Patent Publication Number: US-11387571-B2

Title: Slot antenna apparatus, communication system, and method for adjusting angle of radio waves emitted from slot antenna apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2020-040153 filed on Mar. 9, 2020, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiment discussed herein is related to a slot antenna apparatus, a communication system, and a method for adjusting angle of radio waves emitted from slot antenna apparatus. 
     BACKGROUND 
     Conventionally, there is a dielectric waveguide slot array antenna that includes a dielectric waveguide, a printed circuit board, and a metallic plate. Such dielectric waveguide has a plurality of first slots that emit electromagnetic waves at designated intervals to a surface. The printed circuit board has first through-holes located at positions opposite to the first slots respectively. The metallic plate has first penetrating holes located at positions opposite to the first slots respectively. The dielectric waveguide has a plurality of second slots formed close to the plurality of respective first slots. The printed circuit board has second through-holes located at positions opposite to the second slots respectively. The metallic plate has second penetrating holes located at positions opposite to the second slots respectively (for example, see Patent Document 1). 
     There is a corrugated leaky waveguide that includes a hollow conductor and through-holes formed on the hollow conductor. The through-holes are provided for leaking radio waves and are disposed at intervals in a longitudinal direction. Recesses and projections are provided in the longitudinal direction on the surface of the conductor. Either or both of the intervals of the through-holes and pitches of the recesses and the projections are irregular (for example, see Patent Document 2). 
     There is a slot array antenna in which a slot plate and a dielectric plate are integrated so that the dielectric plate has a tilt angle. A tilt angle θ of a radiation-directing main beam of the slot array antenna is corrected by the tilt angle of the dielectric plate (for example, Patent Document 3). 
     However, none of the documents describes that a slot antenna apparatus including a waveguide having a plurality of slots may be used to variably adjust an angle of radio waves emitted from each of the slots. 
     RELATED-ART DOCUMENTS 
     Patent Documents 
     [Patent Document 1] Japanese Laid-open Patent Publication No. 2005-217864 
     [Patent Document 2] Japanese Laid-open Patent Publication No. 2000-068733 
     [Patent Document 3] Japanese National Publication of International Patent Application No. 2004-147169 
     SUMMARY 
     According to an aspect of the present application, there is provided a slot antenna apparatus that, includes a waveguide including a sidewall and having an extending direction, a slot provided on the sidewall; and a dielectric member that is attached to the waveguide and is slidable in the extending direction with respect to the slot, the dielectric member including a first section and a second section, the first section covering the slot at a first slide position, the second section covering the slot at a second slide position next to the first slide position, the first section and the second section having different relative permittivities or different thicknesses with each other. 
     The object and advantages of the disclosure will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of a configuration of a communication system; 
         FIG. 2  is a diagram illustrating an example of an office room in which the communication system is installed; 
         FIG. 3  is a diagram illustrating a configuration of a waveguide; 
         FIG. 4  is a diagram illustrating a slot antenna apparatus according to an embodiment; 
         FIG. 5  is a diagram illustrating an exploded view of the slot antenna apparatus according to the embodiment; 
         FIG. 6  is a diagram illustrating the slot antenna apparatus according to the embodiment as viewed from two directions; 
         FIG. 7  is a diagram illustrating a slot array antenna; 
         FIG. 8  is a diagram illustrating an operation of the slot antenna apparatus according to the embodiment; 
         FIG. 9  is a diagram illustrating an operation of the slot antenna apparatus according to the embodiment; 
         FIG. 10  is a diagram illustrating an operation of the slot antenna apparatus in a case where the slot antenna apparatus includes four slot array antennas; 
         FIG. 11  is a diagram illustrating a slot antenna apparatus according to a first variation of the embodiment; 
         FIG. 12  is a diagram illustrating a slot antenna apparatus according to a second variation of the embodiment; 
         FIG. 13  is a diagram illustrating an operation of a slot antenna apparatus according to the second variation of the embodiment; 
         FIG. 14  is a diagram illustrating an operation of a slot antenna apparatus according to the second variation of the embodiment; and 
         FIG. 15  is a diagram illustrating a slot antenna apparatus according to a third variation of the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Hereinafter, embodiments to which a slot antenna apparatus, a communication system, and a method for adjusting angle of radio waves emitted from slot antenna apparatus are applied will be described. 
     EMBODIMENT 
       FIG. 1  is a block diagram illustrating an example of a configuration of a communication system  300 . The communication system  300  includes a slot antenna apparatus  100  and an evolved Node B (eNodeB)  200 . The communication system  300  is a system that adopts a cellular system and performs wireless communications. 
     The eNodeB  200  is an example of a base station which includes a base band unit (BBU)  210 , remote radio heads (RRHs)  220 A and  220 B, and coaxial waveguide converters  230 . The eNodeB  200  is connected to a core network  500  via optical fibers. The core network  500  is a high capacity communication line and is an example of a trunk network or backbone. 
     The BBU  210  is an apparatus that performs a baseband processing. The BBU  210  is provided in the eNodeB  200  and is connected to the RRHs  220 A and  220 B via the optical fibers. 
     The RRHs  220 A and  220 B are radio apparatuses. The RRHs  220 A and  220 B are provided in one eNodeB  200 , and two RRHs  220 A and  220 B are as illustrated in  FIG. 1 . The RRHs  220 A and  220 B are connected to the waveguides  110 A and  110 B of the slot antenna apparatus  100 , respectively, via the coaxial waveguide converters  230 . Each of the waveguides  110 A and  110 B is an example of a waveguide and is made of metal. 
     In a case where the RRHs  220 A and  220 B are not specifically distinguished, the RRH of the present embodiment is referred to as an RRH  220 . In a case where the waveguides  110 A and  110 B are not specifically distinguished, the waveguide of the present embodiment is referred to as a waveguide  110 . 
     The coaxial waveguide converters  230  connect coaxial cables of the RRHs  220 A and  220 B and the waveguides  110 A and  110 B of the slot antenna apparatus  100 , respectively. The coaxial waveguide converters  230  are transducers that can perform bi-directional power conversion between the coaxial cables and the waveguides  110 A and  110 B. 
     The slot antenna apparatus  100  includes the waveguides  110 A and  110 B. The waveguide  110 A includes slots  111  ( 111 A to  111 C). Although slots of the waveguide  110 B are omitted in  FIG. 1 , the waveguide  110 B includes the slots similar to the slots  111  ( 111 A to  111 C). Although the waveguide  110 A includes the three slots  111  ( 111 A to  111 C), for example, the number of the slots  111  is not limited to three. 
     The slot  111 A is closest to the RRH  220 A and the slot  111 C is farthest away from the RRH  220 A. Hereinafter, in a case where the slots  111 A to  111 C are not specifically distinguished, the slot of the present embodiment is referred to as a slot ill. 
     The waveguide  110  is connected to the RRH  220  via the coaxial waveguide converter  230 . The slots  111 A to  111 C emit (output) radio waves propagating inside the waveguide  110  to an exterior of the waveguide  110  and provide communication areas in which a cellular equipment can perform the wireless communications. 
     A user equipment (UE)  10  receives the radio waves emitted from slots  111 A to  111 C in the communication areas and can perform bi-directional data communication with the core network  500  via the waveguide  110  and the eNodeB  200 . 
     The slot antenna apparatus  100  has a configuration which enables the user to variably set or adjust the amount of the radio waves emitted from each of the slots  111 A to  111 C. Details of the slot antenna apparatus  100  will be described below with reference to  FIG. 3 . The amount of the radio waves corresponds to an intensity of the radio waves and defines sizes of the communication areas. 
     The UE  10  is, for example, a personal computer (PC), a tablet computer, a smartphone, and other devices that can perform the wireless communications in the cellular system. 
     Although an embodiment in which the communication system  300  adopts the cellular system will be described, for example, the communication system  300  may adopt a wireless local area network (LAN) system. In a case where the communication system  300  adopts the wireless LAN system, the communication system  300  includes an access point (AP) instead of the eNodeB  200  and connects to the Internet instead of the core network  500  so that a terminal similar to the UE  10  can perform data communication. The terminal used in the wireless LAN system may be referred to as a station. 
       FIG. 2  is a diagram illustrating an example of an office room  500  in which the communication system  300  is installed.  FIG. 2  illustrates a shelf  5 , desks  6 , chairs  7 , partitions  8 , and a large monitor  9  or the like that are arranged on a floor  500 A of the office room  500 . PCs  10 A are arranged on the desks  6 . Employees are working in the office room  500 . 
     The BBU  210  is disposed in the shelf  5  as an example, the RRH  220 A is installed in one of the desks  6 , and the RRH  220 B is disposed in a rear side of a ceiling  500 B. In  FIG. 2 , the optical fibers connecting the BBU  210  and the RRHs  220 A and  220 B and the coaxial waveguide converters  230  (see  FIG. 1 ) are omitted. The RRH  220 A may be installed under the floor  500 A. 
     The waveguide  110 A connected to the RRH  220 A is installed along side and upper edges of the partitions  8  provided between the opposite desks  6  and has the slots  111 A to  111 C. The slots  111 A to  111 C emit the radio waves toward the desks  6  and provide communication areas  50  ( 50 A to  50 C), respectively. PCs  10 A are disposed on the desks  6  and can perform the wireless communications through the radio waves emitted from the slots  111 A to  111 C. The waveguide  110 A may be embedded in upper surfaces of the desks  6 . In this case, the slots  111 A to  111 C may be exposed on the upper surfaces of the desks  6 . 
     The slots  111 A to  111 C may be assigned for three employees working at desks  6 , for example. Thus, pitches among the slots  111 A to  111 C correspond to pitches between workspaces of the employees at the desks  6 , for example. 
     The pitches of the slots  111 A to  111 C as described above are largely different from conventional pitches between slots of a typical slot antenna. The conventional pitches are about a half wavelength to about one wavelength at a communication frequency. The pitches of the slots  111 A to  111 C are preferably greater than or equal to ten wavelengths at the communication frequency. In a case where the slots  111 A to  111 C are arranged at pitches that are greater than or equal to ten wavelengths, the radio waves emitted from the adjacent slots  111 A to  111 C are unlikely to interfere with each other. It becomes possible to obtain the communication areas  50 A to  50 C that are independent of each other. 
     The waveguide  110 B connected to the RRH  220 B is disposed in the rear side of a ceiling  500 B, and the slot  111 A of the waveguide  110 B is exposed on the ceiling  500 B. The slot  111 A of the waveguide  110 B emits the radio waves to the large monitor  9  and provides the communication area  50 . The large monitor  9  is disposed in the communication area  50  provided by the radio waves emitted from the slot  111 A of the waveguide  110 B and can perform the wireless communication. The large monitor  9  displays data received in the communication area  50  provided by the slot  111 A of the waveguide  110 B through the wireless communication. 
     As described above, the communication system  300  includes the waveguide  110 . The waveguide  110  has an advantage of low transmission losses, particularly in a case of transmitting data at a high frequency band (e.g., millimeter-wave band). This is an advantage of the waveguide  110  over coaxial cables which have very high transmission losses at the high frequency band, such as the millimeter-wave band. Herein, the millimeter-wave band is, for example, a frequency band ranging from about 30 GHz to about 300 GHz. An example of a cellular communication using the millimeter-wave band is a fifth generation (5G). 5G uses a 28 GHz band and a 39 GHz band. A WiFi system uses 60 GHz band provided by IEEE 802. Had (WiGig). It should be noted that the communication system  300  is not limited to communication in the millimeter-wave band(s), but may be used for communication in bands other than the millimeter-wave band(s). 
       FIG. 3  is a diagram illustrating a configuration of the waveguide  110 . Hereinafter, a common XYZ orthogonal coordinates system will be used to explain the configuration. The waveguide  110  is a rectangular waveguide and has the slots  111 A to  111 C arranged along an extending direction (the X direction) of the waveguide  110 . A cross-sectional shape obtained in the YZ plane of the waveguide  110  is a rectangular shape having short sides extending in the Y direction and long sides extending in the Z direction. The cross-sectional shape in the YZ plane is a cross-sectional shape obtained in a plane perpendicular to the extending direction (the X direction). Accordingly,  FIG. 3  illustrates a sidewall including the long sides of the waveguide  110 . 
     The slots  111 A to  111 C are rectangular openings formed in the sidewall including the long sides. The slots  111 A to  111 C have longitudinal directions extending along the extending direction (the X direction) of the waveguide  110 . The extending direction (the X direction) of the waveguide  110  is the longitudinal direction of the waveguide  110 . However, opening shapes of the slots  111 A to  111 C are not limited to rectangular shapes, the slots  111 A to  111 C may have rounded long sides and/or rounded short sides, for example. As an example, the waveguide  110  has the three slots  111  ( 111 A to  111 C), but the number of slots  111  is not limited to three. 
     The length of the slot  111  in the longitudinal direction (the X direction) of the slot ill is about a half of the wavelength (about one half of the wavelength) at the communication frequency of the slot antenna apparatus  100 . The width of the slot  111  in a short side direction (the Z direction) of the slot  111  may be set to an appropriate width based on emission characteristics or the like of the slot  111 . 
     The waveguide  110  has a length in the extending direction (the X direction) and a width in the  2  direction. The slot  111 A is provided at a position which is slightly offset to an edge located in the −Z direction side from a center of the width of the waveguide  110 . The slots  111 B and  111 C are provided at positions which are offset to the −Z direction from the center of the width of the waveguide  110 . The offset of the slot  111 B from the center is greater than the offset of the slot  111 A from the center, and the offset of the slot  111 C from the center is greater than the offset of the slot  111 B from the center. The positions of the slots  111 A to  111 C are offset to the −Z direction with respect to the center of the width of the waveguide  110 . 
       FIG. 4  is a diagram illustrating a slot antenna apparatus  400  according to the embodiment.  FIG. 5  is a diagram illustrating an exploded view of the slot antenna apparatus  400 .  FIG. 6  is a diagram illustrating the slot antenna apparatus  400  as viewed from two directions. Hereinafter, an XYZ orthogonal coordinate system will be used to explain the slot antenna apparatus  400 . 
     The slot antenna apparatus  400  includes a waveguide  410  and a dielectric member  420 . The slot antenna apparatus  400  may be used in the communication system  300  (see  FIG. 1 ) instead of the slot antenna apparatus  100  (see  FIG. 1 ). 
     The waveguide  410 , similar to the waveguide  110 , has an advantage of low transmission losses, particularly in a case of transmitting data at a high frequency band (e.g., millimeter-wave band). This is an advantage of the waveguide  410  over coaxial cables which have very high transmission losses at the high frequency band, such as the millimeter-wave band. 
     The waveguide  410  is a rectangular waveguide and has slots  1  to  4  arranged along an extending direction (the X direction) of the waveguide  410 . The slots  1  to  4  constitute a slot array antenna  411 . A cross-sectional shape obtained in the YZ plane of the waveguide  410  is a rectangular shape having short sides extending in the Y direction and long sides extending in the Z direction. 
     Here, the slot array antenna  411  will be described with reference to  FIG. 7 .  FIG. 7  is a diagram illustrating an example of the slot array antenna  411 . 
     The slot array antenna  411  includes the slots  1  to  4 . Each of the slots  1  to  4  may be the same as the slot ill (see  FIG. 3 ). Each of lengths of the slots  1  to  4  in the longitudinal direction (the X direction) is about a half of a guide wavelength λg (about one half of the guide wavelength) at the communication frequency of the slot antenna apparatus  400 . Each of widths of the slots  1  to  4  in the short side direction (the Z direction) of the slots  1  to  4  may be set to an appropriate width based on emission characteristics or the like of the slots  1  to  4 . The guide wavelength is a wavelength of the radio wave propagating inside the waveguide  410 . 
     Further, distance D 13  between the centers in the X direction of the slots  1  and  3  and distance D 24  between the centers in the X direction of the slots  2  and  4  may be more than or equal to a half wavelength of a wavelength λ in a free space at the communication frequency of the slot antenna apparatus  400 . A length l, represented by a small l, in  FIG. 7  is a length of the single slot array antenna  411  in the X direction. In other words, the length l represents a length of a section in which the single slot array antenna  411  is provided. In the case where a plurality of the slot array antennas  411  are provided, the slot array antenna  411 , not illustrated in  FIG. 7 , located next to the slot array antenna  411  as illustrated in  FIG. 7  is provided in a section, that has the length l, next to the section having the length l as illustrated in  FIG. 7 . The length l is equal to 2λ, i.e., 1=2λ. 
     Here, for example, the radio waves propagate in the waveguide  410  from the −X direction side to the +X direction side, as indicated by arrow A. In order to equalize radiation intensities of the radio waves emitted from the slots  1  to  4 , coupling of the waveguide  410  and the slot  1  located on the most upstream side may be minimized, and coupling of the waveguide  410  and the slot  4  on the most downstream side may be maximized. 
     With respect to a central axis C passing through the center of the width in the Z direction of the waveguide  410 , the slots  1  and  3  are located on the +Z direction side, and the slots  2  and  4  are located on the −Z direction side. Regarding the slot  1 , a distance d 1  is a distance between the center in the Z direction of the slot  1  and a nearer edge of the waveguide  410  in the Z direction from the center in the Z direction of the slot  1 . Similarly, regarding the slot  2 , a distance d 2  is a distance between the center in the Z direction of the slot  2  and a nearer edge of the waveguide  410  in the Z direction from the center in the Z direction of the slot  2 . Regarding the slot  3 , a distance d 3  is a distance between the center in the Z direction of the sloe  3  and a nearer edge of the waveguide  410  in the Z direction from the center in the Z direction of the slot  3 . Regarding the slot  4 , a distance d 4  is a distance between the center in the Z direction of the slot  4  and a nearer edge of the waveguide  410  in the Z direction from the center in the Z direction of the slot  4 . 
     The distances d 1  and d 3  are distances from a +Z direction-side-edge of the waveguide  410  to the centers of the slots  1  and  3  in the Z direction, respectively. The distances d 2  and d 4  are distances from a −Z direction-side-edge of the waveguide  410  to the centers of the slots  2  and  4  in the Z direction, respectively. In the waveguide  410 , the couplings of the slots  1  to  4  and the waveguide  410  become stronger as locations of the slots  1  to  4  are offset from the center of the width in the Z direction of the waveguide  410 . Therefore, d 1 &gt;d 2 &gt;d 3 &gt;d 4  is established. 
     Phases of the radio waves emitted from the slots  1  to  4  are shifted by λ/2 each in this order. The radio waves emitted from the four slots  1  to  4  are emitted as a single beam of the radio waves. Although the slot array antenna  411  has the four slots  1  to  4  in this embodiment, the number of the slots of the slot array antenna  413  may be any number as long as the number is more than or equal to two. 
     Next, the waveguide  410  and the dielectric member  420  will be described with reference to  FIGS. 4 to 6 . 
     The waveguide  410  has guide rails  415  located on both side surfaces parallel to the XY plane. The guide rails  415  are provided on the both side surfaces located on the +Z direction side and the −Z direction side. The guide rails  415  are rails that have rectangular-shaped cross-sections parallel to the YZ plane and extend in the X direction. For example, the guide rails  415  extend over a section having a length of five l in the X direction, and the centers of the guide rails  415  in the X direction correspond to the center in the X direction of the waveguide  410  (see  FIG. 6 ). The guide rails  415  are, for example, made of metal or an insulator. 
     Positions of the guide rails  415  in the Y direction on the side surfaces of the waveguide  410  may be any position, but in  FIGS. 4-6  the guide rails  415  are offset to the +Y direction side with respect to the center of width in the Y direction of the waveguide  410 . The dielectric member  420  can slide in the X direction more stably by providing the guide rails  415  on the +Y direction side with respect to the center of the width in the Y direction of the waveguide  410 . The positions of the guide rails  415  in the Y direction are constant between ends in the −X direction and ends in the +X direction. 
     The dielectric member  420  includes a base  421 , sloped portions  422 , a recessed portion  423 , and grooves  424 . The dielectric member  420  is a member that is made of dielectric material and has a uniform relative permittivity as a whole. The relative permittivity of the dielectric member  420  is greater than  1 , and more specifically greater than the relative permittivity of the air. 
     The base  421  is an example of a first section of the dielectric member  420 . The base  421  is the thinnest portion in the Y direction and is constant in thickness. Sloped portions  422  are provided on the +X direction side and the −X direction side of the base  421 . Surfaces of the sloped portions  422  facing toward the −Y direction side are sloped, i.e., inclined. 
     Each of the sloped portions  422  is an example of a second section of the dielectric member  420 . For example, thicknesses of the sloped portions  422  in the Y direction increase linearly in accordance with increased distance from the base  421  in the X direction. Each of the lengths of the base  421  and of the two sloped portions  422  in the X direction is equal to the length l in the X direction of the slot array antenna  411 . 
     The recessed portion  423  is formed to recess from the +Y direction side to the −Y direction side of the dielectric member  420  and extends from an end located on the −X direction side of the dielectric member  420  to an end located on the +X direction side of the dielectric member  420 . Inside dimensions of the recessed portion  423  are matched with outside dimensions of the waveguide  410 . 
     The two grooves  424  are provided on an inner wall located on the +Z direction side and an inner wall located on the −Z direction side of the recessed portion  423 , respectively. The two grooves  424  have shapes that are matched with the two guide rails  415 , respectively, and extend from the end located on the −X direction side of the dielectric member  420  to the end located on the +X direction side of the dielectric member  420 . 
     The dielectric member  420  is provided on the waveguide  410  in a state where the dielectric member  420  spans the waveguide  410  and where the grooves  424  are fitted onto the guide rails  415 . Accordingly, the dielectric member  420  is slidable in the X direction with respect to the waveguide  410 . 
     Here, a method for variably adjusting an angle of a beam emitted from the slot antenna apparatus  400  will be described with reference to  FIGS. 8 and 9  in addition to  FIG. 6 .  FIGS. 8 and 9  are diagrams illustrating operations of the slot antenna apparatus  400 . The radio waves emitted from the slots  1  to  4  are synthesized and form the beam. The angle of the beam is an emission angle of the beam. The emission angle corresponds to an emitting direction as illustrated in  FIGS. 6, 8, and 9 . 
     In a case where the base  421  covers the slot array antenna  411  as illustrated in  FIG. 6 , four portions, of the dielectric members  420 , covering the slots  1  to  4 , respectively, have same thicknesses. Accordingly, the beam is emitted in the −Y direction, as indicated by an arrow in an upper illustration of  FIG. 6 . The arrow represents the emitting direction of the beam. 
     In a case where the dielectric member  420  is slid by the length l in the −X direction from a state as illustrated in  FIG. 6  to a state as illustrated in  FIG. 8 , the sloped portion  422  located on the +X direction side covers the slot array antenna  411 . 
     In this situation, a thickness of a portion, of the dielectric member  420 , covering the slot  1  is thinnest, and a thickness of a portion, of the dielectric member  420 , covering the slot  4  is thickest among four thicknesses of four portions, of the dielectric member  420 , covering the slots  1  to  4 , respectively. This means that distances of the four portions through which the radio waves emitted from the slots  1  to  4  pass are different. In a dielectric body, a wavelength becomes shorter as the thickness of the dielectric member  420  becomes thicker, because of wavelength shortening effect. Accordingly, the radio waves emitted from the slot  1  pass through the dielectric member  420  most quickly, and the radio waves emitted from the slot  4  pass through the dielectric member  420  most slowly. Accordingly, the beam that is generated by the synthesization of the radio waves emitted from the slots  1  to  4  is deflected in the +X direction, as illustrated in an upper illustration of  FIG. 8 . 
     Accordingly, in a case where the sloped portion  422  located on the +X direction side covers the slot array antenna  411  as illustrated in  FIG. 8 , it is possible to adjust the emission angle of the beam output from the slot array antenna  411  in the +X direction. 
     In a case where the dielectric member  420  is slid by the length l in the +X direction from the state  33  illustrated in  FIG. 6  to a state as illustrated in  FIG. 9 , the sloped portion  422  located on the −X direction side covers the slot array antenna  411 . 
     In this situation, a thickness of a portion, of the dielectric member  420 , covering the slot  1  is thickest, and a thickness of a portion, of the dielectric member  420 , covering the slot  4  is thinnest among four thicknesses of four portions, of the dielectric member  420 , covering the slots  1  to  4 , respectively. This means that distances of the four portions through which the radio waves emitted from the slots  1  to  4  pass are different. Because of wavelength shortening effect, the radio waves emitted from the slot  1  pass through the dielectric member  420  most slowly, and the radio waves emitted from the slot  4  pass through the dielectric member  420  most quickly. Accordingly, the beam that is generated by the synthesization of the radio waves emitted from the slots  1  to  4  is deflected in the −X direction, as illustrated in an upper illustration of  FIG. 9 . 
     Accordingly, in a case where the sloped portion  422  located on the −X direction side covers the slot array antenna  411  as illustrated in  FIG. 9 , it is possible to adjust the emission angle of the beam output from the slot array antenna  411  in the −X direction. 
       FIG. 10  is a diagram illustrating an operation of the slot antenna apparatus  400  in a case where the waveguide  410  includes four slot array antennas  411 A to  411 D. In  FIG. 1C , the waveguide  410  is provided with the four slot array antennas  411 A to  411 D, and the four slot array antennas  411 A to  411 D are respectively provided with dielectric members  420 A to  420 D that are slidable with respect to the four slot array antennas  411 A to  411 D, respectively, in the X direction. Hereinafter, in a case where the dielectric members  420 A to  420 D are not specifically distinguished, the dielectric members  420 A to  420 D will be described as the dielectric member(s)  420 . 
     Here, a case where the slot array antennas  411 A to  411 D supply electric power to PCs  10 A to  10 D, respectively, will be described. 
     The slot array antennas  411 A to  411 D are arranged in the X direction, and each of the slot array antennas  411 A to  411 D is similar to the slot array antenna  411  as illustrated in  FIGS. 4 to 6, 8 , and  9 . In  FIG. 10 , the slot array antenna  411  is illustrated in a simplified manner. 
     The dielectric members  420 A to  420 D are similar to the dielectric member  420  as illustrated in  FIGS. 4 to 6, 8, and 9 , and are provided to adjust the emission angles of the slot, array antennas  411 A to  411 D, respectively. 
     In  FIG. 10 , beams  411 A 1  to  411 D 1  emitted from the slot array antennas  411 A to  411 D, respectively, are illustrated as solid ovals. The beams  411 A 1  to  411 D 1  represent emission ranges of beams emitted from the slot array antennas  411 A to  411 D through the dielectric members  420 A to  420 D, respectively. 
     For the purpose of comparison, beams  1 A to  1 D are illustrated by dashed lines. The beams  1 A to  1 D are respectively emitted from four slots in a 1 slot-to-1 beam relationship without using the dielectric members  420 A to  420 D, respectively. The four slots that emit the beams  1 A to  1 D, respectively, are not illustrated in  FIG. 10 . Each of the four slots has the same approximate emission range as each other and is approximately the same in size as one of the slots  1  to  4  of the embodiment. The four slots that emit the beams  1 A to  1 D are used instead of the slot array antennas  411 A to  411 D for the purpose of comparison. 
     In a case where each of the slot array antennas  411 A to  411 D and the single slot for comparison emit the radio waves at same power, each of four areas representing the four emission ranges of the beams  411 A 1  to  411 D 1 , respectively, and each of four areas representing the four emission ranges of the beams  1 A to  1 D, respectively, are equal to each other. The emission ranges of the beams  411 A 1  to  411 D 1  reach farther than the emission ranges of the beams  1 A to  1 D, and have narrower widths in the X direction and the Z direction than that of the beams  1 A to  1 D. 
     In a case where the single slot emits the beam  1 A instead of the slot array antenna  411 A, the PC  10 A is positioned in the emission range of the beam  1 A. Accordingly, the PC  10 A can receive electric power of the beam  1 A. The PC  10 A is positioned right in front of the slot array antenna  411 A and is positioned in the emission range of the beam  411 A 1 . Accordingly, the PC  10 A can receive electric power of the beam  411 A 1  that is emitted from the slot array antenna  411 A and passes through the base  421  (see  FIG. 6 ) of the dielectric member  420 A. Since the PC  10 A is positioned at the center of the emission range of the beam  411 A 1 , it is appropriate to use the base  421  of the dielectric member  420 A. Here, the location of the PC  10 A right in front of the slot array antenna  411 A means that there is almost no displacement in the X direction with respect to the slot array antenna  411 A. 
     In a case where the slot array antenna  411 A outputs the electric power, the beam  411 A 1  has a longer emission distance than that of the beam  1 A and converges. The PC  10 A is positioned on a tip of the beam  1 A, i.e., the PC  10 A is positioned at an end portion in the emission distance of the beam  1 A. In contrast, the PC  10 A is positioned approximately in the center of the emission distance of the beam  411 A 1 . Therefore, in a case where the slot array antenna  411 A outputs the electric power through the base  421 , a gain obtained at the position of the PC  10 A is increased compared with a case where the single slot outputs the electric power without using the dielectric member  420 . As a result, a signal to noise ratio (SNR) and a transmission rate are increased at the position of the PC  10 A by supplying the electric power from the slot array antenna  411  through the base  421 . 
     With respect to the PC  10 B, in a case where the single slot emits the beam  1 B instead of the slot array antenna  411 B, the PC  10 B is not positioned in the emission range of the beam  1 B. Accordingly, the PC  10 B cannot receive electric power of the beam  1 B. Regarding the slot array antenna  411 B, the PC  10 B is positioned right in front of the slot array antenna  411 B and is positioned in the emission range of the beam  411 B 1 , even though the PC  10 B is positioned at a tip of the emission range of the beam  411 B 1 . Accordingly, the PC  10 B can receive electric power of the beam  411 B 1  that is emitted from the slot array antenna  411 B and passes through the base  421  (see  FIG. 6 ) of the dielectric member  420 B. 
     In a case where the slot array antenna  411 B outputs the electric power, the beam  411 B 1  has a longer emission distance than that of the beam  1 A. Accordingly, it is possible to supply the electric power to the PC  10 B from the slot array antenna  411 B via the base  421  of the dielectric member  420 B, even though the PC  10 B is positioned relatively far from the slot array antenna  411 B. 
     With respect to the PC  10 C, in a case where the single slot emits the beam  1 C instead of the slot array antenna  411 C, the PC  10 C is positioned in the emission range of the beam  1 C. Accordingly, the PC  10 C can receive electric power of the beam  1 C. Regarding the slot array antenna  411 C, the PC  10 C is offset to the direction side with respect to a front direction of the slot array antenna  411 C. The front direction corresponds to the −Y direction. In this case, it is possible to adjust the emission angle to the +X direction side by sliding the dielectric member  420 C to the −X direction side as illustrated in  FIG. 10 . Accordingly, it becomes possible for the PC  10 C to receive the electric power of the beam  411 C 1 . 
     With respect to the PC  10 D, in a case where the single slot emits the beam  1 D instead of the slot array antenna  411 D, the PC  10 D is not positioned in the emission range of the beam  1 D. Accordingly, the PC  10 D cannot receive electric power of the beam  1 D, because the PC  10 D is positioned relatively far from the slot array antenna  411 D. Regarding the slot array antenna  411 D, the PC  10 D is offset to the −X direction side with respect to a front direction of the slot array antenna  411 D. In this case, it is possible to adjust the emission angle to the −X direction side by sliding the dielectric member  420 D to the +X direction side as illustrated in  FIG. 10 . Accordingly, it becomes possible for the PC  10 D to receive the electric power of the beam  411 D 1 . 
     As described above, it is possible to supply the electric power to the PCs  10 A to  10 D by utilizing the dielectric members  420 A to  420 D and by adjusting the emission angles of the slot array antennas  411 A to  411 D, respectively. Moreover, it is possible to lengthen the emission distances by using the slot array antennas  411 A to  411 D compared with using the single slot antenna. 
     In a case where the relative permittivities of the dielectric members  420 A to  420 D were set to 4, the emission angles, that were obtained similar to the emission angles of the beams  411 C 1  and  411 D 1 , were +10.1 degrees and −10.1 degrees, respectively, with respect to the −Y direction. Here, the emission angle that is offset in the clockwise direction with respect to the −Y direction as viewed in the XY plane is represented as a plus (+) angle, and the emission angle that is offset in the counterclockwise direction with respect to the −Y direction as viewed in the XY plane is represented as a minus (−) angle. Moreover, in a case where the relative permittivities of the dielectric members  420 A to  420 D were set to 6, the emission angles, that were obtained similar to the emission angles of the beams  411 C 1  and  411 D 1 , were +23.3 degrees and −23.3 degrees, respectively, with respect to the −Y direction. Furthermore, in a case where the relative permittivities of the dielectric members  420 A to  420 D were set to 10, the emission angles, that were obtained similar to the emission angles of the beams  411 C 1  and  411 D 1 , were +37.2 degrees and −37.2 degrees, respectively, with respect to the −Y direction. Accordingly, it is confirmed that the slot array antennas  411 A to  411 D can cover the whole emission ranges of the beams  1 A to  1 D by setting the relative permittivities of the dielectric members  420 A to  420 D to appropriate values and by sliding the dielectric members  420 A to  420 D in the X direction with respect to the slot array antennas  411 A to  411 D. 
     As described above, it is possible to adjust the emission angles of the slot array antennas  411 A to  411 D by covering the lot array antennas  411 A to  411 D with the dielectric members  420 A to  420 D, respectively, and by sliding the dielectric members  420 A to  420 D in the X direction with respect to the slot array antennas  411 A to  411 D. Since the dielectric members  420 A to  420 D are slidable with respect to the waveguide  410  in the X direction, it is possible to adjust the emission angles easily by sliding the dielectric members  420 A to  420 D in accordance with the positions of the PCs  10 A to  10 D. Moreover, in a case where the positions of the PCs  10 A to  10 D are changed, it is possible to adjust the emission angles. 
     Accordingly, it is possible to variably adjust the emission angle at which the slot emits the radio waves according to the present embodiment. 
     Although the embodiment in which the slot array antenna  411  is used is described, the single slot may be used instead of the slot array antenna  411 . In particular, it is very beneficial to be able to adjust the emission angle in a case, where the single slot has a relatively narrow beam width. It is also very beneficial to be able to adjust the emission angle even in a case where the single slot has a relatively narrow beam width and a relatively long emission distance. 
     Although the embodiment in which the dielectric member  420  includes the two sloped portions  422  has been described, the dielectric member  420  may include the single sloped portion  422 . The dielectric member  420  may have a configuration in which the four portions covering the slots  1  to  4 , respectively, have different thicknesses and are arranged in stepwise shape, instead of including the two sloped portions  422 . The dielectric member  420  may have a configuration in which the thicknesses of the sloped portions  422  increase nonlinearly in accordance with increased distance from the base  421  in the X direction, instead of the configuration in which the thicknesses of the sloped portions  422  increase linearly in accordance with increased distance from the base  421  in the X direction. For example, the thicknesses may be increased nonlinearly by having a curved configuration in the XY plane view. 
     In addition, a configuration as illustrated in  FIG. 11  may be adopted instead of the slot antenna apparatus  400 .  FIG. 11  is a diagram illustrating a slot antenna apparatus  400 S according to a first variation of the embodiment. The slot antenna apparatus  400 S includes the waveguide  410  and a dielectric member  420 S. The dielectric member  420 S includes the base  421 , the two sloped portions  422 , and two sloped portions  425 . The dielectric member  420 S has a configuration in which the two sloped portions  425  are added to the dielectric member  420  as illustrated in  FIGS. 4-6, 7, and 8 . Each of the sloped portions  425  is an example of a third section. The sloped portions  425  are thicker than the sloped portions  422 . Surfaces, of the sloped portions  425 , located on the −Y direction side have larger tilt angles with respect to the X direction than the surfaces, of the sloped portions  422 , located on the −Y direction side. 
     It becomes possible to further increase the emission angle of the beam emitted from the slot array antenna  411  by sliding the dielectric member  420 S so that the sloped portion  425  covers the slot array antenna  411 . 
     Although the embodiment in which the thickness of the dielectric member  420  varies in the X direction is described, a dielectric member  420 M as illustrated in  FIG. 12  may be used instead of the dielectric member  420 .  FIG. 12  is a diagram illustrating a slot antenna apparatus  400 M according to a second variation of the embodiment. 
     The slot antenna apparatus  400 M includes the waveguide  410  and the dielectric member  420 M. In  FIG. 12 , the waveguide  410  is illustrated in a simplified manner and the guide rails  415  (see FIG.  6 ) are omitted. Further, the dielectric member  420 M is also illustrated in a simplified manner, and differences between the dielectric member  420 M and the dielectric member  420  (see  FIG. 6 ) will be described. 
     The dielectric member  420 M includes a base  421 M and two side portions  422 M. The base  421 M is an example of a first section of the dielectric member  420 M, and each of the side portions  422 M is an example of a second section of the dielectric member  420 M. Thicknesses of the base  421 M and the two side portions  422 M in the Y direction are constant. 
     The base  421 M is a portion having a relative permittivity that is set to ε 0 . Each of the two side portions  422 M has a configuration in which a relative permittivity increases at regular intervals in accordance with increased distance from the base  421 M. More specifically, the side portion  422 M includes four sections (portions) arranged in the X direction, and relative permittivities of the four sections increase in accordance with increased distance from the base  421 M. The relative permittivities of the four sections are set to ε 1 , ε 2 , ε 3 , and ε 4  (ε 0 &lt;ε 1 &lt;ε 2 &lt;ε 3 &lt;ε 4 ). The side portion  422 M is a portion in which the relative permittivities increase in accordance with increased distance from the base  421 M. Each of lengths of the four sections in the X direction is a quarter of the length l, i.e., ¼. 
     Next, adjustments of the emission angles in the slot antenna apparatus  400 M will be described with reference to  FIGS. 13 and 14  in addition to  FIG. 12 .  FIGS. 13 and 14  are diagrams illustrating operations of the slot antenna apparatus  400 M. 
     As illustrated in  FIG. 12 , in a case where the base  421 M covers the slot array antenna  411 , thicknesses of four portions, of the dielectric members  420 M, covering the slots  1  to  4  are same with each other, and the relative permittivities of the four portions are the same with each other. The relative permittivities of the four portions are ε 0 . Accordingly, the beam is emitted in the −Y direction as illustrated by the arrow in an upper illustration of  FIG. 12 . 
     In a case where the dielectric member  420 M is slid by the length l in the −X direction from a state as illustrated in  FIG. 12  to a state as illustrated in  FIG. 13 , the side portion  422 M located on the +X direction side covers the slot array antenna  411 . 
     In this situation, the relative permittivity of the section, of the dielectric member  420 M, covering the slot  1  is smallest, i.e., ε 1 , and the relative permittivity of the section, of the dielectric member  420 M, covering the slot  4  is largest, i.e., ε 4 , among the four relative permittivities of the four sections, of the dielectric member  420 M, covering the slots  1  to  4 , respectively. This means that, relative permittivities of the four sections through which the radio waves emitted from the slots  1  to  4  pass are different. In a dielectric body, a wavelength becomes shorter as the relative permittivity of the dielectric member  420 M becomes greater, because of wavelength shortening effect. Accordingly, the radio waves emitted from the slot  1  pass through the dielectric member  420 M most quickly, and the radio waves emitted from the slot  4  pass through the dielectric member  420 M most slowly. Accordingly, the beam that is generated by the synthesization of the radio waves emitted from the slots  1  to  4  is deflected in the +X direction, as illustrated in an upper illustration of  FIG. 13 . 
     Accordingly, in a case where the side portion  422 M located on the +X direction side covers the slot array antenna  411  as illustrated in  FIG. 13 , it is possible to adjust the emission angle of the beam output from the slot array antenna  411  in the +X direction. 
     In a case where the dielectric member  420 M is slid by the length l in the +X direction from the state as illustrated in  FIG. 12  to a state as illustrated in  FIG. 14 , the side portion  422 M located on the −X direction side covers the slot array antenna  411 . 
     In this situation, the relative permittivity of the section, of the dielectric member  420 M, covering the slot  1  is greatest, i.e., ε 4 , and the relative permittivity of the section, of the dielectric member  420 M, covering the slot  4  is smallest, i.e., ε 1 , among the four relative permittivities of the four sections, of the dielectric member  420 M, covering the slots  1  to  4 , respectively. This means that relative permittivities of the four sections through which the radio waves emitted from the slots  1  to  4  pass are different. Because of wavelength shortening effect, the radio waves emitted from the slot  1  pass through the dielectric member  420 M most slowly, and the radio waves emitted from the slot  4  pass through the dielectric member  420 M most quickly. Accordingly, the beam that is generated by the synthesization of the radio waves emitted from the slots  1  to  4  is deflected in the −X direction, as illustrated in an upper illustration of  FIG. 14 . 
     Accordingly, in a case where the side portion  422 M located on the −X direction side covers the slot array antenna  411  as illustrated in  FIG. 14 , it is possible to adjust the emission angle of the beam output from the slot array antenna  411  in the −X direction. 
     As described above, even in a case where the dielectric member  420 M including the side portion  422 M that has the relative permittivities increase in accordance with increased distance from the base  421 M, it is possible to utilize the shortening effect similar to the shortening effect obtained by the sloped portion  422 . Accordingly, it is possible to adjust the emission angle of the beam emitted from the slot antenna apparatus  400 M. 
     According to the variation of the embodiment, it is possible to provide the slot antenna apparatus  400 M, the communication system, and the method for adjusting the emission angle of the slot antenna apparatus  400 M that are capable of variably adjusting the emission angle of the beam, i.e., an emission angle of the radio waves. 
     Although the embodiment in which the dielectric member  420 M includes the two side portions  422 M is described, the dielectric member  420 M may include the single side portion  422 M. The relative permittivities of the side portions  422 M may increase from ε 2  to ε 4  continuously instead of increasing stepwisely. 
     In addition, a configuration as illustrated in  FIG. 15  may be adopted instead of the slot antenna apparatus  400 M.  FIG. 15  is a diagram illustrating a slot antenna apparatus  400 M 2  according to a third variation of the embodiment. The slot antenna apparatus  400 M 2  includes the waveguide  410  and a dielectric member  420 M 2 . The dielectric member  420 M 2  includes the base  421 M, the two side portions  422 M, and two side portions  425 M. The dielectric member  420 M 2  has a configuration in which the two side portions  425 M are added to the dielectric member  420 M as illustrated in  FIGS. 12-14 . The side portion  425 M is an example of a third section of the dielectric member  420 M 2  and has greater relative permittivities than that of the side portion  422 M. Thicknesses in the Y direction of the side portions  425 M are equal to that of the base  421 M and the side portions  422 M. 
     The side portion  425 M includes four sections arranged in the X direction. The relative permittivities of the four sections of the side portion  425 M are set to ε 5 , ε 6 , ε 7 , and ε 8  (ε 5 &lt;ε 6 &lt;ε 7 &lt;ε 8 ), respectively. The side portion  425 M is a portion in which the relative permittivities increase in accordance with increased distance from the side portions  422 M. Each of lengths in the X direction of the four sections having the relative permittivities ε 5 , ε 6 , ε 7 , and ε 8  is a quarter of the length l, i.e., ¼. The lengths of the four sections of the side portions  425 M are equal to the lengths of the four sections of the side portions  422 M. The relative permittivities ε 5 , ε 6 , ε 7 , and ε 8  satisfy a relationship represented as ε 4 &lt;ε 5 &lt;ε 6 &lt;ε 7 &lt;ε 8 . 
     Accordingly, the side portions  422 M and  425 M have configurations in that the relative permittivities of the side portions  422 M and  425 M increase in a stepwise manner in accordance with increased distance from the base  421 M. 
     It becomes possible to further increase the emission angle of the beam emitted from the slot array antenna  411  by sliding the dielectric member  420 M 2  so that the side portion  422 M or  425 M covers the slot array antenna  411 . 
     In the above description, a slot antenna apparatus, a communication system, and a method for adjusting angle of radio waves emitted from the slot antenna apparatus according to embodiments are described. However, the present invention is not limited to the embodiments specifically disclosed. A person skilled in the art may easily achieve various modifications and changes without departing from the scope of the present invention. 
     The other objects, features, and benefits of the present application may become further clear by referring to the accompanying drawings and embodiments described above. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of superiority or inferiority of the invention. Although the embodiment of the present invention has been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the sprit and scope of the invention.