Patent Publication Number: US-10333214-B2

Title: Antenna radiating elements and sparse array antennas and method for producing an antenna radiating element

Description:
This application is a National Stage Entry of PCT/JP2015/059279 filed on Mar. 19, 2015, the contents of all of which are incorporated herein by reference, in their entirety. 
     TECHNICAL FIELD 
     The present invention relates to an antenna radiating elements, sparse array antennas and method for producing an antenna radiating element. 
     BACKGROUND ART 
     Compact sparse array antennas, operating in a wide frequency band, for radar sensing systems based on specific antenna radiating elements formed in a multilayer substrate and having considerably reduced dimensions due to application of an artificial medium (metamaterial) of a high relative permittivity. 
     As a way to improve the electrical performance of a radar system, a high-gain antenna can be used. Especially, such problem is crucial in remote sensing of an undersurface or hidden object due to its small signal reflectivity. Also, to provide radar imaging of such object, an antenna has to be operating in a wide frequency band. However, a typical wideband antenna (such as phase or sparse array antenna) used in a radar system has large dimensions, especially, at a low-gigahertz frequency range, that considerably limits areas of its applications. 
     Thus, it is important to develop such antenna systems which will be compact and, as a result, can be used in a lightweight radar system having wide application areas. 
     SUMMARY OF INVENTION 
     Technical Problem 
     The present invention enables to provide a technique of solving the above-described problem. 
     Solution to Problem 
     One aspect of the present invention provides an antenna radiating element disposed in a multilayer substrate comprising a signal via, a plurality of ground vias surrounding the signal via, a radiation pad connected to one end of the signal via, a feed pad connected to another end of the signal vias, an artificial medium disposed between the signal via and the ground vias, and wherein the multilayer substrate comprises a plurality of conductor layers isolated by a dielectric material. 
     Another aspect of the present invention provides a sparse array antenna comprising a plurality of antenna radiating elements disposed in a multilayer substrate, wherein the antenna radiating elements comprises a signal via, a plurality of ground vias surrounding the signal via, a radiation pad connected to one end of the signal via, a feed pad connected to another end of the signal vias, an artificial medium disposed between the signal via and the ground vias, and wherein the multilayer substrate comprises a plurality of conductor layers isolated by a dielectric material. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a compact array antennas are provided by development of small antenna radiating elements and a sparse arrangement of these elements. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a top view of a radiating element for a sparse array antenna in an exemplary embodiment of the present embodiment. 
         FIG. 1B  is a vertical cross-sectional view of the radiating element shown in  FIG. 1A  on the A-A section. 
         FIG. 1C  is a horizontal cross-sectional view of the radiating element shown in  FIG. 1B  on  1 L 3  conductor layer. 
         FIG. 1D  is a horizontal cross-sectional view of the radiating element shown in  FIG. 1B  on  1 L 5  conductor layer. 
         FIG. 1E  is a horizontal cross-sectional view of the radiating element shown in  FIG. 1B  on  1 L 7  conductor layer. 
         FIG. 1F  is a horizontal cross-sectional view of the radiating element shown in  FIG. 1B  on  1 L 2 ,  1 L 4  and  1 L 6  conductor layers. 
         FIG. 1G  is a bottom view of the radiating element shown in  FIG. 1B . 
         FIG. 1H  is the vertical cross-sectional view of the radiating element shown in  FIG. 1B  in which a structure between signal and ground vias is replaced by the corresponding homogeneous medium with the effective relative permittivity epsilon eff1 , epsilon eff2 , or epsilon eff3  as dependency on the conductor layer. 
         FIG. 1I  is the vertical cross-sectional view of the radiating element shown in  FIG. 1B . 
         FIG. 2A  is a top view of a radiating element for a sparse array antenna in another exemplary embodiment of the present embodiment. 
         FIG. 2B  is a vertical cross-sectional view of the radiating element shown in  FIG. 2A  on the A-A section. 
         FIG. 2C  is a horizontal cross-sectional view of the radiating element shown in  FIG. 2B  on  2 L 3  conductor layer. 
         FIG. 2D  is a horizontal cross-sectional view of the radiating element shown in  FIG. 2B  on  2 L 5  conductor layer. 
         FIG. 2E  is a horizontal cross-sectional view of the radiating element shown in  FIG. 2B  on  2 L 7  conductor layer. 
         FIG. 2F  is a horizontal cross-sectional view of the radiating element shown in  FIG. 2B  on  2 L 2 ,  2 L 4  and  2 L 6  conductor layers. 
         FIG. 2G  is a bottom view of the radiating element shown in  FIG. 2B . 
         FIG. 3A  is a top view of a radiating element for a sparse array antenna in another exemplary embodiment of the present embodiment. 
         FIG. 3B  is a vertical cross-sectional view of the radiating element shown in  FIG. 3A  on the A-A section. 
         FIG. 3C  is a horizontal cross-sectional view of the radiating element shown in  FIG. 3B  on  3 L 3  conductor layer. 
         FIG. 3D  is a horizontal cross-sectional view of the radiating element shown in  FIG. 3B  on  3 L 5  conductor layer. 
         FIG. 3E  is a horizontal cross-sectional view of the radiating element shown in  FIG. 3B  on  3 L 7  conductor layer. 
         FIG. 3F  is a horizontal cross-sectional view of the radiating element shown in  FIG. 3B  on  3 L 9  conductor layer. 
         FIG. 3G  is a horizontal cross-sectional view of the radiating element shown in  FIG. 3B  on  3 L 2 ,  3 L 4 ,  3 L 6 ,  3 L 8  conductor layers. 
         FIG. 3H  is a bottom view of the radiating element shown in  FIG. 3B . 
         FIG. 3I  is the vertical cross-sectional view of the radiating element shown in  FIG. 3B  in which a structure between signal and ground vias is replaced by the corresponding homogeneous medium with effective relative permittivity epsilon eff1 , epsilon eff2 , epsilon eff3 , or epsilon eff4  as dependency on the conductor layer. 
         FIG. 4A  is a top view of a radiating element for a sparse array antenna in another exemplary embodiment of the present embodiment. 
         FIG. 4B  is a vertical cross-sectional view of the radiating element shown in  FIG. 4A  on the A-A section. 
         FIG. 4C  is a horizontal cross-sectional view of the radiating element shown in  FIG. 4B  on  4 L 2  conductor layer. 
         FIG. 4D  is a horizontal cross-sectional view of the radiating element shown in  FIG. 4B  on  4 L 3  conductor layer. 
         FIG. 4E  is a horizontal cross-sectional view of the radiating element shown in  FIG. 4B  on  4 L 4  conductor layer. 
         FIG. 4F  is a horizontal cross-sectional view of the radiating element shown in  FIG. 4B  on  4 L 5  conductor layer. 
         FIG. 4G  is a horizontal cross-sectional view of the radiating element shown in  FIG. 4B  on  4 L 6  conductor layer. 
         FIG. 4H  is a horizontal cross-sectional view of the radiating element shown in  FIG. 4B  on  4 L 7  conductor layer. 
         FIG. 4I  is a bottom view of the radiating element shown in  FIG. 4B . 
         FIG. 5  is a graph showing simulated return loss of the radiating element shown in  FIGS. 1A-1I . 
         FIG. 6  is an arrangement of the radiation elements (nine) proposed to form a sparse array antenna. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail with reference to the drawings. It should be noted that the relative arrangement of the components, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. 
     First Embodiment 
     Hereinafter, several types of compact radiating elements for sparse array antennas disposed in multilayer substrates according to the present embodiment will be described in details with reference to attached drawings. But, it would be well understood that this description should not be viewed as narrowing the appended claims. 
     In  FIGS. 1A to 1I , an exemplary embodiment of an antenna radiating element  111  disposed in a multilayer substrate is shown. This multilayer substrate is provided with a plurality of conductor layers  1 L 1  to  1 L 8 . Eight conductor layers  1 L 1  to  1 L 8  are isolated by a dielectric material  109 . 
     Note this eight conductor layer substrate is only an example of multilayer substrates and a number of conductor layers, filling material and other substrate parameters can be different that depends on an application. 
     In present embodiment, said radiating element  111  comprises a signal via  101  and ground vias  102  surrounding said signal via  101  and connected to ground planes  108 . Such radiating element  111  has low leakage losses and, as a result, a minor coupling to neighboring radiating elements forming a sparse array antenna. Said radiating element  111  has compact dimensions due to a high effective relative permittivity of an artificial medium (metamaterial) formed between said signal via  101  and said ground vias  102 . This artificial medium is obtained by conductor plates  103  connected to said signal via  101  and conductor plates  108  connected to said ground vias  102 . Said conductor plates  103  are separated from said ground conductor plates  108  by isolating slits  105 , and said ground conductor plates  108  are isolated from said signal via  101  by clearance holes  104 . A radiation pad  106  is connected to one end of said signal via  101  and another end of said signal via  101  is connected to a feed pad  107 . Said radiation pad  106  is separated from the ground plate  108  disposed at the conductor layer  1 L 1  by an isolating slit  105 . Said feed pad  107  is separated from the ground plate  108  disposed at the conductor layer  1 L 8  by an isolated slit  110 . 
     Distinguishing point of said artificial medium is variability of its effective relative permittivity in the vertical direction, that is, perpendicularly to the surface of said multilayer substrate. In  FIG. 1H  a physical model of the artificial medium between signal via  101  and ground vias  102  is presented. This artificial medium can be characterized by the effective relative permittivity, epsilon eff1 , epsilon eff2 , or epsilon eff3  each of which is dependent on dimensions of conductor plates  103 , isolating slits  105  and clearance holes  104 . That is, epsilon eff1 , is function of d 1 , l 1 , r 1  (see  FIG. 1I ): epsilon eff1 =f(d 1 , l 1 , r 1 ). Also, epsilon eff2 =f(d 2 , l 2 , r 2 ) and epsilon eff3 =f(d 3 , l 3 , r 3 ). To provide a wideband operation of said radiating element  111  dimensions of conductor plates are chosen in such way that l 1  greater than l 2  greater than l 3  and, as a result, epsilon eff1  greater than epsilon eff2  greater than epsilon eff3 . This condition leads to widening the operation band of said radiating element  111 . In presented embodiment of said radiating element  111 , ground vias are arranged as a square. And said conductor plates  103  have also a square form. 
     In an aspect of the present embodiment, a compact array antennas are provided by development of small antenna radiating elements and a sparse arrangement of these elements. An antenna radiating element proposed is formed by a signal via surrounding by ground vias. Compactness of such element is provided by an artificial medium (metamaterial) of a high effective permittivity, which is disposed between a signal and ground vias forming the radiating element. Its wideband operation is achieved by development of such artificial medium which has variable effective permittivity in the vertical direction (perpendicular to the substrate surface). 
     An antenna radiating element proposed is formed by a signal via surrounding by ground vias. Compactness of such element is provided by an artificial medium (metamaterial) of a high effective permittivity, which is disposed between a signal and ground vias forming the radiating element. Its wideband operation is achieved by development of such artificial medium which has variable effective permittivity in the vertical direction (perpendicular to the substrate surface). 
     Second Embodiment 
     In  FIGS. 2A to 2G , another embodiment of the antenna radiating element disposed in a multilayer substrate is shown. The multilayer substrate is provided with a plurality of conductor layers  2 L 1  to  2 L 8 . Eight conductor layers  2 L 1  to  2 L 8  are isolated by a dielectric material  209 . In present another embodiment, an antenna radiating element  211  comprises a signal via  201  and ground vias  202  surrounding said signal via  201  and connected to ground planes  208 . In said radiating element  211 , an artificial medium of a high effective relative permittivity is formed between said signal via  201  and said ground vias  202 . This artificial medium is obtained by conductor plates  203  connected to said signal via  201  and conductor plates  208  connected to said ground vias  202 . Said conductor plates  203  are separated from said ground conductor plates  208  by isolating slits  205 , and said ground conductor plates  208  are isolated from said signal via  201  by clearance holes  204 . A radiation pad  206  is connected to one end of said signal via  201  and another end of said signal via  201  is connected to a feed pad  207 . Said radiation pad  206  is separated from the ground plate  208  disposed at the conductor layer  2 L 1  by an isolating slit  205 . Said feed pad  207  is separated from the ground plate  208  disposed at the conductor layer  2 L 8  by an isolated slit  210 . In this embodiment, a change of the effective relative permittivity of the artificial medium in the vertical direction is provided by a corrugation  212  of said conductor plates  203  disposed at conductor layers  2 L 3  and  2 L 5  as well as by the use of a smooth form of said conductor plate  203  arranged at the conductor layer  2 L 7 . The depths h 1  and h 2  of said corrugation  212  are different at conductor layers  2 L 3  and  2 L 5  to obtain the change of the effective relative permittivity in the vertical direction. 
     It should be noted that arrangement of ground vias, the form of conductor plates, and a number of conductor layers in a multilayer substrate can be different to provide a required performance of an antenna radiating element. 
     Third Embodiment 
     In  FIGS. 3A to 3I , another embodiment of the antenna radiating element disposed in a multilayer substrate is shown. The multilayer substrate is provided with a plurality of conductor layers  3 L 1  to  3 L 10 . Ten conductor layers  3 L 1  to  3 L 10  are isolated by a dielectric material  309 . In present another embodiment, an antenna radiating element  311  comprises a signal via  301  and ground vias  302  surrounding said signal via  301  and connected to ground planes  308 . In said radiating element  311  an artificial medium of a high effective relative permittivity is formed between said signal via  301  and said ground vias  302 . This artificial medium is obtained by conductor plates  303  connected to said signal via  301  and conductor plates  308  connected to said ground vias  302 . Said conductor plates  303  are separated from said ground conductor plates  308  by isolating slits  305 , and said ground conductor plates  308  are isolated from said signal via  301  by clearance holes  304 . A radiation pad  306  is connected to one end of said signal via  301  and another end of said signal via  301  is connected to a feed pad  307 . Said radiation pad  306  is separated from the ground plate  308  disposed at the conductor layer  3 L 1  by an isolating slit  305 . Said feed pad  307  is separated from the ground plate  308  disposed at the conductor layer  3 L 10  by an isolated slit  310 . 
     In present embodiment, a change of the effective relative permittivity of said artificial medium in the vertical direction is achieved by the variation of dimensions of said conductor plates  303 . Moreover, to provide a better matching between said feed pad  307  and said radiation pad  306 , dimensions of said conductor plates are chosen in such way that epsilon eff1  less than epsilon eff2  and epsilon eff2  greater than epsilon eff3  greater than epsilon eff3  (see  FIG. 3I ). In this embodiment of said radiating element  311 , ground vias are arranged as a circle. And said conductor plates  303  have also a circular form. 
     Fourth Embodiment 
     In  FIGS. 4A to 4I , another embodiment of the antenna radiating element disposed in a multilayer substrate is shown. The multilayer substrate is provided with a plurality of conductor layers  4 L 1  to  4 L 8 . Eight conductor layers  4 L 1  to  4 L 8  are isolated by a dielectric material  409 . In present another embodiment, an antenna radiating element  411  comprises a signal via  401  and ground vias  402  surrounding said signal via  401  and connected to ground planes  408 . In said radiating element  411  an artificial medium of a high effective relative permittivity is formed between said signal via  401  and said ground vias  402 . As a distinguishing point, this artificial medium is obtained only by conductor plates  403  connected to said signal via  401 . Said conductor plates  403  are separated from said ground conductor plates  408  by isolating slits  405 . A radiation pad  406  is connected to one end of said signal via  401  and another end of said signal via  401  is connected to a feed pad  407 . Said radiation pad  406  is separated from the ground plate  408  disposed at the conductor layer  4 L 1  by an isolating slit  405 . Said feed pad  407  is separated from the ground plate  408  disposed at the conductor layer  4 L 8  by an isolated slit  410 . In this embodiment of the antenna radiating element, ground vias are arranged as an ellipse. And said conductor plates  403  have also an elliptic form. 
     In  FIG. 5  simulated data of the return loss of an antenna radiating element for which its structure is shown in  FIGS. 1A-1I  are presented. Transverse dimensions (limited by ground vias) of this radiating element were 5 mm by 5 mm, 8 copper conductor layers were isolated by FR-4 (Flame Retardant-4) material and the thickness of the substrate was 2 mm. As follows from obtained simulation data, developed antenna radiating element has the bandwidth of about 6 GHz taken at the return loss level of −10 dB. Thus, antenna radiating element developed is compact and broadband one. 
     Based on presented antenna radiating element embodiments, different types of sparse array antennas can be designed. 
     In  FIG. 6 , an arrangement of an antenna radiating element proposed is presented for a sparse array antenna. This sparse array antenna comprises nine radiating elements which can provide a near-square form in a cross-section of the radiation beam. In this arrangement the antenna radiating element 1 is disposed in the center of an imaginary square, while antenna radiating elements 2, 3, 4, and 5 are placed in its vertexes. Such arrangement gives required form of the radiation beam from the sparse array antenna. Moreover, antenna radiating elements 6, 7, 8, and 9 serve to improve the gain of the sparse array antenna. It should be noted, because each antenna radiating element in presented sparse array antenna is highly isolated, then the sidelobe level can be low. 
     Other Embodiments 
     While the present invention has been described in relation to some exemplary embodiments, it is to be understood that these exemplary embodiments are for the purpose of description by example, and not of limitation. While it will be obvious to those skilled in the art upon reading the present specification that various changes and substitutions may be easily made by equal components and art, it is obvious that such changes and substitutions lie within the true scope and spirit of the presented invention as defined by the claims. 
     Other Exemplary Embodiments 
     Some or all of the above-described embodiments can also be described as in the following further exemplary embodiments, but are not limited to the followings. 
     Further Exemplary Embodiment 1 
     An antenna radiating element disposed in a multilayer substrate comprising: 
     a signal via; 
     a plurality of ground vias surrounding said signal via; 
     a radiation pad connected to one end of said signal via; 
     a feed pad connected to another end of said signal vias; and 
     an artificial medium disposed between said signal via and said ground vias; 
     wherein said multilayer substrate comprises a plurality of conductor layers isolated by a dielectric material. 
     Further Exemplary Embodiment 2 
     The antenna radiating element according to further exemplary embodiment 1 wherein said artificial medium is formed by conductor plates connected to said signal via and isolated from ground conductors by isolating slits and conductor plates connected to ground vias and isolated from said signal via by clearance holes. 
     Further Exemplary Embodiment 3 
     The antenna radiating element according to further exemplary embodiment 1 or 2 wherein said artificial medium has an effective relative permittivity variation in the direction perpendicular to the surface of said multilayer substrate. 
     Further Exemplary Embodiment 4 
     The antenna radiating element according to further exemplary embodiment 3 wherein said effective relative permittivity variation is obtained by a change of dimensions of said conductor plates connected to said signal via and disposed at different conductor layers. 
     Further Exemplary Embodiment 5 
     The antenna radiating element according to further exemplary embodiment 3 wherein said effective relative permittivity variation is obtained by a change of dimensions of said conductor plates connected to said signal via and said clearance holes disposed at different conductor layers. 
     Further Exemplary Embodiment 6 
     A sparse array antenna comprising a plurality of antenna radiating elements disposed in a multilayer substrate: 
     wherein said antenna radiating elements comprises: 
     a signal via; 
     a plurality of ground vias surrounding said signal via; 
     a radiation pad connected to one end of said signal via; 
     a feed pad connected to another end of said signal vias; and 
     an artificial medium disposed between said signal via and said ground vias; 
     wherein said multilayer substrate comprises a plurality of conductor layers isolated by a dielectric material. 
     Further Exemplary Embodiment 7 
     A method for producing an antenna radiating element disposed in a multilayer substrate comprising: 
     providing a signal via; 
     providing a plurality of ground vias surrounding said signal via; 
     connecting a radiation pad to one end of said signal via; 
     connecting a feed pad to another end of said signal vias; and 
     disposing an artificial medium between said signal via and said ground vias; 
     wherein said multilayer substrate comprises a plurality of conductor layers isolated by a dielectric material.