JP2001166029A - Dbf radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DBF radar device reduced is erroneous detection caused by secular change and temperature change. SOLUTION: A plurality of element antenna constituting an array antenna are divided into a plurality of groups, one amplifier amplifying a received signal on every element antenna is provided for each group in a receiving circuit part, and a plurality of element antenna belonging to own group are connected with an input terminal of each amplifier through a selector switch. The receiving circuit part is provided with a phase compensation value detection means and a phase compensation means. The phase compensation value detection means detects a difference in phase between a reference element antenna and the other element antenna concerning a digital received signal, estimated a difference in phase between the reference element antenna and the element antenna belonging to the other group using a difference in detected phases of the other element antenna belonging to the group including the reference element antenna among the differences in detected phases as a reference, and compares a difference in assumed phases every element antenna belonging to the other group with a difference in detected phases to determine a phase compensation value. The phase compensation means performs phase compensation of a digital receiving signal using a phase compensation value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar apparatus for performing signal processing by digital operation. More particularly, the present invention relates to a radar apparatus having an array antenna comprising a plurality of element antennas, and generating and scanning an antenna beam by digital operation processing. The present invention relates to a digital beam forming (DBF) radar apparatus for performing the above.

[0002]

2. Description of the Related Art Generally, in a DBF radar device, an RF amplifier, a mixer, a filter, and an A / D converter are connected to an element antenna constituting an array antenna, respectively, and an output from each A / D converter. The received digital reception signal is taken into a digital beam forming processor to perform digital beam forming processing.

[0003] Improvements have been made on such general DBF radar devices for the purpose of cost reduction.
The radar apparatus disclosed in Japanese Patent Application Laid-Open No. 11-160423 is an example of such an apparatus, and includes one expensive mixer such as a mixer or a low-noise amplifier (LNA) as a whole.
By using a changeover switch, it is possible to connect to any one of the element antennas.

[0004]

The number of switches for switching millimeter-wave signals is limited at a practical level. Therefore, if the number of element antennas is larger than the number that can be switched, it is necessary to configure the switches in multiple stages.

On the other hand, LNA is a noise figure (NF)
It is desirable to provide the antenna as close to the element antenna as possible in order to reduce the distance. Therefore, when the changeover switch has a multi-stage configuration, NF can be reduced by arranging a plurality of LNAs in the intermediate stage than by arranging the LNAs in the stage after the changeover switch.

However, since the LNA is an active element,
A phase delay or advance occurs due to a temperature change or an aging change, and the degree thereof is different depending on the LNA. for that reason,
A received signal phase error between element antennas occurs due to a phase delay or advance due to a temperature change or aging of the LNA.

[0007] This phase error has an adverse effect on the generation of the antenna beam in the DBF processing, and lowers the target detection accuracy.

[0008]

The DBF radar apparatus of the present invention has been made to solve such a problem.

A DBF radar apparatus according to the present invention comprises: an array antenna in which a plurality of element antennas including a reference element antenna are arranged; and a down-converted digital signal after amplifying a received signal for each element antenna received by each element antenna. And a receiving circuit unit for performing digital arithmetic processing on the digital received signal and generating and scanning an antenna beam of the array antenna to detect a target.

[0010] The plurality of element antennas are divided into a plurality of groups, and the receiving circuit section is provided with one amplifier for amplifying the reception signal for each element antenna for each group, and the input terminal of each amplifier is provided at the input terminal of each amplifier. A plurality of element antennas belonging to their own group are connected via a changeover switch.

The receiving circuit section has a phase correction value detecting means and a phase correcting means. The phase correction value detection means detects a phase difference between the reference element antenna and another element antenna in the digital reception signal, and detects a detection position of another element antenna belonging to the group including the reference element antenna among the detected phase differences. On the basis of the phase difference, the phase difference of the element antenna belonging to another group is estimated, and the phase correction value is obtained by comparing the estimated phase difference and the detected phase difference for each element antenna belonging to the other group, The phase correction means corrects the phase of the digital reception signal for each element antenna using the phase correction value.

A phase delay or advance occurs based on a change in temperature or aging of the amplifier, and a variable phase difference due to the delay or advance is superimposed on a phase difference between a received signal of the reference element antenna and a received signal of another element antenna. Is done. However, in the phase correction value detecting means, a phase correction value for canceling the fluctuation phase difference included in the detection phase difference of each element antenna is generated,
In the phase correction means, phase correction is performed on the digital reception signal for each element antenna using the phase correction value, so that the variation between the element antennas due to the temperature change and aging of the amplifier from the reception signal for each element antenna. The phase difference component is removed.

[0013]

FIG. 1 is a block diagram showing a DBF radar apparatus according to an embodiment of the present invention.

This DBF radar device has a continuous wave (CW)
-CW using a frequency-modulated (FM) transmission signal
It is also a radar device.

This radar device has n element antennas R
An array antenna 1 in which x1 to Rx (n) are arranged, and a receiving circuit that detects a target by performing various processes on received signals for each element antenna received by each of the element antennas Rx1 to Rx (n). A transmission circuit section for generating a transmission signal; and a transmission antenna for radiating the transmission signal.

The transmission circuit section 3 includes a voltage-controlled oscillator 31 having a center frequency f0 (for example, 76 GHZ), a buffer amplifier 32, and a distributor 33. The voltage-controlled oscillator 31 outputs a modulated wave (transmission signal) that has been subjected to triangular wave modulation with a modulation frequency width of ΔF by a control voltage output from a modulation control unit (not shown). The modulated wave is amplified by the buffer amplifier 32 and radiated from the transmission antenna 4 as an electromagnetic wave.

A part of the transmission signal is distributed by the distributor 33 to the RF amplifier 22 in the receiving circuit unit 2. RF
The signal amplified by the amplifier 22 is used as a local signal for reception detection.

The receiving array antenna 1 includes n element antennas Rx1 to Rx (n) and is divided into m groups G1 to Gm (m = n / 3) by three. The first element antenna Rx1 is particularly called a reference element antenna.

The receiving circuit unit 2 includes m front-end changeover switches SW1 to SW (m). Previous-stage changeover switch SW1
SW (m) each has one movable contact and three fixed contacts, and the movable contact can be connected to any of the fixed contacts based on a switching signal from the DBF processor 28.

The front-stage changeover switches SW1 to SW (m) are
It corresponds to each of the element antenna groups G1 to Gm, and in each front-stage changeover switch, three element antennas belonging to the same group are respectively connected to three fixed contacts.

Low-noise amplifiers LNA1 to LNA are connected to the movable contacts of the front-stage changeover switches SW1 to SW (m), respectively.
Each input terminal of (m) is connected.

A rear-stage changeover switch 21 having one movable contact and m fixed contacts is provided downstream of the low-noise amplifiers LNA1 to LNA (m).
The output terminals of A1 to LNA (m) are connected to fixed contacts of the rear-stage changeover switch 21 on a one-to-one basis.

The switching control of the rear-stage changeover switch 21 is also performed based on a switching signal from the DBF processor 28, similarly to the previous-stage changeover switch.
(M) and one of the element antennas Rx1 to Rx (n) are connected to the movable contact of the rear-stage switch 21 by the cooperative switching operation between the rear-stage switch 21 and the low-noise amplifier LNA.
1 to LNA (m).
This cooperative switching operation is performed at such a high speed that it is considered that the reception of the reflected radio waves by the respective element antennas has been performed substantially simultaneously. Are output continuously.

The movable contact of the rear switch 21 is connected to the second
The second low noise amplifier 23 is connected to an input terminal of the low noise amplifier 23, and a mixer 24, a baseband amplifier 25, a low-pass filter 26, an A / D converter 27
And a digital beam forming processor (DBF processor) 28 are connected in order.

The signals received by the element antennas Rx1 to Rx (n) are amplified by the low-noise amplifiers LNA1 to LNA (m) and the second low-noise amplifier 23, and mixed by the mixer 24 with the local signal from the RF amplifier 22. You. By this mixing processing, the received signal is down-converted, and a beat signal which is a difference signal between the transmitted signal and the received signal is generated.

The beat signal is input to an A / D converter 27 via a baseband amplifier 25 and a low-pass filter 26, and is converted into a digital beat signal (digital reception signal) at a predetermined timing.

The DBF processor 28 includes an A / D converter 2
7, a digital beat signal is input, an antenna beam is generated and scanned by digital calculation, and the distance and relative speed of the target are detected.

Here, the detection principle of the FM-CW radar device will be briefly described.

In the triangular wave modulation FM-CW system, the beat frequency when the relative velocity is zero is fr, the Doppler frequency based on the relative velocity is fd, the beat frequency in the section where the frequency increases (up section) is fb1, and the frequency decreases. Assuming that the beat frequency of the section (down section) is fb2, fb1 = fr-fd (1) fb2 = fr + fd (2) holds.

Therefore, if the beat frequencies fb1 and fb2 in the up and down sections of the modulation cycle are measured separately, fr and fd can be obtained from the following equations (3) and (4).

Fr = (fb1 + fb2) / 2 (3) fd = (fb2-fb1) / 2 (4) If fr and fd are obtained, the distance R and the relative velocity V of the target are calculated by the following (5). It can be obtained by equation (6).

R = (C / (4 · ΔF · fm)) · fr (5) V = (C / (2 · f0)) · fd (6) where C is the speed of light, and fm is FM modulation frequency.

By the way, the generation and scanning of the antenna beam by the DBF process are performed by each of the element antennas Rx1 to Rx
The phase difference of the received signal received in (n) is used.

As shown in FIG. 2, reflected radio waves 52 from a target (not shown) generate element antennas Rx1 to Rx.
Assuming that the light is incident at an angle θ with respect to the front direction 51 of (n), the equal phase plane of the reflected radio wave 52 reaching each of the element antennas Rx1 to Rx (n) is as indicated by a broken line indicated by reference numeral 53.

FIG. 3 is an enlarged view of a portion indicated by a broken-line circle in FIG. The propagation path length of the reflected radio wave arriving at the element antenna Rx2 with respect to the propagation path length of the reflected radio wave arriving at the reference element antenna Rx1 becomes longer by the distance 54. Therefore, the phase of the radio wave arriving at the element antenna Rx2 lags behind the phase of the radio wave arriving at the reference element antenna.

Assuming that the distance between the element antennas Rx1 and Rx2 is d, the distance 54 can be represented by dsin θ, and the phase delay amount is (dsin θ) / λ. Here, λ is the carrier wavelength of the transmission signal.

Other element antennas Rx3 to Rx (n)
Are arranged at an interval d in order following the element antenna Rx2, the phase delay amount of each of the element antennas Rx3 to Rx (n) with respect to the reference element antenna is (2 · dsin
θ) / λ, (3 · dsin θ) / λ,..., ((n−1)
dsin θ) / λ.

The phase of the radio wave received by each of the element antennas Rx1 to Rx (n) is replaced by a beat signal by the mixer 24, and is stored even if it is converted into a digital signal by the A / D converter 27.

Therefore, in the DBF processor 28, if the phase of the signals of the element antennas other than the reference element antenna Rx1 is advanced by the above-mentioned phase delay amount by digital calculation, the radio waves from the θ direction will have the same phase in all the element antennas. And the directivity is θ
You will be facing the direction. That is, the antenna beam of the array antenna 1 is directed in the θ direction. If the value of θ is continuously changed in a predetermined range, the antenna beam can be substantially scanned in the predetermined range.

If an antenna beam can be formed, the distance and the relative speed of the target in that direction are determined by the above-mentioned FM.
-It can be obtained by the detection principle of the CW radar device.

As described above, in order to accurately form and scan an antenna beam, the phase information of the reflected radio wave from the target received by each element antenna must be correctly reflected by the DBF.
It needs to be communicated to the processor 28.

However, low noise amplifiers LNA1 to LNA
Since (m) is an active element, it causes a phase delay or advance due to temperature change or aging. The degree of the phase delay or advance is determined by the low noise amplifiers LNA1 to LNA (m).
Therefore, a phase error occurs between the element antenna groups.

Although the second low-noise amplifier 23 also has a phase delay or advance due to a temperature change or an aging change, since it is single, it does not cause a phase error between element antennas.

In the present embodiment, a phase correction value for correcting the phase error is obtained, and the phase correction of the received signal for each element antenna is performed using the phase correction value.
Perform at step 8. That is, the DBF processor 28 includes a phase correction value detection unit and a phase correction unit.

FIG. 4 is a flowchart showing a calculation processing flow including a phase correction value detection process and a phase correction process in the DBF processor 28.

In step S1, a digital beat signal for each element antenna is fetched. Then step S
In step 2, a fast Fourier transform (FFT) process is performed on the captured digital beat signal.

Next, in step S3, it is determined whether or not an initial phase difference detection command has been issued. If it is determined that the initial phase difference detection command has been issued, the process proceeds to step S4, where the reference element is detected. Initial phase difference Δ2 to Δn between antenna Rx1 and other element antennas Rx2 to Rx (n)
Is detected.

The initial phase difference detection is normally performed by a switch operation or the like by an inspector at the time of shipping the radar apparatus, and the phase difference between the element antennas is obtained by using the reflected radio wave from the reference target. Achieved. This initial phase difference is held in the storage unit until a next instruction to detect the initial phase difference is issued, and is used as one of the phase correction values at the time of DBF synthesis.

More specifically, a standard reflector is installed in the direction of the azimuth angle of 0 ° several tens of meters in front of the array antenna 1 to operate the radar apparatus. At this time, if the standard reflectors are sufficiently separated, the phases of the reflected waves received by the element antennas can be considered to be the same. However, actually, a phase difference occurs due to a path difference for each channel of each element antenna or a manufacturing error of a circuit element in the middle of the path. This phase difference is the initial phase difference.

At the time of normal use by the user of the radar apparatus, a special switch operation for detecting the initial phase difference is not performed, so that the result in step S3 is negative, and the process proceeds to step S5. In step S5, a peak is searched for the power spectrum of the received signal of the reference element antenna.

Subsequently, in step S6, it is determined whether or not the detected peak is larger than a predetermined threshold. If the peak value is equal to or less than the threshold value, it is determined that no target exists, and the process returns to step S1.

The threshold here can be set as appropriate in accordance with the target. For example, when the radar device is an on-vehicle radar device, a threshold value is set for a minimum value of a power value that would be obtained if a reflected radio wave from a vehicle ahead in a predetermined range. If not, the subsequent DBF operation is avoided.

When an affirmative determination is made in step S6, the process proceeds to step S7, where the element antenna Rx2 relative to the reference element antenna Rx1 at the peak frequency is set.
To Rx (n) are detected.

Assume that the initial phase difference (detected and stored in step S5) of the element antennas Rx2 to Rx (n) with respect to the reference element antenna Rx1 is Δ2 to Δn, and low noise caused by a temperature change or a temporal change is obtained. Amplifier LNA
If the phase change at 1 to LNA (m) is Δ′1 to Δ′m, the detected measured phase difference φ2 to φn is φ2ｎd / λ · sinθ + Δ2φ3 ≒ 2 · d / λ · sinθ + Δ3 φ4 ≒ 3 · d / λ · sin θ + Δ4 + (Δ′2 to Δ′1) φ5 ≒ 4 · d / λ · sinθ + Δ5 + (Δ′2 to Δ′1) φ6 ≒ 5 · d / λ · sin θ + Δ6 + (Δ'2 to Δ'1) φ7 ≒ 6 · d / λ · sinθ + Δ7 + (Δ'3 to Δ'1) ・ ・ ・ ・ ・ ・ ・ ・ φn φ (n− 1) d / λ · sin θ + Δ (n) + (Δ′m to Δ′1) (first formula group)

The first term on the right side in each equation of the first equation group is the phase difference based on the propagation path difference described with reference to FIGS. In addition, the phase delay and advance of the passive circuit actually occur due to temperature change and aging. However, since the influence is very small, they are omitted, and instead, ≒
Is used.

In step S8, the initial phase differences Δ2 to Δn obtained in step S5 are subtracted from the actually measured phase differences φ2 to φn obtained in step S7, and the actually measured phase differences φ′2 to φ′n with initial phase correction are obtained. . The measured phase differences φ′2 to φ′n after the initial phase correction are as follows: φ′2 = φ2−Δ2 ≒ d / λ · sinθ φ′3 = φ3−Δ3 ≒ 2 · d / λ · sinθ φ′4 = φ4 −Δ4 ≒ 3 · d / λ · sin θ + (Δ′2 to Δ′1) φ′5 = φ5−Δ5 ≒ 4 · d / λ · sinθ + (Δ′2 to Δ′1) φ′6 = φ6 −Δ6 ≒ 5 · d / λ · sin θ + (Δ′2 to Δ′1) φ′7 = φ7−Δ7 ≒ 6 · d / λ · sinθ + (Δ′3 to Δ′1) ・ ・ ・ ・ ・Φ′n = φn−Δn ≒ (n−1) · d / λ · sinθ + (Δ′m to Δ′1) (second formula group).

Next, in step S9, the actually measured phase differences φ′2 and φ′3 of the first group whose initial phase has been corrected.
Is then averaged using the following equation (7) to obtain an actually measured propagation path phase difference Φ (corresponding to d / λ · sin θ in the theoretical equation) based on the propagation path difference between adjacent element antennas.

Φ = (φ′2 + φ′3 / 2) / 2 (7) Next, in step S10, the element antenna R with respect to the reference element antenna Rx1 is calculated using the actually measured propagation path phase difference Φ.
The estimated phase differences {φ2} to {φn} of x2 to Rx (n) are obtained.

｛Φ2｝ = Φ ｛φ3｝ = 2ΦΦ ｛φ4｝ = 3 ・ Φ ｛5｝ = 4 ・ Φ ｛6｝ = 5 ・ Φ ｛7｝ = 6 ・ Φ φn｝ = (n−1) Φ (third formula group) Further, in step S11, the fourth element antenna R
x4 and thereafter, the measured phase difference φ ′ after the initial phase correction
Error σ between 4-φ′n and estimated phase difference {φ4}-{φn}
4 to? N are obtained. Since Φ is nothing but an actually measured value of d / λ · sin θ, the errors σ4 to σn
Is (Fourth formula group).

In step S12, this error σ4
If any of .sigma.n is larger than the predetermined threshold, the process proceeds to step S13, and the value obtained by adding the error obtained in step S11 to the initial phase difference is used as the phase correction value. That is, the phase correction values C1 to Cn for each element antenna are (Fifth formula group).

When the result in step S12 is NO, the process moves to step S14, and only the initial phase difference is used as the phase correction value. That is, the phase correction values C1 to Cn are (The sixth formula group).

In step S15, phase correction is performed using the phase correction value obtained in step S13 or 14, and a DBF operation is performed on the corrected digital beat signal.

In this embodiment, the element antennas Rx1 to Rx1
xn using all digital beat signals corresponding to xn
BF processing is performed. That is, an array antenna which is a receiving antenna is constituted by all the element antennas Rx1 to Rxn, but the element antennas Rx1 to Rx3 of the first group are used as comparison element antennas exclusively used for phase correction, and the element antennas of the second and subsequent groups are used. Antennas Rx4 to R
xn may constitute a receiving array antenna.

[0064]

As described above, according to the DBF radar apparatus of the present invention, the phase correction value for canceling the phase lag or advance due to the temperature change or the aging change of the low noise amplifier is detected for each element antenna. Since the phase correction unit detects the phase and performs phase correction using the respective phase correction values on the digital beat signal corresponding to each element antenna in the phase correction unit, the antenna beam can be accurately synthesized. Therefore, erroneous detection of the target due to a change over time or a change in temperature of the low-noise amplifier can be suppressed, and high detection accuracy can be maintained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a DBF radar apparatus according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating a reception state of a reflected radio wave from a target in each of the element antennas Rx1 to Rxn.

FIG. 3 is an enlarged view of a part of FIG. 2;

FIG. 4 is a flowchart showing the operation of the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Array antenna, 2 ... Receiving circuit part, 3 ... Transmitting circuit part, 4 ... Transmitting antenna, Rx1-Rxn ... Element antenna, SW1-SW (m) ... Previous stage switch, LNA1
LNA (m): low-noise amplifier, 21: rear-stage changeover switch, 23: second low-noise amplifier, 27: A / D converter, 2
8 ... DBF processor.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J021 AA05 AA06 CA06 DB02 DB03 DB04 EA04 FA14 FA15 FA16 FA17 FA20 FA26 FA29 FA31 FA32 GA02 HA05 HA10 5J070 AB17 AB24 AC02 AC06 AD09 AD10 AE01 AF03 AH35 AH40 AK22 BA01

Claims (2)

[Claims] An array antenna in which a plurality of element antennas including a reference element antenna are arranged, and a reception signal for each element antenna received by each of the element antennas is amplified, down-converted and converted into a digital signal. A receiving circuit unit that performs digital arithmetic processing on a digital received signal and generates and scans an antenna beam of the array antenna to detect a target, and the plurality of element antennas are divided into a plurality of groups. The receiving circuit unit is provided with one amplifier for amplifying the received signal for each element antenna for each group, and an input terminal of each amplifier includes a plurality of element antennas belonging to its own group. Digital beam forming (DBF) connected via a changeover switch
In the radar device, the receiving circuit unit includes a phase correction value detection unit and a phase correction unit, and the phase correction value detection unit determines a position of the digital reception signal between the reference element antenna and the other element antenna. Detecting a phase difference; estimating a phase difference of an element antenna belonging to another group based on a detected phase difference of another element antenna belonging to the group including the reference element antenna among the detected phase differences; A phase correction value is obtained by comparing the estimated phase difference and the detected phase difference for each element antenna belonging to the group, and the phase correction unit uses the phase correction value to correct the phase of the digital reception signal. A DBF radar device for performing the following. 2. An array antenna in which a plurality of element antennas are arranged, and a receiving signal for each element antenna received by each of the element antennas is amplified, down-converted and converted into a digital signal. A receiving circuit unit for performing digital arithmetic processing and generating and scanning an antenna beam of the array antenna to detect a target, wherein the plurality of element antennas are divided into a plurality of groups, The circuit unit is provided with one amplifier for amplifying the reception signal for each element antenna for each group, and a plurality of element antennas belonging to the own group are provided at the input terminal of each amplifier via a changeover switch. Digital beam forming (DBF) connected
In the radar device, the array antenna includes a plurality of comparison element antennas including a reference element antenna, the reception circuit unit includes a phase correction value detection unit and a phase correction unit, and the phase correction value detection unit includes: Detecting the phase difference between the digital reception signal of the reference element antenna and the digital reception signal of the comparison element antenna and the element reception antenna other than the reference element antenna, based on the detection phase difference of the comparison element antenna, Estimating a detected phase difference of an element antenna, and calculating a phase correction value by comparing the estimated phase difference and the detected phase difference for each of the element antennas, wherein the phase correction unit performs the phase correction in accordance with the phase correction value. A DBF radar device for correcting the phase of a digital reception signal.