JPH10300845A - Pulse radar distance measuring device and pulse radar distance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse radar distance measuring device and its method capable of extremely reducing the effect of unnecessary reflected waves from plural reflecting sources. SOLUTION: Electromagnetic pulses corresponding to impulses from an impulse generating circuit 12 are repeatedly transmitted from a transmission antenna 14 to a target T, reflected waves are received from the target T by a receiving antenna 16, sampling of received signals is performed in a sample holding circuit 18 for a receiving circuit 20 at timings delayed a gradually changed delay time from electromagnetic pulse transmission for every electromagnetic pulse transmission and high frequency components are cut with a low pass filter 19. When an output value from the receiving circuit 20 is over a preset threshold value, a signal is generated in a voltage comparator 32, and, after the signal from the voltage comparator 32 is generated in a detecting circuit 34 and when the output value from the receiving circuit becomes zero for the first time, a detection signal is generated to allow the computation of a distance to the target in an arithmatic circuit 42 in accordance with the detection signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to transmitting an electromagnetic pulse having a short pulse width toward a target, receiving a reflected wave from the target, and converting a received signal into a low-frequency signal using an equivalent sampling technique. The present invention relates to a pulse radar distance measuring device and a pulse radar distance measuring method for measuring a distance to a target by processing the signal.

[0002]

2. Description of the Related Art In recent years, it has been proposed to apply a radar having a wide band (a narrow transmission pulse width and a wide band width of a receiver) with a small power that does not violate the Radio Law to various measurements. (For example, WO960845A
No. 1). It has also been proposed to apply this radar to a distance measuring device that measures the distance to the target, transmitting electromagnetic wave pulses toward the target, receiving reflected waves from the target, and receiving using an equivalent sampling technique. Devices for measuring a distance to a target by converting a signal into a low-frequency signal and obtaining a reception time of a reflected wave from the low-frequency signal have been developed. In a device that has already been developed, the reception time stores the previous reception waveform, and determines the time when the amplitude intensity at a certain ratio with respect to the peak amplitude intensity of the previous reception waveform is determined as the reception time.

[0003]

However, since the received waveform appears not only as a reflected wave from the target but also as an unnecessary reflected wave from a plurality of reflecting sources, the conventional method for determining the receiving time does not. However, there is a problem that it is difficult to obtain an accurate reception time. The present invention has been made in view of such a problem, and the invention according to claims 1 to 4 has a pulse radar distance measuring device capable of minimizing the influence of unnecessary reflected waves from a plurality of reflection sources. And a pulse radar distance measuring method.

[0004]

To achieve the above object, a pulse radar distance measuring device according to claim 1 of the present invention comprises: a pulse generating means for generating a repetitive pulse;
Transmitting antenna means for transmitting an electromagnetic wave pulse corresponding to the pulse of the pulse generating means toward the target, receiving antenna means for receiving a reflected wave from the target, timing signal generating means, and receiving signals from the timing signal generating means hand,
Delay time adjusting means for outputting a signal corresponding to a gradually changing delay time; and a signal from the reception antenna means at a timing delayed by the delay time from the electromagnetic wave pulse transmission by a signal from the delay time adjusting means. And a receiving circuit having a low-pass filter, a comparing means for generating a signal when an output value from the receiving circuit exceeds a predetermined threshold value, and a signal after the signal is generated by the comparing means. A detecting means for generating a detection signal when the output value from the receiving circuit becomes zero for the first time, and a time interval between the timing signal from the timing signal generating means and the detection signal from the detecting means, and from the time interval Calculating means for calculating the distance to the target.

[0005] The pulse generated by the pulse generating means can be an impulse signal or a burst signal. Also,
The invention according to claim 2 is the invention according to claim 1,
After the signal is generated by the comparing means, the rate of change of the delay time of the delay time adjusting means is reduced, and the cutoff frequency of the low-pass filter of the receiving circuit is reduced.

According to a third aspect of the present invention, there is provided a pulse radar distance measuring method, wherein an electromagnetic wave pulse is repeatedly transmitted to a target, a reflected wave from the target is received, and a delay time gradually changing for each transmission of the electromagnetic wave pulse. Sampling of the received signal at the timing delayed from the electromagnetic wave pulse transmission and filtering of low frequency components, after the output value exceeds a predetermined threshold, the first time the output value becomes zero, the time is detected, A time interval between the detection time and a start time at which the delay time is gradually changed is obtained, and the time interval is converted into a distance to a target.

According to a fourth aspect of the present invention, in the third aspect, after the output value exceeds a predetermined threshold, the rate of change of the delay time is reduced, and the cutoff frequency of the filtering is reduced. It is characterized by the following. Normal,
In the distance measurement, it is assumed that the target is located closest to the antenna means, and the unnecessary reflected wave is often behind the reflected wave from the target and located later in the received waveform. . The present invention utilizes such a property, and reduces the influence of unnecessary reflected waves by setting the first zero-cross point as a reception time after a predetermined S / N ratio that can be distinguished from noise is obtained. Measurement accuracy can be improved.

Although a high-frequency noise component is superimposed on the received waveform, the received waveform immediately before the first zero-crossing point is converted into a lower-frequency signal, and the high-frequency component is cut off. The zero cross point is accurately obtained, and the measurement accuracy can be further improved. Compared to converting all signals received by the receiving antenna means to low-frequency signals, by converting the received waveform immediately before the required zero-cross point to a lower-frequency signal, measurement can be performed more efficiently. it can.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a pulse radar distance measuring apparatus according to the present invention and an apparatus for executing the pulse radar distance measuring method according to the present invention. In the figure, reference numeral 10 denotes a trigger generation circuit,
For example, it outputs a trigger signal of about 1 MHz. An impulse generation circuit (pulse generation means) 12 is connected to the trigger generation circuit 10. The impulse generation circuit 12 synchronizes with a trigger signal from the trigger generation circuit 10 and has a narrow impulse (for example, 200 ps to 2 ps).
0 ps). The impulse generation circuit 12 is connected to a wide-band transmission antenna 14 that is disposed to face the target T to be measured and transmits an electromagnetic pulse corresponding to the impulse from the impulse generation circuit 12 toward the target T. I have.

A wide-band receiving antenna 16 is arranged at substantially the same position as the transmitting antenna 14 with respect to the target T. The receiving circuit 16 is connected to the receiving antenna 16. The receiving circuit 20 includes a sample-and-hold circuit 18 that samples a signal received from the receiving antenna 16 by a signal from a delay time adjusting unit 22 described later, and a low-pass filter 19 that cuts high-frequency components. Specifically, the sample and hold circuit 18 includes a diode driven by the delay time adjusting unit 22 and a capacitor that holds a voltage level sampled by the diode.

The delay time adjusting means 22 appropriately divides the frequency of the trigger signal from the trigger generation circuit 10 and counts the divided pulses.
And a voltage for outputting a time-delayed impulse signal corresponding to the output from the D / A converter 28 in response to the trigger signal from the trigger generation circuit 10. An impulse signal from the voltage-delay conversion circuit 30 is sent to the sample-and-hold circuit 18 of the receiving circuit 20 to control the sampling timing of the sample-and-hold circuit 18.

A voltage comparator 32 is connected to the receiving circuit 20. The voltage comparator 32 compares the output from the receiving circuit 20 with a threshold voltage Vth of a predetermined level. When the output from the receiving circuit 20 is larger than the threshold voltage Vth,
High level output is provided. Further, a detection circuit 34 including a voltage comparator 36 and flip-flops 38 and 40 is connected to the reception circuit 20. Voltage comparator 36
Performs a comparison between the output from the receiving circuit 20 and the voltage 0. When the output from the receiving circuit 20 is higher than the voltage 0, a high-level output is made. In the flip-flop 38, a high-level signal of the voltage Vcc from the D terminal is set by the output from the voltage comparator 32, and is input to the D terminal of the flip-flop 40. A signal from the voltage comparator 36 is input to a clock terminal of the flip-flop 40, and the flip-flop 40 is set in synchronization with the signal.

An arithmetic circuit 42 is connected to the detection circuit 34. The arithmetic circuit 42 includes a gate circuit 44 and a multiplier 46
The count value from the counter 26 is sent to the gate circuit 44, and the gate circuit 44 captures and holds the count value from the counter 26 every time the flip-flop 40 is set. Be composed. The multiplier 46 multiplies the output from the gate circuit 44 by a certain coefficient and outputs the result.

Further, a timing signal generating circuit 48 for outputting a timing signal for determining one measurement interval is provided.
A timing signal of about 0 Hz is output to the counter 26 and the flip-flops 38 and 40 to reset them. The operation of the present embodiment configured as described above will be described below with reference to the timing chart of FIG.

First, in synchronization with a trigger signal (FIG. 2A) from the trigger generation circuit 10, an impulse generation circuit 12
Generates an impulse (FIG. 2 (b)), whereby the transmitting antenna 14 repeatedly emits an electromagnetic wave pulse. Each time each electromagnetic wave pulse is emitted, a signal from the target T is received by the receiving antenna 16 and sent to the receiving circuit 20.

On the other hand, the counter 26 starts counting the trigger signal from the trigger generation circuit 10 from 1 in response to the timing signal (FIG. 2C) from the timing signal generation circuit 48 (FIG. 2D). The figure shows a case where the frequency division ratio is 1 for the sake of explanation, and the count value increases by one at the same time when the trigger signal from the trigger generation circuit 10 is generated. Thereby, the output of the D / A converter 28 gradually increases (FIG. 2E), and the delay time of the impulse signal generated by the voltage-delay conversion circuit 30 from the trigger signal gradually increases in accordance with this output. The sampling timing in the receiving circuit 20 is gradually and continuously delayed. In this way, by gradually changing the delay time, the time axis of the received signal can be equivalently converted, and as shown in FIG. Is converted to a low-frequency signal.

When the signal from the receiving circuit 20 becomes larger than the threshold voltage Vth, the voltage comparator 32 outputs a high-level signal and sets the flip-flop 38 (FIG. 2 (g)). Further, with the flip-flop 38 set, the voltage comparator 36 outputs a high-level signal when the signal from the receiving circuit 20 becomes larger than 0, and sets the flip-flop 40 (FIG. 2).
(H)). That is, the point at which the flip-flop 40 is set exceeds the threshold value and crosses zero for the first time, and this point is detected as the reception time.

The gate circuit 44 includes a flip-flop 40
Is set, the count value of the counter 26 is taken in, and held and output. The multiplier 46 calculates the radio wave propagation speed and the voltage-delay conversion circuit 30
Conversion rate of voltage and delay time, frequency of trigger generation circuit,
Multiply by a coefficient determined by the frequency division ratio of the frequency divider, etc.
Convert to distance and output.

As described above, in the present embodiment, the distance to the target T is obtained by using the zero crossing point for the first time after the output from the receiving circuit 20 exceeds the threshold voltage Vth. It is possible to reduce the influence of unnecessary reflected signals, which are often present in the rear part of the reflected reception waveform, so that accurate distance measurement can be performed. Next, a second embodiment of the present invention is shown in FIG. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. The difference from the first embodiment is that the output from the flip-flop 38 is
0 '. The counter 26 'has a built-in switch, and its frequency division ratio can be switched by a signal from the flip-flop 38. When a high-level signal is output from the flip-flop 38, the frequency division ratio is increased. It is switched to go down.

The receiving circuit 20 'also includes the switch 54 and has a plurality of low-pass filters 19-1 and 19-2 having different cutoff frequencies. The switch 54 can be switched by a signal from the flip-flop 38, and the flip-flop 3
When a high-level signal is output from 8, the switch 54 is switched so that the low-pass filter 19-2 having a low cutoff frequency is connected to the subsequent stage.

Next, the operation of this embodiment will be described below with reference to the timing chart of FIG. The main difference from FIG. 2 is that, as shown in FIG.
Is set, the frequency division ratio of the counter 26 'changes and changes as shown in FIG. 4 (a'). Along with this, the counting speed of the counter 26 'also decreases (FIG. 4D), and D
The rate of change of the output of the / A converter 28 decreases (FIG. 4
(E)).

In this way, the frequency of the received waveform is reduced by delaying the change in the delay time of the sampling timing in the receiving circuit 20 ', and the cutoff frequency is reduced in the receiving circuit 20'. Can be removed. That is, since a large number of high-frequency components are present in the actual waveform, the zero-cross point is detected in a state where the waveform is averaged and smoothed and the S / N ratio is good by lowering the cutoff frequency of the low-pass filter. Therefore, accuracy can be improved.

In each of the above embodiments, the threshold voltage Vth needs to be determined in advance so as to be a level corresponding to the noise level. Alternatively, the noise level may be obtained each time between measurements. FIG. 5 shows an example of a block diagram for obtaining the noise level. When an approximate prediction of the distance of the target T can be made in advance, the count values of the counters 26 and 26 'corresponding to the predicted distance of the target T are obtained, and the output of the D / A converter 28 is converted to the predetermined count value. It is good to fix to the corresponding constant voltage. In this case, the output from the receiving circuits 20 and 20 'is a temporal change in the noise level from the target and the expected position. Therefore, this voltage value is output to the sample-and-hold circuit 50 and the A / D converter 52. Can be sought through.

Alternatively, when it is impossible to realize a state in which no target exists, the noise level of a portion other than the target can be measured and its average value can be taken.

[0025]

As described above, according to the first and third aspects of the present invention, the time when the output value becomes zero for the first time after the received output value exceeds the predetermined threshold value is detected. Then, a time interval between the detection time and the start time at which the delay time is gradually changed is determined, and the time interval is converted into a distance to a target. The measurement accuracy can be improved by setting the front part of the reception waveform having a small value as the reception time.

According to the second and fourth aspects of the present invention, after the received output value exceeds a predetermined threshold, the rate of change of the delay time is reduced to convert the received waveform into a lower frequency signal, and Since the cutoff frequency of the low-pass filter is reduced, more accurate high-frequency noise components can be removed, and a more accurate zero-cross point can be obtained with a good S / N ratio. Therefore, the measurement accuracy can be further improved.

Compared to converting all signals received by the receiving antenna means to low-frequency signals, by converting the received waveform immediately before the necessary zero-cross point to a lower-frequency signal, measurement can be performed more efficiently. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a pulse radar distance measuring device according to the present invention and a device in which a pulse radar distance measuring method according to the present invention is executed.

FIG. 2 is a timing chart illustrating the operation of FIG.

FIG. 3 is a block diagram illustrating a pulse radar distance measuring apparatus according to a second embodiment of the present invention and an apparatus for executing the pulse radar distance measuring method according to the present invention.

FIG. 4 is a timing chart illustrating the operation of FIG.

FIG. 5 shows an example of a block diagram for obtaining a noise level.

[Explanation of symbols]

 Reference Signs List 12 impulse generation circuit (pulse generation means) 14 transmission antenna (transmission antenna means) 16 reception antenna (reception antenna means) 18 sample hold circuit 19 low-pass filter 20 reception circuit 22 delay time adjustment means 32 voltage comparator (comparison means) 34 detection Circuit (detection means) 42 Arithmetic circuit (arithmetic means) 48 Timing signal generation circuit

Claims (4)

[Claims] 1. A pulse generating means for generating a repetitive pulse, a transmitting antenna means for transmitting an electromagnetic wave pulse corresponding to the pulse of the pulse generating means toward a target, a receiving antenna means for receiving a reflected wave from the target, A timing signal generating unit, a delay time adjusting unit that receives a signal from the timing signal generating unit, and outputs a signal corresponding to a gradually changing delay time. A sample-and-hold circuit for sampling a reception signal from the reception antenna means at the timing delayed by the delay time, a reception circuit having a low-pass filter, and a circuit for controlling the output value from the reception circuit to exceed a predetermined threshold. A comparison means for generating a signal, and an output from the receiving circuit for the first time after the signal is generated by the comparison means Detecting means for generating a detection signal when the value becomes zero, calculating a time interval between the timing signal from the timing signal generating means and the detection signal from the detecting means, and calculating a distance from the time interval to a target. And a means for measuring a pulse radar distance. 2. After the signal is generated by the comparing means,
2. The pulse radar distance measuring apparatus according to claim 1, wherein a rate of change of the delay time of the delay time adjusting means is reduced, and a cutoff frequency of a low-pass filter of the receiving circuit is reduced. 3. An electromagnetic wave pulse is repeatedly transmitted toward a target, a reflected wave from the target is received, and a reception signal is transmitted at a timing delayed from the transmission of the electromagnetic wave pulse by a gradually changing delay time for each transmission of the electromagnetic wave pulse. And the low-frequency component is filtered, and after the output value exceeds a predetermined threshold, the time when the output value becomes zero is detected for the first time, and the detection time and the delay time are started to be gradually changed. A pulse radar distance measuring method, wherein a time interval between the time and a time is determined, and the time interval is converted into a distance from the time to a target. 4. After the output value exceeds a predetermined threshold,
4. The pulse radar distance measuring method according to claim 3, wherein the rate of change of the delay time is reduced and the cutoff frequency of the filtering is reduced.