JPH10300843A - Pulse radar distance measuring device and pulse radar distance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a pulse radar distance measuring device and its method as being capable of measuring a target, if in any range, in the good condition of a S/N ratio. SOLUTION: Electromagnatic pulses corresponding to impulses from an impulse generating circuit are repeatedly transmitted from a transmission antenna to a target, reflected waves are received from the target by a receiving antenna 16, sampling of received signals from the receiving antenna is performed in a sample holding circuit 51 of a receiving circuit 50 at timings delayed from the repeated pulses, a delay time from a delay time adjusting circuit 53, and high frequency components are cut with a low pass filter 52. The delay time adjusting circuit 53 is formed with a feedback loop which consists of a computation amplifier 54 to subtract an output value from the receiving circuit 50 from a preset value, an integrator 56 to integrate a subtraction result from the computation amplifier 54 and a voltage-delay converting circuit 57 to adjust the delay time in accordance with an integration value from the integrator 56.

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 small power that does not violate the Radio Law and a wide band (a narrow transmission pulse width and a wide receiver bandwidth) to various measurements. (For example, WO960845A
1 gazette). It has also been proposed to apply this radar to a distance measuring device that measures the distance to a target, transmitting an electromagnetic wave pulse toward the target, receiving a reflected wave from the target,
By sampling the received signal at a timing delayed from the electromagnetic wave pulse transmission for the gradually changing delay time, the received signal is converted into a low frequency signal, and the reception time of the reflected wave is obtained from the low frequency signal, Devices for measuring the distance to a target 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, in the conventional apparatus, when the measurement interval is fixed, if the change of the delay time gradually changing is made faster, the measurement range can be widened, while the waveform is compressed. Therefore, there is a problem that the bandwidth of the received signal is widened and the S / N ratio is deteriorated. On the other hand, if the delay time change is slowed down,
Although the received waveform becomes smooth and the S / N ratio can be increased, there is a problem that the measurement range cannot be widened.

The present invention has been made in view of such a problem, and the invention according to claim 1 can perform measurement with a good S / N ratio regardless of the range of the target to be measured. An object of the present invention is to provide a pulse radar distance measuring device. Another object of the present invention is to provide a pulse radar distance measuring method which achieves the same object.

[0005]

According to a first aspect of the present invention, there is provided a pulse radar distance measuring apparatus comprising: a pulse generating means for generating a repetitive pulse; Transmitting antenna means for transmitting a corresponding electromagnetic wave pulse toward a target, receiving antenna means for receiving a reflected wave from the target, delay time adjusting means for adjusting a delay time, and a delay time from the delay time adjusting means. A sample-and-hold circuit that samples a reception signal from the reception antenna unit at a timing delayed from the electromagnetic wave pulse transmission, and a reception circuit having a low-pass filter, and the delay time adjustment unit includes: It is configured with a feedback loop that adjusts the delay time so that the output value from the receiving circuit becomes a predetermined value, And obtains the distance from the delay time which is adjusted by the length of time adjusting means to a target.

The delay time adjusting means includes, for example, a subtracting means for subtracting an output value from the receiving circuit from a predetermined value,
The delay time conversion can be configured by a feedback loop including an integration means for integrating a result of the subtraction from the subtraction means, and a delay time conversion means for adjusting a delay time according to the integration value from the integration means. The distance to the target can be obtained from the delay time adjusted by the means.

The pulse generated by the pulse generating means is
It can be an impulse signal or a burst signal. In the pulse radar distance measuring method according to the second aspect of the invention, the electromagnetic wave pulse is repeatedly transmitted toward the target, the reflected wave from the target is received, and the electromagnetic wave pulse is delayed from the transmission of the electromagnetic wave pulse by the adjusted delay time. Sampling of the received signal at the timing, filtering low frequency components,
The delay time is adjusted so that the filtered output value always becomes a predetermined value, and a distance from the adjusted delay time to a target is obtained.

Conventionally, a signal received from a receiving antenna means is sampled at a timing delayed from the transmission of the electromagnetic wave pulse by a gradually changing delay time, thereby converting the received signal into a low-frequency signal. On the other hand, in the present invention, the delay time for determining the sampling timing is adjusted so that the output value from the receiving circuit always becomes a predetermined value. For example, if the delay time is adjusted so that the output value of the receiving circuit becomes equal to zero, the waveform of only the zero cross point in the received waveform is obtained. As described above, by outputting only the local portion of the received waveform, reducing the bandwidth of the received signal, and cutting the high-frequency component with the low-pass filter,
/ N ratio can be improved, and measurement accuracy can be improved.

When the predicted distance to the target is known in advance, the initial value of the delay time may be a delay time corresponding to the predicted distance. In addition, if the distance to the target is not known at all, for example, a timing signal generating unit and a signal from the timing signal generating unit,
Second delay time adjusting means for outputting a signal corresponding to the gradually changing delay time, and receiving antenna means at a timing delayed by the delay time from the transmission of the electromagnetic wave pulse by the signal from the second delay time adjusting means. A sample-and-hold circuit that performs sampling of a received signal from the first filter, a low-pass filter, and a unit that calculates a delay time when an output value from the low-pass filter matches the predetermined value. A delay time when the value coincides with the value can be set as an initial value of the integrating means.

[0010]

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). Connected to the impulse generating circuit 12 is a broadband transmitting antenna 14 that is disposed to face the target T to be measured and transmits an electromagnetic wave pulse corresponding to the impulse from the impulse generating circuit 12 toward the target T to be measured. Have been.

For a target T to be measured, a transmitting antenna 1
A broadband receiving antenna 16 is arranged substantially at the same position as that of the receiving antenna 4, and a scanning circuit 17 and a tracking circuit 18 are connected to the receiving antenna 16. The scanning circuit 17 finds a reflected wave from the target in a wide range in advance, obtains the approximate distance of the target, and sends a signal Vin corresponding to the distance to the tracking circuit 18. Further, the tracking circuit 18 uses the signal Vin from the scanning circuit 17 as an initial value, and thereafter performs tracking of a reflected wave from a target to acquire a signal of a local portion of a received waveform.

The scanning circuit 17 is configured as shown in FIG. 2, and includes a receiving circuit 20 connected to the receiving antenna 16,
A counter 26 for dividing the frequency of the trigger signal from the trigger generation circuit 10 and counting the frequency-divided pulses, and a D / A converter 28 for D / A converting the output from the counter 26
D / with respect to the trigger signal from the trigger generation circuit 10
A voltage-delay conversion circuit 30 that outputs an impulse signal delayed by a time corresponding to the output from the A converter 28
And a voltage comparator 32 connected to the receiving circuit 20 for comparing the output from the receiving circuit 20 with a voltage Vth of a predetermined level.
A voltage comparator 36, which is also connected to the receiving circuit 20 and compares the output from the receiving circuit 20 with the voltage 0, flip-flops 38 and 40, a gate circuit 44 connected to the flip-flop 40, And a timing signal generating circuit 48 for outputting a timing signal of, for example, about 100 Hz for determining a measurement interval.

The receiving circuit 20 further includes a sample-and-hold circuit 21 for sampling a signal received from the receiving antenna 16 based on a signal from the voltage-delay conversion circuit 30, and a low-pass filter 2 for cutting high-frequency components.
And 2. Specifically, the sample and hold circuit 21 includes a diode driven by the voltage-delay conversion circuit 30 and a capacitor that holds a voltage level sampled by the diode.

The tracking circuit 18 is configured as shown in FIG. 3, and includes a receiving circuit 5 connected to the receiving antenna 16.
0 and a delay time adjustment circuit 53. The delay time adjusting circuit 53 subtracts the output from the receiving circuit 50 from the voltage 0, and outputs a signal corresponding to the difference between the two, and an integration for integrating the output from the operational amplifier 54. And a voltage-delay conversion circuit 57 that outputs an impulse signal delayed by a time corresponding to the output from the integrator 56 with respect to the trigger signal from the trigger generation circuit 10. . Further, the tracking circuit 18 includes an A / D converter 58 to which the integration signal from the integrator 56 is input and an A / D converter 5
And a multiplier 60 that is connected to the multiplier 8.

The receiving circuit 50 further includes a sample-and-hold circuit 51 for sampling a signal received from the receiving antenna 16 based on a signal from the voltage-delay converting circuit 57, and a low-pass filter 5 for cutting high-frequency components.
And 2. The sample and hold circuit 51 has the same configuration as the sample and hold circuit 21. The low-pass filter 52 has a lower cutoff frequency than the low-pass filter 22 of the receiving circuit 20.

Before the tracking of the reflected wave from the target by the tracking circuit 18 according to the gist of the present invention and the acquisition of the signal of the local portion of the received waveform, first, the scanning circuit 17 is used to roughly determine the target. Find the distance. However, when the target distance can be predicted in advance, for example, when the target is moving and the target is located at a position not so far from the target position obtained in the previous measurement, etc. No processing is required.

First, a process of finding a reflected wave from a target in a wide range in advance by using the scanning circuit 17 is shown in FIG.
This will be described below using the timing chart of FIG. First,
In synchronization with the trigger signal (FIG. 4A) from the trigger generation circuit 10, an impulse (FIG. 4B) is generated from the impulse generation circuit 12, whereby the transmission antenna 14 repeatedly emits an electromagnetic pulse. . Each time each electromagnetic pulse is emitted, a signal from the target T
And is sent to the receiving circuit 20 of the scanning circuit 17.

On the other hand, the timing signal (FIG. 4 (c)) from the timing signal generating circuit 48 causes the counter 26,
The flip-flops 38 and 40 are reset, and the counter 26 starts counting the trigger signal from the trigger generation circuit 10 from 1 (FIG. 4D). Note that, for the sake of explanation, the figure shows a case where the frequency division ratio is 1, and the count value increases by one at the same time when the trigger signal from the trigger generation circuit 10 is generated. As a result, the output of the D / A converter 28 gradually increases (FIG. 4E), 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 receiving circuit 20
Is gradually and continuously delayed. As described above, by gradually and continuously changing the delay time, the time axis of the received signal can be equivalently converted. As shown in FIG.
The received signal from 0 is converted to a low frequency signal.

The voltage comparator 32 outputs a signal when the signal from the receiving circuit 20 becomes larger than the threshold voltage Vth, and sets the flip-flop 38 (FIG. 4).
(G)). Further, with the flip-flop 38 set, the voltage comparator 36 outputs a signal when the signal from the receiving circuit 20 becomes larger than 0, and sets the flip-flop 40 (FIG. 4 (h)). ). In the present embodiment, the point of time when the zero crossing is first performed beyond the threshold voltage Vth which is considered to exceed the noise level is determined as the reception time, and the reception is performed using the reference point (zero cross point) in the front part of the reception waveform. By taking time,
The effects of unnecessary reflected waves from multiple reflection sources are eliminated.

In the gate circuit 44, the flip-flop 4
The output of the D / A converter 28 when 0 is set is fetched and the output Vin is sent to the tracking circuit 18. In the example of FIG. 4, the division ratio is set to 1 for explanation, but it is measured that the change of the delay time in the voltage-delay conversion circuit 30 is increased by adjusting the division ratio under the condition that the frequency of the timing signal is constant. The range can be widened and the slower the change, the narrower the measurement range. By appropriately selecting the frequency division ratio, the target reflected wave is detected within the range.

When the approximate distance to the target T is detected in this manner, the tracking circuit 18 performs tracking of the target. That is, V output from the scanning circuit 17
in is output as an initial value of the integrator 56, and the voltage-delay conversion circuit 57 outputs an impulse signal delayed by a time corresponding to the voltage Vin to the reception circuit 50. Thus, in the sample and hold 51 of the receiving circuit 50, the sampling of the received waveform is performed at the timing of the impulse signal, and the high-frequency component is cut by the low-pass filter 52.

Next, in the operational amplifier 54, the output from the receiving circuit 50 and the voltage 0 are subtracted, and the result is sent to the integrator 56, where the voltage-delay conversion circuit 5
7, the delay time is adjusted. That is, in this feedback loop, when the output from the receiving circuit 50 is smaller than 0, the delay time is reduced, and when the output from the receiving circuit 50 is larger than 0, the delay time is increased.
When the output from the receiving circuit 50 is equal to 0, the delay time is kept unchanged without changing the delay time.

Since the signal corresponding to the delay time outputted from the integrator 56 when this feedback loop is repeated corresponds to the propagation time of the electromagnetic wave pulse, the integrator 56
The A / D converter 58 converts the output from the A / D converter into an A / D signal. Further, the multiplier 60 calculates a coefficient determined by the propagation speed of the radio wave, the voltage-delay conversion circuit 57 voltage / delay time conversion rate, and the like. Multiply, convert to distance and output.

From the signal from the receiving circuit 50, the high-frequency component is cut by the low-pass filter 52 having a low cut-off frequency, and an averaged average signal is obtained.
If the target T is stationary, the signal from the receiving circuit 50 shows a constant value. When the target T moves, the signal from the receiving circuit 50 is no longer 0, so that the receiving circuit 5
The feedback loop operates so that the output of 0 becomes 0. For example, as shown in FIG. 5, when the target T approaches, the zero-cross point shifts forward as indicated by the phantom line, so that the output from the receiving circuit 50 becomes a negative value. Detected at 54, the delay time in the voltage-delay conversion circuit 57 is reduced. As a result, the output from the receiving circuit 50 is kept at 0.

As described above, the receiving circuit 50 extracts only the signal near the zero cross of the received waveform and outputs the signal to the low-pass filter 5.
By smoothing at 2, the S / N ratio can be significantly improved. In the present embodiment, the operational amplifier 54
Performs the subtraction between the output from the receiving circuit 50 and 0 volt, because the first zero-cross point after the received waveform first exceeds the threshold voltage Vth is set as the receiving time. As the time, for example, when the time when the reception waveform reaches a predetermined voltage level Vref is set as the reception time, Vref may be input to the minus terminal of the operational amplifier 54.

[0026]

As described above, according to the present invention,
By adjusting the delay time for determining the sampling timing in the receiving circuit so that the output value from the receiving circuit always becomes a predetermined value, the receiving circuit outputs only a specific part of the received waveform. be able to. In this way, the S / N ratio can be improved by reducing the bandwidth of the received signal and performing averaging by cutting high-frequency components with a low-pass filter. Therefore,
Measurement accuracy can be improved.

[Brief description of 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.

FIG. 2 is a block diagram illustrating a configuration of a scanning circuit of FIG. 1;

FIG. 3 is a block diagram illustrating a configuration of a tracking circuit in FIG. 1;

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

FIG. 5 illustrates an example of a reception waveform, and a virtual line indicates a reception waveform when a target approaches.

[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) 50 reception circuit 51 sample and hold circuit 52 low-pass filter 53 delay time adjustment circuit (delay time adjustment means) 54 operational amplifier ( Subtraction means) 56 integrator 57 voltage-delay conversion circuit (delay time conversion means)

Claims (2)

[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 delay time adjusting means for adjusting a delay time; a sample hold circuit for sampling a reception signal from the reception antenna means at a timing delayed from the electromagnetic pulse transmission by an amount corresponding to the delay time from the delay time adjustment means; A receiving circuit having a filter, wherein the delay time adjusting means is configured by a feedback loop for adjusting a delay time so that an output value from the receiving circuit becomes a predetermined value, and the delay time A pulse radar distance measuring method for obtaining a distance to a target from the delay time adjusted by the adjusting means. Setting device. 2. An electromagnetic wave pulse is repeatedly transmitted to a target, a reflected wave from the target is received, and a reception signal is sampled at a timing delayed from the transmission of the electromagnetic wave pulse by an adjusted delay time. A pulse radar distance measuring method, comprising filtering components, adjusting the delay time so that a filtered output value always becomes a predetermined value, and obtaining a distance from the adjusted delay time to a target.