JP6872808B2 - Antenna array, RF tag direction search device, and trailer direction search device - Google Patents

Description

The present invention includes an antenna array composed of two, three, or four antennas for searching the position of an RF tag, an RF tag direction search device provided with the antenna array, and an RF tag direction search device. Regarding the trailer direction search device.

In Patent Document 1 (Japanese Unexamined Patent Publication No. 2007-303972), while switching the frequency used for reading, radio waves having different polarization directions are vertically polarized, horizontally polarized, clockwise circularly polarized, and counterclockwise. Read the unique ID from the wireless IC tag that stores the unique ID using circularly polarized light, etc., and read the unique ID to the reader / writer using radio waves with different polarization directions. As a result of this, a position identification system having a position identification device that calculates the position of the wireless IC tag using the strength of the received signal for each unique ID obtained for each radio wave having a different polarization direction. Are listed.

In Patent Document 2 (Japanese Unexamined Patent Publication No. 2012-73245), a computer reads a target tag in a linear arrangement for each of a plurality of designated emission powers a predetermined number of times by using an antenna of an RFID reader, and a designated launch is performed for each target tag. Each target tag is recorded by recording the number of successful readings by the antenna for each power source, calculating the total number of successful readings by the antenna for each target tag, and sorting against the total number of successful readings for each target tag. The sequence order for the antennas of the tags is specified, the read probability of the normalization for the antenna for each target tag is calculated, and the read probability of the normalization for the antenna of the tag is calculated based on the read probability of the normalization for the antenna for each target tag. Describes an RFID tag position measuring method characterized in that the distance to the antenna for each target tag is specified by searching a reading probability map in which the correspondence between the tag and the distance to the antenna of the tag is recorded. ..

Patent Document 3 (Japanese Unexamined Patent Publication No. 2000-115041) provides a wireless LAN system provided with an antenna unit having a plurality of directional antennas and a control unit having a function of controlling switching of the antennas. In the wireless communication device of the above, the wireless communication device of the wireless LAN system in which the control unit is shared and the number of antennas is changed is described.

In Patent Document 4 (Japanese Unexamined Patent Publication No. 54-9521), the control logic circuit means causes an antenna switch to sequentially switch each antenna to one receiver means, and the logic circuit means is the receiver means. Spurious generated in a multi-element antenna switching system that includes detector means for processing the output of the antenna and detecting the signal received by each antenna and controls the antenna switch in a pre-determined manner relating to it. Described is an antenna sampling system characterized in that it comprises means for disabling the actuation of the detector means during a pre-determined time interval following each moment of antenna switching to eliminate response detection. Has been done.

Japanese Unexamined Patent Publication No. 2007-303972 Japanese Unexamined Patent Publication No. 2012-73245 Japanese Unexamined Patent Publication No. 2000-115041 JP-A-54-9521

As described above, the semi-trailer, which is the most common trailer, has a structure in which the trailer and the tractor (also called a trailer head) are connected. In this case, it is necessary to find out in which direction the trailer is from the perspective of the tractor.

The direction of the trailer can be detected by attaching an RF tag reader to the back surface of the tractor, attaching the RF tag to the trailer, and detecting the position of the RF tag with the RF tag reader. Detecting the position of an RF tag with an RF tag reader has been conventionally performed.

The position identification system described in Patent Document 1 can calculate the position including the distance of the wireless IC tag by using the strength of the received signal for each unique ID obtained for each radio wave having a different polarization direction. There is a feature in. However, the invention described in Patent Document 1 has a problem that the structure is too complicated.

Further, the RFID tag position measuring method described in Patent Document 2 calculates the reading probability of normalization of the target tag with respect to the antenna, and the reading probability of recording the correspondence between the reading probability of normalization and the distance of the tag to the antenna. The feature is that the distance of the target tag to the antenna can be specified by searching the map. However, the invention described in Patent Document 2 also has a problem that the configuration is too complicated.

Further, the wireless communication device of the wireless LAN system described in Patent Document 3 is a wireless device provided with an antenna unit having a plurality of directional antennas and a control unit having a function of controlling switching of the antennas. It is a wireless communication device of a LAN system. However, the invention described in Patent Document 3 also has a problem that the configuration is too complicated.

The antenna sampling system described in Patent Document 4 includes eight antenna elements and a 45 ° reflector, and each antenna sector is a multi-element antenna capable of receiving a transmission signal generated from a limited horizontal angle. The switching system is described. However, the invention described in Patent Document 4 also has a problem that the configuration is too complicated.

A main object of the present invention is to provide an antenna array consisting of a plurality of antennas having the directivity necessary for detecting the direction of the RF tag with respect to the reader, and to provide an antenna array. It is an object of the present invention to provide the RF tag direction search apparatus used.
Another object of the present invention is to provide a trailer direction search device for searching in which direction the trailer is viewed from the tractor.

(1)
The antenna array according to one aspect is an antenna array including a first loop antenna, a second loop antenna, a conductive reflector, and a conductive metal plate, the first loop antenna and the first loop antenna. The second loop antenna is arranged perpendicular to the first axis whose loop surface connects the centers of the loop surfaces, respectively, and the reflector is perpendicular to the first axis and is between the first loop antenna and the second loop antenna. The metal plate is arranged on the unidirectional side of the second axis orthogonal to the first axis, perpendicular to the second axis, and at the unidirectional end of the first loop antenna and the second loop antenna. An RF tag that is in contact with or placed at a predetermined distance from the one-way end, the reflector and the metal plate are electrically conductive with each other, and are placed on the other side of the second axis of the antenna array. Therefore, it is used to compare the intensity of the radio wave received through the first loop antenna with the intensity of the radio wave received through the second loop antenna.

In this case, the first loop antenna has a high gain in the far field on the first loop antenna side in the first axis direction, and the second loop antenna is on the second loop antenna side in the first axis direction. The gain in the distant world is high. Therefore, by alternately communicating with the RF tag via the first loop antenna and the second loop antenna and comparing the intensities of the radio waves received through the first loop antenna and the second loop antenna, It is possible to search whether the RF tag is located on the first loop antenna side or the second loop antenna side in the first axis direction.

(2)
The antenna array according to the second invention is an antenna array according to one aspect, in which the shapes of the first loop antenna and the second loop antenna are formed by polygons having the same shape, and the metal plate is formed on one side of the polygon. They may be in contact with each other or may be close to each other at a predetermined distance from one side of the polygon.

In this case, even when one side is brought close to or in contact with another metal, matching can be easily performed by the matching circuit, and the influence of return loss can be eliminated.

(3)
The antenna array according to the third invention is the antenna array according to the first aspect to the second invention, in which the distance between the first loop antenna and the reflector and the distance between the second loop antenna and the reflector are radio waves. The wavelength of λ may be 1/4 λ.

In this case, the maximum gain of the antenna can be maximized and the directivity of the antenna can be strengthened.

(4)
The antenna array according to the fourth invention is the antenna array according to the third aspect to the third aspect, and the element lengths of the first loop antenna and the second loop antenna are integral multiples of λ, where λ is the wavelength of the radio wave. be equivalent to.

It is known that a high gain can be obtained by setting the element length to one wavelength in a loop antenna, and in the present invention as well, the element length of the loop antenna may be an integral multiple of λ.

(5)
The antenna array according to the fifth invention is the antenna array according to the first aspect to the fourth aspect, wherein the first loop antenna and the second loop antenna have a long side of 1 / 2λ, where the wavelength of the radio wave is λ. It may be a hentenna in which the short side is composed of a rectangular element of 1 / 6λ and a feeding point is provided at one point on each of the long sides of the rectangle.

In this case, the maximum gain of the loop antenna can be further increased to enhance the directivity of the antenna.

(6)
The antenna array according to the sixth invention further includes a front antenna in the antenna array according to the fifth aspect to the fifth aspect, and the front antenna includes the strength of the radio wave received through the front antenna and the first. It may be used to compare the strength of the radio wave received through the loop antenna with the strength of the radio wave received through the second loop antenna.

In this case, by adding the front antenna, when the RF tag is located near the front (the other direction side of the second axis), the strength of the radio wave received through the front antenna increases, so that the RF tag You can search for the position of.

(7)
The antenna array according to the seventh invention is the antenna array according to the sixth invention, in which the front antenna is a plate-shaped inverted F antenna or a patch antenna, and the radiation plate of the front antenna is arranged perpendicular to the second axis. It may have been done.

In this case, since the plate-shaped inverted-F antenna and the patch antenna have a high gain in the far field in the front (the other direction side of the second axis) perpendicular to the radiation plate, the search for whether the RF tag is in front of the antenna array. Becomes easier.

(8)
The antenna array according to the eighth invention is a third loop antenna and a fourth loop antenna having the same shape as the first loop antenna and the second loop antenna in the antenna array according to the first aspect to the fifth invention. including.
The third loop antenna and the fourth loop antenna are arranged plane-symmetrically with respect to the first loop antenna and the second loop antenna and the metal plate, respectively, and the reflecting plate extends in one direction of the second axis. It may also be arranged between the third loop antenna and the fourth loop antenna.

In this case, by comparing the intensities of the radio waves received through the first, second, third, and fourth loop antennas, the RF tag is on the plane defined by the first axis and the second axis. You can search in which direction you are located.

(9)
A ninth invention is an invention of an RF tag direction search device, which includes an antenna array, an antenna switching circuit, a transmission / reception circuit, and a control circuit according to the first aspect to the seventh invention.
The antenna switching circuit sequentially switches the connection between multiple antennas and the transmission / reception circuit, the transmission / reception circuit sequentially transmits / receives via each of the RF tag and the multiple antennas, and the control circuit compares the strength of the received radio waves for each antenna. Finds in which direction the RF tag is located with respect to the antenna array.

In this case, a simple procedure of sequentially transmitting and receiving to and from the RF tag via the two loop antennas of the RF tag direction search device or via the two loop antennas and the front antenna and comparing the strength of the received radio waves for each antenna. Therefore, whether the RF tag is located on either the first loop antenna side or the second loop antenna side in the first axis direction, or is located near the other direction side of the second axis. You can search.

(10)
The tenth invention is the invention of the trailer direction search device, wherein the RF tag direction search device according to the ninth invention is attached to the back surface of the tractor, the RF tag is attached to the front surface of the trailer towed by the tractor, and the RF tag direction search device is used. The direction of the trailer as seen from the tractor is searched by sequentially transmitting and receiving to and from the RF tag via each of the plurality of antennas of the device and comparing the strength of the received radio waves for each antenna.

In this case, a simple procedure of transmitting and receiving sequentially to and from the RF tag via the two loop antennas of the RF tag direction search device or via the two loop antennas and the front antenna and comparing the strength of the received radio waves for each antenna is used. , It is possible to accurately search in which direction the trailer is located when viewed from the tractor.

(11)
The eleventh invention is an invention of an RF tag direction search device, which includes an antenna array, an antenna switching circuit, a transmission / reception circuit, and a control circuit according to the eighth invention.
The antenna switching circuit sequentially switches the connection between the plurality of antennas and the transmission / reception circuit, and the transmission / reception circuit sequentially transmits / receives via each of the RF tag and the plurality of antennas, and compares the strength of the received radio waves for each antenna. Find out in which direction the RF tag is located with respect to the antenna array.

In this case, the RF tag is first in the first axis direction by a simple procedure of sequentially transmitting and receiving to and from the RF tag via the four loop antennas of the RF tag direction search device and comparing the strength of the received radio waves for each antenna. Which of the loop antenna side and the second loop antenna side is located, and which of the one direction side (rear side) and the other direction side (front side) is located in the second axis direction. You can search.

It is a schematic perspective view of the antenna array of 1st Embodiment. It is a schematic plan view seen from the + X direction (left direction when viewed from the front) of the antenna array of the first embodiment. It is a graph which shows the directivity of the 1st loop antenna and the 2nd loop antenna of the antenna array of 1st Embodiment. In the first embodiment, it is a schematic perspective view of an antenna array using hentenna as a loop antenna. In the first embodiment, it is a schematic plan view seen from the + X direction (left direction when viewed from the front) of an antenna array using hentenna as a loop antenna. In the first embodiment, it is a graph which shows the directivity of the 1st loop antenna of the antenna array which used hentenna as a loop antenna. It is a schematic perspective view of the antenna array of the 2nd Embodiment. It is a schematic perspective view of the plate-shaped inverted F antenna used as a front antenna in the 2nd Embodiment. It is a schematic perspective view of the patch antenna used as a front antenna in the 2nd Embodiment. It is a graph which shows the directivity of the 1st loop antenna, the 2nd loop antenna, and the patch antenna used as a front antenna of the antenna array of 2nd Embodiment. In the third embodiment, it is a schematic plan view seen from the + Z direction (upper side) of the antenna array using the first to fourth loop antennas. It is a block diagram of the RF tag direction search apparatus of 4th Embodiment. It is a schematic plan view seen from the lateral direction of the trailer direction search apparatus of 5th Embodiment. It is explanatory drawing which shows the directivity of the 1st loop antenna, the 2nd loop antenna, and the forward antenna in the trailer direction search apparatus of 5th Embodiment. It is a block diagram of the RF tag direction search apparatus of 6th Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Moreover, in the case of the same code, their names and functions are also the same. Therefore, the detailed description of them will not be repeated.

[First Embodiment]
FIG. 1 is a schematic perspective view of the antenna array 30 of the first embodiment, and FIG. 2 is a schematic view of the antenna array 30 of the first embodiment seen from the + X direction (leftward when viewed from the front). It is a plan view.

(Structure of antenna array 30)
The antenna array 30 includes a first loop antenna 100, a second loop antenna 200, a reflector 300, a metal plate 400, a first feeder line 500, and a second feeder line 600.
In the present embodiment, the first loop antenna 100 and the second loop antenna 200 are formed of rectangles having the same shape. The first loop antenna 100 is arranged on the left (+ X) side of the antenna array 30, and the second loop antenna 200 is arranged on the right (−X) side of the antenna array 30 so that the loop surfaces are parallel to each other. There is.
The reflector 300 is arranged between the first loop antenna 100 and the second loop antenna 200 in parallel with the loop surface of the first loop antenna 100 and the second loop antenna 200.
The metal plate 400 is arranged at the rear portion (−Y direction) of the antenna array 30 perpendicular to the loop surface of the first loop antenna 100 and the second loop antenna 200. Further, the metal plate 400 is arranged close to the first loop antenna 100 and the second loop antenna 200 at a predetermined distance from one side. The metal plate 400 may be connected to one side of the first loop antenna 100 and the second loop antenna 200.
The reflector 300 and the metal plate 400 are electrically conductive (connected).

As shown in FIG. 2, the first loop antenna 100 is square, has a feeding point in the middle of the upper (+ Z) side, and the first feeding line 500 extends from the feeding point.
Similarly, for the second loop antenna 200, the second feeder line 600 extends from the feeder point. In the first embodiment, the frequency of the transmitted / received radio wave is 1 GHz, and the wavelength of the 1 GHz radio wave is 300 mm. Therefore, the total length of the four sides of the first loop antenna 100 and the second loop antenna 200 is a radio wave. It is 300 mm, which is the same as the wavelength of.
In the first embodiment, the shapes of the first loop antenna 100 and the second loop antenna 200 are square, but the shape of the loop antenna may be any other shape such as a rectangle, a circle, or an ellipse. You may.

(Directivity of loop antenna)
FIG. 3 is a graph showing the directivity of the first loop antenna 100 and the second loop antenna 200 of the antenna array 30 of the first embodiment.
FIG. 3 shows the gains of the first loop antenna 100 and the second loop antenna 200 of the first embodiment calculated by the FDTD method (Finite Difference Time Domain method) in the far field.
The first loop antenna 100 has a high gain centered in the left (+ X) direction and a low gain in the right (−X) direction.
On the other hand, as can be understood from the fact that the second loop antenna 200 is plane-symmetric with respect to the first loop antenna 100 and the reflector 300, the gain is high mainly in the right (-X) direction, and the left is left. The gain decreases in the (+ X) direction.
Therefore, when the RF tag 43 is arranged to the left or right in front of the antenna array 30 (+ Y direction), the strength of the radio wave from the RF tag 43 when received through the first loop antenna 100 and the second loop. By comparing the strength of the radio wave from the RF tag 43 when it is received through the antenna 200, the RF tag 43 is located on the left (+ X) side or the right (-X) side of the antenna array 30. You can easily search for the location.

The distance between the first loop antenna 100 and the reflector 300 and the distance between the second loop antenna 200 and the reflector 300 are both preferably 1/4 λ, where the wavelength of the radio wave is λ. This is because when the distance between the first loop antenna 100 and the reflector 300 is 1 / 4λ, the maximum gain in FIG. 3 can be maximized.
Further, when the distance between the second loop antenna 200 and the reflector 300 is 1 / 4λ, the maximum gain in FIG. 3 can be maximized.

It is desirable that the element lengths of the first loop antenna 100 and the second loop antenna 200 (the sum of the lengths of the four sides of the loop antenna) be equal to an integral multiple of the wavelength λ of the radio wave. This is because by making the element length of the loop antenna equal to the wavelength λ of the radio wave, a standing wave can be generated in the element and the gain of the antenna can be increased.
The loop antennas of FIGS. 1 and 2 in the present embodiment are composed of squares having a length of 1 / 4λ on each side.

In FIG. 4, in the first embodiment, the loop antenna is composed of hentenna (a rectangular element having a long side of 1 / 2λ and a short side of 1 / 6λ, where the wavelength of the radio wave is λ, and the long side of the rectangle. A schematic perspective view of the antenna array 30 is shown in the case of a loop antenna in which a feeding point is provided at one point each.
Further, FIG. 5 shows a schematic plan view of the antenna array 30 as viewed from the + X direction (leftward when viewed from the front) when the loop antenna is a hentenna.
The hentenna used as the first loop antenna 100 and the second loop antenna 200 has a long side of 1 / 2λ and a short side of 1 / 6λ, and is lateral to 1 / 6λ from the short side on the upper (+ Z) side. A first power feeding unit 700 and a second power feeding unit 800 (not shown) are formed in the (Y) direction. Both ends of the first feeding section 700 and the second feeding section 800 are connected to the long side of the hentenna. Further, the first feeder line 500 and the second feeder line 600 are connected to the midpoints of the first feeder unit 700 and the second feeder unit 800.

FIG. 6 shows the directivity and gain of the hentenna in the distant field without the reflector 300 and the metal plate 400 calculated by the FDTD method (Finite Difference Time Domain method), and the shape of the hentenna shown in FIGS. 4 and 5. It is a graph which showed the directivity and gain in the far field of the first loop antenna 100, and the directivity and gain in the far field of the square first loop antenna 100 shown in FIGS. 1 and 2.
Hentenna in the absence of a reflector and a metal plate has the same gain in the far field in the left (+ X) and right (-X) directions. However, by installing the reflector 300 and the metal plate 400, the gain in the right (−X) direction is significantly reduced.
Further, when the gain in the far field of the hentenna shown in FIGS. 4 and 5 is compared with the gain in the far field of the square loop antenna shown in FIGS. 1 and 2, the hentenna is on the left (+ X). It can be seen that the gain in the direction and the forward (+ Y) direction is high.
That is, as the loop antenna of the present invention, the gain is higher when a hentenna is used than when a square loop antenna is used. Therefore, the strength of the radio wave from the RF tag 43 when received via the first loop antenna 100 is compared with the strength of the radio wave from the RF tag 43 when received via the second loop antenna 200. When searching the direction of the RF tag 43, it is possible to search more accurately by using hentenna than by using a square loop antenna.

[Second Embodiment]
FIG. 7 is a diagram showing a schematic perspective view of the antenna array 30 of the second embodiment.
The antenna array 30 of the second embodiment is the first loop antenna 100, the second loop antenna 200, the reflector 300, the metal plate 400, and the second of the antenna array 30 of the first embodiment shown in FIG. In addition to the first feeder 500 and the second feeder 600, the front antenna 900 and the third are used to search for whether the RF tag 43 is present in the front (+ Y) direction of the antenna array 30. A feeder line 10 has been added. In the present embodiment, the front antenna 900 is a plate-shaped inverted F antenna or a patch antenna.

FIG. 8 is a diagram showing a schematic perspective view of a plate-shaped inverted F antenna 11 used as the front antenna 900.
As shown in FIG. 8, the plate-shaped inverted F antenna 11 electrically connects the metal plate 400, the radiation plate 12 arranged to face the metal plate 400 via the dielectric 13, and the metal plate 400 and the radiation plate 12. It is composed of a short-circuiting portion 15 and a third feeding portion 14. The third feeding unit 14 is connected to the third feeding line 10. The radiation plate 12 is arranged so as to be perpendicular to the front (+ Y) direction.

FIG. 9 is a diagram showing a schematic perspective view of the patch antenna 16 used as the front antenna 900.
As shown in FIG. 9, in the patch antenna 16, the dielectric 13 is placed on the metal plate 400, and the radiation plate 12 smaller than the dielectric 13 is placed in the center of the surface of the dielectric 13. Further, a fourth power feeding unit 17 is provided at a position slightly off the center of the radiation plate 12. Further, the fourth feeding unit 17 is connected to the third feeding line 10. The radiation plate 12 of FIG. 9 is arranged so as to be perpendicular to the front (+ Y) direction.

FIG. 10 shows the directivity and gain of the first loop antenna 100 in the far field, the directivity and gain of the second loop antenna 200 in the far field, and the directivity and gain of the second loop antenna 200 calculated by the FDTD method. It is a figure which shows the directivity and gain in the distant field of the front antenna 900 which consists of a patch antenna 16.
The gain in the far field of the first loop antenna 100 and the gain in the far field of the second loop antenna 200 are substantially the same as those in FIG.
On the other hand, the gain of the front antenna 900 composed of the patch antenna 16 in the far field is significantly higher in the front (+ Y) direction than that of the first loop antenna 100 and the second loop antenna 200. ..
Therefore, when the RF tag 43 is arranged in front (+ Y direction) of the antenna array 30 to the left or right, the strength of the radio wave received through the first loop antenna 100 and the reception via the second loop antenna 200 are received. By comparing the strength of the radio wave with the strength of the radio wave received via the front antenna 900, the RF tag 43 is located on the left (+ X) side or the right (-X) side of the antenna array 30. It is possible to easily search whether the antenna is located in the front (+ Y) direction.

[Third Embodiment]
FIG. 11 is a diagram showing a schematic plan view of the antenna array 30 using the first to fourth loop antennas of the third embodiment as viewed from above (+ Z) direction.
As shown in FIG. 11, in the antenna array 30 of the third embodiment, an antenna having the same shape and structure as the first loop antenna 100 and the second loop antenna 200 shown in FIG. 7 is formed on the metal plate 400. The third loop antenna 18 and the fourth loop antenna 19 are arranged so as to be plane-symmetric with respect to each other.
Further, a fourth feeder line 20 and a fifth feeder line 21 are connected to the third loop antenna 18 and the fourth loop antenna 19, respectively.
The antenna array 30 of the third embodiment is not provided with the front antenna 900, but the present invention is not limited to this, and the front antenna 900 may be further provided. Further, an antenna that is plane-symmetric with respect to the front antenna 900 and the metal plate 400 may be provided as the rear antenna.

In the antenna array 30 of the third embodiment, the gain of the far field of the third loop antenna 18 and the fourth loop antenna 19 is the far field of the first loop antenna 100 and the second loop antenna 200 of FIG. It becomes line symmetric with the gain of and the X axis as the axis of symmetry.
Therefore, the intensities of the radio waves received through the first loop antenna 100, the second loop antenna 200, the third loop antenna 18, and the fourth loop antenna 19 are compared.
As a result, the RF tag 43 is located in any of the left front (+ X + Y) direction, the right front (-X + Y) direction, the left rear (+ XY) direction, and the right rear (-XY) direction of the antenna array 30. You can easily search for it.

[Fourth Embodiment]
FIG. 12 is a diagram showing a block diagram of the RF tag direction search device 40 of the fourth embodiment.
As shown in FIG. 12, the RF tag direction search device 40 includes an antenna array 30, an antenna switching circuit 31, a transmission / reception circuit 32, and a control circuit 33.
The antenna array 30 includes a first loop antenna 100, a second loop antenna 200, and a front antenna 900.
The antenna switching circuit 31 sequentially switches the connection between the first loop antenna 100, the second loop antenna 200, the front antenna 900, and the transmission / reception circuit 32.
The transmission / reception circuit 32 sequentially transmits / receives via the RF tag 43, the first loop antenna 100, the second loop antenna 200, and the front antenna 900.
Then, the control circuit 33 searches in which direction the RF tag 43 is located with respect to the antenna array 30 by comparing the intensities of the radio waves received through the respective antennas.
The control signal to the antenna switching circuit 31 can be sent directly from the control circuit 33 to the antenna switching circuit 31, but the control circuit 33 once sends the control signal to the transmission / reception circuit 32, and the transmission / reception circuit 32 sends the transmission / reception signal to the antenna. It can also be superposed on the antenna and sent to the antenna switching circuit 31.

[Fifth Embodiment]
FIG. 13 is a diagram showing a schematic plan view of the trailer direction search device 50 according to the fifth embodiment as viewed from the lateral direction.
The trailer direction search device 50 of the fifth embodiment is composed of the RF tag direction search device 40 and the RF tag 43 of the fourth embodiment. The RF tag direction search device 40 is attached to the back surface of the tractor (also referred to as a trailer head) 41, and the RF tag 43 is attached to the front surface of the trailer 42 at a position facing the RF tag direction search device 40 when the trailer 42 goes straight. ..

FIG. 14 shows the directivity (direction of high antenna gain) 44 of the first loop antenna 100 of the RF tag direction search device 40 mounted on the back surface of the tractor 41, the directivity 45 of the second loop antenna 200, and the front. It is a figure which shows the directivity 46 of the antenna 900.
FIG. 14 is drawn based on the gain in the far field of each antenna depicted in the graph of FIG.
As shown in FIG. 14, in the trailer direction search device 50 of the fifth embodiment, each antenna of the RF tag direction search device 40 has the directivity of FIG. 14, and RF when the trailer 42 goes straight in front of the trailer 42. The RF tag 43 is attached at a position facing the tag direction search device 40. In this case, the RF tag direction search device 40 can search the direction of the trailer 42 as seen from the tractor 41 by comparing the received radio wave intensities of each antenna.

[Sixth Embodiment]
FIG. 15 is a diagram showing a block diagram of the RF tag direction search device 40 of the sixth embodiment.
As shown in FIG. 15, the RF tag direction search device 40 includes an antenna array 30, an antenna switching circuit 31, a transmission / reception circuit 32, and a control circuit 33.
The antenna array 30 includes a first loop antenna 100, a second loop antenna 200, a third loop antenna 18, and a fourth loop antenna 19.
The operation of the antenna switching circuit 31, the transmission / reception circuit 32, and the control circuit 33 in the sixth embodiment is the same as that in the fourth embodiment, and the antenna array 30 connected to the antenna switching circuit 31 is the first loop antenna 100. It differs from the fourth embodiment in that it includes a second loop antenna 200, a third loop antenna 18, and a fourth loop antenna 19.

In the present invention, the first loop antenna 100 corresponds to the "first loop antenna", the second loop antenna 200 corresponds to the "second loop antenna", and the reflector 300 becomes the "reflector". The metal plate 400 corresponds to the "metal plate", the X-axis corresponds to the "first axis", the Y-axis corresponds to the "second axis", and the front antenna 900 corresponds to the "front antenna". , The plate-shaped inverted F antenna 11 corresponds to the "plate-shaped inverted F antenna", the patch antenna 16 corresponds to the "patch antenna", the third loop antenna 18 corresponds to the "third loop antenna", and the third The loop antenna 19 of 4 corresponds to the "fourth loop antenna", the antenna array 30 corresponds to the "antenna array", the antenna switching circuit 31 corresponds to the "antenna switching circuit", and the transmission / reception circuit 32 corresponds to the "transmission / reception circuit". The control circuit 33 corresponds to the "control circuit", the RF tag direction search device 40 corresponds to the "RF tag direction search device", the tractor 41 corresponds to the "tractor", and the trailer 42 corresponds to the "trailer". , The RF tag 43 corresponds to the “RF tag”, and the trailer direction search device 50 corresponds to the “trailer direction search device”.

Preferred embodiments of the present invention are as described above, but the present invention is not limited thereto. It will be appreciated that various embodiments are made that do not deviate from the spirit and scope of the invention. Further, in the present embodiment, the actions and effects according to the constitution of the present invention are described, but these actions and effects are examples and do not limit the present invention.

100 1st loop antenna 200 2nd loop antenna 300 Reflector 400 Metal plate 500 1st feeding line 600 2nd feeding line 700 1st feeding part 800 2nd feeding part 900 Front antenna 10 3rd feeding Electric wire 11 Plate-shaped inverted F antenna 12 Radiation plate 13 Dielectric 14 Third feeding part 15 Short-circuit part 16 Patch antenna 17 Fourth feeding part 18 Third loop antenna 19 Fourth loop antenna 20 Fourth feeding line 21 Fifth feeding line 30 Antenna array 31 Antenna switching circuit 32 Transmission / reception circuit 33 Control circuit 40 RF tag direction search device 41 Tractor 42 Trailer 43 RF tag 44 Direction of first loop antenna 45 Direction of second loop antenna 46 Forward antenna directional 50 Trailer direction search device

Claims (11)

The first loop antenna and
With the second loop antenna,
Conductive reflector and
An antenna array that includes a conductive metal plate.
The first loop antenna and the second loop antenna are arranged perpendicular to the first axis whose loop surfaces connect the centers of the loop surfaces, respectively.
The reflector is arranged perpendicular to the first axis and between the first loop antenna and the second loop antenna.
The metal plate is arranged perpendicular to the second axis on the one-way side of the second axis orthogonal to the first axis, and the ends of the first loop antenna and the second loop antenna on the one-way side. Placed in contact with the portion or at a predetermined distance from the one-way end.
The reflector and the metal plate are electrically conductive with each other.
The intensity of the radio wave received from the RF tag arranged on the other direction side of the second axis of the antenna array via the first loop antenna and the radio wave received via the second loop antenna. Antenna array used to compare with the strength of. The shapes of the first loop antenna and the second loop antenna are formed by polygons having the same shape.
The antenna array according to claim 1, wherein the metal plate is in contact with one side of the polygon or is close to the metal plate at a predetermined distance from one side of the polygon. The distance between the first loop antenna and the reflector and the distance between the second loop antenna and the reflector are 1/4 λ, where λ is the wavelength of the radio wave, according to claim 1 or 2. Antenna array. The antenna array according to any one of claims 1 to 3, wherein the element lengths of the first loop antenna and the second loop antenna are equal to an integral multiple of λ, where λ is the wavelength of the radio wave. The first loop antenna and the second loop antenna are composed of rectangular elements having a long side of 1 / 2λ and a short side of 1 / 6λ, where the wavelength of the radio wave is λ, and each of the long sides of the rectangle is 1. The antenna array according to any one of claims 1 to 4, which is a hentenna with a feeding point provided at the point. Including the front antenna,
The front antenna
The strength of the radio wave received through the front antenna and
The intensity of the radio wave received through the first loop antenna and
The antenna array according to any one of claims 1 to 5, which is used for comparing the intensity of radio waves received through the second loop antenna. The antenna array according to claim 6, wherein the front antenna is a plate-shaped inverted F antenna or a patch antenna, and the radiation plate of the front antenna is arranged perpendicular to the second axis. Further, the first loop antenna and the third loop antenna and the fourth loop antenna having the same shape as the second loop antenna are included.
The third loop antenna and the fourth loop antenna are arranged symmetrically with respect to the first loop antenna, the second loop antenna, and the metal plate, respectively.
The one according to any one of claims 1 to 5, wherein the reflector is extended in one direction of the second axis and is also arranged between the third loop antenna and the fourth loop antenna. Antenna array. The antenna array including the plurality of antennas according to any one of claims 1 to 7, an antenna switching circuit, a transmission / reception circuit, and a control circuit are included.
The antenna switching circuit sequentially switches the connection between the plurality of antennas and the transmission / reception circuit.
The transmission / reception circuit sequentially transmits / receives via the RF tag and the plurality of antennas, and the control circuit compares the intensity of the received radio wave for each antenna in which direction the RF tag is viewed from the antenna array. RF tag direction search device that searches if it is located in. The RF tag direction search device according to claim 9 is attached to the back surface of a tractor, the RF tag is attached to the front surface of a trailer towed by the tractor, and the RF tag direction search device is attached via each of the plurality of antennas of the RF tag direction search device. A trailer direction search device that searches for the direction of the trailer as seen from the tractor by sequentially transmitting and receiving with an RF tag and comparing the strength of received radio waves for each antenna. The antenna array including the plurality of antennas according to claim 8, an antenna switching circuit, a transmission / reception circuit, and a control circuit are included.
The antenna switching circuit sequentially switches the connection between the plurality of antennas and the transmission / reception circuit.
The transmission / reception circuit sequentially transmits / receives via each of the RF tag and the plurality of antennas, and by comparing the strength of the received radio waves for each antenna, the RF tag is located in which direction as viewed from the antenna array. RF tag direction search device that searches for antennas.

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