Patent Publication Number: US-11050158-B2

Title: Dielectric lens

Description:
This is a continuation of International Application No. PCT/JP2018/022725 filed on Jun. 14, 2018 which claims priority from Japanese Patent Application No. 2017-128878 filed on Jun. 30, 2017. The contents of these applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a dielectric lens for concentrating high-frequency radio waves, such as millimeter waves. 
     A known example of a dielectric lens is formed of a laminate of a plurality of discs made of a dielectric material (see, for example, Non Patent Document 1). In the dielectric lens described in Non Patent Document 1, each of the discs has multiple holes, and the density of the holes in its radially outer area is higher than that in its radially inner area. Thus, the disc has permittivity distribution with respect to the radial direction.
     Non Patent Document 1: S. Rondineau, M. Himidi, J. Sorieux, “A Sliced Spherical Luneburg Lens,” IEEE Antennas and Wireless Propagation Letters, vol. 2, 2003   

     BRIEF SUMMARY 
     For the dielectric lens described in Non Patent Document 1, it is necessary to have, for example, several hundreds to several thousands of holes in the discs in order to obtain an appropriate permittivity distribution. If these holes are formed by drilling, the processing time is long, and resulting low productivity is a problem. Additionally, the density of the holes in the vicinity of the outer regions of the discs is high in order to reduce the permittivity on the outer side. Thus, if the discs are formed by, for example, injection molding, the large number of holes positioned in the outer regions hinder the flow of resin, and resulting difficulty in molding is a problem. 
     The present disclosure provides dielectric lenses excellent in mass-productivity. 
     To solve the above-described problems, the present disclosure is a dielectric lens including a laminate of a plurality of disc members, each of the disc members having distribution of permittivity varying with respect to a radial direction thereof. The disc member includes a planar section in which a thickness dimension of a radially outer area is smaller than a thickness dimension of a radially inner area and a fin section which extends in a radial manner from a central portion of the planar section toward a radially outer side and in which a radially inner area and a radially outer area have the same thickness dimension. 
     The present disclosure can provide dielectric lenses excellent in mass-productivity. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a perspective view that illustrates a Luneburg lens antenna device according to a first embodiment. 
         FIG. 2  is a plan view that illustrates the Luneburg lens antenna device in  FIG. 1 . 
         FIG. 3  is a perspective view that illustrates a dielectric lens in  FIG. 1 . 
         FIG. 4  is a perspective view that illustrates an enlarged disc member in  FIG. 3 . 
         FIG. 5  is a plan view that illustrates the disc member in  FIG. 4 . 
         FIG. 6  is a cross-sectional view of the disc member viewed from a direction of the indication VI-VI with arrows in  FIG. 5 . 
         FIG. 7  is a cross-sectional view that illustrates an enlarged portion of the disc member in  FIG. 6 . 
         FIG. 8  is a diagram that illustrates a state where a beam is emitted from a patch antenna on a first side in a circumferential direction. 
         FIG. 9  is a diagram that illustrates a state where a beam is emitted from a patch antenna on a central side in the circumferential direction. 
         FIG. 10  is a diagram that illustrates a state where a beam is emitted from a patch antenna on a second side in the circumferential direction. 
         FIG. 11  is a radiating pattern diagram that illustrates a result of electromagnetic-field simulation of the Luneburg lens antenna device. 
         FIG. 12  is a plan view that illustrates a Luneburg lens antenna device according to a second embodiment. 
         FIG. 13  is a cross-sectional view that illustrates a disc member according to the second embodiment at substantially the same position as that in  FIG. 6 . 
         FIG. 14  is a cross-sectional view that illustrates an enlarged portion of the disc member in  FIG. 13 . 
         FIG. 15  is a cross-sectional view that illustrates a disc member according to a first variation at substantially the same position as that in  FIG. 6 . 
         FIG. 16  is a cross-sectional view that illustrates a disc member according to a second variation at substantially the same position as that in  FIG. 6 . 
         FIG. 17  is a perspective view that illustrates a dielectric lens according to a third variation. 
     
    
    
     DETAILED DESCRIPTION 
     Dielectric lenses according to embodiments of the present disclosure are described in detail below with reference to accompanying drawings by using a case where they are applied to a Luneburg lens antenna device as an example. 
       FIGS. 1 to 10  illustrate a Luneburg lens antenna device  1  (hereinafter referred to as antenna device  1 ) according to a first embodiment. The antenna device  1  includes a dielectric lens  2  and an array antenna  10 . 
     The dielectric lens  2  forms a cylindrical shape having distribution of permittivity varying with respect to the radial direction. As illustrated in  FIGS. 3 to 7 , the dielectric lens  2  is a laminate of a plurality of disc members  3  having the distribution of permittivity varying with respect to the radial direction. The disc members  3  are integrally formed from a resin material that allows injection molding and that has relative permittivity near two (e.g., polypropylene). The plurality of disc members  3  have the same outer diameter dimension and form a cylindrical laminate. 
     As illustrated in  FIG. 7 , each of the disc members  3  includes a planar section  4  and fin sections  9 . In the planar section  4 , a thickness dimension Tp 4  of a radially outer area  4 B is smaller than a thickness dimension Tp 1  of a radially inner area  4 A. The fin sections  9  extend in a radial manner from a central portion of the planar section  4  toward a radially outer side. In each of the fin sections  9 , a thickness dimension Tf 1  of a radially inner area  9 A and a thickness dimension Tf 2  of a radially outer area  9 B are the same. 
     Specifically, the planar section  4  includes four disc areas  5  to  8  having different thickness dimensions Tp 1  to Tp 4 , respectively. The disc areas  5  to  8  are concentrically arranged and positioned from the inner side toward the outer side in the radial direction, and their respective thickness dimensions Tp 1  to Tp 4  gradually decrease. 
     Thus, the first disc area  5  is the central area of the disc member  3 , is positioned on the innermost side, and has the thickness dimension Tp 1 , which is the largest among the thickness dimensions of the disc areas  5  to  8 . The second disc area  6  surrounds the first disc area  5  and is adjacent to the first disc area  5  on the radially outer side. The thickness dimension Tp 2  of the second disc area  6  is smaller than the thickness dimension Tp 1  of the first disc area  5  (Tp 2 &lt;Tp 1 ). The third disc area  7  surrounds the second disc area  6  and is adjacent to the second disc area  6  on the radially outer side. The thickness dimension Tp 3  of the third disc area  7  is smaller than the thickness dimension Tp 2  of the second disc area  6  (Tp 3 &lt;Tp 2 ). The fourth disc area  8  surrounds the third disc area  7  and is adjacent to the third disc area  7  on the radially outer side. The thickness dimension Tp 4  of the fourth disc area  8  is smaller than the thickness dimension Tp 3  of the third disc area  7  (Tp 4 &lt;Tp 3 ). The fourth disc area  8  is the outer edge area of the disc member  3 , is positioned on the outermost side, and has the thickness dimension Tp 4 , which is the smallest among the thickness dimensions of the disc areas  5  to  8 . 
     The back surfaces (bottom surfaces) of the disc areas  5  to  8  share a single flat surface. The front surfaces (top surfaces) of the disc areas  5  to  8  are different in height and are annular stepped surfaces. 
     The fin section  9  extends radially from the center of the planar section  4  (central axis C). The fin section  9  has a thin plate shape with a small width dimension and stands in the state where it protrudes from the front surfaces of the second to fourth disc areas  6  to  8 . The thickness dimension of the fin section  9  is fixed over the full length in the radial direction. Thus, a thickness dimension Tf 1  of the radially inner area  9 A and a thickness dimension Tf 2  of the radially outer area  9 B in the fin section  9  are the same value. In addition, the thickness dimensions Tf 1  and Tf 2  of the fin section  9  are the same as the thickness dimension Tp 1  of the radially inner area  4 A in the planar section  4 . 
     The dielectric lens  2  has a cylindrical shape formed by a laminate of the plurality of disc members  3 . Of the two neighboring disc members  3  in the axial direction, the projecting ends of the fin sections  9  in one of the disc members  3  are in contact with the bottom surface of the other disc member  3 . Thus, gaps are present in the radially outer area  4 B of the planar section  4  between the two disc members  3 . The dimension of each of the gaps with respect to the thickness dimension in the radially outer area  4 B is larger than that in the radially inner area  4 A. Accordingly, in the dielectric lens  2 , the dielectric density reduces and the effective permittivity decreases toward the outer region. Therefore, by appropriately adjusting the thickness dimensions and the sizes of the disc areas  5  to  8  in the radial direction, the dielectric lens  2  has permittivity distribution that approximates Equation 1 (distribution of effective relative permittivity ε r,eff (r)), where r is the radius dimension. Consequently, the dielectric lens  2  operates as a Luneburg lens (lens for radio waves). Thus, the dielectric lens  2  has a plurality of focal points at different positions in the circumferential direction on its outer surface side with respect to an electromagnetic wave of a predetermined frequency. 
                       ɛ     r   ⁢           ⁢   _   ⁢           ⁢   eff       ⁡     (   r   )       =     2   -       (     r   R     )     2               [     Equation   ⁢           ⁢   1     ]               
where r≤R
 
R: disc radius
 
     The array antenna  10  includes a plurality of (e.g.,  12 ) patch antennas  11 A to  11 C, feeding electrodes  13 A to  13 C, and a ground electrode  14 . 
     The 12 patch antennas  11 A to  11 C are attached to an outer surface  2 A of the dielectric lens  2 . These patch antennas  11 A to  11 C are arranged in a matrix (4 rows and 3 columns) at different positions in the circumferential direction and the axial direction. The patch antennas  11 A to  11 C may be made of, for example, a conductive film (metal film) having a rectangular shape expanding in the circumferential direction and the axial direction of the dielectric lens  2  and are connected to the feeding electrodes  13 A to  13 C. The patch antennas  11 A to  11 C function as antenna elements (radiating elements) by receiving high-frequency signals supplied from the feeding electrodes  13 A to  13 C. Thus, the patch antennas  11 A to  11 C can transmit or receive high-frequency signals of, for example, submillimeter waves or millimeter waves, depending on, for example, their lengths or dimensions. 
     The patch antennas  11 A, patch antennas  11 B, and patch antennas  11 C are disposed in different columns and can transmit or receive high-frequency signals independently of each other. The patch antennas  11 A to  11 C may be arranged, for example, side by side and spaced uniformly in the circumferential direction. 
     Thus, as illustrated in  FIGS. 8 to 10 , the patch antennas  11 A to  11 C form directional beams toward an opposite side beyond the central axis C of the dielectric lens  2 . The patch antennas  11 A to  11 C are arranged at different positions in the circumferential direction of the dielectric lens  2 . Thus, the radiating directions of the beams from the patch antennas  11 A to  11 C are different from each other. 
     As illustrated in  FIGS. 1 and 2 , an insulating layer  12  covering all the patch antennas  11 A to  11 C is disposed on the outer surface  2 A of the dielectric lens  2 . The insulating layer  12  is formed of a tubular covering member and may include, for example, a bonding layer for closely bonding the patch antennas  11 A to  11 C to the outer surface  2 A of the dielectric lens  2 . 
     Each of the feeding electrodes  13 A to  13 C is formed of a long narrow conductive film. The feeding electrodes  13 A to  13 C are disposed on the outer surface  2 A of the dielectric lens  2 , together with the patch antennas  11 A to  11 C, and are covered with the insulating layer  12 . The feeding electrode  13 A axially extends along the four patch antennas  11 A and are connected to the four patch antennas  11 A. The feeding electrode  13 B axially extends along the four patch antennas  11 B and are connected to the four patch antennas  11 B. The feeding electrode  13 C axially extends along the four patch antennas  11 C and are connected to the four patch antennas  11 C. The base ends of the feeding electrodes  13 A to  13 C are connected to a transmission and reception circuit (not illustrated). 
     The ground electrode  14  is disposed on the outer surface of the insulating layer  12 . The ground electrode  14  is formed of a rectangular conductive film (metal film) expanding in the circumferential direction and axial direction of the dielectric lens  2  and covers all the patch antennas  11 A to  11 C. The ground electrode  14  is connected to an external ground and is retained at a ground potential. Thus, the ground electrode  14  may be formed at an angular range of, for example, not larger than 90 degrees with respect to the central axis C of the dielectric lens  2  and functions as a reflector. 
     In the present embodiment, the case where the array antenna  10  uses the patch antennas  11 A to  11 C as antenna elements is described as an example. The antenna elements are not limited to the patch antennas. Another example may be a slot array antenna that uses slot antennas as antenna elements. 
     Next, actions of the antenna device  1  according to the present embodiment are described with reference to  FIGS. 8 to 10 . 
     When electricity is supplied from the feeding electrode  13 A toward the patch antennas  11 A, a current may flow through the patch antennas  11 A, for example, in the axial direction. Thus, the patch antennas  11 A emit high-frequency signals corresponding to the dimension in the axial direction toward the dielectric lens  2 . Consequently, as illustrated in  FIG. 8 , the antenna device  1  can emit high-frequency signals (beams) toward a direction Da, which is opposite to the patch antennas  11 A beyond the central axis C of the dielectric lens  2 . The antenna device  1  can also receive high-frequency signals coming from the direction Da by using the patch antennas  11 A. 
     Similarly, as illustrated in  FIG. 9 , when electricity is supplied from the feeding electrode  13 B toward the patch antennas  11 B, the antenna device  1  can transmit high-frequency signals toward a direction Db, which is opposite to the patch antennas  11 B beyond the central axis C of the dielectric lens  2 , and can also receive high-frequency signals from the direction Db. 
     As illustrated in  FIG. 10 , when electricity is supplied from the feeding electrode  13 C toward the patch antennas  11 C, the antenna device  1  can transmit high-frequency signals toward a direction Dc, which is opposite to the patch antennas  11 C beyond the central axis C of the dielectric lens  2 , and can also receive high-frequency signals from the direction Dc. 
     The above-described example is the case where a current is made to flow in the patch antennas  11 A to  11 C in the axial direction and emit polarized electromagnetic waves parallel with the thickness direction of the disc member  3 . The present disclosure is not limited to this example. The current may be made to flow in the patch antennas  11 A to  11 C in the circumferential direction, and the patch antennas  11 A to  11 C may emit polarized electromagnetic waves perpendicular to the thickness direction of the disc member  3  or emit circularly polarized waves. 
     Hence, in the first embodiment, the dielectric lens  2  is formed of the cylindrical laminate of the plurality of disc members  3 . Each of the disc members  3  includes the planar section  4 , in which the thickness dimension of the radially outer area  4 B is smaller than that of the radially inner area  4 A, and the fin sections  9 . The fin sections  9  extend in a radial manner from the central portion of the planar section  4  toward the radially outer side. In each of the fin sections  9 , the radially inner area  9 A and radially outer area  9 B have the same thickness dimension. 
     Of the two neighboring disc members  3  in the axial direction, the projecting ends of the fin sections  9  in one of the disc members  3  are in contact with the bottom surface of the other disc member  3 . Thus, gaps are present in the radially outer area  4 B of the planar section  4  between the two disc members  3 . The dimension of each of the gaps with respect to the thickness dimension in the radially outer area  4 B is larger than that in the radially inner area  4 A. Consequently, because the effective permittivity on the radially outer side is lower than that on the radially inner side in the dielectric lens  2 , in which the plurality of disc members  3  are laminated, the dielectric lens  2  operates as a Luneburg lens. 
       FIG. 11  illustrates a result of electromagnetic-field simulation calculated on the configuration with a lens whose radius is 15 mm in the 79 GHz band. As illustrated in  FIG. 11 , when the dielectric lens  2  is used, the waveform of the directional beam of the antenna device  1  is narrower and the antenna gain is improved by about 7 dB, in comparison with the case where the dielectric lens  2  is not used. 
     Because the disc member  3  is composed of the planar section  4 , which becomes thinner from the central portion toward the circumferential portion, and the fin sections  9 , whose thicknesses are fixed, the structure of the disc member  3  can be easily formed by injection molding. Thus, the disc members  3  can be easily mass-produced, and the mass-productivity of the dielectric lenses  2  can be enhanced. Moreover, the plurality of disc members  3  have the same outer diameter dimension and form a cylindrical laminate. Thus, the cylindrical Luneburg lens can be formed. 
     Next, a Luneburg lens antenna device  21  (hereinafter referred to as antenna device  21 ) according to a second embodiment of the present disclosure is illustrated in  FIG. 12 . The second embodiment has the characteristics of the fin sections, each including a plurality of depressions positioned between the center and outer edge in the radial direction and having small thickness dimensions and a plurality of projections positioned other than the depressions and having large thickness dimensions. In the description about the antenna device  21 , the same reference numerals are used in the same configuration as that in the antenna device  1  according to the first embodiment, and the description on that configuration is omitted. 
     The antenna device  21  according to the second embodiment is similar to the antenna device  1  according to the first embodiment. The antenna device  21  includes a dielectric lens  22  and the array antenna  10 . 
     The dielectric lens  22  according to the second embodiment is formed of a laminate of a plurality of disc members  23  having distribution of permittivity varying with respect to the radial direction, as in the case of the dielectric lens  2  according to the first embodiment. As illustrated in  FIGS. 13 and 14 , each of the disc members  23  is similar to the disc member  3  according to the first embodiment. Thus, the disc member  23  includes the planar section  4 , in which the thickness dimension of the radially outer area  4 B is smaller than the thickness dimension of the radially inner area  4 A, and fin sections  24  extending in a radial manner from the central portion of the planar section  4  toward the radial outer side. In each of the fin sections  24 , a thickness dimension Tf 21  of a radially inner area  24 A and a thickness dimension Tf 22  of a radially outer area  24 B are the same. 
     The fin section  24  includes a plurality of depressions  25  positioned between the center and outer edge in the radial direction and having smaller thickness dimensions (i.e., a length from the bottom surface of the disc member  23  to a surface of the depressions  25 ) and a plurality of projections  26  positioned other than the depressions  25  and having larger thickness dimensions (i.e., a length from the bottom surface of the disc member  23  to a top surface of the projections  26 ). In this respect, the fin section  24  according to the second embodiment differs from the fin section  9  according to the first embodiment, whose thickness dimension is fixed over the full length in the radial direction. The depressions  25  slope to the projections  26  and have tapered shapes in which their thickness dimensions continuously increase toward the projections  26 . Thus, the depressions  25  and projections  26  are smoothly connected to each other along the radial direction. 
     A length dimension L 1  of the depression  25  in the radial direction is set at a value smaller than ¼ of a wavelength of high-frequency signals emitted from the patch antennas  11 A to  11 C as a radio wave to be used. A length dimension L 2  of the projection  26  in the radial direction is set at a value smaller than ¼ of the wavelength of the radio wave to be used. The length dimensions L 1  of the plurality of depressions  25  are not necessarily the same and may be different values. Similarly, the length dimensions L 2  of the plurality of projections  26  are not necessarily the same and may be different values. 
     Hence, the second embodiment can also obtain substantially the same operational advantages as in the first embodiment. The fin section  24  includes the plurality of depressions  25 , which are positioned between the center and outer edge in the radial direction and have smaller thickness dimensions, and the plurality of projections  26 , which are positioned other than the depressions  25  and have larger thickness dimensions. This can lead to a reduction in the difference between the effective permittivity of the dielectric lens  22  to a polarized wave parallel with the thickness direction of the disc member  23  and the effective permittivity of the dielectric lens  22  to a polarized wave perpendicular to the thickness direction of the disc member  23 . Consequently, the effective permittivity can obtain desired distribution for not only the polarized wave parallel with the axis of the dielectric lens  22  but also the polarized wave perpendicular to the axis of the dielectric lens  22 . Thus, the effective permittivity is easily controllable for a polarized wave perpendicular to the cylinder axis of the dielectric lens  22 . Each of the length dimension L 1  of the depression  25  in the radial direction and the length dimension L 2  of the projection  26  in the radial direction is set at a value smaller than ¼ of the wavelength of a high-frequency signal. Thus, discontinuity between the depression  25  and projection  26  can be reduced with respect to the high-frequency signal. 
     In the above-described first embodiment, the disc member  3  includes the planar section  4 , whose thickness dimension decreases in stages (in steps) with respect to the radial direction. The present disclosure is not limited to this configuration. As in a first variation illustrated in  FIG. 15 , a disc member  31  may include a planar section  32 , whose thickness dimension continuously decreases with respect to the radial direction. This configuration is also applicable to the second embodiment. 
     As in a second variation illustrated in  FIG. 16 , a disc member  41  may have a through hole  42  at the center of the planar section  4 . In this case, in the state where a plurality of disc members  41  are laminated, a core member  43  made of the same dielectric material as that of the planar section  4  is placed in the through holes  42 . In this case, the centers of the plurality of disc members  41  can be easily aligned by the use of the core member  43 . This configuration is also applicable to the second embodiment. 
     Moreover, in the above-described first embodiment, the dielectric lens  2  has a cylindrical shape formed by the laminate of the disc members  3  having the same outer diameter dimension. The present disclosure is not limited to this example. As in a third variation illustrated in  FIG. 17 , for example, a plurality of disc members  52  similar to the disc members  3  may be formed with different outer diameter dimensions. The laminate of the plurality of disc members  52  with different outer diameter dimensions can form a spherical dielectric lens  51 . This configuration is also applicable to the second embodiment. 
     The above-described embodiments are illustrated as examples, and the configurations illustrated in different embodiments may be replaced in part or combined. 
     Next, the disclosure included in the above-described embodiments is described. The present disclosure is a dielectric lens formed of a laminate of a plurality of disc members having distribution of permittivity varying with respect to the radial direction. Each of the disc members includes a planar section in which the thickness dimension of a radially outer area is smaller than that of a radially inner area and fin sections extending in a radial manner from the central portion of the planar section toward the radially outer side. In each of the fin sections, the radially inner area and radially outer area have the same thickness dimension. 
     In this configuration, when the plurality of disc members are laminated, the fin sections can form gaps in the radially outer area. The dimension of each of the gaps with respect to the thickness direction in the radially outer area is larger than that in the radially inner area. Consequently, because the effective permittivity on the radially outer side is lower than that on the radially inner side, the dielectric lens formed of the laminate of the plurality of disc members operates as a Luneburg lens. The disc members do not need to have many holes, and they can be easily formed by injection molding. Thus, the mass-productivity of the dielectric lenses can be enhanced. 
     In the present disclosure, each of the fin sections include a plurality of depressions positioned between the center and outer edge in the radial direction and having smaller thickness dimensions and a plurality of projections positioned other than the depressions and having larger thickness dimensions. The length dimension of each of the depressions in the radial direction is set at a value smaller than ¼ of the wavelength of a radio wave to be used, and the length dimension of each of the projections in the radial direction is set at a value smaller than ¼ of the wavelength of the radio wave to be used. 
     In the present disclosure, the fin section includes the plurality of depressions, where are positioned between the center and outer edge in the radial direction and have smaller thickness dimensions, and the plurality of projections, which are positioned other than the depressions and have larger thickness dimensions. This can lead to a reduction in the difference between the effective permittivity of the dielectric lens to a polarized wave parallel with the thickness direction of the disc member and the effective permittivity of the dielectric lens to a polarized wave perpendicular to the thickness direction of the disc member. Consequently, the effective permittivity can obtain desired distribution for not only the polarized wave parallel with the thickness direction of the disc member but also the polarized wave perpendicular to the thickness direction of the disc member. Each of the length dimension of the depression in the radial direction and the length dimension of the projection in the radial direction is set at a value smaller than ¼ of the wavelength of the radio wave to be used. Thus, discontinuity between the depression and projection can be reduced with respect to the radio wave to be used. 
     In the present disclosure, the plurality of disc members have the same outer diameter dimension and form the cylindrical laminate. Thus, the cylindrical Luneburg lens can be formed. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  21  Luneburg lens antenna device (antenna device) 
               2 ,  22 ,  51  dielectric lens 
               3 ,  23 ,  31 ,  41 ,  52  disc member 
               4 ,  32  planar section 
               9 ,  24  fin section 
               25  depression 
               26  projection 
               10  array antenna