JP5340212B2 - Distance measuring device and distance measuring method - Google Patents

Description

  The present invention relates to an apparatus for transmitting and receiving a signal between two transmission / reception apparatuses and measuring a distance between the two transmission / reception apparatuses.

As an apparatus for measuring the distance to an object that reflects electromagnetic waves, an apparatus described in Patent Document 1 is known. This device forms a phase-locked loop between a transmission / reception device and a reflection object, and measures the distance from the synchronization frequency at that time.
Further, as in Patent Documents 2 and 3 invented by the present inventor, two transmitting / receiving devices are used as one set, a phase-locked loop is formed between the two transmitting / receiving devices, and several hundreds of square waves of several MHz are generated. There is known an apparatus for detecting a phase delay of a rectangular wave of about several MHz on a high frequency carrier wave of several GHz.

JP2004-198306 JP2008-032535 JP2008-122255A

However, the method disclosed in Patent Document 1 detects a frequency that is synchronized between the transmission signal and the reception signal of the reflected wave, and measures the distance between the transmitter and the reflector from the frequency. Is the method. There is a problem that it is difficult to detect the frequency to be synchronized by sequentially changing the frequency. Further, in the methods of Patent Documents 2 and 3, since a phase-locked loop is used between two transmission / reception apparatuses, the circuit configuration becomes complicated.
SUMMARY OF THE INVENTION An object of the present invention is to provide a distance measuring device and a distance measuring method with a simple structure and high accuracy.

  1st invention consists of a 1st transmission / reception apparatus and a 2nd transmission / reception apparatus, The distance measurement apparatus which measures the distance between a 1st transmission / reception apparatus and a 2nd transmission / reception apparatus WHEREIN: A 1st transmission / reception apparatus is a 2nd transmission / reception apparatus. A first transmission antenna that transmits a signal toward the first reception antenna, a first reception antenna that receives a signal from the second transceiver, a first reference oscillator that outputs a first reference signal having a predetermined reference frequency, and a first reference oscillator Modulation that outputs to the first transmitting antenna a transmission signal having a first state and a second state in which the frequency or phase of the carrier wave is changed every half cycle of the first reference signal based on the first reference signal output by , A first demodulator that demodulates a transmission signal output from the modulator by a received signal received by the first receiving antenna, and periods of two different states relating to frequency or phase in the signal demodulated by the first demodulator A distance calculation device that obtains a distance based on the length of at least one of the periods, and the second transmission / reception device receives a signal transmitted from the first transmission / reception device and transmits the signal to the first transmission / reception device. , A second demodulator that demodulates the first state and the second state from the received signal received from the second antenna, and the signal output from the second demodulator is the first state and the second state. A second reference oscillator that outputs a second reference signal whose frequency and phase are controlled so that the reception periods of the states are equal, a return carrier oscillator that outputs a return carrier of a predetermined frequency, and an output of the second reference oscillator For each half cycle of the second reference signal, the second antenna receives the signal so that the received signal of the second antenna is output to the second demodulator and the return carrier wave output from the carrier oscillator is output to the second antenna. Switching between transmission and off And vessels, is a distance measuring apparatus characterized by having a.

  In the present invention, the first transmitting antenna and the first receiving antenna of the first transmission / reception apparatus do not necessarily have to be independent antennas. For example, by using a circulator or a duplexer, a configuration may be adopted in which one antenna for both transmission and reception is provided in the first transmission / reception device. The second antenna of the second transmission / reception device is composed of one antenna that can be switched between transmission and reception. The modulator, the first demodulator, the second demodulator, the carrier wave oscillator, the first reference oscillator, and the second reference oscillator optionally include an amplifier. The two different states relating to the frequency or phase in the signal demodulated by the first demodulator may coincide with the frequency or phase in the first state and the frequency or phase in the second state in the transmission signal. And it doesn't have to match. Since the transmission signal is a binary-modulated signal, a signal obtained by demodulating the transmission signal with a return carrier wave can obtain a binary state with respect to frequency or phase.

  In the present invention, the first state and the second state of the transmission signal output from the modulator of the first transmission / reception device use FSK modulation in which the frequency of the carrier wave is different or PSK modulation in which the phase of the carrier wave is different. Can do.

  The second invention transmits a signal from the first transmission / reception device to the second transmission / reception device, transmits a signal from the second transmission / reception device to the first transmission / reception device, and based on the transmission signal and the reception signal in the first transmission / reception device. In the distance measuring method for measuring the distance between the first transmission / reception device and the second transmission / reception device, based on the first reference signal from the first transmission / reception device, the frequency of the carrier wave or every half cycle of the first reference signal A transmission signal having a first state and a second state whose phases are changed is transmitted to the second transmission / reception device, and the second transmission / reception device demodulates the reception signal from the first transmission / reception device, and the first state The second state is detected, and a return carrier wave having a predetermined frequency is transmitted to the first transmitter / receiver only during a half-cycle period in which the reception periods of the first state and the second state are equal. Send signal from second transceiver Demodulating the return carrier wave signal, a distance measuring method for determining the distance based on the length of the at least one period among the periods of the two different states regarding the frequency or phase of the demodulated signal. In the first transmission / reception apparatus, the two different states relating to the frequency or phase in the signal obtained by demodulating the transmission signal by the return carrier are the frequency or phase in the first state and the frequency or phase in the second state in the transmission signal. , May or may not match. Since the transmission signal is a binary-modulated signal, a signal obtained by demodulating the transmission signal with a return carrier wave can obtain a binary state with respect to frequency or phase. The distance can be measured based on the length of at least one of the periods in the binary state. Of course, the average value of the distances obtained from the lengths of the periods of the two states may be used as the distance to be obtained. Further, as will be described later, the distance can also be obtained from the absolute value of the difference between the periods.

  Also in this method invention, the first state and the second state of the transmission signal output from the modulator of the first transmitting / receiving device are FSK modulation in which the frequency of the carrier wave is different or PSK modulation in which the phase of the carrier wave is different. Can be used.

  In the present invention, the transmission signal from the first transmission / reception device to the second transmission / reception device is a signal having a first state and a second state in which the frequency or phase of the carrier wave is changed every half cycle of the first reference signal. . The transmission signal is demodulated in the second transmission / reception device, and the first state and the second state are detected. Then, a return carrier wave having a predetermined frequency is transmitted from the second transmission / reception device to the first transmission / reception device only during a half cycle in which the reception periods of the first state and the second state are equal. In the first transmission / reception device, the transmission signal from the first transmission / reception device is demodulated by the return carrier wave received from the second transmission / reception device. Then, the distance is obtained based on the length of the period of the first state or the second state in the demodulated signal. Thus, in the present invention, the half-cycle period in which the reception periods of the first state and the second state of the first transmission / reception device are equal is the electromagnetic wave length of the round-trip transmission path length between the first transmission / reception device and the second transmission / reception device. In the period delayed by the propagation time necessary for propagation, the return carrier wave is received by the first transmitting / receiving device. Therefore, two different states, which are demodulation of the second state and the first state, are detected by demodulating the transmission signal consisting of the second state preceding by delay time + 1 period / 4 and the first state following this by the return carrier wave. Is done. At this time, in two different states, the longer the delay time, the shorter the period of the state corresponding to the second state, and the longer the period of the state corresponding to the first state. The distance between the first transmitter / receiver and the second transmitter / receiver can be obtained from the length of at least one of the two states. Further, the distance can be obtained from the average value of the period of the first state and the period of the second state after demodulation. In these cases, since the length of the period of the first state, that is, the half cycle period is included in the measurement value, it is necessary to correct the measurement value by this half cycle period. Further, the distance can be obtained from the absolute value of the difference between the period of the first state and the period of the second state after demodulation. In this case, since the half-cycle period included in each measurement value is canceled, the distance can be obtained more accurately. If the first state after demodulation is defined as the state having the longer period as the state, the distance is obtained not by the absolute value of the difference but by the value obtained by subtracting the period of the second state from the period of the first state. Can do. In this way, since a delay signal synchronized with the first reference signal can be obtained, the distance can be accurately measured.

  In the first invention, since the second transmitting / receiving apparatus uses a common antenna for switching between reception and transmission, the structure is simplified. In addition, since the frequency and phase of the second reference signal are controlled using the switch so that the reception periods of the first state and the second state of the signal received by the second transmission / reception device are equal, With this structure, the first reference signal generated by the first transmitter / receiver can be synchronized with the received signal at the second transmitter / receiver with a delay of one cycle / 4. Then, in synchronization with the second reference signal, a return carrier wave is output in a half-cycle period in which the reception periods of the first state and the second state are equal. Thereby, the structure can be simplified and an accurate distance can be measured.

The block diagram of the 1st transmitter / receiver of the distance measuring device which concerns on the specific Example 1 of this invention. The block diagram of the 1st transmission / reception apparatus of the distance measuring device which concerns on Example 1. FIG. 4 is a timing chart for explaining the operation of the distance measuring apparatus according to the first embodiment.

  Hereinafter, specific embodiments of the present invention will be described with reference to block diagrams. The present invention is not limited to the following examples.

  FIG. 1 is a configuration diagram of the first transmission / reception device 100. The first reference oscillator 10 is an oscillator that oscillates a 1 MHz square wave first reference signal S1. The first reference signal S1 is input to the base terminal of the transistor Tr1 that is a gate circuit, and the inverted first reference signal S2 by the inverter 11 of the first reference signal S1 is input to the base terminal of the transistor Tr2 that is a gate circuit. ing. The first sine wave oscillator 12 is an oscillator that oscillates a first modulation signal S3 having a sine wave of 20 MHz. The second sine wave oscillator 13 is an oscillator that oscillates a 120 MHz sine wave second modulation signal S4. The first modulation signal S3 is input to the collector terminal of the transistor Tr1, and the second modulation signal S4 is input to the collector terminal of the transistor Tr2. The emitters of the transistors Tr1 and Tr2 are connected to the modulation signal input terminal of the modulator 15. A carrier wave which is a 180 MHz sine wave output from the carrier wave oscillator 14 is input to the carrier wave input terminal of the modulator 15.

  The transistors Tr1 and Tr2 are alternately turned on and off every half cycle of the first reference signal S1. Therefore, a 20 MHz first modulation signal S3 and a 120 MHz second modulation signal S4 are alternately input to the modulation signal input terminal of the modulator 15 every half cycle of the first reference signal S1. Become. The modulator 15 is a multiplexer, that is, an amplitude modulator, and a frequency shifter, and includes a band-pass filter that separates only an upper side band, that is, a signal having a sum frequency of a carrier wave and a modulated signal. Therefore, the transmission signal S5 output from the modulator 15 becomes a sine wave of 200 MHz (= 180 + 20 MHz) and 300 MHz (= 180 + 120 MHz) for each half cycle of the first reference signal S1 of 1 MHz. The transmission signal S5 is amplified by the transmission amplifier 16, and is radiated from the first transmission antenna 17 toward the second transmission / reception device 200 as an electromagnetic wave. As shown in FIG. 3B, the transmission signal S5 is a signal that alternately repeats two states of a first state A having a frequency of 200 MHz and a second state B having a frequency of 300 MHz for every half cycle of 1 MHz. It becomes.

  The above is the configuration and operation of the transmission system of the first transmission / reception device 100. Next, the configuration of the reception system of the first transmission / reception device 100 will be described. The first reception antenna 20 is an antenna that receives a return carrier wave from the second transmission / reception device 200. The signal received by the first receiving antenna 20 is amplified by the receiving amplifier 21 and input to the second demodulator 22 as the received signal S6. The transmission signal S5 output from the modulator 15 is input to the demodulated carrier input terminal of the second demodulator 22. The output signal S7 of the second demodulator 22 is amplified by the amplifier 23 and input to the band pass filter 24, and only the signal corresponding to the first state is extracted. The output signal of the bandpass filter 24 is shaped into a square wave by the envelope detector 25. The signal after waveform shaping is input to the integrator 26, and the period of the first state is output as an average value of a large number of cycles. Based on this period, the distance between the first transmission / reception device 100 and the second transmission / reception device 200 is obtained. The distance calculation device includes a band pass filter 24, an envelope detector 25, and a timer 26. The operation of the receiving system will be described after the description of the second transmitting / receiving apparatus 200 in which the form of the signal received by the first receiving antenna 20 becomes clear.

  FIG. 2 is a block diagram showing the configuration of the second transmission / reception device 200. A signal radiated from the first transmission antenna 17 of the first transmission / reception device 100 is received by the second antenna 40. The output signal of the second antenna 40 is input to the switch 41. The switch 41 sends a signal output from the second antenna 40 to the reception terminal R and the transmission terminal S every half cycle of the second reference signal S10 which is a 1 MHz square wave output from the second reference oscillator 42. , Switching control to pass.

  As shown in FIG. 3C, the signal S9 received by the second antenna 40 is input to the amplifier 46 via the reception terminal R of the switch 41, and the signal S11 output from the amplifier 46 is the second signal S11. The signal is input to the demodulator 47. Further, the return carrier S12 which is a 180 MHz sine wave oscillated by the return carrier oscillator 48 is inputted to the demodulated carrier input terminal of the second demodulator 47. The output of the second demodulator 47 is input to a bandpass filter 49 that extracts a signal of only the 20 MHz band and a bandpass filter 50 that extracts a signal of only the 120 MHz band. The output signal S14 of the band pass filter 49 is amplified by the amplifier 51 and input to the first detection circuit 53. The output signal S15 of the bandpass filter 50 is amplified by the amplifier 52 and input to the second detection circuit 54. Since the output signal S14 of the band pass filter 49 is a 20 MHz sine wave and is demodulated in the first state A, the state corresponding to the first state A is shown. The output signal S15 of the bandpass filter 50 is a 120 MHz sine wave and is demodulated in the second state B, and therefore shows a state corresponding to the second state B. These output signals S14 and S15 appear only in a half cycle of 1 MHz. The first detection circuit 53 and the second detection circuit 54 are circuits that detect the envelope of a sine wave and output it as a square wave as shown in FIG. The output of the first detection circuit 53 is input to the first integration circuit 56, and the output of the second detection circuit 54 is input to the second integration circuit 57. Both the first integration circuit 56 and the second integration circuit 57 are circuits that integrate square waves to obtain an averaged DC level. The outputs of the first integrating circuit 56 and the second integrating circuit 57 are input to the non-inverting input terminal and the inverting input terminal of the comparator 58, respectively. The control signal S16 output from the comparator 58 is input via an amplifier 59 to a voltage controlled oscillator 43 that includes an oscillator that transmits a center frequency of 1 MHz.

  The second reference oscillator 42 includes a voltage control oscillator 43 and a binarization circuit 44 that converts its output into a square wave. The voltage controlled oscillator 43 is a device that controls the phase and frequency of the 1 MHz reference signal in accordance with the voltage level of the control signal S16 output from the comparator 58. That is, the frequency and phase of the signal output from the voltage controlled oscillator 43 are controlled so that the voltage level of the control signal S16 output from the comparator 58 becomes zero. A square wave synchronized with the sine wave output from the voltage controlled oscillator 43 is obtained by the binarization circuit 44. The output of the binarization circuit 44 becomes the second reference signal S10. Therefore, the second reference signal S10 is synchronized with the first reference signal received by the second transmitting / receiving apparatus 200 with a time delay of T / 2. However, T is the length of the half cycle of the first reference signal S1, as shown in FIG.

  The return carrier wave S12 output from the return carrier oscillator 48 is amplified by the amplifier 55 and radiated from the second antenna 40 toward the first transmitter / receiver 100 as a radio wave via the transmission terminal S of the switch 41. Is done.

  As shown in FIG. 3D, the second reference signal S10 has a half period of 1 MHz as a reception period, and rises at a timing when the period of the first state and the second state becomes equal in the half period of the reception signal. It is a wave signal. Since the frequency and the phase of the second reference signal S10 are feedback-controlled, the frequency of the second reference signal S10 is equal to the length of the period of the first state of 20 MHz after demodulation and the period of the second state of 120 MHz. And the phase is stable. In this state, as shown in FIG. 3E, the input signal S11 of the second demodulator 47 is 200 MHz, which is the first state of exactly 1 period / 4 (T / 2) of 1 MHz, followed by this. It becomes a 300 MHz sine wave which is the second state of exactly 1 cycle / 4 (T / 2). Therefore, as shown in FIG. 3F, the output signal S14 of the bandpass filter 49 becomes a sine wave of 20 MHz for exactly 1 period / 4 (T / 2) of 1 MHz. Further, as shown in FIG. 3G, the output signal S15 of the bandpass filter 50 becomes a 120 MHz sine wave of exactly 1 period / 4 (T / 2) of 1 MHz. The rising time t3 in the first state is delayed by Δt1 + T / 2 with respect to the rising time t1 of the first reference signal S1 in the first transmitting / receiving apparatus 100 shown in FIG. Δt1 is a delay time of radio waves from the first transmission / reception device 100 to the second transmission / reception device 200.

  As shown in FIG. 3 (h), the return carrier S12, which is a sine wave of 180 MHz, is transmitted from the second antenna 40 to the first transmission / reception as shown in FIG. Radiated towards the device 100.

  This return carrier wave S12 is received by the first receiving antenna 20 of the first transmitting / receiving apparatus 100 shown in FIG. The received signal S6 input to the first demodulator 22 is, as shown in FIG. 3 (i), the rising time t5 of the received signal S6 is the rising of the return carrier 12 transmitted in the second transmitting / receiving device 200. Delayed by Δt2 from time t4. This delay time Δt2 is a propagation delay time of radio waves from the second transmission / reception device 200 to the first transmission / reception device 100.

  Next, the 180 MHz sine wave reception signal S6 is demodulated in the first demodulator 22 using the transmission signal S5 in the first transmitting / receiving apparatus 100 as a demodulated carrier wave. Therefore, when only the low sideband (that is, the difference frequency) is extracted from the output of the first demodulator 22, the output signal S7 of the first demodulator 22 is 20 MHz and 120 MHz as shown in FIG. Is a signal that appears in divided periods in a half cycle of 1 MHz. The period demodulated with the transmission signal in the first state A at 200 MHz becomes the first state A at 20 MHz, and the period demodulated with the transmission signal in the second state B at 300 MHz becomes the second state B at 120 MHz.

ただし、Δｔ１＋Δｔ２は、往復の伝搬遅延時間である。
また、第２状態Ｂの期間長ΔＴｂは、次式で表される。

Assume that the propagation delay times Δt1 and Δt2 are zero. Then, the first demodulator 22 has a second state B of 300 MHz in the period of 1 cycle / 4 (T / 2) and 200 MHz in the period of 1 cycle / 4 (T / 2) following this period. In the period for transmitting the transmission signal in the first state A, a return carrier wave of 180 MHz is input. Therefore, the output signal S7 of the first demodulator 22 is in the second state B of 120 MHz for a period of 1 cycle / 4 (T / 2) in a half cycle of 1 MHz, and 1 cycle / 4 (T / During the period 2), the first state A is 20 MHz. In the output signal S7 of the first demodulator 22, the period length ΔTa of the first state A is expressed by the following equation.

However, Δt1 + Δt2 is a round-trip propagation delay time.
Further, the period length ΔTb of the second state B is expressed by the following equation.

また、第１送受信装置１００と第２送受信装置２００との間の距離Ｌは、次式で得られる。

Ｔは、既知の値（０．５μｓ）であるので、積分器２６の出力値Ｍから、第１送受信装置１００と第２送受信装置２００との間の距離Ｌを求めることができる。ただし、ｃは高速度である。これらの演算はコンピュータにより実施できる。したがって、距離演算装置は、コンピュータを含むものである。 Therefore, the bandpass filter 24 is a filter that detects only the 20 MHz band in the first state A. Then, the output signal S9 from the envelope detector 25 becomes a signal that becomes H level for the period length ΔTa of the first state A, as shown in FIG. The output signal S9 that is repeatedly output at a period of 1 MHz is integrated by the integrator 26 to obtain an averaged DC level. This DC level M is proportional to ΔTa in the equation (1). Therefore, the following equation is established.

Further, the distance L between the first transmission / reception device 100 and the second transmission / reception device 200 is obtained by the following equation.

Since T is a known value (0.5 μs), the distance L between the first transmission / reception device 100 and the second transmission / reception device 200 can be obtained from the output value M of the integrator 26. However, c is a high speed. These operations can be performed by a computer. Therefore, the distance calculation device includes a computer.

したがって、積分器２６の出力値Ｍから、（５）式により、距離Ｌを求めることができる。 If the bandpass filter 24 is a filter that detects only the 120 MHz band of the second state B, the output signal S9 from the envelope detector 25 becomes a signal that is at the H level for the period length ΔTb of the second state B. Therefore, ΔTb is expressed by the following equation (2), and the distance L is expressed by the following equation.

Therefore, the distance L can be obtained from the output value M of the integrator 26 by the equation (5).

  The bandpass filter 24 is provided with two integrators for integrating the respective outputs as two filters for detecting two states of the first state A of 20 MHz and the second state B of 120 MHz. Then, the distance is obtained by the above method. The arithmetic average value of the distances obtained by these two methods can be used as the distance between the first transmitting / receiving device 100 and the second receiving device 200.

よって、

このように、往復距離Ｌは、積分器の出力値をＭ１とＭ２の差だけで、求めることができる。上記において、ΔＴａ≧ΔＴｂである。この関係を満たすように、第１状態と第２状態とが定義れる。また、測定可能な最大距離では、ΔＴａ＝Ｔ、ΔＴｂ＝０となる。したがって、（６）式より、測定可能最大往復距離Ｌ_MAX は、次式で表される。

すなわち、往復の伝搬遅延時間Δｔ１＋Δｔ２が、第１基準信号の１周期の１／４、すなわち、Ｔ／２となる範囲までである。Ｌは、第１送受信装置と第２送受信装置間の往復距離として定義しているので、実際の距離Ｌ／２の測定可能最大値は、片道の遅延時間が、第１基準信号の１周期の１／８、すなわち、Ｔ／４までの範囲である。第１基準信号の周波数を１ＭＨｚとすると、７５ｍまで、測定可能となる。 Further, when the band-pass filter 24 detects two states of a first state A of 20 MHz and a second state B of 120 MHz, respectively, the following formula is obtained without interposing T as follows. Thus, the distance L can be obtained. However, the output value of the integrator 26 that detects the length of the period of the first state A is M1, and the output value of the integrator 26 that detects the length of the period of the second state B is M2.

Therefore,

Thus, the round-trip distance L can be obtained from the integrator output value only by the difference between M1 and M2. In the above, ΔTa ≧ ΔTb. A first state and a second state are defined so as to satisfy this relationship. In the maximum measurable distance, ΔTa = T and ΔTb = 0. Therefore, from equation (6), the maximum measurable reciprocating distance L _MAX is expressed by the following equation.

That is, the round-trip propagation delay time Δt1 + Δt2 is 1/4 of one cycle of the first reference signal, that is, a range where T / 2. Since L is defined as the round trip distance between the first transmitter / receiver and the second transmitter / receiver, the maximum measurable value of the actual distance L / 2 is the one-way delay time of one cycle of the first reference signal. The range is 1/8, that is, up to T / 4. When the frequency of the first reference signal is 1 MHz, measurement is possible up to 75 m.

  In the above embodiment, the first state A and the second state B use FSK modulation in which the frequency is changed every half cycle of the first reference signal of 1 MHz. Alternatively, BPSK modulation in which the frequency is constant and the phase is changed by π every half cycle of the first reference signal of 1 MHz may be used.

  When there are a plurality of second transmission / reception devices, the first state, the second state, and the frequency of the return carrier may be set to different values for each second transmission / reception device. In this way, even if there are a plurality of second transmission / reception devices, each distance can be measured. The first transmission / reception device may be used in a one-to-one correspondence with the second transmission / reception device, or by using only one first transmission / reception device, and for different second transmission / reception devices by time shearing, The distance may be measured by transmitting and receiving at different frequencies.

  The present invention can be used to determine a distance and a position in a moving body in which the first transmission / reception device is a reader and the second transmission / reception device is a tag.

DESCRIPTION OF SYMBOLS 100 ... 1st transmitter / receiver 200 ... 2nd transmitter / receiver 12 ... 1st sine wave oscillator 13 ... 2nd sine wave oscillator 14 ... Carrier wave oscillator 15 ... Modulator 22 ... 1st demodulator 41 ... Switch 42 ... 2nd reference | standard oscillator 47 ... second demodulator 48 ... return carrier oscillator

Claims (6)

In a distance measuring device that includes a first transmitting / receiving device and a second transmitting / receiving device and measures a distance between the first transmitting / receiving device and the second transmitting / receiving device,
The first transmitting / receiving device includes:
A first transmitting antenna for transmitting a signal to the second transmitting / receiving device;
A first receiving antenna for receiving a signal from the second transmitting / receiving device;
A first reference oscillator for outputting a first reference signal having a predetermined reference frequency;
Based on the first reference signal output from the first reference oscillator, the transmission signal having the first state and the second state in which the frequency or phase of the carrier wave is changed every half cycle of the first reference signal is the first signal. A modulator that outputs to the transmit antenna;
A first demodulator that demodulates the transmission signal output from the modulator based on a reception signal received by the first reception antenna;
A distance calculation device for obtaining the distance based on a length of at least one of two periods of different states related to frequency or phase in the signal demodulated by the first demodulator;
Have
The second transmission / reception device includes:
A second antenna that receives a signal transmitted from the first transmission / reception device and transmits the signal toward the first transmission / reception device;
A second demodulator that demodulates the first state and the second state from a received signal received from the second antenna;
A second reference oscillator that outputs a second reference signal whose frequency and phase are controlled such that the signal output from the second demodulator is equal in the reception period of the first state and the second state;
A return carrier oscillator that outputs a return carrier of a predetermined frequency;
The received signal of the second antenna is output to the second demodulator every half cycle of the second reference signal output from the second reference oscillator, and the return carrier wave output from the carrier oscillator is output to the second antenna. A switch that switches between receiving and transmitting a signal to the second antenna so as to output,
A distance measuring device comprising:   2. The FSK modulation according to claim 1, wherein the first state and the second state of the transmission signal output from the modulator of the first transmission / reception device are FSK modulations in which the frequency of the carrier wave is different. Distance measuring device.   2. The PSK modulation according to claim 1, wherein the first state and the second state of the transmission signal output from the modulator of the first transmission / reception device are PSK modulations in which phases of the carrier waves are different from each other. Distance measuring device. A signal is transmitted from the first transmission / reception device to the second transmission / reception device, and a signal is transmitted from the second transmission / reception device to the first transmission / reception device. In the first transmission / reception device, based on the transmission signal and the reception signal, In the distance measuring method for measuring the distance between the second transmitting and receiving device,
A transmission signal having a first state and a second state in which the frequency or phase of a carrier wave is changed every half cycle of the first reference signal from the first transmission / reception device based on the first reference signal. Send it to the device,
In the second transmitter / receiver, the received signal from the first transmitter / receiver is demodulated to detect the first state and the second state, and the reception periods of the first state and the second state are equal. Transmitting a return carrier wave having a predetermined frequency to the first transmitting / receiving device only during the half cycle period,
In the first transmission / reception device, the transmission signal is demodulated by the return carrier wave received from the second transmission / reception device, and at least one of the two periods having different frequencies or phases in the demodulated signal is transmitted. A distance measuring method for obtaining the distance based on a length.   The distance measuring method according to claim 4, wherein the first state and the second state of the transmission signal output from the first transmitting / receiving apparatus are FSK modulation in which frequencies of the carrier waves are different.   5. The PSK modulation according to claim 4, wherein the first state and the second state of the transmission signal output from the modulator of the first transmission / reception device are PSK modulation in which phases of the carrier waves are different from each other. Distance measurement method.

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