JP2802671B2 - Millimeter wave radar transceiver - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an FM radar device used as a device for configuring a collision warning device to be mounted on a vehicle.

[Conventional technology]

A short-range radar sensor for a vehicle equipped with a single FM-CW radar module is disclosed in Japanese Patent Application Laid-Open Nos.
-86085 and the like. Japanese Patent Application Laid-Open No. 56-18774, which is related to the applicant's earlier application, discloses a plurality of FMs.
An automotive radar device in which a CW radar module is mounted on the front and rear sides of a vehicle is disclosed.

[Problems to be solved by the invention]

As an essential problem with the FM radar system, the frequency of the beat signal decreases as the reflector approaches, and 1 / f noise and F
There is a problem that the disturbance of the M-AM conversion noise becomes large and the detection becomes impossible.

Also, with respect to recent on-vehicle radar devices, not only the distance to an obstacle that generated a reflected wave, but also an azimuth resolution that indicates in which direction the obstacle is viewed from the vehicle has been required. I have. In order to increase the azimuth resolution, the beam pattern radiated from the antenna is made sharper than that of the conventional device, and a plurality of beams are provided so that a certain range such as not only in front of the vehicle but also obliquely forward can be monitored. Must be radiated adjacent to each other.

As the number of radiation beams increases, FM
There is a problem in that the number of components for configuring the radar module increases and the entire apparatus becomes expensive.

Further, how to prevent mutual interference between beams, which is expected when a plurality of beams are radiated while being adjacent to each other, is also a major problem.

[Means for solving the problem]

The FM radar apparatus of the present invention divides an FM signal having a frequency that changes with time into a transmission signal and a local FM signal, radiates the transmission FM signal to the outside, receives a reflection signal of the transmission FM signal, and mixes the reflection signal with the local FM signal. And generating a beat signal, and detecting, from the frequency of the beat signal, the distance of the reflector that caused the reflection signal, the transmission FM
Frequency changing means for making the center frequencies of the signal and the local FM signal different from each other.

[Action]

In the FM radar device of the present invention, transmission is performed by changing the order of frequency multiplication and the local oscillation frequency during frequency conversion.
Since the frequency of the FM signal is shifted from the frequency of the local FM signal, the beat frequency is raised to a high frequency that is less susceptible to interference such as 1 / f noise, and the detection accuracy is improved.

 Hereinafter, the present invention will be described in more detail with reference to Examples.

〔Example〕

FIG. 1 is a block diagram showing a configuration of a module portion of an FM radar apparatus according to one embodiment of the present invention, wherein 10 is an FM signal generating circuit, 11 is an amplifier, 20 is an FM signal distribution circuit, and 30a to 30n are plural. And 41, a signal distributor, 42a to 42n, antennas (feeder horns) commonly used for transmission and reception, 50, a beat signal selection circuit, 61, a mixer, and 62, a local oscillator.

Each of the transmission / reception units 30a to 30n includes a signal branch circuit 31a to 3
1n, frequency n multiplier 32a-32n, frequency (n-1) multiplier
33a-33n, band-pass filter (BPF) 34a-34n, 35a-35
n, circulators 36a to 36n, mixers 37a to 37n, and amplifiers 38a to 38n.

The FM signal oscillating circuit 10 generates a continuous wave FM signal (FM-CW; continuous wave signal) in a millimeter wave band having a portion whose frequency changes linearly with time, such as a sawtooth wave and a triangular wave.
Such an FM signal generation circuit 10 is configured by a combination of a solid-state oscillation element such as a Gunn diode that generates a high frequency signal in a microwave band and a frequency modulation element such as a varactor diode, and converts the FM signal in the microwave band. Occur.

The FM signal in the microwave band generated by the FM signal generation circuit 10 is amplified by the amplifier 11, and then is supplied to the FM signal distribution circuit 20.
Thus, the signals are sequentially distributed to the transmission / reception units 30a to 30n at different timings. The FM signal distribution circuit 20 is composed of an array of high-speed and low-loss switching elements such as PIN diodes, and each switching element has a timing signal TI supplied from a timing signal generation circuit (not shown).
By selectively conducting according to M, the FM signal in the microwave band is distributed to each of the transmission / reception units 30a to 30n at the subsequent stage.

The microwave band FM signals sequentially distributed to the transmission / reception units 30a to 30n are supplied to frequency n multipliers (n is a natural number of 2 or more) 32a to 32n via signal branch circuits 31a to 31n. Converted to waveband FM signals. Millimeter-wave FM
The signal is passed through bandpass filters 34a-34n and circulator 36a.
Through 36n are supplied to a transmission / reception antenna composed of a signal distributor 41 and feeder horns 42a to 42n, and radiated to the outside. That is, as illustrated in the timing chart of FIG. 4, the transmission FM signal is transmitted to the outside as shown by the waveforms TXa to TXn from the respective feeder horns 42a to 42n that are commonly used for transmission and reception.

A part of the millimeter-wave band FM signal transmitted to the outside at different timings from each of the transmission / reception common feeder horns 42a to 42n is reflected by an external reflector, becomes a reflection FM signal, and serves as a transmission / reception common feeder horn. 42a to 42n. This reception FM signal is transmitted by the corresponding transmission FM signal as exemplified by waveforms RXa to RXn in the timing chart of FIG.
Are delayed from the signals RXa to RXn by time τa, τb.

Some of the FM signals distributed to each of the transmission / reception units 30a to 30n through the FM signal distribution circuit 20 are divided into signal branch circuits 31a to 31n.
Is supplied to each of the frequency (n-1) frequency multipliers 33a to 33n. The local FM signal in the millimeter wave band whose frequency has been multiplied by (n-1) passes through each of the band-pass filters 35a to 35n, and has waveforms Loa to Lon in the timing chart of FIG.
As shown in the example, the local signal is synchronized with the transmission timing TXa to TXn of the FM signal at the corresponding mixer 37.
It is supplied to the other input terminals of a to 37n. As a result, of the transmitting and receiving units 30a to 30n, the corresponding transmitting and receiving antenna is reflected.
A beat signal in the microwave band is generated only from the one that receives the FM signal and supplies the local signal to the corresponding mixer.

The beat signals in the microwave band generated by the mixers 37a to 37n in the transmission / reception units 30a to 30n are supplied to the beat signal selection circuit 50 after being amplified by the amplifiers 38a to 38n. The beat signal selection circuit 50 is configured substantially the same as the FM signal distribution circuit 20, selects one of the beat signals in accordance with the same timing signal TIM as that supplied to the FM signal distribution circuit 20, and selects the beat signal of the subsequent mixer 61. Supply to one input terminal.

The other input terminal of the mixer 61 has a local oscillator 62
, And a low frequency beat signal is output from the output terminal of the mixer 61. That is, the oscillation frequency of the local oscillator 62 is set to a value slightly lower than the frequency of the FM signal generated by the FM signal generation circuit 10, and the frequency of the beat signal of the generated difference frequency is as low as several MHz or less. The frequency is set. The low-frequency beat signal is supplied to a signal processing circuit (not shown) composed of a digital processor or the like, and the distance and direction of the reflector that has generated the reflected wave are detected.

That is, the signal processing circuit detects the frequency (beat frequency) of the beat signal output from each transmission / reception unit,
The time required for propagation of the radio wave from the detected beat frequency to the reflector is calculated, and the distance to the reflector that generated the reflected wave is calculated from the required time for propagation. Also, this signal processing circuit detects the ratio of the level of each beat signal, and from the level ratio of the detected beat signal, the direction of the reflector viewed from the vehicle equipped with this FM radar transmission (the direction of the reflector) Angle).

For example, as illustrated in FIG. 5, let the beam patterns of the FM signals radiated from two adjacent antennas be Ba and Bb, respectively. In the illustrated example, the level of the reflected wave of the beam Bb is higher than the level of the reflected wave of the beam Ba because the reflector exists closer to the beam Bb than the beam Ba. The signal processing circuit reflects the reception level in the azimuth angle detection result by calculating a weighted average value or the like based on the reception level of the reflected wave with respect to the azimuth angle of each beam.

FIG. 3 shows a case where the multiplication order n of the frequency is set to 4 in the transmission / reception unit 30a of FIG.
And an example of the frequency and amplitude in the frequency multipliers 32a and 33a at the subsequent stage. A microwave band FM signal with a frequency of 15 GHz and an amplitude of 25.4 dBm is divided into two at a ratio of 8 dB. And then transmitted to the outside. The small-amplitude side of the two-divided microwave band FM signal has a frequency of 3
The signal is multiplied to be a local signal in the millimeter wave band having a frequency of 45 GHz and an amplitude of 7 dbm.

FIG. 2 is a block diagram showing a configuration of a module portion of an FM radar apparatus according to another embodiment of the present invention, in which 10 is an FM signal generating circuit, 12 is a signal branching circuit, 13, 14 are mixers, 15, 16
Is a local oscillator, 17 and 18 are amplifiers, 20 is an FM signal distribution circuit, 21 is a local FM signal distribution circuit, 30a to 30n are a plurality of transmission / reception units, 41 is a signal distributor, and 42a to 42n are transmission / reception shared antennas (feeders). Horn), 50 is a beat signal selection circuit, 61
Is a mixer, and 62 is a local oscillator.

Each of the transmission / reception units 30a to 30n includes a signal branch circuit 31a to 3
1n, frequency n multipliers 32a to 32n, band-pass filters 34a to 34
n, circulators 36a to 36n, mixers 37a to 37n, and amplifiers 38a to 38n.

The FM signal oscillation circuit 10 generates an FM signal in a microwave band. The microwave band FM signal generated by the FM signal generating circuit 10 is divided into two by a signal branching circuit 12, one of which is supplied to a mixer 13 and mixed with a local signal output from a local oscillator 15 so that the frequency is reduced. It becomes an FM signal in the microwave band shifted upward. The other of the two divided FM signals in the signal branch circuit 12 is supplied to the mixer 14 and mixed with the local signal output from the local oscillator 16 to become a local FM signal in the microwave band whose frequency is shifted upward. .

The FM signal output from the mixer 13 is amplified by an amplifier 17 and then transmitted and received by a transmitting / receiving unit 30 by an FM signal distribution circuit 20.
a to 30n are sequentially distributed at different timings. After being amplified by the amplifier 18, the local FM signal output from the mixer 14 is sequentially distributed by the FM signal distribution circuit 21 to the transmission / reception units 30 a to 30 n at different timings. The switching elements in the FM signal distribution circuits 20 and 21 are selectively turned on in accordance with a timing signal TIM supplied from a timing signal generation circuit (not shown), so that the FM signal in the microwave band and the local FM signal can It is distributed to each of the transmitting / receiving units 30a to 30n.

The microwave band FM signals sequentially distributed to the transmission / reception units 30a to 30n in the arrangement order are converted into millimeter wave band FM signals in frequency n multipliers 32a to 32n, and the band-pass filter 34
a-34n and circulators 36a-36n, respectively, are supplied to a transmission / reception antenna composed of a signal distributor 41 and feeder horns 42a-42n, and radiated to the outside from each.

The FM signal reflected by the external reflector is received by each of the transmitting and receiving antennas, separated from the above-described transmission system by each of the circulators 36a to 36n in the transmitting and receiving units 30a to 30n, and separated by the mixers 37a to 37n. It is supplied to one input terminal of each.

The local FM signal distributed to each of the transmission / reception units 30a to 30n through the FM signal distribution circuit 21 is a frequency n multiplier 32a.
In each of .about.32n, a local FM signal in the millimeter wave band whose frequency is multiplied by n is supplied to the other input terminal of the corresponding mixer 37a-37n through each of the band-pass filters 34a-34n. As a result, among the transmission / reception units 30a to 30n, the corresponding transmission / reception shared antenna receives the reflected FM signal,
In addition, a beat signal in the microwave band is generated only from a local signal supplied to the corresponding mixer.

The beat signals in the microwave band generated by the mixers 37a to 37n in the transmission / reception units 30a to 30n are supplied to the beat signal selection circuit 50 after being amplified by the amplifiers 38a to 38n. The beat signal selection circuit 50 selects one of the beat signals in accordance with the same timing signal TIM as that supplied to the FM signal distribution circuit 20 or the local FM signal distribution circuit 21 and supplies the selected signal to one input terminal of a mixer 61 at the subsequent stage. Supply.

The other input terminal of the mixer 61 has a local oscillator 62
The low-frequency local signal of several MHz or less generated by the mixer 61 is supplied, and a low-frequency beat signal is output from the output terminal of the mixer 61. The low-frequency beat signal is supplied to a signal processing circuit (not shown) composed of a digital processor or the like, and the distance and direction of the reflector that has generated the reflected wave are detected.

〔The invention's effect〕

As described above in detail, in the FM radar apparatus of the present invention, the order of frequency multiplication performed in each transmitting / receiving section is different as in the configuration of FIG. 1 or the same order of frequency multiplication as in the configuration of FIG. Since the center frequency of the transmission FM signal and the center frequency of the local FM signal are shifted by shifting the center frequency of the FM signal branched in the previous stage, the beat frequency is 1 / compared to the conventional case as illustrated in FIG. f Raised to a high frequency that is less susceptible to disturbances such as noise, improving detection accuracy.

Also, the FM radar apparatus of the present invention has a configuration in which an FM signal is generated by a single FM signal generating circuit 1 and distributed to a plurality of transmitting / receiving sections.
Compared to a device having an individual FM signal generation circuit for each transmission / reception unit as disclosed in JP-A-18774, there is an advantage that the number of components is significantly reduced and the manufacturing cost is significantly reduced.

Further, in the FM radar device of the present invention, all the FM signals transmitted from the plurality of transmission / reception units are a single FM signal generation circuit 1.
Therefore, even if interference occurs between beams radiated adjacent to each other, individual transmission / reception units are individually provided as in the FM radar apparatus disclosed in the above-mentioned JP-A-56-18774. As a result, the problem that a false reflector is detected due to the variation in the frequency of each beam can be effectively solved.

Further, in the FM radar device of the present invention, the FM signal of the low frequency microwave band is
a to 30n, then the microwave band
Since the frequency of the FM signal is multiplied to convert it into a high-frequency millimeter-wave band FM signal, there is an advantage that the passage loss of the switching element in the FM signal unit circuit 20 can be reduced.

Furthermore, since the FM radar apparatus according to one embodiment of the present invention is configured to detect the azimuth of the reflector from the ratio of the amplitudes of the beat signals generated in the adjacent transmitting and receiving units, the effect of realizing a high azimuth resolution can be obtained. Is played.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an FM radar apparatus according to one embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a module portion of the FM radar apparatus according to another embodiment of the present invention.
FIG. 4 is a conceptual diagram showing an example of the amplitude and frequency of the FM signal at the input / output terminals of the signal branch circuit 31a and the frequency multipliers 32a and 33a in the transmission / reception section 30a of FIG. 2, and FIG. FIG. 5 is a timing chart for explaining the operation of the radar device, FIG. 5 is a conceptual diagram for explaining the principle of azimuth detection of the reflector by the FM radar device of the present invention, and FIG. 6 is for explaining the effect of the present invention. FIG. 1,10 FM signal generation circuit 2,20,21 FM signal distribution circuit 3a-3n transmission / reception units 4a-4n antennas for transmission and reception 5a-5n signal branching circuits 6a-6n Circulators 7a to 7n Mixer 30a to 30n Transmitter / receiver 32a to 32n Frequency multiplier 33a to 33n Frequency multiplier 36a to 36n Circulator 37a to 37n Mixer 42a to 42n Feeder horn 50 …… Beat signal selection circuit 61 …… Mixer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01S 7/00-7/42 G01S 13/00-13/95

Claims (4)

(57) [Claims] 1. An FM signal generating circuit for generating an FM signal having a frequency that changes with time, a signal branching circuit for dividing the FM signal into two, and frequency multiplying each of the two divided FM signals by different multiplication orders. A first and second frequency multiplying circuit, a transmitting unit for transmitting the FM signal multiplied by the first frequency multiplying circuit to the outside, and a reflection wave of the transmitted FM signal received from outside to A transmission / reception unit including a reception unit that generates a beat signal by mixing with the FM signal frequency-multiplied by the second frequency multiplication circuit; and the reflected wave is generated from the beat signal generated by each of the transmission / reception units. An FM radar device comprising: a signal processing unit that detects information related to the position of an object. 2. The transmission / reception unit according to claim 1, wherein the transmission / reception unit includes a plurality of transmission / reception channels, and each transmission / reception channel is shared by a plurality of transmission / reception channels whose beam radiation directions are slightly shifted in an arrangement order while causing adjacent beams to overlap. An FM radar device comprising an antenna. 3. An FM signal generating circuit for generating an FM signal having a frequency that changes with time, and an FM signal generated by the FM signal generating circuit is used as first and second FM signals.
A frequency conversion circuit for converting to an FM signal of a second different frequency, a transmitting unit for transmitting the FM signal of the first frequency to the outside,
A transmitting / receiving unit comprising: a receiving unit that receives a reflected wave of the FM signal transmitted from the outside from the outside and mixes the reflected wave with the FM signal of the second frequency to generate a beat signal; A signal processing unit for detecting information on the position of the object that caused the reflected wave from the beat signal obtained. 4. The transmission / reception unit according to claim 3, wherein the transmission / reception unit comprises a plurality of transmission / reception channels, and each transmission / reception channel is shared by a plurality of transmission / reception channels whose beam radiation directions are slightly shifted in the arrangement order while causing adjacent beams to overlap. An FM radar device comprising an antenna.