Patent Publication Number: US-10312579-B2

Title: Array antenna device

Description:
CROSS-REFERENCE TO RELATED APPLICATION (S) 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2016-032196, filed Feb. 23, 2016; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an array antenna device. 
     BACKGROUND 
     A protection method is known in which a resin foam, serving as an antenna protecting layer, is bonded to the surface of an array antenna composed of a dielectric material on the radiating element side. This protection method leads to a smaller thickness of the antenna device than in the case where the antenna is protected by use of a radome which is out of mechanical contact with the radiating elements of the antenna. In addition, this protection method reduces an impact on the electric characteristics of the antenna body, thereby restraining a reduction in antenna gain, compared to the case where a plastic film layer, serving as a radome for protecting the antenna, is directly bonded to the surface of the array antenna on the radiating element side. Further, this protection method improves the planarity and mechanical strength of the antenna body. 
     However, bonding a resin foam to an antenna surface cause a problem of degrading the reflection characteristics of the radiating elements and the entire antenna since the non-uniformity of the adhesive or the adhesive layer causes variations in the impedance of each radiating element of the array antenna. Since the radiating elements have different reflection characteristics, the electromagnetic field distribution deviates from the designed values on the antenna aperture, so that the radiation pattern is degraded and the antenna gain is reduced. 
     There are still other problems such as the degradation in the cross polarization discrimination of the antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view illustrating an example schematic configuration of an array antenna device according to the first embodiment; 
         FIG. 2  is a cross sectional view illustrating an example schematic configuration of the array antenna device according to the first embodiment; 
         FIG. 3  is an exploded perspective view illustrating an example schematic configuration of an array antenna device according to the second embodiment; 
         FIG. 4  is an exploded perspective view illustrating an example schematic configuration of an array antenna device according to the third embodiment; 
         FIG. 5  is an exploded perspective view illustrating an example schematic configuration of an array antenna device according to the fourth embodiment; 
         FIG. 6  is a cross sectional view illustrating an example schematic configuration of the array antenna device according to the fourth embodiment; 
         FIG. 7  is an exploded perspective view illustrating an example schematic configuration of an array antenna device according to the fifth embodiment; 
         FIG. 8  is a cross sectional view illustrating an example schematic configuration of the array antenna device according to the fifth embodiment; and 
         FIG. 9  is an exploded perspective view illustrating an example schematic configuration of an array antenna device according to the sixth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An array antenna device according to an embodiment of the present invention includes an array antenna, a core layer, and a first adhesive layer. 
     The array antenna has a first surface on which one or more radiating elements are disposed. 
     The core layer is disposed facing the first surface. 
     The first adhesive layer is present between the array antenna and the core layer and bonds the array antenna and the core layer to each other. 
     The first adhesive layer includes one or more first openings and one or more radiating elements are disposed inside the first opening. 
     An embodiment of the present invention provides an array antenna device that has good antenna characteristics while the antenna is protected and the mechanical strength of the antenna is improved. 
     Below, a description is given of embodiments of the present invention with reference to the drawings. The present invention is not limited to the embodiments. 
     (First Embodiment) 
       FIG. 1  is an exploded perspective view illustrating an example schematic configuration of an array antenna device according to the first embodiment. An array antenna device  100  according to the first embodiment includes an array antenna  101 , a low dielectric constant core (core layer)  102 , and a first adhesive layer  103 . 
     The array antenna  101  has one or more radiating elements  104  on a surface. These radiating elements  104  emit electromagnetic waves. The array antenna  101  can be formed, for example, on a dielectric substrate. As the dielectric substrate, substrate of a resin such as polytetrafluoroethylene (PTFE) and epoxy or substrate of a film such as a resin foam and a liquid crystal polymer can be used. 
     Examples of the radiating elements  104  include patch antennas, slot antennas, and slot loop antennas. 
     The low dielectric constant core  102  is disposed to face a surface of the array antenna  101  having the radiating elements  104 . For example, a resin foam is used as the low dielectric constant core  102 . 
     The first adhesive layer  103  is present between the array antenna  101  and the low dielectric constant core  102 , bonding the array antenna  101  and the low dielectric constant core  102  to each other. For example, the first adhesive layer  103  may be a sheet-shaped thermoplastic resin or thermosetting resin. Using sheet-shaped resin layer as an adhesive layer enable to simplify the process of bonding. Alternatively, the first adhesive layer  103  may be formed of a fluid adhesive. A fluid adhesive may be applied to the array antenna  101  or the low dielectric constant core  102 , and the applied adhesive may be used as the first adhesive layer  103 . 
     The first adhesive layer  103  includes one or more first openings  105 . One or more first openings  105  are provided in an adhesive surface for bonding the array antenna  101  and the first adhesive layer  103  to each other, in positions where they face the radiating elements  104  on a surface of the array antenna  101 . In other words, one or more the radiating elements  104  are disposed inside the first openings  105  in bonding the array antenna  101  and the first adhesive layer  103 . Thereby, the radiating element  104  and the first adhesive layer  103  are not bonded to each other. 
       FIG. 2  is an example cross sectional view of the array antenna device  100  according to the first embodiment. The drawing shows the radiating elements  104  disposed on a surface of the array antenna  101  are inside the first openings  105  and are not bonded to the first adhesive layer  103 . 
     When a sheet-shaped resin layer are used as the first adhesive layer  103 , the first opening  105  should be provided in advance. When a fluid adhesive forms the first adhesive layer  103 , the fluid adhesive may be applied avoiding the radiating elements  104 . 
     When the first adhesive layer  103  bonds the array antenna  101  and the low dielectric constant core  102  which is a resin foam, the first adhesive layer  103  penetrates into the foams in the low dielectric constant core  102  (resin foam). Since the foams are not uniform in the low dielectric constant core  102  (resin foam), the first adhesive layer  103  becomes non-uniform. When the non-uniform first adhesive layer  103  covers the radiating elements  104 , the impedance of each radiating element changes, which degrades the reflection characteristics of the radiating elements and the entire antenna. Since the reflection characteristics vary between the radiating elements, the electromagnetic field distribution deviates from the designed values on the antenna apertures, so that the radiation pattern is degraded and the antenna gain is reduced. Besides, there arises a problem that the cross-polar discrimination of the antenna degrades. To avoid these, the first adhesive layer  103  according to this embodiment has the first openings  105  and passes many electromagnetic waves from the radiating elements  104  through the first openings  105  in order to prevent degradation in the various characteristics of the antenna. Electromagnetic waves which may possibly pass through not the first opening  105  but the first adhesive layer  103  are so little that they have a very little impact on the various characteristics of the antenna. Consequently, this embodiment can achieve good antenna characteristics. 
     Here, it is assumed that none of the radiating elements  104  are bonded to the first adhesive layer  103 . Alternatively, one or more particular radiating elements  104  may not be bonded to the first adhesive layer  103 . 
     In  FIGS. 1 and 2 , when the array antenna  101  and the low dielectric constant core  102  are bonded to each other, one first opening  105  contains one radiating element  104 . In other words, each first opening  105  and the corresponding radiating element  104  are paired with each other. However, the number, positions, and width of first openings  105  are not necessarily like these. One first opening  105  may contain a plurality of radiating elements  104 . For example, more than one first openings  105  shown in the drawing may be collected into one big opening. 
     Although the openings of first openings  105  are circular in  FIG. 1 , they may be in a rectangular, polygonal, or any other complex shape as long as the regions other than the first openings  105  are not in contact with the radiating elements  104 . 
     As described above, in the first embodiment, the array antenna  101  and the low dielectric constant core  102  are bonded to each other with the first adhesive layer  103  having a plurality of first openings  105  in regions facing a plurality of radiating elements  104  disposed on the surface of the array antenna  101 . Thereby, it is possible to restrain degradation in the various characteristics of the antenna due to non-uniformity of an adhesive or adhesive sheet for bonding the antenna surface and the antenna protective layer while achieving the protection of the array antenna and an improvement in mechanical strength. Moreover, the thickness of the array antenna device can be reduced. 
     (Second Embodiment) 
       FIG. 3  is an exploded perspective view illustrating an example schematic configuration of an array antenna device  200  according to the second embodiment. The second embodiment differs from the first embodiment in that the second embodiment further includes a skin (skin layer)  201  which has a higher dielectric constant than the low dielectric constant core  102 . The description of the points similar to those in the first embodiment will be omitted. 
     The skin  201  is disposed in contact with the surface of the low dielectric constant core  102  opposite to the surface bonded to the array antenna  101 . The skin  201  may be a polytetrafluoroethylene (PTFE) that is highly resistant to climate and radiowave attenuation, a fiber-reinforced plastic (FRP) that has high mechanical strength, or the like. 
     With the skin  201  disposed as in  FIG. 3 , the protective performance for the array antenna device  200  is higher than in the first embodiment which uses only the low dielectric constant core  102  that has low strength. Since the protective performance for the array antenna device  100  is improved, an insulating honeycomb structure without a function for protecting an antenna can be used as the low dielectric constant core  102 . Since an insulating honeycomb structure has a lower specific gravity than a resin foam, the weight of the array antenna device  200  can be reduced. 
     When a honeycomb structure is used, the first adhesive layer  103  is non-uniform as in a resin foam and the various characteristics of the antenna are degraded. However, in this embodiment, the non-uniform first adhesive layer  103  does not cover the radiating elements  104  because of a plurality of first openings  105  disposed facing a plurality of radiating elements  104  disposed on a surface of the array antenna  101 . Thereby, it is possible to prevent degradation in various characteristics of the antenna. 
     As described above, in the second embodiment, the array antenna device  200  includes the skin  201 , providing higher protective performance for the antenna than in the first embodiment. In addition, when the low dielectric constant core  102  is an insulating honeycomb structure, the array antenna device  200  is more lightweight than in the first embodiment. 
     (Third Embodiment) 
       FIG. 4  is an exploded perspective view illustrating an example schematic configuration of an array antenna device  300  according to the third embodiment. The third embodiment differs from the second embodiment in that the third embodiment further includes a second adhesive layer  301  between the low dielectric constant core  102  and the skin  201 . The description of the points similar to those in the second embodiment will be omitted. 
     The second adhesive layer  301  bonds the low dielectric constant core  102  and the skin  201  to each other. The second adhesive layer  301  may be, like the first adhesive layer  103 , a thermosetting resin sheet or a fluid adhesive. With the low dielectric constant core  102  and the skin  201  bonded to each other, the mechanical strength of the antenna is higher than that in the second embodiment. 
     As described above, in the third embodiment, the array antenna device  300  further includes the second adhesive layer  301  for bonding the low dielectric constant core  102  and the skin  201  to each other, providing higher mechanical strength of the array antenna device than in the second embodiment. 
     (Fourth Embodiment) 
       FIG. 5  is an exploded perspective view illustrating an example schematic configuration of an array antenna device  400  according to the fourth embodiment. The fourth embodiment differs from the third embodiment in that the low dielectric constant core  102  includes second openings  401 . The description of the points similar to those in the third embodiment will be omitted. It should be noted that the low dielectric constant core  102  according to the second embodiment may have the second openings  401 . an embodiment where the low dielectric constant core  102  according to the second embodiment has the second openings  401  differs from the fourth embodiment only in that it does not have the second adhesive layer  301 . Accordingly, its description will be also omitted. 
     When the array antenna device  400  is used as a transmitting antenna, electromagnetic waves emitted by each radiating element  104  partly pass through the second openings  401  provided in the low dielectric constant core  102 . In other words, electromagnetic waves emitted by each radiating element  104  are partly propagated without being blocked by the low dielectric constant core  102 , thereby reducing a dielectric loss generated by the low dielectric constant core  102 . Thus, the antenna performance is higher than those in the previous embodiments. 
       FIG. 6  is a cross sectional view illustrating an example schematic configuration of the array antenna device  400  according to the fourth embodiment. The drawing shows that electromagnetic waves emitted by the radiating elements  104  and passing through the first openings  105  provided in the array antenna  101  directly pass through the second openings  401  provided in the low dielectric constant core  102 . 
     In  FIGS. 5 and 6 , each second opening  401  formed in the low dielectric constant core  102  and the corresponding radiating element  104  formed in the array antenna  101  are paired with each other. However, the number, positions, and width of second openings  401  are not necessarily like these. When the array antenna  101  and the low dielectric constant core  102  are bonded to each other, a plurality of radiating elements  104  may be disposed in a portion in the array antenna  101  which is directly below one second opening  401 . For example, more than one second openings  401  shown in the drawing may be collected into one big opening. 
     Although the openings of second openings  401  are circular in  FIG. 5 , they may be in a rectangular, polygonal, or any other complex shape. 
     When the array antenna device  400  is used as a receiving antenna, a dielectric loss generated by the low dielectric constant core  102  is reduced according to the reciprocity theorem. For this reason, in the case that the array antenna device  400  is used as a receiving antenna, the antenna performance is higher than those in the previous embodiments. 
     As described above in the fourth embodiment, a dielectric loss generated by the low dielectric constant core  102  can be reduced with the low dielectric constant core  102  having the second openings  401  in regions facing the plurality of radiating elements  104  on the array antenna  101 . Thus, the antenna characteristics are higher than those in the second and third embodiments. 
     (Fifth Embodiment) 
       FIG. 7  is an exploded perspective view illustrating an example schematic configuration of an array antenna device  500  according to the fifth embodiment. The fifth embodiment differs from the fourth embodiment in that the second adhesive layer  301  includes third openings  501 . The description of the points similar to those in the fourth embodiment will be omitted. It should be noted that the second adhesive layer  301  according to the third embodiment may have the third openings  501 . an embodiment where the second adhesive layer  301  according to the third embodiment has the third openings  501  differs from the fifth embodiment only in that the low dielectric constant core  102  does not have the second openings  401 . Accordingly, its description will be also omitted. 
     When the array antenna device  500  is used as a transmitting antenna, electromagnetic waves emitted by each radiating element  104  partly pass through the third openings  501  provided in the second adhesive layer  301 . In other words, electromagnetic waves emitted by each radiating element  104  are partly propagated without being blocked by the second adhesive layer  301 , thereby reducing a dielectric loss generated by the second adhesive layer  301 . Thus, the antenna performance is higher than those in the previous embodiments. 
       FIG. 8  is a cross sectional view illustrating an example schematic configuration of the array antenna device  500  according to the fifth embodiment. The drawing shows that electromagnetic waves emitted by the radiating elements  104  and passing through the first openings  105  provided in the array antenna  101  and the second openings  401  provided in the low dielectric constant core  102  directly pass through the third openings  501  provided in the second adhesive layer  301 . 
     Although each third opening  501  formed in the second adhesive layer  301  and the corresponding radiating element  104  formed in the array antenna  101  are paired, this is not necessarily the case. As for the third openings  501 , when the array antenna  101  and the low dielectric constant core  102  are bonded to each other, a plurality of radiating elements  104  may be disposed in a portion in the array antenna  101  which is directly below one third opening  501 . 
     In  FIGS. 7 and 8 , each third opening  501  formed in the second adhesive layer  301  and the corresponding radiating element  104  formed in the array antenna  101  are paired with each other. However, the number, positions, and width of third openings  501  are not necessarily like these. When the second adhesive layer  301  and the low dielectric constant core  102  are bonded to each other, a plurality of radiating elements  104  may be disposed in a portion in the array antenna  101  which is directly below one third opening  501 . For example, more than one third openings  501  shown in the drawing may be collected into one big opening. 
     Although the plurality of third openings  501  in  FIG. 7  are circular, they may be in a rectangular, polygonal, or any other complex shape. 
     When the array antenna device  500  is used as a receiving antenna, a dielectric loss generated by the second adhesive layer  301  is reduced according to the reciprocity theorem. For this reason, in the case that the array antenna device  500  is used as a receiving antenna, the antenna performance is higher than those in the previous embodiments. 
     As described above in the fifth embodiment, a dielectric loss generated by the second adhesive layer  301  can be reduced with the second adhesive layer  301  having the third openings  501  in regions facing the plurality of radiating elements  104  on the array antenna  101 . Thus, the antenna characteristics are higher than those in the third and fourth embodiments. 
     (Sixth Embodiment) 
       FIG. 9  is an exploded perspective view illustrating an example schematic configuration of an array antenna device  600  according to the sixth embodiment. The sixth embodiment differs from the third embodiment in that the sixth embodiment further includes a reinforcement  601  and a third adhesive layer  602 . The description of the points similar to those in the third embodiment will be omitted. The other embodiments may also further include the reinforcement  601  and the third adhesive layer  602 . 
     The reinforcement  601  is fixed to the surface of the array antenna  101  opposite to the surface on which the radiating elements  104  are disposed. The reinforcement  601  may be composed of, a metal, a resin foam, a honeycomb structure, an FRP, or a combination of part or all of them. With the reinforcement  601 , the mechanical strength of the array antenna device  600  becomes higher than those in the previous embodiments. 
     The third adhesive layer  602  fixes the array antenna  101  and the reinforcement  601  to each other. The third adhesive layer  602  may be the same as the first adhesive layer  103  or the second adhesive layer  301 . Alternatively, the third adhesive layer  602  may be either an adhesive sheet or an adhesive coating. It should be noted that when the third adhesive layer  602 , the first adhesive layer  103 , and the second adhesive layer  301  are composed of the same material, the array antenna  101 , the low dielectric constant core  102 , the skin  201 , and the reinforcement  601  can be bonded to each other in one step, thereby simplifying a process for manufacturing the array antenna device  600 . It should be noted that the reinforcement  601  and the array antenna  101  may be fixed to each other by screws without the use of the third adhesive layer  602 . 
     As described above, in the sixth embodiment, the reinforcement  601  fixed to the surface of the array antenna  101  opposite to the surface on which the radiating elements  104  are disposed makes the mechanical strength of the array antenna device  600  higher than the previous embodiments. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.