Abstract:
A plurality of signal lines are provided on one main surface of a dielectric substrate. A plurality of other signal lines are provided on the other main surface of dielectric substrate. The plurality of signal lines on one main surface and the plurality of other signal lines on the other main surface are provided so as to extend in parallel to one another. A ground pattern having its potential fixed is provided between neighboring signal lines on one main surface, and a ground pattern having its potential fixed is provided between neighboring signal lines on the other surface. According to such a structure, a microstrip line that can include a larger number of signal lines on the main surfaces of the dielectric substrate, without increasing a size of the dielectric substrate is obtained.

Description:
[0001]     This nonprovisional application is based on Japanese Patent Application No. 2004-029180 filed with the Japan Patent Office on Feb. 5, 2004, the entire contents of which are hereby incorporated by reference.  
       FIELD OF THE INVENTION  
       [0002]     The present invention relates to a microstrip line having a signal line and a ground conductive layer opposed to each other with a dielectric substrate being interposed.  
       DESCRIPTION OF THE BACKGROUND ART  
       [0003]     Improvement in satellite broadcasting service has recently be demanded. Accordingly, the number of channels used for satellite broadcasting has increased. A single LNB (Low Noise Block Downconverter) receives radio waves transmitted from respective ones of a plurality of satellites. In addition, a circuit such as an LNB including a plurality of output terminals for tuning serving for connection to a tuner and an SW (Switch)-BOX including a plurality of input ports and output ports for IF (Intermediate Frequency) has a complicated structure.  
         [0004]     In an SW-BOX in which a microstrip line is shielded by a chassis  300  and a frame  200  as shown in  FIG. 7 , a larger number of signal lines should be provided on a dielectric substrate  01 , than in a conventional example.  
         [0005]     When a large number of signal lines  102   a ,  102   b , and  102   c  are provided on one main surface of dielectric substrate  101  as shown in  FIG. 8 , a problem of electro-magnetic interference between signal lines  102   a  and  102   b  as well as electro-magnetic interference between signal lines  102   c  and  102   b  arises. In order to suppress the electro-magnetic interference among signal lines and in order to prevent electro-magnetic interference of an external electro-magnetic wave to the signal line, conductive layers attaining a function as ground such as ground patterns  103   a ,  103   b ,  103   c , and  103   d  in  FIG. 8  are provided. Ground patterns  103   a  and  103   d  are provided in order to prevent the electro-magnetic interference of the external electro-magnetic wave to the signal line. Ground patterns  103   a ,  103   b ,  103   c , and  103   d  are connected to a ground pattern  50  through a plurality of plugs (such as through holes)  104  penetrating dielectric substrate  101 , so that potentials of the ground patterns are fixed to a prescribed level.  
         [0006]     In the microstrip line as described above, further increase in the number of signal lines has been desired. To that end, the ground pattern should have a further smaller width. On the other hand, if the width of the ground pattern is too small, the ground pattern will no longer be able to suppress the electromagnetic interference among the signal lines, and accordingly, the width of the ground pattern cannot be made smaller. Instead, an area of the main surface of the dielectric substrate should be increased. Increase in a size of the dielectric substrate, however, is contrary to the demand for a smaller size of the microstrip line.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention was made to solve the above-described problems. An object of the present invention is to provide a microstrip line that can include a larger number of signal lines without increasing a size of the dielectric substrate.  
         [0008]     A microstrip line according to one aspect of the present invention includes at least two signal lines extending in parallel to one another, and a dielectric substrate having one main surface and the other main surface. At least two signal lines are provided such that at least one signal line is present on one main surface and the other main surface respectively.  
         [0009]     According to the structure above, when two signal lines are provided respectively on one main surface and the other main surface, the dielectric substrate is present between the two signal lines, and a large ground conductive layer can be provided on each of one main surface and the other main surface of the substrate. Accordingly, prevention of electromagnetic interference between two signal lines can further be ensured.  
         [0010]     If three or more signal lines are distributed on one main surface and the other main surface, for example, an interval between signal lines on one main surface can be larger than in a microstrip line where two or more signal lines are provided solely on one main surface. Consequently, the ground conductive layer provided between neighboring signal lines can have a larger width. Accordingly, suppression of electro-magnetic interference between the neighboring signal lines can be ensured without increasing an area of the main surface of the dielectric substrate. Accordingly, a microstrip line that includes a larger number of signal lines without increasing a size of the dielectric substrate can be provided.  
         [0011]     Preferably, at least two signal lines described above are provided alternately on one main surface and on the other main surface in a direction in which the dielectric substrate extends, when viewed in a cross section perpendicular to at least two signal lines.  
         [0012]     According to the structure above, when one signal line is provided on each of one main surface and the other main surface, a size of the ground conductive layer can be smaller than in the microstrip line structured such that two signal lines are provided solely on one main surface. Accordingly, prevention of the electro-magnetic interference between two signal lines can further be ensured, while attaining a smaller area of the main surface of the dielectric substrate.  
         [0013]     If four or more signal lines are distributed on one main surface and the other main surface, for example, an interval between signal lines can be substantially identical on a layer on one main surface and on a layer on the other main surface respectively. In other words, a width of a ground conductive layer provided between the signal lines can be substantially identical. Consequently, electro-magnetic interference can be suppressed equally with regard to respective combinations of neighboring signal lines, on the layer in one main surface and on the layer in the other main surface respectively.  
         [0014]     Preferably, when a plurality of signal lines are provided on the other main surface, the plurality of signal lines are opposed to one ground conductive layer on one main surface, with the dielectric substrate being interposed.  
         [0015]     According to the structure above, as compared with a microstrip line in which one signal line is opposed to one ground conductive layer on one-to-one basis, a conductive layer on one main surface can have a width larger than that of another connection conductor. Accordingly, electro-magnetic interference between the signal lines provided so as to opposite each of side surfaces of the ground conductive layer on one main surface can be suppressed in a more ensured manner than electro-magnetic interference between other signal lines.  
         [0016]     A microstrip line according to another aspect of the present invention includes: at least two signal lines extending in parallel to one another; a first dielectric substrate; and a second dielectric substrate provided in parallel to the first dielectric substrate. At least two signal lines are distributed in any at least two layers out of a layer on an outer main surface of the first dielectric substrate, a layer lying between the first dielectric substrate and the second dielectric substrate, and a layer on an outer main surface of the second dielectric substrate.  
         [0017]     According to the structure above, the signal lines are distributed in any two layers out of the three layers. Accordingly, as compared with the microstrip line in which all of the plurality of signal lines are provided solely in any one of the layers on the main surfaces of one dielectric substrate, suppression of electro-magnetic interference between the signal lines can further be ensured, without increasing an area of the main surface of the dielectric substrate. Therefore, a microstrip line that includes a larger number of signal lines without increasing a size of the dielectric substrate can be provided.  
         [0018]     A microstrip line according to yet another aspect of the present invention includes at least three signal lines. Desirably, at least three signal lines are provided such that at least one signal line is present in respective ones of the layer on the outer main surface of the first dielectric substrate, the layer lying between the first dielectric substrate and the second dielectric substrate, and the layer on the outer main surface of the second dielectric substrate. Then, the three layers as above can effectively be utilized.  
         [0019]     In addition, preferably, in the microstrip line including three or more layers and having three or more signal lines, any two signal lines in proximity are provided respectively in any two layers out of the layer on the outer main surface of the first dielectric substrate, the layer lying between the first dielectric substrate and the second dielectric substrate, and the layer on the outer main surface of the second dielectric substrate.  
         [0020]     When specific two signal lines are provided adjacent to each other in one layer, an interval between the adjacent specific signal lines may extremely be smaller than an interval between other adjacent signal lines. Such a disadvantage is avoided if the microstrip line as described above is employed.  
         [0021]     Preferably, when a plurality of signal lines that are adjacent are provided in any at least one layer out of the layer on the outer main surface of the first dielectric substrate, the layer lying between the first dielectric substrate and the second dielectric substrate, and the layer on the outer main surface of the second dielectric substrate, the plurality of signal lines are opposed to one ground conductive layer with the first dielectric substrate or the second dielectric substrate being interposed.  
         [0022]     According to the structure above, as compared with a microstrip line in which one signal line is opposed to one ground conductive layer on one-to-one basis, a ground conductive layer between a plurality of specific signal lines that are adjacent can have a width larger than that of another ground conductive layer between other adjacent signal lines. Accordingly, electro-magnetic interference between the adjacent, specific signal lines can be suppressed in a more ensured manner than electro-magnetic interference between other adjacent signal lines.  
         [0023]     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  illustrates a microstrip line in a first embodiment.  
         [0025]      FIG. 2  illustrates another microstrip line in the first embodiment.  
         [0026]      FIG. 3  illustrates yet another microstrip line in the first embodiment.  
         [0027]      FIG. 4  illustrates a microstrip line in a second embodiment.  
         [0028]      FIG. 5  illustrates another microstrip line in the second embodiment.  
         [0029]      FIG. 6  illustrates yet another microstrip line in the second embodiment.  
         [0030]      FIG. 7  illustrates an apparatus using a conventional microstrip line.  
         [0031]      FIG. 8  illustrates a structure of the conventional microstrip line. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     A microstrip line in embodiments of the present invention will be described hereinafter with reference to the drawings.  
       First Embodiment  
       [0033]     A microstrip line according to the first embodiment will be described with reference to FIGS.  1  to  3 . It is noted that FIGS.  1  to  3  show top views of the microstrip line respectively; section (b) in  FIG. 1  shows a cross-sectional view along the line I-I in section (a) in  FIG. 1 ; section (b) in  FIG. 2  shows a cross-sectional view along the line II-II in section (a) in  FIG. 2 ; and section (b) in  FIG. 3  shows a cross-sectional view along the line III-III in section (a) in  FIG. 3 .  
         [0034]     The microstrip line shown in  FIG. 1  according to the present embodiment includes a dielectric substrate  1 . A signal line  2   a  and a signal line  2   b  are provided on one main surface of dielectric substrate  1 . Signal line  2   a  and signal line  2   b  are parallel to each other. In addition, ground patterns  3   a ,  3   b , and  3   c  are provided on one main surface of dielectric substrate  1 , in parallel to signal line  2   a  and signal line  2   b  respectively.  
         [0035]     A signal line  2   c  is provided on the other main surface of dielectric substrate  1 . Signal line  2   c  extends in parallel to each signal line  2   a  and  2   b . Signal line  2   c  is provided in a position on dielectric substrate  1 , opposite to a position where ground pattern  3   b  is provided. In addition, on the other main surface of dielectric substrate  1 , a ground pattern  3   d  is provided so as to opposite to one side surface of signal line  2   c , while a ground pattern  3   e  is provided so as to opposite to the other side surface of signal line  2   c . Signal line  2   b  is provided in a position on dielectric substrate  1 , opposite to a position where ground pattern  3   d  is provided. Signal line  2   a  is provided in a position on dielectric substrate  1 , opposite to a position where ground pattern  3   e  is provided.  
         [0036]     Ground patterns  3   a ,  3   b ,  3   c ,  3   d , and  3   e  are electrically connected to one another by a plurality of plugs (such as through holes)  4  penetrating dielectric substrate  1 , so as to implement one conductor.  
         [0037]     It is noted that ribs of a conductor cover for electrically shielding the microstrip line from the outside may be connected to ground patterns  3   a ,  3   b ,  3   c ,  3   d , and  3   e  respectively.  
         [0038]     According to the microstrip line in the present embodiment as described above, as compared with the microstrip line in which three signal lines  2   a ,  2   b , and  2   c  are collectively provided solely on one main surface of dielectric substrate  1 , an interval between signal lines  2   a  and  2   b  can be larger. Accordingly, ground pattern  3   b  can have a larger width. Consequently, possibility of electro-magnetic interference between signal lines  2   a  and  2   b  is further reliably reduced. If the rib of the conductor cover for shielding is connected to ground pattern  3   b , the rib having a larger width can be connected to ground pattern  3   b . As a result, prevention of electro-magnetic interference between signal lines  2   a  and  2   b  can further be ensured. Moreover, prevention of electro-magnetic interference between signal lines  2   a  and  2   c  as well as electro-magnetic interference between signal lines  2   b  and  2   c  can further be ensured.  
         [0039]      FIG. 2  illustrates another microstrip line in the present embodiment.  
         [0040]     The structure of the microstrip line shown in  FIG. 2  is substantially similar to that of the microstrip line shown in  FIG. 1 . As portions having the same reference numerals attain substantially similar functions in respective structures shown in FIGS.  1  and  2 , description thereof will not be repeated.  
         [0041]     The microstrip line shown in  FIG. 2  is different from the microstrip line shown in  FIG. 1  in that a ground pattern  3   f  is provided on the other main surface of dielectric substrate  1  and that a signal line  2   d  is provided between ground patterns  3   e  and  3   f . Signal line  2   d  extends in parallel to each signal line  2   a ,  2   b , and  2   c . In addition, signal line  2   d  is provided in a position on dielectric substrate  1 , opposite to a position where ground pattern  3   a  is provided.  
         [0042]     The microstrip line shown in  FIG. 2  has a plurality of signal lines arranged on one main surface and the other main surface of dielectric substrate  1  respectively. In addition, signal lines  2   a ,  2   b ,  2   c , and  2   d  are arranged alternately on one main surface and on the other main surface in a direction in which dielectric substrate  1  extends, when viewed in the cross section along the line II-II. Moreover, respective ground patterns are provided in positions on dielectric substrate  1  opposite to positions on dielectric substrate  1  where the plurality of signal lines are provided respectively.  
         [0043]     According to another microstrip line in the present embodiment as above, a plurality of signal lines can be arranged in high density on one main surface and on the other main surface of dielectric substrate  1  respectively.  
         [0044]      FIG. 3  illustrates yet another microstrip line in the present embodiment. As portions having the same reference numerals attain substantially similar functions in respective structures shown in  FIGS. 1 and 2 , description thereof will not be repeated.  
         [0045]     In the structure shown in  FIG. 3 , signal lines  2   c  and  2   d  are opposed to one ground pattern  3   b , with dielectric substrate  1  being interposed. Therefore, an interval between signal lines  2   a  and  2   b  in the structure shown in  FIG. 3  is larger than that between signal lines  2   a  and  2   b  in the structure shown in  FIG. 2 , and an interval between signal lines  2   c  and  2   d  in the structure shown in  FIG. 3  is smaller than that between signal lines  2   c  and  2   d  in the structure shown in  FIG. 2 . In addition, signal line  2   a  is opposed to ground pattern  3   f , with dielectric substrate  1  being interposed. The microstrip line having such a structure shown in  FIG. 3  is effective when it is necessary to reliably prevent solely electro-magnetic interference between signal lines  2   a  and  2   b , for example.  
       Second Embodiment  
       [0046]     A microstrip line in the second embodiment will be described with reference to FIGS.  4  to  6 . It is noted that sections (a) in FIGS.  4  to  6  show top views of the microstrip line respectively; section (b) in  FIG. 4  shows a cross-sectional view along the line IV-IV in section (a) in  FIG. 4 ; section (b) in  FIG. 5  shows a cross-sectional view along the line V-V in section (a) in  FIG. 5 ; and section (b) in  FIG. 6  shows a cross-sectional view along the line VI-VI in section (a) in  FIG. 6 .  
         [0047]     The microstrip line shown in  FIG. 4  according to the present embodiment includes a dielectric substrate  11   a  and a dielectric substrate  11   b . A signal line  12   a  and a signal line  12   b  are provided on an outer main surface of dielectric substrate  11   a . Signal line  12   a  and signal line  12   b  are parallel to each other. A ground pattern  13   b  is provided on the outer main surface of dielectric substrate  11   a  in a region lying between signal lines  12   a  and  12   b . In addition, ground patterns  13   a  and  13   c  are provided on the outer main surface of dielectric substrate  11   a . Ground patterns  13   a ,  13   b , and  13   c  extend in parallel to each signal line  12   a  and  12   b.    
         [0048]     A signal line  12   d  and a signal line  12   e  are provided between dielectric substrate  11   a  and dielectric substrate  11   b . Signal line  12   d  and signal line  12   e  are parallel to each other. Adhesive layers  15   c  and  15   d  are provided on walls on opposing sides of signal line  12   d . Adhesive layers  15   c  and  15   d  adhere to dielectric substrates  11   a  and  11   b . In addition, adhesive layers  15   a  and  15   b  are provided on walls of opposing sides of signal line  12   e . Adhesive layers  15   a  and  15   b  adhere to dielectric substrates  11   a  and  11   b . Therefore, adhesive layers  15   a ,  15   b ,  15   c , and  15   d  fix a positional relation between dielectric substrates  11   a  and  11   b.    
         [0049]     A ground pattern  13   k  is provided between adhesive layers  15   b  and  15   c  and between dielectric substrates  11   a  and  11   b . In addition, a ground pattern  131  is provided between dielectric substrates  11   a  and  11   b , in a portion outside adhesive layer  15   a . Moreover, a ground pattern  13   j  is provided between dielectric substrates  11   a  and  11   b , in a portion outside adhesive layer  15   d.    
         [0050]     A signal line  12   c  is provided on an outer main surface of dielectric substrate  11   b . In addition, ground patterns  13   d  and  13   e  are provided on the outer main surface of dielectric substrate  11   b . Signal lines  12   a ,  12   b ,  12   c ,  12   d , and  12   e  are provided in parallel to one another.  
         [0051]     Ground patterns  13   a ,  13   b ,  13   c ,  13   d ,  13   e ,  13   j ,  13   k , and  131  are electrically connected to one another by a plurality of plugs (through holes)  14  penetrating dielectric substrate  1 , so as to implement one conductor.  
         [0052]     According to the microstrip line in the present embodiment as described above, the plurality of signal lines are distributed in three layers consisting of a layer on the outer main surface of dielectric substrate  11   a , a layer lying between dielectric substrates  11   a  and  11   b , and a layer on the outer main surface of dielectric substrate  1   b . According to the microstrip line as above, as compared with an example in which all of the plurality of signal lines are provided on one main surface of one dielectric substrate, an interval between the signal lines in one layer can be larger. Accordingly, a ground pattern provided between the signal lines in one layer can have a larger width. Consequently, prevention of electro-magnetic interference between the signal lines in one layer can be ensured. In addition, according to the structure shown in  FIG. 4 , for example, ground pattern  13   b  can have a larger width. As a result, a rib of a shielding conductor connected to ground pattern  13   b  can have a larger width. Therefore, suppression of interference between signal lines  12   a  and  12   b  can further be ensured.  
         [0053]     In the structure shown in  FIG. 4 , in order to implement a microstrip line, a ground pattern is unfailingly provided in a position on the dielectric substrate, opposite to a position on the dielectric substrate where a signal line is provided.  
         [0054]     Another microstrip line in the present embodiment will now be described with reference to  FIG. 5 . The structure of the microstrip line in the present embodiment is substantially similar to that of the microstrip line described with reference to  FIG. 4 . In addition, portions having the same reference numerals attain substantially similar functions in the microstrip lines shown in  FIGS. 4 and 5 . The microstrip line shown in  FIG. 4  is different from the microstrip line shown in  FIG. 5  only in arrangement of a plurality of signal lines.  
         [0055]     More specifically, the microstrip line shown in  FIG. 5  includes signal lines  12   a ,  12   b ,  12   f ,  12   g , and  12   h . Signal lines  12   a ,  12   b ,  12   f ,  12   g , and  12   h  are provided in parallel to one another. In addition, ground patterns  13   a ,  13   b ,  13   c ,  13   f ,  13   g ,  13   h ,  13   j , and  131  are provided in the microstrip line. The microstrip line structured as shown in  FIG. 5  can also attain an effect similar to that obtained by the microstrip line shown in  FIG. 4 .  
         [0056]      FIG. 6  illustrates a structure of yet another microstrip line in the present embodiment. The structure of the microstrip line shown in  FIG. 6  is also substantially similar to that of the microstrip line shown in  FIG. 5 . In addition, portions having the same reference numerals attain substantially similar functions in FIGS.  4  to  6 . The structure shown in  FIG. 6  is different from that shown in  FIG. 5  only in the number and arrangement of a plurality of signal lines.  
         [0057]     More specifically, the microstrip line shown in  FIG. 6  includes signal lines  12   a ,  12   c ,  12   d , and  12   e . Signal lines  12   a ,  12   c ,  12   d , and  12   e  are provided in parallel to one another. In addition, ground patterns  13   a ,  13   b ,  13   d ,  13   e ,  13   j ,  13   k , and  131  are provided in the microstrip line shown in  FIG. 6 . Moreover, adhesive layers  15   a ,  15   b ,  15   c , and  15   d  are provided in the microstrip line shown in  FIG. 6 . The microstrip line structured as shown in  FIG. 6  can also attain an effect similar to that obtained by the microstrip lines shown in  FIGS. 4 and 5 .  
         [0058]     When neighboring signal lines  12   e  and  12   d  are provided in an identical layer as in the microstrip line shown in  FIG. 6 , an interval between signal lines  12   d  and  12   e  in  FIG. 6  may extremely be smaller than an interval between other signal lines. On the other hand, the microstrip line shown in  FIGS. 4 and 5  can avoid such a disadvantage. That is, if two signal lines in proximity are provided in two different layers respectively as shown in  FIGS. 4 and 5 , the disadvantage as above is avoided.  
         [0059]     Meanwhile, if neighboring signal lines  12   d  and  12   e  are provided in an identical layer and opposed to one ground pattern  13   a  with dielectric substrate  11   a  being interposed as in the microstrip line shown in  FIG. 6 , an interval between signal lines  12   d  and  12   e  is small whereas an interval between the signal lines in other layers can be larger. Therefore, when it is necessary to reliably prevent electro-magnetic interference between specific signal lines, such arrangement of the plurality of signal lines as shown in  FIG. 6  may be effective.  
         [0060]     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.