JP3101635B2 - Moving object detection device for data transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission apparatus for wirelessly transmitting data from a fixed position to a moving object, and more particularly, to a method for detecting the presence or absence of a moving object by detecting a reflected wave of a transmitted radio wave from the moving object. The present invention relates to a moving object detection device of a data transmission device that detects and simultaneously measures the speed of a moving object.

[0002]

2. Description of the Related Art A function of wirelessly transmitting various data such as accumulated error information generated by self-contained navigation from a fixed base on a moving object such as an airplane, a car, a train, a ship, or the like. In addition, a data transmission device incorporating a function of measuring a moving speed of a moving object has been proposed (Japanese Patent Application Laid-Open No. H1-2).
67486).

In this data transmission device, for example, as shown in FIG. 6, an antenna 3 for transmitting and receiving high-frequency radio waves is mounted on a support 2 standing on the side of the road 1 so as to face the road 1 at a specified depression angle θ. I have. When a moving object 4 such as an automobile enters a beam range (directivity range) of a radio wave transmitted and received by the antenna 3, the radio wave is received by an antenna 5 attached to the moving object 4.

For example, referring to the time chart of FIG. 7, a carrier signal a having a frequency f _{C of 10} to 15 GHz is used.
1 is amplitude-modulated by the digital data signal b1 to be transmitted to the moving object 4. Then, the amplitude-modulated transmission signal h1 is radiated toward the moving object 4 via the antenna 3. The moving object 4 transmits the transmission signal h1 by the mounted antenna 5.
, And detects and demodulates the received signal to obtain a demodulated signal q1 corresponding to the original digital data signal b1.

On the other hand, a part of the radio wave output from the antenna 3 is reflected on the surface of the moving object 4 which has entered the beam range of the radio wave and is orthogonal to the beam direction, and is incident on the antenna 3 again. Therefore, the moving object 4 is generated by using the reflected radio wave.
Can be detected. That is, since the beam direction of the antenna 3 is set to, for example, a 70 ° depression angle with respect to the road surface, if the moving object 4 does not exist in the beam range of the transmission radio wave, the transmission radio wave is reflected by the road surface, It is not reflected in four directions.

More specifically, the reception signal i1 that has reentered the antenna 3 is delayed from the transmission signal h1 by the time that the radio wave reciprocates between the antenna 3 and the moving object 4. During this delay time ΔT, the signal emitted and incident on the antenna 3 is the received signal i1 reflected from the moving object 4.
Only.

Since the radio wave output from the antenna 3 is greatly attenuated during the period of reciprocation between the antenna 3 and the moving object 4, the signal level of the reception signal i1 is 50 to 60 dB as compared with the signal level of the transmission signal h1. The above also decreases. Therefore, even if the received signal i1 is separated by a circulator inserted at the input end of the antenna 3, the received signal i1 contains a large component of the transmission signal h1.

Therefore, in order to extract only the received signal i1, only the signal component of the delay time ΔT of the received signal i1 needs to be detected. If the received signal i1 within the delay time ΔT can be detected, it means that the reflected radio wave of the moving object 4 has been reliably detected, and it is detected that the moving object 4 exists within the beam range of the antenna 3.

As a method for simply measuring the velocity V of the moving object 4, a method using the Doppler effect has been considered.

In this measuring principle, as is well known,
A transmission wave having a fixed frequency is transmitted to a moving object, and a reflected wave from the moving object is received. Then, the frequency difference between the frequency f _C of the transmitted wave and the frequency f _R of the reflected wave (f _R -f _C), i.e. to detect the Doppler frequency f _D. From the Doppler frequency f _D and the propagation speed of the transmission wave, the speed V of the moving object is calculated by the equation (1).

V = Cf _D / (2f _C COS θ) (1) V: velocity C: propagation velocity of transmission wave f _D : Doppler frequency f _C : frequency of transmission wave θ: beam direction (depression angle) of antenna In the data transmission device in FIG. 6, in order to accurately measure the speed V of the moving object 4 traveling on the road 1, the larger the value of [COSθ] is, as can be understood from the equation (1), the better. The smaller the depression angle θ, the better.

On the other hand, in order to accurately detect the presence of the moving object 4, it is desirable to detect the moving object 4 at a position close to the data transmission device (transmitter) installation position. Values are desirable. If the beam direction of the antenna 3 is set to exactly 90 degrees, the reflected radio wave from the road 1 enters the antenna 3 when the moving object 4 (vehicle) does not exist. Therefore, it is necessary to set a value slightly shifted from 90 degrees.

In data transmission, it is preferable that the distance between the antenna 3 and the antenna 5 of the moving object 4 be short in order to prevent interference or the like, so that the depression angle θ is preferably close to 90 degrees.

Therefore, normally, the depression angle θ of the data transmission apparatus with respect to the road 1 is set to one optimum value of about 70 degrees. In this way, by setting the depression angle θ to one optimal value such as 70 degrees, data such as position information can be accurately transmitted to a receiver mounted on the moving object 4 and the presence of the moving object 4 can be detected. And the speed measurement is maintained at a certain accuracy or higher.

[0015]

However, as described above, the data transmission device in which the beam direction of the antenna 3 is fixed to one specific value has the following problems to be improved.

That is, the shape of the moving object 4 such as a vehicle traveling on the road 1 may be an ordinary passenger car shown in FIG. 6, a box-shaped bus, or a trailer shown in FIG. I do.

When the moving object 4 is traveling at a certain speed or higher, as shown in FIG.
When a plane orthogonal to this beam direction on the surface of the moving object 4 enters the beam range defined by the depression angle θ, the radio wave output from the antenna 3 is vertically reflected by the orthogonal plane and enters the same antenna 3 Is done. Therefore,
The speed V is measured at the timing shown in FIG.
In addition, the moving object 4 is detected.

When the moving object 4 reaches the position shown in FIG. 8C, the radio wave output from the antenna 3 is reflected in the opposite direction by the flat roof of the moving object 4. As a result, no reflected radio wave enters the antenna 3. Therefore, at this timing, the presence detection and the speed measurement of the moving object 4 cannot be executed.

As described above, when the moving object 4 is traveling at a certain speed or more, FIGS.
Since the state shown in (c) is a very short timing, the data in FIG. 8 (b) can be regarded as the information on the moving object 4, and the subsequent data processing can be performed.

However, when this data transmission device is installed on a road, when traffic congestion or the like occurs, a slow operation at a speed of, for example, 1 to 2 km / h may occur, or the data transmission device may be completely stopped.

For example, when the moving object 4 stops in the state shown in FIG. 8 (c), the data transmission apparatus enters a state where the presence of the moving object 4 is not detected. Generally, this data transmission device is installed on a highway or an elevated road, and its presence (the number of passing vehicles) and the speed V are monitored by a distant road management office. Therefore, if the state of FIG. 8C continues for a long time, the road manager at the road management office will find that the moving object 4 does not exist at the installation position of the data transmission device, and congestion will occur. Judge that you have not.

The present invention has been made in view of such circumstances, and by switching the beam direction of an antenna between a prescribed direction suitable for normal speed measurement and a direction suitable for moving object detection, even if a moving object is detected. Data that can accurately detect the presence or absence of a moving object even when stopped near the installation position of the data transmission device, and can greatly improve object detection accuracy while maintaining high data transmission accuracy and high speed measurement accuracy An object of the present invention is to provide a moving object detection device of a transmission device.

[0023]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an amplitude modulation circuit for amplitude-modulating a high-frequency carrier signal with a modulation signal corresponding to a digital data signal, and as a transmission signal via a circulator. When applied to the antenna, the antenna transmits radio waves in the specified beam direction from this antenna, and receives the radio waves reflected by the moving object that has entered the beam direction via the antenna, and receives the received signal separated by the circulator with the received signal. Data transmission that extracts the Doppler signal consisting of the difference signal from the transmission signal, measures the speed of the moving object from the frequency of this Doppler signal, and detects the presence or absence of the moving object from the presence or absence of a time delay with respect to the transmission signal of the reception signal. In the moving object detection device of the device,
A beam direction switching control circuit for outputting a beam direction control signal for switching a beam direction of the antenna in response to a change in the signal level of the digital data signal to a direction in which the depression angle is increased as viewed from the moving object side in comparison with the prescribed beam direction; A beam direction switcher interposed between the circulator and the antenna for switching a beam direction of the antenna in response to a beam direction switching signal, and extracting a Doppler signal in a prescribed beam direction period in response to a beam direction control signal A Doppler signal selection and extraction circuit.

[0024]

According to the moving object detecting device of the data transmission device having such a configuration, a high-frequency carrier signal is modulated by a modulation signal corresponding to a digital data signal and transmitted as a transmission signal from an antenna in a specified beam direction. Is done. When a moving object enters in this beam direction, a radio wave is reflected by the moving object, and the reflected radio wave enters the antenna. Then, a Doppler signal is generated from the reception signal and the transmission signal received by the antenna.

In this case, in response to a change in the signal level of the digital data signal, the beam direction of the antenna is alternately switched between a prescribed beam direction mainly suitable for velocity measurement and a beam direction suitable for object detection. Therefore, for a moving object that moves in the vicinity of the data transmission device, the position at which the transmission radio wave output from the antenna is received and the angle of incidence of the radio wave change very quickly. That is, when viewed from the moving object side, the depression angle of the radio wave changes.

In general, since the surface of a moving object has many flat portions, if the depression angle θ is large, as shown in FIG. 8D, the radio wave reflected by the moving object has a high probability of being incident on the same antenna again. Become. Therefore, even if the moving object is stopped, the moving object can be detected by using the reflected wave.

Also, during the period when the beam direction of the antenna is switched to the one where the depression angle is larger, the measurement error becomes large. Therefore, only the Doppler signal during the period when the beam direction of the antenna is switched to the specified beam direction is obtained. It is extracted by a Doppler signal selection and extraction circuit. Therefore, since the velocity is obtained using the Doppler signal in the beam direction with the smaller depression angle, high velocity measurement accuracy can be maintained.

[0028]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a data transmission device in which a moving object detection device according to an embodiment is incorporated.

Moving object 31 input from input terminal 11
Digital data signal b to be transmitted to, as shown in the time chart of FIG. 3, the duration T _S of the unit data 3
It is a 1.25 μs 16 kbps split phase signal.
The input digital data signal b is input to the inverter 13 via the input / output port 12. The inverter 13 inverts the signal level of the output signal of the input / output port 12 and sends it out as a modulation signal g to the modulation terminal of the modulator 15 in the amplitude modulation circuit 14.

The input digital data signal b is input via the input / output port 12 to the input terminal of a flip-flop 16 as a beam direction switching control circuit. As shown in FIG. 3, the flip-flop 16 has an output terminal which synchronizes with the timing at which the signal level of the digital data signal b applied to the input terminal rises from a low (L) level to a high (H) level. And inverts the signal level of the beam direction control signal c output from. The beam direction control signal c output from the flip-flop 16 is applied to the control terminal of the beam direction switching circuit 17 and
It is applied to the control terminal of the sample and hold circuit 19 of the Doppler signal selection and extraction circuit 18. Further, the input digital data signal b is applied to the control terminal of the attenuator 20 via the input / output port 12 as an attenuator control signal j.

In the amplitude modulation circuit 14, for example, 10 GHz
Oscillator 2 that outputs a carrier signal a having a frequency f _C of
1 is incorporated. The carrier signal a output from the oscillator 21 is input to the modulator 15 via the isolator 22, and as shown in FIG. Amplitude modulated. Specifically, when the modulation signal g is at the H level, the attenuation is large, the amplitude of the transmission signal h output from the amplitude modulation circuit 14 is small, and when the modulation signal g is at the L level, the degree of modulation is minimum. Therefore, the amplitude of the transmission signal h increases.

The carrier signal amplitude-modulated by the modulator 15 is applied to the beam direction switch 17 via the circulator 23 as a transmission signal h.

As shown in FIG. 2, for example, the beam direction switch 17 is roughly divided into an in-phase power distributor 24 and two 9-phase power distributors.
It is composed of 0 ° hybrid (bidirectional) circuits 25a and 25b. Then, the in-phase power divider 24 converts the transmission signal h input from the terminal 26 on the circulator 23 side into the same 90 ° hybrid (bidirectional) circuit 25 with the same phase.
Branch equally to a and 25b. Each of the 90 ° hybrid circuits 25a and 25b has a function of delaying an input signal when a DC current is applied. Since the input signals are not delayed when the beam direction control signal c applied to the control terminal 28 is at the L level, the phases of the transmission signals output from the terminals 29a and 29b on the antenna 30 side are equal.

On the other hand, when the beam direction control signal c applied to the control terminal 28 is at the H level, a DC bias is applied to the input transmission signal, and one of the diodes 27a and 27b is connected. Since a DC current flows through the 90 ° hybrid circuit 25b,
° Only the input signal of the hybrid circuit 25ba is delayed. Therefore, the antenna 3 is connected to each terminal 29a, 29b.
A phase difference occurs between the signals output to 0.

The antenna 30 is a planar antenna having two input terminals. If there is no phase difference between the transmission signals input from each input terminal, the direction of the beam of the radio wave output from the antenna 30 is equal to the antenna direction. 30 front 30a
With respect to the vertical direction. However, if there is a phase difference between the transmission signals input from the input terminals, the beam direction changes in a direction corresponding to the phase difference. That is, the directivity of the antenna 30 changes.

In the apparatus of the embodiment, when the beam direction control signal c is at the H level, the beam direction of the radio wave output from the antenna 30 is changed from the angle of depression 70 in FIG. When the beam direction control signal c is at the L level, the DC current flowing through the mounting direction of the antenna 30 and the DC current flowing through the 90 ° hybrid circuit 25b are adjusted so that the beam direction is directed at a depression angle of 83 °. Is set.

Then, radio waves are radiated from the antenna 30 toward a moving object 31 such as a car. The moving object 31 receives the transmission radio wave by its own antenna 32, detects the received signal by a receiver mounted therein, extracts a demodulated signal corresponding to the original digital data signal, and displays the demodulated signal on a display, for example. I do.

On the other hand, a part of the transmission radio wave output from the antenna 30 is reflected on the surface of the moving object 31 and reenters the antenna 30 as a reflected radio wave. The received signal i incident on the antenna 30 is separated by the circulator 23 and input to the attenuator 20. The ability of the circulator 23 to separate the transmission signal h and the reception signal i is 15d
It is about B. The signal level of the reception signal i is lower than the signal level of the transmission signal h by 50 to 60 dB or more. Therefore, the received signal i input to the attenuator 20 contains the component of the transmitted signal h passing through the circulator 23 at a high signal level.

The attenuator 20 has a function of controlling the amount of attenuation of the input signal according to the signal level of the attenuator control signal j applied to the control terminal. Therefore, when the attenuator control signal i is at the H level period, the signal level of the input received signal i is greatly attenuated, and when the attenuator control signal j is at the L level period, the input received signal i is not attenuated. Pass as it is.

In an actual device, the attenuator 20 and the modulator 15 use circuit components having the same specifications, one of which is used as the modulator 15 and the other is used as the attenuator 20.
We use as. In both cases, the signal levels of the input signals a and i are reduced by 60 dB during the period when the modulation signal g and the attenuator control signal j are at the H level.

The output signal k of the attenuator 20 is supplied to a detection circuit 33
Is input to The output signal k input to the detection circuit 33 is amplified by the high-frequency amplifier 34 and then detected by the detector 35 into a pulse-like waveform. The detected signal is output to the amplifier 3 again.
After being amplified at 6, the signal is output from the detection circuit 33.
The output signal m of the detection circuit 33 is input to the peak hold circuit 37. As shown in FIG. 3, the peak hold circuit 37 detects the peak level of the input output signal m, holds it until the next digital data signal b falls, and outputs it as an output signal n. Peak hold circuit 37
Is input to the next output circuit 38. The output circuit 38 includes a low-pass filter 39 and an amplifier 40, averages the input output signal n, and outputs the result as an object detection signal o from an output terminal 41.

On the other hand, the mixer 42 combines the transmission signal h output from the amplitude modulation circuit 14 and the reception signal i separated by the circulator 23. Since the frequency f _R of the received signal i is shifted by a value corresponding to the speed V of the moving object 30 from the frequency f _C of the transmitted signal h due to the Doppler effect, the difference frequency f _D (= f _R −f _C ). Is sent to the sample and hold circuit 19 of the next Doppler signal selection / extraction circuit 18.

The beam direction control signal c output from the flip-flop 16 is input to the control terminal of the sample and hold circuit 19, and the beam direction control signal c
Sample the waveform of the Doppler signal input only during the H level period, that is, the period in which the beam direction of the antenna 30 is set to the depression angle of 70 degrees. Then, during the next L-level period, that is, a period when the beam direction of the antenna 30 is set to the depression angle of 83 degrees, the Doppler signal is held and a Doppler signal waveform of the depression angle of 70 degrees is output. Therefore,
The sample and hold circuit 19 outputs a continuous Doppler signal. The Doppler signal output from the sample-and-hold circuit 19 is subjected to removal of unnecessary high-frequency components by a low-pass filter 43, then amplified by an amplifier 44, and output as a normal Doppler signal p from an output terminal.

The Doppler signal p output from the Doppler signal selection / extraction circuit 18 is a signal during a period in which the beam direction of the antenna 30 is set at a depression angle of 70 degrees (θ = 70) as viewed from the moving object 31 side. . Therefore, the speed V of the moving object 31 is calculated by the monitoring computer connected to the data transmission device via the data line by using the above-described equation (1).

A part of the output signal of the mixer 42 is compared with a reference signal by a comparator 46 through a low-pass filter 45. In the case of an abnormal signal, the signal is output as an abnormal signal to an output terminal via a switch circuit 47. You.

Next, the operation of the moving object detecting device of the data transmission device thus configured will be described with reference to the time charts of FIGS.

For example, at time t _{1, the} digital data signal b
Falls, the modulation signal g rises. Therefore, the amplitude of the transmission signal h output from the amplitude modulation circuit 14 at the time t ₁ becomes smaller. At the same time, since the attenuator control signal j falls, the attenuator 20 passes the input signal as it is.
In this state, the beam direction control signal c is L
The level is maintained. Therefore, antenna 3
The beam direction of 0 is maintained at an optimum depression angle of 83 degrees for detecting the presence or absence of the moving object 30.

If the moving object 31 is within the beam range of the antenna 30, the received signal i reflected by the moving object 31, incident on the antenna 30 and separated by the circulator 23 is transmitted from the antenna 30 to the moving object 31. distance falls at delayed time t ₂ [Delta] t time corresponding example 13～20Ns. The attenuator 20 is not signal input to the time t ₁ previously passed since passing a signal input to the time t ₁ later, of the received signal i separated in the circulator 23, the time from time t ₁ t Only the signal component corresponding to the delay time ΔT up to ₂ passes through this attenuator 20. That is, the reception signal i including the component of the transmission signal h does not pass through the attenuator 20.

The output signal k, which is a part of the received signal i that has passed through the attenuator 20, is detected by the detection circuit 33 to become an output signal m having a pulse-like waveform having a time width of the delay time ΔT. Then, the peak hold circuit 37 detects the peak level of the output signal m. Thus, the output circuit 38 outputs the H-level object detection signal o.

Next, at time t _{3, the} digital data signal b
Rises, flip-flop 20 is set, and beam direction control signal c changes to H level. as a result,
The beam direction of the antenna 30 changes to an optimum depression angle of 70 degrees for measuring the velocity V of the moving object 1.

Then, the sample and hold circuit 19 of the Doppler signal selection / extraction circuit 18 starts taking in the Doppler signal output from the mixer 42. Accordingly, the Doppler signal selection / extraction circuit 18 continuously outputs a Doppler signal p in a state where the beam direction of the antenna 30 is set to 70 degrees.

Further, for example, the moving object 31 after time t ₆
Moves, and goes out of both directivity ranges of the antenna 30, the reflected radio wave from the moving object 31 is cut off. Therefore, the received signal separated by the circulator 23 includes the received signal i from the moving object 31. Instead, only the component of the transmission signal h wrapping around from the circulator 23 is included. Therefore, the falling time t ₆ of the reception signal i is the transmission signal h
Coincides with the fall time of Therefore, since the delay time ΔT does not exist, nothing is output from the attenuator 20. Therefore, no peak waveform is output to the output signal m of the detection circuit 33. As a result, the object detection signal o changes to the L level.

According to the moving object detecting device of the data transmission device thus configured, the beam direction of the antenna 30 is optimal for speed measurement in synchronization with the rise of the digital data signal b from the L level to the H level. The angle is alternately switched between 70 degrees and 83 degrees, which is optimal for object detection.

Since the velocity measurement is performed using the Doppler signal o extracted during the period in which the beam direction is 70 degrees, it is almost the same as the conventional apparatus in which the beam direction of the antenna shown in FIG. 6 is fixed at 70 degrees. Similar measurement accuracy can be maintained. The presence or absence of the moving object 31 is detected when the beam direction of the antenna 30 is both normal 70 degrees and 83 degrees, which is optimal for object detection.

Here, it is assumed that, for example, as shown in FIG. 5A, a large moving object 31 such as a trailer stops at the installation position of the data transmission device on the congested road 1, as shown in FIG. With only the conventional 70 degree beam direction,
Although the reflected radio wave does not enter the antenna 30, according to the embodiment, the reflected radio wave is transmitted to the antenna
Incident at 0. As a result, even if the moving object 31 is stopped, the presence of the moving object 31 can be reliably detected. Therefore, the object detection accuracy of the entire apparatus can be improved.

Also, the object detection signal o output from the data transmission device can be separated into a 70-degree beam direction detection signal and a 83-degree beam direction detection signal using the beam direction control signal c. It is possible. By comparing and synthesizing the two types of detection signal waveforms or combining them, the type and shape of the moving object 31 can be specified to some extent. Therefore, even when the vehicle is running slowly at a speed of, for example, 1 to 2 km / h, one vehicle is not erroneously counted as two vehicles.

[0058]

As described above, according to the moving object detecting device of the data transmission device of the present invention, the beam direction of the antenna is suitable for ordinary speed measurement in accordance with the signal level change of the digital data signal to be transmitted. The direction is alternately switched to a prescribed direction and a direction suitable for object detection. Then, the speed is measured using the Doppler signal during the period when the beam direction is set to the specified direction, and the object detection is performed in both beam directions.

Therefore, even if the moving object stops near the installation position of the data transmission device, the presence / absence of the moving object can be accurately detected, and the object can be detected while maintaining high data transmission accuracy and high speed measurement accuracy. Detection accuracy can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an entire data transmission device in which a moving object detection device according to one embodiment of the present invention is incorporated;

FIG. 2 is a block diagram showing a beam direction switch of the apparatus of the embodiment;

FIG. 3 is a time chart showing the operation of the apparatus of the embodiment;

FIG. 4 is a diagram showing the time axis of the time chart in a reduced scale,

FIG. 5 is a view for explaining an effect of the apparatus according to the embodiment;

FIG. 6 is a schematic diagram showing an attached state of a conventional data transmission device;

FIG. 7 is a time chart showing the operation of the conventional device,

FIG. 8 is a diagram for explaining a problem of the conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Road, 14 ... Amplitude modulation circuit, 15 ... Modulator, 16 ...
Flip-flops (beam direction switching control circuits), 17 ...
Beam direction switcher, 18 ... Dobler signal selection and extraction circuit,
Reference Signs List 20 attenuator, 23 circulator, 30 antenna, 31 moving object, 33 detection circuit, 37 peak hold circuit, 38 output circuit, a carrier signal, b digital data signal, c beam direction control Signal, h: transmission signal, i: reception signal, o: object detection signal, p: Doppler signal.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01P 13/00 G01S 13 / 04,13 / 58

Claims (1)

(57) [Claims] An amplitude modulation circuit converts a high-frequency carrier signal (a).
In (14), the signal is amplitude-modulated with the modulation signal (g) corresponding to the digital data signal (b) and applied as a transmission signal (h) to the antenna (30) via the circulator (23). While transmitting the radio wave in the beam direction, the radio wave reflected by the moving object (31) entering the beam direction is received via the antenna, and the reception signal (i) separated by the circulator and the transmission A Doppler signal (p) consisting of a difference signal from the signal is extracted, the speed of the moving object is measured from the frequency of the Doppler signal, and the presence or absence of a time delay of the reception signal with respect to the transmission signal indicates that the moving object In the moving object detection device of the data transmission device that detects the presence / absence, the beam direction of the antenna in response to a change in the signal level of the digital data signal is compared with the specified beam direction. A beam direction switching control circuit (16) for outputting a beam direction control signal (c) for switching to a direction in which the depression angle increases when viewed from the moving object side, and the beam direction switching control circuit (16) inserted between the circulator and the antenna to switch the beam direction Beam direction switch for switching the beam direction of the antenna in response to a signal
A moving object detection device for a data transmission device, comprising: (17) a Doppler signal selection / extraction circuit (18) for extracting a Doppler signal in the prescribed beam direction period in response to the beam direction control signal.