JP2750781B2 - FM radar - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an FM radar used for preventing rear-end collision of a vehicle.

(Prior art) An on-vehicle radar mounted on a vehicle and used to prevent rear-end collisions needs to be able to measure close distances of about several tens of centimeters.
FM radar is more suitable than pulse radar. In addition, since the longest measurement distance is only a few hundred meters, radiated radio waves must be propagated farther than necessary, and interference with existing equipment using microwave bands should be avoided.
Millimeter-wave radio waves with large attenuation on the order of GHz are used.

As shown in FIG. 8, the FM radar is configured such that an FM signal output from an FM signal generation circuit 101 is divided into two by a division circuit 102, and one of the two is radiated from an antenna 104 through a circulator 103. . The reflected wave received by the antenna 104 is supplied to one input terminal of a mixer 105 through a circulator 103. The other input terminal of the mixer 105 is supplied with the other of the two divided FM signals, and generates a beat with the reflected wave. This beat frequency is detected by the detection unit 106, and is converted into a distance to the reflection object.

The amplitude of the FM signal is maintained at a substantially constant value, and the frequency is changed in a triangular wave or sawtooth shape at a constant period. Since this FM signal is generated continuously or at least intermittently for a period sufficiently long as compared with the propagation delay time of the radio wave with the object, the FM-signal is used to make the distinction from the pulse radar clearer. Also called CW radar.

The frequency F1 of the FM signal changes in proportion to time, as shown in the following equation, when focusing on a period shorter than the period of the triangular wave or the sawtooth wave.

F1 = Fo + (δF / T) t (1) where Fo and δF are constants having a frequency dimension, T is a constant having a time dimension, and t is a variable having a time dimension.

The FM signal radiated from the antenna 104 of FIG.
If it is assumed that the reflected wave is received by the antenna 104 after elapse of the time, the frequency F2 of the reflected wave is as follows.

F2 = Fo + (δF / T) (t−τ) (2) If the difference in the delay time of the signal in the FM radar is negligible compared to the delay time τ of the reflected wave,
The frequency F3 of the beat output from the mixer 105 is as follows: F3 = F1-F2 = (τ / T) δF (3) However, the Doppler shift due to the relative speed difference between the vehicle equipped with the FM radar and the other vehicle that generated the reflected wave is ignored because it is sufficiently smaller than the shift due to the propagation delay time.

Therefore, assuming that the propagation speed of the radio wave is c, the distance D to the object that generated the reflected wave is calculated as follows: D = c · τ / 2 = c · T · F3 / (2δF) (4) Is done.

Referring to equation (3), the beat frequency decreases as the distance to the object decreases and the delay time τ decreases. As the beat frequency decreases, the disturbance of 1 / f noise during mixing increases, making it difficult to detect this beat frequency.

For example, if the distance D to the object is 1 m, τ is about 7 ns. In this case, if T is 100 μs and δF is 400 MHz, the beat frequency F3 is a low frequency of about 28 KHz.

In order to increase the beat frequency, it is necessary to increase the modulation speed 1 / T of the FM modulation or to increase the modulation frequency width δF, but this is limited.

In order to solve the above-mentioned problem, the applicant of the present application has disclosed a configuration as shown in FIG.
Disclosed FM radar.

According to this FM radar, an FM signal in a microwave band or a quasi-millimeter wave band is generated by the FM signal generation circuit 201,
This FM signal is divided into two by a dividing circuit 202, one of which is converted to a millimeter wave band by a frequency multiplying circuit 203, and radiated from an antenna 206 through a band-pass filtering circuit 204 and a circulator 205. The reflected wave received by the antenna 206 is supplied to one input terminal of the mixer 209 through the circulator 205. The other input terminal of the mixer 209 is connected to the other of the two divided FM signals by a frequency multiplier.
The signal converted into a millimeter wave band by the filter 207 is supplied through a band-pass filter circuit 208, and a beat with the reflected wave is generated. By shifting the beat frequency from several GHz to a high frequency side of several tens of GHz by making the multiplication orders of the frequency multiplication circuits 203 and 207 different by about 1, interference of 1 / f noise can be effectively avoided.

As a method of shifting the beat frequency to the higher frequency side,
A configuration as shown in FIG. 11 is also conceivable.

That is, the FM signal in the microwave band or the quasi-millimeter wave band is generated by the FM signal
, And one of them is converted into a millimeter wave band by the up-converter 303, and then radiated from the antenna 306 through the band-pass filter circuit 304 and the circulator 305. The reflected wave received by the antenna 306 is supplied to one input terminal of the mixer 309 through the circulator 305. The other input terminal of the mixer 309, the other of the two divided FM signals, which is converted into a millimeter wave band by the up-converter 307, is supplied through a band-pass filter circuit 308, and the beat with the reflected wave is supplied to the other input terminal. Generated. By shifting the beat frequency from several GHz to the high frequency side of several tens of GHz by making the frequencies of the local oscillators of the up-converters 303 and 307 different, interference of 1 / f noise can be effectively avoided.

(Problem to be Solved by the Invention) In the configuration shown in FIG. 10 in which the beat frequency is shifted to the higher frequency side by changing the multiplication order, a multiplication circuit of a different order and a band-pass circuit having different characteristics are required. However, there is a problem that the type and the number of parts increase and the cost increases.

Also, in the configuration shown in FIG. 11 in which the beat frequency is shifted to a higher frequency side by changing the local oscillation frequency of the upconverter, a local oscillator having a frequency different from that of the mixer is required, and the type and the number of parts are reduced. There is a problem that the cost increases. Further, in this configuration, there is also a problem that the measurement accuracy is reduced because the local oscillation frequency independently varies depending on the ambient temperature or the like.

(Means for Solving the Problems) The FM radar of the present invention shifts the beat frequency to the high frequency side by inserting a delay circuit for giving a delay to the side of the divided FM signal emitted from the antenna. /
f While avoiding noise interference, frequency-multiplying or frequency-converting the delayed FM signal and radiating it from the antenna reduces the frequency of the FM signal passing through the delay circuit, It is configured to reduce loss.

(Operation) The operation of the present invention will be described in detail with the following examples.

(Embodiment) FIG. 1 is a block diagram showing a configuration of an FM radar according to an embodiment of the present invention, wherein 1 is an FM signal generation circuit, 2 is a division circuit, 3 is a delay circuit, 4 is a circulator, and 5 is An antenna, 6 is a mixer, and 7 is a detection circuit.

The FM signal generating circuit 1 generates an FM signal in a microwave band or a quasi-millimeter wave band by a voltage controlled oscillator (VCO) configured by combining an FET and a variable capacitance diode, and frequency-multiplies the signal to a millimeter wave band. Or VCO by gun diode
Is directly operated in the millimeter wave band. FM
The signal is divided into two by a dividing circuit 2 including a directional coupler of an FM signal in the millimeter wave band output from the signal oscillation circuit 1, and one of them is radiated from the antenna 5 through the delay circuit 3 and the circulator 4. . The reflected wave received by the antenna 5 passes through the circulator 4 in the opposite direction and is supplied to one input terminal of the mixer 6. The other input terminal of the mixer 6 is supplied with the other of the two divided FM signals, and generates a beat with the reflected wave. This beat frequency is detected by the detection circuit 7 and is converted into a distance to the reflecting object.

Directly supplied from the dividing circuit 2 to the input terminal of the mixer 6
Assuming that the frequency of the FM signal is given by the above equation (1), the frequency F2 'of the reflected wave passing through the circulator 4 and supplied to the mixer 6 is given by the following equation.

F2 ′ = Fo + (δF / T) (t−τd−τ) (5) where τd is the delay time of the FM signal by the delay circuit 3,
τ is a propagation delay time from when the FM signal radiated from the antenna 5 is reflected by the object and received by the antenna 5.

 The frequency F3 'of the beat output from the mixer 6 is as follows: F3' = F1-F2 '= [(τd + τ) / T] δF (6)

Since the beat frequency F3 when the delay circuit 3 is not inserted is given by the equation (3), the shift amount ΔF of the beat frequency F3 ′ to the high frequency side due to the insertion of the delay circuit 3 is ΔF = F3′−F3 = (Τd / T) δF (7)

 The distance D to the object is calculated by the detection unit 7 as D = c · T (F3′−ΔF) / (2δF) (8).

When T is set to 100 μs and δF is set to 400 MHz, if a delay circuit gives a delay time of about 70 ns, the beat frequency can be shifted to a higher side by about 300 KHz. Such a delay circuit can be realized by a microstrip type meander circuit using a dielectric substrate having a high dielectric constant.

As described above, with the insertion of the delay circuit 3, ΔF in the equation (7)
Only the beat frequency is shifted to the higher frequency side, and 1 / f noise interference is effectively avoided.

FIG. 2 is a block diagram showing a configuration of an FM radar according to another embodiment of the present invention. In this figure, components denoted by the same reference numerals as those in FIG. 1 are the same as those described with reference to FIG.

In this embodiment, the delay circuit 3 is inserted not between the dividing circuit 3 and the circulator 4 but between the circulator 3 and the mixer 6, and the reflected wave is delayed by τd. The shift amount of the beat frequency to the higher frequency side and the distance D to the object are given by equations (7) and (8), respectively.

FIG. 3 is a block diagram showing a configuration of an FM radar according to still another embodiment of the present invention. In this figure, components denoted by the same reference numerals as those in FIG. 1 are the same as those described with reference to FIG.

In this embodiment, a delay circuit 3 'is inserted between the circulator and the antenna 5. in this case,
The FM signal radiated from the antenna 5 is converted into τd /
While being delayed by two, the reflected wave received by the antenna 5 is further delayed by τd / 2 when passing through the delay circuit 3 ′, and is delayed by τd in the round trip and supplied to the mixer 6. Therefore, the shift amount of the beat frequency to the high frequency side and the distance D to the object are given by the equations (7) and (8), respectively.

FIG. 4 is a block diagram showing a configuration of an FM radar according to another embodiment of the present invention. Reference numeral 11 denotes an FM that generates a quasi-millimeter wave FM signal.
A signal generating circuit, 12 is a dividing circuit, 13 is a delay circuit, 14 and 19 are up-converters, 15 and 20 are band-pass filtering circuits, 16 is a circulator, 17 is an antenna, 18 is a mixer, and 21 is a detection circuit.

In this embodiment, after the division and delay of the FM signal are performed in the microwave band or the quasi-millimeter wave band, the up converter
It is converted to the millimeter wave band by 14 and 19. One of the FM signals converted to the millimeter wave band is radiated from the antenna 17 through the band-pass filter circuit 15 and the circulator 16, and the reflected wave received by the antenna 17 passes through the circulator 16 to one input terminal of the mixer 18. Supplied. The other FM signal converted into the millimeter wave band by the up-converter 19 is supplied to the other input terminal of the mixer 18 through the band-pass filter circuit 20, and the beat with the reflected wave is output to the detection circuit 21.

Also in the FM radar of this embodiment, the insertion of the delay circuit 13 shifts the beat frequency to the higher frequency side by the value given by the equation (7), and reduces 1 / f noise. In this example,
What is necessary is just to implement | achieve a delay circuit by low frequency of a microwave band or a quasi-millimeter wave band. 1 to 3 in which this delay circuit is realized by a three-dimensional circuit in the millimeter wave band, there is an advantage that the delay circuit can be realized by a MIC circuit such as a microstrip, and the device can be formed small, highly accurate, and inexpensively. .

FIG. 5 is a block diagram showing a configuration of an FM radar according to still another embodiment of the present invention. Reference numeral 31 denotes an FM signal generating circuit that generates a quasi-millimeter wave FM signal, 32 denotes a dividing circuit, 33 denotes a delay circuit, 34
And 37 are a tripler circuit, 35 is a circulator, 36 is an antenna, 38 is a mixer, and 39 is a detection circuit.

Also in this embodiment, after the division and the delay of the FM signal are performed in the quasi-millimeter wave band, they are converted into the millimeter wave band by the tripler circuits 34 and 37. One FM signal converted to the millimeter wave band is radiated from the antenna 36 through the circulator 35,
The reflected wave received by the antenna 36 is applied to the circulator 35
Is supplied to one input terminal of the mixer 38. The other FM signal converted to the millimeter wave band by the tripler circuit 37 is supplied to the other input terminal of the mixer 38, and the beat with the reflected wave is output to the detection circuit 39.

Also in the FM radar of this embodiment, the beat frequency is shifted to the high frequency side by the amount given by the equation (7) by inserting the delay circuit 13, and the 1 / f noise is reduced. However, in this FM radar, δF in the equations (1) to (8) becomes 3δF as the frequency is multiplied by the tripler circuits 34 and 37. For this reason, there is an advantage that a frequency shift to the same high frequency side can be realized with a delay amount of 1/3 as compared with the apparatus of FIG.

FIG. 6 is a block diagram showing a configuration of an FM radar according to another embodiment of the present invention.

In the FM radar of this embodiment, four FM radars 30A, 30B, 30C, and 30D having the same configuration as the embodiment of FIG. 5 are installed in parallel with the FM signal generation circuit 31 and the detection circuit 39 in common. FM
The signal generation circuit 31 and the input terminals of the division circuits of each system were connected via a switch 41, and the output terminals of the mixers of each system and the common detection circuit 39 were connected via a switch 44. It has a configuration.

The FM signal generated by the common FM signal generation circuit 31 is sequentially and repeatedly supplied to each system via a switch 41 switched according to a periodic switching control signal supplied from a switching control circuit. Beats output from the mixers of each system are supplied to a common detection circuit 39 via a switch 44 that is switched in synchronization with the switching operation of the switch 41. In parallel with the switching operation of the switches 41 and 44, the quasi-millimeter wave band
The oscillation frequency of the FM signal generation circuit 31 composed of a VCO is periodically changed according to the sweep signal generated by the sweep signal generation circuit 43.

Typically, the switching cycle of switches 41 and 44 is 100 μs
The sweep waveform output from the sweep circuit 43 is a triangular wave having the same cycle as the switching cycle. 4 antennas
36a, 36b, 36c and 36d are typically composed of a common secondary radiator and four primary radiators opposed to the primary radiator at different angles, which are sequentially and repetitively added to the primary radiator. As the FM signal is supplied, spatial beam scanning is performed in a time-division manner.

Beam A radiated from each of antennas 36a and 36b
The beam B is a pencil beam having a sharp directivity as shown in FIG. 8, and the center axes of the beams are set to be shifted from each other by a certain angle. Beam A,
Systems 30A and 30B depending on the angle of deviation between the center axis of B and the target
And the level of the reflected wave received, and hence the level of the generated beat, will be different. The detecting unit 39 detects the angle to the target based on the beat level deviation. As an example, an azimuth angle is detected by a pair of antennas 36a and 36b, and an elevation angle is detected by a pair of antennas 36c and 36d. Further, the distance to the target is detected in each system. Thus, according to the embodiment of FIG. 6, the distance to the target and the angle are detected.

FIG. 7 is a block diagram showing a configuration of an FM radar according to still another embodiment of the present invention.

In the FM radar of this embodiment, four FM radars having the same configuration as the embodiment of FIG. 5 are installed in parallel with the FM signal generation circuit 31, the division circuit 32, the delay circuit 33, and the detection circuit 39 in common. Delay circuit 33 and tripler circuits 34a, 34b of each system,
34c and 34d are connected via a switch 51, and one output terminal of the common dividing circuit 32 and the tripler circuits 37a and 37
7b, 37c, and 37d are connected via the switch 52, and between the mixers 38a, 38b, 38c, 38d of each system and the common detection circuit 39 are connected via the switch 55, By switching the three switches 51, 52, 55 synchronously in accordance with the switching control signal output from the switching control circuit 53, the switches shown in FIG.
Like FM radar, it has a configuration to detect the distance and angle to the target. This FM radar has an advantage that the number of components can be reduced as compared with the FM radar of FIG. 6 by sharing the dividing circuit and the delay circuit.

6 and 7, the switches 41, 51,
By replacing 52 with a division circuit, it is also possible to adopt a configuration in which a beam is continuously emitted from each antenna or a local signal is continuously supplied to each mixer.

(Effects of the Invention) As described in detail above, the FM radar of the present invention includes a delay circuit for providing a predetermined delay time in the path of an FM signal or a reflected wave from a division circuit to a beat generation mixer. Since the beat frequency is shifted to the high frequency side by a predetermined amount by insertion, an effect that short distance measurement can be realized while reducing disturbance of 1 / f noise is achieved.

[Brief description of the drawings]

1 to 7 are block diagrams showing the configuration of an FM radar according to each embodiment of the present invention. FIG. 8 explains the principle of detecting the angle to a target in the embodiments of FIGS. 6 and 7. 9 and 10 are block diagrams showing the configuration of a conventional FM radar, and FIG. 11 is a block diagram showing the configuration of an FM radar which can be considered as an alternative to the FM radar of FIG. . 1,11,31 …… FM signal generation circuit, 2,12,32 …… Division circuit, 3,
3 ′, 13,33 …… Delay circuit, 4,16,35 …… Circulator,
5,17,36 …… antenna, 6,18,38 …… mixer, 7,21,39…
... Detection circuits, 41,44,51,52,55 ... Switches, 42,53 ...
Switching control circuit, 43, 54 ... sweep circuit.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-86084 (JP, A) JP-A-64-86085 (JP, A) JP-A-56-18774 (JP, A)

Claims (7)

(57) [Claims] An FM signal generating circuit for generating an FM signal whose frequency changes with time; a dividing circuit for dividing the generated FM signal to obtain first and second FM signals; A first multiplier for increasing the frequency of the delayed first FM signal by a predetermined multiple, an antenna for emitting the frequency-multiplied FM signal and receiving a reflected wave thereof, the second A second multiplier circuit for increasing the frequency of the FM signal by the predetermined multiple, a mixer circuit for mixing the output of the second multiplier circuit and the reflected wave received by the antenna to generate a beat signal of both, and An FM radar comprising: a detection circuit that detects a frequency of a beat signal and converts the frequency into a distance to a reflector that generates the reflected wave. 2. A common part including an FM signal generating circuit for generating an FM signal whose frequency changes with time, and a detecting circuit for detecting the frequency of a beat signal and converting the frequency to a distance to a reflector which has generated a reflected wave; A plurality of individual parts connected to this common part in a time-division manner via a switch, and each of the plurality of individual parts divides an FM signal supplied in a time-division manner via the switch. 1st and 2nd FM
A dividing circuit for obtaining a signal, a delay circuit for delaying the first FM signal by a predetermined time, a first multiplier circuit for increasing the frequency of the delayed first FM signal by a predetermined multiple, and radiating the frequency-multiplied FM signal An antenna for receiving the reflected wave, a second multiplying circuit for increasing the frequency of the second FM signal by the predetermined multiple, and mixing the output of the second multiplying circuit and the reflected wave received by the antenna. An FM radar comprising a mixing circuit for generating both beat signals. 3. An FM signal generating circuit for generating an FM signal whose frequency changes with time, a dividing circuit for dividing the generated FM signal to obtain first and second FM signals, and a first FM signal Circuit, and a detection circuit for detecting the frequency of the beat signal and converting it to the distance to the reflector that generated the reflected wave. A plurality of transmission circuits connected in a time-division manner, and a plurality of reception circuits connected to the division circuit of the common portion in a time-division manner via a second switch. Comprises a first multiplying circuit for increasing the frequency of the first FM signal supplied in a time-division manner via the first switch by a predetermined multiple, and an antenna for radiating the frequency-multiplied FM signal The plurality of receiving circuits This includes a second multiplier circuit for increasing the frequency of the second FM signal supplied in a time-division manner via the second switch to the predetermined multiple, an antenna for receiving the reflected wave, and the second An FM radar, comprising: a mixing circuit that mixes an output of a frequency multiplier and the reflected wave received by the antenna to generate a beat signal of both. 4. An FM signal generating circuit for generating an FM signal whose frequency changes with time; a dividing circuit for dividing the generated FM signal to obtain first and second FM signals; A first frequency conversion circuit that raises the frequency of the delayed first FM signal to a predetermined value, an antenna that emits the FM signal of the increased frequency and receives a reflected wave thereof, A second frequency conversion circuit for increasing the frequency of the second FM signal to the predetermined value, generating an beat signal by mixing the output of the second frequency conversion circuit and the reflected wave received by the antenna; An FM radar comprising: a mixing circuit that detects the frequency of the beat signal; and a detection circuit that converts the frequency of the beat signal into a distance to a reflector that generates the reflected wave. 5. The FM radar according to claim 4, wherein said first and second frequency conversion circuits comprise a common local signal generation circuit and a separate mixing circuit. 6. A common part including an FM signal generation circuit for generating an FM signal whose frequency changes with time, a detection circuit for detecting the frequency of a beat signal and converting the frequency to a distance to a reflector which has generated a reflected wave, and A plurality of individual parts connected to this common part in a time-division manner via a switch, and each of the plurality of individual parts divides an FM signal supplied in a time-division manner via the switch. 1st and 2nd FM
A dividing circuit for obtaining a signal; a delay circuit for delaying the first FM signal for a predetermined time; a first frequency conversion circuit for increasing the frequency of the delayed first FM signal to a predetermined value; An antenna that emits a signal and receives the reflected wave, a second frequency conversion circuit that raises the frequency of the second FM signal to the predetermined value, and an output of the second frequency conversion circuit and the signal received by the antenna And a mixing circuit for mixing the reflected waves to generate the beat signal. 7. An FM signal generating circuit for generating an FM signal whose frequency changes with time; a dividing circuit for dividing the generated FM signal to obtain first and second FM signals; A common part including a delay circuit for delaying, and a detection circuit for detecting the frequency of the beat signal and converting it to a distance to a reflector that has generated a reflected wave; A plurality of transmission circuits connected in a time-division manner, and a plurality of reception circuits connected in a time-division manner to the division circuit of the common portion via a second switch; each of the plurality of transmission circuits is A first frequency conversion circuit that raises the frequency of a first FM signal supplied in a time-division manner via the first switch to a predetermined value, and an antenna that radiates the frequency-converted FM signal. Each of the plurality of receiving circuits A second frequency conversion circuit that increases the frequency of the second FM signal supplied in a time-division manner via the second switch to the predetermined value, an antenna that receives the reflected wave, and the second 2. An FM radar, comprising: a mixing circuit that mixes the output of the frequency conversion circuit and the reflected wave received by the antenna to generate a beat signal of both.