ANTENNA DEVICE

there is provided an antenna device comprising a flat dielectric substrate a radiating element disposed on a surface of the dielectric substrate and a ground plane disposed on another surface opposite to the surface of the dielectric substrate wherein the radiating element has a size corresponding to operating frequency of the radiating element, and the ground plane has a plurality of openings that are periodically made at a pitch less than ¼ wavelength of the operating frequency.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims benefit of priority from Japanese Patent Application No. 2021-177857, filed on Oct. 29, 2021, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to an antenna device.

Electronic component modules to be installed in electronic equipment have been downsized with miniaturization of the electronic equipment. For example, JP 2009-111287A listed below discloses a circuit board including an insulating layer of glass epoxy resin and wiring comprising a metal thin film of, for instance, copper foil, formed on surfaces of the insulating layer.

Microstrip antennas having been attracting attention as antennas that are easily formable on such a circuit board. The microstrip antenna is an antenna including a parallel plate resonator constituted by a radiating element formed on a surface of a substrate and a ground plane formed on the other surface of the substrate.

SUMMARY

However, reducing usage amounts of conductive materials such as metal for the circuit board has been considered due to recent increase in resource prices and raising of environmental awareness.

Accordingly, the present invention is made in view of the aforementioned issues, and an object of the present invention is to provide a novel and improved antenna device that makes it possible to reduce the usage amounts of conductive materials.

SUMMARY OF INVENTION

Technical Problem

To solve the above described problem, according to an aspect of the present invention, there is provided an antenna device comprising a flat dielectric substrate a radiating element disposed on a surface of the dielectric substrate and a ground plane disposed on another surface opposite to the surface of the dielectric substrate wherein the radiating element has a size corresponding to operating frequency of the radiating element, and the ground plane has a plurality of openings that are periodically made at a pitch less than ¼ wavelength of the operating frequency.

As described above, according to the present invention, it is possible to reduce the usage amounts of conductive materials.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, referring to the appended drawings, preferred embodiments of the present invention will be described in detail. It should be noted that, in this specification and the appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated explanation thereof is omitted.

First, a configuration example of an antenna device according to a first embodiment of the present invention will be described with reference toFIG.1andFIG.2.FIG.1is a perspective view of a configuration of an antenna device1according to the first embodiment of the present invention.FIG.2is a vertical cross-sectional view of the configuration of the antenna device1according to the first embodiment of the present invention.

As illustrated inFIG.1andFIG.2, the antenna device1according to the present embodiment includes a dielectric substrate10, a radiating element20, a ground plane30, and a feed probe40. The antenna device1according to the present embodiment is a so-called microstrip antenna formed on the dielectric substrate10.

The dielectric substrate10is a flat substrate including dielectric material. As an example, the dielectric substrate10may be a printed circuit board such as a paper phenol board, a paper epoxy board, or a glass epoxy board obtained by impregnating paper, glass fiber cloth, or the like with organic resin or the like. As another example, the dielectric substrate10may be a ceramic substrate including aluminium oxides.

The radiating element20includes conductive material and is disposed on a first surface S1of the dielectric substrate10. The radiating element20has a circular or rectangular open boundary, and functions as an antenna capable of radiating or absorbing electromagnetic waves. For example, the radiating element20may include metal foil such as copper foil attached to the first surface S1of the dielectric substrate10. In addition, the radiating element20has a size capable of having desired properties in a desired operating frequency band. Specifically, the radiating element20may have a planar shape and has a size corresponding to the desired operating frequency (for example, approximately ½ wavelength). However, the radiating element20may have the planar shape but have a size smaller than the ½ wavelength of the desired operating frequency by using a publicly known technology of downsizing the radiating element20as long as the radiating element20has the desired properties.

For example, the radiating element20may have a circular shape having a diameter which is approximately ½ wavelength of the operating frequency, an oval shape having a major axis which is approximately ½ wavelength of the operating frequency, or a rectangular shape having a side length which is approximately1/2wavelength of the operating frequency. In addition, the radiating element20may have one of these shapes with slits or a notches.

The ground plane30includes conductive material and is disposed on a second surface S2, which is opposite to the first surface Si of the dielectric substrate10. The ground plane30constitutes a parallel plate resonator between the ground plane30and the radiating element20, and this causes the radiating element20to function as an antenna. Specifically, when the ground plane30is supplied with a ground potential and the radiating element20is supplied with electric power in a high-frequency band, the radiating element20and the ground plane30resonate at a frequency in such a manner that the size of the planar shape of the radiating element20corresponds to ½ wavelength. At this time, an electric field is generated at the edge of the radiating element20, and a portion of an electromagnetic field generated from a magnetic current source and equivalent to the electric field is radiated into a space as electromagnetic waves. This allows the antenna device1to radiate the electromagnetic waves in such a manner that the size of the planar shape of the radiating element20corresponds to ½ wavelength.

Note that, the ground plane30is disposed at least in an area corresponding to an area including the radiating element20. In other words, the ground plane30is disposed at least in a projection area obtained by projecting the area including the radiating element20onto the second surface S2. For example, the ground plane30may include metal foil such as copper foil attached to the second surface S2of the dielectric substrate10.

The radiating element20and the ground plane30may be formed by using same metal foil. In this case, the radiating element20and the ground plane30include same conductive material and have a same thickness. In this case, it is possible to further simplify the process of manufacturing the antenna device1.

The feed probe40is disposed on the second surface S2of the dielectric substrate10and extends into an inside of the dielectric substrate10. Specifically, the feed probe40is disposed in the projection area on the second surface S2, extends into the inside of the dielectric substrate10, and is bent in such a manner that the bent feed probe40becomes parallel to the radiating element20. The projection area is on the opposite side to the area including the radiating element20. The feed probe40is capable of supplying electric power in a high-frequency band to the radiating element20through capacitive coupling between the feed probe40and the radiating element20. The feed probe40may include conductive material. The conductive material include metal such as copper, aluminium, titanium, or tungsten.

Since the ground plane30constitutes the parallel plate resonator, the ground plane30occupies a wider area (for example, the whole second surface S2of the dielectric substrate10) than the area including the radiating element20. Therefore, more conductive material is attached to the second surface S2than the first surface51of the dielectric substrate10. The ground plane30of the antenna device1according to the present embodiment has a plurality of openings that are periodically made at a pitch less than ¼ wavelength of the operating frequency of the radiating element20. By making the periodic openings in the ground plane30, it is possible to reduce the usage amount of conductive material included in the ground plane30of the antenna device1according to the present embodiment without reducing the area including the ground plane30.

The periodic openings made in the ground plane30also makes it possible to reduce a difference between the usage amount of conductive material included in the ground plane30and the usage amount of conductive material included in the radiating element20of the antenna device1according to the present embodiment. This makes it possible to suppress warpage of the dielectric substrate10of the antenna device1according to the present embodiment when temperature changes.

Specifically, when the temperature changes, stress is generated in the dielectric substrate10by a difference in thermal expansion rate between the dielectric material included in the dielectric substrate10and the conductive material included in the ground plane30. At this time, the dielectric substrate10may warp due to increase in a difference between stress generated in the first surface51and stress generated in the second surface S2in the case where there is a large difference between the usage amount of the conductive material included in the ground plane30and the usage amount of the conductive material included in the radiating element20. When using the antenna device1according to the present embodiment, it is possible to reduce the difference in usage amount between conductive material of the first surface51and conductive material of the second surface S2. Therefore, it is possible to suppress the warpage of the dielectric substrate10.

Next, with reference toFIG.3andFIG.4, a shape and arrangement pattern of openings made in the ground plane30of the antenna device1according to the present embodiment will be described.FIG.3is a plan view of an example of the shape and arrangement pattern of the openings made in the ground plane30.FIG.4is an enlarged plan view of a partial area PA illustrated inFIG.3.

As illustrated inFIG.3, for example, the ground plane30may have a plurality of periodic openings31, and the ground plane30may be disposed on the whole second surface S2of the dielectric substrate10. For example, the openings31may have a circular planar shape and may be periodically made at positions corresponding to respective vertices of an equilateral triangle (in other words, equilateral triangular lattice).

To further improve antenna characteristics of the antenna device1, the ground plane30is desirably disposed on the whole second surface S2of the dielectric substrate10. However, in this case, the usage amount of conductive material included in the ground plane30drastically increases. By making the periodic openings31in the ground plane30, it is possible to dispose the ground plane30on the whole second surface S2of the antenna device1according to the present embodiment and reduce the usage amount of the conductive material.

Specifically, as indicated by the partial area PA illustrated inFIG.4, the openings31have the circular planar shape and are periodically arrayed at a pitch b, which is less than ¼ wavelength of the operating frequency of the radiating element20. The pitch b of the openings31is a distance between centers of the circular openings31. An interval a between the openings31made in the ground plane30is a distance obtained by subtracting a diameter2R of the opening31from the pitch b.

The openings31may be made in such a manner that the interval a between the openings31made in the ground plane30is minimized as long as acceptable manufacturing cost and acceptable strength are maintained. In this case, it is possible to suppress effects on the antenna characteristics and further reduce the usage amounts of the conductive materials by further reducing the interval a between the openings31made on the remaining ground plane30.

Since the openings31are arrayed as described above, it is possible to prevent the intervals a on the remaining ground plane30from having a size of ¼ wavelength or more of the operating frequency of the radiating element20of the antenna device1. For example, in the case where the interval a on the remaining ground plane30has the size of ¼ wavelength or more of the operating frequency of the radiating element20, a plurality of reflection points are formed on the ground plane30, an unintended resonator is formed, and the resonator makes a standing wave. In this case, the standing wave made by the unintended resonator deteriorates the antenna characteristics of the antenna device1. The antenna device1according to the present embodiment makes it possible to prevent formation of the unintended resonator. This makes it possible to prevent the deterioration in antenna characteristics.

In addition, by arraying the openings31as described above, it is possible to prevent the remaining ground plane30from having a complicated geometric pattern.

For example, in the case where the remaining ground plane30has the complicated geometric pattern (such as a meander pattern or an interdigitated pattern), inductance and capacitance are unintentionally applied to the ground plane30. This may deteriorate the antenna characteristics of the antenna device1. The antenna device1according to the present embodiment makes it possible to prevent the unintended inductance and capacitance. This makes it possible to prevent the deterioration in antenna characteristics.

Note that, it is also possible to change the arrangement of the openings31as long as the antenna characteristics of the antenna device1do not deteriorate. For example, in the case where some intervals a on the remaining ground plane30have the size of ¼ wavelength or more of the operating frequency of the radiating element20, this may affect the antenna characteristics of the antenna device1. Accordingly, the openings31may deviate from the periodic array as long as the some intervals a on the remaining ground plane30have the size less than ¼ wavelength of the operating frequency of the radiating element20. In other words, the openings31do not have to be arrayed in a completely periodic manner, but may be arrayed in a partially deviated manner or other manners.

For example, the feed probe40is electrically separated from the ground plane30. Therefore, it is also possible to dispose the feed probe40in the opening31. In this case, the openings31may be made at positions deviated from the respective vertices of the equilateral triangle, the positions corresponding to the positions of the feed probes40.

FIG.3andFIG.4illustrate the example of arraying the openings31having the circular planar shape at positions corresponding to the respective vertices of the equilateral triangle. However, the present embodiment is not limited thereto. For example, as illustrated inFIG.5, openings31A may have a rectangular planar shape and may be made at positions corresponding to respective vertices of a square (in other words, square lattice).FIG.5is a plan view of another example of a shape and arrangement pattern of the openings31A made in the ground plane30.

Specifically, the openings31A has a rectangular planar shape and are arrayed at a pitch b, which is less than ¼ wavelength of the operating frequency of the radiating element20, in a vertical direction (Y axis direction) and in a horizontal direction (X axis direction). The pitch b of the openings31A is a distance between centroids of the rectangular openings31A. An interval a between the openings31A made in the ground plane30is a distance obtained by subtracting the length of a side of the opening31from the pitch b. The openings31A may be made in such a manner that the interval a between the openings31A made in the ground plane30is minimized as long as acceptable manufacturing cost and acceptable strength are maintained. In this case, it is possible to suppress effects on the antenna characteristics and reduce the usage amounts of the conductive materials by further reducing the interval a between the openings31made on the remaining ground plane30.

Instead of the circular planar shape or the rectangular planar shape, the openings31may have an oval planar shape, a polygonal planar shape, or other planar shapes. However, in view of ease of making the openings31in the ground plane30, the openings31preferably has the circular planar shape or the oval planar shape with no corner. In addition, to further increase the number of openings31made in the ground plane30and to further reduce the usage amounts of the conductive materials, the openings31are preferably arrayed in such a manner that the openings31correspond to respective vertices of an equilateral triangle having a high tessellation level.

An embodiment of the antenna device1will be described on the basis of the array of the openings31illustrated inFIG.3.andFIG.4. Note that, the size of the openings31and the like of the antenna device1according to the present embodiment is not limited to examples to be described below.

For example, the radiating element20has a size of about 7 mm in the case where the radiating element20having the operating frequency 10 GHz is disposed on the dielectric substrate10having relative permittivity of 4.8 and having a size of 40 mm×40 mm. In addition, a pad connected to the feed probe40has a diameter of 1 mm, and a distance between the pad and the ground plane30is 0.5 mm.

In the case where no opening31is made in the ground plane30, a ratio of the area of the radiating element20to the area of the first surface S1is 2.41% of the area of the whole first surface S1. In addition, a ratio of the area of the ground plane30to the area of the second surface S2is 99.85% of the area of the whole second surface S2.

However, a ratio of the area of the ground plane30to the area of the second surface S2is 19.38% of the area of the whole second surface S2in the case where the openings31are made in the ground plane30, the pitch b of the openings31is 3.5 mm, the circular openings31has the diameter2R of 3.3 mm, and the intervals a on the ground plane30is 0.2 mm.

This makes it possible to drastically reduce the usage amount of conductive material included in the ground plane30of the antenna device1according to the present embodiment from 99.85% to 19.38%. In addition, it is possible to reduce the difference between the ratio of the area of the radiating element20to the first surface Si and the ratio of the area of the ground plane30to the second surface S2of the antenna device1according to the present embodiment. This makes it possible to reduce a difference between stress generated in the first surface Si and stress generated in the second surface S2, and suppress the warpage of the dielectric substrate10of the antenna device1according to the present embodiment.

Next, an antenna device2according to a second embodiment of the present invention will be described with reference toFIG.6.FIG.6is a vertical cross-sectional view of the configuration of the antenna device2according to the second embodiment of the present invention.

As illustrated inFIG.6, the antenna device2according to the present embodiment includes the dielectric substrate10, the radiating element20, the ground plane30, the feed probe40, a wiring substrate51, electronic components52, and wiring53. The antenna device2is different from the first embodiment in that the wiring substrate51on which the electronic components52are disposed is stacked on the second surface S2of the dielectric substrate10on which the radiating element20and the ground plane30are disposed. The dielectric substrate10, the radiating element20, the ground plane30, and the feed probe40are substantially similar to the first embodiment. Therefore, repeated description thereof will be omitted here.

The wiring substrate51is a printed circuit board such as a paper phenol board, a paper epoxy board, or a glass epoxy board. The electronic component52may be an integrated circuit, a resistor, a capacitor, or the like. For example, the electronic components52are disposed on a surface opposite to a surface through which the wiring substrate51are stacked on the dielectric substrate10. The electronic components52are electrically connected to each other via the wiring53. In addition, the feed probe40disposed in the dielectric substrate10penetrates the wiring substrate51, extends to the surface on which the electronic components52are disposed, and are electrically connected to the electronic components52via the wiring53. The electronic components52controls supply of electric power to the radiating element20.

In the antenna device1according to the present embodiment, the electronic components52and the wiring53are disposed near the radiating element20. Therefore, electromagnetic waves radiated from the radiating element20may affect the electronic components52and the wiring53. In this case, it is possible to protect the electronic components52and the wiring53from the electromagnetic waves radiated from the radiating element20when the ground plane30disposed between the radiating element20and a group of the wiring53and the electronic components52has an effect of blocking the electromagnetic waves (so-called electromagnetic-wave shielding effect).

Specifically, it is possible for the ground plane30to have the electromagnetic-wave shielding effect when the pitch of the periodic openings31made in the ground plane30is 1/10 wavelength or less of the operating frequency of the radiating element20. The openings31made at the above-described pitch is sufficiently smaller than the wavelength of the electromagnetic waves radiated from the radiating element20. Therefore, the openings31do not transmit the electromagnetic waves radiated from the radiating element20, and the electromagnetic waves are blocked by the ground plane30. This allows the antenna device2according to the present embodiment to suppress effects of the electromagnetic waves on the electronic components52and the wiring53, by using the ground plane30to block the electromagnetic waves radiated from the radiating element20.

Next, an antenna device3according to a third embodiment of the present invention will be described with reference toFIG.7.FIG.7is a vertical cross-sectional view of the configuration of the antenna device3according to the third embodiment of the present invention.

As illustrated inFIG.7, the antenna device3according to the present embodiment includes the dielectric substrate10, the radiating element20, the ground plane30, the feed probe40, the wiring substrate51, the electronic components52, the wiring53, a substrate-side ground plane55, and junctions57.

The antenna device3is different from the first embodiment in that the wiring substrate51is stacked below the second surface S2of the dielectric substrate10on which the radiating element20and the ground plane30are disposed, and the ground plane30of the dielectric substrate10is electrically connected to the substrate-side ground plane55of the wiring substrate51via the junctions57. The dielectric substrate10, the radiating element20, the ground plane30, and the feed probe40are substantially similar to the first embodiment. Therefore, repeated description thereof will be omitted here. In addition, the wiring substrate51, the electronic components52, and the wiring53are substantially similar to the second embodiment. Therefore, repeated description thereof will be omitted here.

The substrate-side ground plane55is electrically separated from a junction57that is electrically connected to the feed probe40. The substrate-side ground plane55is disposed on a whole surface of the wiring substrate51, the surface being opposed to the dielectric substrate10. For example, the substrate-side ground plane55may be uniformly disposed in an area other than an area around the junction57that is electrically connected to the feed probe40. The substrate-side ground plane55is electrically connected to the ground plane30of the dielectric substrate10via junctions57. The substrate-side ground plane55functions as a reference potential supply source of the wiring substrate51when the ground potential is supplied.

The junctions57is an inter-substrate connection structures including solder joints. The junctions57connect the ground plane30to the substrate-side ground plane55electrically and physically. For example, the junction57may be a connection structure including a bump formed on the ground plane30, a bump formed on the substrate-side ground plane55, and a solder ball sandwiched between these bumps.

In the antenna device3according to the present embodiment, the ground plane30and the substrate-side ground plane55are electrically and physically connected via the junctions57. Therefore, for preventing the openings31from being made at positions corresponding to the junctions57in the ground plane30, it is also possible to change the arrangement of the openings31as long as the antenna characteristics of the antenna device3do not deteriorate. Specifically, the openings31made in the ground plane30may deviate from the periodic array in such a manner that the openings31deviate from the positions of the junctions57. This makes it possible to connect the ground plane30to the substrate-side ground plane55of the antenna device3according to the present embodiment while the junctions57are arranged more flexibility.

Heretofore, preferred embodiments of the present invention have been described in detail with reference to the appended drawings, but the present invention is not limited thereto. It should be understood by those skilled in the art that various changes and alterations may be made without departing from the spirit and scope of the appended claims.

For example, the planar shape of the radiating element20is not specifically limited. The radiating element20may have a square planar shape, a rectangular planar shape, a polygonal planar shape, a circular planar shape, an oval planar shape, or an interdigitated planar shape. In addition, the radiating element20may have one of these planar shapes with slits or notches.

For example, in the above-described embodiments, the single radiating element20is disposed on the first surface Si of the dielectric substrate10. However, the present invention is not limited thereto. For example, a plurality of the radiating elements20may be disposed on the first surface Si of the dielectric substrate10, and the plurality of radiating elements20may constitute an antenna array.