited number of antennas If the measurement error of grating lobes is not permitted, there is a problem that it is impossible to secure the antenna opening length that can achieve the target measurement accuracy.

  The present invention has been made to solve the above-described problems, and a radar device and an object recognition capable of improving the measurement accuracy by eliminating an erroneous measurement angle due to a grating lobe with a limited number of antennas It aims to provide a method.

A radar apparatus according to the present invention is a radar apparatus having a plurality of receiving antennas for receiving a reflected wave reflected by a target, wherein among the plurality of receiving antennas, the receiving antenna spacing is equal to or more than a half wavelength of the used frequency. A main antenna for receiving the reflected wave and a predetermined receiving antenna among the plurality of receiving antennas arranged at d1 are arranged at equal intervals d2 to form a beam in the same direction as the main beam of the main antenna, The amplitude difference between the received signal of the main antenna and the sub antenna and the sub antenna that receives the reflected wave is calculated with an amplitude pattern in which the reception intensity is suppressed at the grating lobe generation angle of the main antenna, and the threshold is set in advance. comprising a determining signal processor of the presence of the basis target object, wherein the three the number of sub-antennas, the amplitude pattern of the sub antenna in phase excitation The distance between the receiving antennas is set so that the relationship of d1 = 3d2 holds, or the amplitude pattern of the sub antenna is formed by central reverse phase excitation so that the distance between the receiving antennas holds the relationship d1 = 6d2 The

The object recognition method according to the present invention comprises a first step of receiving a reflected wave reflected by a target at a main antenna having a half wavelength of a used frequency or more at equal intervals d1 among the plurality of receiving antennas; wherein forming a main beam and the beam in the same direction of the main antenna, with an amplitude pattern of suppressing the reception intensity by the grating lobe occurrence angle generated by the reception of the main antenna, a predetermined receiving antenna in the sub antenna equidistant d2 A second step of receiving a reflected wave, and a third step of calculating an amplitude difference between the received waves of the first step and the second step, and recognizing the presence of an object based on a preset threshold. wherein the number of sub-antennas 3 and the distance the relationship d1 = 3d2 of the receiving antenna is formed by in-phase excitation of the amplitude pattern of the auxiliary antenna Ri and so stand, or the one in which the amplitude pattern of the sub antenna to the distance of the receiving antenna is formed by a central reversed-phase excitation as the relationship d1 = 6d2 is established.

  According to the radar apparatus according to the present invention, it is possible to provide a radar apparatus capable of improving the angle measurement accuracy and accurately eliminating the erroneous side angle due to the grating lobe with a limited number of antennas.

It is a block diagram of a receiving system which shows a common part of a radar installation in an embodiment of this invention. It is a flowchart figure which shows the common part of the radar apparatus in embodiment of this invention. It is a figure which shows the structure of the equally-spaced array antenna which comprises a radar apparatus. It is a figure which shows the relationship between receiving antenna aperture length and beam width. It is a figure which shows the relationship between a receiving antenna space | interval, a grating lobe, and a null generation | occurrence | production angle. It is a block diagram of a receiving system which shows a radar installation in Embodiment 1 of this invention. A figure showing an amplitude pattern of a main antenna and a sub antenna (in-phase excitation) of a radar device in a first embodiment of the present invention It is a figure which shows the amplitude pattern of the main antenna of the radar apparatus in Embodiment 1 of this invention, and a subantenna (center reverse phase excitation). It is a figure which shows an amplitude pattern when making a beam shift with the main antenna and subantenna (in-phase excitation) of the radar apparatus in Embodiment 2 of this invention. It is a block diagram of the receiving system which shows the radar apparatus in Embodiment 3 of this invention.

Embodiment Hereinafter, a radar apparatus and an object recognition method according to an embodiment of the present invention will be described.
FIG. 1 is a block diagram of a reception system showing a common part of a radar device according to an embodiment of the present invention.
In FIG. 1, the radar apparatus processes a signal received by a receiving antenna 1 including a main antenna 2 and a sub antenna 3, an RF (radio frequency) receiver 4 that receives a signal from the receiving antenna 1, and an RF receiver 4. The signal processing unit 5 detects the position of the target. Of course, the transmission system is also necessary, but this invention does not depend on the configuration of the transmission system, so the description will be omitted.

The main antenna 2 is configured by a total of m reception antennas 1 of A1 to Am, and the reception antennas 1 are equally spaced array antennas arranged at an interval d1 of a half wavelength or more of the used frequency. Further, the sub antenna 3 is configured by a total of n receiving antennas 1 of B1 to Bn, and is an equidistant array antenna arranged at an interval d2 of each predetermined receiving antenna 1. Note that the receiving antenna 1 may be configured of one antenna element or an array antenna in which a plurality of antenna elements are connected by a feeding circuit.

  The RF receiver 4 is configured to be connected to the main antenna 2 and the sub antenna 3, and the received signal obtained from each of the receiving antennas 1 is, for example, a high frequency frequency by superhetrodyne method (mixing of transmitted signal and received signal) It converts and amplifies to an intermediate frequency, and finally has a function of outputting a digital signal by A / D conversion.

The signal processing unit 5 is connected to the RF receiver 4, performs signal processing on the digital signal output from the RF receiver 4 based on the flowchart shown in FIG. 2, and recognizes an object (target). This signal processing operation is described below.
In FIG. 2, step S1 performs fast Fourier transform (FFT) of the digital signal obtained from each receiving antenna 1 to the frequency axis.
Step S2 performs predetermined weighting on the FFT signals obtained from the receiving antenna 1 of the main antenna 2 and performs digital beam forming (digital beam forming = DBF) combining.

Steps S3 and S4 detect the peak of the FFT signal obtained by DBF synthesis, and measure the arrival direction of the reflected wave from the target from the amplitude and phase information of this peak.
Step S5 performs predetermined weighting on the FFT signal of the receiving antenna 1 of the sub antenna 3 corresponding to the peak frequency of the FFT signal from the main antenna 2, and performs DBF combining to be added.
A step S6 compares the amplitude of the FFT signal after DBF combination of the main antenna 2 with the amplitude of the FFT signal after DBF combination of the sub antenna 3, and calculates the difference in amplitude.

In step S7, if the amplitude difference between the main antenna 2 and the sub antenna 3 after DBF combining is equal to or greater than a predetermined threshold α, the target is determined to have no object in the angle measurement direction, and the amplitude difference is the threshold α If it is the following, it will be output as target information (position, angle measurement value) with the object being an object in the angle measurement direction.
Note that the combination of the main antenna 2 and the reception antenna 1 of the sub antenna 3 may be performed by RF (radio frequency) combination at the antenna unit before being connected to the RF receiver 4. The signal processing in this case is omitted because the DBF combination of the main antenna 2 and the sub antenna 3 in FIG. 2 is simply omitted.

Next, the amplitude pattern (radiation pattern) after DBF synthesis obtained by the main antenna 2 and the sub antenna 3 will be described.
An array antenna in which m (m ≧ 2) reception antennas 1 shown in FIG. 3 are arranged at equal intervals with an interval d is multiplied by weighting coefficients W ( ₁ to _m ) to the reception signals of the respective reception antennas 1. Consider the amplitude pattern of the array antenna when added together by the combiner 6. The amplitude pattern when the weighting factors W of the respective receiving antennas 1 are added at 1, ie, the same amplitude, is expressed by the following equation (1).

但し、ｋは使用周波数での波数、θは反射波の角度、βは受信アンテナ１の重みづけ係数で与える初期位相成分である。

Where k is the wave number at the frequency used, θ is the angle of the reflected wave, and β is the initial phase component given by the weighting factor of the receiving antenna 1.

但し、λは使用周波数での波長、Ｌは受信アンテナ開口長、θ_Ｓはビームシフト角である。 The beam widths of the above-mentioned equal-amplitude equidistant array antennas are approximated by the following equations (3) and (4).

Where λ is the wavelength at the used frequency, L is the receiving antenna aperture length, and θ _S is the beam shift angle.

FIG. 4 shows the beam width with respect to the aperture length L of the receiving antenna 1 normalized by the wavelength obtained from the equations (3) and (4) when the beam shift angle θ _S = 0 degrees. Since the angle measurement accuracy of the radar apparatus is inversely proportional to the beam width of the receiving antenna 1, the beam width can be reduced by increasing the aperture length L of the receiving antenna 1, and the angle measurement accuracy can be improved.

Next, the number of m (m22) receiving antennas 1 shown in FIG. 3 is an odd number, and the same amplitude and center ((m-1) / 2 + 1) receiving antennas 1 have an opposite phase to the other receiving antennas. The amplitude pattern of the array antenna when multiplied by the weighting factor so as to be and added by the synthesizer 6 is expressed by the following equation (5).

  From equations (1) and (5), it can be seen that beams are in the same direction (in the case of β = 0, θ = 0 direction). Further, from Eqs. (1) and (5), it is possible to obtain the incidence angle of null in which the grating lobe and the reception intensity are suppressed with respect to the receiving antenna spacing of the array antenna. For example, when m = 3, the grating lobe and the null generation angle of equation (1) and the null generation angle of equation (5) become the following equations (6), (7) and (8).

ここでβ＝０の時の受信アンテナ間隔に対する、式（１）における第１グレーティングローブ発生角度（式（６）でｎ＝１）、第１ナル発生角度（式（７）でｎ＝１）と式（５）における第１ナル発生角度（式（８）でｎ＝０）の関係を図５に示す。

Here, the first grating lobe generation angle in the equation (1) (n = 1 in the equation (6)) and the first null generation angle (n = 1 in the equation (7)) with respect to the receiving antenna spacing when β = 0 The relationship between the first null generation angle in equation (5) and n = 0 in equation (8) is shown in FIG.

It can be seen from FIG. 5 that, if the first grating lobe generated in equation (1) is appropriately selected for the receiving antenna spacing, nulls can be directed in the same direction to the grating lobe generation angle.
From the above, even when the main antenna 2 receives the receiving antenna spacing at which grating lobes occur, the grating lobe generation angle with the beam in the main beam direction of the main antenna 2 by changing the receiving antenna spacing and weighting coefficient of the sub antenna 3 It is possible to target null in the main beam direction by calculating the amplitude difference between the amplitude patterns of the main antenna 2 and the sub antenna 3 and judging with a predetermined threshold. Become.

Further, by permitting generation of grating lobes of the main antenna 2, the aperture length of the receiving antenna 1 in the main antenna 2 can be increased, and the beam width of the main antenna 2 becomes narrow. It can be improved.
Next, specific embodiments of the present invention will be described.

Embodiment 1
The radar apparatus according to the first embodiment of the present invention will be described below with reference to FIGS.
6 is a block diagram of a reception system showing a radar apparatus according to the first embodiment, FIG. 7 shows an amplitude pattern of a main antenna and a sub antenna (in-phase excitation) according to the first embodiment, and FIG. It is a figure which shows the amplitude pattern of a main antenna and a subantenna (center reverse phase excitation).
FIG. 6 shows an embodiment in which six receiving antennas 1 of the main antenna 2 and three receiving antennas 1 of the sub antenna 3 are arranged, and the RF receiver 4 and the signal processing unit 5 are connected to the receiving antenna 1 respectively. It is done.

The receiving antenna spacing d1 of the main antenna 2 and the receiving antenna spacing d2 of the subantenna 3 are respectively appropriate receiving antenna spacings under the conditions that the equations (7) and (6) and the formula (8) are satisfied. And the following relational expressions (9) and (10) hold.
When the secondary antenna 3 has the amplitude pattern of equation (1) (in-phase excitation): d1 = 3 d2 (9)
When the secondary antenna 3 has the amplitude pattern of equation (5) (center antiphase excitation): d1 = 6 d2 (10)
Assuming that the receiving antenna spacing d1 of the main antenna 2 is 1.5λ according to the equations (9) and (10), the receiving antenna spacing d2 of the subantenna 3 is 0.5λ if the receiving antenna spacing d2 is in-phase excitation. In the case of phase excitation, it is 0.25 λ. From this, it can be seen that the sub-antenna 3 with center-in-phase excitation can make the antenna aperture length smaller than in-phase excitation.

The amplitude patterns after DBF synthesis of the main antenna 2 and the sub antenna 3 at this time are shown in FIG. 7 and FIG. From the figure, it can be seen that the sub antenna 3 forms a null at the generation angle of the grating lobe of the main antenna 2.
Then, the signal processing unit 5 calculates the difference in amplitude between the FFT signals of the main antenna 2 and the sub antenna 3 and, if it exceeds the predetermined threshold α, the target does not measure in the main beam direction, and It can be judged as the result of an erroneous measurement. As the predetermined threshold value α of the amplitude difference at this time, for example, it is desirable to set to -22 dB which is the minimum side lobe level of the main antenna 2.

  Further, in the first embodiment, while the antenna aperture length of the main antenna 2 is 7.5λ, the beam of the radar apparatus in the case where the number of receiving antennas (six main antennas and three sub antennas) is the same and grating lobes are not permitted Since the antenna aperture length is 4λ when the receiving antenna spacing is 0.5λ, the beam width is about 0.5 times that of the conventional radar in FIG. 4 to FIG. As a result, the angle measurement accuracy is improved twice.

  As described above, according to the invention of the first embodiment, the main antennas 2 are arranged at intervals of a half wavelength or more of the used frequency, and the sub antenna 3 forms a beam in the same direction as the main beam of the main antenna 2. The reflected wave is received in an amplitude pattern in which the reception intensity is suppressed at the grating lobe generation angle of the main antenna 2, and the signal processing unit 5 which is a recognition means of the target detects the difference in amplitude between the reception signals of the main antenna 2 and the sub antenna 3. Since the calculation is made to determine the presence of a target based on a preset threshold, a radar apparatus and an object recognition method are obtained in which the erroneous side angle due to the grating lobe is properly eliminated to improve the angle measurement accuracy. Be

Also, at that time, the main antenna 2 forms an amplitude pattern by RF combining or DBF combining, and the sub antenna is an odd number of receiving antennas and the central receiving antenna is in opposite phase to other receiving antennas, or all receiving antennas are in phase. By forming an amplitude pattern by performing RF combining or DBF combining, a radar device capable of easily recognizing an object can be obtained simply by calculating the amplitude difference of the received signal.
Next, consider the case of performing beam shift by changing the phase term of the weighting factor when DBF combining the receiving antenna 1 is performed. In the case of the in-phase excitation, the sub antenna 3 in the case of the beam shift is optimum, and an example thereof will be described as a second embodiment with reference to the drawings.

Second Embodiment
Next, a radar apparatus according to a second embodiment of the present invention will be described based on FIG.
FIG. 9 is a diagram showing an amplitude pattern when beam shifting is performed by the main antenna 2 and the sub antenna 3 (in-phase excitation) of the radar device in the second embodiment.
As in the first embodiment, the main antenna 2 and the sub antenna 3 are radar apparatuses in which six columns of the main antenna 2 have a receiving antenna spacing of 1.5 λ and three sub antennas 3 have a receiving antenna spacing of 0.5 λ. An amplitude pattern when beam shift is performed to 10 degrees to 90 degrees is shown in FIG.
As shown in FIG. 9, it can be seen that the null of the sub antenna 3 can be directed to the grating lobe generated in the main antenna 2 up to the beam shift of +90 deg.

This is because the main antenna 2 can shift the detection angle area of the target by beam shifting while maintaining the angle measurement accuracy, and the sub antenna 3 can also be beam shifted similarly to the main antenna of the sub antenna 3 The fact that it can be directed to the grating log generation angle of 2 can eliminate the mismeasurement angle due to the grating lobe. However, if the beam shift amount is increased, high side lobes are also generated in the amplitude pattern of the sub antenna 3, so in practice the side lobe level of the sub antenna 3 does not exceed the side lobe level of the main antenna 2 It is desirable to

Third Embodiment
Next, a radar system according to a third embodiment of the present invention will be described with reference to FIG.
FIG. 10 is a block diagram of a reception system showing a radar system according to the third embodiment. When amplitude pattern formation of the main antenna 2 and the sub antenna 3 is performed by DBF combination, it is possible to share and use a part of the receiving antenna 1 by the main antenna 2 and the sub antenna 3.

  As shown in FIG. 10, the first receiving antenna 1 is shared by the main antenna 2 and the sub antenna 3, and the other sub antennas are used during a wide receiving antenna interval (interval between A 1 and A 2) of the main antenna 2. Three receiving antennas 1 (B1 to B3) are arrayed. By doing so, the total number of the receiving antennas 1 of the main antenna 2 and the sub antenna 3 can be reduced, and the area of the entire antenna aperture length can be reduced.

  As mentioned above, although the embodiment of this invention was described, this invention is not limited to the embodiment, It is possible to make various design changes, and within the scope of the invention, each embodiment Can be combined freely, and each embodiment can be appropriately modified or omitted.

1: Receive antenna, 2: Main antenna, 3: Secondary antenna, 4: RF receiver,
5: Signal processing unit

Claims (4)

In a radar device provided with a plurality of receiving antennas for receiving a reflected wave reflected by a target,
Among the plurality of receiving antennas, receiving antenna intervals are arranged at equal intervals d1 equal to or more than a half wavelength of a used frequency, and a main antenna that receives the reflected wave;
Among the plurality of receiving antennas, predetermined receiving antennas are arranged at equal intervals d2 , and a beam is formed in the same direction as the main beam of the main antenna, and the amplitude is obtained by suppressing the receiving strength at the grating lobe generating angle of the main antenna A secondary antenna that receives the reflected wave in a pattern;
The signal processing unit calculates an amplitude difference between reception signals of the main antenna and the sub antenna, and determines the presence of a target based on a preset threshold value.
The number of secondary antennas is three ,
The distance of the receiving antenna is formed by in-phase excitation of the amplitude pattern of the sub antenna as relation of d1 = 3d2 is established, or,
A radar apparatus characterized in that the amplitude pattern of the sub antenna is formed by central reverse phase excitation so that the distance between the receiving antennas is in the relationship of d1 = 6 d2 .   The radar apparatus according to claim 1, wherein the main antenna forms an amplitude pattern by RF combination or DBF combination.   The radar apparatus according to claim 1, wherein the main antenna and the sub antenna form an amplitude pattern using a common receiving antenna by DBF combination. Among the plurality of receiving antennas, a first step of receiving a reflected wave reflected on a target by a main antenna having a receiving antenna interval of equally spaced d1 and a half wavelength or more of a used frequency;
Wherein forming a main beam and the beam in the same direction of the main antenna, with an amplitude pattern of suppressing the reception intensity by the grating lobe occurrence angle generated by the reception of the main antenna, a predetermined receiving antenna in the sub antenna equidistant d2 A second step of receiving the reflected wave;
Calculating a difference in amplitude between the received waves in the first step and the second step, and recognizing a presence of an object based on a preset threshold value;
The number of secondary antennas is three ,
The distance of the receiving antenna is formed by in-phase excitation of the amplitude pattern of the sub antenna as relation of d1 = 3d2 is established, or,
A method of object recognition characterized in that the amplitude pattern of the sub antenna is formed by central reverse phase excitation so that the distance between the receiving antennas is in the relationship of d1 = 6 d2 .

Images