JPS5942268B2 - FM/CW radar - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an FM-CW radar, especially a vehicle radar, in which a beat frequency of a reflected wave from a target is out of the passband width of an amplifier, and a calculated relative Distance and relative velocity are relevant for FM-CW radar I to improve reliability.

The FM-CW method in Doppler radar 1 transmits FM carrier waves with modulated wave P, receives echoes that have undergone Doppler shift and propagation delay, and mixes them with transmitted waves to identify them. The Doppler frequency fd is determined by selecting the sideband (np±fd) and comparing it with the reference sideband np.

Figure 1 is the basic block diagram of the FM-0M radar.
Figure 2 11 Figure 1 Diagram explaining the relationship between transmitted and received waves and their beat frequencies when the target is fixed in Figure 1;
The figure is a diagram illustrating the relationship between transmitted and received waves and their beat frequencies when the target is moving.

In FIG. 1, MOD is a modulator, O8C is an oscillator, MIX is a mixer, AMP is an amplifier, SIG is a signal processing unit, and TG is a target.

The microcarrier generated by the oscillator O8C is transmitted to the modulator MO
DI From this, for example, a triangular wave as shown in Fig. 2 a1 is used for FMt, and the first transmission wave whose frequency increases sequentially and the second transmission wave whose frequency decreases sequentially are created alternately, and a continuous wave is transmitted from the transmitting antenna. f.

(1) is sent.

The radio waves are reflected by the target, for example a stopped car at a distance R, and the returning signal is naturally delayed.

If the delay time is T, this received @ radio wave fo(t-T) is the transmitted radio wave f.

(t) is mixed with the mixer MIX1, the beat frequency fr of both radio waves is extracted and amplified, and then the presence/absence of a target TG, relative distance El, and relative velocity (2) are displayed by signal processing 1.

In this case, the delay time T1 is the time it takes for the received wave to arrive, so if the speed of the radio wave is C, then T=2R/C... (+,) horizontal axis 1 time If we take t and frequency f on the vertical axis, the frequency of the transmitted wave is the second
Like the solid line in figure a! In addition, when the target TG is fixed, the received wave is 1 m, the dotted line is 1, and the transmitted wave is f.
.

The radio wave fo(t-T) is delayed by T from t.

Therefore, due to a time difference of 1 between the transmitted and received waves, a beat frequency fr as shown in the mixer MIX output f shown in FIG. 1 and b1 in FIG. 2 is generated.

This fr is called a range frequency, and the distance can be calculated from it.

Next, if the target TG is moving, the received wave will be
The drub frequency fd is superimposed by one time shift shown in Figure a.

That is, the received radio wave f as shown by the dotted line 1 in FIG. 3a.

(t-T)'+fa is input.

In this case, as shown in FIG. 3 b1, the beat frequency differs by one frequency fb1° fb2 alternately by one frequency.

In Fig. 3 b1, the beat frequency fb1. fb2 is fb1=fr+fd ・・・・・・・・・
(2) f b2 = f r - f d -
=−−−−・−(3).

Therefore, range frequency fr, drab frequency fd
It becomes lha.

The distance and speed are determined from the range frequency fr and the drab frequency fd, respectively.

In this way, when a triangular wave FM-CW radar receives reflected waves from a moving object, up beat (UP B
The frequency 1 of ``eat'' and ``DownBeat'' is fr+fd, respectively.

It becomes fr-fd.

Now, when a beat amplification device has a limited band, there may be cases where only one of the amplifier outputs, f r + f d or f r - f d, appears, and the speed and distance are calculated from this output. This will result in a large error.

The present invention solves the above-mentioned problems when either the up beat or down beat is out of the band of the amplifier, or when the reflected signal from the target is so weak that it cannot be received above a certain level. This is an FM-CW radar whose purpose is to display only accurate values without calculating speed and distance.

In the present invention 1, for example, in a triangular wave FM-CW radar, a level detection circuit is added for each of the up beat and down beat outputs, and only when there is a signal higher than the set level for both at the same time. , it determines that the signal is "present" and outputs the distance and speed information, while (other than the above conditions) it determines that the signal "i" is "absent" and displays the distance as (a) and the speed as 0. Therefore, the above objective is achieved.

FIG. 4 is a block diagram of an FM-CW radar showing an embodiment of the present invention, and FIG. 5 is a signal waveform diagram of each part in FIG.

In Figure 1, BeatAMP is a beat amplifier, BPF
is a bandpass waver, PULSI''i pulse shaping circuit, G
is a gate circuit, UP/DN 5WI-4 up beat and down beat switching circuit, Gate is a gate signal, f -VCNV is a frequency-voltage conversion circuit, 5UBI'
i subtraction circuit, EET-8W is analog switch, D.
■ is a detection/integration circuit, CMP is a comparison circuit for level detection, AND is an AND gate, 5IG (ON-OFF
)+"ii signal no output signal, vl"i relative speed, R1-
1 relative distance.

The circuit above the chain line X in FIG. 4 is a conventional circuit.

The circuit below the chain line X is the circuit according to the present invention.

For example, if the frequency band of the bandpass filter BPF of the beat amplifier is 50 KHz, the range frequency fr is 45K
Hz and the drab frequency fd is 10 KHz, the up beat (UP.Beat) is 55 KHz and the Dhawan beat is 35 KHz, which is a part of the up beat by 11 attenuation bands.

Then, the output of the beat amplifier is passed through the pulse shaping circuit PULS.
After frequency-voltage conversion is performed through , a signal of relative distance R appears by integrating and calculating an average value, but this value (1) causes a large error.

In addition, the output of the beat amplifier is passed through the pulse circuit PULS, added to the beat switching circuit UP/DN SWI, and the gate signal shown in Figure 5 is applied.1 From this, the up beat pulse UP-BT-PS and the down beat - Separate the pulses DN and BT - Psi, convert this by 1 to the voltage I, subtract it, and then divide by 2 to obtain the relative velocity vE, but this naturally also includes an error.

Furthermore, as the target TG moves a long distance, the reflected signal becomes weaker, and if it cannot be received, a similar error will occur.

Therefore, in the method of the present invention shown in FIG. 4, a part of the output of the beat amplifier is connected to the analog switch FE T-8WI to give control signals with opposite phases to each other as shown in FIG. 1, the up beat UP-BT and the down beat DN-BTI are separated, rectified and integrated to obtain an average value, which is compared with the threshold level TF (LD) of the comparator circuit COM.

Both outputs exceed the level 1. Therefore, only when both signals are detected, the output of the AND gate AND becomes bi-level, and from this output 1, the gate circuit G for speed calculation is activated.
and operates a frequency-voltage conversion circuit for distance calculation.

However, either or both of the up beat and down beat detection/integration outputs may exceed the threshold.
When the level is below the level THLD, the output of the AND gate AND becomes a low level, and ρ turns the gate circuit G into an off state. It is determined that there is no.

When the signal is "no", the distance is displayed as "O" or infinity, and the speed is displayed as "0" by Genit.

As explained above, the present invention has a method for separating and extracting up beats and down beats.
Embodiment 1 In this embodiment, the up-beat and down-beat levels are detected using an analog switch (FET SW, etc.), and either the up-beat or the down-beat is below a predetermined level. Calculation means for calculating the relative distance and relative speed (in Example 1, frequency-voltage conversion circuit f-V CVN, subtraction circuit S)
Control means for stopping the operation (consisting of UB, etc.) (Embodiment) In this case, the detection/integration circuit D/2 and the comparison circuit CMP.

(and gate AND, gate circuit G, etc.), and only when both the up beat, down beat, and down beat outputs are simultaneously equal to or higher than the threshold level, the symbol "Yes" is given. Because it determines this and outputs speed and distance information, large errors are eliminated and reliability is improved.

Therefore, if one FM-CW radar according to the present invention is installed in a vehicle such as an automobile that requires extremely high precision, it will be extremely effective in preventing rear-end collisions.

[Brief explanation of the drawing]

Figure 1 is a basic block diagram of the FM-CW radar. Figures 2 and 3 are similar to Figure 1 and show the transmitted and received waves when the target is fixed and when the target is moving. FIG. 4 is a block diagram of an FM-CW radar showing an embodiment of the present invention, and FIG. 5 is a signal waveform diagram of each part of FIG. 4. Beat AMP: Beat amplifier, BPM: Bandpass wave generator, PULS: Pulse shaping circuit. G: Gate circuit, UP/DN SW near beat and down beat switching circuit, Gate: Gate ri, f-VCNV: Frequency-voltage conversion circuit, SUB: Subtraction circuit, FET-8W: Analog switch, D・■: Detection/integration circuit, comparison circuit for CMP two-level detection,
AND: AND gate, SIG (ON-OFF):
Presence/absence output of f'g, V: relative velocity, R: relative distance, f
r: beat frequency, fd: Doppler frequency, THLD: threshold level.

Claims (1)

[Claims] 1. Sending means for alternately sending out a first transmission wave whose frequency increases sequentially and a second transmission wave whose frequency sequentially decreases, mixing the reflected wave from a moving object and the first and second transmission waves. A mixer for obtaining a beat signal, an amplifier having a predetermined passband for amplifying the beat signal output from the mixer, and a calculation means for calculating the relative distance and relative velocity based on the output signal of the amplifier. Equipped with an FM-CW radar,
Up beat and down beat signals are obtained from the output signal of the amplifier.
Separation and extraction means for separating and extracting the beats, detecting the level of the up beat and down heat separated and extracted by the separation and extraction means, and determining whether at least one of the up beat or down beat is below a predetermined level 1
An FM-CW radar characterized in that the FM-CW radar is further provided with a control means for stopping the operation of the calculation means when this occurs.