Abstract:
The present invention provides electric circuits in which the line width of a conductor, which becomes close to a metal flange of a connector or a conductor wall, is gradually reduced from a predetermined position thereon, thereby the reduction of the impedance of the conductor line can be compensated.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to electronic circuits capable of preventing the degradation of signal propagating characteristics due to the change of the impedance characteristics of conductor lines provided on the upper surface of a substrate.  
         [0003]     2. Description of the related art  
         [0004]     Electronic circuits including conductor lines formed on a substrate are housed in metal cases to isolate respective circuit blocks from one another or are provided with conductor walls for the respective circuit blocks to electromagnetically isolate the respective circuit blocks from one another.  
         [0005]     Further, there are provided connectors for outputting signals from the conductor lines formed on the substrate to the outside and for inputting signals from the outside to the conductor lines so that the conductor lines are electrically connected to the connectors. The center conductors of the connectors have a diameter smaller than the line widths of the conductor lines and, therefore, if the conductor lines are connected to the center conductors of the connectors, this will cause impedance mismatching at the connection points therebetween. Therefore, there has been disclosed a technique for reducing the line width of a conductor line to be equal to the diameter of a center conductor for enabling connection therebetween (for example, refer to Microwave Filers, Impedance-Matching Networks, And Coupling Structures, P. 475, 1980, ARTECH HOUSE BOOKS).  
       SUMMARY OF THE INVENTION  
       [0006]     When a conductor line becomes close to a metal flange of a connector or a conductor wall, the impedance of the conductor line is reduced due to the influences of the conductor. The reduction of the impedance of the conductor line causes impedance mismatching, which induces reflection at the portion having the reduced impedance, thus resulting in degradation of signal propagating characteristics.  
         [0007]     However, the aforementioned technique for reducing the line width of a conductor line to be equal to the diameter of a center conductor for enabling connection therebetween is a technique for attaining impedance matching between the conductor line and the connector. Therefore, this technique can not alleviate the influences of metal flanges of connectors and conductor walls. Particularly, in cases where signals having higher frequencies are employed, greater parts of signals are influenced thereby, relative to the wavelengths of the signals, which increases the influences of the reduction of the impedance of the conductor line induces, thus resulting in significant degradation of the signal propagating characteristics.  
         [0008]     It is an object of the present invention to provide electronic circuits capable of alleviating the degradation of signal propagating characteristics due to the influences of the metal flanges of connectors or conductor walls, even when conductor lines formed on the upper surface of a substrate are connected to the connectors or pass through through-holes provided through the conductor walls.  
         [0009]     In order to attain the aforementioned object, the present invention provides electric circuits in which the line width of a conductor, which becomes close to a metal flange of a connector or a conductor wall, is gradually reduced from a predetermined position thereon, thereby the reduction of the impedance of the conductor line can be alleviated.  
         [0010]     More specifically, a first aspect of the present invention is an electronic circuit including a substrate made of a dielectric, a conductor line provided on the upper surface of the substrate, a coaxial connector connected to the end portion of the conductor line in the direction of signal propagation and a conductor wall to which the connector is mounted, wherein the line width of the conductor line is gradually reduced to be smaller than the specific line width of the conductor line which is determined by a set impedance of the conductor line from a predetermined position thereon as the conductor line becomes close to the aforementioned end portion.  
         [0011]     With the present invention, by gradually reducing the line width of the conductor line as the conductor line becomes close to its end portion which is connected to the connector in the direction of propagation, the reduction of the impedance of the conductor line can be compensated.  
         [0012]     When the connector includes a metal flange and the metal flange becomes close to the substrate on which the conductor line is provided, the metal flange forms the conductor wall according to the first aspect of the present invention.  
         [0013]     Preferably, in the first aspect of the present invention, a gap is provided between the aforementioned end portion and the conductor wall such that the distance between the aforementioned end portion and the conductor wall is in the range of 3% or more to 10% or less of the specific line width of the conductor line which is determined by the set impedance of the conductor line.  
         [0014]     By providing a gap between the end portion of the conductor line and the conductor wall, it is possible to enhance the effect of compensating for the reduction of the impedance of the conductor line.  
         [0015]     Preferably, in the first aspect of the present invention, the line width of the aforementioned end portion of the conductor line is within the range of 80% or more to 90% or less of the specific line width of the conductor line which is determined by the set impedance of the conductor line.  
         [0016]     By setting the line width of the conductor line to be equal to or less than 90% of the specific line width of the conductor line which is determined by the set impedance of the conductor line, it is possible to compensate for the reduction of the impedance of the conductor line. If the line width of the conductor line is set to be smaller than 80% of the specific line width of the conductor line, this will cause over-compensation for the impedance of the conductor line, thus resulting in an increase of the impedance of the conductor line. Accordingly, it is preferable that the line width of the conductor line is within the range of 80% or more to 90% or less of the specific line width of the conductor line which is determined by the set impedance of the conductor line.  
         [0017]     In the first aspect of the present invention, the distance between the aforementioned end portion of the conductor line and the aforementioned predetermined position is preferably equal to or greater than one-half of the difference between the specific line width of the conductor line which is determined by the set impedance of the conductor line and the line width of the aforementioned end portion and is more preferably equal to or greater than the specific line width of the conductor line which is determined by the set impedance of the conductor line.  
         [0018]     It is preferable that the reduction of the line width of the conductor line is started from a position as far from the conductor wall as possible however, when the distance between the predetermined position at which the reduction of the line width of the conductor line is started and the end portion of the conductor line is equal to or greater than one-half of the difference between the specific line width of the conductor line which is determined by the set impedance of the conductor line and the line width of the aforementioned end portion, it is possible to stably compensate for the reduction of the impedance of the conductor line. Further, when the aforementioned distance is equal to or greater than the specific line width of the conductor line which is determined by the set impedance of the conductor line, it is possible to compensate for the reduction of the impedance of the conductor line with higher stability.  
         [0019]     A second aspect of the present invention is an electronic circuit including a substrate made of a dielectric, a conductor line provided on the upper surface of the substrate and a conductor wall straddling the conductor line, wherein the line width of the conductor line is gradually reduced to be smaller than the specific line width of the conductor line which is determined by a set impedance of the conductor line from a predetermined position thereon as the conductor line becomes close to the conductor wall and the portion of the conductor line which is straddled by the conductor wall has a constant line width.  
         [0020]     With the present invention, the line width of the conductor line is gradually reduced from a predetermined position as the conductor line becomes close to the conductor wall, which can compensate for the reduction of the impedance of the conductor line. Further, the conductor line is formed to have a reduced line width at its portion passed through a through hole provided through the conductor wall, which can compensate for the reduction of the impedance of the conductor line.  
         [0021]     Preferably, in the second aspect of the present invention, the conductor line has a line width within the range of 80% or more to 90% or less of the specific line width of the conductor line which is determined by the set impedance of the conductor line, at a portion straddled by the conductor wall.  
         [0022]     By setting the line width of the portion of the conductor line which is straddled by the conductor wall to be equal to or less than 90% of the specific line width of the conductor line which is determined by the set impedance of the conductor line, it is possible to compensate for the reduction of the impedance of the conductor line. If the aforementioned line width is set to be smaller than 80% of the specific line width of the conductor line, this will result in an increase of the impedance of the conductor line. Accordingly, it is preferable that the line width of the conductor line is set to within the range of 80% or more to 90% or less of the specific line width of the conductor line.  
         [0023]     In the second aspect of the present invention, the distance between the conductor wall and the aforementioned predetermined position is preferably equal to or greater than one-half of the difference between the specific line width of the conductor line which is determined by the set impedance of the conductor line and the line width of the portion of the conductor line which is straddled by the conductor wall and is more preferably equal to or greater than the specific line width of the conductor line which is determined by the set impedance of the conductor line.  
         [0024]     It is preferable that the reduction of the line width of the conductor line is started from a position as far from the conductor wall as possible however, when the distance between the predetermined position at which the reduction of the line width of the conductor line is started and the conductor wall is equal to or greater than one-half of the difference between the specific line width of the conductor line which is determined by the set impedance of the conductor line and the line width of the portion of the conductor line which is straddled by the conductor wall, it is possible to stably compensate for the reduction of the impedance of the conductor line. Further, when the aforementioned distance is equal to or greater than the specific line width of the conductor line which is determined by the set impedance of the conductor line, it is possible to compensate for the reduction of the impedance of the conductor line with higher stability.  
         [0025]     The aforementioned inventions can be arbitrarily combined.  
         [0026]     The electronic circuits according to the present invention can alleviate the degradation of signal propagating characteristics due to the influences of metal flanges of connectors or conductor walls, even when conductor lines formed on the upper surface of a substrate are connected to the connectors or pass through through-holes provided through the conductor walls. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  is a top view of an electronic circuit  100  for explaining an embodiment of the present invention as an example.  
         [0028]      FIG. 2  is a top view of an electronic circuit  200  for explaining another embodiment of the present invention as an example.  
         [0029]      FIG. 3  is a top view illustrating, in an enlarged manner, the portion at which a micro-strip line and the center conductor of the coaxial connector are connected to each other.  
         [0030]      FIG. 4  is a top view of an electronic circuit for explaining an embodiment of another invention of the present application as an example.  FIG. 5  is a top view illustrating, in an enlarged manner, the portion at which the micro-strip line is passed through the through hole provided through the conductor wall.  
         [0000]     Description of the Reference Numerals  
         [0000]    
       
           10 : substrate  
           11 : micro-strip line  
           15 : coaxial connector  
           16 : metal flange  
           17 : center conductor  
           18 : inter-electrode dielectric  
           21 : conductor wall  
           22 : conductor wall  
           23 : through hole  
           100 ,  200  and  300 : electronic circuits 
       
     
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0041]     Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments.  
         [0042]      FIG. 1  is a top view of an electronic circuit  100  for explaining an embodiment of the present invention as an example. In  FIG. 1, 10  is a substrate made of a dielectric,  11  is a micro-strip line as a conductor line provided on the upper surface of the substrate  10 ,  15  is a coaxial connector connected to the end portion of the micro-strip line  11  in the direction of signal propagation,  16  is a metal flange for mounting the coaxial connector  15  onto a conductor wall,  17  is a center conductor of the coaxial connector  15 ,  18  is an inter-electrode dielectric surrounding the center conductor  17  of the coaxial connector  15 , and  21  is a conductor wall to which the coaxial connector  15  is mounted.  
         [0043]     In  FIG. 1 , the coaxial connector  15  is mounted to the conductor wall  21  through the metal flange  16  and the inter-electrode dielectric  18  is filled in through holes provided through the coaxial connector  15  and the conductor wall  21 . The center conductor  17  passes through the inter-electrode dielectric  18  at the center thereof and is connected to the micro-strip line  11 . The conductor wall  21  and the metal flange  16  are connected to the ground of the substrate  10 .  
         [0044]     The micro-strip line is constituted by a ground formed on one surface of the substrate made of a dielectric and a conductor line as a distributed constant line formed on the other surface thereof from the ground. The set impedance of the micro-strip line is determined by the thickness of the conductor line, the line width of the conductor line, the thickness of the substrate and the permittivity of the dielectric constituting the substrate. When the inputting/outputting coaxial connector  15  is connected to the micro-strip line  11  as illustrated in  FIG. 1 , the impedance of the micro-strip line  11  is reduced due to the induction between the conductor wall  21  to which the coaxial connector  15  is mounted and the micro-strip line  11 , at the portion of the micro-strip line  11  near the coaxial connector  15 .  
         [0045]     On the other hand, the specific line width of the micro-strip line  11  is determined by the thickness of the conductor line, the thickness of the substrate, and the permittivity of the dielectric constituting the substrate, for a desired set impedance. The set impedance is increased with decreasing line width of the micro-strip line.  
         [0046]     Therefore, the line width of the micro-strip line  11  is reduced at the portion thereof near the conductor wall  21  to compensate for the reduction of the impedance of the micro-strip line  11  due to the induction. In order to reduce the line width, the line width may be either straightly reduced as illustrated in  FIG. 1  or reduced along a gentle curve such as an arc. Further, the present invention is not limited to the reduction of the line width in an axisymmetric manner in the direction of signal propagation.  
         [0047]      FIG. 2  is a top view of an electronic circuit  200  for explaining another embodiment of the present invention as an example. In  FIG. 2 , the same reference symbols as those in  FIG. 1  represent the same meanings. The electronic circuit  200  is different from that in  FIG. 1  in that the metal flange  16  of the coaxial connector  15  is mounted to the conductor wall  21 , the substrate  10  or a case (not shown) such that the metal flange  16  is in contact with the substrate  10 . In any of the cases, the metal flange  16  is connected to the ground of the substrate  10 . In this case, the metal flange  16  functions as a conductor wall and the impedance of the micro-strip line  11  is reduced at the portion thereof near the metal flange  16 , due to the induction with the metal flange  16 .  
         [0048]     Therefore, the line width of the micro-strip line  11  is reduced at the portion thereof near the metal flange  16  to compensate for the reduction of the impedance of the micro-strip line  11  due to the induction. In order to reduce the line width, the line width may be either straightly reduced as illustrated in  FIG. 2  or reduced along a gentle curve such as an arc. Further, the present invention is not limited to the reduction of the line width in an axisymmetric manner in the direction of signal propagation.  
         [0049]      FIG. 3  is a top view illustrating, in an enlarged manner, the portion at which the micro-strip line  11  illustrated in  FIG. 2  and the center conductor  17  of the coaxial connector  15  are connected to each other. The same reference symbols as those in  FIG. 2  represent the same meanings. The specific line width of the micro-strip line  11  which is determined by a desired set impedance (hereinafter, “the specific line width of the micro-strip line  11  which is determined by a desired set impedance” will be abbreviated to “the specific line width of the micro-sprit line”) is W, the line width of the end portion of the micro sprit line  11  is H, the distance between the end portion of the micro-sprit line  11  and the position at which the reduction of the line width on the micro-sprit line  11  is started is L and the distance between the end portion of the micro-sprit line  11  and the metal flange  16  is S.  
         [0050]     In order to compensate for the reduction of the impedance of the micro-strip line  11  due to the induction with the metal flange  16 , it is preferable that the line width H of the end portion of the micro-strip line  11  is reduced to equal to or less than 90% of the specific line width W of the micro-strip line  11 . This is the amount required for compensating for the reduction of the impedance of the micro-strip line  11 . However, it has been empirically proven that, if the line width is reduced to be smaller than  80 % of the specific line width W of the micro-strip line  11 , this will cause over-compensation for the impedance reduction of the micro-strip line  11 . Accordingly, it is preferable that the line width H falls within the range which satisfies the following equation.
 
0.9 ×W≧H≧ 0.8 ×W   (1)
 
         [0051]     While the line width of the micro-strip line  11  is reduced in an axisymmetric manner in the direction of signal propagation in  FIG. 3 , the present invention is not limited to reduction in an axisymmetric manner.  
         [0052]     The distance L between the end portion of the micro-sprit line  11  and the position at which the reduction of the line width of the micro-strip line  11  is started is preferably equal to or greater than one-half of the difference between the specific line width W of the micro-strip line  11  and the line width H of the end portion of the micro-strip line. Accordingly, it is preferable that the distance L falls within the range which satisfies the following equation.
 
 L≧ ( W−H )/2  (2)
 
         [0053]     Namely, the distance between the end portion of the micro-sprit line  11  and the position at which the reduction of the line width of the micro-strip line  11  is started is preferably equal to or greater than one-half of the amount of reduction of the line width of the micro-strip line  11 . Since the impedance of the micro-strip line  11  is reduced as it becomes close to the metal flange  16 , the line width of the micro-strip line  11  is gradually reduced to compensate for the reduction of the impedance.  
         [0054]     Further, the greater the distance L between the end portion of the micro-sprit line  11  and the position at which the reduction of the line width of the micro-strip line  11  is started, the more preferable. Accordingly, it is preferable that the distance L between the end portion of the micro-sprit line  11  and the position at which the reduction of the line width of the micro-strip line  11  is started falls within the range which satisfies the following equation with respect to the specific line width W of the micro-strip line  11 .
 
L≧W  (3)
 
         [0055]     Namely, the distance between the end portion of the micro-sprit line  11  and the position at which the reduction of the line width of the micro-strip line  11  is started is preferably equal to or greater than the aforementioned specific line width of the micro-strip line  11 .  
         [0056]     Since the impedance of the micro-strip line  11  is significantly reduced due to induction at the region in which the micro-strip line  11  becomes close to the metal flange  16 , it is preferable that a gap is provided between the end portion of the micro-strip line  11  and the metal flange  16  so that the distance S between the end portion of the micro-strip line  11  and the metal flange  16  is equal to or greater than 3% of the specific line width W of the micro-strip line  11 . This is the amount required for preventing significant reduction of the impedance. However, if the distance is increased to be greater than 10%, this will cause impedance mismatching. Accordingly, it is preferable that the distance S falls within the range which satisfies the following equation.
 
0.10 ×W≧S≧ 0.03 ×W   (4)
 
         [0057]     While, in  FIG. 3 , there has been exemplified a case where the micro-strip line  11  becomes close to the metal flange  16 , the present invention may be similarly applied to cases where the micro sprit line  11  becomes close to the conductor wall.  
         [0058]     As previously described, with the electronic circuits according to the embodiments of the present invention, when the conductor line becomes close to the conductor wall, the line width of the conductor line is reduced to be smaller than the specific line width of the conductor line to compensate for the reduction of the impedance. While, in the embodiments of the present invention, the coaxial connector has been exemplified as a connector, the present invention is not limited to a coaxial connector.  
         [0059]     Next, there will be described an electronic circuit partitioned by a conductor wall.  FIG. 4  is a top view of an electronic circuit  300  for explaining another embodiment of the present invention. In  FIG. 4, 10  is a substrate made of a dielectric,  11  is a micro-strip line as a conductor line provided on the upper surface of the substrate  10 ,  22  is a conductor wall straddling the conductor line  11 , and  23  is a through hole provided through the conductor wall  22 .  
         [0060]     In  FIG. 4 , the micro-strip line  11  provided on the upper surface of the substrate  10  passes through the through hole  23  provided through the conductor wall  22 . As previously described, the impedance of the micro-strip line  11  is reduced at the portion thereof near the conductor wall  22 , due to the induction between the micro-strip line  11  and the conductor wall  22 . On the other hand, the set impedance is increased as line width of the micro-strip line  11  is reduced.  
         [0061]     Therefore, the line width of the micro-strip line  11  is gradually reduced to be smaller than the specific line width of the micro-strip line  11  which becomes close to the conductor wall  22  while the line width of the portion of the micro-strip line  11  which is straddled by the conductor wall  22  is maintained at a constant value, so as to compensate for the reduction of the impedance of the micro-strip line  11  due to induction. The line width of the micro-strip line  11  may be either straightly reduced as illustrated in  FIG. 4  or reduced along a gentle curve such as an arc. Further, the present invention is not limited to reduction of the line width in an axisymmetric manner in the direction of signal propagation.  
         [0062]      FIG. 5  is a top view illustrating, in an enlarged manner, the portion of the micro-strip line  11  illustrated in  FIG. 4  which passes through the through hole  23  provided through the conductor wall  22 . The same reference symbols as those in  FIG. 4  represent the same meanings. The specific line width of the micro-strip line  11  is W, the line width of the portion of the micro-strip line  11  which is straddled by the conductor wall  22  is J, and the distance between the conductor wall  22  and the position at which the reduction of the line width of the micro-strip line is started is R.  
         [0063]     In order to compensate for the reduction of the impedance of the micro-strip line  11  due to the induction with the conductor wall  22 , it is preferable that the line width of the portion of the micro-strip line  11  which is straddled by the conductor wall  22  is set to equal to or smaller than 90% of the specific line width W of the micro-strip line  11 . This is the amount required for compensating for the reduction of the impedance of the micro-strip line  11 . However, it has been empirically proven that, if the line width is reduced to be smaller than 80% of the specific line width W of the micro-strip line  11 , this will cause over-compensation for the impedance reduction. Accordingly, it is preferable that the aforementioned line width falls within the range which satisfies the following equation.
 
0.9 ×W≧J≧ 0.8 ×W   (5)
 
         [0064]     While the line width of the micro-strip line  11  is reduced in an axisymmetric manner in the direction of signal propagation in  FIG. 5 , the present invention is not limited to reduction in an axisymmetric manner.  
         [0065]     The distance R between the conductor wall  22  and the position at which the reduction of the line width of the micro-strip line  11  is started is preferably equal to or greater than one-half of the difference between the specific line width W of the micro-strip line  11  and the line width J of the portion of the micro-trip line  11  which is straddled by the conductor wall  22 . Accordingly, it is preferable that the distance R falls within the range which satisfies the following equation.
 
 R≧ ( W−J )/2  (6)
 
         [0066]     Namely, the distance between the conductor wall  22  and the position at which the reduction of the line width of the micro-strip line  11  is started is preferably equal to or greater than one-half of the amount of reduction of the line width of the micro-strip line  11 . Since the impedance of the micro-strip line  11  is reduced as the micro-strip line becomes close to the conductor wall  22 , the line width of the micro-strip line  11  is gradually reduced to compensate for the reduction of the impedance.  
         [0067]     Further, the greater the distance R between the conductor wall  22  and the position at which the reduction of the line width of the micro-strip line  11  is started, the more preferable. Accordingly, it is preferable that the distance R between the conductor wall  22  and the position at which the reduction of the line width of the micro-strip line  11  is started falls within the range which satisfies the following equation, with respect to the specific line width W of the micro-strip line  11 .
 
R≧W  (7)
 
         [0068]     Namely, the distance between the conductor wall  22  and the position at which the reduction of the line width is started is preferably equal to or greater than the specific line width of the micro-strip line which is determined by the aforementioned set impedance of the micro-strip line.  
         [0069]     As previously described, with the electronic circuit according to the embodiment of the present invention, when the conductor line passes through the through hole provided through the conductor wall, the line width of the conductor line is reduced to be smaller than the specific line width of the conductor line to compensate for the reduction of the impedance.  
         [0070]     While there have been described embodiments where a micro-strip line becomes close to a conductor wall, the same effects can be obtained when a coplanar line is employed instead of a micro-strip line. Such a coplanar line is employed for a higher signal frequency region similarly to micro-strip lines, and the specific line width of a coplanar line is determined by the thickness of the conductor line, the thickness of the substrate and the permittivity of the dielectric constituting the substrate, for a desired set impedance. Similarly to a micro-strip line, the impedance of a coplanar line is increased as line width of the coplanar line is reduced. Accordingly, by reducing the line width of such a coplanar line, it is possible to offer a higher effect of compensating for the impedance reduction as aforementioned.  
         [0071]     The present invention can alleviate the degradation of signal propagating characteristics due to the influences of the metal flanges of connectors or conductor walls, even when conductor lines formed on the upper surface of a substrate are connected to the connectors or pass through through-holes provided through the conductor walls.  
         [0072]     The electronic circuits according to the present invention can be utilized in radio units which utilize high-frequency waves, coaxial CATV amplifiers which utilize carrier waves and adjustment thereof.