Patent Publication Number: US-2011050356-A1

Title: Waveguide converter and manufacturing method for the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-204115, filed on Sep. 3, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a conversion structure that performs signal conversion for a substrate-side line in a high-frequency band and are related to, for example, a waveguide converter that performs signal conversion between a substrate-side line and a waveguide and a manufacturing method for the waveguide converter. 
     BACKGROUND 
     In order to transmit a signal between a transmission circuit or a reception circuit and an antenna in a short-wavelength band (such as, e.g., a millimeter-wave band used for automotive radars), a hollow waveguide is interposed between the transmission circuit or the reception circuit and the antenna. In the signal transmission in which the waveguide is used, a waveguide converter is used as signal conversion mechanism. 
     For the waveguide converter, an input/output coupling structure for a dielectric waveguide is known (see Japanese Laid-open Patent Publication No. 2005-142884, for example). In the input/output coupling structure, a first conductor pattern is provided on a printed circuit board, a second conductor pattern is provided on a dielectric waveguide to cover the first conductor pattern, and the first and second conductor patterns are disposed opposite each other. In the input/output coupling structure, a microstrip line is provided on the printed circuit board, and the first conductor pattern is formed at a terminal portion of the microstrip line. A conductor wall or a spacer is provided to surround the first conductor pattern. The dielectric waveguide is mounted on the printed circuit board to cover the first conductor pattern such that the second conductor pattern formed on the dielectric waveguide and the first conductor pattern on the printed circuit board are disposed opposite each other. 
     A known technique for providing an interconnection between RF (radio frequency) printed circuit boards is to arrange a waveguide transmission line to connect between the RF printed circuit boards. In the known technique, each RF printed circuit board is integrally provided with a waveguide transmission/reception section (see Japanese Laid-open Patent Publication No. 2006-191077, for example). 
     A known high-frequency line-waveguide converter includes a dielectric layer, a line conductor disposed on the upper surface of the dielectric layer, and a high-frequency line disposed on the same surface to surround a part of the line conductor (see Japanese Laid-open Patent Publication No. 2005-286435, for example). In the high-frequency line-waveguide converter, the dielectric layer is configured to have a thickness that is smaller than one-fourth a wavelength λ of a high-frequency signal transmitted through the high-frequency line. In addition, a patch conductor is formed directly below one end of the ground conductor on the lower surface of the dielectric layer. 
     SUMMARY 
     According to an aspect of the embodiments, a waveguide converter includes a waveguide configured with an opening, a patch disposed inside the opening of the waveguide, a first ground conductor provided substantially along the opening of the waveguide and a port that opens in a side surface of the waveguide through which a signal line connected to the patch extends. 
     The object and advantages of the embodiments 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 perspective view illustrating an exemplary waveguide converter according to a first embodiment; 
         FIG. 2  illustrates the waveguide converter as seen from a port portion side; 
         FIG. 3  illustrates the waveguide converter as seen from a direction orthogonal to the port portion side; 
         FIG. 4  is a perspective view illustrating the waveguide converter with a waveguide and a circuit substrate separated from each other; 
         FIG. 5  illustrates the waveguide converter as seen from a waveguide side with the port portion cut away; 
         FIG. 6  illustrates the details of a patch conductor, opening portions of the waveguide and a ground conductor, and the port portion; 
         FIG. 7  is a cross-sectional view taken along the line VII-VII of  FIG. 5 ; 
         FIG. 8  is a cross-sectional view taken along the line VIII-VIII of  FIG. 5 ; 
         FIG. 9  is a cross-sectional view taken along the line IX-IX of  FIG. 5 ; 
         FIG. 10  is a cross-sectional view taken along the line X-X of  FIG. 5 ; 
         FIG. 11  is a cross-sectional view taken along the line XI-XI of  FIG. 5 ; 
         FIG. 12  is a cross-sectional view taken along the line XII-XII of  FIG. 5 ; 
         FIG. 13  is a cross-sectional view taken along the line XIII-XIII of  FIG. 5 ; 
         FIG. 14  illustrates a ground via; 
         FIG. 15  is a flowchart illustrating an exemplary manufacturing method for the waveguide converter; 
         FIG. 16  is an exploded perspective view illustrating an exemplary waveguide converter according to a second embodiment; 
         FIG. 17  illustrates a ground via; 
         FIG. 18  is an exploded perspective view illustrating an exemplary waveguide converter according to a third embodiment; 
         FIG. 19  illustrates the waveguide converter as seen from a waveguide side with the port portion cut away; 
         FIG. 20  illustrates an exemplary waveguide converter according to a fourth embodiment; 
         FIG. 21  illustrates an exemplary waveguide converter according to a fifth embodiment; 
         FIG. 22  illustrates an exemplary waveguide converter according to a sixth embodiment; 
         FIG. 23  illustrates an exemplary waveguide converter according to a seventh embodiment; 
         FIG. 24  is a perspective view illustrating an exemplary waveguide converter according to an eighth embodiment; 
         FIG. 25  illustrates an exemplary radar device according to a ninth embodiment; 
         FIG. 26  is a perspective view illustrating the exemplary radar device with an antenna partially cut away; and 
         FIG. 27  illustrates a waveguide converter used in simulation. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In a waveguide converter, a semiconductor circuit chip is mounted, or a passive circuit is formed, on an insulated substrate. In the waveguide converter, a signal is converted and guided to a waveguide, or a signal guided from the waveguide is converted. A substrate made of ceramics may be used as the insulated substrate. While a ceramic substrate may offer a high pattern accuracy, it is expensive. 
     In order to promote cost reduction, it is conceivable to use a substrate made of a material other than ceramics, such as a resin, for example. However, while the resin substrate is inexpensive, it may offer a low pattern accuracy compared to the ceramic substrate, and therefore may result in significant positional (dimensional) variations caused in or during manufacture. 
     In view of the above, a first object of the present disclosure is to provide a waveguide converter that maintains the pattern accuracy and enhances the product accuracy without being affected by the substrate material used. Affected herein refers to being noticeably and/or significantly affected. 
     A second object of the present disclosure is to provide a waveguide converter with a structure that allows the use of an inexpensive substrate material such as a resin without degrading the pattern accuracy and that resists positional (dimensional) variations caused in or during manufacture. 
     In order to achieve the foregoing object, the present disclosure provides a waveguide converter that performs signal conversion for a substrate-side line. The waveguide converter includes, for example, a waveguide portion, a patch, a ground conductor portion, and a port portion. The waveguide portion may be formed by a waveguide. The patch is disposed inside an opening of the waveguide portion. The ground conductor portion is provided along the opening of the waveguide portion. The port portion opens in a side surface of the waveguide portion, and serves as a mechanism for leading out a signal line connected to the patch from the waveguide portion. According to such a configuration, it is possible to maintain the pattern accuracy and enhance the product accuracy without being affected by the substrate material used. 
     In order to achieve the foregoing object, the present disclosure also provides a manufacturing method for a waveguide converter that performs signal conversion for a substrate-side line. The manufacturing method for a waveguide converter includes: forming a waveguide portion including a port portion; forming a substrate portion with a ground conductor portion, a patch, and a signal line; and mounting the waveguide portion on the substrate portion. 
     The waveguide converter according to the present disclosure has a configuration in which the ground conductor portion which surrounds the patch is disposed inside the opening of the waveguide portion, and the signal line for the patch is led out from a side surface of the waveguide portion. Thus, it is possible to obtain stable conversion characteristics that are not affected by positional or dimensional variations between the opening of the waveguide portion and the patch. 
     According to the waveguide converter of the present disclosure, stable signal conversion and propagation modes can be obtained even if the ground conductor portion is provided on the substrate portion formed by a resin substrate which offers a low pattern accuracy compared to a ceramic substrate. 
     In the waveguide converter according to the present disclosure, the signal line is led out from a side surface of the waveguide portion. Thus, it is possible to prevent a waveguide mode from leaking out by using an opening size to prevent leakage of a waveguide mode. 
     First Embodiment  
     According to a first embodiment, a ground conductor surrounding a patch overreaches into an opening of a waveguide, and a signal line for the patch is led out from a side surface of the waveguide by cutting away a part of the waveguide, achieving stable conversion characteristics that are not affected by the positional accuracy. 
     The first embodiment will be described with reference to  FIGS. 1 ,  2 , and  3 .  FIG. 1  illustrates an exemplary configuration of a waveguide converter.  FIG. 2  illustrates the waveguide converter as seen from a port portion side, and  FIG. 3  illustrates the waveguide converter as seen from a direction orthogonal to the port portion side (when the port portion side is defined as a front side,  FIGS. 2 and 3  are a front view and a left side view, respectively, of the waveguide converter). The configuration illustrated in  FIGS. 1 ,  2 , and  3  is exemplary, and the present invention is not limited to such a configuration. 
     A waveguide converter  2  is a signal conversion mechanism coupled to a waveguide to perform signal conversion. As illustrated in  FIGS. 1 ,  2 , and  3 , the waveguide converter  2  includes a waveguide  4  and a circuit substrate  6 . The waveguide  4  is an example of a waveguide portion, and forms a transmission line through which a radio wave is transmitted. The waveguide  4  may be a rectangular pipe formed from a conductor, and includes a hollow portion  8 . That is, the hollow portion  8  of the waveguide  4  is surrounded by a conductor, and substantially forms a transmission line or a waveguide path. The waveguide  4  may be provided on the upper surface of the circuit substrate  6  with an opening portion of the hollow portion  8  coupled to the circuit substrate  6 . In the embodiment, the waveguide  4  is formed from a metal material with a uniform thickness. The waveguide  4  may be formed from a conductor material as described above, or may be formed by providing a conductor layer on a rectangular tube formed from a resin. 
     A port portion  10  is formed in a side surface of the waveguide  4 . The port portion  10  is a mechanism for leading out a signal line  12  from the inside of the waveguide  4 . The port portion  10  is a hollow that communicates the hollow portion  8  of the waveguide  4  with the side surface of the waveguide  4 . As shown in  FIGS. 1 and 2 , the port portion  10  is a rectangular notch formed along and above the upper surface of the circuit substrate  6 . The signal line  12  is an exemplary high-frequency line provided on the circuit substrate  6 , and formed by a microstrip line, for example. A gap portion  17  is formed in a ground conductor  16  of the circuit substrate  6  to lead out the signal line  12  from the port portion  10 . 
     When the opening width and the opening height of the port portion  10  are defined as c 1  ( FIG. 6 ) and h, respectively, as illustrated in  FIG. 2 , the opening width c 1  and the opening height h are set to be sufficiently smaller than half (=λ/2) a wavelength λ of a frequency of use f (λ/2&gt;c 1  and λ/2&gt;h). With λ/2&gt;c 1  and λ/2&gt;h, it is possible to prevent a waveguide mode propagating through the hollow portion  8  of the waveguide  4  from leaking out from the port portion  10 . 
     The circuit substrate  6  is an example of the substrate portion according to the present disclosure. The circuit substrate  6  includes an insulated substrate  14 , ground conductor  16 , and second ground conductor  18 . The insulated substrate  14  may have a square shape, for example. The ground conductor  16  discussed above is provided on one surface (for example, upper surface) of the insulated substrate  14  and serves as a first ground conductor. A second ground conductor  18  is provided on the other surface (for example, the lower surface) of the insulated substrate  14 . The ground conductor  16  is an example of the ground conductor portion according to the present disclosure. An exposed surface portion  19  is provided adjacent to the ground conductor  16 . The exposed surface portion  19  is a surface portion of the insulated substrate  14  where the ground conductor  16  is not formed and where the bare insulated substrate  14  is exposed. 
     The insulated substrate  14  may be formed in the shape of a flat plate with a uniform thickness. The insulated substrate  14  may be formed from an insulating material, specifically a synthesized resin such as, a Bakelite or ceramics, for example. The ground conductor  16  is a conductor layer with a uniform thickness provided on the upper surface of the insulated substrate  14 . In the embodiment, the ground conductor  16  conforms to the end-surface shape of the waveguide  4 . The ground conductor  18  is a conductor layer with a uniform thickness provided on the lower surface of the insulated substrate  14 . In the embodiment, the ground conductor  18  is in the shape of a flat surface conforming to the shape of the insulated substrate  14   14 . That is, the ground conductor  16  has a smaller surface area than the ground conductor  18 , and the ground conductors  16  and  18  are two flat plates extending in parallel to each other and sandwiching the insulated substrate  14 . 
     Next, the circuit substrate  6  will be described with reference to  FIG. 4 .  FIG. 4  is an exploded perspective view illustrating the waveguide and the circuit substrate separated from each other. The configuration illustrated in  FIG. 4  is exemplary, and the present invention is not limited to such a configuration. Components in  FIG. 4  that are the same as those in  FIG. 1  are denoted by the same reference numerals. 
     A patch conductor  20  is provided on the circuit substrate  6 . The patch conductor  20  is a mechanism for electromagnetic coupling with the waveguide  4  that radiates a signal (radio wave) from the signal line  12  to the waveguide  4  or receives a signal from the waveguide  4 . The patch conductor  20  is a conductor layer that is provided on the insulated substrate  14  exposed from the circuit substrate  6 . The patch conductor  20  has a smaller area than the hollow portion  8  of the waveguide  4 . In the embodiment, the patch conductor  20  has a rectangular shape that is analogous to the shape of the hollow portion  8  of the waveguide  4 . The patch conductor  20  is provided inside the opening of the hollow portion  8  of the waveguide  4 . The signal line  12  discussed above is connected to the patch conductor  20 . The patch conductor  20  and the signal line  12  are formed on the same surface of the insulated substrate  14 , as well as the ground conductor  16 . 
     An opening portion  22  is formed in the ground conductor  16  of the circuit substrate  6  to expose the insulated substrate  14 . The patch conductor  20  discussed above is formed inside the opening portion  22 . The gap portion  17  discussed above is a mechanism for allowing the signal line  12  discussed above to pass therethrough. A uniform gap for insulation is provided between the ground conductor  16  and the signal line  12 . Thus, a portion of the signal line  12  that passes through the waveguide  4  forms a coplanar line  26 . 
     The ground conductor  16  and the ground conductor  18  are coupled to each other by a plurality of ground vias  28  to be electrically connected to each other. The ground vias  28  are an example of a single or a plurality of connection portions that connect the ground conductor  16  and the ground conductor  18 . The ground vias  28  are not formed under the coplanar line  26 . 
     Next, the shape and the arrangement of the waveguide  4 , the ground conductor  16 , and the patch conductor  20  will be described with reference to  FIGS. 5 and 6 .  FIG. 5  illustrates the waveguide converter as seen from the upper-surface side (waveguide side) with the port portion cut away.  FIG. 6  illustrates the details of the patch conductor, the opening portions of the waveguide and the ground conductor, and the port portion. The configuration illustrated in  FIGS. 5 and 6  is exemplary, and the present invention is not limited to such a configuration. Components in  FIGS. 5 and 6  that are the same as those in  FIGS. 1 and 4  are denoted by the same reference numerals. 
     As illustrated in  FIG. 5 , the waveguide  4  is provided on the upper surface of the ground conductor  16  of the circuit substrate  6 . The patch conductor  20  is disposed inside the opening of the hollow portion  8  of the waveguide  4 . The ground conductor  16  is provided along the opening of the hollow portion  8  of the waveguide  4 . That is, the opening portion  22  of the ground conductor  16 , which is disposed to surround the patch conductor  20 , is configured to have an opening that is analogous to and smaller than the opening of the hollow portion  8  of the waveguide  4 . Thus, an overreaching portion  24  that peripherally surrounds the patch conductor  20  is formed inside the opening of the hollow portion  8  of the waveguide  4 . That is, the overreaching portion  24  of the ground conductor  16  surrounds the patch conductor  20 . In addition, the plurality of ground vias  28  that connect the ground conductors  16  and  18  are disposed along the periphery of the hollow portion  8  of the waveguide  4 . The plurality of ground vias  28  surround the opening portion  22  of the ground conductor  16  and the opening of the waveguide  4 . 
     Thus, as illustrated in  FIG. 6 , when the long-side length and the short-side length of the hollow portion  8  of the waveguide  4  are defined as a 1  and b 1 , respectively, the long-side length and the short-side length of the opening portion  22  of the ground conductor  16  are defined as a 2  and b 2 , respectively, and the long-side length and the short-side length of the patch conductor  20  are defined as a 3  and b 3 , respectively, the relationship a 1 &gt;a 2 &gt;a 3  and b 1 &gt;b 2 &gt;b 3  is established. 
     When the widths of the overreaching portion  24  of the ground conductor  16  with respect to the hollow portion  8  of the waveguide  4  are defined as Δa 12  and Δb 12 , the following formulas are satisfied: 
       Δ a   12 =( a   1   −a   2 )/2   (1)
 
       Δ b   12 =( b   1   −b   2 )/2   (2)
 
     In this case, X-axis and Y-axis that intersect at center axis O corresponding to the center of the hollow portion  8  of the waveguide  4  are defined, and it is assumed that the left and right widths Δa 12  are the same as each other and the upper and lower widths Δb 12  are the same as each other. However, the left and right widths Δa 12  may be different from each other, and the upper and lower widths Δb 12  may be different from each other. 
     When the width of gaps between the patch conductor  20  and the overreaching portion  24  of the ground conductor  16  are defined as Δa 23  and Δb 23 , the following formulas are satisfied: 
       Δ a   23 =( a   2   −a   3 )/2   (3)
 
       Δ b   23 =( b   2   −b   3 )/2   (4)
 
     In this case, it is assumed that the left and right widths Δa 23  are the same as each other and the upper and lower widths Δb 23  are the same as each other on X-axis and Y-axis that intersect at center axis O. However, the left and right widths Δa 23  may be different from each other, and the upper and lower widths Δb 23  may be different from each other. 
     When the width of the port portion  10  of the waveguide  4  is defined as c 1 , the width of the gap portion  17  of the ground conductor  16  in the port portion  10  is defined as c 2 , and the width of the signal line  12  is defined as c 3 , the relationship c 1 &gt;c 2 &gt;c 3  is established. When the width of the overreaching portion  24  of the ground conductor  16  in the port portion  10  is defined as Δc 12 , the following formula is satisfied: 
       Δc 12 =( c   i   −c   2 )/2   (5)
 
     When the width of the gap between the signal line  12  and the overreaching portion  24  of the ground conductor  16  is defined as Δc 23 , the following formula is satisfied: 
       Δ c   23 =( c   2   −c   3 )/2   (6)
 
     In  FIG. 6 , d corresponds to the length of the coplanar line  26 . 
     The waveguide converter  2  will be described with reference to  FIGS. 7 ,  8 ,  9 ,  10 ,  11 ,  12 , and  13 .  FIG. 7  is a cross-sectional view taken along the line VII-VII of  FIG. 5 .  FIG. 8  is a cross-sectional view taken along the line VIII-VIII of  FIG. 5 .  FIG. 9  is a cross-sectional view taken along the line IX-IX of  FIG. 5 .  FIG. 10  is a cross-sectional view taken along the line X-X of  FIG. 5 .  FIG. 11  is a cross-sectional view taken along the line XI-XI of  FIG. 5 .  FIG. 12  is a cross-sectional view taken along the line XII-XII of  FIG. 5 .  FIG. 13  is a cross-sectional view taken along the line XIII-XIII of  FIG. 5 . As is clear from the cross-sectional views, the circuit substrate  6  is provided with the plurality of ground vias  28  which penetrate through the insulated substrate  14 . The ground vias  28  are provided along the extension of the hollow portion  8  of the waveguide  4 . In other words, the ground vias  28  surround the hollow portion  8 . As illustrated in  FIG. 14 , each ground via  28  penetrates through the insulated substrate  14  to connect the ground conductor  16  and the ground conductor  18 .  FIG. 14  illustrates the circuit substrate  6  cut at a ground via  28 . 
     Next, a manufacturing method for the waveguide converter will be described with reference to  FIG. 15 .  FIG. 15  is a flowchart illustrating an exemplary manufacturing method for the waveguide converter. 
     The manufacturing process is an example of the manufacturing method according to the present disclosure. As illustrated in  FIG. 15 , the manufacturing method includes forming a waveguide  4  (step S 101 ), forming a circuit substrate  6  serving as a substrate portion (step S 102 ), and coupling the waveguide  4  and the circuit substrate  6  (step S 103 ). 
     In the formation of a waveguide  4  (step S 101 ), the waveguide  4  discussed above is formed. As illustrated in  FIG. 4 , the waveguide  4  is formed with a port portion  10  at the lower end of a wall portion of a rectangular tube. 
     In the formation of a circuit substrate  6  (step S 102 ), the circuit substrate  6  discussed above is formed. The circuit substrate  6  includes an insulated substrate  14 , a ground conductor  16  formed on the front surface of the insulated substrate  14 , and a ground conductor  18  formed on the back surface of the insulated substrate  14 . The ground conductors  16  and  18  may be a conductor layer made of a metal conductor formed by a coating formation method such as plating or vapor deposition. The ground conductor  16  and the ground conductor  18  are connected by ground vias  28  formed by drilling the insulated substrate  14 , for example. 
     The ground conductor  16  is formed with a gap portion  17  and an opening portion  22 . A patch conductor  20  is formed in the opening portion  22 . A signal line  12  is formed on a portion of the exposed surface portion  19  of the insulated substrate  14 . The signal line  12  is connected to the patch conductor  20 , and extends from the opening portion  22  through the gap portion  17 . The signal line  12  may be a conductor layer made of a metal conductor formed by a coating formation method such as plating or vapor deposition, as with the ground conductors  16  and  18 . 
     In the coupling of the waveguide  4  and the circuit substrate  6  (step S 103 ), the waveguide  4  is mounted on the ground conductor  16  provided on the upper surface of the circuit substrate  6  discussed above to obtain the waveguide converter  2  discussed above. 
     The characteristics of the waveguide converter  2  according to the above embodiment are listed as follows. 
     (1) In the thus configured waveguide converter  2 , a signal transmitted from the signal line  12  enters into the waveguide  4  by way of the coplanar line  26 , and is radiated from the patch conductor  20  to the hollow portion  8  of the waveguide  4  as an electromagnetic wave. That is, the high-frequency signal is converted into a waveguide mode propagating from the patch conductor  20  through the hollow portion  8  of the waveguide  4 , and is propagated through the waveguide  4 . 
     Also, an electromagnetic wave propagating through the hollow portion  8  of the waveguide  4  is guided to the patch conductor  20 , and is propagated from the waveguide  4  to the signal line  12  by way of the patch conductor  20  and then the coplanar line  26 . A waveguide mode is thus converted into a signal propagating through the signal line  12 . 
     (2) In the waveguide converter  2 , the opening area of the opening portion  22  of the ground conductor  16  is small compared to the opening area of the waveguide  4 . No signal line vias are formed on the signal line  12 , and the signal line  12  and the patch conductor  20  are provided on the same surface of the insulated substrate  14 . In addition, the port portion  10  has a width that is smaller than a length corresponding to half (=λ/2) the wavelength λ of the frequency of use f. The waveguide  4  on the patch conductor  20  side is continuous with the ground conductor  16 , and the opening of the waveguide  4  is closed by the ground conductor  18  which is connected to the ground conductor  16  by the ground vias  28 . The waveguide  4  is closed by the port portion  10  formed in a side surface of the waveguide  4 . Thus, it is possible to prevent a waveguide mode from leaking out from the circuit substrate  6 . 
     In the waveguide converter  2 , further, the signal line  12  serving as a signal line pattern and the ground conductor  16  serving as a ground pattern are provided on the upper-surface side of the circuit substrate  6 , the ground conductor  18  serving as a ground pattern is provided on the lower-surface side of the circuit substrate  6 , and the ground conductors  16  and  18  are connected by the ground vias  28 . In addition, the hollow portion  8  of the waveguide  4  is surrounded by the ground vias  28 . Thus, an input signal from the signal line  12  enters into the coplanar line  26 , and is radiated from the patch conductor  20  to the hollow portion  8  of the waveguide  4 . However, no vias are provided on the signal line  12 . Therefore, although signal line vias provided on the signal line  12  may degrade the conversion characteristics unless such vias were provided by forming holes accurately, the configuration in which no signal line vias are provided on the signal line does not cause such an inconvenience. 
     (3) The signal line  12  and the patch conductor  20  are formed on the same surface of the insulated substrate  14 , and in addition, the opening portion  22  of the ground conductor  16  is configured to have a small opening area compared to the waveguide  4 . This contributes to preventing a waveguide mode from leaking out from the circuit substrate  6 . 
     (4) The gaps between the ground vias  28  have a width e ( FIG. 6 ) that is smaller than a length corresponding to half (=λ/2) the wavelength λ of the frequency of use f. This contributes to preventing a waveguide mode from leaking out from the circuit substrate  6 . 
     (5) The port portion  10  of the waveguide  4  is configured to have an opening width c 1 , which is smaller than half (=λ/2) the wavelength λ of the frequency of use f. This contributes to preventing a waveguide mode from leaking out from the port portion  10 . 
     (6) The hollow portion  8  of the waveguide  4  is configured to have opening widths a 1  and b 1 , and the opening portion  22  of the ground conductor  16  is configured to have opening widths a 2  and b 2 , which are smaller than the opening widths a 1  and b 1  in order to provide for the overreaching portion  24 . Therefore, as is clear from the formulas (1) and (2) discussed above, the hollow portion  8  of the waveguide  4  may be displaced within ±Δa 12 =(a 1 −a 2 )/2 in the left-right direction and ±Δb 12 =(b 1 −b 2 )/2 in the up-down direction with reference to the center O to obtain the same conversion characteristics. 
     (7) According to the configuration described above, the conversion characteristics are not affected by the positional accuracy of the waveguide  4  with respect to the circuit substrate  6 . The conversion characteristics are not affected by the distance to the short-circuit plane between the waveguide  4  and the ground conductor  16  of the circuit substrate  6 . A high processing accuracy is not required, which reduces the cost. In addition, no signal line vias are provided. Although a high pattern position accuracy is not required for the ground conductors  16  and  18  provided on the circuit substrate  6 , a waveguide mode is not likely to leak out. Thus, in the waveguide converter  2 , the conversion characteristics are not affected by positional (dimensional) variations caused in manufacture. With the conversion characteristics not affected by the positional accuracy and without the need for a high positional accuracy or a high processing accuracy, a resin substrate which is inexpensive may be used as the circuit substrate  6 , which allows cost reduction. 
     Second Embodiment  
     In a second embodiment, the ground vias  28  according to the first embodiment are configured to have a rectangular shape. In the second embodiment, as illustrated in  FIGS. 16 and 17 , the rectangular ground vias  28  are disposed in the same way as the first embodiment. Such a configuration is also expected to provide a substantially similar effect as that of the first embodiment.  FIG. 16  is an exploded perspective view illustrating an exemplary waveguide converter according to the second embodiment, in which the waveguide and the circuit substrate are separated from each other.  FIG. 17  illustrates the circuit substrate  6  cut at a ground via  28 . 
     Third Embodiment  
     In a third embodiment, a continuous ground pattern is provided in place of the plurality of ground vias  28  according to the first embodiment. 
     The third embodiment will be described with reference to  FIGS. 18 and 19 .  FIG. 18  is an exploded perspective view illustrating a waveguide converter according to the third embodiment.  FIG. 19  illustrates the waveguide converter as seen from the upper-surface side (waveguide side) with the port portion cut away. The configuration illustrated in  FIGS. 18 and 19  is exemplary, and the present invention is not limited to such a configuration. 
     While the ground conductor  16  and the ground conductor  18  are connected by the plurality of ground vias  28  ( FIGS. 4 ,  14 ,  16 , and  17 ) on the insulated substrate  14  in the above embodiments, a ground pattern portion  30  is provided to connect the ground conductors  16  and  18  in the embodiment as illustrated in  FIGS. 18 and 19 . The ground pattern portion  30  is a C-shaped pattern connection portion provided to penetrate through the insulated substrate  14 . Therefore, the ground pattern portion  30  has a height g which is the same as that of the insulated substrate  14 . The ground pattern portion  30  is formed with a gap portion  17 . 
     In the waveguide converter  2  according to the embodiment, conductor patterns such as the signal line  12  and the ground conductor  16  are formed on the upper-surface side of the insulated substrate  14 , and the ground conductor  18  is formed on the lower-surface side of the insulated substrate  14 . The ground pattern portion  30  surrounds the opening of the hollow portion  8  of the waveguide  4  as with the ground vias  28  discussed above. Such a configuration also provides a substantially similar effect as that of the above embodiments. 
     Fourth Embodiment  
     A fourth embodiment relates to a modification of the patch. In the fourth embodiment, as illustrated in  FIG. 20 , a patch conductor  20 A in the shape similar to that of a silkworm cocoon that is substantially symmetrical in the left-right direction is provided inside the opening portion  22  of the ground conductor  16 . Such a configuration is also expected to provide a substantially similar effect as that of the above embodiments. 
     Fifth Embodiment  
     A fifth embodiment relates to a modification of the patch. In the fifth embodiment, as illustrated in  FIG. 21 , a patch conductor  20 B in the shape of a hexagon obtained by cutting off corners of the patch conductor  20  on the signal line  12  side is provided inside the opening portion  22  of the ground conductor  16 . Such a configuration is also expected to provide a substantially similar effect as that of the above embodiments. 
     Sixth Embodiment 
     A sixth embodiment relates to a modification of the patch. In the sixth embodiment, as illustrated in  FIG. 22 , a patch conductor  20 C in the shape of a triangle that is symmetrical in the left-right direction with its vertex angle on the port portion  10  side is provided inside the opening portion  22  of the ground conductor  16 . Such a configuration is also expected to provide a substantially similar effect as that of the above embodiments. 
     Seventh Embodiment  
     A seventh embodiment relates to a modification of the ground vias. In the seventh embodiment, as illustrated in  FIG. 23 , a large number of ground vias  28  are provided through the insulated substrate  14  to couple the ground conductor  16  and the ground conductor  18 . Such a configuration is also expected to provide a substantially similar effect as that of the above embodiments. 
     Eighth Embodiment 
     An eighth embodiment relates to a modification of the waveguide portion. While the outer shape of the waveguide  4  conforms to the shape of the ground conductor  16  in the above embodiments, the waveguide  4  is configured to be smaller than the ground conductor  16  in the eighth embodiment as illustrated in  FIG. 24 , with the hollow portion  8  of the waveguide  4  configured in the same way as the above embodiments. In this case, a conductor portion  32  of the waveguide  4  is configured to be thin. Thus, a projecting portion  34  may be formed to surround the port portion  10  so that the projecting portion  34  which is integral with the waveguide  4  covers the coplanar line  26  in the same way as the above embodiments. Such a configuration is also expected to provide a substantially similar effect as that of the above embodiments. 
     Ninth Embodiment 
     A ninth embodiment provides a radar device that uses the waveguide converter discussed above. 
     The radar device will be described with reference to  FIGS. 25 and 26 .  FIG. 25  illustrates a radar device according to the ninth embodiment.  FIG. 26  illustrates the radar device with an antenna partially cut away. The configuration illustrated in  FIGS. 25 and 26  is exemplary, and the present invention is not limited to such a configuration. Components in  FIGS. 25 and 26  that are the same as those in  FIG. 1  are denoted by the same reference numerals. 
     As illustrated in  FIGS. 25 and 26 , a radar device  40  includes an RF section  42  that is provided on the circuit substrate  6  of the waveguide converter  2  discussed above and that is connected to the signal line  12  discussed above. The RF section  42  is an example of a transmission/reception section for millimeter waves, and may be formed by a monolithic microwave integrated circuit (MMIC), for example. An antenna  44  is provided on top of the waveguide  4 . 
     According to such a configuration, it is possible to provide a radar device  40  with excellent conversion characteristics achieved by effectively utilizing the conversion characteristics of the waveguide converter  2  discussed above. 
     Simulation Results 
     A simulation performed using the waveguide converter according to the present disclosure will be described with reference to  FIG. 27 .  FIG. 27  illustrates a waveguide converter used in the simulation. The waveguide converter illustrated in  FIG. 27  is exemplary, and the waveguide converter according to the present disclosure is not limited to such a configuration. 
     In the simulation, a resin waveguide converter in which the insulated substrate  14  of the circuit substrate  6  was made of a resin was used. In the resin waveguide converter, the opening width c 1  of the port portion  10  was set to 600 [μm]. 
     According to the simulation, a waveguide mode leaked out significant when the opening width c 1  of the port portion  10  was larger than half (=λ/2) the wavelength λ of the frequency of use f. 
     The waveguide converter and the manufacturing method for the waveguide converter according to the present disclosure are widely applicable to waveguide converters for automotive radars used in a millimeter-wave frequency band or the like, and are thus useful. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor 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 the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.