JPS6034707B2 - FM-CW radar - Google Patents

Description

Detailed Description of the Invention The present invention extracts a beat signal from a continuous transmission wave whose frequency is modulated with a modulated wave and a reflected wave from a target, and calculates the relative speed and distance to the target based on this beat signal. FM you want
- Regarding CW radar.

FIG. 1 is a schematic configuration for explaining the operating principle of an FM-CW radar, in which 1 is an oscillator, 2 is a modulator, 3 is a transmitting antenna, 4 is a receiving antenna, 5 is a mixer, and 6 is an amplifier. The mixer 5 includes a received wave (directional coupler)
8, a part of the transmitted signal is added, mixed with the received wave, and the beat signal Sb is extracted. B is oscillator 1
This is the bias signal applied to the Carrier wave from oscillator 1 w
When the radar approaches the target 7 using a triangular wave as the modulation wave m that modulates the A reflected wave w2 is received by the receiving antenna 4 with a time delay according to the distance R or according to the relative velocity V, and this has a certain relationship with the transmitted wave w, as shown by the dashed line in the figure. Note that a wave w3 indicated by a dotted line in the figure is a received wave when the distance R is constant, that is, when the relative velocity V is zero. When a part of the transmitted wave w and the received wave w2 are mixed by the mixer 5, a beat signal having a frequency difference between them is generated. The beat signal Sb is an upbeat frequency ratio when the modulation frequency increases. and has a downbeat frequency fQ when decreasing fb. as shown in FIG. 2b. <
It is related to point 2. This beat signal Sb is expressed in the time axis direction as shown in FIG. 2c. upbeat fb
．． And the downbeat ratio 2 is expressed by the following equation, where h is the beat frequency (range frequency) and the ratio is the Doppler frequency. ratio, = fr−fd ・
...'1} ratio 2=fr+fd
・・・・・・【2}), fr=4△f
Book m-RR illusion = Raw v △f: Triangular wave modulation amplitude fm: Triangular wave modulation frequency input: Wavelength of transmitted wave R: Distance between radar and target V: Relative speed c: Speed of light Relative speed with target V is the Doppler frequency obtained by calculating the distance R from the sum of the above m and formula (2), and calculating the difference between method A and formulas {1} and {2) from the rate of change. There is a method B that calculates from fd.

The latter method B directly obtains the Doppler frequency phantom by subtraction, and is superior to the former method A in terms of response speed and accuracy. However, when an in-vehicle radar receives reflected waves from a continuous target object, such as a guardrail on a curve, rain, or the road surface, it calculates the Doppler frequency based on the speed of the target vehicle and indicates the speed of the target vehicle, which is inconvenient. There is a side. That is, as shown in Fig. 3, the road 11 is curved and there is a guardrail on the outside. 12, the direction of the vehicle 13 changes along the curve when the steering wheel is operated, so the distance R between the radar target and the vehicle 13 is always constant and there is no danger. In method B, an output is output indicating that there is a relative speed with the guardrail and the guardrail is approaching. Therefore, it is necessary to add some kind of restriction because it will interfere with the normal operation of alarm or brake control. In this respect, in the former method A, the speed is determined from the rate of change in distance, so the speed is not detected and becomes zero. Therefore, the present invention aims to take advantage of the advantages of both methods to provide an FM-CW radar that has good responsiveness and accuracy and can always send accurate control signals regardless of the target. be.

The present invention is an FM-C that extracts a beat signal from a sustained transmission wave whose carrier wave is frequency modulated and a reflected wave from a target, and calculates the relative speed and distance to the target based on this beat signal.
In the W radar, a distance calculation section that calculates distance from each upbeat and downbeat frequency of the beat signal, a speed calculation section that calculates speed, and a differentiation circuit that obtains a speed signal by differentiating the output of the distance calculation section; The present invention is characterized by comprising a speed comparator circuit that calculates the difference between the outputs of the speed calculation section and the differentiating circuit and outputs a prohibition signal when the difference is greater than a reference value. This will be explained in detail.

FIG. 4 shows an embodiment of the present invention, in which reference numeral 21 indicates both the upbeat and downbeat frequencies fq, a speed calculation unit that directly calculates the relative velocity V from the ratio 2, 22 indicates both the upbeat and downbeat frequencies fq,
23 is a differentiation circuit that differentiates the calculation output of this distance calculation section 22 to obtain a speed signal; 24 is the speed calculation section 21 and the differentiation circuit 2 that calculates the relative distance R from fb2;
A differential amplifier that takes the difference between the outputs of 3, 25 is an absolute value circuit, and 2
A comparator 6 compares the output of the absolute value circuit 25 with a reference value and generates a high level or low level output Sa depending on the magnitude thereof, and forms a speed comparison circuit together with circuits 24 and 25.

And 27 is the purpose of the recorder output, for example, alarm/
This is a control circuit, and the high level output of the comparator 26 is input as an inhibit signal. In addition, absolute value circuit 2
5 is provided considering the case where the relative speed is both positive and negative, and may be omitted when the relative speed is only positive (approaching). As shown in FIG. 5, the speed calculation unit 21 receives the beat signal f
a pulse shaping circuit 211 whose pulse waveforms are q and fb2;
A switch circuit 212 that performs switching at a frequency fm that is twice the modulated wave m to separate signals 5 and fQ, each signal fb
, fb2 frequency-voltage (F-V) conversion circuit 213
, 214, a differential amplifier 215 that takes the difference between the outputs of both conversion circuits 213 and 214, and output 1 of the differential amplifier 215.
/2 (fb, one ratio 2) is obtained as the speed signal V.

The distance calculating section 22 also includes a waveform shaping circuit 2 which converts both beat signals fb and fb2 into pulse waveforms as shown in FIG.
1 and an F-V conversion circuit 222, the conversion circuit 22
2 output 1/2 (fq+ratio 2) is output as the distance signal R.

Next, the operation of the FM-CW radar with the above configuration will be explained.

First, when the radar-equipped wheels approach a discontinuous radar target such as a car mackerel at a constant speed, the output of the distance calculation section 22 gradually decreases as time t elapses, as shown in FIG. 7a. In this process, the reception output may be smeared due to reflection, or actually due to the influence of multipath, etc., resulting in smearing d. On the other hand, the output of the speed calculation unit 21 remains constant, and a drop d2 occurs at a point corresponding to the drop d (Fig. 7b).
. The output of the distance calculation unit 22 is differentiated by a differentiating circuit 23 to become a substantially constant speed signal as shown in FIG. ' occurs. Here, the peaks d,' in FIGS. 7b and 7c may exceed the reference value Vs, but the time is very short and can be ignored. The difference between these speed signals is taken by the differential amplifier 24, and since they are equal in this case, the inputs d, , , as shown in FIG.
The output is approximately zero except for the output at the portion d2, and the absolute value is taken by the absolute value circuit 25, as shown in FIG. 7e. The output of this absolute value circuit 25 is sent to the comparator 26 as a reference value V.
As a result, as shown in FIG. 7f, a low-level output Sa is produced as the speed comparison circuit output. Therefore, no inhibit signal is input to the alarm circuit 27, and the circuit generates an alarm in a predetermined operation, for example, in a predetermined state, based on the output speed signal and distance signal of both the calculation units 21 and 22. On the other hand, when the radar target is a continuous target such as a guardrail on a curve, the output of the distance calculation unit 22 is constant except for a drop d here and there as shown in FIG. The output of the section 21 is also constant as shown in FIG. 8b.

When the constant output of the distance calculating section 22 is differentiated by the differentiating circuit 23, as shown in FIG. As a result, a large differential output with a substantially constant level is generated in the differential amplifier 24, as shown in FIG. 8d. After this differential output is converted into an absolute value by an absolute value circuit 25, it is converted to an absolute value by a comparator 26 as shown in FIG.
- compared with the reference value Vs as shown in FIG. In this case, the output of the absolute value circuit 25 is greater than the reference value Vs, and the output Sa of the comparator 26, that is, the speed comparison circuit output, becomes a high level as shown in FIG. 8f. That is, the comparator 26 outputs the fact that a target such as a continuous object has been captured, and this is also applied to the alarm circuit 27 as an inhibit signal, that is, a prohibition signal, to prevent an alarm from being issued based on the output of the speed calculation section 21. do. In this way, the alarm operation is limited by the output of the comparator 26 when the target is a guardrail on a curve where speed detection using the Doppler frequency detects the vehicle's own speed instead of the relative speed.
For discontinuous targets that do not have the above-mentioned effects, such as car balls, the detection is always performed accurately and quickly because it follows the signal obtained from the Doppler frequency. It should be noted that although warning is given as an example of the use of the radar output, there are also other uses such as actuator control of a brake system. As explained in detail above, according to the present invention, the relative speed with respect to the target is determined from the Doppler frequency and control such as alarm control and brake control is performed with excellent response speed and accuracy. Based on this result, it is possible to detect that the velocity determined from the Doppler frequency is not the relative velocity but the eye wheel velocity for a special target, and to maintain control using the Doppler frequency accurately. Therefore, the device of the present invention is capable of processing risk determination for various consecutive targets such as guardrails. Furthermore, the absolute value circuit allows correction not only when approaching but also when moving away.

[Brief explanation of the drawing]

Fig. 1 and Fig. 2 a to c are a combined schematic diagram and waveform diagram to explain the operating principle of the FM-CW radar, Fig. 3 is a plan view showing an example of a special radar target, and Fig. 4 is a plan view showing an example of a special radar target. A block diagram of the main parts showing an embodiment of the FM-CW radar according to the present invention, FIGS. 5 and 6 are block diagrams of the calculation section, and FIGS. 7 a to f and 8 a to f are for explanation of operation. FIG. 1... Oscillator, 2... Modulator, 3... Transmitting antenna, 4... Receiving antenna, 5... Mixer, 6...
Amplifier, 7...Target, 11...Road, 12...Guardrail, 13...Car, 21...Speed calculation unit, 2
2...Distance calculation unit, 23...Differential circuit, 24...Differential amplifier,...Absolute value circuit, 26...Comparator,
27...Alarm circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Closed view Figure 8

Claims (1)

[Claims] 1. In an FM-CW radar that extracts a beat signal from a frequency-modulated continuous transmission wave and a reflected wave from a target, and calculates the relative speed and distance to the target based on this beat signal, a distance calculation unit that calculates distance from each upbeat and downbeat frequency of the beat signal; a speed calculation unit that calculates speed; a differentiation circuit that obtains a speed signal by differentiating the output of the distance calculation unit; An FM-CW radar comprising: a speed comparison circuit that calculates the difference between the respective outputs of the circuit and outputs a prohibition signal that prohibits processing based on the output of the speed calculation section when the difference is equal to or greater than a reference value. 2. The FM-CW radar according to claim 1, wherein the speed comparison circuit includes an absolute value circuit that takes the absolute value of the difference between both speed signals.