JP2017125807A - M code-modulated microwave distance measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a precise distance measurement with weak radio waves of microwaves, and minimize noise such as aliasing using a coherent laser beam such as infrared light and quickly obtain a cell-level image with a high S/N ratio.SOLUTION: Correlation characteristics of M series codes are used to limit a distance, and the limited distance section is subjected to Fourier transform of frequency spectra and distance spectra, in order to enable a precise measurement with a high S/N ratio.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a high-precision distance measuring apparatus using M code modulated microwave / millimeter wave and light.

The pulse method and the FMCW method have been conventionally used as a method for measuring the distance to a reflection point such as a liquid surface or powder using electromagnetic waves.
The pulse method and SS-OCT (Swept Source) have also been used in OCT that measures distance using light. In addition, a method such as SD-OCT (Spectrum Domain) for measuring a distance from a frequency domain spectrum has been used.

The pulse method is a method of transmitting a microwave / millimeter wave pulse wave, measuring the time delay of the reflected pulse wave, and calculating the distance to the reflection point.

In addition, FMCW and SS-OCT send a signal whose frequency is linearly changed with respect to time and measure the difference frequency from the reflected signal to find the time delay of the reflected wave to the reflection point. The distance is measured.

Japanese Patent No. 4362631

    The first problem is that in the conventional pulse method and FMCW method, the output of electromagnetic waves becomes large and interferes with other communication systems. The reason is that, in the conventional FMCW or pulse method, a received signal level higher than the noise level is required to detect a reflected wave, so that the transmission output must be increased.

The second problem is that it is difficult to obtain accuracy. In FMCW, there is a time difference by measuring the frequency difference between the transmitted signal and the received signal, but the linearity of the FMCW frequency change is required, but since it is generated in analog, it realizes strict linearity It is difficult. Moreover, in order to obtain accuracy, it is difficult to obtain accuracy because a small frequency difference must be detected.
Further, in the pulse method, the pulse width cannot be made zero (delta function), so that it is difficult to accurately measure the propagation time.
Furthermore, the method using M-sequence signals is difficult to obtain accuracy only by obtaining the maximum correlation value.

  The present invention relates to an electromagnetic wave transmission signal such as a microwave, a millimeter wave, or light that is two-phase-phase modulated with an M-sequence code signal having a symbol time length of T seconds in a distance measuring device that uses electromagnetic waves. Hz) at a plurality of continuous frequencies, sequentially or unsteadily sending the signal from the antenna 10 to the space, and the antenna 10 or another antenna receives the signal reflected and scattered by the target or the like, A means for demodulating the received signal into a complex signal, and a bipolar RZ- having the same M-sequence code synchronized with the transmission M-sequence code signal and having the same pulse interval T as the symbol length T of the transmission signal The M-sequence pulse train signal, the pulse train signal obtained by delaying the pulse train signal with respect to the transmission M-sequence code by a delay time td, means for correlating the demodulated complex signal, and means for measuring the delay time td, Transmission signal The correlation and delay time are obtained by the same means as described above at each of a plurality of continuous frequencies with a frequency interval of 1 / T, and the measurement result is obtained from the correlation result obtained at each frequency and the delay time td. A distance measuring device characterized by measuring a distance to an object.

  In the above, the M-sequence code transmission signal and the pulse train signal are controlled by clocks synchronized with each other, and the delay time td is set to a multiple of an integer of the symbol time T, that is, td = q · T / p ( p: natural number, q: zero or positive integer), and td is changed digitally.

  In the above description, the distance measuring device is characterized in that td is obtained by counting the clocks whose period is T / p.

  In the distance measuring device, the reference minimum transmission frequency is a multiple of p / T, and the distance is measured by changing the frequency from the minimum transmission frequency every 1 / T (Hz). apparatus.

  A shift register having the same number of stages as the M-sequence code length, a code converter corresponding to the M-sequence code at each stage output, and a correlator provided with an accumulator that takes the sum of the outputs of each code converter are provided, A ranging device obtained by sampling the IQ demodulated signal at intervals of T seconds and inputting the sampled signal to the correlator.

  A shift register having a number of stages p times the M-sequence code length, a shift time of one stage being T / p seconds, and a code converter corresponding to the M-sequence code at each stage output are provided, and p-stage intervals (that is, (Corresponding to T seconds), a correlator comprising p accumulators that take the sum of the output of each code converter for each group is provided, and p-1 consecutive accumulators among the p accumulators. If the accumulator is non-zero, the output of the p / 2 accumulator out of p-1 accumulators (if p is an even number) or (p-1) / 2th (if p is an odd number) Is a correlator characterized in that the IQ demodulated signal is sampled at T / p second intervals and input to the correlator to obtain a correlation value.

  In the distance measuring apparatus, a signal folding circuit is provided between transmission and reception, or a reference reflector is provided in the vicinity of the antenna. That is, by measuring the phase / amplitude at the transmission point td = 0 and taking the ratio with the received signal from the reflection point based on this, the spectrum of the space can be obtained more accurately.

The present invention relates to a ranging imaging apparatus that uses electromagnetic waves such as light beams, and branches a light beam from a light source 1 that emits a coherent light beam into a first light beam and a second light beam,
The first light beam is two-phase-phase-modulated by an M-sequence code with a first phase modulator, and this phase-modulated light beam is further branched into a first modulated light beam and a second modulated light beam,
Irradiating the object with the first modulated light beam and applying the reflected first modulated light beam to the first photodetector;
Irradiating the reference reflector with the second modulated light beam and applying the reflected second modulated light beam to the second photodetector;
The frequency of the second light beam is displaced by a frequency shifter, and the second light beam, which is further frequency-shifted, has the same M-sequence code as the phase modulation of the first light beam, and two phases at the same timing. Phase-modulating, branching the phase-modulated light beam into a third modulated light beam and a fourth modulated light beam,
The object is irradiated with the third modulated light beam, the reflected third modulated light beam is applied to the first photodetector, and the reflected first modulated light beam and the reflected third light beam are reflected. A modulated light beam is mixed by a first photodetector, and a first difference frequency signal having a difference frequency shifted by the frequency shifter is detected,
The reference modulated reflector is irradiated with the fourth modulated light beam, the reflected fourth modulated light beam is applied to the second photodetector, and reflected by the reflected second modulated light beam. A fourth phase modulated light is mixed by a second photodetector, and a second difference frequency signal having a difference frequency shifted by the frequency shifter is detected;
A reflection distribution measuring device for detecting an IQ component of an object having a first difference frequency, that is, a complex frequency spectrum by an IQ signal demodulator using a second difference frequency signal as a local oscillation signal.

  In the reflection distribution measuring device, the frequency of the light beam from the light source 1 is changed in steps of 1 / (2T) (Hz) with respect to the symbol length T (Sec) of the M-sequence code, and a complex frequency spectrum is obtained at each frequency. A reflection distribution measuring device characterized by obtaining a reflection distribution function of the object from the complex frequency spectrum group

,
The first effect is that highly accurate distance measurement can be realized regardless of the distance.
The reason is that the transmission delay time is measured by counting the number of samplings by measuring the propagation delay time by taking the autocorrelation between the transmission signal modulated by the M-sequence signal of symbol time T and the reflected reception signal, and the transmission signal and the reflection The reflection coefficient function is displayed as a Fourier series based on the frequency domain spectrum obtained by measuring the phase difference and amplitude ratio of the received signal, and this correction can be combined with this correction for accurate distance measurement. This is because distance measurement can be performed with The frequency is currently the most accurate standard, and high-precision measurement can be easily performed by using a crystal oscillator or an oscillator compensated by GPS.

The second effect can be used without disturbing other communication systems when used outdoors and at short distances. That is, measurement can be performed within the range of weak radio waves by the Radio Law.
The reason is that the transmission signal power density level can be suppressed to a minimum by improving the signal-to-noise by the spread spectrum by the M-sequence signal and the correlation gain.

The third effect is that by shortening the symbol long time of the M-sequence code, the step width of the finite frequency is increased to reduce the number of steps, thereby reducing the measurement time and simplifying the hardware.
The reason is that in the distance measurement by Fourier transform, the maximum measurable length L is determined by the frequency step width Δω, and there is a relationship of L = 2π / Δω. Further, since the accuracy is determined by the bandwidth (maximum frequency−minimum frequency), Δω decreases when L is long, and if the accuracy is the same, the number of steps increases dramatically when L is long. By taking the autocorrelation of the transmission / reception signal according to the present invention, the observed reflected wave has an error range of delay time within +/− T / 2, that is, the metric space can be finite by the symbol time T. The Fourier series can be expanded in a discrete frequency spectrum with a large Δω, the reflection function can be tightened, and the frequency interval is 1 / T (Hz). Therefore, high accuracy can be achieved with a large frequency step. That is, if the accuracy is the same, the number of steps can be greatly reduced.

The fourth effect is that the signal processing time can be greatly reduced.
The reason for this is that by first calculating the presence or absence of reflection by correlation, calculation processing such as Fourier transform is performed only on the correlated part, and signal processing such as Fourier transform is not performed on the section without reflection, which is efficient. It is.

The fifth effect is that it is possible to reduce the influence of multipath, reflection from outside the target, and influence of aliasing, and it is possible to perform distance measurement with a high S / N ratio and high accuracy.
The reason is that, due to autocorrelation, the observed distance range is limited to a narrow range due to the symbol time T of the transmission signal, and the reflected signal outside the limited range is scattered by autocorrelation and can be ignored. Because it becomes. In addition, since the time integration is performed, the S / N ratio becomes high.

The sixth effect is that it is not easily influenced by other communication systems and ranging systems. In particular, there is no influence or interference from the same system using M series. The frequency can be reused.
The reason is that the M-sequence signal has a very strong autocorrelation, and other signals can be diffused and dropped to a negligible level.

As a seventh effect, measurement with a high S / N ratio is possible without being affected by reflection or scattering outside the measurement range.

FIG. 1 shows a configuration example of a microwave level meter. FIG. 2 shows an embodiment of the correlator of the microwave level meter. FIG. 3 shows an embodiment of an optical coherence tomography.

The present invention is a distance measuring apparatus that uses electromagnetic waves, and uses an electromagnetic wave transmission signal such as microwaves, millimeter waves, and light that are two-phase modulated with an M-sequence code signal having a symbol time of T seconds. In addition, by continuously changing the frequency at 1 / T (Hz) intervals, the spatial reflection distribution is measured as a frequency domain spectrum, and this is Fourier transformed to obtain the original spatial reflection distribution. .
The frequency corresponding to the distribution of reflection points in the finite space by evaluating the correlation value of the received signal returned after being reflected and scattered and the transmission signal of the symbol period T (Sec) and the same M-sequence pulse signal Domain spectrum is obtained. By correlating with the M-sequence pulse signal, the space can be finite and minimized, so that highly accurate distance measurement can be performed with a small number of steps.
The method of the present invention first obtains the correlation of the M series digitally, grasps the approximate distance digitally, obtains the deviation from the true value from the frequency domain spectrum described above, and performs high-precision measurement. It is characterized by a smaller number of steps.
Furthermore, by performing two-phase phase modulation with M-sequence codes and performing spread spectrum, the power density can be greatly reduced, and radio resources that are public resources can be effectively used. In addition, power integration has become possible through time integration to determine the correlation.
Another feature of the present invention is that, due to the characteristics of the M-sequence code, even if a plurality of distance measuring devices operate simultaneously at the same frequency, they do not interfere with each other.

  Next, in order to show the effectiveness of the present invention, it will be described below using mathematical formulas.

An electromagnetic wave transmission signal that is two-phase-phase modulated with an M-sequence code signal is expressed by the following equation.

  If the distance from the transmission point to the reflection point is r, the received signal returned from the reflection point is as follows. ω is the frequency of the electromagnetic wave radiated into the space, and ωi is the frequency after the reception frequency is converted by the frequency converter. C represents the propagation speed of the electromagnetic wave in the medium.

here
Is the reflection coefficient at the reflection point r.

  An M-sequence code pulse train signal having the same M-sequence code as the transmission M-sequence code signal and having a symbol time interval T seconds delayed by a delay time td (seconds) is expressed by the following equation.

The correlation Sδ of Equation 2 and Equation 3 is obtained.
Here, when the calculation is performed with the following substitutions for each variable, Equation 5 is obtained.

  As can be seen from Equation 5, Sδ is a frequency domain spectrum in a finite distance section, and a (r ′) is a function defined in a range of ± C · T / 2 around C · td / 2. r ′) · exp (−j · ω0 · r ′ / C) is expressed by a Fourier series 6 having ωd as the minimum period. Note that the actual distance r is (r '+ C / td) / 2.

  Here, an is given by the following equation (7).

Sδ is a value that can be directly measured as described later in the examples of the present invention. As for td, the clock can be counted from the difference between the clock timing at the time of transmission and the clock timing at the time of correlation, and can be easily and accurately known.
All the frequencies and clocks can be calculated by synchronizing the above with a sufficiently accurate reference oscillator, and the above equation can be established.

    R ′ vs. a (r ′) is obtained from the equations (6) and (7). By calculating r 'in steps sufficiently small for the required accuracy, r' vs. | a (r ') | is determined regardless of ω0. Since | exp (jω0 r · C) | is always 1 regardless of r ′, | a (r ′) | is determined only by the right side of Equation (6).

    The maximum value of | a (r ′) | is the position of the reflection point. Furthermore, in order to obtain accuracy, numerical accuracy of | a (r ') | is taken near the maximum value, and the point of d | a (r') | / dr '= 0 is obtained by Newton's method, etc. It is possible to obtain the position of a high reflection point.

    More

    Then, equation (7) is rewritten into equation (9) and does not explicitly include ω 0, thereby simplifying the calculation process.

  Furthermore, in equation (9), if p = 4, exp [j2πn · q / p] is a cycle of (1, j, -1, -j), and the sign conversion of the I and Q components of Sδ that is the result of the correlation And an is required only by replacement, and it is further simplified.

  Next, when the wavelength is very short, such as light, and the observation range is several tens of millimeters or less, the M-sequence code two-phase signal method is an effective solution for removing aliasing noise and noise outside the observation range. Explain that.

In measurement in units of microns with light, it is very important to increase the observation speed by making the measurement range finite and increasing the frequency step width. When the measurement range is limited by the M-sequence code, the symbol time is required to be very short. For example, if the symbol time is 10 pSec, the corresponding length is 1.5 mm. This is a reasonable value for measurements in microns.
This is because it seems that it is very difficult to obtain the correlation by sampling as in the case of microwave, so the problem of aliasing is solved by the method of autocorrelation as described below, and Improve signal-to-noise ratio.

This will be described with reference to FIG.
The present invention superimposes an optical signal 132 that is modulated with the same M-sequence code as the M-sequence two-phase modulated light beam 124 that irradiates the target with a signal 125 reflected from the target. This is a method for obtaining a correlation. When the two signals are correlated, the frequency difference signal 134 is detected from the detector output.
This frequency difference signal 134 includes information on reflection points in a finite section. Information on reflection points outside the finite interval is scattered as very high frequency noise. In order to extract information on the reflection points in the finite section, a means for creating a reference frequency difference signal 135 is provided. When the reference difference signal 135 is used as a local transmission signal and the frequency difference signal 134 from the reflector is IQ demodulated, information on reflection points in a finite section, that is, a frequency domain spectrum is obtained. By applying an inverse Fourier transform to this, the position of the reflection point can be obtained. Actually, the position and strength of the reflection point can be known by performing DFT or Fourier series expansion. In the case of DFT, further interpolation is required.
In the method of the present invention, since autocorrelation is complete, if the symbol length of the M sequence is T, the finite interval is T · C corresponding to 2T (the optical path is doubled in the case of reflection, so the interval is half) Becomes).

Hereinafter, description will be made using mathematical expressions.

When the signal 125 and the signal 132 are simultaneously input to the photodetector 7, they are mixed by the square characteristic of the photodetector to obtain a difference frequency signal 134 expressed by the following equation (10).
Here, the same symbols as those for the microwave level meter are used. Ie

: M-sequence code 1 or -1 (
)




R represents the distance between the reference reflector 105 and the reflection point of the observation object. td is the time delay due to the reference reflector.

  Similarly, the signal 127 and the signal 133 are incident on the photodetector 108 to obtain a difference frequency signal 135. The signal 127 and the signal 133 are reflected by a common reference reflector, and the delay time td is the same.

  Therefore, the output of the IQ demodulator 109 is the product of Equation 10 and Equation 11.

  Therefore, it has been found that, even in the case of light, Fourier transformation in a finite region can be obtained by taking autocorrelation, and the problem of aliasing can be solved.

  Hereinafter, means for solving the problem more specifically in accordance with hardware will be described.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.

    FIG. 1 shows a configuration example of a microwave level meter, 1 is an M-sequence code generator, 2 is a phase modulator, 3 is a frequency control unit, 4 is a numerically controlled oscillator, 5 is a multiplier, 6 is a frequency converter, 7 is a local oscillator, 8 is a bandpass filter, 9 is a transmission / reception separator, 10 is an antenna, 11 is a low noise amplifier, 12 is a frequency converter, 13 is an IQ demodulator, 14 is a carrier recovery unit, and 15 is a frequency converter. , 16 is a frequency control unit, 17 is a numerically controlled oscillator, 18 is an amplifier, 19 is an AD converter, 20 is a correlator, 21 is a signal processing unit, 22 is a display unit, and an external interface.

The M-sequence code generator 1 consists of a general M-sequence code generator consisting of a shift register and a feedback circuit or a memory storing the M-sequence code, and sequentially generates M-sequence code sequences corresponding to a clock with a period T Output. On the other hand, the frequency control unit 3 issues a frequency command to the numerically controlled oscillator 4. At the output of the multiplier 5, it is necessary to obtain a signal having a frequency step and a band necessary for ranging. When the multiplication factor of the multiplier 5 is U, the frequency step is 1 / (U · T) and the phase shift is (0, (2n + 1) π / U) at the output of the phase modulator 2. A numerically controlled oscillator 4 and a phase modulator 2 are configured. Since the multiplier 5 has a multiplication number U, the step frequency of the output of the multiplier 5 is 1 / T and the phase shift is (0, π).
The frequency converter 6 converts the frequency into a predetermined frequency. When the lowest frequency of the transmission frequency group is a multiple of p / T, when sampling is performed at intervals of T / p, the phase is always constant at the sampling point, and Equation 7 becomes Equation 8 and is simplified.
The local signal oscillator 7 used for the frequency converter 6 is used for both transmission and reception, thereby minimizing the influence on the measurement with respect to phase fluctuations caused by the PLL.
The output of the frequency converter 6 is radiated from the antenna 10 through the band filter 8 and the transmission / reception separator 9.

The reflected electromagnetic wave is received by the antenna 10, amplified by the low noise amplifier 11 through the transmission / reception separator 9, and frequency-converted by the frequency converter 12.
Note that the output frequency of the frequency converter 12 is the same as the output frequency of the multiplier 5. On the other hand, the output of the multiplier 5 is a two-phase phase-modulated wave. When this is doubled and divided by 2, a continuous wave having the output frequency of the multiplier 5 is obtained. The carrier reproducing unit 14 has this function. The carrier recovered signal is shifted by the frequency converter 15 by the same frequency as the clock frequency of the AD converter 19, amplified and applied as a local oscillation signal to the IQ demodulator 13, and has the same frequency as the clock signal of the AD converter 19. An IQ demodulated signal having a center frequency is obtained, amplified by an amplifier 18 separately for I and Q, and digitally converted by an AD converter 19 to obtain a digital baseband IQ signal having a center frequency of 0.
The digital baseband IQ signal is input to the correlator 20.
The IQ demodulator 13 uses an analog demodulator here, but the same effect can be obtained by using a digital IQ demodulator after analog-digital conversion.

The configuration of the correlator 20 is shown in FIG.
Correlator 20 is composed of a combination of X1 column multiplier 31 and X-1 column multiplier 32 corresponding to M-sequence codes 1 and -1. Each column multiplier has a shift register 33 in which data is sequentially shifted every clock and a signal output node between each register stage. When the sampling clock is at a T / p interval, each column multiplier (31or32) ) Has p registers and p output terminals. The X1 column multiplier of 31 uses the signal of the interstage node as an output signal as it is, and in the case of 32 X-1 column multipliers, the signal from the interstage is code-converted by the code converter 34 and output. Therefore, there is no calculation at each stage of the shift register 33, and very high-speed processing is possible.
The 35 I correlators have column multipliers (31 or 32) as many as the code length of the M-sequence code, and the code of each column multiplier 36 is provided to match the code of the transmission M-sequence code.
The p outputs of each column multiplier 36 are collected in the output order, applied to p−1 adders 37, and added. Since the p-th output group is not used for correlation determination, it is terminated by the terminator 38. This is because the output of the terminal located at the end may coincide with the code boundary of the received signal and may be indefinite, so it is not used for correlation determination. From this point, p needs to be 2 or more. The output of each adder 37 is the correlation between the M-sequence code pulse sequence at intervals of T seconds and the received M-sequence code signal.
The Q correlator 40 has the same configuration and operation as the I correlator 35, and outputs of p-1 adders 37 are obtained. The correlation is determined by summing the squares of the outputs of the adders 37 in the same order of the I and Q correlators 35 and 40.
When all of p−1 are non-zero and become larger than a predetermined value, it is determined that the correlation is strongest, and among the p−1 adders 37 of the I and Q correlators 35 and 40, The I and Q outputs of the central adder 37 are assumed to be a spectrum in a finite space expressed by Equation 8 when the delay time is td = q · T / p. q is a number obtained by subtracting the number of clocks corresponding to the length of the M-sequence code from the number of counts from the start of transmission to the count of clocks until the correlation is obtained.
In this way, by changing the transmission frequency and taking the delay time td and the I and Q outputs, that is, the complex frequency spectrum, a spatial reflection distribution can be obtained from Equation (8).

FIG. 3 shows the case where it is applied to light.
The present invention relates to a ranging imaging apparatus that uses electromagnetic waves such as light rays, and a means for branching a signal 121 from a light source 101 that emits a coherent light beam into a signal 122 and a signal 128, and an M code string phase modulator 102. Means for performing two-phase phase modulation with M-sequence code to make signal 123, means for branching signal 123 to signal 126 and signal 124, signal irradiating observation object 106 with signal 124, and signal reflected and scattered from observation object Means for capturing the signal 125, means for irradiating the reference reflector 105 with the signal 126 and capturing the reflected and scattered signal 127; means for shifting the frequency of the signal 128 by the frequency shifter 103 to obtain the signal 129; M-phase code phase modulator 104 performs two-phase phase modulation with an M-sequence code identical to and synchronized with the M-sequence code for signal 123 to obtain output signal 130; Means for irradiating the reference reflector 105 and capturing the reflected signal 131; means for branching the reflected signal 131 into a signal 132 and signal 133; means for simultaneously irradiating the photodetector 107 with the signal 125 and signal 132; Means for extracting the difference frequency signal 134 between the signals 125 and 132 from the detector 107, means for irradiating the photodetector 108 with the signals 127 and 133, and a difference frequency signal 135 between the signal 127 and signal 133 from the photodetector 108. And means for taking out the signal 135 as a local oscillation signal and IQ demodulating the signal 134 by the IQ demodulator 109 to obtain the I signal 136 and the Q signal 137, changing the frequency of the light beam from the light source 101, and the same object A frequency domain spectrum group is obtained by obtaining an IQ signal at each frequency for an object, and a fault of the observation object 106 is obtained by Fourier transform. Optical coherence tomography, which was characterized by obtaining a morphism distribution.

There is a possibility that it can be applied and used for the following purposes.
Microwave level meter
Automotive radar
General radar
Surveying
Optical coherence tomography
Industrial nondestructive inspection equipment

1 M-sequence code generator 2 Phase modulator 3 Frequency controller 4 Numerically controlled oscillator 5 Multiplier 6 Frequency converter 7 Local signal oscillator 8 Bandpass filter 9 Transmitter / receiver separator 10 Antenna 11 Low noise amplifier 12 Frequency converter 13 IQ demodulation 14 Carrier recovery unit 15 Frequency converter 16 Frequency control unit 17 Numerical control oscillator 18 Amplifier 19 AD converter 20 Correlator 21 Signal processing unit 22 Display unit / external interface unit 31 X1 column multiplier 32 X-1 column multiplier 33 Shift register 34 Code converter 35 I correlator 36 Multiplier 37 Adder 38 Terminator 39 Terminator 40 Q correlator 41 Terminator

Claims (9)

In a distance measuring device that uses electromagnetic waves, two-phase phase-modulated microwave, millimeter wave, light, and other electromagnetic wave transmission signals with an M-sequence code signal with a symbol time of T seconds are continuously transmitted at a frequency interval of 1 / T (Hz). Means for sequentially or unsteadily transmitting to the space at a plurality of frequencies, and receiving the signal reflected and scattered by the target signal etc. by the antenna or another antenna, and demodulating the received signal by IQ demodulation And a bipolar RZ-M sequence pulse train signal having the same M sequence code synchronized with the transmission M sequence code signal and having the same pulse interval T as the symbol length T of the transmission signal, And a means for correlating the pulse train signal obtained by delaying the pulse train signal with respect to a transmission M sequence code by a delay time td and the demodulated complex signal, a means for measuring the delay time td, and a frequency of the transmission signal, Zhou Correlation and delay time are obtained by the same means as described above at each of a plurality of continuous frequencies of several intervals 1 / T, and the distance to the measurement object is obtained from the correlation result and delay time td obtained at each frequency. Ranging device characterized by measuring 2. The M-sequence code transmission signal and the pulse train signal are controlled by clocks synchronized with each other, and the delay time td is a multiple of an integral number of the symbol time T, that is, td = q · T / A distance measuring device characterized by p (p: natural number, q: zero or positive integer) and td changed digitally. 3. The distance measuring device according to claim 1, wherein td is obtained by counting the clocks having a cycle of T / p. 4. The measurement according to claim 1, wherein the reference minimum transmission frequency is a multiple of p / T, and ranging is performed by changing the transmission frequency for each frequency 1 / T from the minimum transmission frequency. Distance device. A shift register having the same number of stages as the M-sequence code length, a code converter corresponding to the M-sequence code at each stage output, and a correlator provided with an accumulator that takes the sum of the outputs of each code converter are provided, 5. The distance measuring apparatus according to claim 1, wherein the IQ demodulated signal is sampled at intervals of T seconds and input to the correlator. A shift register having the number of stages p times the M-sequence code length and a code converter corresponding to the M-sequence code are provided for each stage output, grouped at p-stage intervals, and the sum of the outputs of each code converter for each group Correlator comprising p accumulators to be provided is provided, and among the p accumulators, p (when p is an odd number) or p when consecutive p-1 accumulators are non-zero or p -1 (when p is an even number) of the accumulator outputs, the output of the central accumulator is used as a correlation value, and the IQ demodulated signal is converted into T / p seconds. 6. The distance measuring device according to claim 1, wherein sampling is performed at intervals and the correlation value is obtained by inputting to the correlator. 7. The distance measuring device according to claim 1, wherein a signal folding circuit is provided between transmission and reception, or a reference reflector is provided in the vicinity of the antenna.
In a ranging imaging device using electromagnetic waves such as light rays, the light rays from the light source 1 that emits coherent light rays are split into a first light ray and a second light ray,
The first light beam is two-phase-phase-modulated by an M-sequence code with a first phase modulator, and this phase-modulated light beam is further branched into a first modulated light beam and a second modulated light beam,
Irradiating the object with the first modulated light beam and applying the reflected first modulated light beam to the first photodetector;
Irradiating the reference reflector with the second modulated light beam and applying the reflected second modulated light beam to the second photodetector;
The frequency of the second light beam is displaced by a frequency shifter, and the second light beam, which is further frequency-shifted, has the same M-sequence code as the phase modulation of the first light beam, and two phases at the same timing. Phase-modulating, branching the phase-modulated light beam into a third modulated light beam and a fourth modulated light beam,
The object is irradiated with the third modulated light beam, the reflected third modulated light beam is applied to the first photodetector, and the reflected first modulated light beam and the reflected third light beam are reflected. A modulated light beam is mixed by a first photodetector, and a first difference frequency signal having a difference frequency shifted by the frequency shifter is detected,
The reference modulated reflector is irradiated with the fourth modulated light beam, the reflected fourth modulated light beam is applied to the second photodetector, and reflected by the reflected second modulated light beam. A fourth phase modulated light is mixed by a second photodetector, and a second difference frequency signal having a difference frequency shifted by the frequency shifter is detected;
A reflection distribution measuring device for detecting an IQ component of an object having a first difference frequency, that is, a complex frequency spectrum by an IQ signal demodulator using a second difference frequency signal as a local oscillation signal.
In Claim 8, the frequency of the light beam from the light source 1 is changed in steps of 1 / (2T) (Hz) with respect to the symbol length T (Sec) of the M-sequence code to obtain a complex frequency spectrum at each frequency, A reflection distribution measuring device that obtains a reflection distribution function of the object from the complex frequency spectrum group.