JPH07120549A - Fm-cw radar - Google Patents

Abstract

PURPOSE:To selectively ignore detection information from a region which is desired to be excluded from a radar detection range for FM-CW radar. CONSTITUTION:This radar consists of a transmission radar part 10 a reception radar part 20 with a frequency converter 22 for obtaining a baseband signal from the reflection signal from a target object, a signal processing part 30 for calculating radar information, a beam scanning means 41 for scanning either a transmission beam or a reception beam, a scanning angle setting means 42 for setting the scanning angle, and a variable band filtering means 43 for changing the pass band of the baseband signal corresponding to the scanning angle.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an FM-CW (Freque).
energy Modulation-Continuou
s Wave) radar. As will be described in detail later, the FM-CW radar has a function between the transmission signal and the reception signal depending on the distance between the radar and the target object and the Doppler shift due to the relative velocity change between them. Focusing on the occurrence of the shift, the reception radar unit is configured to perform frequency conversion on the reception signal by the high frequency signal in the transmission radar unit.

This FM-CW radar can measure the relative velocity and distance with respect to a target object by a simple signal processing section, and the transmission radar section can be simply constructed.
In particular, it is being widely used as an anti-collision radar for automobiles that are required to be compact and low-priced. It is, so to speak, forward protection in the operation of cars. Such FM-CW radar should be applicable not only to the above-mentioned front protection but also to the side-rear protection because of its function. Generally, when driving an automobile, there is a so-called blind spot zone, and it is difficult for a driver to confirm other vehicles or the like existing in the blind spot zone. It is the above-mentioned side-rear protection that confirms an object (vehicle or the like) in this blind spot zone.

The present invention describes an FM-CW radar suitable for application to the above-mentioned side / rear protection.

[0004]

2. Description of the Related Art FIG. 6 is a diagram showing a principle configuration of a conventional FM-CW radar. The configuration of both the FM-CW radar (hereinafter also simply referred to as radar) shown in the figure and the radar according to the present invention is roughly divided into a transmission radar unit 10, a reception radar unit 20, and a signal processing unit 30. In addition, TG (tar in the figure
6, which is a target object, first, the oscillator 12 is FM-modulated by the triangular wave of several 100 Hz from the modulation signal generator 11, and the FM-modulated wave is transmitted by the transmission antenna 13
From the target object TG, the reflected signal from the target object TG is received by the receiving antenna 21, and a frequency converter 22 such as a mixer is received.
Then, the received signal is FM-detected with the FM-modulated wave as a local.

At this time, the reflected wave from the target object TG is
Depending on the distance between the radar and the target object, and the Doppler shift due to the relative speed, a frequency shift (beat) from the transmission signal occurs. FIG. 7 is a graph (No. 1) for explaining the principle of the conventional FM-CW radar, and FIG. 8 is a graph (No. 2) for explaining the principle of the conventional FM-CW radar.

This beat frequency component fb is (distance frequency fr depending on distance) ± (velocity frequency f depending on velocity)
Since it is represented by d), it is possible to measure the distance and the relative velocity from this frequency shift. Here, fr = (4Δ
Ω / Tc) R, fd = (2f ₀ / c) v, where ΔΩ is the modulation width, T is the period of the modulated wave, c is the speed of light, and R is
Is the distance to the target object TG, fo is the transmission center frequency, v
Is the relative velocity to the target object.

Now, when using this radar as an automobile radar, the distance is 100 m at most and the relative speed is 100 m.
Since it is about km / h, the maximum frequency deviation should be about 100MHz to ensure sufficient distance measurement accuracy, and the millimeter waveband as the transmission frequency band to ensure sufficient relative speed measurement accuracy. Must be used. In FIG. 6, the bass band (BB) signal down-converted by the frequency converter 22 includes the above-mentioned beat component, and is applied to the signal processing unit 30 and processed. For example, if the beat frequency is 1.5 kHz, the target object TG is 2 m, 3.0 kHz is 3 m, and 4.5 kHz is 4 m ... 75
If it is kHz, it is determined to be 100 m.

FIG. 9 is a plan view showing how a conventional FM-CW radar is used to monitor the rear side of a vehicle. In this figure, it is assumed that a vehicle C is traveling along a lane (low speed) on a highway consisting of three lanes (lane and) on one side. Here, the driver of the vehicle C tries to change course to a higher speed lane. At this time,
By using the FM-CW radar L according to the present invention provided on both side surfaces of the vehicle C, it is confirmed whether or not there is another vehicle that is catching up behind the side. A radar similar to the radar L mounted on the right side of the vehicle C is also mounted on the left side thereof and is indicated by L'in the figure.

[0009]

In FIG. 9, the same applies to the radar L (radar L '.
The detection range covered by () is a fan-shaped range indicated by W in the figure. Therefore, both the vehicle C2 that follows the lane from behind and the vehicle C1 that follows the lane from behind are detected by the radar.

However, when actually driving a car,
There is almost no problem in terms of safe operation of the vehicle C1 that runs in the one lane. That is, the problem is to detect only the vehicle C2 running in the adjacent lane. Therefore, it is preferable that the rear vehicle C1 traveling in the lane is not included in the radar detection range W. This is a problem because meaningless alarms are frequently issued. That is, the radar detection range W in FIG.
Of these, the range with dots (the range of approximately triangles) should rather be ignored for radar detection.

Therefore, in view of the above problems, it is an object of the present invention to provide an FM-CW radar capable of narrowing the radar detectable range according to the detection direction in order to ignore unnecessary target objects. Is.

[0012]

FIG. 1 is a diagram showing the principle configuration of the present invention. As shown in this figure, basically, similar to FIG. 6, a transmission radar unit 10 that transmits a high frequency signal frequency-modulated by a modulation signal from a transmission antenna 13, and a reception antenna 21 that receives a reflection signal from a target object TG1 or TG2.
Reception radar section 20 having a frequency converter 22 for receiving the received signal and converting the frequency of the received signal by the high frequency signal.
And a signal processing unit 30 that calculates relative velocity and distance information with respect to the target object based on the output from the frequency converter 22, and is an FM-CW radar.

On the other hand, the component added by the present invention is a beam scanning means 41 for scanning one or both of the transmission beam from the transmission antenna 13 and the reflection beam to the reception antenna 21 within a predetermined scanning angle. A scanning angle setting means 42 for variably setting the scanning angle by the beam scanning means, and a different band limitation according to each scanning angle set by the scanning angle setting means 42 for the output from the frequency converter 22. Variable bandwidth filtering means 4
It is 3.

[0014]

In each of the beams of the radar shown in FIG. 9, the detectable distance is set to the scanning angle α as shown by d1, d2 ... Accordingly, it is adjusted and excluded from the range W. Detectable distance d
Since 1, d2 ... dn correspond one-to-one with the beat frequency (baseband signal) already described, the output stage of the frequency converter 22 is matched with the detection distances of d1, d2. A filter is provided to apply different band limitation depending on the. This is the band variable filtering means 43.

[0015]

FIG. 2 is a diagram showing a first embodiment according to the present invention. In the first embodiment, the beam scanning means 41
Causes electronically beam scanning at least one of the transmitting antenna 13 and the receiving antenna 21. Electronic beam scanning includes (1) frequency changing (frequency scanning) (2) phase shifting by inserting a phase shifter in the middle of the feeder line (phase scanning) (3) beam forming It is categorized as one that scans the circuit by switching the circuit to the power feeding section with a built-in switch (feeding point switching scanning). These three types are called electronic scanning antennas,
In particular, a phased array antenna (p
It is preferably referred to as "hased array antenna" and is preferably used.

In FIG. 2, reference numeral 14 indicates a directional coupler, and 23 indicates a low frequency amplifier. FIG. 3 is a diagram showing a second embodiment according to the present invention. In the second embodiment, the beam scanning means 41 mechanically scans at least one of the transmitting antenna 13 and the receiving antenna 21 with a beam.

As an example of the mechanical beam scanning, rotators 15 and 24 are used as shown in the figure,
The angle of the antenna can be changed with a fine pitch. In addition, in the first embodiment (FIG. 2) and the second embodiment (FIG. 3), at least one of the transmitting antenna 13 and the receiving antenna 21 is beam-scanned. The configuration is shown. If only one antenna is used for beam scanning (narrow directivity), the other antenna has a wide directivity.

FIG. 4 is a diagram showing a third embodiment according to the present invention. In the third embodiment, the variable band filtering means 4
Reference numeral 3 is composed of a plurality of filters 51-1 ... 51-n having mutually different fixed pass bands, and a selector 52 for selecting one filter corresponding to each scanning angle set by the scanning angle setting means 42. It Reference numeral 53 in the figure
Is a selection control circuit for selectively selecting the contact of the selector 52.

The variable band filtering means 43 shown in FIGS. 1, 2 and 3 is a switched capacitor filter,
It can be realized by using a circuit whose characteristics can be changed electrically from the outside, such as an active filter. Alternatively,
As shown in FIG. 4, it is also possible to combine individual filters into a filter bank and select the corresponding one from the filter banks.

FIG. 5 is a diagram showing a fourth embodiment according to the present invention. In the fourth embodiment, the beam scanning means 41
Is composed of a transmitting antenna 13 having a wide directivity covering the entire scanning angle and a plurality of receiving antennas 21-1 ... 21-n in which the receiving directions of the reflected beams are different from each other. Further, the band variable filtering means 43 is similar to that shown in FIG.
A plurality of filters 51-1 ... 51 having fixed pass bands different from each other and connected to corresponding receiving antennas
-N. The frequency converter 22- is provided between the output stage of each receiving antenna 21 and each filter 51.
1 ... 22-n are provided.

In this case, the angle setting means 42 sequentially selects a plurality of receiving systems, and determines which scanning angle the receiving system at which the relative speed and distance are currently obtained from.
Notify the signal processing unit 30.

[0022]

As described above, according to the present invention, F
In the M-CW radar, its detection range can be limited, and when applied to side-rear protection of vehicles (elimination of blind spots), it is more convenient to ignore this for rear objects (other vehicles) that are convenient to ignore. It can be selectively excluded from detection targets.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention.

FIG. 2 is a diagram showing a first embodiment according to the present invention.

FIG. 3 is a diagram showing a second embodiment according to the present invention.

FIG. 4 is a diagram showing a third embodiment according to the present invention.

FIG. 5 is a diagram showing a fourth embodiment according to the present invention.

FIG. 6 is a diagram showing a principle configuration of a conventional FM-CW radar.

FIG. 7 is a graph (No. 1) for explaining the principle of the conventional FM-CW radar.

FIG. 8 is a graph (No. 2) for explaining the principle of the conventional FM-CW radar.

FIG. 9 is a plan view showing how a conventional FM-CW radar is used to monitor the side and rear of a vehicle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Transmission radar section 11 ... Modulation signal generator 12 ... Oscillator 13 ... Transmission antenna 20 ... Reception radar section 21 ... Reception antenna 22 ... Frequency converter 30 ... Signal processing section 41 ... Beam scanning means 42 ... Scan angle setting means 43 ... Bandwidth variable filtering means 51-1 to 51-n ... Filter 52 ... Selector 53 ... Selection control circuit

(72) Inventor Yoji Ohashi, 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, within Fujitsu Limited (72) Inventor, Kawasaki, Yoshihiro 1015, Kamedota, Nakahara-ku, Kawasaki, Kanagawa Within Fujitsu Limited ( 72) Inventor Naofumi Okubo 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, Osamu Isaji 1-228, Gosho-dori, Hyogo-ku, Kobe, Hyogo Prefecture

Claims (5)

[Claims] 1. A transmission radar section (10) for transmitting a high frequency signal frequency-modulated by a modulation signal from a transmission antenna (13) and a reflection signal from a target object by a reception antenna (21), and the received signal. Reception radar section (20) having a frequency converter (22) for frequency-converting the
And a signal processing unit (30) that calculates relative velocity and distance information with respect to the target object based on the output from the frequency converter, in an FM-CW radar, wherein: Beam scanning means (41) for scanning one or both of a transmission beam from a transmission antenna and a reflected beam to the reception antenna, and a scanning angle setting means (42) for variably setting the scanning angle by the beam scanning means. , And a variable band filtering means (43) for applying different band limitation to the output from the frequency converter according to each scanning angle set by the scanning angle setting means. CW radar. 2. The beam scanning means (41) electronically beam scans at least one of the transmitting antenna (13) and the receiving antenna (21).
FM-CW radar according to item 1. 3. The beam scanning means (41) mechanically scans at least one of the transmitting antenna (13) and the receiving antenna (21) with a beam.
FM-CW radar according to item 1. 4. The variable band filtering means (43) comprises a plurality of filters (51-) having fixed pass bands different from each other.
51-n) and a selector (52) for selecting one filter corresponding to each scanning angle set by the scanning angle setting means (42). Radar. 5. The beam scanning means (41) has a wide directivity of the transmitting antenna (1) that covers the scanning angle.
3) and a plurality of receiving antennas (21-1 ... 21-n) in which the reception directions of the reflected beams are different from each other, and the variable band filtering means (43) has fixed pass bands different from each other. And a plurality of filters (1-1 ... 51-n) each of which is connected to each corresponding reception antenna, and the frequency is provided between the output stage of each reception antenna and each filter. The FM-CW radar according to claim 1, wherein converters (22-1 ... 22-n) are provided.