JP3521763B2 - Radar system, object detection method, and recording medium - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar device, an object detection method, and a recording medium, and more particularly, to a set of radar devices by transmitting and receiving electromagnetic waves and comparing the received electromagnetic waves. The present invention relates to a radar device capable of detecting an object existing between devices, an object detection method, and a recording medium.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting whether or not an object exists on a predetermined straight line, a method of using a pair of opposed measuring devices is well known. However, this method may cause false detection of an object due to external factors such as rain, fog, snow, and dust.

Therefore, the applicant of the present invention discloses a method of detecting an object by using a pair of measuring devices facing each other and setting a threshold value in a receiving level in the measuring device by a predetermined method, as disclosed in Japanese Patent Laid-Open No. 7-221623. I proposed earlier.

[0004]

However, in the method proposed above, when the temporal change due to external factors such as rain, fog, snow, and dust is small, and the amount of attenuation of electromagnetic waves due to them is small, Although it is not so problematic, there is a possibility that an object may be erroneously detected when the external factor has a large temporal change and the amount of attenuation of the electromagnetic wave based on them is large.

The present invention has been made in view of such a situation, and makes it possible to accurately detect an object even when an external factor has a large time change and the amount of attenuation caused thereby is large. .

[0006]

A radar system according to claim 1 comprises a first transmitting / receiving means for transmitting and receiving electromagnetic waves,
It is possible to transmit and receive electromagnetic waves to and from the first transmitting / receiving means.
The result of comparison by the second transmitting / receiving means arranged at such a position and transmitting / receiving the electromagnetic wave, comparing means comparing the electromagnetic waves received by the first transmitting / receiving means and the second transmitting / receiving means, and the comparing means. Based on the first
The transmitting / receiving means and the detecting means for detecting an object existing between the second transmitting / receiving means.

An object detecting method according to a seventh aspect of the present invention is the object detecting method for a radar device comprising a first transmitting / receiving device and a second transmitting / receiving device for transmitting and receiving electromagnetic waves,
Transmission and reception of the first transmission and reception step of receiving an electromagnetic wave, said first transceiver and another electromagnetic wave by the transceiver device
A second transmitting / receiving step of transmitting / receiving an electromagnetic wave by the second transmitting / receiving device arranged at a position where it can be received, and a comparing step of comparing the electromagnetic waves received in the first transmitting / receiving step and the second transmitting / receiving step. And a detection step of detecting an object existing between the first transmission / reception device and the second transmission / reception device based on the result of the comparison in the comparison step.

A recording medium according to claim 8 is a first transmission / reception step of transmitting / receiving an electromagnetic wave to / from a radar device including a first transmission / reception device and a second transmission / reception device for transmitting / receiving an electromagnetic wave. And the first transmission / reception
Placed at a position where it can send and receive electromagnetic waves to and from the communication device
A second transmitting / receiving step of transmitting / receiving an electromagnetic wave by the second transmitting / receiving device, a comparing step of comparing the electromagnetic waves received in the first transmitting / receiving step and the second transmitting / receiving step, and a comparison in the comparing step. A computer-readable program for executing a process including a detection step of detecting an object existing between the first transmission / reception device and the second transmission / reception device based on the result Is characterized by.

In the radar system according to the first aspect, the radar system is placed at a position where mutual electromagnetic waves can be transmitted and received.
Was based on the first and second transceiver means electromagnetic wave comparison result received by an object present between the first and second transmitting and receiving means is detected.

In the object detection method according to claim 7 and the recording medium according to claim 8 , electromagnetic waves are transmitted to each other.
An object existing between the first and second transmission / reception devices is detected based on the comparison result of the electromagnetic waves received by the first and second transmission / reception devices arranged at positions where they can be received .

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. To clarify the correspondence between each means of the invention described in the claims and the following embodiments, The features of the present invention will be described below by adding a corresponding embodiment (but one example) in parentheses after each means. However, of course, this description does not mean that each means is limited to the described one.

According to a first aspect of the present invention, there is provided a radar system in which a first transmitting / receiving means for transmitting / receiving an electromagnetic wave (for example, the radar device 1 in FIG. 1) and a first transmitting / receiving means transmit / receive an electromagnetic wave to / from each other.
A second transmission / reception unit (for example, the radar device 2 in FIG. 1) arranged at a position where it can be received and transmitting / receiving an electromagnetic wave is compared with the electromagnetic waves received by the first transmission / reception unit and the second transmission / reception unit. Comparison means (for example, the amplitude comparator 3 in FIG. 1) and detection means for detecting an object existing between the first transmission / reception means and the second reception means based on the result of comparison by the comparison means ( For example, the output device 4 in FIG. 1)
And is provided.

FIG. 1 is a block diagram showing a configuration example of a radar system to which the present invention is applied. The radar device 1 and the radar device 2 are installed so as to face each other and transmit electromagnetic waves of the same frequency in the millimeter wave band with the same output. The radar device 1 and the radar device 2 are arranged so that the directions of the electromagnetic fields having the maximum intensity of the transmitted electromagnetic waves are directed toward the radar device 2 and the radar device 1, respectively.

The amplitude comparator 3 compares the amplitudes of the respective electromagnetic waves received by the radar device 1 and the radar device 2 and outputs the comparison result to the output device 4. Output device 4 is LC
It is composed of a D, a speaker, a display device, etc., and detects the presence or absence of an object existing between the radar device 1 and the radar device 2.

Next, the operation of the radar system of FIG. 1 will be described with reference to the flowchart of FIG. In step S1, the radar device 1 and the radar device 2 each sense an object. That is, the radar device 1 and the radar device 2 transmit electromagnetic waves of the same frequency in the millimeter wave band with the same output. Therefore, the radar device 1 receives the electromagnetic wave transmitted by the radar device 1, and the radar device 2 receives the electromagnetic wave transmitted by the radar device 1. The radar device 1 and the radar device 2 respectively detect the reception level (amplitude) of the received electromagnetic waves and supply the detected results to the amplitude comparator 3.

At step S2, the amplitude comparator 3
The amplitudes (hereinafter, also referred to as reception levels) of electromagnetic waves received by the radar device 1 and the radar device 2 are compared.

In step S2, the amplitude comparator 3
Determine whether there is a difference in the received levels of the compared electromagnetic waves. When the amplitude comparator 3 determines in step S2 that there is no difference in the reception level, the process returns to step S1.
The sensing process is repeated until a difference occurs in the reception level.

When there is no object between the radar device 1 and the radar device 2, since the electromagnetic waves of the same frequency and the same output are transmitted from the radar device 1 and the radar device 2, the radar device 1 and the radar device 2 The reception levels of the electromagnetic waves received by are the same.

For example, the distance between the radar device 1 and the radar device 2 is 10 m, the output of the electromagnetic wave transmitted from the radar device 1 and the radar device 2 is 10 dBm, and the attenuation rate (propagation due to external factors such as molecules existing in the atmosphere) Loss) is 0.1 dB / m
Assuming that, the reception level of the electromagnetic waves transmitted from the radar device 2 and the radar device 1 in the radar device 1 and the radar device 2 is 9 dB.

The reception level of electromagnetic waves received by the radar device 1 and the radar device 2 when an object exists between the radar device 1 and the radar device 2 will be described with reference to FIG. The horizontal axis of FIG. 3 represents the distance of the object from the radar device 1, and the vertical axis represents the radar device 1 and the radar device 2.
The received level of the electromagnetic wave received by is shown. In FIG. 3, it is assumed that the object has no size, the reflection loss of the electromagnetic wave by the object is 3 dB, and all the reflected electromagnetic waves are received by the radar device 1 or the radar device 2.

Under such an assumption, the radar device 1
The reception level of the electromagnetic wave received by is as follows. That is, when the object exists at a position 0 m from the radar device 1 (virtually the position of the radar device 1), the reflection loss of the electromagnetic wave by the object is 3 dB, and therefore the reception level of the electromagnetic wave received by the radar device 1 is It becomes 7 dB. Then, as the position of the object gradually moves away from the radar device 1, the reception level is attenuated at an attenuation rate of 0.1 dB / m, and the object is at a midpoint between the radar device 1 and the radar device 2, that is, the radar device. When the distance from 1 exists at a position of 5 m, the electromagnetic wave propagates a distance of 10 m in a round trip, so the reception level is 6 dB. Furthermore, as the distance from the radar device 1 to the object increases, the reception level decreases by 0.1 dB.
When the object is attenuated at / m and the object exists at a position 10 m from the radar device 1 (virtually the position of the radar device 2), the propagation distance of the electromagnetic wave is 20 m in a round trip, so the reception level of the electromagnetic wave is 5 dB. .

Similarly, the reception level of the electromagnetic wave received by the radar device 2 is as follows. That is, when the object exists at a position 0 m from the radar device 2 (virtually the position of the radar device 2 and a position 10 m from the radar device 1), the reflection loss of the object is 3 dB, and therefore the object is received by the radar device 2. The reception level of the electromagnetic wave is 7 dB. Then, as the position of the object gradually moves away from the radar device 2 (approaching gradually to the radar device 1), the reception level is attenuated at an attenuation rate of 0.1 dB / m, and the object is separated from the radar device 2 and the radar device 1. When the distance between the radar device 2 (radar device 1) and the midpoint between them is 5 m, the reception level is 6 dB. Further, as the distance from the radar apparatus 2 increases (approaches the radar apparatus 1), the reception level attenuates at an attenuation rate of 0.1 dB / m, and the object is at a position 10 m from the radar apparatus 2 (virtual position of the radar apparatus 1). Is present in
The reception level of electromagnetic waves is 5 dB.

Thus, the radar device 1 and the radar device 2
Except when an object is present at the midpoint between
Also, a difference occurs in the reception level of the electromagnetic wave at the radar device 2. Therefore, the amplitude comparator 3 is connected to the radar device 1
And the reception levels of the electromagnetic waves received by the radar device 2 are compared, and the comparison result is output to the output device 4.

In step S3, the output device 4 determines that there is an object between the radar device 1 and the radar device 2 when there is a difference in the reception level of the electromagnetic waves received by the radar device 1 and the radar device 2, When there is no difference, it is determined that there is no object between the radar device 1 and the radar device 2.

As described above, according to the radar system of FIG. 1, a pair of the radar device 1 and the radar device 2 respectively transmit electromagnetic waves, respectively receive the electromagnetic waves, and the radar device 1 and the radar device 2 respectively receive the electromagnetic waves. Since the reception levels of the received electromagnetic waves are compared and if there is a difference, it is determined that there is an object, and if there is no difference, it is determined that there is no object. Therefore, there is a presence between the radar device 1 and the radar device 2. It is possible to determine the presence or absence of an object to be moved.

Further, according to the radar system of FIG. 1, since the frequency of the electromagnetic waves transmitted and received by the radar device 1 and the radar device 2 is set to the frequency in the millimeter wave band, fog,
False detection of an object due to external factors such as snow and dust can be suppressed.

In the radar system of FIG. 1, the radar device 1 and the radar device 2 transmit and receive electromagnetic waves, but electromagnetic wave pulses may be transmitted and received and the received levels of the received electromagnetic wave pulses may be compared.

FIG. 4 shows another configuration example of the radar system to which the present invention is applied. The radar system of FIG.
Although the object at the midpoint between the radar device 1 and the radar device 2 could not be detected, the radar system of FIG. 4 can not only detect the object at the midpoint between the radar devices but also detect the distance to the object. Can be measured. Figure 4
In this radar system, instead of the radar devices 1 and 2 of the radar system of FIG. 1, radar devices 11 and 12 are provided, and pulse detectors 13 and 14 and a signal processor 15 are further provided.

The radar device 11 and the radar device 12 are
It is designed to send and receive electromagnetic pulses. The pulse detector 13 and the pulse detector 14 detect the phase difference between the electromagnetic wave pulse transmitted by the radar device 11 and the received electromagnetic wave pulse, respectively. The signal processor 15 is adapted to comprehensively determine the presence or absence of an object from the information supplied from the amplitude comparator 3, the pulse detector 13, and the pulse detector 14.

Next, the operation of the radar system of FIG. 4 will be described with reference to the flowchart of FIG. In step S11, the radar device 11 and the radar device 12
Respectively sense the object. That is, the radar device 11 and the radar device 12 transmit electromagnetic wave pulses of the same frequency in the millimeter wave band with the same output. Then, the radar device 11 receives the electromagnetic wave pulse reflected by the object or the radar device 12. Similarly, the radar device 12 also receives the electromagnetic wave pulse reflected by the object or the radar device 11. The radar device 11 and the radar device 12 supply a signal corresponding to the level of the received electromagnetic wave pulse to the amplitude comparator 3, and send a signal corresponding to the transmission timing and the reception timing of the electromagnetic wave pulse to the pulse detector 13
And pulse detector 14.

The amplitude comparator 3 compares the reception levels (amplitudes) of the electromagnetic wave pulses received from the radar device 11 and the radar device 12, and outputs the comparison result to the signal processor 15. In step S12, the signal processor 15
From the output of the amplitude comparator 3, it is determined whether or not there is a difference in the reception levels of the electromagnetic wave pulses received by the radar device 11 and the radar device 12. If it is determined that there is a difference, step S
Proceeding to 14, the detection signal of the object is output. The operation in this case is similar to that in the radar system of FIG.

When there is no difference in the amplitude of the received electromagnetic wave pulse, the signal processor 15 outputs the electromagnetic wave transmitted by the radar device 11 or the radar device 12 from the output of the pulse detector 13 or the pulse detector 14 in step S13. Determine if there is a phase difference between the pulse and the received electromagnetic pulse. When it is determined in step S13 that there is a difference in the phase of the electromagnetic wave pulse, step S14
If it is determined that there is no difference in the phase of the electromagnetic wave pulse, the process returns to step S11.

Here, steps S11 to S1
The processing in No. 3 will be described with reference to FIGS. 6 to 8 separately for the case where there is no object between the radar device 11 and the radar device 12 and for the case where there is an object.

FIG. 6 shows a radar device 11 and a radar device 12.
It is a figure explaining transmission / reception of radar device 11 when there is no detected object between. As shown in FIG. 6A, the radar device 11 has an initial phase (time) of γ and a cycle of L / C.
(L is the distance between the radar device 11 and the radar device 12,
C is the speed of light (velocity of electromagnetic wave), and transmits an electromagnetic wave pulse of 3 × 10 ⁸ m / s). That is, the radar device 1
1 transmits the next electromagnetic wave pulse at the timing when the previously transmitted electromagnetic wave pulse arrives at the radar device 12.

The electromagnetic wave pulse transmitted from the radar device 11 is reflected by the radar device 12 and, as shown in FIG. 6 (B), at a timing when it propagates a total of 2L, that is, phase 2 × (L / C ) + Γ, which is received by the radar device 11. Since the received electromagnetic wave pulse is attenuated during the propagation and at the time of reflection, its level is smaller than that of the transmitted electromagnetic wave pulse. The radar device 12 has the same timing as the radar device 11 (the initial phase is γ,
Since the electromagnetic wave pulse is adjusted in advance so that the electromagnetic wave pulse is transmitted so that the period becomes L / C, the electromagnetic wave pulse transmitted from the radar device 12 is generated by the radar device 11 as shown in FIG.
As shown in (C), the initial time L / C + γ and the cycle L / C
Then, it is received. Since the propagation distance is L and there is no reflection, the reception level at this time is higher than the reception level of the reflected wave of the electromagnetic wave pulse transmitted by the radar device 11 itself shown in FIG. 6B.

After all, the radar device 11 transmits and receives electromagnetic wave pulses at the initial time L / C + γ and the cycle L / C, as shown in FIG. 6 (D).

FIG. 7 shows a radar device 11 and a radar device 12.
FIG. 9 is a diagram showing a case where the object 20 exists at a position of a distance x from the radar device 11 during the period, and FIG. 8 is a diagram explaining transmission and reception of electromagnetic waves in the radar device 11 in that case. As the object 20, like a metal flat plate,
Electromagnetic waves are reflected, but the size is said to be negligible.

As shown in FIG. 8A, the radar device 11 has an initial phase of γ as in the case of FIG. 6A,
An electromagnetic wave pulse with a period of L / C is transmitted. The transmitted electromagnetic wave pulse is reflected by the object 20, and the reflected electromagnetic wave pulse is reflected by the radar device 11 as shown in FIG.
Therefore, it is received at the initial time (2x / C) + γ and the cycle L / C.

Among the electromagnetic wave pulses transmitted from the radar device 11, the electromagnetic wave pulse that is not reflected by the object 20 is reflected by the radar device 12 and the radar device 11
Then, as shown in FIG. 8C, the initial time is 2 × (L / C) +
γ, received at cycle L / C. Among the electromagnetic wave pulses transmitted from the radar device 12, the electromagnetic wave pulse which is not disturbed by the object 20 is received by the radar device 11 at the initial time L / C + γ and the cycle L / C as shown in FIG. To be done.

Therefore, as a whole, the radar device 11 has the time (2x / C) + during the two periods as shown in FIG. 8 (E).
The electromagnetic wave pulse is received at the timings of γ, time (L / C) + γ, time (2x / C) + (L / C) + γ, and time 2 × (L / C) + γ. Of these, electromagnetic wave pulses received at time (2x / C) + γ and time (2x / C) + (L / C) + γ
This is due to the reflection on the object 20.

That is, the object 20 is placed between the radar devices 11 and 12.
, The electromagnetic wave pulse is received at a time other than the time n × (L / C) + γ (n is a natural number). Therefore, when the electromagnetic wave pulse is received at a time other than the time n × (L / C) + γ, it can be detected that the object 20 is present. Then, the position of the object 20 from the radar device 11 can be determined by performing back calculation from the detected time.

Although the transmission / reception of the electromagnetic wave pulse in the radar device 11 has been described with reference to FIGS. 6 to 8, the same applies to the transmission / reception of the electromagnetic wave pulse in the radar device 12.

The pulse detectors 13 and 14 detect the timing (time) of the electromagnetic wave pulse described above and supply the detection result to the signal processor 15. The signal processor 15 determines the presence or absence of an object from the supplied detection result. That is,
If there is no difference in the reception level but there is a phase difference in the timing of transmitting and receiving the electromagnetic wave pulse, the signal processor 15 determines that there is an object in step S14. Such a state occurs when the object is located at the midpoint between the radar device 11 and the radar device 12. Thus, in this system,
The presence or absence of two objects that are equidistant from the radar device 11 and the radar device 12 can also be detected.

In step S14, the signal processor 15 determines the presence or absence of an object as described above, and if there is an object, supplies the detection result including the position of the object to the output device 14.

As described above, from the phase difference between the electromagnetic wave pulses transmitted and received by the radar device 11 or the radar device 12, if there is a phase difference, it is judged that there is an object, and if there is no phase difference, the object is Since it is determined that there is no object, the presence or absence of the object can be determined, and the distance from the radar device 11 or the radar device 12 to the object can also be measured.

In the radar system of FIG. 4, the electromagnetic wave pulse is a rectangular wave, but it may be a sine wave or a cosine wave.

In the radar system of FIG. 4, the received pulse in the time zone near the timing of transmitting the electromagnetic wave pulse by the radar apparatus 11 and the radar apparatus 12, for example, the received pulse in the time zone of 30% of the time L / C. You may ignore it. Thereby, the reflection of the electromagnetic wave on the object and the reflection of the electromagnetic wave on the radar devices 11 and 12 can be clearly distinguished.

Further, in the radar system of FIG. 4, the radar device 11 and the radar device 12 transmit and receive electromagnetic wave pulses, but the electromagnetic waves not pulse-weighted are transmitted and received, and the phases of the transmitted electromagnetic wave and the received electromagnetic wave are transmitted and received. You may make it compare the difference of.

In the above, the radar device 1 (radar device 11) and the radar device 2 (radar device 12) are arranged so as to face each other, but as shown in FIG.
May be provided, and the radar device 1 (radar device 11) and the radar device 2 (radar device 12) may be obliquely arranged with respect to the wall 30 to transmit and receive electromagnetic waves in an oblique direction. In this case, by transmitting electromagnetic waves from the radar device 1 (radar device 11) and the radar device 2 (radar device 12) and comparing the reception level differences (reception level difference and phase difference) of the received electromagnetic waves, the object It is possible to determine the presence or absence of. The output levels of the radar device 1 (radar device 11) and the radar device 2 (radar device 12) may be different as long as they are known.

Further, in the above, the electromagnetic wave (electromagnetic wave pulse) in the millimeter wave band is transmitted and received, but the electromagnetic wave in the millimeter wave band and above, for example, light and infrared rays may be transmitted and received.

In the present specification, the recording medium for providing the user with the computer program for executing the above-mentioned processing includes an information recording medium such as a magnetic disk and a CD-ROM, as well as a network such as the Internet and a digital satellite. Transmission media is also included.

[0052]

As described above, according to the radar system described in claim 1, the object detection method described in claim 7, and the recording medium described in claim 8, the first and second transmitting / receiving means are provided. Since the electromagnetic waves transmitted and received by are compared with each other, even if the change of external factors is large,
And an object existing between the second transmitting / receiving means can be accurately detected.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a radar system to which the present invention is applied.

FIG. 2 is a flowchart showing an operation of the radar system of FIG.

FIG. 3 is a diagram illustrating reception levels of radar devices 1 and 2.

FIG. 4 is a block diagram showing another configuration example of a radar system to which the present invention has been applied.

5 is a flowchart illustrating the operation of the radar system of FIG.

FIG. 6 is a diagram illustrating electromagnetic wave pulses transmitted and received from the radar devices 11 and 12.

FIG. 7 is a diagram illustrating the position of an object 20.

FIG. 8 is another diagram illustrating electromagnetic wave pulses transmitted and received from the radar devices 11 and 12.

FIG. 9 is a diagram for explaining another arrangement of the radar devices 1, 2 (11, 12).

[Explanation of symbols]

1, 2, 11, 12 radar device, 3 Amplitude comparator, 4 output devices, 13, 14 pulse detector, 15 signal processor, 20 objects, 30 walls

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01S ⁷ /00-7/64 G01S 13/00-13/95 G01S 15/04 G01S 17/02 G01V 3 / 00 G01N 22/00 G08B 13/00

Claims (8)

(57) [Claims] 1. A first transmitting / receiving means for transmitting / receiving an electromagnetic wave, and an electromagnetic wave can be transmitted / received to / from the first transmitting / receiving means .
A second transmitting / receiving means arranged at such a position for transmitting / receiving electromagnetic waves, a comparing means for comparing the electromagnetic waves received by the first transmitting / receiving means and the second transmitting / receiving means, and a result of comparison by the comparing means. Based on the above, a radar system comprising: a detection means for detecting an object existing between the first transmission / reception means and the second transmission / reception means. 2. The radar system according to claim 1, wherein the electromagnetic waves transmitted and received by the first transmitting / receiving unit and the second transmitting / receiving unit have the same frequency and level. 3. The first transmitting / receiving means and the second transmitting / receiving means are arranged so as to face each other so as to be able to receive the other transmitted electromagnetic wave. Radar system. 4. The comparing means compares the electromagnetic waves received by the first transmitting / receiving means and the second transmitting / receiving means.
4. Amplitudes are compared, wherein the amplitudes are compared.
The radar system according to. 5. The electromagnetic wave is an electromagnetic wave pulse, and the comparing means compares the phases of the electromagnetic wave pulse transmitted by the first transmitting / receiving means or the second electromagnetic wave transmitting / receiving means with each other. The radar system according to any one of claims 1 to 4, wherein: 6. The radar system according to claim 1, wherein the frequency of the electromagnetic wave is a frequency in the millimeter wave band or higher. 7. A method for detecting an object of a radar device comprising a first transceiver and a second transceiver for transmitting and receiving electromagnetic waves, comprising: a first transmitting and receiving step of transmitting and receiving electromagnetic waves by the first transceiver . You can send and receive electromagnetic waves to and from the first transceiver.
A second transmitting / receiving step of transmitting / receiving an electromagnetic wave by the second transmitting / receiving device arranged at such a position; a comparing step of comparing the electromagnetic waves received in the first transmitting / receiving step and the second transmitting / receiving step; An object detection method comprising: a detection step of detecting an object existing between the first transmission / reception device and the second transmission / reception device based on the result of comparison in the comparison step. 8. A radar device comprising a first transmitting / receiving device and a second transmitting / receiving device for transmitting / receiving an electromagnetic wave, the first transmitting / receiving step of transmitting / receiving the electromagnetic wave by the first transmitting / receiving device, and the first transmitting / receiving device. Can send and receive electromagnetic waves to and from each other
A second transmitting / receiving step of transmitting / receiving an electromagnetic wave by the second transmitting / receiving device arranged at such a position; a comparing step of comparing the electromagnetic waves received in the first transmitting / receiving step and the second transmitting / receiving step; A computer-readable program for executing a process including a detection step of detecting an object existing between the first transmission / reception device and the second transmission / reception device is recorded based on the result of the comparison in the comparison step. A recording medium characterized by being recorded.