JP4786572B2 - Approach detection system - Google Patents

Description

The present invention relates to an approach detection system that detects the position of a target using a cable-shaped radio wave transmission / reception means .

  Nowadays, an approach detection system for detecting approach of a target using a leaky transmission line such as a leaky cable is known. Conventionally, as such an approach detection system, for example, it is arranged around a site where a leaky transmission line is desired to be monitored, radio waves are transmitted / received through such a leaky transmission line, and electric field fluctuations that occur when a target approaches the leaky transmission line There is one that detects a target based on the above (for example, see Patent Document 1).

  Further, in addition to the above-described configuration, there is one that can detect a position in a direction away from the leaky transmission path (see, for example, Patent Document 2). This is realized by a configuration in which a reflector for reflecting radio waves is installed at the far end from the leaky transmission line.

  Furthermore, using a leaky coaxial cable whose radiation directivity changes depending on the frequency on the transmitting side, observe alternately at different frequencies, and target existing in the plane sandwiched between the transmitting leak cable and the receiving leak cable, There is one that uses the difference to specify the position (see, for example, Patent Document 3).

Japanese Patent Laid-Open No. 10-95338 International Publication No. 05/013223 Pamphlet JP 2004-125604 A

  However, the conventional system has the following problems. For example, in the system as shown in Patent Document 1, only the distance in the direction of the target leaky transmission path can be measured, and the distance in the direction away from the leaky transmission path cannot be calculated. For this reason, there is a problem in that even if it is not originally desired to detect a distant object, if the object size is large and the level of the reflected wave is large, the object is erroneously detected.

  Moreover, in the system as shown in Patent Document 2, it is possible to measure the position in the direction away from the leaky transmission path for only one target, but it is not possible to measure the positions of a plurality of targets individually. There was a problem. For example, when there are two targets, the reflected waves of the two targets are combined and reflected at the open end of the leaky transmission path. For this reason, the distances between the two targets in the perpendicular direction cannot be distinguished. Furthermore, the system as in Patent Document 2 has a problem that the distance in the perpendicular direction cannot be known unless the target is far from the leaky transmission path. This is because the distance in the perpendicular direction is calculated by observing the target component that appears farther than the signal component of the far-end coupled wave, but the far-end coupled wave is so strong that the target is far away from the leaky transmission line. Otherwise, the target component is covered with the far-end coupled wave and cannot be detected.

  Further, even in the system as disclosed in Patent Document 3, there is a problem that accurate measurement cannot be performed when a plurality of targets are included. Further, in such a system, in principle, only a target existing between two leaky coaxial cables can be detected, so there is no guarantee of operation with respect to targets outside the two leaky coaxial cables. There was a problem that the position could not be detected. Moreover, in the system of Patent Document 3, if the frequency to be used is poorly selected, a phenomenon such as no radio wave being output from the leaked cable or simultaneous radio wave output in a plurality of directions occurs. When measuring at such a frequency, there is a problem that the target position cannot be measured.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an approach detection system that can reliably detect a target at any position. .

In the proximity detection system according to the present invention, when transmitting radio waves in a plurality of frequency bands from a radio wave transmitting / receiving means consisting of a cable-shaped radio wave transmitting means and a radio wave receiving means whose radiation directivity changes depending on the frequency, Measuring means for acquiring a propagation delay time from transmission to reception for each of a plurality of frequency bands based on radio waves of a plurality of frequency bands reflected by the target and received by the radio wave receiving means; extract the function curve of the propagation delay time versus the frequency bands and the plurality of frequency bands, by a predetermined operation from the coefficient of the function curve in the longitudinal direction of the direction of the target away from the distance and the electric wave transmitting and receiving means of the target radio wave transmitting and receiving means And a calculating means for calculating the distance.

The proximity detection system of the present invention utilizes the fact that the directivity of the radio wave transmission means depends on the frequency, radiates radio waves in a plurality of frequency bands from a plurality of directions to the target, measures its propagation delay time, A function curve of propagation delay times for a plurality of frequency bands and a plurality of frequency bands is extracted, and the target of the radio wave transmission / reception means in the longitudinal direction and the target away from the radio wave transmission / reception means by a predetermined calculation from the coefficients of the function curves Since the distance of the target is calculated, it is possible to reliably detect the presence of the target regardless of the positional relationship of the target with respect to the radio wave transmission / reception means. Can be detected individually.

Embodiment 1 FIG.
1 is a block diagram showing an approach detection system according to Embodiment 1 of the present invention.
In the figure, the approach detection system includes a sensor 100, radio wave transmission / reception means 200, coaxial cables 202 and 212, terminators 203 and 213, and an alarm device 300.
The sensor 100 detects the position of the target 400 using the radio wave transmission / reception unit 200 and includes a signal generation unit 110, a signal reception unit 120, a storage unit 130, and a control unit 140. Here, the signal generating means 110 includes a sine wave generator 111 and an amplifier 112, and the signal receiving means 120 includes a filter 121, an amplifier 122, and a quadrature demodulator 123. In addition, the control unit 140 includes a measuring unit 141, a calculating unit 142, and an approach determining unit 143. Further, the radio wave transmission / reception means 200 includes a leak cable 201 that realizes radio wave transmission means and a leak cable 211 that realizes radio wave reception means.

In the signal generation unit 110, the sine wave generator 111 generates a sine wave having a commanded frequency in accordance with a command from the control unit 140 and outputs the sine wave to the amplifier 112. The amplifier 112 amplifies the output of the sine wave generator 111 to a predetermined level and sends it to the leakage cable 201 of the radio wave transmission / reception means 200 via the coaxial cable 202.
In the signal receiving unit 120, the filter 121 is a filter that removes a signal having an unnecessary spectrum different from the spectrum radiated from the leakage cable 201 from the signal input through the coaxial cable 212. The amplifier 122 is an amplifier that amplifies the signal output from the filter 121 to a predetermined level.

  The quadrature demodulator 123 performs quadrature detection of the received signal in the reception leakage cable 211 with reference to the signal of the sine wave generator 111. Here, the quadrature detection is also called I / Q detection, and the received signal input from the leakage cable 211 with respect to the reference signal is an In-Phase component (hereinafter referred to as I component) and a Quadrature component ( Hereinafter, this is divided into Q components). Further, the sine wave signal is removed by quadrature detection, and a baseband component is output.

  Note that a low-pass filter (LPF) (not shown) is included in the output stage of the quadrature demodulator 123 so that the spectrum of the high frequency band is removed and only the necessary low frequency band (baseband component) is output. It is configured. Further, the quadrature demodulator 123 includes an A / D converter (not shown), and is configured to output an I component and a Q component, which are digitally converted baseband components.

  The storage unit 130 is a storage unit for holding the signal data output from the signal receiving unit 120 and holding the processing data of the measurement unit 141 to the approach determination unit 143 in the control unit 140. Details of these data will be described later.

  The control unit 140 includes a CPU, a memory, and the like, and controls each unit in the sensor 100. When the measuring unit 141 transmits radio waves in a plurality of frequency bands from the leaky cable 201, the measurement unit 141 reflects the reflected waves for each frequency band based on the radio waves in the plurality of frequency bands reflected by the target 400 and received by the leak cable 211. Measurement information comprising the signal strength and phase of the signal and the propagation delay time from transmission to reception is output. The calculation unit 142 classifies the measurement information for each target 400 based on the signal intensity and phase information of the reflected wave in each frequency band in the measurement information output from the measurement unit 141, and based on the classified measurement information, The distance Z of the target 400 in the longitudinal direction of the radio wave transmission / reception means 200 and the distance R to the target 400 in the direction away from the radio wave transmission / reception means 200 are calculated.

  The approach determining means 143 determines the presence or absence of the approach of the target 400 based on the value calculated by the computing means 142 and information on a predetermined alarm area determined in advance, and determines the presence or absence of the approach, the distance Z, and the distance R. The approach information including the information is output to the alarm device 300. Note that the measurement unit 141, the calculation unit 142, and the approach determination unit 143 are configured by software corresponding to each function and hardware such as a CPU and a memory for executing the software.

  In the radio wave transmission / reception means 200, the leakage cables 201 and 211 are cable-shaped radio wave transmission means and radio wave reception means whose radiation directivity changes according to the frequency. For example, a leaky coaxial cable (LCX: Leaky CoaXial cable) or a leaky waveguide may be used as the leaky cables 201 and 211. Here, the leaky coaxial cable and the leaky waveguide leak radio waves through a slot opened in the outer conductor. At this time, radiation directivity is generated by the slot interval, and the angle depends on the frequency. The relationship between frequency and radiation directivity is shown in FIG. FIG. 2 illustrates the characteristics of the basic structure of a leaky coaxial cable. The items such as the basic mode and the higher order mode in FIG. 2 will be described in detail later.

  The coaxial cables 202 and 212 are cables that constitute a signal transmission path for connecting the sensor 100 and the radio wave transmission / reception means 200, respectively. The terminators 203 and 213 are connected to the ends of the leaky cables 201 and 211 opposite to the sensor 100 (hereinafter referred to as the far ends), and absorb signals in the leaky cables 201 and 211. It is. That is, a signal input from the coaxial cable 202 to the leakage cable 201 is transmitted as a radio wave from the leakage cable 201 into the space. The signal that has not been transmitted is absorbed by the terminator 203.

  The radio wave transmitted from the leakage cable 201 is reflected by the target 400, and the reflected wave that is the reflected radio wave is received by the leakage cable 211. Leakage cable 211 is generally arranged substantially parallel to leaky cable 201, but it is not necessary to be completely parallel, and the interval between them may partially increase or decrease. However, the laying interval between the leaky cable 201 and the leaky cable 211 needs to be narrower than the distance measurement accuracy determined by the frequency bandwidth used for observation. When the laying interval is increased from the distance measurement accuracy, the distance Z between the targets in the longitudinal direction of the radio wave transmitting / receiving means 200 composed of the “cable radio wave transmitting means” and the “cable radio wave receiving means” and the direction away from the radio wave transmitting / receiving means 200 The distance R cannot be obtained with high accuracy. For example, when the frequency bandwidth used for the observation is 10 MHz, the distance measurement accuracy is the speed of light / (2 × bandwidth) = 3 × 10 ^ 8 ÷ (2 × 10 × 10 ^ 6) = 15 m. It needs to be narrowed.

  The terminator 213 connected to the far end of the leaky cable 211 is for absorbing a signal propagating toward the terminator 213 among the signals received by the leaky cable 211. Further, a signal that propagates toward the sensor 100 among signals received by the leakage cable 211 is configured to be input to the signal receiving unit 120 through the coaxial cable 212.

  The alarm device 300 includes a display unit such as a display and a sound output unit such as a speaker. The alarm device 300 sounds an alarm based on the approach information output from the approach determination unit 143, and is a radio wave transmitting / receiving unit 200 that is an approach position. And the distance Z between the target 400 and the target 400 are displayed.

Next, the operation of the first embodiment will be described. First, data stored in the storage unit 130 will be described.
FIG. 3 is an explanatory diagram illustrating a relationship between data stored in the storage unit 130 and each unit in the control unit 140.
The I component and Q component, which are the outputs of the quadrature demodulator 123 of the signal receiving means 120, are stored in the storage unit 130 as the quadrature detection result 131 as shown in FIG. The measuring means 141 outputs the intruder information 136 with reference to the quadrature detection result 131, that is, the I component and the Q component, and the processing is as follows.

  The intruder information 136 is the amplitude of the reflected wave signal from the target 400 approaching the radio wave transmitting / receiving means 200 and the propagation delay time from transmission to reception. Note that methods for realizing this measurement include a pulse method, FM-CW method, spread spectrum method, and the like used in UWB (ultra-wide band). Here, a configuration method using a frequency chirp method will be described.

  The measuring unit 141 sets an oscillation frequency for the sine wave generator 111 of the signal generating unit 110, and stores the orthogonal detection result 131 observed at this time in the frequency axis data string 132 of the storage unit 130. Then, the set oscillation frequency is gradually changed, and the respective quadrature detection results 131 are arranged in a row and stored in the storage unit 130. Then, a frequency axis data string 132 that is a quadrature detection result 131 for each frequency is created in the storage unit 130. This frequency axis data sequence 132 is a sequence of I component and Q component, but for numerical calculation, the I component is treated as a real number and the Q component is treated as an imaginary number. Therefore, the frequency axis data string 132 can be subjected to inverse Fourier transform as a complex number, and the time axis data string 133 obtained by the inverse Fourier transform is stored in the storage unit 130. The time axis data string 133 corresponds to an impulse response when a so-called pulse wave is transmitted, and the time axis data string includes information on the radio wave reflected by the target 400. Therefore, in order to obtain information on the radio wave reflected by the target 400, it is only necessary to obtain a difference based on a time axis data string obtained in advance and without the target 400 in an initial state.

  The storage unit 130 stores the reference time axis data sequence 134 in the initial state acquired in advance as described above, and the measuring unit 141 calculates the difference between the reference time axis data sequence 134 and the time axis data sequence 133. To obtain the target time axis data sequence 135. In the target time axis data string 135, a peak appears at a time position corresponding to the propagation delay time from when the signal generating means 110 outputs a signal until it is received by the signal receiving means 120. That is, a pulse wave is transmitted, and a waveform appears in which the pulse wave hitting the target 400 returns with a time delay. Here, when there are a plurality of targets 400, peaks corresponding to the respective targets 400 appear. Therefore, all peaks exceeding a predetermined threshold are extracted, and the amplitude, phase, and propagation delay time, which are the sizes of the peaks, are extracted.

  Now, the measuring means 141 acquires the frequency axis data string 132 while setting the oscillation frequency to the sine wave generator 111 of the signal generating means 110, and the above-described propagation delay time and amplitude from transmission to reception. Is also performed in another frequency range. Then, two sets of amplitude, phase, and propagation delay time are obtained, and the measuring means 141 outputs the intruder information 136 including these two sets of amplitude, phase, and propagation delay time to the storage unit 130.

The meaning of this operation will be described with reference to FIG.
The leaky cables 201 and 211 have a characteristic that the radiation directivity changes depending on the frequency. Therefore, as shown in FIG. 4A, in the radiation angle 511 of the frequency F1 and the radiation angle 512 of the frequency F2, the frequencies F1 and F2 at which the central angle of the radiation angle is 90 degrees are selected. The target time axis data string 135 is acquired by the measuring means 141 by multiplying the frequency F1 to F2, and the propagation delay time 521 is obtained therefrom. In addition, in the radiation angle 513 of the frequency F3 and the radiation angle 514 of the frequency F4, the frequencies F3 and F4 at which the central angle of the radiation angle is 45 degrees are selected. The target time axis data string 135 is acquired by the measuring means 141 by multiplying the frequency F3 to F4, and the propagation delay time 522 is obtained therefrom. The propagation delay time 521 is as shown in FIG.
T1 = 2 × (t1 + t2) (1)
And the propagation delay time 522 is as shown in FIG.
T2 = 2 × (t1 + t3 + t4) (2)
It is. 4B and 4C, the peak of the waveform in the target time axis data string 135 indicates a reflected wave.

The leakage cables 201 and 211 have a dielectric constant different from that of the air, so that the speed of radio waves is reduced and the wavelength is shortened. This shortening rate is referred to as a wavelength shortening rate (hereinafter referred to as K). In addition, the electrical length is increased by 1 / wavelength reduction rate due to the slower radio wave speed. Considering these points, from FIG. 4A to FIG. 4C, t2 = t3 ÷ K (3)
t2 = t4 cos (45 °) = t4 ÷ (√2) (4)
The relationship is also guided.

  By solving these simultaneous equations, t1 and t2 are obtained. This calculation is performed by the calculation means 142. If t1 and t2 are known, the target distance Z in the longitudinal direction of the radio wave transmission / reception means 200 comprising the cable-like radio wave transmission means and the cable-like radio wave reception means and the radio wave transmission / reception means 200 are obtained. It is possible to calculate the distance R in the direction away from the distance.

Next, the range of the frequencies F1 and F2 and the frequencies F3 and F4 will be described.
In general, the wider the frequency range, the sharper the impulse response in the time waveform, so that the target ranging accuracy improves. However, since a leaky cable is used, if the frequency range is expanded, the radiation angle range is expanded. As a result, the target image is blurred. In addition, as shown in the range of “II” in FIG. 2, the leakage cable has a high-order mode in which directivity is directed in a plurality of directions when the frequency is high. Here, the size of each element of the target time axis data string 135 is examined in order from the earliest time, and the peak that appears first is targeted, so when radio waves are emitted in multiple directions, one target A plurality of peaks exist, and calculation is not valid. Therefore, the frequencies F1 and F2 and the frequencies F3 and F4 are selected from the frequency band in which only one radiation direction exists, that is, from the range of “I” in FIG. In the present invention, the range of “I” in FIG. 2 is referred to as a basic mode region.

The frequency band in which there is only one radiation direction is in the range of the following equation depending on the pitch of the slot opened in the outer conductor of the leaky coaxial cable or leaky waveguide and the wavelength shortening rate.
C / [p (1 / K + 1)] <frequency used <2C / [p (1 / K + 1)]
Here, C is the speed of light and p is the slot pitch. Further, since the above equation is known, description of the derivation method and the like is omitted.

The above equation is based on the basic structure of the leaky coaxial cable, and in order to widen the frequency band in which there is only one radiation direction, subslots are placed at 1/2 or 1/3 of the conventional slot pitch. The technique to open is taken. In this case, the above equation is
C / [p (1 / K + 1)] <frequency used <3C / [p (1 / K + 1)],
C / [p (1 / K + 1)] <frequency used <5C / [p (1 / K + 1)].

  Now, to increase the accuracy of target position measurement, we want to make the difference between the two angles as wide as possible. By the way, in the above description, the radiation angles are selected to be 90 degrees and 45 degrees, for example. At this time, if the target 400 enters the vicinity of the far end at this angle, the measurement accuracy is significantly deteriorated. This is because the remaining leaked cables 201 and 211 are short near the far end, and the 45-degree radiation waves are weakened. As a method of avoiding this, there is a method of observing the vicinity of the far end with a combination of 135 degrees and 90 degrees. That is, by observing by changing the combination of frequencies, it is possible to measure the target 400 without reducing the measurement accuracy even at the ends of the leaky cables 201 and 211.

  By the way, the range of the use frequency is not managed so strictly in a normal leaky coaxial cable. This is because a normal leaky coaxial cable is mainly intended for broadcasting, and the purpose can be achieved if radio waves are emitted around the leaky coaxial cable. However, the accuracy of the radiation direction and the number of radiation directions are important factors for the measurement of the position required in the present invention.

Next, specific measurement processing by the measurement unit 141 will be described.
FIG. 5 is a flowchart showing an operation example of the measuring means 141.
First, the number of processing times is counted, and the writing position of the frequency axis data string 132 and the writing position of the time axis data string 133 are initialized (step ST101). Next, the processing count is inspected, and if it is the first time, the process proceeds to step ST103, and if it is the second time, the process proceeds to step ST104. In step ST103, the value of frequency F1 is set as a frequency setting variable, and the value of frequency F2 is set as an end confirmation variable, and the process proceeds to step ST105. In step ST104, the value of frequency F3 is set as a frequency setting variable, and the value of frequency F4 is set as an end confirmation variable, and the process proceeds to step ST105.

  In step ST105, the value of the frequency setting variable is set for the sine wave generator 111 of the signal generating means 110. After setting, the frequency setting variable for the next setting is updated to a frequency slightly shifted toward the value of the end confirmation variable. Next, the system waits for the quadrature detection result 131 in the storage unit 130 to be updated. When the quadrature detection result 131 is updated, the quadrature detection result 131 is written in the frequency axis data string 132 (step ST106). The I component is the real part and the Q component is the imaginary part. After writing, the next writing position is updated.

  Next, in step ST107, it is confirmed whether or not the frequency setting variable exceeds the end confirmation variable. If not, the process returns to step ST105, and if it exceeds, the process proceeds to step ST108. In step ST108, the value of the frequency axis data string 132 is Fourier-transformed and written in the time axis data string 133. After writing, for the next processing, the writing position of the frequency axis data string 132 and the position of the time axis data string 133 are initialized to positions that can be distinguished for each processing count.

  Next, in step ST109, the process count is checked. If the process count is the first, the process count is set to the second (step ST110), and the process returns to step ST102. If the process count is the second, The process moves to step ST111. In step ST111, the difference between the reference time axis data string 134 and the time axis data string 133 acquired in advance is taken and written in the target time axis data string 135. Since the reference time-axis data string 134 and the time-axis data string 133 include two sets of data strings corresponding to the frequencies F1 to F2 and F3 to F4, respectively, the difference is obtained in each data string and two sets of target times are set. An axis data string 135 is obtained.

Next, in step ST112, all peaks exceeding a predetermined threshold are extracted from the two sets of target time axis data strings 135, and the amplitude, phase, and propagation delay time, which are the sizes of the peaks, are extracted, and the intruder is extracted. The information 136 is output to the storage unit 130. There are two sets of intruder information 136.
Thus, the processing by the measuring unit 141 is completed, and then the operation unit 142 is performed.

  As described above, the computing unit 142 classifies the intruder information 136 of the target 400 for each target 400, and based on the classified measurement information, the distance Z of the target 400 in the longitudinal direction of the radio wave transmitting / receiving unit 200 and the radio wave transmitting / receiving unit. The distance R in the direction away from 200 is calculated. Here, when there are a plurality of targets 400, the calculation unit 142 needs to determine a combination for each target between the two sets of intruder information 136. For example, when there are two targets, each set of intruder information 136 includes information on two targets. Therefore, if this combination is mistaken, the target position is completely wrong.

  As a simple method of this combination, there is a method of using the amplitude in the intruder information 136. That is, it is a method of combining those having close amplitude values. However, when the target is close to the leaking cable, the amplitude value is close, but when the target is far away, the difference opens. If there are multiple targets at various distances, there is a risk of incorrect combinations. However, near the leaky cable, the amplitude value is close, and the propagation delay time is almost the same value. For this reason, the combination accuracy is improved, and there is no problem as an approach detection system.

However, in order to further improve the accuracy, the temporal change in amplitude and phase is used.
A time differential value of amplitude and phase is a simple example, but it is effective to perform a frequency analysis by a Fourier transform or the like on the time change of the signal, amplitude, or phase.
FIG. 6 is a diagram for explaining the observation situation of two targets, and shows the observation situation by the targets 401 and 402.
In the observation of the frequencies F1 to F2, two reflected waves of the reflected wave A and the reflected wave B are detected as the target time axis data string 135 (see FIG. 6B). In the observation of the frequencies F3 to F4, two reflected waves of the reflected wave C and the reflected wave D are detected as the target time axis data string 135 (see FIG. 6C). Next, between the propagation delay time 521 of the reflected wave A, the propagation delay time 523 of the reflected wave B, the propagation delay time 522 of the reflected wave C, and the propagation delay time 524 of the reflected wave D, each target 401, The combinations of propagation delay times corresponding to 402 are classified.

As described above, this classification includes a method using amplitude.
When compared in terms of amplitude, there is a relationship of reflected wave A <reflected wave B, reflected wave C <reflected wave D, and (reflected wave A and reflected wave C) and (reflected wave B and reflected wave D) can be classified ( (See broken line portions 530 and 540 in FIGS. 6B and 6C).

Moreover, since there is a risk of misclassification only with the amplitude, the timing at which the signal changes can also be used.
FIG. 7 is a diagram of the time history of the reflected wave intensity observed at each propagation delay time.
In the figure, (a) to (d) correspond to the waveforms of reflected wave A to reflected wave D, respectively.
In FIG. 7, the reflected wave A (a) and the reflected wave C (c) rise simultaneously and a signal change occurs. In addition, the reflected wave B (b) and the reflected wave D (d) rise simultaneously and a signal change occurs. Therefore, (reflected wave A and reflected wave C) and (reflected wave B and reflected wave D) can be classified. Further, the reflected wave A and the reflected wave C fluctuate finely at the apex portion where each signal rises, and the reflected wave A and the reflected wave C fluctuate greatly and gently. This difference can be easily detected by analyzing the frequency as a variable frequency, and can be classified by combinations of variable frequencies.
As described above, it is possible to extract a combination with high accuracy by performing classification based on the rising timing of each peak, frequency analysis of temporal changes, and performing classification by combining the same frequencies.

By the combination described above, the calculation unit 142 obtains propagation delay times T1 and T2 corresponding to the target 400 (in the case shown in FIG. 4). The position of the target 400 is calculated from these T1 and T2. In this calculation, t1 and t2 are obtained using the following (5) and (6) obtained by solving the serial equations (1) to (4) described above.
t1 = T1 ÷ 2− (T2−T1) ÷ (2 × (K + √2-1)) (5)
t2 = (T2−T1) ÷ (2 × (K + √2−1)) (6)

Here, T1 is the first propagation delay time stored in the intruder information 136 obtained using the frequencies F1 to F2, and T2 is the intruder information obtained using the frequencies F3 to F4. 136 is the second stored propagation delay time.
As shown in FIG. 4A, t1 is the distance from the sensor 100 side of the radio wave transmission / reception means 200 to the intersection of the perpendicular line dropped from the target 400 to the radio wave transmission / reception means 200, that is, the length of the target in the longitudinal direction of the radio wave transmission / reception means 200. This is the time for the signal to propagate through the distance Z. T2 is the time for the signal to propagate the distance between the intersection point and the target 400, that is, the distance R in the direction away from the radio wave transmitting / receiving means 200.

Then, the distance Z and the distance R are obtained from t1 and t2 using the following (7) and (8).
Z = t1 × K × C (7)
R = t2 × C (8)
Here, C is the speed of light (= 3 × 10 ^ 8).
The calculation unit 142 outputs intruder position information 137 including the distance Z and the distance R to the storage unit 130 by performing such calculation.

Next, the operation of the approach determination unit 143 will be described.
As described above, the approach determination unit 143 detects the approach of the target 400 using the intruder position information 137. This is executed by searching in advance whether the distance Z and distance R of the target 400 are within the range indicated by the alarm area information 138 of the storage unit 130.
In the alarm area information 138, only the threshold value of the distance R needs to be set in order to detect all targets that are close to a certain level in the radio wave transmitting / receiving unit 200. In addition, for example, a part that is allowed to approach, such as an entrance / exit, can be realized by finely specifying the alarm range of the distance Z and the distance R. Furthermore, in combination with a clock, the detection range can be changed during the day and at night.
When the target 400 enters the range set by the warning area information 138, the approach determination unit 143 outputs the presence / absence of approach, the distance Z, and the distance R to the alarm device 300 as approach information. When the alarm device 300 detects that there is an approach from the approach information, the alarm device 300 generates a predetermined alarm sound and displays the distance Z and the distance R that are the approach positions.

  By the way, it is desirable to observe the transmission frequencies F1, F2, F3, and F4 in various combinations. This is because, as described above, for example, when 90 degrees and 45 degrees are selected, if the target 400 enters the vicinity of the far end at this angle, the measurement accuracy is significantly deteriorated.

ここで、θ１＝π／２、θ２＝π／４とすると（９）は（５）と一致し、（１０）は（６）と一致する。更に、送信周波数の組合せを常に変化させることにより、一部の周波数が電波妨害等で利用できなくとも、別の周波数で観測できるなど、妨害に強くなり、セキュリティシステムとしての価値も向上する。また、漏洩ケーブル２０１，２１１の端の部分でも測定精度を落とすことなく、ターゲット４００の測定が可能となる。 When the frequency is changed and the radiation direction is changed, the following equation is used instead of (5) and (6).

Here, if θ1 = π / 2 and θ2 = π / 4, (9) matches (5) and (10) matches (6). Furthermore, by constantly changing the combination of transmission frequencies, even if some frequencies cannot be used due to radio interference, etc., they can be observed at other frequencies, and the value as a security system is improved. In addition, the target 400 can be measured without reducing the measurement accuracy even at the ends of the leakage cables 201 and 211.

  Further, there is a method for fundamentally solving a combination of a plurality of peaks that appear when a plurality of targets are observed by changing a combination of frequencies. That is, the combination of the two frequencies is initially set to the same value or close to each other, and is observed while gradually expanding. As a result, the difference between the plurality of peaks, which initially had the same propagation delay time between the two sets of intruder information 136, gradually increases. Then, the position can be calculated when the difference is wide enough to obtain the required measurement accuracy without worrying about incorrect combinations.

  Also, if it takes time to open the combination of two frequencies little by little, obtain the frequency axis data string in a sufficiently wide range, extract the necessary frequencies from it, and perform the subsequent processing. If this is done, only one measurement is required and only the calculation is performed after that. Therefore, position measurement can be performed at a very high speed and with high accuracy.

  Furthermore, the use of a two-dimensional table in which equations (5), (6) and equations (9), (10) are calculated in advance can speed up the calculation. By the way, in a real environment, there may be a case where the value does not become as expected from the surrounding radio wave condition. If an error in the actual environment is added to this two-dimensional table in advance, high accuracy and high speed detection are possible.

  In the first embodiment, the signal generating means, the signal receiving means, and the measuring means are configured by the frequency chirp method to measure the amplitude of the reflected wave and the propagation delay time of the target. However, as a method for realizing this measurement, a pulse method, an FM-CW method, a spread spectrum method, or the like used in UWB (ultra wide band) can be used, and these methods may be used. However, the frequency range of the spectrum of the transmission frequency needs to be within the range indicated by the predetermined formula (within the basic mode region).

  As described above, according to the approach detection system of the first embodiment, the cable-shaped radio wave transmission means whose radiation directivity changes depending on the frequency and the radio wave transmission means are laid substantially parallel to each other and transmitted from the radio wave transmission means. Radio wave transmission / reception means comprising a cable-shaped radio wave reception means for receiving received radio waves and multiple frequency bands that are reflected by the target and received by the radio wave reception means when radio waves of multiple frequency bands are transmitted from the radio wave transmission means Measurement means for outputting measurement information consisting of the signal intensity and phase of the reflected wave for each frequency band and the propagation delay time from transmission to reception based on the radio wave, and the reflected wave signal for each frequency band Based on the intensity and phase information, the measurement information is classified for each target. Based on the classified measurement information, the distance of the target in the longitudinal direction of the radio transmission / reception means and the radio transmission / reception means And calculating means for calculating the distance to the target in the direction away from the target, so that the presence of the target can be reliably detected regardless of the positional relationship of the target with respect to the radio wave transmitting / receiving means. Even if there are a plurality of targets, the positions of these targets can be individually detected.

  Further, according to the approach detection system of the first embodiment, the frequency band of the radio wave transmitted from the radio wave transmission means is such that the radiation direction of the signal output when a single signal is given to the radio wave transmission means. Since it is a single basic mode area range, and signals in multiple frequency bands are given to the radio wave transmission means within the basic mode area range, multiple directions according to the higher order mode of the leaky cable The target can be detected reliably and accurately by preventing the emission of radio waves.

  Further, according to the approach detection system of the first embodiment, an alarm device that outputs an alarm is provided, and when a target is present in a predetermined alarm area, an alarm is generated from the alarm device. Even if the target enters the designated alarm area, the situation can be easily recognized.

Embodiment 2. FIG.
In the second embodiment, a high-order mode region (which will be described later) is used as a frequency range used for observation.

Since the configuration on the drawing is the same as that of the first embodiment, it will be described with reference to FIGS. The measurement unit 141 according to the second embodiment is different from the first embodiment in that the signal generation unit 110 is instructed to output a frequency within the range of the higher-order mode region of the leakage cables 201 and 211. . That is, the signal generation unit 110 is instructed so that the frequency of the radio wave transmitted from the leakage cable 201 falls within the following range.
2C / [p (1 / K + 1)] <frequency used where C is the speed of light and p is the slot pitch.
This corresponds to the region “II” in FIG. 2, and radio waves are radiated from the leakage cable 201 in a plurality of directions when the frequency in this region is used. In the present invention, the region “II” in FIG. 2 is referred to as a high-order mode region. Since the above equation is also known, detailed description thereof is omitted here.

  Since the configuration of each part in the other sensor 100 is the same as that of the first embodiment, the description thereof is omitted here.

Next, the operation of the approach detection system of the second embodiment will be described.
In the present embodiment, the target 400 is observed only in one frequency range, the distance Z between the target in the longitudinal direction of the radio wave transmission / reception means 200 including the cable-like radio wave transmission means and the cable-like radio wave reception means, and the radio wave transmission / reception means 200. The distance R in the direction away from is determined.

  Since the frequency band used for observing the target 400 is the region “II” in FIG. 2, when an appropriate frequency F5 to F6 is selected, the target 400 can be observed at two angles simultaneously. Therefore, the acquisition of the frequency axis data string 132 executed by the measuring unit 141 may be performed once. Instead, two peaks appear in the target time axis data sequence 135 obtained by the difference from the reference time axis data sequence 134 after Fourier transform. This peak corresponds to the observation result for each angle. Therefore, these two peaks are measured to obtain propagation delay times T1 and T2. Hereinafter, the operation of the measuring unit 141 will be described in detail.

FIG. 8 is a flowchart showing the operation of the measuring means 141.
First, in step ST201, the writing position of the frequency axis data string 132 and the writing position of the time axis data string 133 are initialized. Further, the value of the frequency F5 is set as a frequency setting variable, and the value of the frequency F6 is set as an end confirmation variable. Note that the values of these frequencies F5 and F6 are the frequencies of the higher-order mode region described above, as shown in FIG.

  Next, in step ST202, the value of the frequency setting variable is set for the sine wave generator 111 of the signal generating means 110. After setting, the frequency setting variable for the next setting is updated to a frequency slightly shifted toward the value of the end confirmation variable. Next, in step ST203, the process waits for the quadrature detection result 131 in the storage unit 130 to be updated. When the quadrature detection result 131 is updated, the quadrature detection result 131 is written in the frequency axis data string 132. The I component is the real part and the Q component is the imaginary part. After writing, the next writing position is updated.

  Next, in step ST204, it is confirmed whether or not the frequency setting variable exceeds the end confirmation variable. If not, the process returns to step ST202, and if it exceeds, the process proceeds to step ST205. In step ST205, the value of the frequency axis data string 132 is Fourier-transformed and written in the time axis data string 133. Next, in step ST <b> 206, the difference between the reference time axis data sequence 134 and the time axis data sequence 133 acquired in advance is taken and written in the target time axis data sequence 135.

  Next, in step ST207, the target time axis data sequence 135 is searched for the amplitude that is the square root of the square sum of the real part and the imaginary part in order from the earliest time. A peak exceeding a predetermined threshold is detected, and the time axis value and amplitude at that time are output to the storage unit 130 as intruder information 136. There are two sets of intruder information 136. Thus, the process of the measuring unit 141 is completed, and then the process of the calculating unit 142 is performed.

  The computing means 142 calculates times t1 and t2 with a predetermined mathematical formula, calculates distances Z and R, and outputs intruder position information 137. Here, since the radiation angle is not necessarily the same as that of the first embodiment, the formula used in the first embodiment may not be used, but a simultaneous equation is established and solved at any angle. Thus, (5) and (6) shown in the first embodiment can be derived. For example, if two types of angles based on the first frequency are θ1 and θ2, the equations corresponding to (5) and (6) are (9) and (10) in the first embodiment. Here, if θ1 = π / 2 and θ2 = π / 4, (9) matches (5) and (10) matches (6). And the distance Z and the distance R are calculated | required using (7) and (8) shown in Embodiment 1 from t1 and t2. The calculation unit 142 outputs intruder position information 137 including the distance Z and the distance R to the storage unit 130 by performing such calculation. The approach determination unit 143 detects the approach of the target 400 using the intruder position information 137, but the subsequent operation is the same as that of the first embodiment, and thus the description thereof is omitted here.

  In the second embodiment as well, the calculation unit 142 operates in the same manner as in the first embodiment even when there are a plurality of targets as shown in FIGS. 6 and 7. Can be detected.

  As described above, according to the proximity detection system of the second embodiment, the frequency band of the radio wave transmitted from the radio wave transmission unit is the signal output when a single signal is given to the radio wave transmission unit. A signal in a single frequency band is given to the radio wave transmission means within the range of the higher-order mode region where there are multiple radiation directions and within the range of the higher-order mode region. Since radio waves can be emitted to the target from a plurality of directions, the time required for measurement can be shortened.

Embodiment 3 FIG.
In the third embodiment, a plurality of sets of the approach detection system according to the first or second embodiment are provided, and the three-dimensional position of the target 400 is measured.

FIG. 9 is an explanatory diagram showing the configuration and operating principle of the approach detection system of the third embodiment.
The approach detection system of the third embodiment includes two sets of sensors and radio wave transmission / reception means. That is, from one set of sensor 100a, coaxial cables 202a and 212a, leaky cables 201a and 211a, terminators 203a and 213a, sensor 100b, coaxial cables 202b and 212b, leaky cables 201b and 211b, and terminators 203b and 213b. And the other set. Each configuration is the same as that of the sensor 100, the coaxial cables 202 and 212, the leakage cables 201 and 211, and the terminators 203 and 213 in the first embodiment or the second embodiment, and thus the description thereof is omitted here. However, in the third embodiment, it is assumed that the configuration corresponding to the approach determination unit 143 and the warning area information 138 is provided in the three-dimensional position measurement unit 500.

  In Embodiment 3, the distance of the target 400 in the longitudinal direction on the radio wave transmitting / receiving means 200a side is Z1, the distance to the target 400 is R1, and the distance of the target 400 in the longitudinal direction on the radio wave transmitting / receiving means 200b side is Z2. Let the distance to 400 be R2.

  As described above, the three-dimensional position measuring unit 500 is separated from the distances Z1 and Z2 in the longitudinal direction of the radio wave transmission / reception units 200a and 200b of the target 400 obtained by the sensors 100a and 100b, and the radio wave transmission / reception units 200a and 200b. Based on the distances R1 and R2 in the direction, the three-dimensional position of the target 400 is obtained, the approach of the target 400 is determined based on the three-dimensional position, and the presence / absence of approach and the radio wave transmitting / receiving means 200a, 200b The distance from the target 400 is output to the alarm device 300. The alarm device 300 is the same as that in the first embodiment or the second embodiment.

Next, the operation of the third embodiment will be described.
The method of obtaining the distances Z1, Z2 and R1, R2 of the target 400 using the leakage cables 201a, 211a and the leakage cables 201b, 211b is the same as in the case of the distance Z and the distance R in the first embodiment or the second embodiment. It is.

  In the three-dimensional position measuring means 500, the first approach information including information on the presence / absence of approach, distance Z1, and distance R1 from the sensor 100a, and the information on the presence / absence of approach, distance Z2, and distance R2 from the sensor 100b. Second approach information is input. As a result, the three-dimensional position measuring means 500 uses the distances Z1, Z2, R1, R2 obtained as the first and second approach information based on the arrangement of the leakage cables 201a, 211a and the leakage cables 201b, 211b as a target 400. It is possible to measure the three-dimensional position.

For example, in the case of the configuration shown in FIG. 9, the three-dimensional position can be measured by the following equation.

  When the three-dimensional position of the target 400 is calculated, the three-dimensional position measuring unit 500 compares the obtained z, y, and h with a predetermined spatial alarm area value. Then, approach information including the three-dimensional position of the target 400 is output to the alarm device 300 as being approached when the three-dimensional position of the target enters the alarm area. As a result, the alarm device 300 outputs an alarm and displays the three-dimensional position of the target 400.

  As described above, according to the proximity detection system of the third embodiment, the cable-shaped radio wave transmission means whose radiation directivity changes depending on the frequency and the radio wave transmission means are laid substantially in parallel and transmitted from the radio wave transmission means. Radio wave transmission / reception means comprising a cable-shaped radio wave reception means for receiving received radio waves and multiple frequency bands that are reflected by the target and received by the radio wave reception means when radio waves of multiple frequency bands are transmitted from the radio wave transmission means Measurement means for outputting measurement information consisting of the signal intensity and phase of the reflected wave for each frequency band and the propagation delay time from transmission to reception based on the radio wave, and the reflected wave signal for each frequency band Based on the intensity and phase information, the measurement information is classified for each target. Based on the classified measurement information, the distance of the target in the longitudinal direction of the radio transmission / reception means and the radio transmission / reception means A plurality of sets of calculation means for calculating the distance to the target in the direction away from each other, and the three-dimensional position of the target based on the distances of the plurality of sets of targets obtained by the plurality of sets of radio wave transmission / reception means, measurement means, and calculation means 3D position measuring means for measuring the three-dimensional position of the target can be measured. Thereby, for example, a three-dimensional fine alarm area can be set, and it is also possible to distinguish whether it is an intrusion from the sky or an intrusion from the ground.

Embodiment 4 FIG.
In the fourth embodiment, a function curve is extracted from the relationship between propagation delay times in a plurality of frequency bands, and the distance from the target in the longitudinal direction of the radio wave transmitting / receiving unit and the direction away from the radio wave transmitting / receiving unit are calculated from the coefficients of the function curve. The target distance is calculated.

  The configuration on the drawing in the approach detection system of the fourth embodiment is the same as that in FIG. 1 and FIG. 3 used in the first embodiment, and will be described with reference to these drawings. The measurement unit 141 according to the fourth embodiment, when transmitting radio waves of a plurality of frequency bands from the leak cable 201, reflects the plurality of radio waves based on the radio waves of the plurality of frequency bands reflected by the target 400 and received by the leak cable 211. It is configured to acquire a propagation delay time from transmission to reception for each frequency band. In addition, the calculation unit 142 calculates the distance Z of the target 400 in the longitudinal direction of the radio wave transmission / reception unit 200 and the radio wave transmission / reception unit 200 based on the relationship between the plurality of frequency bands and the propagation delay time corresponding to the plurality of frequency bands. The distance R to the target 400 in the away direction is calculated. Since other configurations are the same as those of the first embodiment, description thereof is omitted here.

Next, the operation of the fourth embodiment will be described.
The method for acquiring the propagation delay time of the intruder information 136 in the preset frequency band has been described in the first embodiment. In the fourth embodiment, the propagation delay time of the intruder information 136 observed in each frequency band is associated with each frequency band, and is handled as two-dimensional information with the X axis as the frequency axis and the Y axis as the propagation delay time.

ここで、Ｚはターゲットの電波送受信手段２００方向の距離、Ｒは電波送受信手段２００から直角方向の距離、φは観測周波数から図２によって導かれる放射角度、Ｃ′は漏洩ケーブル２０１，２１１内の電波の速度である。φ＜＜１とすると、伝搬遅延時間Ｔは、次式（１５）のように近似できる。 The propagation delay time T when observed in a certain observation frequency band is expressed by the following equation (14).

Here, Z is the distance in the direction of the radio wave transmission / reception means 200 of the target, R is the distance in the direction perpendicular to the radio wave transmission / reception means 200, φ is the radiation angle derived from the observation frequency by FIG. 2, and C ′ is in the leakage cables 201 and 211. It is the speed of radio waves. If φ << 1, the propagation delay time T can be approximated by the following equation (15).

上式（１５）は１／ｆの関数であり、距離Ｒが大きいほど係数ａが大きくなることが分かる。また、この関数を求めることができれば、つまり、関数の係数ａとｂが求められれば、ターゲット座標（Ｚ，Ｒ）が求められる。
そのためには、異なる周波数帯域で観測した伝搬遅延時間を収集する。

The above equation (15) is a function of 1 / f, and it can be seen that the coefficient a increases as the distance R increases. If this function can be obtained, that is, if the coefficients a and b of the function are obtained, the target coordinates (Z, R) are obtained.
For this purpose, the propagation delay times observed in different frequency bands are collected.

FIG. 10 shows a plot of the target time-axis data string 135 obtained by observing three targets in five frequency bands and the propagation delay time of the intruder information 136 on a two-dimensional plane, and an approximation obtained by Hough transformation. It is explanatory drawing which shows the straight line 601. FIG.
The Hough transform is one of techniques often used for image analysis, and is a technique for extracting a function of an arbitrary shape from a level distribution of two-dimensional values. Here, the function of the propagation delay time T is extracted using the Hough transform. In the Hough transform, when there are a plurality of functions, each function can be extracted individually. In FIG. 10, three function curves are extracted. When the coefficients a and b are obtained in this way, the target coordinates are obtained by the following equation (16).

このような動作を実行するため、実施の形態１の計測手段１４１では、二つの周波数帯域の伝搬遅延時間を計測しているが、実施の形態４の計測手段１４１では、二つ以上の周波数帯域を計測できるように拡張すればよい。尚、図１０の例では、５種類の周波数帯域を計測しているが、２種類以上であればどのような値であってもよい。

In order to execute such an operation, the measurement unit 141 of the first embodiment measures the propagation delay time of two frequency bands, but the measurement unit 141 of the fourth embodiment measures two or more frequency bands. Can be expanded so that can be measured. In the example of FIG. 10, five types of frequency bands are measured, but any value may be used as long as it is two or more types.

  In the calculation means 142, the propagation delay time of the intruder information 136 is Y, the observation frequency is X, and a curve is obtained by Hough transformation. In the process of obtaining this curve, a preset threshold value is used, and curve parameters exceeding this threshold value are extracted. The number of curves exceeding this threshold is the target number.

  As described above, in the fourth embodiment, the number of targets, the distance Z of each target, and the distance R can be extracted by using a curve extraction method such as Hough transform. In addition, the problem of the classification of multiple targets, which is a problem in the first embodiment, can be solved. For example, as shown in the frequency band F3 of FIG. 10, there is a frequency band in which the propagation delay times of the two targets are the same, but in this case, it is difficult to reliably classify in the first embodiment. . However, in the fourth embodiment, it can be easily and reliably separated.

  As described above, according to the proximity detection system of the fourth embodiment, the cable-shaped radio wave transmission means whose radiation directivity changes depending on the frequency and the radio wave transmission means are laid substantially in parallel and transmitted from the radio wave transmission means. Radio wave transmission / reception means comprising a cable-shaped radio wave reception means for receiving received radio waves and multiple frequency bands that are reflected by the target and received by the radio wave reception means when radio waves of multiple frequency bands are transmitted from the radio wave transmission means The relationship between the measurement means for obtaining the propagation delay time from transmission to reception for each of the plurality of frequency bands based on the radio wave, and the propagation delay times corresponding to the plurality of frequency bands and the plurality of frequency bands And calculating means for calculating the distance to the target in the direction away from the radio wave transmitting / receiving means. Even when the target was present, it is possible to classify these targets reliably.

  Further, according to the proximity detection system of the fourth embodiment, the calculation means extracts a function curve from the two-dimensional distribution of the observed frequency versus the propagation delay time, and the distance of the target in the longitudinal direction of the radio wave transmission / reception means from the coefficient of the function curve Since the distance R to the target in the direction away from Z and the radio wave transmission / reception means is calculated, the number of targets, the distance Z and the distance R of each target can be easily and reliably extracted.

  In the fourth embodiment, the present invention is applied to the measurement unit 141 and the calculation unit 142 in the approach detection system of the first embodiment, but is applied to the configurations of the second and third embodiments. May be.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the approach detection system by Embodiment 1 of this invention. It is explanatory drawing which shows the radiation directivity characteristic of the leakage cable of the proximity detection system by Embodiment 1 of this invention. It is explanatory drawing which shows the relationship between the data of the memory | storage part of the approach detection system by Embodiment 1 of this invention, and a control part. It is explanatory drawing which shows the operation principle of the proximity detection system by Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the measurement means of the approach detection system by Embodiment 1 of this invention. It is explanatory drawing of the principle of operation in case there exist multiple targets of the proximity detection system by Embodiment 1 of this invention. It is explanatory drawing which shows the time history of the reflected wave intensity observed in each propagation delay time of the proximity detection system by Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the measurement means of the approach detection system by Embodiment 2 of this invention. It is explanatory drawing which shows the structure and operating principle of the proximity detection system by Embodiment 3 of this invention. It is explanatory drawing which shows the operation principle of the proximity detection system by Embodiment 4 of this invention.

Explanation of symbols

  100, 100a, 100b sensor, 141 measuring means, 142 calculating means, 143 approach determining means, 200, 200a, 200b radio wave transmitting / receiving means, 201, 201a, 201b leakage cable (radio wave transmission means), 211, 211a, 211b leakage cable ( Radio wave receiving means), 300 alarm device, 400, 401, 402 target, 500 three-dimensional position measuring means.

Claims (4)

A radio wave comprising a cable-shaped radio wave transmitting means whose radiation directivity changes depending on the frequency, and a cable-shaped radio wave receiving means laid substantially parallel to the radio wave transmitting means and receiving a radio wave transmitted from the radio wave transmitting means. Transmitting and receiving means;
When radio waves of a plurality of frequency bands are transmitted from the radio wave transmission means, transmission is performed for each of the plurality of frequency bands based on the radio waves of the plurality of frequency bands reflected by the target and received by the radio wave reception means. A measuring means for acquiring a propagation delay time from reception to reception,
Extract the function curve of the propagation delay time versus the plurality of frequency bands and the plurality of frequency bands, the longitudinal distance and the radio wave transmission and reception of the target of the radio wave transmitting and receiving means by a predetermined operation from the coefficient of the function curve An approach detection system comprising: a calculation unit that calculates a distance to the target in a direction away from the unit. The frequency band of the radio wave transmitted from the radio wave transmission means is the range of the basic mode region in which the radiation direction of the signal output when the single signal is given to the radio wave transmission means is single, and , the basic range of mode region, claim 1 Symbol placement approach detecting system and a signal of a plurality of frequency bands is given to the wave transmission means. The frequency band of the radio wave transmitted from the radio wave transmission means is a range of a higher-order mode region where there are a plurality of radiation directions of signals output when a single signal is given to the radio wave transmission means, and , the range of the high-order mode region, claim 1 Symbol placement approach detecting system and a signal of a single frequency band is given to the wave transmission means. Including an alarm unit for outputting an alarm, if the target is present in the predetermined alarm region, set forth in any one of claims 1 to claim 3, characterized in that for generating an alarm from the alarm device Proximity detection system.

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