JP4023972B2 - Distance measuring device by pulse wave - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a distance measuring device using a pulse wave, and more particularly to a configuration of a distance measuring device that can be used as a millimeter wave pulse radar.
[0002]
[Prior art and problems to be solved by the invention]
Conventionally, a pulse radar that measures the distance of a target by transmitting and receiving pulse waves in the microwave band, etc. has been used, but this pulse radar stops its reception function during transmission, so its minimum detection The distance is limited to the distance determined by the transmitted pulse width.
[0003]
That is, FIG. 7 (A), (B) as shown in, send the pulse wave width t ₁ (seconds), a long time the received waves than the _{t 1 t 2 (t 1 <} t 2) If the signal is detected after the reception function, the distance L to the target (reflecting object) is determined by the time t ₂ .
[Formula 1]
L = (t · c) / 2 (where t: time, c: speed of light)
Can be measured.
[0004]
However, as shown in FIGS. 7C and 7D, when the time t ₂ when the received wave returns is shorter than the time width t _{1 of the} transmitted wave (t ₁ > t ₂ ), microwaves or the like are used. In the used radar apparatus, the receiving function during transmission is stopped because of the necessity of avoiding saturation of the received signal, and the received wave of FIG. 7D cannot be extracted. Therefore, conventionally, when the width t ₁ = 0.1 μsec, L = (t · c) / 2 = (1 × 10 ⁻⁷ ) × (3 × 10 ⁸ ) ÷ 2 = 15 according to the above formula 1. Thus, there is an undetectable distance of 15 m.
[0005]
The present invention has been made in view of the above problems, and an object thereof is to provide a distance measurement device using a pulse wave that enables distance measurement even at a short distance within a time width of a transmission pulse wave.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a distance measurement apparatus using a pulse wave according to claim 1 is symmetrical with respect to a rotation axis, and a rotation antenna for transmitting and receiving a pulse wave while rotating, and receiving from the rotation antenna A phase-locked detection circuit that detects the Doppler component of the reflected wave from the target by phase-locked detection, and a band-pass filter that inputs an output signal of the phase-locked detector circuit, and is obtained by rotating the rotating antenna. A Doppler component detection circuit for detecting a differential Doppler component of a phase Doppler frequency through the bandpass filter, and measuring a time from the rising of the transmission pulse to the generation of the differential Doppler component detected by the Doppler component detection circuit A time measurement circuit and measure the distance to the target based on the output of this time measurement circuit And wherein the door.
[0007]
The invention according to claim 2 is characterized in that an array antenna is used as the rotating antenna.
[0008]
According to the configuration of the first aspect, a Doppler frequency can be generated in the reflected signal from the target object even when the target object is not moving by transmitting a pulse wave from the rotating antenna. That is, the Doppler frequency is generated by the movement on the pulse transmission side, and the signal of the Doppler frequency is detected by phase-locked detection within the pulse transmission time. Then, the time from the rise of the transmission pulse to the generation of the Doppler signal is detected, and the distance to the target is measured by this time.
[0009]
As the rotating antenna, an array antenna such as a slot antenna or a patch antenna can be used.
[0010]
Then, using a general-purpose rotating antenna comprising a symmetrical, when this Ru rotated, cause the Doppler frequency of the left and right opposite phase to the reflected wave, when the radar device or a target attached to the antenna does not move at all, these Doppler The difference between the frequencies is 0, but when the radar apparatus or the target moves, a left-right difference Doppler frequency is generated. Therefore, if this Doppler frequency is detected via a narrow band pass filter, the distance of the target can be measured in the same manner as described above.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
1 and 2 show the configuration of a first reference example radar apparatus (apparatus to which a pulse wave distance measuring apparatus is applied) for explaining an embodiment described later . The radar apparatus of FIG. A parabolic or horn type rotating antenna 10 is provided. As shown in FIG. 2, the rotating antenna 10 is obtained by offsetting the radio wave radiating portion 10A from the rotating shaft 10B by a radius r ₁ (for example, 6 cm) at a speed of, for example, about 3 cm / second around the rotating shaft 10B. Rotate.
[0012]
When a pulse transmitted from the rotating radio wave radiating unit 10A of the antenna 10 is reflected from the target F, a Doppler component (Doppler frequency) is generated in the reflected signal. This Doppler frequency fd It can be expressed by Equation 2 below.
[Formula 2]
fd = {(2 · f ₀ ) / c} × V × θ [Hz]
(Where f _{0 is the} transmission pulse frequency, c is the speed of light, V is the rotational speed of the radio wave radiation section, θ is the rotational angle)
[0013]
For example, the fd is about 7 Hz when the frequency f _{0 of the} transmission pulse is 35 GHz (millimeter wave), about 12 Hz when the frequency is 60 GHz, and about 1.8 Hz when the frequency is 9 GHz (microwave). Therefore, a higher Doppler frequency than the microwave can be obtained. Therefore, in this example, a millimeter wave is used to generate a high Doppler frequency that is easy to detect. Further, as can be seen from Equation 2, in order to obtain a high Doppler frequency fd, the rotational speed V can be increased, or the offset r ₁ can be increased when the angular speed is constant.
[0014]
In FIG. 1, the rotating antenna 10 is connected to a circulator (demultiplexer) 13 through a rotary joint 12, and this circulator 13 has an HPA (High Power Amplifier) 14, a pulse modulator 15, and a transmission as a transmission side circuit. A wave oscillator 16 is connected. On the other hand, the circulator 13 is provided with an LNA (Low Noise Amplifier) 18, a mixer 19, a reception local (local) oscillator 20, and an IF (intermediate frequency) amplifier 21 as a receiving side circuit. Distance measurement of a long distance target is performed by the intermediate frequency signal. That is, short distance measurement is performed within the pulse transmission time, and thereafter, it is operated as a normal pulse radar.
[0015]
For short-range measurement using the Doppler frequency, the phase synchronization local control circuit 23 for phase-synchronizing the signals of the transmission wave oscillator 16 and the reception local oscillator 20 and the video signal (several numbers) output from the mixer 19 are used. (a DC voltage component equal to the envelope of the Doppler signal of kHz to several hundred kHz), for example, a high-speed counter 25 that outputs a clock pulse with a frequency of 100 MHz, a transmission pulse based on the clock pulse of the high-speed counter 25 An analog-to-digital converter (ADC) 26 is provided for measuring the time from the rise to the generation of the Doppler signal and calculating the distance from this time.
[0016]
The first reference example has the above configuration, and its operation will be described with reference to FIG. In the transmission wave oscillator 16 and the pulse modulator 15 shown in FIG. 1, for example, a 35 GHz (others, 60 GHz, etc.) millimeter wave pulse is formed, and this transmission pulse is radiated from the antenna 10 via the HPA 14 and the circulator 13. This transmission pulse is shown in FIG. 3A. In this example, for example, the pulse width is 1 μsec and the pulse repetition time is 1 msec.
[0017]
The antenna 10 receives a reflected pulse reflected from the target F (FIG. 2), and the received pulse is supplied to the mixer 19 through the circulator 13 and the LNA 18. In the mixer 19, a local frequency, for example, 34.04 GHz signal from the reception local oscillator 20 is mixed with the received pulse, and a 60 MHz IF (intermediate frequency) signal is obtained. The long distance measurement is performed.
[0018]
On the other hand, since the transmission pulse is radiated from the rotating radio wave radiating unit 10A of the antenna 10, a Doppler frequency signal is generated in the reflected wave from the target F, and this Doppler signal is within the pulse transmission time width. It is detected as a DC voltage by the mixer 19 that performs phase-locked detection. That is, since the transmission wave oscillator 16 and the reception local oscillator 20 are phase-synchronized by the phase-locked local control circuit 23, the mixer 19 operates as a phase detector, and as shown in FIG. A phase voltage Vphase indicating the presence of the Doppler frequency is output. Here, the Doppler frequency fd of each pulse changes as a dotted curve by the rotation of the antenna 10.
[0019]
The Doppler signal output from the mixer 19 is amplified by the video amplifier 24, and then the distance is measured at a short distance by the ADC 26. That is, FIGS. 3C to 3E show enlarged one transmission pulse and mixer output in FIGS. 3A and 3B, but the output voltage Vphase of the mixer 19 is transmitted. Since the amplitude value changes for each pulse, the ADC 26 is configured to recognize the voltage peak value, and based on the clock signal of FIG. 3F output from the high-speed counter 25, the Doppler signal from the rising edge of the transmission pulse. The time t ₂ until the occurrence of is measured.
[0020]
In this example, since a clock signal of 100 MHz is used, the time t ₂ is obtained, for example, in N × 10 n (nano) seconds, and the distance to the target F is calculated from this time t ₂ . That is, the distance L is calculated by the above formula 1, and this distance data is output to the display and displayed. According to the distance measurement using the ADC 26, there is an advantage that a minute time in nano units can be accurately measured by digital processing.
[0021]
FIG 4, there is shown a rotating antenna according to a reference second example, the second example this reference is intended the length of the slot antenna (or antenna effect) is configured to be asymmetrical in the rotation axis lateral . That is, the slot antenna 30 in FIG. 4A is formed in an inverted L shape having a plurality of slits 31 on the side surface, and rotates with a radius r ₂ (for example, 30 cm) with respect to the rotation axis O ₁ that is a feeding point. Configured as follows. The slot antenna 32 in FIG. 4B has a T-shape that is symmetrical in shape, is configured to rotate around the rotation axis O ₁ with a radius r ₂ , and has a pulse on either the left or right side. A pin diode switch 33 is provided to block the passage of waves. Therefore, in this case, only the one where the pin diode switch 33 is not arranged functions as an antenna. In FIG. 4B, the right and left radii are r ₂ and r ₃ (r so that the rotation axis O ₁ (feed point) is deviated from the center of the slot antenna 32 without providing the pin diode switch 33. ₂ ≠ r ₃ ), and the lengths of the left and right antennas may be different.
[0022]
FIG. 4C shows the rotation state of the slot antenna 30 of FIG. 4A. When the antenna 30 rotates about the rotation axis O ₁ with a radius r ₂ , the slot antenna 30 is shown. The Doppler frequency can be generated in the reflected wave of the transmitted wave from The same applies to the configuration in which the pin diode switch 33 of FIG. 4B is provided. Also, when the left and right turning radii are different, Doppler frequencies corresponding to different lengths are generated.
[0023]
The configuration other than the antennas 30 and 32, the width t _{1 of the} transmission pulse, and the repetition time are the same as those in the first reference example. As described above, the mixer 19 converts the Doppler frequency to the phase voltage Vphase by phase synchronous detection. Detected. The ADC 26 measures a time t ₂ from the rising edge of the transmission pulse to the generation of the Doppler frequency, and measures a distance L from the time t ₂ to the target.
[0024]
5 and 6 show, there is shown a radar system embodiment, this embodiment uses a slot antenna becomes symmetric, through narrow band filter Doppler component generated by the movement of the radar system and the target to detect. That is, the antenna 36 of FIG. 5 is intended to remove the pin diode switch 33 from the slot antenna 32 in FIG. 4 described above (B), as shown in FIG. 6, the left and right of the rotary shaft O ₂ length ( Rotating antennas having the same radius of rotation r ₂ ). For example, the turning radius r ₂ is 30 cm.
[0025]
5, in this embodiment as well as in FIG. 1, the circuit from the rotary joint 12 to the transmission wave oscillator 16, the LNA 18, the mixer 19, the reception local oscillator 20, the IF amplifier 21, the phase synchronization local control circuit 23, and the high-speed counter 25. And an ADC (analog-digital converter) 26, and the output of the IF amplifier 21 is used for long-distance measurement as in the prior art. The transmission pulse from the transmission wave oscillator 16 has a pulse width of 1 μsec and a pulse repetition time of 1 msec.
[0026]
In this embodiment , a narrow band pass filter 38 (for example, a crystal filter) and a DC (direct current) amplifier 39 for extracting a Doppler signal are provided between the ADC 26 and the ADC 26 after the mixer 19. That is, since the Doppler frequency captured in this example is a low frequency of, for example, several to several tens Hz, the Doppler frequency signal is extracted using the filter 38 having a high Q and is amplified.
[0027]
According to such an embodiment , as shown in FIG. 6, when the slot antenna 36 rotates about the rotation axis O ₂ , for example, −fd is received in the reflected signal received by the left antenna 36A in the figure, and the right antenna 36B is used. A + fd Doppler frequency occurs in the received reflected signal. Here, when the radar apparatus and the target do not move at all, the above-fd and + fd cancel each other and no Doppler frequency is generated, but either the radar apparatus or the target often moves, and in this case A Doppler frequency corresponding to the difference between -fd and + fd is generated.
[0028]
In the embodiment , the difference Doppler signal is extracted by the filter 38, and a phase voltage indicating the difference Doppler frequency is supplied to the ADC 26 via the DC amplifier 39. In this ADC 26, as in the other examples, the time from the rising edge of the transmission pulse to the generation of the differential Doppler signal is measured, and the distance from this time to the target is measured.
[0029]
In the detection of the differential Doppler signal, since the band of the signal received by the filter 38 can be narrowed, the S / N ratio (signal-to-noise ratio) can be increased compared to the other embodiments, and the radar apparatus. There is an advantage that the maximum detection distance (within a short distance range) can be increased.
[0030]
【The invention's effect】
As described above, according to the present invention, a pulse wave is transmitted and received by a bilaterally symmetric rotating antenna, thereby generating a differential Doppler component having a Doppler frequency of opposite phase in the reflected wave from the target, and this differential Doppler The component is detected by a phase-locked wave detection circuit and a bandpass filter, and the time from the rise of the transmission pulse to the generation of the differential Doppler component is measured to measure the distance to the target. It is possible to measure the distance even at a short distance corresponding to the inside.
[0031]
In addition , by detecting the differential Doppler component via a narrow band filter, it is possible to measure a short distance using a general-purpose antenna and to increase the maximum detection distance by measuring with a good S / N ratio. It becomes. Conventionally, there is an FM-CW system as a short-range radar, but the maximum detection distance can be made larger than this FM-CW radar.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a radar apparatus according to a first reference example of the present invention.
FIG. 2 is a diagram illustrating a configuration of an antenna according to a first reference example.
FIG. 3 is a waveform diagram showing the operation of the radar apparatus of the first reference example.
FIG. 4 is a diagram illustrating an antenna configuration of a radar apparatus according to a second reference example.
5 is a block diagram showing a configuration of a radar apparatus according to the actual 施例.
FIG. 6 is a diagram illustrating the operation of the antenna according to the embodiment .
FIG. 7 is a diagram illustrating a relationship between a transmission wave and a reception wave in a conventional radar device.
[Explanation of symbols]
10: Antenna, 10A: Radio wave radiation section,
10B, O ₁ , O ₂ ... rotating shaft,
16 ... transmit wave oscillator,
19 ... mixer, 20 ... receiving local oscillator,
23 ... Phase synchronous local control circuit,
24 ... Video amplifier,
26 ... ADC (analog-digital converter),
30, 36 ... slot antenna,
38: Narrow band pass filter.

Claims (2)

A rotating antenna for transmitting and receiving a pulse wave while rotating, being symmetrical about the rotation axis ,
A phase-locked detection circuit that detects the Doppler component of the reflected wave from the target received from the rotating antenna by phase-locked detection, and a band-pass filter that inputs an output signal of the phase-locked detector circuit, and the rotation of the rotating antenna A Doppler component detection circuit that detects the difference Doppler component of the Doppler frequency of the left and right antiphase obtained in Step 1 through the bandpass filter ;
A time measurement circuit that measures the time from the rise of the transmission pulse to the occurrence of the differential Doppler component detected by the Doppler component detection circuit;
A distance measuring device using a pulse wave that measures the distance to the target based on the output of this time measuring circuit. 2. The distance measuring apparatus using pulse waves according to claim 1, wherein an array antenna is used as the rotating antenna .

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