Patent Publication Number: US-11043750-B2

Title: Antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Priority Patent Application No. 2019-007103, filed Jan. 18, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present invention relates to an antenna. 
     For an antenna to be mounted on a flying object such as a rocket and an aircraft, it is required to radio waves uniformly radiated in a wide area and to withstand aerodynamic loading and aerodynamic heating that occur in flight. In the current state, a blade antenna, a monopole antenna, or a patch antenna is mainly used as an antenna to be mounted on a rocket or the like (see Japanese Patent Application Laid-open No. 2003-60426). 
     SUMMARY 
     However, those antennas have the following circumstances.
         An antenna beam has null points (hollow). In the case of the blade antenna and the monopole antenna, the antenna patterns of linear polarization and circular polarization have null points. In the case of the patch antenna, the antenna pattern of circular polarization has null points.   The patch antenna is incapable of radiating radio waves in a wide area because the linear polarization of the patch antenna is not radiated in a direction of the mounting surface of the antenna.   The body of the flying object functions as an antenna element because the blade antenna, the monopole antenna, and the patch antenna are all unbalanced-type antennas. The antenna pattern can be thus affected by the shape of the body and an antenna-mounting portion, and the antenna pattern can significantly differ from the pattern of the antenna itself.   The blade antenna, the monopole antenna, and the patch antenna have a portion(s) projected from the surface of the body of the flying object. It is thus necessary to provide a rigid structure to withhold aerodynamic loading and heating or an additional structure to protect the antenna. In this case, the antenna pattern can be affected by those structures and the antenna pattern can significantly differ from the pattern of the antenna itself   A flying object such as a rocket is imposed operational restrictions of changing vehicle attitude in flight and flight path due to the pattern characteristics of an antenna mounted on the flying object.       

     In view of the above-mentioned circumstances, one or more aspects of the present invention are directed to provide a high-gain antenna having uniformly stable pattern characteristics in a wide area. 
     One or more aspects of the present invention are also directed to provide an antenna which eliminates operational restrictions of a flying object due to the antenna pattern characteristics, in the case where the antenna is mounted on the flying object. 
     One or more aspects of the present invention are also directed to sufficiently alleviate aerodynamic loading and heating that occur on the antenna, in the case where the antenna is mounted on the flying object. 
     The antenna according to the present invention employs a parabolic antenna form. Parabolic antennas are widely used for applications including an antenna for receiving satellite broadcasting, a ground fixed communication antenna, a ground-station antenna for space communications, a radio astronomy antenna, and the like. It is because an antenna pattern having high antenna gain and sharp directivity can be provided by setting the aperture diameter of the parabolic antenna to be larger than the wavelength. The dimension of a parabolic reflector for the use in the antenna for receiving satellite broadcasting is typically 17 times or more as large as the wavelength, for example. The parabolic antenna is typically used with the aperture diameter set to be larger than the wavelength. 
     The antenna according to the present invention employs the parabolic antenna form. Note that for using the antenna according to the present invention, the aperture diameter of the antenna according to the present invention is reduced to be equal to or smaller than an aperture diameter with which no null points are generated in an antenna pattern in a semi-sphere where radio waves are radiated in contrast to typical usage of the parabolic antenna. 
     That is, an antenna according to an aspect of the present invention includes: a primary radiator configured to radiate radio waves; and a parabolic reflector configured to reflect the radio waves radiated by the primary radiator and has an aperture diameter reduced to be equal to or smaller than an aperture diameter with which no null points are generated in an antenna pattern in a semi-sphere where the radio waves are reflected and radiated. 
     Any type of antenna element can be employed as the primary radiator. The primary radiator is favorably disposed in a region inside an aperture plane of the parabolic reflector, specifically, on the aperture plane or inside the aperture plane. 
     The region inside the aperture plane may be filled with a dielectric material. It should be noted that the dielectric material may have a cavity portion. Moreover, the primary radiator may be disposed in the dielectric material. 
     The antenna according to the aspect of the present invention has the following characteristics.
         The antenna beam becomes wide and radio waves are radiated in a wide area. The radio waves are also radiated downward from the antenna-mounting surface.   No null points and hollow are generated in a semi-sphere above the antenna-mounting surface.   No side lobes are generated in a semi-sphere above the antenna-mounting surface.       

     In addition, the antenna according to the aspect of the present invention has the following characteristics.
         As it is a reflector antenna, the antenna pattern is hardly affected by the shape of the mounting object on which the antenna is mounted and an antenna-mounting portion.   The antenna can be mounted without projecting from the surface of the mounting object by forming a hole having the same shape and dimension as the parabolic reflector in a surface of the mounting object or inside the mounting object. With this configuration, aerodynamic loading and heating on a flying object such as a rocket and an aircraft are sufficiently alleviated, for example. Owing to the small aperture diameter of the antenna according to the present invention, influence of forming the hole on the flying object is ignorably small. Moreover, in the case where the antenna according to the aspect of the present invention is mounted inside or outside an electronic apparatus having a wireless communication function, such as a personal computer (PC), or a building, the antenna can be mounted without projecting from the surface by forming a hole having the same shape and dimension as the parabolic reflector in a substrate of electronic components, an outer wall, interior wall, ceiling surface of the building, or inside the mounting object, for example. In addition, the footprint can also be reduced due to the reduced aperture diameter. The thickness and weight can be thus reduced in comparison with stick antennas and the like in the related art. Higher antenna gain can be obtained because the parabolic antenna is used as a basic configuration. The antenna can be made unremarkable by using the same color and patterns for a front surface of the antenna as the wall or ceiling of the building.       

     In accordance with the antenna according to the present invention, the antenna has the characteristics of uniformly stable pattern in a wide area, and the gain is increased in comparison with an antenna mounted on a flying object in the current state. 
     Moreover, in the case where the antenna according to the present invention is mounted on a flying object, the flying object mounts the antenna is not imposed on operational restrictions due to the pattern characteristics of the antenna. 
     Moreover, in the case where the antenna according to the aspect of the present invention is mounted on a flying object, aerodynamic loading and heating that occur on the antenna are sufficiently alleviated. 
     Furthermore, the antenna according to the aspect of the present invention is reduced in thickness and weight and becomes unremarkable in comparison with antennas in the related art. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a configuration of an antenna according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view taken along the line A-A of  FIG. 1 ; 
         FIG. 3  is a schematic perspective view of a dummy rocket body on which the antenna according to the embodiment is mounted; 
         FIG. 4  depicts an antenna pattern (right-handed polarization) obtained by the analysis as three dimensional whole spherical models, in the case where the antenna according to the present invention shown in  FIG. 3  is mounted on the dummy rocket body; 
         FIG. 5  is a diagram showing line-of-sight directions indicated as (1) to (5) of  FIG. 4  and  FIGS. 6 to 8 ; 
         FIG. 6  depicts an antenna pattern (right-handed polarization) obtained by the analysis as three dimensional whole spherical models, in the case where a blade antenna is mounted on the dummy rocket body as a comparative example; 
         FIG. 7  depicts an antenna pattern (right-handed polarization) obtained by the analysis as three dimensional whole spherical models, in the case where a patch antenna is mounted on the dummy rocket body as a comparative example; 
         FIG. 8  depicts an antenna pattern (right-handed polarization) obtained by the analysis as three dimensional whole spherical models, in the case where a monopole antenna is mounted on the dummy rocket body as a comparative example; and 
         FIG. 9  is a cross-sectional view of a substrate mounted on an electronic apparatus according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. 
       FIG. 1  is a perspective view showing a configuration of an antenna according to an embodiment of the present invention.  FIG. 2  is a cross-sectional view taken along the line A-A of  FIG. 1 . 
     As shown in  FIGS. 1 and 2 , an antenna  10  includes a primary radiator  11  and a parabolic reflector  12 . The parabolic reflector  12  is filled with a dielectric material  13 . A feed cable  14  is connected to the primary radiator  11 . 
     The primary radiator  11  is an antenna element configured to radiate radio waves. Any antenna element can be used as the primary radiator  11  as long as the antenna element has a predetermined impedance. An example using a cross-dipole antenna is shown in this embodiment. Alternatively, a dipole antenna, a horn antenna, or the like may be used. 
     The parabolic reflector  12  is formed like a paraboloid of revolution made of an electrically conductive material, having a diameter D of the aperture (aperture diameter) and a focal distance f. The primary radiator  11  is positioned at a focal point of the parabolic reflector  12 . Moreover, the parabolic reflector  12  has an aperture diameter D reduced to be equal to or smaller than an aperture diameter with which no null points are generated in an antenna pattern of a semi-sphere where the radio waves radiated by the primary radiator  11  are reflected by the parabolic reflector  12 . In this case, the aperture diameter D and the dimension of the primary radiator  11  can be reduced within a range enabling the antenna to function. The range enabling the antenna to function means a range enabling the primary radiator  11  to obtain a predetermined impedance. In other words, the range enabling the antenna to function means a range in which the voltage standing wave ratio (VSWR) of the primary radiator  11  is equal to or smaller than a value intended by a system using the antenna. Since no null points are generated by the antenna  10  according to this embodiment, side lobes are also not generated as a matter of course. That is, the antenna  10  according to this embodiment is capable of uniformly radiating radio waves in the semi-sphere where radio waves are radiated. 
     The dielectric material  13  is filled in a region from an aperture plane of the parabolic reflector  12  to an inner surface  123  of the parabolic reflector  12 . The primary radiator  11  is disposed in the dielectric material  13 . For example, the primary radiator  11  is disposed at the position of the aperture plane or at a position inside that position. The feed cable  14  is a cable for feeding power to the primary radiator  11 .  FIGS. 1 to 2  show an example in which the feed cable  14  is wired from a lowermost surface of the parabolic reflector  12  to the primary radiator  11 . Alternatively, how to wire the feed cable  14  is not limited as long as it is wired inside the aperture plane of the parabolic reflector  12 . 
     With this configuration, the dielectric material  13  has a function of retaining the primary radiator  11  and the feed cable  14  at predetermined positions. The dielectric material  13  also has a function of protecting the primary radiator  11  and the feed cable  14  from aerodynamic loading and aerodynamic heating that occur in flight of a rocket or the like and achieves a further reduction in size of the antenna  10  owing to the wavelength shortening effect of the dielectric material. It should be noted that the dielectric material  13  may have a cavity portion (not shown). With this configuration, a reduction in weight of the antenna  10  is achieved. 
       FIG. 3  shows a dummy rocket body used for analyzing an antenna pattern of the antenna  10  according to this embodiment in the case where the antenna  10  is mounted on a flying object. 
     The dummy rocket body was a metal cylinder having a diameter d and a height h. The antenna  10  according to this embodiment was mounted at the center of the cylindrical surface. 
     An analysis result in this case is shown in  FIG. 4 . 
     Here, the antenna  10  was set to have a frequency of 2.3 GHz. The primary radiator  11  and the parabolic reflector  12  were made of copper. The parabolic reflector  12  was filled with Teflon (registered trademark) as the dielectric material  13 . The antenna  10  was set to have D=88 mm and f=21 mm. Moreover, in  FIG. 3 , the dummy rocket body was made of copper. The dummy rocket body was set to have d=2500 mm and h=2000 mm. A hole  124  having the same shape and dimension as the parabolic reflector was formed at a position p=1000 mm of the dummy rocket body. The antenna  10  was mounted inside the dummy rocket body.  FIG. 4  shows an antenna pattern of right-handed polarization obtained by the analysis. 
     The figure depicts as three dimensional whole spherical models in which the antenna absolute gain is −30 dBi to 10 dBi, using gray scale gradation and radial lengths. 
     In  FIG. 4 , 
     (1) is a representation as viewed from +z direction (lower: +x direction, right: +y direction), 
     (2) is a representation as viewed from −y direction (right: +x direction, upper: +z direction), 
     (3) is a representation as viewed from +x direction (right: +y direction, upper: +z direction), 
     (4) is a representation as viewed from +y direction (left: +x direction, upper: +z direction), and 
     (5) is a representation as viewed from −z direction (upper: +x direction, right: +y direction) (see  FIG. 5 ). 
     It should be noted that the wavelength is approximately 130 mm, D is approximately 0.67 wavelength, and f is approximately 0.16 wavelength. As can be seen from  FIG. 4 , the antenna pattern in the state in which the antenna which is the antenna  10  according to this embodiment is mounted on the dummy rocket body is substantially isotropic in the semi-sphere of +x direction on which the antenna  10  is mounted. Moreover, as can also be seen from  FIG. 4 , there are no null points and side lobes in the antenna pattern and radiation is performed downwards (−x direction) from the mounting surface of the antenna  10 . 
       FIGS. 6 to 8  show comparative examples. 
       FIG. 6  depicts an antenna pattern (right-handed polarization) obtained by analysis as three dimensional whole spherical models in the state in which a blade antenna is mounted on the dummy rocket body.  FIG. 7  depicts an antenna pattern (right-handed polarization) obtained by analysis as three dimensional whole spherical models in the state in which a patch antenna is mounted on the dummy rocket body.  FIG. 8  depicts an antenna pattern (right-handed polarization) obtained by analysis as three dimensional whole spherical models in the state in which a monopole antenna is mounted on the dummy rocket body. The depiction way and the antenna absolute gain range of  FIGS. 6 to 8  are similar to those of  FIG. 4 . 
     Comparing the antenna patterns according to the comparative examples of  FIGS. 6 to 8  with the antenna pattern according to this embodiment shown in  FIG. 4 , the antenna pattern of the antenna  10  according to this embodiment is more isotropic in the semi-sphere of +x direction on which the antenna  10  is mounted in comparison with the antenna patterns according to the comparative examples. 
     As described above, it can be seen that the antenna  10  according to this embodiment has an ideal antenna pattern for the antenna to be mounted on a flying object. 
     In the antenna  10  according to this embodiment, the aperture diameter D of the parabolic reflector  12  is set to be equal to or smaller than an aperture diameter with which no null points are generated in the antenna pattern in the semi-sphere where reflected radio waves are radiated. The inventor of the present invention analyzed the antenna itself by varying the aperture diameter D. The antenna itself refers to the antenna  10  according to this embodiment disposed in a free space and does not refer to the antenna  10  embedded in the dummy rocket body as shown in  FIG. 4 . 
     Those results confirmed that in the case where the parabolic reflector  12  is filled with Teflon (registered trademark) as the dielectric material  13 , no hollows are generated in the antenna pattern in the semi-sphere on which the antenna  10  is mounted as long as the aperture diameter D is equal to or smaller than approximately 1.23 wavelength. 
     Moreover, those results also confirmed that in the case where the parabolic reflector  12  is not filled with the dielectric material, no hollows are generated in the antenna pattern in the semi-sphere on which the antenna  10  is mounted as long as the aperture diameter D is equal to or smaller than approximately 1.7 wavelength. 
     From those results, the inventor of the present invention can conclude that the aperture diameter only needs to be set to be equal to or smaller than approximately 1.7 wavelength in the present invention. 
     The present invention can be applied to a movable object such as an aircraft, a train, an automobile, and an underwater craft, an electronic apparatus such as a portable terminal and a personal computer (PC), and a building as well as the rocket. 
       FIG. 9  is a cross-sectional view of a substrate to be mounted on an electronic apparatus according to another embodiment of the present invention. 
     As shown in  FIG. 9 , a hole  92  having a paraboloid-of-revolution shape is formed in a substrate  91 . An electrically conductive thin film  96  is formed on a surface of the hole  92 . The hole  92  thus constitutes a reflector portion that functions as the parabolic reflector. 
     A region inside an aperture plane of the hole  92  is filled with a dielectric material  93 . 
     A primary radiator  94  is typically disposed on the aperture plane of the hole  92  and is retained by the dielectric material  93 . 
     The aperture diameter of the hole  92  is reduced to be equal to or smaller than an aperture diameter with which no null points are generated in an antenna pattern in a semi-sphere where radio waves radiated by the primary radiator  94  are reflected on the above-mentioned reflector. A coaxial cable  95  is retained by the dielectric material  93  and is connected to the primary radiator  94 . 
     In this embodiment, the hole  92  with the electrically conductive thin film  96  with the hole  92  formed thereon, the dielectric material  93 , and the primary radiator  94  constitutes an antenna  90 . 
     With an electronic apparatus on which such an antenna  90  is mounted, the antenna  90  can be mounted without projecting from the surface of the substrate  91 . In addition, the footprint can also be reduced due to the reduced aperture diameter. The thickness and weight can be thus reduced in comparison with stick antennas and the like in the related art. Higher antenna gain can be obtained because the parabolic antenna is used as a basic configuration. 
     The present invention is not limited to the above-mentioned embodiments and various modifications and applications can be made without departing from the gist of the technical idea of the present invention, and such modifications and implementations as applications fall within the technical scope of the present invention. 
     For example, in the case where the antenna according to the present invention is mounted outside or inside a building, the antenna can be made unremarkable by using the same color and patterns for a front surface of the antenna as the wall or ceiling of the building.