JP2829790B2 - FM-CW radar device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM-CW radar device capable of measuring a target distance and speed.

[0002]

2. Description of the Related Art An FM-CW radar which modulates a carrier wave (CW) with an FM signal such as a triangular wave can measure a target distance and a speed, and is therefore used for a vehicle collision prevention device and the like.

The accuracy of measuring the relative speed by the FM-CW can be improved by lowering the repetition frequency of the FM signal.

[0004]

However, when the repetition frequency of the FM signal is reduced, (1) since the beat signal frequency greatly changes depending on the relative speed, the signal deviates from the filter band, causing detection errors and measurement errors. Or
(2) There is a disadvantage that a phenomenon in which the relative distance and the relative speed cannot be calculated for a target having a large relative speed at a short distance easily occurs.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the detection accuracy of a distance and a speed by variably setting an optimum filter characteristic according to a target distance and a speed.

[0006]

SUMMARY OF THE INVENTION An FM-CW radar apparatus according to the present invention comprises a CW mode for transmitting only a carrier and a high FM-CW mode for transmitting the carrier by modulating the frequency with an FM signal having a high frequency. , A low frequency FM on the carrier
Periodically switches between a low FM-CW mode to transmit by applying frequency modulation with a signal, and from the speed information obtained in the CW mode and the distance information obtained in the high FM-CW mode,
It is characterized in that upper and lower cutoff frequencies of a variable band type band pass filter used in the low FM-CW mode are calculated, and characteristics of the filter are changed as needed.

[0007]

When an attempt is made to accurately measure a target distance and speed with an FM signal of a low frequency (referred to as f _mb ) as shown in section b of FIG. 1, the BPF used in the sensor signal input section is used.
(Bandpass filter) upper and lower cutoff frequency f _CH ,
f _CL (see FIG. 2) is set based on the approximate speed and distance information obtained in section a.

[0008] The first half a1 of the section a is a CW mode using only a carrier wave, and here, an outline of a target relative speed is obtained. In the latter half a2, an approximate target distance is obtained using an FM signal of a high frequency ( _fma ).

In this section a, since the speed and the distance are independently obtained in a1 and a2, even if the relative speed of the target is large, there is no occurrence of a phenomenon that the filter is disconnected or the distance or the speed cannot be calculated. However, the speed detection accuracy is poor because the repetition frequency f _ma of the FM signal is high.

On the other hand, in section b, although the repetition frequency f _{mb of the} FM signal is low, the speed detection accuracy is high. However, if a BPF having a fixed characteristic is used, a problem such as disconnection of the filter occurs.
Therefore, from the approximate values of the speed and the distance obtained in the section a, the section b
By variably setting the characteristics of the BPF used in the above, it is possible to accurately measure the target distance and speed without causing a problem such as a filter separation.

[0011] Specifically, it is to variably set by calculating f _CH of the BPF of FIG. 2, the f _CL from the distance and speed information obtained in section a. Hereinafter, this method will be described.

When the FM signal (transmitted wave) in the FM-CW radar is a triangular wave T as shown by a solid line in FIG. 3, the triangular wave R included in the reflected wave from the target becomes a broken line, and the distance L from the target is L. And a deviation in the direction of the frequency axis f in accordance with the target velocity V.

The beat signal IF of such a triangular wave T, R
Is that if T is an upbeat frequency f _up higher than R, then T is R
Have lower downbeat frequency f _dn, which have each of the following relationship between the Doppler frequency f _d which is proportional to the velocity V, the distance frequency f _r which is proportional to the distance L.

[0014]

F _d = (f _dn −f _up ) / 2

F _r = (f _dn + f _up ) / 2

## _EQU3 ## f _up = _fr -f _d

## EQU4 ## f _dn = f _r + f _d

[0015] When the f _r »f _d in Equation 3 above, that is, if you increase the repetition frequency f _m of the FM signal,

Equation 5] f _{Stay up-≒} f _r, and the distance frequency f _r can be accurately detected.

[0016] The higher the f _r in the interval a2 of Figure 1 F
Suppose that it was obtained at M frequency f _ma (several KHz). Can be obtained even f _r Similarly, in section b, this section b
FM the frequency f _mb to be set to a value lower than the f _ma interval a (several 100 Hz), between the beat frequency f _ba distance frequency f _r and the section a2 of segment b, (f _mb × in
f _ma ) as a conversion coefficient, the following relationship holds.

F _r = (f _mb × f _ma ) × f _ba Therefore, f _up and f _dn of the section b are respectively

Equation 7] _{f up = (f mb × f} ma) × f ba -f d f dn = (f mb × f ma) × f ba + f since represented as _d, the f _{Stay up-limit} cut-off frequency f
Using the BPF of FIG. 2 with _CL as the lower limit cutoff frequency f _CH and f _dn as the lower limit, the low FM frequency f _mb can accurately measure the distance and speed in the section b.
Note that the velocity (Doppler) frequency f _d in Equation 7 is obtained by using only the carrier CW in the section a1.

In the present invention, such CW modes a1 and f
This is repeated periodically with the _ma mode a2 and the _fmb mode b as one frame.

[0018]

FIG. 4 is a block diagram showing an embodiment of the present invention.
Reference numeral 0 denotes a homodyne detection type radar sensor, reference numeral 20 denotes an FM signal generation unit, reference numeral 30 denotes a sensor signal input unit, and reference numeral 40 denotes a microcomputer.

The radar sensor 10 includes a carrier CW oscillator 1
1 and its output is transmitted from the transmitting antenna 12.
The reflected wave from the target is received by the receiving antenna 13 and converted into a beat signal IF by the mixer 14. The local used at this time is a part of the transmission wave, and the directional coupler 15
Is extracted by The beat signal IF is amplified by the amplifier 16 and input to the sensor signal input unit 30.

The FM signal generator 20 has a pulse generator 21 of f _{ma and} a pulse generator 22 of f _mb , and their outputs are converted into triangular waves by integrators 23 and 24. An analog SW 25 selects one of two triangular waves.
Is an analog SW for switching whether or not to input the output of the analog SW 25 to the oscillator 11 of the radar sensor 10 as a modulation signal. By controlling these from the microcomputer 40, the three types of modes a1, a2, and b in FIG. Generate periodically.

The sensor signal input section 30 comprises a filter suitable for each mode and a pulse shaping circuit. That is, BPF3
1 and the pulse shaping circuit 32 is for CW mode a1, also BPF33 a pulse shaping circuit 34 is for f _ma mode a2. On the other hand, SCF (switched capacitor capacitor)
The filters 35 and 36 and the pulse shaping circuit 37 are for the _fmb mode b.

The filter characteristics of the SCFs 35 and 36 can be variably set by the microcomputer 40. In this example, the first stage SCF
35 is used as an LPF (low-pass filter) with a cut-off frequency f _CL , and the next stage SCF 36 is used as an HPF (high-pass filter) with a cut-off frequency f _CH , and both form a BPF having the characteristics shown in FIG. .

The microcomputer 40 controls the switching of the analog SWs 25 and 26, calculates f _CL and f _CH from the outputs of the pulse shaping circuits 32 and 34, and variably sets the characteristics of the SCFs 35 and 36. Then, the target distance and speed are calculated from the output of the pulse shaping circuit 37.

[0024] While the output of the pulse shaping circuit 37 is due to a low FM frequency f _mb, the characteristics of SCF35,36 are optimally set according to the distance and velocity of the target, filter out even the relative velocity is large The speed and distance can be measured with high accuracy (absolute value, polarity) without problems such as the above.

[0025]

As described above, according to the present invention, in an FM-CW radar device capable of measuring a target distance and a speed, the optimum filter characteristic according to the target distance and the speed is variably set as needed. The accuracy of distance and speed detection can be improved.

[Brief description of the drawings]

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

FIG. 2 is an ideal filter characteristic diagram.

FIG. 3 is an explanatory diagram of an FM-CW radar.

FIG. 4 is a configuration diagram of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Radar sensor 20 FM signal generation part 30 Sensor signal input part 35, 36 Variable band type band pass filter element 40 Microcomputer

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01S 7/00-7/42 G01S 13/00-13/95

Claims (1)

(57) [Claims] 1. A CW mode in which only a carrier is transmitted, a high FM-CW mode in which the carrier is frequency-modulated with a high-frequency FM signal, and a frequency modulation is performed in the carrier with a low-frequency FM signal. The low frequency band used in the low FM-CW mode is periodically switched between the low frequency FM-CW mode and the distance information obtained in the high frequency FM-CW mode. Characterized by calculating upper and lower cutoff frequencies of a bandpass filter and changing the characteristics of the filter as needed.
W radar device.