JP5104425B2 - Distance measuring method and distance measuring device - Google Patents

Description

  The present invention combines the distance measurement by the FMCW method and the distance measurement by the monopulse, the long distance range is FMCW, the short distance range is the monopulse, and the distance measurement method that can be measured by a single device, and It relates to a measuring device.

Conventionally, techniques described in Patent Documents 1 and 2 below are known as distance measuring apparatuses using FMCW. Moreover, the technique described in the following patent document 3 is known as a distance measuring apparatus using a monopulse.
JP-A-7-159522 JP-A-6-94829 JP 2003-248054 A

  However, these distance measurement methods are independent methods, and there is no known method that combines them to measure the distance to an object by two methods. For example, FMCW is suitable for measuring long distance ranges, and monopulse is a suitable method for measuring short distance ranges. If the distance measuring device by FMCW and the distance measuring device by monopulse are provided separately and independently, the long distance range and the short distance range can be measured with high accuracy.

However, providing the above devices separately is not desirable because it is wasteful in terms of equipment.
Therefore, the present invention has been made to solve this problem, and the object of the present invention is to take advantage of the advantages of both methods by a completely new method, and to set the distance to an object with a common device. The purpose is to enable measurement by two methods. As a result, it is an object to enable distance measurement with high accuracy over a wide range without complicating the apparatus.

  According to the first aspect of the present invention, in a distance measuring method for measuring a distance to an object by a radar, a signal obtained by amplitude-modulating an FMCW signal whose frequency is continuously changed by a pulse as a carrier wave and a FMCW signal are superimposed and radiated as a radio wave. Receiving a reflected wave from the object, demodulating the received signal using the FMCW signal at the time of reception as a carrier wave, extracting a signal in the beat frequency band of the FMCW signal from the demodulated signal, A distance measurement method is characterized in that a first distance is measured from an extracted signal, and a second distance is measured from a pulse signal obtained by demodulation.

  Here, the FMCW signal is a signal obtained by frequency-modulating a carrier wave with a waveform such as a triangular wave or a sawtooth wave whose frequency changes regularly in time. The present invention is characterized in that the FMCW signal is a carrier wave. That is, the carrier wave is amplitude-modulated with a pulse and then transmitted without suppressing the carrier wave. In other words, the present invention is characterized in that a transmission signal is a superimposed signal of a signal obtained by amplitude-modulating an FMCW signal with a pulse and the FMCW signal. The present invention is characterized in that, at the time of demodulation, the reflected wave is received and the received signal is amplitude demodulated using the FMCW signal at the reception time as a demodulated carrier wave. By this amplitude demodulation, a signal obtained by modulating the pulse train with the cosine wave of the beat frequency and the cosine wave of the beat frequency is obtained (product of the cosine wave of the beat frequency and the pulse train function). The beat frequency is detected from the former beat frequency band component, and the first distance is measured from this beat frequency. This is the measurement of the first distance by FMCW. Since the latter signal includes a pulse train, that is, includes pulse rise time information, the propagation delay time is obtained from this time information and the pulse rise time at the time of transmission. The second distance is measured from the delay time. The present invention is characterized by this.

  When an FMCW signal is used as a carrier wave and amplitude-modulated with the pulse, the carrier wave may be transmitted with both sideband waves, or may be transmitted with the carrier wave and the lower sideband wave, or the carrier wave and the upper sideband wave. The method for detecting the beat frequency is arbitrary regardless of whether it is an analog method or a digital method. However, if FFT is used, a frequency component can be easily detected. The second distance is detected from a pulse train modulated with a cosine wave having a beat frequency. For example, a positive pulse train can be obtained by passing through a full-wave rectifier circuit. Of course, a full-wave rectifier circuit is not necessary when measuring the distance using only the positive polarity cycle. The repetition period of the pulse train may be set to be longer than the maximum propagation delay time determined from the measurable range. For example, if the maximum measurable range is 60 m in a round trip, the maximum propagation delay time is 0.2 μs, so the pulse repetition frequency can be set to a high frequency of about 5 MHz. On the other hand, since the beat frequency can be set to about 100 kHz, 50 pulses appear in one cycle of the cosine wave of the beat frequency. Since the pulse is amplitude-modulated with a cosine wave having a beat frequency, the amplitude of the pulse becomes small near the zero point of the cosine wave. However, distance measurement is possible even if only 25 pulses having a large amplitude among these 50 pulses are used. That is, since 25 pulses can be detected within 10 μs, sufficient detection accuracy can be obtained even if the object is a moving object.

  In the present invention, it is desirable to measure the second distance from the pulse signal after removing the beat frequency band of the FMCW signal from the signal obtained by demodulation. The second distance can be detected without removing the beat frequency band of the FMCW signal from the demodulated signal. If not removed, the demodulated baseband waveform is a waveform in which a pulse train whose amplitude changes with the cosine wave of the beat frequency is superimposed on the cosine wave of the beat frequency. Therefore, the pulse train can be extracted by changing the threshold value for extracting the pulse. For example, if one pulse can be detected within 10 μs, the second distance can be detected every 10 μs. Further, the measurement of the second distance every 10 μs is repeated for 100 ms, and a process such as setting the average value to the second distance is performed, thereby making it possible to measure the distance with high accuracy. Further, by extracting only a pulse train having a noise level or higher and saturating the amplitude with an amplifier, a pulse train having a constant amplitude can be obtained.

  In another aspect of the invention, the pulse is a signal obtained by amplitude-modulating a subcarrier having a frequency exceeding twice the maximum frequency of the frequency band of the pulse. The pulses need not necessarily be amplitude modulated with subcarriers. However, in this way, the pulse may be amplitude-modulated with a subcarrier, the modulated signal may be used as the pulse of the invention, and the FMCW signal may be amplitude-modulated with the pulse. In this case, the frequency band of the pulse and the frequency band of the FMCW signal can be separated. Therefore, distance measurement with higher accuracy is possible. As the signal obtained by modulating the subcarrier with a pulse, the lower sideband, the upper sideband, the double sideband, the subband added with the subcarrier, the upper sideband, and the double sideband can be used.

  In the present invention, it is desirable that the measurement range of the first distance is a far range than the measurement range of the second distance. This is because FMCW is suitable for measuring a long distance range, and monopulse is a suitable method for measuring a short distance range. However, the present invention is not limited to this application.

  The present invention provides a distance measuring device for measuring a distance to an object by a radar, a pulse generating device for generating a pulse, a frequency modulating device for generating an FMCW signal for continuously changing the frequency, and an output from the frequency modulating device. Receiving a reflected wave of a signal output from the transmitter, and a transmitter having an amplitude modulation device that modulates the generated FMCW signal with a pulse output from the pulse generator and outputs it together with the carrier of the FMCW signal. A demodulator that demodulates the received signal using the FMCW signal at the time of reception as a carrier wave, extracts a beat frequency band signal of the FMCW signal from the demodulated signal, and measures the first distance from the extracted signal A receiver having a first measuring device for measuring and a second measuring device for measuring a second distance from a pulse signal obtained by demodulation. A distance measuring apparatus according to claim.

  Since it is the same as the technical idea in the first method invention, the matters described in the description of the method also apply to the device invention.

In the device invention, the second measuring device preferably measures the second distance from the pulse signal after removing the beat frequency band of the FMCW signal from the demodulated signal.
In addition, another device invention includes a sub-amplitude modulation device that amplitude-modulates a subcarrier having a frequency exceeding twice the maximum frequency of the pulse frequency band with a pulse output from the pulse generator in the above device invention, The amplitude modulation device is a device that modulates the FMCW signal with a signal output from the sub-amplitude modulation device. Thereby, the band of the pulse and the band of the FMCW signal can be separated. Even if it is not separated, the apparatus can measure the first distance and the second distance as described above. The matters described in the above method invention can be applied to this apparatus.

  In another device invention, in the above device invention, the antenna, the amplitude modulation device, and the demodulation device have n systems, and each FMCW signal supplied to the amplitude modulation device of each system is sequentially phase-differed. A phase shifter that sequentially delays or advances by θ and supplies each FMCW signal supplied to the demodulator of each system with a phase difference θ, and a multiplexer that combines the outputs of the demodulator of each system, It is characterized by having. According to this apparatus, the radio wave radiation direction and the reception direction θ can be scanned. Further, the amount of rotation of the phase shifter can be reduced, and there is no need to demultiplex the output (carrier wave) of the frequency modulation device. Further, since the phase of the transmission signal is controlled by the phase of the carrier wave and the phase of the reception signal is controlled by the phase of the demodulated carrier wave, NF deterioration can be prevented.

  In the measurement apparatus, it is desirable that the measurement range of the first distance is a far range than the measurement range of the second distance.

  In the present invention, an FMCW signal is used as a carrier wave, the carrier wave is amplitude-modulated by a pulse, and the carrier wave is attached and transmitted. At the time of demodulation, the received signal is demodulated using the FMCW signal as a demodulated carrier wave. . Therefore, this method is a novel modulation method. Further, the distance measurement between the FMCW method and the pulse method can be performed by a common device, and the device becomes simple.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

ただし、α（ｔ）は、三角波の時間積分であり、瞬時位相を表す。ω_c は、ＦＭＣＷの基準周波数、すなわち、搬送波の周波数である。 Hereinafter, the principle of this method will be described.
The FMCW transmission signal is expressed by the following equation.

Here, α (t) is a time integral of a triangular wave and represents an instantaneous phase. ω _c is the reference frequency of the FMCW, that is, the frequency of the carrier wave.

ただし、また、g(t)は、パルス列信号である。 A feature of the present invention is that the FMCW of the formula (1) is used as a carrier wave and is subjected to pulse modulation with a monopulse. The modulated signal is expressed by the following equation.

However, g (t) is a pulse train signal.

この単一パルスだけの送信信号のスペクトルは、図１に示すものとなる。この送信信号を角周波数ω対時間特性で、誇張して表示すると、図２に示すような特性となる。すなわち、パルスが出力されている時間期間だけ占有帯域幅が広くなり、パルスが存在しない期間は、単一スペクトルが時間的に変動したものとなる。 When the signals represented by the above (1) and (2) are added and transmitted, the transmission signal at the transmission time t is expressed by the following equation.

The spectrum of the transmission signal with only a single pulse is as shown in FIG. When this transmission signal is exaggeratedly displayed with the angular frequency ω versus time characteristic, the characteristic is as shown in FIG. That is, the occupied bandwidth is widened only for the time period in which the pulse is output, and the single spectrum is temporally fluctuated during the period in which no pulse exists.

ただし、Δｔは、電波を放射してから対象物で反射されて、反射波が受信されるまでの遅延時間である。したがって、ｔ−Δｔは、送信時刻を意味する。 The reception signal at the reception time t when the transmission signal is expressed by the expression (3) is expressed by the following expression.

However, Δt is a delay time from when a radio wave is radiated until it is reflected by an object and a reflected wave is received. Therefore, t−Δt means a transmission time.

Next, when the received signal represented by the equation (4) is demodulated with the MFCW signal at the reception time t, the demodulated signal is represented by the following equation.

If only the lower sideband wave lower than ω _c is extracted from this signal, the lower sideband wave is expressed by the following equation.

ただし、ｋは、角周波数の増加係数で、三角波α(t) の傾きである。 The time derivative of α (t) −α (t−Δt), that is, the beat angular frequency Δω between FMCWs is expressed by the following equation.

Here, k is an increase coefficient of the angular frequency and is a slope of the triangular wave α (t).

第１項は、ＦＭＣＷ間のビート信号、第２項はそのビート信号をパルス変調した信号となる。ω_c Δｔは、対象物の移動速度に依存する値であるが、d(ω_c Δｔ)/dt≪Δωを満たすように、ω_c ，ｋを設定することが可能である。したがって、第１項をＦＦＴにより周波数スペクトルを求める場合には、Δωのスペクトルだけを検出することができる。 Therefore, Equation (6) becomes Equation (8).

The first term is a beat signal between FMCWs, and the second term is a pulse-modulated signal of the beat signal. ω _c Δt is a value depending on the moving speed of the object, but ω _c , k can be set so as to satisfy d (ω _c Δt) / dt << Δω. Therefore, when obtaining the frequency spectrum by FFT of the first term, only the spectrum of Δω can be detected.

g(t −Δｔ) を幅τのパルス関数とする。このスペクトルは、図１に示すように、Δωを中心とするsin(ω)/ωの関数となる。一方、第１項は、角周波数Δωの線スペクトルとなる。したがって、（８）式のスペクトルは、図１に示すものとなる。レーダが、方位角を走査するものを想定すると、対象物の方位角分布にしたがって、Δωは走査時間と共に変化する。したがって、図１のスペクトルが、時間的に変動するΔωにしたがって、時間的に平行移動したものとなる。 Next, consider the spectrum of the second term. When d (ω _c Δt) / dt << Δω is satisfied, ω _c Δt is a constant phase. Therefore, when considering the spectrum, this component is ignored and the spectrum of the signal of the following equation is considered.

Let g (t −Δt) be a pulse function of width τ. As shown in FIG. 1, this spectrum is a function of sin (ω) / ω centered on Δω. On the other hand, the first term is a line spectrum having an angular frequency Δω. Therefore, the spectrum of equation (8) is as shown in FIG. Assuming that the radar scans the azimuth angle, Δω varies with the scanning time according to the azimuth angle distribution of the object. Therefore, the spectrum in FIG. 1 is temporally translated according to Δω that varies with time.

Next, the separation of the first term and the second term will be considered. The maximum value of Δω is determined in advance by FMCW. Its value and Δω _M. Then, the existence range of the beat angular frequency Δω is 0 to Δω _M.

Now, let the pulse signal g (t) be a UWB pulse with a pulse width τ of 1 ns. 1 / τ is 1 GHz, and the bandwidth is about 1.2 GHz. In addition, the measurable range by this monopulse is set to 0 to 15 m (30 m in a round trip). The carrier angular frequency ω _c is assumed to be 2π × 24.175 GHz. Further, the measurable range by FMCW is set to 300 m (600 m in a round trip), and the beat angular frequency Δω _M corresponding to the maximum value 600 m is set to 2π × 100 kHz. Then, only the 100 kHz width in the band of 2 GHz width between the first zeros in FIG. 1 is extracted. That is, in the center of the spectrum of the pulse, a spectrum having a width of 1/2000 of the width between zeros of the spectrum and 1 / 2,000 of the bandwidth of the pulse is superimposed on the beat angular frequency Δω. It will be. Since the spectrum of the pulse of this width is uniform, it can be regarded as white noise. Therefore, about 12,000th of the power of the pulse is uniformly added to each beat frequency Δω, so that only the beat angular frequency Δω can be separated by determining the threshold value with FFT. Become.

Next, the remaining band (hereinafter referred to as “residual band”) obtained by extracting the band 0 to Δω _M from the signal of the equation (8) will be considered. The signal of the remaining band is expressed by the second term of the equation (8). Only the band of 0 to 100 kHz, which is 1 / 1,000 of the 1.2 GHz band, is removed. Since only the low frequency component of 100 kHz in the pulse signal is removed, the pulse waveform is not affected. The second term of the equation (8) is obtained by amplitude-modulating the pulse train signal g (t) with a cosine wave having a beat frequency Δω. Therefore, it is possible to extract the pulse train g (t) at the antinode portion of the cosine wave. Therefore, since the pulse phase can be measured accurately, the distance can be measured from the delay time of the pulse. Further, the period of the cosine wave of the beat frequency is 10 μs, and if the pulse repetition frequency is 5 MHz, 50 pulses exist within this 10 μs. Therefore, many pulses can be detected even if not all 50 pulses can be detected in a period of 10 μs.

Next, the configuration of the transmitter 1 is shown in FIG. The transmitter 1 mainly includes a pulse generator 10, a triangular wave generator 12, a carrier wave generator 14, a frequency modulator 16, an amplitude modulator 18 (mixer), a multiplexer 19, an amplifier 20, and an antenna 22. Yes. The pulse generator 10 generates a pulse having a pulse width of 1 ns and a repetition frequency of 5 MHz. The triangular wave generator 12 generates a triangular wave having a period of 500 kHz. The carrier wave generator 14 generates a cosine wave having a frequency of 24.175 GHz. The frequency modulator 16 is a VOC (voltage controlled oscillator) that frequency-modulates the carrier wave cos (ω _c t) with a triangular wave. The amplitude modulator 18 amplitude-modulates the pulse signal using the FMCW signal that is the output of the frequency modulator 16 as a carrier wave. The multiplexer 19 superimposes the signal modulated by the amplitude modulator 18 and the FMCW signal of the frequency modulator 16. If the amplitude modulator 18 transmits a modulated signal with an FMCW signal as a carrier wave, the multiplexer 19 is unnecessary.

  The output signal s1 of the frequency modulator 16 is a signal represented by equation (1). The amplitude modulator 18 modulates the amplitude of the pulse signal g (t) using the FMCW of equation (1) as a carrier wave. Then, the output signal s2 of the multiplexer 19 is a signal expressed by equation (3). This signal is amplified by the amplifier 20 and radiated from the space to the object as a radio wave by the antenna 22.

Next, the configuration of the receiver 2 will be described. The receiver 2 mainly includes an antenna 30, an amplifier 32, a demodulator 34 (mixer), low-pass filters 35 and 36, a fast Fourier transformer (FFT) 38, a high-pass filter 40, a full-wave rectifier circuit 41, and a phase difference detector 42. Consists of. The signal s4 amplified by the amplifier 32 by the reflected wave from the object received by the antenna 30 becomes a signal expressed by the equation (4). Next, the demodulator 34 demodulates this signal using the FMCW signal at the reception time t expressed by the equation (1) as a demodulated carrier wave. The demodulated signal s5 is a signal expressed by the equation (5). This signal s5 is extracted by the low-pass filter 35 and only the lower sideband wave having a frequency lower than the angular frequency ω _c is obtained as a signal s6 expressed by the equation (6). This signal s6 becomes the signal s7 represented by the first term of the equation (8) by the low-pass filter 36. The signal s7 is Fourier transformed by the FFT 38, and the spectrum of the signal s7 is calculated. As a result, the frequency Δω of the beat signal between the FMCWs is detected. The delay time Δt can be determined from the beat angular frequency Δω by the equation (7), and the round trip distance from the Δt to the object can be obtained.

  Further, the signal s6 is obtained by the high-pass filter 40 as the signal s8 represented by the second term of the equation (8). This signal s8 is input to the full-wave rectifier circuit 41, the output of the circuit 41 is input to the phase difference detector 42, and the time difference (phase difference) from the pulse input from the pulse generator 10 is obtained. It is done. The signal s8 is a signal whose pulse train is amplitude-modulated with cos (Δωt). By inputting this into the full-wave rectifier circuit 41, it is possible to obtain a positive polarity pulse train that is amplitude-modulated by | cos (Δωt) |. The output of the phase difference detector 42 represents the measurement distance by monopulse. The value obtained by dividing the delay time of the pulse by the speed of light is the round trip distance to the object. In the vicinity of the zero point of cos (Δωt), the amplitude of the pulse becomes small. However, in other sections, a pulse with a large amplitude is obtained, so that there is no problem in distance measurement.

  In this way, the distance measurement range by FMCW is 300 m (round trip 600 m) and the distance measurement range by pulse is 15 m (round trip 30 m), so that it is possible to accurately measure a long distance and a short distance.

  If the range of 600 m in the round trip is measured with an accuracy of 0.6 m, since the maximum beat frequency is 100 kHz, the frequency resolution needs to be 0.1 kHz. Therefore, if FFT of 2048 points and 0.1 kHz sampling is used, the FFT time window is 10 ms. When the signal s7 in the time window of 10 ms is sampled at 2048 points (4.88 μs interval) and FFT is performed, a spectrum of 2048 points is obtained in a range of −102.4 kHz to 102.4 kHz at 0.1 kHz intervals. It is. Therefore, this FFT is equivalent to that passed through a low-pass filter having a cutoff frequency of 204.8 kHz. Therefore, the low-pass filters 35 and 36 are not necessary, and the demodulated baseband signal s5 expressed by the equation (5) may be directly FFTed.

  The signal s6 expressed by the equation (8) has a waveform in which a pulse train of g (t−Δt) amplitude-modulated with Ecos (Δωt) is superimposed on the Dcos (Δωt) waveform. That is, a pulse having a pulse width of 1 ns and amplitude of 5 ns, which is amplitude-modulated by the cosine wave, is superimposed on a cosine wave having a maximum of 100 kHz. Therefore, if a low frequency component of 100 kHz or less is removed from the signal s6 by the high-pass filter 40, only the first term of the equation (8) is removed, and the pulse train of only the second term of the equation (8) is extracted. can do. Further, since the entire equation (8) is a pulse train as described above, the amplitude of the pulse is large near the antinode of the cosine wave cos (Δωt) without removing the beat frequency band, and the leading value of the pulse. Is also big. Therefore, with respect to the waveform of Dcos (Δωt) that is a beat frequency component, the leading value of the pulse is prominent near the antinode. Therefore, since a pulse train can be extracted, the high-pass filter 40 for removing the beat frequency band is not necessarily required. In addition, the full-wave rectifier circuit 41 is also used to measure a pulse train in the negative polarity region of cos (Δωt) for distance measurement. Therefore, if only the pulse train in the positive polarity region of cos (Δωt) is used, the full-wave rectifier circuit 41 is not necessarily required.

Note that g (t) cos [ω _c t + α (t)] in the transmission signal S2 (Equation (3) above) is a double-sided wave of the pulse signal, which is obtained from ω _c + Δω _M. Only a small signal may be extracted and transmitted as a lower sideband. Conversely, only a signal larger than ω _c may be extracted and transmitted as an upper side band. Since the spectrum of g (t) only shifts at a frequency of ω _c + FMCW, even a single sideband only has no effect on demodulation.

  In the second embodiment, the distance measurement apparatus of the first embodiment can scan the radiation and reception direction of radio waves. FIG. 4 shows the configuration. The same components as those in FIG. 1 are denoted by the same reference numerals, and the symbols “a”, “b”, and “c” are appended to the end of the same component symbols for each system. In FIG. 4, three transmission / reception systems are illustrated, but actually, the number of systems n is arbitrary. In the apparatus of this embodiment, the transmitting antenna and the receiving antenna are shared. The apparatus according to the present embodiment includes transmission / reception antennas 52a, 52b, and 52c, and circulators 51a that transmit transmission signals from the transmitters 1a, 1b, and 1c to the antennas, and transmit reception signals from the antennas to the receivers 2a, 2b, and 2c, 51b and 51c. In addition, this apparatus includes phase shifters 50a, 50b, and 50c that shift the output signal of the frequency modulator 16 by the same phase + θ and −θ. For modulation, the FMCW carrier is sequentially shifted by + θ, and for demodulation, the FMCW carrier is sequentially shifted by −θ. Therefore, the output signal s1a of the multiplexer 19a is as follows.

一般的には、第ｎ系統での送信信号ｓ２ｎは、次式となる。

すなわち、アンテナの配列面の法線に対する角度θで電波を放射する時（ただし、θの正方向は、アンテナ５２ａでの法線からアンテナ５２ｂへ向かう方向とする）、アンテナ系統がａ、ｂ、ｃとなるに従って、位相をθづつ遅らせる。この時、θ方向に進行する電波は、同一位相の平面となる。逆に、θ方向からアンテナに入射する受信電波の信号は、アンテナ系統がａ、ｂ、ｃとなるに連れて、位相がθづつ進む。

In general, the transmission signal s2n in the n-th system is expressed by the following equation.

That is, when radio waves are radiated at an angle θ with respect to the normal of the antenna array surface (where the positive direction of θ is the direction from the normal at the antenna 52a toward the antenna 52b), the antenna system is a, b, As c is reached, the phase is delayed by θ. At this time, radio waves traveling in the θ direction are planes having the same phase. Conversely, the received radio wave signal incident on the antenna from the θ direction advances in phase by θ as the antenna system becomes a, b, and c.

次に、このｎθをキャンセルするには、第ｎ系統のＦＭＣＷの復調搬送波を、次式の信号にする必要がある。

このとき、復調後の信号の信号ｓ５は、次式となる。

このように各アンテナ系統での位相差θをキャンセルとして、全てを同相とすることができる。 That is, the n-th system received signal s4n is expressed by the following equation.

Next, in order to cancel this nθ, the demodulation carrier of the n-th FMCW needs to be a signal of the following equation.

At this time, the signal s5 of the demodulated signal is expressed by the following equation.

In this way, the phase difference θ in each antenna system can be canceled and all can be in phase.

  Next, the signals s5a to s5b are synthesized by the multiplexer 53. Since the values of the coefficients D and E in the equation (14) are different in each system, the coefficients after synthesis are changed to D and E again. The output signal s6 of the multiplexer 53 is expressed by equation (6). The signal s6 is input to the circuit A in FIG. That is, it inputs into the low pass filter 35 of FIG. The subsequent processing is the same as in the first embodiment.

  In this way, the phase shift amount of the phase shifter can be reduced by using the phase shifters 50a to 50c as cascade connection. In addition, the phase shift of the FMCW signal that is a carrier wave is changed without directly changing the phase shift of the transmission signal and reception signal of each antenna system during modulation and demodulation. There is no deterioration.

In this embodiment, the pulse signal s3 in the first and second embodiments is not a baseband signal but a signal whose band is shifted by a subcarrier. That is, as shown in FIG. 5, the output signal S3 of the pulse generator 10 is amplitude-modulated by the amplitude modulator 24 (mixer) with the output of the subcarrier generator 26, and the output signal s9 is The input of the modulator 18 is used. That is, the subcarrier cos (ω _s t), the pulse width 1ns pulse generator 10, a signal amplitude-modulated by the output signal s3 cycle 5MHz to s9. However, ω _s is a frequency higher than the pulse signal bandwidth of 1.2 GHz, for example, 1.4 GHz. This signal is expressed by the following equation.

この（１５）式の信号を、上記のパルス信号g(t)と見做して、実施例１と同様に変調して送信すると、送信信号は、次式となる。

When the signal of the equation (15) is regarded as the pulse signal g (t) and modulated and transmitted in the same manner as in the first embodiment, the transmission signal is expressed by the following equation.

また、（４）式で表される受信信号ｓ４は、次式で表される。

また、ＦＭＣＷ信号の復調した後の信号の下側帯波は、次式となる。すなわち、ローパスフィルタ３５で抽出された信号は次式となる。

Further, the received signal s4 expressed by the equation (4) is expressed by the following equation.

Further, the lower sideband of the signal after demodulating the FMCW signal is given by the following equation. That is, the signal extracted by the low-pass filter 35 is represented by the following equation.

Furthermore, the high-pass filter 40 extracts only frequencies above the maximum beat angular frequency Δω _M. That is, when the second term of the equation (18) is extracted, a signal of the following equation is obtained.

The frequency band of the first term of the equation (19) is 0 to Δω _M , and in the above example, is the 100 kHz band. In the second term, the band 1.2 GHz of the pulse signal g (t) has a subcarrier frequency of 1.4 GHz + beat angular frequency Δω and is arranged on both sides thereof. Therefore, the first term and the second term are not superimposed in the frequency domain. As a result, in the measurement of the first distance by FMCW, measurement with high accuracy is obtained without being affected by the pulse.

  In order to obtain a pulse signal, the second term of equation (18) may be extracted by the high-pass filter 40 and further demodulated by the sub-demodulator 44 using the sub-carrier. Thereby, since the second term of the formula (8) in the first embodiment is obtained, the subsequent processing is the same as in the first and second embodiments.

Note that (16) of _{g (t) cos (ω s} t) is the both side band of the spectrum of the pulse, the angular frequency omega _s following lower sideband, or only side bands above omega _s It may be. Similarly, when modulating by FMCW, only one sideband may be used in addition to the doubleband.
In the above embodiment, distance measurement has been described, but the present invention can also be used for azimuth measurement.

  The present invention can be used for distance measurement of a long distance range and a short distance range.

The characteristic view which showed the spectrum of the transmission signal of the specific one Example apparatus of this invention. The characteristic view which showed the relationship between the frequency and time in the modulation method which concerns on the Example apparatus. The block diagram which showed the structure of the Example apparatus. The block diagram which showed the structure of the distance measuring device which concerns on the specific Example 2 of this invention. The block diagram which showed the structure of the distance measuring device which concerns on the specific Example 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Pulse generator 18 ... Modulator 34 ... Demodulator

Claims (9)

In the distance measurement method that measures the distance to the object by radar,
By the pulse, the FMCW signal whose frequency is continuously changed is amplitude-modulated as a carrier wave and the FMCW signal is superimposed and radiated as a radio wave,
The reflected wave from the object is received, the FMCW signal at the time of reception is used as a carrier wave, and the received signal is demodulated,
Extracting the beat frequency band signal of the FMCW signal from the demodulated signal, measuring the first distance from the extracted signal,
A distance measuring method comprising measuring a second distance from a pulse signal obtained by demodulation.   2. The distance measurement according to claim 1, wherein the second distance is measured from a pulse signal obtained by removing a beat frequency band of the FMCW signal from the signal obtained by the demodulation. Method.   3. The distance measuring method according to claim 1, wherein the pulse is a signal obtained by amplitude-modulating a subcarrier having a frequency exceeding twice the maximum frequency of the frequency band of the pulse.   4. The distance measuring method according to claim 1, wherein the measurement range of the first distance is a far distance range than the measurement range of the second distance. 5. In a distance measuring device that measures the distance to an object with a radar,
A pulse generator for generating pulses;
A frequency modulation device for generating an FMCW signal for continuously changing the frequency;
An amplitude modulator that modulates the FMCW signal output from the frequency modulator as a carrier wave using a pulse output from the pulse generator and outputs the carrier wave together with the carrier of the FMCW signal;
A transmitter having
A demodulator that receives a reflected wave of the signal output from the transmitter and demodulates the received signal using the FMCW signal at the time of reception as a carrier;
A first measuring device for extracting a signal in the beat frequency band of the FMCW signal from the demodulated signal and measuring a first distance from the extracted signal;
A receiver having a second measuring device for measuring a second distance from a pulse signal obtained by demodulation;
A distance measuring device comprising:   6. The distance measurement according to claim 5, wherein the second measuring device measures a second distance from a pulse signal after removing a beat frequency band of the FMCW signal from the signal obtained by the demodulation. apparatus. A sub-amplitude modulation device that amplitude-modulates a subcarrier having a frequency exceeding twice the maximum frequency of the frequency band of the pulse with a pulse output from the pulse generation device;
The distance measuring device according to claim 5 or 6, wherein the amplitude modulation device is a device that amplitude-modulates an FMCW signal with a signal output from the sub-amplitude modulation device. The antenna, the amplitude modulation device, and the demodulation device have n systems,
Each FMCW signal to be supplied to the amplitude modulator of each system is sequentially delayed or advanced by the phase difference θ, and each FMCW signal to be supplied to the demodulator of each system is sequentially advanced or delayed by the phase difference θ. And
A multiplexer that multiplexes the outputs of the demodulator of each system;
The distance measuring device according to claim 5, wherein the distance measuring device includes:   9. The distance measuring device according to claim 5, wherein the measurement range of the first distance is a far distance range than the measurement range of the second distance. 10.

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