JP2008177660A - Slot antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slot antenna for radio communication whose directivity can be made narrow without taking the dielectric constant of a dielectric used for a substrate into consideration. <P>SOLUTION: A pair of first slots 16 extends in parallel to each other along a pair of opposite sides 14A of a first substrate 14, and is in the same shape. Similarly, a pair of second slots 18 extends in parallel to each other along the other opposite sides 14B of the first substrate 14, and is in the same shape. With this constitution, the distance L1 between the pair of first slots 16 and the distance L2 between the pair of second slots 18 can be widened unlike a patch antenna without taking the dielectric constant of the first substrate 14 into consideration, so the pair of first slots 16 mutually increase radio waves and the pair of second slots 18 mutually increase radio waves, thereby making the directivity narrow as compared with the patch antenna having a substrate in the same shape. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a slot antenna as an antenna of a wireless communication terminal.

  A small patch antenna is often used as an antenna of a wireless communication terminal.

  This patch antenna includes a flat substrate, and a film-like patch electrode (for example, copper foil) having a smaller area than the substrate is formed at the center of the surface (one plate surface) of the substrate. Patch electrode) is formed. A film-like ground portion (for example, a ground made of copper foil) is entirely formed on the back surface (the other plate surface) opposite to the surface on which the patch electrode of the substrate is formed. .

  The patch electrode is electrically connected to the inner conductor of the coaxial cable for high-frequency signal transmission by solder, and the ground portion is electrically connected to the outer conductor of the coaxial cable by solder.

  Such a small patch antenna is used in, for example, an ETC vehicle-mounted device that constitutes an automatic toll collection system (hereinafter referred to as ETC) that automatically pays tolls on toll roads by wireless communication.

  The patch antenna of the ETC on-vehicle device is, for example, erected in a state of being housed in a case in the on-vehicle state, and can transmit radio waves to the front of the vehicle or receive from the front of the vehicle.

  When traveling on a toll road with a vehicle equipped with such an ETC on-board device (for example, when passing through an ETC gate of an interchange on a highway), this patch antenna is used to connect the ETC on-vehicle device and the gate side of the vehicle. Data is transmitted and received by wireless communication with the communication terminal.

  However, since the communication terminal on the gate side is installed at a position higher than the vehicle height, when the vehicle passes through the ETC gate, the ETC on-board unit is positioned in front of the vehicle and above the vehicle from the traveling vehicle. Must communicate with a communication terminal.

  Therefore, when the pointing direction of the patch antenna is not directed to the communication terminal on the ETC gate side, there is a possibility that data transmission / reception may not be performed satisfactorily.

Therefore, a punch antenna has been proposed in which the patch electrode is moved from the central portion of the substrate to control the antenna directivity direction. (Patent Document 1)
JP 2006-197429 A

  However, even if the direction of the antenna is controlled, when the car passes through the ETC gate, the radio wave from the communication terminal on the ETC gate side directly enters the patch antenna and the one reflected by various objects. In some cases, interference (multipath) by reflected waves occurs, and data transmission / reception may not be performed well.

  As a countermeasure, it is conceivable to reduce the dielectric constant in the vicinity of the patch electrode without changing the size of the substrate, to enlarge only the patch electrode, and to narrow the directivity of the patch antenna.

  However, the size of the patch electrode is determined by the dielectric constant of the dielectric used for the substrate and the frequency of the radio wave to be transmitted / received, and the patch electrode may not be made large in order to narrow the directivity.

  In view of the above facts, an object of the present invention is to provide a slot antenna for wireless communication capable of narrowing directivity without considering the dielectric constant of a dielectric used for a substrate.

  A slot antenna according to claim 1 of the present invention is a pair of a first substrate that is a dielectric having a conductor film formed on an upper surface thereof, and a pair of conductor films that are formed by peeling off the conductor film and extending in parallel in a uniaxial direction. A first slot and a pair of second slots formed by peeling off the conductor film and extending in parallel in a biaxial direction orthogonal to the uniaxial direction are provided.

  According to the above configuration, unlike the patch antenna, since the slot is formed by stripping the conductor film, the distance between the pair of first slots extending in parallel in the uniaxial direction without considering the dielectric constant of the first substrate. And a distance between the pair of second slots extending in parallel in the biaxial direction can be increased. For this reason, the pair of first slots can intensify each other's radio waves, and the pair of second slots can intensify the radio waves from each other, so that the directivity can be narrowed compared to a patch antenna having the same shape substrate.

  A slot antenna according to a second aspect of the present invention is the slot antenna according to the first aspect, further comprising a strip conductor provided on a lower side of the first substrate and forming an electric field with the first slot and the second slot on an upper surface. Two substrates and a ground part provided on the lower surface of the second substrate are provided.

  According to the above configuration, an electric field is formed between the strip conductor provided on the upper surface of the second substrate and the first slot and the second slot to transmit and receive radio waves.

  Here, since the ground portion is provided on the lower surface of the second substrate, only necessary radio waves from the side where the first slot and the second slot are formed can be transmitted and received.

  A slot antenna according to a third aspect of the present invention is the slot antenna according to the first or second aspect, wherein the first substrate is rectangular, and the pair of the first slot and the second slot are sides of the first substrate. It is characterized by extending along each.

  According to the above configuration, the first substrate has a rectangular shape, and the pair of the first slot and the second slot each extend along the side of the first substrate. Therefore, the shape of the first substrate is effectively used. The distance between the pair of first slots and the distance between the pair of second slots can be increased, and the directivity of the antenna can be reduced.

  A slot antenna according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the slot antenna is used as a radio antenna of an ETC on-vehicle device of a vehicle.

  According to the above configuration, since the slot antenna is used as a radio antenna of the vehicle ETC on-board unit, the directivity can be narrowed, and interference (multipath) due to reflected waves is suppressed when passing through the ETC gate. As a result, data can be transmitted and received satisfactorily.

  According to the slot antenna of the present invention, the directivity can be narrowed without considering the dielectric constant of the dielectric used for the substrate.

  A slot antenna 10 according to the present invention will be described with reference to FIGS.

  As shown in FIG. 3, the slot antenna 10 is provided with a square-shaped first substrate 14 which is a dielectric (in this embodiment, glass epoxy) having a copper foil 12 as a conductor film formed on the upper surface. Yes.

  Further, the copper foil 12 is peeled off and formed on the upper surface of the first substrate 14, and a pair of first slots 16 extending parallel to the uniaxial direction along the periphery of the first substrate 14, and orthogonal to the uniaxial direction. A pair of second slots 18 extending in parallel to the two axial directions are provided.

  Specifically, as shown in FIG. 1, the pair of first slots 16 extend along a pair of opposing sides 14 </ b> A of the first substrate 14 and have the same shape. Similarly, the pair of second slots 18 extend along other opposing sides 14B of the first substrate 14 and have the same shape.

  Furthermore, the lower side of the first substrate 14 includes an end portion 20B orthogonal to the first slot 16 and the second slot 18 when viewed from above, and a broken line that forms an electric field with the first slot 16 and the second slot 18. A strip conductor 20 is provided on the upper surface of the second substrate 22 (see FIG. 3).

  As shown in FIG. 3, the second substrate 22 has the same shape as the first substrate 14, and is formed of a dielectric (in this embodiment, glass epoxy) as with the first substrate 14.

  Further, the strip conductor 20 is provided with a circular hole 20A. As shown in FIG. 2, the circular hole 20A is provided on the lower surface of the second substrate 22, and is a ground portion formed of a film-like copper foil. 24 is connected to a cylindrical through-hole 26 which is electrically connected to 24. The through hole 26 is a feeding point that is electrically insulated from the copper foil 12.

  A coaxial cable 28 for high-frequency signal transmission is provided below the ground portion 24.

  Specifically, as shown in FIGS. 2 and 4, the central conductor 30 at one end of the coaxial cable 28 is bent into an L shape, inserted into the through hole 26, and the through hole 26 serving as a feeding point It is connected to the inner wall with solder. Further, a net-like outer conductor 34 is provided around the cylindrical dielectric portion 32 covering the center conductor 30, and the outer conductor 34 is connected to the ground portion 24 by solder.

  Further, as shown in FIG. 3, a connector 36 is provided at the other end of the coaxial cable 28, and the slot antenna 10 is connected to a transmission / reception module (not shown) via this connector 36.

  This transmission / reception module is supplied with electric power from a power source, and can supply power to the slot antenna 10 from the transmission / reception module via the coaxial cable 28. Further, the transmission / reception module manages radio waves transmitted and received by the first slot 16 and the second slot 18.

  According to the slot antenna 10 having the above configuration, unlike the patch antenna, the distance (L1 shown in FIG. 1) between the pair of first slots 16 and the pair of first slots without considering the dielectric constant of the first substrate 14. The distance between the two slots 18 (L2 shown in FIG. 1) can be increased. For this reason, the pair of first slots 16 intensify each other's radio waves, and the pair of second slots 18 intensify each other's radio waves, thereby narrowing the directivity compared to a patch antenna having the same shape substrate. it can.

  Here, in the case of a patch antenna, it is conceivable that the directivity is narrowed by lowering the dielectric constant of the substrate by floating the substrate and further widening the patch electrode. However, such an air suspend type patch antenna is an expensive antenna. In the case of the slot antenna 10 described above, the distance between the pair of first slots 16 and the distance between the pair of second slots 18 are increased. Therefore, the directivity can be narrowed with an inexpensive configuration.

  The slot antenna 10 can be used for a radio antenna of an on-board ETC device that constitutes an automatic toll collection system (ETC) that automatically pays a toll on a toll road by radio communication. For example, radio waves from a communication terminal on the ETC gate side of an expressway can directly enter the antenna of the ETC on-board unit mounted on the vehicle, or can be reflected by various objects, and can be interfered by reflected waves (multiple Pass), and a good communication state may not be secured.

  However, since the directivity of the slot antenna 10 can be narrowed by using the slot antenna 10 for an ETC on-vehicle device, multipath can be suppressed and a good communication state can be maintained.

  Further, by changing the position of the through hole 26 as a feeding point, the directionality of the radio wave that can be transmitted and received can be changed, and can be installed without difficulty on the rear surface of the interior mirror in the vehicle.

  Further, since the film-like ground portion 24 is provided on the lower surface of the second substrate 22, only necessary radio waves from the side where the first slot 16 and the second slot 18 are formed can be transmitted and received. .

  In addition, since the first substrate 14 and the second substrate 22 are formed of the same material, the linear expansion coefficient of the first substrate 14 and the linear expansion coefficient of the second substrate 22 are the same, and the environmental temperature changes. It expands and contracts in the same way.

  That is, even if the environmental temperature to which the device on which the slot antenna 10 is mounted changes after shipment from the factory, the first substrate 14 and the second substrate 22 expand and contract in the same manner, so that excessive stress is applied to each other. There is nothing. For this reason, the durability of the slot antenna 10 due to a change in environmental temperature can be improved.

  Although the slot antenna 10 of the present invention has been described as an antenna that constitutes a part of an ETC on-vehicle device, the slot antenna 10 is an antenna that constitutes a part of a receiver of a VICS (road traffic information communication system), for example. Various antennas such as an antenna constituting a part of a RKE (remote keyless entry device), an antenna constituting a part of a TPMS (tire pressure monitoring system), an antenna constituting a part of a wireless communication system using Bluetooth As applicable.

It is a top view of the slot antenna which concerns on embodiment of this invention. It is sectional drawing of the slot antenna which concerns on embodiment of this invention. It is the disassembled perspective view which showed the slot antenna which concerns on embodiment of this invention. It is a bottom view of the slot antenna which concerns on embodiment of this invention.

Explanation of symbols

10 Slot antenna 12 Copper foil (conductor film)
14 First board 14A Side 14B Side 16 First slot 18 Second slot 20 Strip conductor 22 Second board 24 Ground portion

Claims (4)

A first substrate which is a dielectric having a conductor film formed on the upper surface;
A pair of first slots formed by stripping the conductor film and extending parallel to a uniaxial direction;
The conductor film is formed by peeling off,
A pair of second slots extending parallel to a biaxial direction perpendicular to the uniaxial direction;
A slot antenna comprising: A second substrate provided on a lower side of the first substrate and having a strip conductor forming an electric field with the first slot and the second slot on an upper surface;
A ground portion provided on the lower surface of the second substrate;
The slot antenna according to claim 1, further comprising:   3. The slot antenna according to claim 1, wherein the first substrate has a rectangular shape, and the pair of the first slot and the second slot respectively extend along a side of the first substrate.   The slot antenna according to any one of claims 1 to 3, wherein the slot antenna is used for a radio antenna of an ETC on-vehicle device of a vehicle.

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