Patent Publication Number: US-2023135990-A1

Title: Antenna device

Description:
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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a configuration of an antenna device according to a first embodiment of the present invention. 
         FIG.  2    is a vertical cross-sectional view of the configuration of the antenna device according to the embodiment. 
         FIG.  3    is a plan view of an example of a shape and arrangement pattern of openings made in a ground plane. 
         FIG.  4    is an enlarged plan view of a partial area illustrated in  FIG.  3   . 
         FIG.  5    is a plan view of another example of the shape and arrangement pattern of openings made in the ground plane. 
         FIG.  6    is a vertical cross-sectional view of a configuration of an antenna device according to a second embodiment of the present invention. 
         FIG.  7    is a vertical cross-sectional view of a configuration of an antenna device according to a third embodiment of the present invention. 
     
    
    
     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. 
     &lt;1. First Embodiment&gt; 
     (1.1 Antenna Device) 
     First, a configuration example of an antenna device according to a first embodiment of the present invention will be described with reference to  FIG.  1    and  FIG.  2   .  FIG.  1    is a perspective view of a configuration of an antenna device  1  according to the first embodiment of the present invention.  FIG.  2    is a vertical cross-sectional view of the configuration of the antenna device  1  according to the first embodiment of the present invention. 
     As illustrated in  FIG.  1    and  FIG.  2   , the antenna device  1  according to the present embodiment includes a dielectric substrate  10 , a radiating element  20 , a ground plane  30 , and a feed probe  40 . The antenna device  1  according to the present embodiment is a so-called microstrip antenna formed on the dielectric substrate  10 . 
     The dielectric substrate  10  is a flat substrate including dielectric material. As an example, the dielectric substrate  10  may 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 substrate  10  may be a ceramic substrate including aluminium oxides. 
     The radiating element  20  includes conductive material and is disposed on a first surface S 1  of the dielectric substrate  10 . The radiating element  20  has a circular or rectangular open boundary, and functions as an antenna capable of radiating or absorbing electromagnetic waves. For example, the radiating element  20  may include metal foil such as copper foil attached to the first surface S 1  of the dielectric substrate  10 . In addition, the radiating element  20  has a size capable of having desired properties in a desired operating frequency band. Specifically, the radiating element  20  may have a planar shape and has a size corresponding to the desired operating frequency (for example, approximately ½ wavelength). However, the radiating element  20  may 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 element  20  as long as the radiating element  20  has the desired properties. 
     For example, the radiating element  20  may 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 approximately  1 / 2  wavelength of the operating frequency. In addition, the radiating element  20  may have one of these shapes with slits or a notches. 
     The ground plane  30  includes conductive material and is disposed on a second surface S 2 , which is opposite to the first surface Si of the dielectric substrate  10 . The ground plane  30  constitutes a parallel plate resonator between the ground plane  30  and the radiating element  20 , and this causes the radiating element  20  to function as an antenna. Specifically, when the ground plane  30  is supplied with a ground potential and the radiating element  20  is supplied with electric power in a high-frequency band, the radiating element  20  and the ground plane  30  resonate at a frequency in such a manner that the size of the planar shape of the radiating element  20  corresponds to ½ wavelength. At this time, an electric field is generated at the edge of the radiating element  20 , 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 device  1  to radiate the electromagnetic waves in such a manner that the size of the planar shape of the radiating element  20  corresponds to ½ wavelength. 
     Note that, the ground plane  30  is disposed at least in an area corresponding to an area including the radiating element  20 . In other words, the ground plane  30  is disposed at least in a projection area obtained by projecting the area including the radiating element  20  onto the second surface S 2 . For example, the ground plane  30  may include metal foil such as copper foil attached to the second surface S 2  of the dielectric substrate  10 . 
     The radiating element  20  and the ground plane  30  may be formed by using same metal foil. In this case, the radiating element  20  and the ground plane  30  include same conductive material and have a same thickness. In this case, it is possible to further simplify the process of manufacturing the antenna device  1 . 
     The feed probe  40  is disposed on the second surface S 2  of the dielectric substrate  10  and extends into an inside of the dielectric substrate  10 . Specifically, the feed probe  40  is disposed in the projection area on the second surface S 2 , extends into the inside of the dielectric substrate  10 , and is bent in such a manner that the bent feed probe  40  becomes parallel to the radiating element  20 . The projection area is on the opposite side to the area including the radiating element  20 . The feed probe  40  is capable of supplying electric power in a high-frequency band to the radiating element  20  through capacitive coupling between the feed probe  40  and the radiating element  20 . The feed probe  40  may include conductive material. The conductive material include metal such as copper, aluminium, titanium, or tungsten. 
     Since the ground plane  30  constitutes the parallel plate resonator, the ground plane  30  occupies a wider area (for example, the whole second surface S 2  of the dielectric substrate  10 ) than the area including the radiating element  20 . Therefore, more conductive material is attached to the second surface S 2  than the first surface  51  of the dielectric substrate  10 . The ground plane  30  of the antenna device  1  according 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 element  20 . By making the periodic openings in the ground plane  30 , it is possible to reduce the usage amount of conductive material included in the ground plane  30  of the antenna device  1  according to the present embodiment without reducing the area including the ground plane  30 . 
     The periodic openings made in the ground plane  30  also makes it possible to reduce a difference between the usage amount of conductive material included in the ground plane  30  and the usage amount of conductive material included in the radiating element  20  of the antenna device  1  according to the present embodiment. This makes it possible to suppress warpage of the dielectric substrate  10  of the antenna device  1  according to the present embodiment when temperature changes. 
     Specifically, when the temperature changes, stress is generated in the dielectric substrate  10  by a difference in thermal expansion rate between the dielectric material included in the dielectric substrate  10  and the conductive material included in the ground plane  30 . At this time, the dielectric substrate  10  may warp due to increase in a difference between stress generated in the first surface  51  and stress generated in the second surface S 2  in the case where there is a large difference between the usage amount of the conductive material included in the ground plane  30  and the usage amount of the conductive material included in the radiating element  20 . When using the antenna device  1  according to the present embodiment, it is possible to reduce the difference in usage amount between conductive material of the first surface  51  and conductive material of the second surface S 2 . Therefore, it is possible to suppress the warpage of the dielectric substrate  10 . 
     (1.2. Ground Plane) 
     Next, with reference to  FIG.  3    and  FIG.  4   , a shape and arrangement pattern of openings made in the ground plane  30  of the antenna device  1  according to the present embodiment will be described.  FIG.  3    is a plan view of an example of the shape and arrangement pattern of the openings made in the ground plane  30 .  FIG.  4    is an enlarged plan view of a partial area PA illustrated in  FIG.  3   . 
     As illustrated in  FIG.  3   , for example, the ground plane  30  may have a plurality of periodic openings  31 , and the ground plane  30  may be disposed on the whole second surface S 2  of the dielectric substrate  10 . For example, the openings  31  may 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 device  1 , the ground plane  30  is desirably disposed on the whole second surface S 2  of the dielectric substrate  10 . However, in this case, the usage amount of conductive material included in the ground plane  30  drastically increases. By making the periodic openings  31  in the ground plane  30 , it is possible to dispose the ground plane  30  on the whole second surface S 2  of the antenna device  1  according to the present embodiment and reduce the usage amount of the conductive material. 
     Specifically, as indicated by the partial area PA illustrated in  FIG.  4   , the openings  31  have 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 element  20 . The pitch b of the openings  31  is a distance between centers of the circular openings  31 . An interval a between the openings  31  made in the ground plane  30  is a distance obtained by subtracting a diameter  2 R of the opening  31  from the pitch b. 
     The openings  31  may be made in such a manner that the interval a between the openings  31  made in the ground plane  30  is 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 openings  31  made on the remaining ground plane  30 . 
     Since the openings  31  are arrayed as described above, it is possible to prevent the intervals a on the remaining ground plane  30  from having a size of ¼ wavelength or more of the operating frequency of the radiating element  20  of the antenna device  1 . For example, in the case where the interval a on the remaining ground plane  30  has the size of ¼ wavelength or more of the operating frequency of the radiating element  20 , a plurality of reflection points are formed on the ground plane  30 , 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 device  1 . The antenna device  1  according 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 openings  31  as described above, it is possible to prevent the remaining ground plane  30  from having a complicated geometric pattern. 
     For example, in the case where the remaining ground plane  30  has the complicated geometric pattern (such as a meander pattern or an interdigitated pattern), inductance and capacitance are unintentionally applied to the ground plane  30 . This may deteriorate the antenna characteristics of the antenna device  1 . The antenna device  1  according 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 openings  31  as long as the antenna characteristics of the antenna device  1  do not deteriorate. For example, in the case where some intervals a on the remaining ground plane  30  have the size of ¼ wavelength or more of the operating frequency of the radiating element  20 , this may affect the antenna characteristics of the antenna device  1 . Accordingly, the openings  31  may deviate from the periodic array as long as the some intervals a on the remaining ground plane  30  have the size less than ¼ wavelength of the operating frequency of the radiating element  20 . In other words, the openings  31  do 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 probe  40  is electrically separated from the ground plane  30 . Therefore, it is also possible to dispose the feed probe  40  in the opening  31 . In this case, the openings  31  may be made at positions deviated from the respective vertices of the equilateral triangle, the positions corresponding to the positions of the feed probes  40 . 
       FIG.  3    and  FIG.  4    illustrate the example of arraying the openings  31  having 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 in  FIG.  5   , openings  31 A 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.  5    is a plan view of another example of a shape and arrangement pattern of the openings  31 A made in the ground plane  30 . 
     Specifically, the openings  31 A 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 element  20 , in a vertical direction (Y axis direction) and in a horizontal direction (X axis direction). The pitch b of the openings  31 A is a distance between centroids of the rectangular openings  31 A. An interval a between the openings  31 A made in the ground plane  30  is a distance obtained by subtracting the length of a side of the opening  31  from the pitch b. The openings  31 A may be made in such a manner that the interval a between the openings  31 A made in the ground plane  30  is 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 openings  31  made on the remaining ground plane  30 . 
     Instead of the circular planar shape or the rectangular planar shape, the openings  31  may have an oval planar shape, a polygonal planar shape, or other planar shapes. However, in view of ease of making the openings  31  in the ground plane  30 , the openings  31  preferably has the circular planar shape or the oval planar shape with no corner. In addition, to further increase the number of openings  31  made in the ground plane  30  and to further reduce the usage amounts of the conductive materials, the openings  31  are preferably arrayed in such a manner that the openings  31  correspond to respective vertices of an equilateral triangle having a high tessellation level. 
     (1.3. Embodiments) 
     An embodiment of the antenna device  1  will be described on the basis of the array of the openings  31  illustrated in  FIG.  3   .and  FIG.  4   . Note that, the size of the openings  31  and the like of the antenna device  1  according to the present embodiment is not limited to examples to be described below. 
     For example, the radiating element  20  has a size of about 7 mm in the case where the radiating element  20  having the operating frequency 10 GHz is disposed on the dielectric substrate  10  having relative permittivity of 4.8 and having a size of 40 mm×40 mm. In addition, a pad connected to the feed probe  40  has a diameter of 1 mm, and a distance between the pad and the ground plane  30  is 0.5 mm. 
     In the case where no opening  31  is made in the ground plane  30 , a ratio of the area of the radiating element  20  to the area of the first surface S 1  is 2.41% of the area of the whole first surface S 1 . In addition, a ratio of the area of the ground plane  30  to the area of the second surface S 2  is 99.85% of the area of the whole second surface S 2 . 
     However, a ratio of the area of the ground plane  30  to the area of the second surface S 2  is 19.38% of the area of the whole second surface S 2  in the case where the openings  31  are made in the ground plane  30 , the pitch b of the openings  31  is 3.5 mm, the circular openings  31  has the diameter  2 R of 3.3 mm, and the intervals a on the ground plane  30  is 0.2 mm. 
     This makes it possible to drastically reduce the usage amount of conductive material included in the ground plane  30  of the antenna device  1  according 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 element  20  to the first surface Si and the ratio of the area of the ground plane  30  to the second surface S 2  of the antenna device  1  according 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 S 2 , and suppress the warpage of the dielectric substrate  10  of the antenna device  1  according to the present embodiment. 
     &lt;2. Second Embodiment&gt; 
     Next, an antenna device  2  according to a second embodiment of the present invention will be described with reference to  FIG.  6   .  FIG.  6    is a vertical cross-sectional view of the configuration of the antenna device  2  according to the second embodiment of the present invention. 
     As illustrated in  FIG.  6   , the antenna device  2  according to the present embodiment includes the dielectric substrate  10 , the radiating element  20 , the ground plane  30 , the feed probe  40 , a wiring substrate  51 , electronic components  52 , and wiring  53 . The antenna device  2  is different from the first embodiment in that the wiring substrate  51  on which the electronic components  52  are disposed is stacked on the second surface S 2  of the dielectric substrate  10  on which the radiating element  20  and the ground plane  30  are disposed. The dielectric substrate  10 , the radiating element  20 , the ground plane  30 , and the feed probe  40  are substantially similar to the first embodiment. Therefore, repeated description thereof will be omitted here. 
     The wiring substrate  51  is a printed circuit board such as a paper phenol board, a paper epoxy board, or a glass epoxy board. The electronic component  52  may be an integrated circuit, a resistor, a capacitor, or the like. For example, the electronic components  52  are disposed on a surface opposite to a surface through which the wiring substrate  51  are stacked on the dielectric substrate  10 . The electronic components  52  are electrically connected to each other via the wiring  53 . In addition, the feed probe  40  disposed in the dielectric substrate  10  penetrates the wiring substrate  51 , extends to the surface on which the electronic components  52  are disposed, and are electrically connected to the electronic components  52  via the wiring  53 . The electronic components  52  controls supply of electric power to the radiating element  20 . 
     In the antenna device  1  according to the present embodiment, the electronic components  52  and the wiring  53  are disposed near the radiating element  20 . Therefore, electromagnetic waves radiated from the radiating element  20  may affect the electronic components  52  and the wiring  53 . In this case, it is possible to protect the electronic components  52  and the wiring  53  from the electromagnetic waves radiated from the radiating element  20  when the ground plane  30  disposed between the radiating element  20  and a group of the wiring  53  and the electronic components  52  has an effect of blocking the electromagnetic waves (so-called electromagnetic-wave shielding effect). 
     Specifically, it is possible for the ground plane  30  to have the electromagnetic-wave shielding effect when the pitch of the periodic openings  31  made in the ground plane  30  is 1/10 wavelength or less of the operating frequency of the radiating element  20 . The openings  31  made at the above-described pitch is sufficiently smaller than the wavelength of the electromagnetic waves radiated from the radiating element  20 . Therefore, the openings  31  do not transmit the electromagnetic waves radiated from the radiating element  20 , and the electromagnetic waves are blocked by the ground plane  30 . This allows the antenna device  2  according to the present embodiment to suppress effects of the electromagnetic waves on the electronic components  52  and the wiring  53 , by using the ground plane  30  to block the electromagnetic waves radiated from the radiating element  20 . 
     &lt;3. Third Embodiment&gt; 
     Next, an antenna device  3  according to a third embodiment of the present invention will be described with reference to  FIG.  7   .  FIG.  7    is a vertical cross-sectional view of the configuration of the antenna device  3  according to the third embodiment of the present invention. 
     As illustrated in  FIG.  7   , the antenna device  3  according to the present embodiment includes the dielectric substrate  10 , the radiating element  20 , the ground plane  30 , the feed probe  40 , the wiring substrate  51 , the electronic components  52 , the wiring  53 , a substrate-side ground plane  55 , and junctions  57 . 
     The antenna device  3  is different from the first embodiment in that the wiring substrate  51  is stacked below the second surface S 2  of the dielectric substrate  10  on which the radiating element  20  and the ground plane  30  are disposed, and the ground plane  30  of the dielectric substrate  10  is electrically connected to the substrate-side ground plane  55  of the wiring substrate  51  via the junctions  57 . The dielectric substrate  10 , the radiating element  20 , the ground plane  30 , and the feed probe  40  are substantially similar to the first embodiment. Therefore, repeated description thereof will be omitted here. In addition, the wiring substrate  51 , the electronic components  52 , and the wiring  53  are substantially similar to the second embodiment. Therefore, repeated description thereof will be omitted here. 
     The substrate-side ground plane  55  is electrically separated from a junction  57  that is electrically connected to the feed probe  40 . The substrate-side ground plane  55  is disposed on a whole surface of the wiring substrate  51 , the surface being opposed to the dielectric substrate  10 . For example, the substrate-side ground plane  55  may be uniformly disposed in an area other than an area around the junction  57  that is electrically connected to the feed probe  40 . The substrate-side ground plane  55  is electrically connected to the ground plane  30  of the dielectric substrate  10  via junctions  57 . The substrate-side ground plane  55  functions as a reference potential supply source of the wiring substrate  51  when the ground potential is supplied. 
     The junctions  57  is an inter-substrate connection structures including solder joints. The junctions  57  connect the ground plane  30  to the substrate-side ground plane  55  electrically and physically. For example, the junction  57  may be a connection structure including a bump formed on the ground plane  30 , a bump formed on the substrate-side ground plane  55 , and a solder ball sandwiched between these bumps. 
     In the antenna device  3  according to the present embodiment, the ground plane  30  and the substrate-side ground plane  55  are electrically and physically connected via the junctions  57 . Therefore, for preventing the openings  31  from being made at positions corresponding to the junctions  57  in the ground plane  30 , it is also possible to change the arrangement of the openings  31  as long as the antenna characteristics of the antenna device  3  do not deteriorate. Specifically, the openings  31  made in the ground plane  30  may deviate from the periodic array in such a manner that the openings  31  deviate from the positions of the junctions  57 . This makes it possible to connect the ground plane  30  to the substrate-side ground plane  55  of the antenna device  3  according to the present embodiment while the junctions  57  are 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 element  20  is not specifically limited. The radiating element  20  may 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 element  20  may have one of these planar shapes with slits or notches. 
     For example, in the above-described embodiments, the single radiating element  20  is disposed on the first surface Si of the dielectric substrate  10 . However, the present invention is not limited thereto. For example, a plurality of the radiating elements  20  may be disposed on the first surface Si of the dielectric substrate  10 , and the plurality of radiating elements  20  may constitute an antenna array.