JP2964947B2 - Time-division radar system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time-division radar system used as an in-vehicle millimeter-wave radar system.

[0002]

2. Description of the Related Art Among in-vehicle radar systems mounted on vehicles such as passenger cars and used for warning devices for preventing rear-end collisions and collisions, those which use radio waves include a pulse radar for transmitting and receiving pulses, and an FM wave. Of the FM radar for transmitting and receiving The present inventor considers that an in-vehicle radar system needs to detect even a short distance of about several tens of cm, and therefore, compared to a pulse radar type, FM
I think the form of radar is suitable. In this FM radar system, an FM wave whose frequency changes with time, preferably linearly changes with time, is generated.
The generated FM wave is divided equally by the power divider, one is radiated from the antenna as a transmission wave, and the other is supplied as a local oscillation signal to the local oscillation signal input terminal of the mixing circuit. The reflected wave generated by the target is received by the antenna, and the received reflected wave is supplied to a reception signal input terminal of the mixing circuit, and is mixed with the local oscillation signal to generate a beat signal. By detecting the frequency of the beat signal, the time difference between the local oscillation signal and the reception signal supplied to each input terminal of the mixing circuit, that is, the time required for the FM wave to propagate between the antenna and the target Therefore, the distance between the antenna and the object is detected.

In such an on-vehicle FM radar system, considering that the longest distance measurement range to a target such as a preceding vehicle or an oncoming vehicle is limited to a relatively short distance of about several hundred meters,
In order to prevent the radiated radio wave from propagating farther than necessary or interfering with the existing communication equipment in the microwave band, the inventor has proposed a radio wave in the millimeter wave band having a large propagation attenuation of about 60 GHz. I think that is suitable.

[0004] In the FM radar system, a plurality of transmission / reception systems are installed in order to detect not only the distance to the target but also the azimuth of the target as viewed from the vehicle. In other words, a plurality of antennas that emit beams having substantially the same radiation pattern are arranged at an appropriate angle so that a part of each radiation beam overlaps, and the same level of FM wave is radiated from each antenna. The azimuth of the target is detected by detecting the ratio of the level of the reflected wave received by the antenna. In order to avoid mutual interference between transmission / reception systems, a frequency division method in which FM waves having different frequencies are assigned to each other and a time division method in which FM waves having the same frequency are assigned at different timings are considered. The present inventor considers that the latter time division method is preferable in terms of effective use of frequency.

[0005] Further, for each transmission / reception system, a transmission / reception separation type in which a transmission-only antenna and a reception-only antenna are separately installed, and the transmission system and the reception system are completely separated from each other,
It is possible to consider a transmission / reception type in which only one transmission / reception antenna is provided, and a circulator is provided between the antenna and the transmission / reception system. The present inventor has proposed that, for a radar system that requires a plurality of antennas to detect the direction of a target, the number of antennas is reduced to reduce the size and cost of the entire system. I think that is suitable. A millimeter wave band time-division FM radar system using the above-mentioned dual-use antenna is disclosed in Japanese Patent Application No. 2-303 of the applicant's earlier application.
No. 810 and Japanese Patent Application No. 3-42979.

[0006]

SUMMARY OF THE INVENTION In the above-mentioned FM radar system, in order to detect the azimuth of a target over a wide angle range with high accuracy, a large number of antennas and transmission / reception circuits are required, and the scale and cost of the system are reduced. There is a problem of increasing.

That is, as exemplified in FIG. 4, beams Ba, Bb, Bc, and Bd having the same radiation pattern (directivity).
Four antennas A, B, C, and D that radiate
It is assumed that an FM radar system is installed with the angles slightly shifted so as to partially overlap radiation beams between adjacent ones. Assuming that a target having a size illustrated by a circle is present at a position illustrated by a circle, the target is radiated from the shared antenna B and then reflected by the target and received by the shared B. The level Lb of the received reflected wave is maximized, and the level La of the received reflected wave radiated from the shared antenna A and received by the shared antenna A is the next largest. Further, the level L of the received reflected wave radiated from the shared antenna C and received by the antenna C is
c and the level Ld of the received reflected wave radiated from the shared antenna D and received by the antenna D are both zero. In this case, the azimuth of the target is detected from the ratio of La and Lb.

In order to improve the azimuth detection accuracy, it is desirable that as many as possible non-zero received reflected wave levels exist. This can be achieved by reducing the angle between the beams (δθ). That is, in the case of FIG. 4, when the angle between the beams is slightly reduced, the level Lc of the received reflected wave is reduced.
Is not zero. In this case, the azimuth angle (θa, θb, θc) of each beam based on an appropriate azimuth angle is weighted by the corresponding received reflected wave level La, Lb, Lc, and the angle Θ is averaged. = (La · θa + Lb · θb + Lc · θ
c) / (La + Lb + Lc) can be detected with higher accuracy as the azimuth of the target. However, if the angle (δθ) between the beams is narrowed to increase the detection accuracy, there is a problem that the angle range detectable by the four beams Ba to Bd also becomes narrow. Therefore, in order to increase both the detection accuracy and the detectable angle range, it is necessary to install a larger number of antennas, which causes a problem that the scale and cost of the entire system are increased.

[0009]

According to the time-division radar system of the present invention, beams having substantially the same radiation pattern are radiated while partially and partially overlapping, and a reflected wave of the beam is received. A plurality of beam transmitting and receiving means, an FM signal generating section for generating an FM signal of a frequency varying and of a substantially constant level, and transmitting the FM signal generated by the FM signal generating section to each of the beam transmitting and receiving means at different timings. A transmitting unit that distributes and radiates the beam, and the level of the received reflected wave received by each of the beam transmitting / receiving units is distinguishable with respect to a pair of beam transmitting / receiving units related to the emission and reception of the beam, that is, which A receiving unit that radiates from the antenna and generates a state in which it is possible to discriminate the level of the received reflected wave received by which antenna, and this receiving unit is generated. It includes a bell detection signal, and a direction detecting means for detecting the orientation of the object that caused the reflected wave based on the arrangement and the beam transmitting and receiving means.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a time-division radar system according to the present invention, a substantially constant level FM signal is output from a plurality of antennas arranged so as to radiate beams having substantially the same radiation pattern while partially overlapping each other. Emitted at different times. For example, as shown in FIG.
To D having substantially the same radiation pattern and substantially the same level are emitted from. The receiving unit radiates a reception level detection signal for detecting the level of the reflected reflected wave radiated from the object after being radiated from each of the antennas A to D and received by each of the antennas A to D. It is generated in a state where it is possible to discriminate whether the received data is received.

[0011] As an example in the case of FIG.
The reception level detection signal for detecting the level Laa of the received reflected wave radiated from the antenna A and received by the antenna A, and the level Lab of the received reflected wave radiated from the antenna A and received by the adjacent antenna B are It generates a reception level detection signal for detection, a reception level detection signal for detecting the level Lbb of a reception reflected wave radiated from the antenna B and received by the antenna B, and the like. here,
Referring to FIG. 4, the level Lab of the received reflected wave radiated from the antenna A and received by the adjacent antenna B is the same virtual beam as the overlapping portion (shown by hatching) between the beams Ba and Bb. Bab is radiated from a virtual antenna disposed between antennas A and B, and the level of the reflected wave received by the target becomes equal to the level of the received reflected wave when it is assumed that the reflected wave is received by the virtual antenna.

As described above, by receiving the radio wave radiated from the antenna A by the antenna B, the same effect as when one virtual antenna is added between the adjacent antennas A and B is exerted. Similarly, by receiving a radio wave radiated from the antenna B by the antenna C, a beam Bbc is radiated between the adjacent antennas B and C, and one virtual antenna for receiving the reflected wave is added. The effect of the above is achieved, and one virtual antenna that radiates the beam Bcd between the adjacent antennas C and D by receiving the radio wave radiated from the antenna C with the antenna D and receives the reflected wave is added. The same effect as described above is exerted. As described above, according to the time division radar system of the present invention, it is possible to realize the same detection accuracy and detection angle range as the case where seven antennas are installed by the actually installed four antennas.

[0013]

FIG. 1 is a block diagram showing a configuration of a time division type FM radar system according to an embodiment of the present invention.
10d is four antennas, 20 is an FM wave generation circuit, 30
Is a transmission unit, 40 is a reception unit, 50 is a detection / control unit, 60a
６０60d is a circulator. Four antennas 10
a to 10d are arranged so as to emit beams having substantially the same radiation pattern while partially overlapping each other.
The four antennas 10a to 10d include, for example, a common parabolic reflector and four primary radiators arranged near the focal point of the reflector at different angles to face the reflector. It consists of an offset, defocus, parabolic, multi-beam antenna, etc. The FM wave generating circuit 20 includes a voltage controlled oscillator (VCO) 21 for generating a quasi-millimeter wave radio wave, a sweep circuit 22 for supplying a triangular modulation voltage to the voltage controlled oscillator, and a power dividing circuit 23. The transmission unit 30 includes a transmission switching circuit 31 and tripler circuits 32a to 32d. The receiving unit 40 includes a local switching circuit 41, tripler circuits 42a to 42d, and a mixing circuit 43.
a to 43d and a beat selector 44. The detection / control circuit 50 includes a CPU 51 and an amplification circuit 5
2, an A / D conversion circuit 53, a fast Fourier transform circuit (FFT) 54, and a timing control circuit 55.

The FM wave generating circuit 20 has a frequency F of 20 GHz as shown in the uppermost stage of the timing chart of FIG.
Generates a quasi-millimeter wave band FM wave of a substantially constant level which linearly increases and decreases with a predetermined cycle before and after the power dividing circuit 23.
, And one is supplied to the transmission unit 30 and the other is supplied to the reception unit 40. The transmission unit 30 switches the quasi-millimeter wave band FM wave supplied from the FM wave generation circuit 20 at the preceding stage by the transmission switching circuit 31 and then triples the frequency multiplier circuits 32 a to 32 a.
The frequency is converted into FM waves TXa to TXa in the millimeter wave band of about 60 GHz by multiplying by 3 at 32d.
The antennas 10a to 10d are supplied to the antennas 10a to 10d at different timings through 0a to 60d, that is, supplied to the antennas 10a to 10b in order so as not to overlap with each other, and radiated from each of them, as illustrated by the waveforms TXa to TXa in FIG.

F radiated from antennas 10a to 10d
Some of the M waves TXa to TXa are reflected by the target and received by the antennas 10a to 10d. Antenna 1
Received reflected waves RXa to RXd received at 0a to 10d
Are separated from the transmitting unit by the circulators 60a to 60d, and supplied to one input terminal of the mixing circuits 43a to 43d installed in the receiving unit 40 corresponding to each antenna. To the other input terminals of these mixing circuits 43a to 43d, the FM wave supplied from the FM wave generation circuit 20 at the preceding stage is switched at a predetermined timing by the local oscillation switching circuit 41, and then the tripler circuits 42a to 42d. 42
The signal d is converted into the local wave LOa to LOd in the millimeter wave band and supplied. That is, the local oscillation waves are represented by waveforms LOa to LOa in FIG.
As illustrated by Od, each of the FM waves distributed to two adjacent antennas has a time overlapping portion, and each antenna has a timing that does not cause a time overlapping portion. The signals are sequentially distributed to the corresponding mixing circuits 43a to 43d.

As a result, a beat signal is generated in each mixing circuit over a period in which each of the FM waves distributed to two adjacent antennas and the local oscillation wave overlap. For convenience of explanation, assuming that the target is at a close distance,
The appearance timings of the reception reflected waves RXa to RXd and the FM waves TXa to TXd are substantially equal. In this case, in the waveform diagram of FIG. 2, the FM reflected waves RXa
~ RXd. Therefore, in the waveform diagram of FIG. 2, the FM waves TXa to TXd and the local oscillation waves LOa to LOd
Are mixed with each other within a period in which
The beat signals BTa to BTd are output from each of d.

The first half Na of the beat signal BTa is within the period during which the local oscillation LOa is supplied to the mixing circuit 43a even though no FM wave is emitted from any of the four antennas A to D. This is the output of the mixing circuit 43a. Therefore, the first half Na is nothing but a signal in which the beat signal generated by the external radio wave received by the antenna A and the internal noise generated in the mixing circuit 42a are combined.
On the other hand, the latter half part BTaa of the beat signal BTa
Is the output of the mixing circuit 43a during the period when the FM wave TXa is radiated from the antenna A and the local oscillation wave LOa is supplied to the mixing circuit 43a. Therefore, this second half B
Taa is nothing but a beat signal radiated by the antenna A and generated by a reflected wave received by the antenna A.

The first half BTab of the beat signal BTb is
This is an output of the mixing circuit 43a during a period in which the FM wave TXa is radiated from the antenna A and the local oscillation wave LOb is supplied to the mixing circuit 43b. Therefore, this beat signal BT
The first half BTab of b is nothing but a beat signal radiated by the antenna A and generated by the received reflected wave received by the adjacent antenna B. This beat signal emits a virtual beam Bab indicated by hatching in FIG. 4 from a virtual antenna installed between antennas A and B,
This is nothing but a beat signal generated from a received reflected wave when it is supposed to be reflected by the target and received by this virtual antenna. Further, the latter half B of the beat signal BTb
Tbb is the output of the mixing circuit 43b during the period in which the FM wave TXb is radiated from the antenna B and the local oscillation wave LOb is supplied to the mixing circuit 43b, which is radiated by the antenna B and radiated by the antenna B. It is nothing but a beat signal caused by the received reflected wave.

Similarly, the first half BTbc of the beat signal BTc is radiated by the antenna B and
Is a beat signal generated by the received reflected wave received by the antenna C. The first half BTcd of the beat signal BTd is the antenna C
And a beat signal generated by a reflected reflected wave received by the adjacent antenna D. Also, the beat signal BT
The latter part BTcc of c is a beat signal radiated by the antenna C and generated by the reflected wave received by the antenna C, and the latter part BTdd of the beat signal BTd is radiated by the antenna D and received by the antenna D This is a beat signal generated by the reflected wave.

The beat signals BTa to BTd sequentially output from the mixing circuits 43a to 43d are
5 are sequentially selected by a beam selector 44 controlled to be opened and closed by 5, and supplied to a detection / control circuit 50. The beat signals BTa to BTd supplied to the detection / control circuit 50 are amplified by an amplifier circuit 52, converted to digital signals by an A / D conversion circuit 53, converted to a frequency spectrum by a fast Fourier conversion circuit 54, and converted to a CPU 51. Supplied to
The CPU 51 includes seven types of beat signals BTaa, BTab,
BTbb ... BTdd frequencies faa, fab, fb
b... fdd is subjected to appropriate statistical processing (for example, a simple average value is calculated) to determine the beat frequency, and based on this, the propagation delay time of the FM wave is calculated,
Calculate the distance to the target.

The CPU 51 has seven types of beat signals B
Taa, BTab, BTbb... BTdd level L
From among aa, Lab, Lbb... Ldd, only those larger than a predetermined threshold set for noise removal are selected, and the average value of the azimuth of the corresponding antenna is calculated while weighting at each selected level. To detect the direction to the target. For example, three types of beat signals BTaa, BTa
When the levels Laa, Lab, and Lbb of b and BTbb exceed the threshold, the azimuth Θ of the target is calculated as Θ = (Laa · θa + Lab · θab + Lcc · θc) / (Laa + Lab + Lbb). Here, θab is the azimuth of the virtual antenna AB installed between the antennas A and B, and is set as θab = (θa + θb) / 2.

As described above, the first half Na of the beat signal BTa is nothing but a signal obtained by combining the beat signal generated by the external radio wave received by the antenna A and the internal noise generated in the mixing circuit 42a. . In this case, if necessary, the frequency spectrum of this noise
In the detection of the level and frequency of the beat signal of the received reflected wave, a method of eliminating external noise and internal noise of the mixing circuit by subtracting the noise component being stored from the beat signal when detecting the level and frequency of the received reflected wave can be adopted. . This is because the external noise is mixed at the same frequency and the same level in all the beat signals generated with a time lag, and the internal noise of the other three mixing circuits 43b, 43c and 43d is actually measured. This is effective when it is equal to the internal noise of the mixing circuit 43a.

FIG. 3 is a timing chart in the case where the noise detection / elimination function is focused on and distributed to all the mixing circuits. For convenience of illustration, the beat signal is omitted, but the hatched period Na in the drawing is a period during which the local oscillation LOa is supplied to the mixing circuit 43a, and therefore, the beat signal generated during this period is The external noise received by the antenna A and the internal noise of the mixing circuit 43a are synthesized. The beat signal generated in the period Nb is a signal in which the external noise received by the antenna B and the internal noise of the mixing circuit 43b are combined. Similarly, the beat signals generated in the periods Nc and Nd are equal to the external noise received by the antennas C and D and the mixing circuit 43, respectively.
c43d and the internal noise. CPU
The 51 can detect and store the noise component within each period, and can remove the noise by subtracting it from the beat signal generated by the corresponding mixing circuit.

The configuration in which the antennas are installed so that the beams of the two adjacent antennas overlap each other has been described above. However, it is also possible to adopt a configuration in which the deviation angle is further narrowed so that beams of three or more adjacent antennas overlap each other. Also, the configuration in which four antennas are arranged has been illustrated, but the number of antennas is two,
An appropriate value such as three or five can be set.

Although the configuration in which only the FM wave is radiated from each antenna has been illustrated, the Doppler shift amount of the received reflected wave is detected by inserting a period for radiating a radio wave of a constant frequency at an appropriate timing. A function of detecting the relative speed with respect to the target based on the information can also be added.

Although the configuration of the FM radar has been exemplified, the part of the present invention that detects the direction of a target can be applied to a pulse radar.

As described above in detail, according to the time division radar system of the present invention, the radio wave radiated from one of the plurality of antennas is received by the other antenna, so that the radio wave is typically transmitted to the adjacent antenna. The same function as when one virtual antenna is added between each antenna to be performed is realized. As a result, a high detection accuracy and a wide detection angle range can be realized with a limited number of antennas, and a reduction in system size and cost can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a time-division FM radar system according to an embodiment of the present invention.

FIG. 2 is a timing chart for explaining an example of the operation of the time division type FM radar system of FIG. 1;

FIG. 3 is a timing chart for explaining another example of the operation of the time division type FM radar system of FIG. 1;

FIG. 4 is a conceptual diagram for explaining a solution problem and an operation principle of the present invention.

[Explanation of symbols]

 10a to 10d Antenna 20 FM signal generation circuit 30 Transmitter 31 Transmission switching circuit 40 Receiver 41 Reception switching circuit 43a to 43d Mixing circuit (mixer) 50 Detection / control unit

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-259874 (JP, A) JP-A-57-84377 (JP, A) JP-A-56-1443967 (JP, A) 150036 (JP, A) Japanese Patent Application Laid-Open No. Sho 50-132953 (JP, A) Japanese Patent Application Laid-Open No. Sho 50-134466 (JP, A)

Claims (5)

(57) [Claims] 1. A beam having substantially the same radiation pattern is radiated while being spatially and partially overlapped, and radiated by itself.
A plurality of beam transmitting / receiving means arranged to receive a reflected beam of a beam and a beam emitted by another beam; an FM signal generating unit for generating an FM signal having a frequency that changes and having a substantially constant level; and an FM signal generating unit F in which
A transmitting unit for distributing and radiating the M signal to each of the beam transmitting / receiving units at different timings; and transmitting and receiving a level detection signal for detecting the level of the received reflected wave received by each of the beam transmitting / receiving units. A receiving unit that is generated in a discriminable state with respect to a pair of beam transmitting and receiving means related to each of the above, and the reflected wave is generated based on a level detection signal generated by the receiving unit and an arrangement of the beam transmitting and receiving means And a bearing detecting means for detecting the bearing of the object. 2. A radio wave generator for generating a substantially wave of constant level, different receiving and transmitting unit which emits a radio wave which the radio wave generating unit has occurred, the reflected wave reflected by the object is emitted from the transmitting unit a receiving unit including a plurality of receiving channels with azimuth, averaging the azimuth angle of the reception channel while weighting the level of the signal received by each receiving channel of the receiving section
Radar system characterized by comprising a direction detection unit for detecting the orientation of the object by. 3. The radar system according to claim 2, wherein the plurality of reception channels of the reception unit are selected in a time-division manner and output the levels of the respective reception signals. 4. The radio wave generation unit according to claim 2, further comprising: an FM wave generation circuit that generates an FM wave whose frequency changes at a predetermined cycle as the radio wave, wherein the reception unit radiates from the transmission unit. A mixing circuit that mixes the received FM wave with the reflected wave received by each of the receiving units; and a distance detecting unit that detects a distance to the object based on a frequency of a beat signal generated by the receiving unit. A time-division radar system characterized by comprising: (5) Spatial distribution of almost identical radiation patterns
And radiated while partially overlapping
To receive the reflected wave of the beam and the beam emitted by others
A plurality of beam transmitting and receiving means arranged in the Transmission signal generator that generates a transmission signal of almost constant level
When, The transmission signal generated by the transmission signal generation unit is used for each beam.
Transmission to transmit and receive at different timing to the transmitting and receiving means
Department and The level of the received reflected wave received by each beam transmitting / receiving means
The level detection signal for detecting the
Of the beam transmitting and receiving means associated with
And a receiving unit that is generated in a discriminable state, The level detection signal generated by the receiving unit and each of the
The reflected wave is generated based on the arrangement of the
Azimuth detecting means for detecting the azimuth of the object.
Time-sharing radar system.