Patent Publication Number: US-9419323-B2

Title: Power combiner/divider of a radial line type impedance matched between a center connector and peripheral outer connectors

Description:
TECHNICAL FIELD 
     The present invention relates to a power combiner/divider, and more particularly relates to a power combiner/divider for combining or dividing power in a VHF band, a UHF band, a microwave band or millimeter-wave band, for example. 
     BACKGROUND ART 
     As a power combiner, there has been known a power combiner in which Wilkinson-type couplers, directional couplers, hybrid couplers or the like are connected in multi-stages or a power combiner which uses radial lines and a power combiner which uses conical lines. When the power combiner is used by setting an input end as an output end and the output end as the input end, the power combiner functions as a power divider and hence, hereinafter, both “power combiner” and “power divider” are referred to as “power combiner/divider”. 
     For example, patent literature 1 discloses a power combiner/divider which uses radial lines as a power combiner/divider used for large power. The power combiner/divider disclosed in patent literature 1 which uses the radial lines is explained in conjunction with  FIG. 4 .  FIG. 4  is a view showing the schematic constitution of the power combiner/divider of the prior art which uses radial lines (a view showing the schematic constitution of the power combiner/divider described in patent literature 1). 
     As shown in the drawing, the power combiner/divider  100  includes a circular box-shaped case  104  which is formed of a top plate  104   a  having a circular shape as viewed in a plan view, a bottom plate  104   b  which faces the top plate  104   a  in an opposed manner, and a side plate  104   c  which covers outer peripheries of the top plate  104   a  and the bottom plate  104   b . A center coaxial connector (center coaxial terminal)  101   a  is formed on a center portion of the top plate  104   a , and a plurality of peripheral coaxial connectors (peripheral coaxial terminals)  101   b  are formed on an outer peripheral portion of the top plate  104   a  equidistantly. A conversion element (coaxial line)  102   a  which extends to the bottom plate  104   b  in the inside of the case  104  is connected to the center coaxial connector  101   a . A conversion element (coaxial line)  102   b  which extends to the bottom plate  104   b  in the inside of the case  104  is connected to each peripheral coaxial connector  101   b . A gap portion which is formed by the top plate  104   a , the bottom plate  104   b  and the side plate  104   c  constituting the case  104  forms a radial line  103 . 
     Further, the power combiner/divider  100  is configured to function as a power combiner when the center coaxial connector  101   a  is used as an output terminal and the peripheral coaxial connectors  101   b  are used as input terminals, and is configured to function as a power divider when the center coaxial connector  101   a  is used as the input terminal and the peripheral coaxial connectors  101   b  are used as the output terminals. When the power combiner/divider  100  functions as the power divider, for example, the power combiner/divider  100  is operated as follows. To be more specific, an incident wave from the center coaxial connector  101   a  is converted into a radial line mode from a coaxial TEM mode by the center conversion element  102   a . A wave which is converted into a radial line mode propagates concentrically toward the outside from the center, and the wave is converted into the coaxial TEM mode from the radial line mode in the same manner by the peripheral conversion elements  102   b , and is outputted to the respective peripheral coaxial connectors  101   b  at the same phase and equal amplitude. 
     Impedance Z of the radial line  103  of the power combiner/divider  100  is set, as expressed by the following formula (formula 1), proportional to a height of radial line  103 , inversely proportional to a distance R from a center portion of the radial line  103 . Assuming the number of combining (or the number of dividing) as N and impedance of the coaxial connector  101   a ,  101   b  as Z 0  in the power combiner/divider  100 , impedance Z of the radial line  103  is expressed by the following formula (formula 2).
 
 Z =√(μ/ε)× H /(2 πR )=η× H /(2 πR )  (formula 1)
     H: height of radial line   η: natural impedance of medium (377Ω in this case)   R: distance from the center of radial line
 
 Z=Z   0   /N   (formula 2)
   

     Further, for example, non-patent literature 1 is disclosed a power combiner/divider which uses a conical line as a power combiner/divider used for large power. 
     The schematic constitution of the power combiner/divider disclosed in non-patent literature 1 which uses a conical line is explained in conjunction with  FIG. 5 .  FIG. 5  is a view showing the schematic constitution of the power combiner/divider of the prior art which uses the conical, line (view showing the schematic constitution of the power combiner/divider disclosed in non-patent literature 1). 
     As shown in the drawing, the power combiner/divider  200  includes a body portion  204  having a circular shape as viewed in a plan view, and a center coaxial connector  201   a  which is formed on a center portion on one surface of the body portion  204 . A plurality of peripheral coaxial connectors  201   b  are formed on an outer peripheral portion of the other surface of the body portion  204 . A coaxial line  202   a  which extends to the inside of the body portion  204  is connected to the center coaxial connector  201   a . Coaxial lines  202   b  which extend to the inside of the body portion  204  are connected to the peripheral coaxial connectors  201   b . A gap portion indicated by symbol  203  in the drawing forms a conical line. In this power combiner/divider  200 , the coaxial line  202   a  constitutes “¼ wavelength impedance converter”, wherein “D 1 ” in the drawing indicates an inner diameter of a coaxial line outer conductor, and “D 2 ” in the drawing indicates an outer diameter of a coaxial line inner conductor. 
     Characteristic impedance (Z 1   0 ) of the coaxial line  202   a  is set so as to satisfy the relationship expressed by the following formula 3 between the inner diameter (D 1 ) of the coaxial line outer conductor and the outer diameter (D 2 ) of the coaxial line inner conductor. Accordingly, the characteristic impedance (Z 1   0 ) of the coaxial line  202   a  can be obtained based on the inner diameter (D 1 ) of the coaxial line outer conductor and the outer diameter (D 2 ) of the coaxial line inner conductor using the following formula 3.
 
 Z 1 0 =60ln D 1 /D 2  (formula 3)
 
     CITATION LIST 
     Patent Literature 
     [patent literature 1]JP-A-5-175712 paragraphs 0002 and 0003, FIG. 6 
     [non-patent literature 1](in Dirk L L.de Villiers, two others, “Design of a Ten-Way Conical Transmission Line Power Combiner”, IEEE transactions on microwave theory and techniques Vol 55, No. 2 (USA) February, 2007, p. 302-308) 
     [non-patent literature 2]“Tsuuken Sousho 1, microwave or millimeter wave circuit” written by Bunichi Oguchi, edited by Electrical Communication Laboratories of Nippon Telegraph and Telephone Public Corporation, published by Maruzen Ltd. 1964, p. 318-325) 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     When the above-mentioned power combiner/divider of the prior art is able to have the constitution which makes possible the designing and manufacture of the power combiner/divider which can easily realize required performance such as required frequency band width, a manufacturing cost can be lowered so that the constitution becomes extremely useful. However, the above-mentioned power combiner/divider of the prior art does not have such a constitution which enables the above-mentioned designing and manufacture of the power combiner/divider. 
     To be more specific, in the power combiner/divider  100  shown in  FIG. 4 , it is necessary to provide an impedance converter having the constitution where impedance on an input end side of the radial line  103  takes the value “Z (see (formula 1), (formula 2))” as viewed from an input end side. However, in patent literature 1, there is no disclosure of an impedance converter having the constitution which takes into account a frequency band width or the like. 
     Further, in the power combiner/divider  200  shown in  FIG. 5 , the impedance converter is provided only to the coaxial line  202   a , when the number of combining (or the number of dividing) becomes large, there arises a technical drawback that the designing and manufacture of the power combiner/divider  200  become difficult. For example, in the above-mentioned power combiner/divider  200 , when characteristic impedance of an output end of “¼ wavelength impedance converter” is set to a value which matches 50Ω and the number of combining N is set to 100 (N=100), impedance of the conical line  203  is matched to “0.5Ω” based on a logic described in non-patent literature 2, and characteristic impedance of an input end of “¼ wavelength impedance converter” is determined (characteristic impedance of the input end of the coaxial line  202   a  is determined). 
     An N-type connector is used in the power combiner/divider  200 , and “the inner diameter (D 1 ) of the coaxial line outer conductor is 7 mm” and hence, when “the outer diameter (D 2 ) of the coaxial line inner conductor” is obtained using the above-mentioned (formula 3), “the outer diameter (D 2 ) of the coaxial line inner conductor becomes 6.94 mm”. In this case, a distance between the inner conductor and the outer conductor of the coaxial line  202   a  ((D 1 −D 2 )/2) becomes “0.03 mm” and hence, the manufacture of the power combiner/divider  200  becomes substantially impossible. That is, in the power combiner/divider  200 , when the number of combining is increased (for example, N=100), the distance between the inner conductor and the outer conductor of the coaxial line  202   a  ((D 1 −D 2 )/2) becomes extremely small so that the manufacture of the power combiner/divider  200  becomes virtually impossible. 
     In the power combiner/divider  200 , it may be possible to make use of a “20D connector” or a “39D connector” having a larger size than the N-type connector in place of the N-type connector. However, the difficulty in manufacture also cannot be overcome in this case. For example, even when the 39D connector having the larger size of these connectors (the 20D connector, the 39D connector) is used, assuming characteristic impedance of an input end of the coaxial line  202   a  as “0.5Ω”, “the outer diameter (D 2 ) of the inner conductor becomes 38.47 mm” for “the inner diameter (D 1 ) of the outer conductor becomes 38.79 mm”. Also in this case, the distance ((D 1 -D 2 )/2) between the inner diameter (D 1 ) of the outer conductor and the outer diameter (D 2 ) of the inner conductor becomes “0.16 mm” and hence, the manufacture of the power combiner/divider  200  becomes extremely difficult. 
     The present invention has been made in view of the above-mentioned technical drawbacks, and it is an object of the present invention to provide a power combiner/divider having the constitution which enables the designing and manufacture of the power combiner/divider which can easily realize required performance such as required frequency band width. 
     Solution to Problem 
     To overcome the above-mentioned drawbacks, according to one aspect of the present invention, there is provided a power combiner/divider which includes: a body portion in which a cavity is formed; a center coaxial connector which is formed on an approximately center portion of the body portion; a plurality of peripheral coaxial connectors which are arranged outside the center coaxial connector concentrically with the center coaxial connector, and are formed on an outer peripheral portion side of the body portion; a radial line which is formed in the cavity formed in the body portion; a center coaxial line which has one end thereof connected to the center coaxial connector and the other end thereof connected to a center portion of the radial line; and a peripheral coaxial line which has one end thereof connected to the peripheral coaxial connector and the other end thereof connected to an outer peripheral portion of the radial line, wherein the peripheral coaxial line is provided for every peripheral coaxial connector, the power combiner/divider is configured to function as a power combiner when the center coaxial connector is used as an output terminal and the peripheral coaxial connector is used as an input terminal, and is configured to function as a power divider when the center coaxial connector is used as the input terminal and the peripheral coaxial connector is used as the output terminal, and an impedance conversion part is provided to the radial line in one or plural stages, and the impedance conversion part is configured to perform impedance matching between the input terminal and the output terminal. 
     In this manner, according to the present invention, in the power combiner/divider, the impedance conversion part is provided to the radial line in one or plural stages and hence, compared to the above-mentioned prior art, the designing and manufacture of the power combiner/divider which can easily realize required performances can be made. To be more specific, the impedance of the radial line is relevant to a height (H) of the radial line, and a distance (R) from the center of the radial line and hence, it is possible to provide the impedance conversion part in the radial line by adjusting the height (H) and the distance (R) (by designing the height (H) and the distance (R) to proper values). Then, the height (H) and the distance (R) are sizes which are sufficiently large compared to a distance between an inner conductor and an outer conductor of the coaxial line and hence, according to the present invention, there is no possibility that the designing and manufacture of the power combiner/divider will become difficult different from the above-mentioned power combiner/divider  200  described in non-patent literature 1. Particularly, by adopting “¼ wavelength multi-stage impedance conversion part” disclosed in non-patent literature 2 as the impedance conversion part, the designing and manufacture of the power combiner/divider which can easily realize required performances can be made. 
     Further, it is preferable that an impedance conversion part is provided to the center coaxial line in one or plural stages. 
     The reason such a constitution is adopted is as follows. That is, in the power combiner/divider, to acquire a large band characteristic, it is necessary to increase the number of stages of the impedance conversion part provided to the radial line. However, when the size of the power combiner/divider per se is limited, the number of stages of the impedance conversion part cannot be increased. This is because when the number of stages is increased, the size of the power combiner/divider will become large. In view of the above, by arranging the impedance conversion part both at the radial line and at the center coaxial line which is connected to the radial line, even when the size of the power combiner/divider is limited, the power combiner/divider can acquire advantageous effects substantially equal to the above-mentioned advantageous effects. 
     Further, it is preferable that an impedance conversion part is provided to said each peripheral coaxial line in one or plural stages. 
     The reason such a constitution is adopted is as follows. That is, the height of the radial line and the number of combining (or the number of dividing) have the inverse proportional relationship and hence, when the number of combining becomes large, the height of the radial line becomes extremely small so that a manufacturing (working) error will influence a characteristic of the radial line. On the other hand, the height of the radial line and the impedance of the radial line have the proportional relationship. Accordingly, the impedance conversion part is provided to the peripheral coaxial line, characteristic impedance of an output end of the peripheral coaxial line is set higher than characteristic impedance of an input end of the peripheral coaxial line, and impedance of an input end of the radial line is increased thus setting the height of the input end of the radial line higher. Accordingly, even when the number of combining of the power combiner/divider becomes large, the height of the input end of the radial line can be set high and hence, the occurrence of a manufacturing (working) error can be prevented. 
     Further, it is preferable that a high impedance part is arranged parallel to the peripheral coaxial line at a connecting portion between the peripheral coaxial line and the radial line. 
     By providing the high impedance part as described above, the generation of undesired reactance can be prevented and hence, the influence exerted by a manufacturing error (irregularities of performance or the like) can be suppressed. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a power combiner/divider having the constitution which enables the designing and manufacture of the power combiner/divider which can easily realize required performance such as required frequency band width. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view showing a cross section of a power combiner/divider according to a first embodiment of the present invention; 
         FIG. 2  is schematic view for explaining sizes specific to the power combiner/divider according to the first embodiment of the present invention; 
         FIG. 3  is a view showing a cross section of a power combiner/divider according to a fourth embodiment of the present invention; 
         FIG. 4  is a view showing the schematic constitution of a power combiner/divider of a related art which uses a radial line; and 
         FIG. 5  is a view showing the schematic constitution of a power combiner/divider of the related art which uses a conical line. 
     
    
    
     DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, the power combiner/divider according to the respective embodiments of the present invention is explained in conjunction with drawings. In these embodiments, for the sake of convenience of explanation, an example where a power combiner/divider is used as a power combiner is given. Also in the explanation of this embodiment, formulae and symbols indicating height, distance and the like used in these embodiments are equal to those explained above in conjunction with the prior art. 
     &lt;&lt;First embodiment&gt;&gt; 
     Firstly, the power combiner/divider according to the first embodiment of the present invention is explained in conjunction with  FIG. 1  and  FIG. 2 . The power combiner/divider W 1  of the first embodiment is characterized by an impedance conversion part provided to a radial line  13 . The principal of combining or dividing power is equal to the conventionally known principle. Accordingly, the above-mentioned technical feature is explained in detail, while the constitutions other than the above-mentioned technical feature are explained in a simplified manner. 
     As shown in the drawing, the power combiner/divider W 1  of the first embodiment includes: a body portion  10  in which a cavity is formed; a center coaxial connector  11  which is formed on a center portion on one surface (upper surface) of the body portion  10 ; a plurality of peripheral coaxial connectors  14  which are formed on an outer peripheral portion of the body portion  10 ; a radial line  13  which is formed of a cavity formed in the inside of the body portion  10 ; a center coaxial line  12  which is formed on the center portion of the body portion  10 ; and a plurality of peripheral coaxial lines  15  which are formed on an outer peripheral portion of a radial line  13 . The peripheral coaxial connectors  14  are arranged outside the center coaxial connector  11  and concentrically around a center portion of the center coaxial connector  11  equidistantly. Further, the cavity formed in the inside of the body portion  10  is formed into a circular shape as viewed in a plan view ranging from a center portion to the outer peripheral portion of the body portion  10 . 
     Further, the center coaxial line  12  has one end thereof connected to the center coaxial connector  11  and the other end thereof connected to a center portion of the radial line  13 . Further, the peripheral coaxial line  15  has one end thereof connected to the peripheral coaxial connector  14  and the other end thereof connected to an outer peripheral portion of the radial line  13 . The peripheral coaxial line  15  is provided for every peripheral coaxial connector  14 , and the number of peripheral coaxial lines  15  is equal to the number of peripheral coaxial connectors  14  (the number of combining N). That is, in the power combiner/divider W 1 , N pieces of peripheral coaxial connectors  14  are connected in parallel. 
     The body portion  10  is constituted of “a lid body portion  10   a  and a box body portion  10   b ” which are formed using a conductor as shown in  FIG. 1 . Further, the lid body portion  10   a  is formed into a circular shape as viewed in a plan view, and a cylindrical projecting portion  10   a   1  ( FIG. 1 ) which projects toward one side (an upper side in  FIG. 1  and  FIG. 2 ) is formed on a center portion of the lid body portion  10   a . An upper end portion of the projecting portion  10   a   1  is closed, and the center coaxial connector  11  is provided to the upper end portion. The center coaxial line  12  which has one end thereof connected to the center coaxial connector  11  passes through an inner cylindrical side of the cylindrical projecting portion  10   a   1 . The center coaxial line  12  which passes through the inner cylindrical side of the projecting portion  10   a   1  extends to a center portion of the box body portion  10   b  on an upper surface side. Although the body portion  10  is formed of the lid body portion  10   a  and the box body portion  10   b  in this embodiment, the present invention is not particularly limited to such a constitution. For example, the body portion  10  may be constituted of an integrally formed part. 
     The box body portion  10   b  has a circular shape as viewed in a plan view (being formed into a circular shape having the same diameter as the lid body portion  10   a ). The box body portion  10   b  has one surface (upper surface) thereof recessed in a concave shape, and the other surface (lower surface) thereof formed into a planar shape thus forming a bottom portion. On the upper surface having a concave shape, stepped portions are formed concentrically from a center portion of the box body portion  10   b . In this embodiment, a circular center portion is formed at the center portion of the upper surface, and the stepped portions are concentrically formed on the outer periphery of the circular center portion in 3 stages. 
     The upper surface of the box body portion  10   b  and a lower surface of the lid body portion  10   a  are arranged to face each other in an opposed manner, and the lid body portion  10   a  is placed on and fixed to the upper surface of the box body portion  10   b  thus forming the body portion  10  having a circular box shape as viewed in a plan view. The cavity having the stepped portions is formed in the inside of the body portion  10  by the lower surface of the lid body portion  10   a  and the upper surface (the upper surface on which the stepped portions are formed) of the box body portion  10   b . The cavity having the stepped portions forms the radial line  13 , and an impedance conversion part is formed. The impedance conversion part performs impedance matching between the peripheral coaxial connector (input end)  14  and the center coaxial connector (output end)  11 . A range indicated by symbol “L 1 ” shown in  FIG. 2  indicates a range of the radial line  13  in the radial direction. A range indicated by symbol “L 2 ” indicates a range of the impedance conversion part provided in the radial line  13  in the radial direction. 
     Further, in this embodiment, a case is exemplified where all of the center coaxial connector  11 , the peripheral coaxial connector  14 , the center coaxial line  12  and the peripheral coaxial line  15  have the same characteristic impedance of “50Ω”. Further, in this embodiment, the peripheral coaxial lines  15  having characteristic impedance of “50Ω” are connected in parallel with the same number of combining N and hence, the impedance of an input end of the radial line  13  becomes ((50/N)Ω). 
     On the other hand, the impedance of an output end of the radial line  13  is connected to the center coaxial line  12  having characteristic impedance of 50Ω and hence, it is necessary to set the impedance of the output end of the radial line  13  to “50Ω”. 
     In this manner, in this embodiment, the impedance conversion part provided to the radial line  13  is designed to convert impedance from “(50/N)Ω” to “50Ω”. 
     Although the constitution of the impedance conversion part provided to the radial line  13  is not particularly limited, it is desirable that the impedance conversion part adopts the constitution such as “Chebyshev ¼ wavelength multi-stage type” or “maximally flat ¼ wavelength multi-stage type”. This is because by adopting the constitution of the impedance conversion part of a ¼ wavelength multi-stage type, the impedance conversion part can be designed to acquire a matching condition within a required frequency band width. In this embodiment, the impedance conversion part is constituted of ¼ wavelength portions in 3 stages. The principle of the impedance conversion part of a ¼ wavelength multi-stage type is disclosed in the above-mentioned non-patent literature 2 and hence, the detailed explanation is omitted. 
     As described in the above-mentioned (formula 1), impedance (Z) of the radial line  13  is decreased toward the outer peripheral portion from the center portion of the radial line  13  inversely proportional to a distance R from the center portion of the radial line  13  as shown in  FIG. 2 . Accordingly, when the impedance conversion part in plural stages is provided to the radial line  13 , impedance does not become constant within a range of “¼ wavelength” in respective stages of the impedance conversion part thus giving rise to a drawback that the designing of the impedance conversion part becomes complicated. 
     Accordingly, in this embodiment as shown in  FIG. 2 , “the height (H) of the radial line  13 ” is increased proportional to “the distance (R) from the center portion of the radial line  13 ” such that the impedance of each stage becomes constant within a range of “¼ wavelength” thus facilitating the designing and manufacture of the impedance conversion part whereby the above-mentioned drawback can be overcome. 
     To be more specific, as shown in  FIG. 2 , in the first-stage stepped portion adjacent to the center portion of the radial line  13 , the height (H 1 ) is set to be increased proportional to the distance (R) from the center portion of the radial line  13 . Also in the second-stage stepped portion from the center portion of the radial line  13 , the height (H 2 ) is designed to be increased proportional to the distance (R) from the center portion of the radial line  13 . In the same manner, also in the third-stage stepped portion from the center portion of the radial line  13 , the height (H 3 ) is designed to be increased proportional to the distance (R) from the center portion of the radial line  13 . In this manner, according to this embodiment, the above-mentioned drawback can be overcome by setting the height (H) corresponding to the distance (R) for every stage. 
     The size of the impedance conversion part depends on frequency (wavelength). For example, the size of the impedance conversion part becomes “75 mm” in case of a microwave band (3GHz, wavelength=100 mm), and becomes “25 mm” in case of a millimeter wave band (9GHz, wavelength=33.3 mm). 
     As a factor employed for determining the size of the power combiner/divider W 1 , besides frequency (wavelength), a size of a flange of the coaxial connector (peripheral coaxial connector  14 ) which constitutes an input end is named. Although it depends on inputted power, in general, an “N type” coaxial connector or a “SMA type” coaxial connector is used as the coaxial connector of the power combiner/divider W 1 . A flange size of the “N type” coaxial connector is “25 mm”, and a flange size of the “SMA type” coaxial connector is “13 mm”. 
     For example, assuming the number of combining N to “50(100)”, when the “N type” coaxial connectors (peripheral coaxial connectors  14 ) are continuously arranged on the same circumference, a radius of the power combiner/divider W 1  becomes approximately “200 mm (400 mm)”. Further, assuming the number of combining N to “50 (100)”, when the “SMA type” coaxial connectors (peripheral coaxial connectors  14 ) are continuously arranged on the same circumference, a radius of the power combiner/divider W 1  becomes approximately “105 mm (210 mm)”. These sizes are sufficient for providing the impedance conversion part to the radial line  13  and hence, these sizes are not sizes which make the designing and manufacture of the power combiner/divider difficult different from the above-mentioned power combiner/divider  200  of the prior art (see  FIG. 5 ). 
     As has been explained heretofore, according to the first embodiment of the present invention, the impedance conversion part is provided to the radial line  13  and hence, compared to the above-mentioned prior art, the designing and manufacture of the power combiner/divider which can easily realize required performances can be made. To be more specific, “the height (H) of the radial line  13 ” and “the distance (R) from the center portion of the radial line  13 ” are sufficiently large compared to the distance between the inner conductor and the outer conductor of the coaxial line and hence, there is no possibility that the designing and manufacture of the power combiner/divider becomes difficult different from the above-mentioned power combiner/divider  200  of the prior art (see  FIG. 5 ). Particularly, in the first embodiment, the impedance conversion part is constituted of “¼ wavelength multi-stage-type impedance conversion part” and “the height (H) of the radial line  13 ” is increased proportional to “the distance (R) from the center portion of the radial line  13 ” such that the impedance of each stage becomes constant within a range of “¼ wavelength” thus facilitating the designing and manufacture of the impedance conversion part whereby the required performance can be realized. 
     &lt;&lt;Second Embodiment&gt;&gt; 
     Next, the second embodiment of the present invention is explained. The second embodiment is an embodiment obtained by partially modifying the constitution of the first embodiment and hence, for the sake of convenience of explanation, the constitutions of this embodiment identical to (and corresponding to) the constitutions of first embodiment are explained using the same symbols. Further, in the explanation of the second embodiment, parts which make this embodiment differ from the above-mentioned first embodiment are explained mainly and the explanation of the constitution of this embodiment similar to the constitution of the first embodiment is simplified. 
     To acquire a large band characteristic in the above-mentioned first embodiment, it is necessary to increase the number of stages of “¼ wavelength multi-stage-type impedance conversion part” provided to a radial line  13 . In this case, although the size of the power combiner/divider W 1  of the first embodiment becomes large, this constitution has a drawback that the constitution cannot cope with a case that the size of the power combiner/divider W 1  is limited. 
     Accordingly, the second embodiment overcomes the above-mentioned drawback by arranging “¼ wavelength multi-stage-type impedance conversion part” on both a radial line  13  and a center coaxial line  12  which follows the radial line  13  in a dividing manner in the power combiner/divider W 1 . 
     To be more specific, in the power combiner/divider W 1  of the second embodiment, in addition to the constitution of the first embodiment, the “¼ wavelength multi-stage-type impedance conversion part” is also provided to the center coaxial line  12 . The number of stages of the “¼ wavelength multi-stage-type impedance conversion part” provided to the radial line  13  and the number of stages of the “¼ wavelength multi-stage-type impedance conversion part” provided to the center coaxial line  12  are determined by taking into account the allowable size of the power combiner/divider W 1 , the characteristic impedance of an input end of the center coaxial line  12  and the like (that is, the outer diameter of the inner conductor/the inner diameter of the outer conductor of the center coaxial line  12 ). 
     In this manner, the second embodiment can acquire advantageous effects substantially equal to the advantageous effects of the above-mentioned first embodiment. Further, according to the second embodiment, by arranging “¼ wavelength multi-stage-type impedance conversion part” on both the radial line  13  and the center coaxial line  12  which follows the radial line  13  in a dividing manner, this embodiment can cope with the case where the size of the power combiner/divider W 1  is limited or the like. 
     &lt;&lt;Third Embodiment&gt;&gt; 
     Next, the third embodiment of the present invention is explained. The third embodiment is an embodiment obtained by partially modifying the constitution of the first embodiment or the second embodiment and hence, for the sake of convenience of explanation, the constitutions of this embodiment identical to (and corresponding to) the constitutions of the first embodiment are explained using the same symbols. Further, in the explanation of the third embodiment, parts which make this embodiment differ from the first embodiment are explained mainly and the explanation of the constitution of this embodiment similar to the constitution of the first embodiment is simplified. 
     In the power combiner/divider (for example, the power combiner/divider W 1  of the first embodiment) which uses a radial line, the height (H) of the radial line and the number of combining (N) have the inverse proportional relationship (H=(Z 0 ·2π·R)/(N·ρ)). Accordingly, when the number of combining (N) is increased, the height of the radial line  13  becomes extremely low so that a manufacturing (working) error influences a characteristic of the radial line  13 . For this reason, the power combiner/divider W 1  of the first embodiment (and the second embodiment) has a drawback that extremely high working accuracy is required when the number of combining (N) becomes large. 
     In the third embodiment, an impedance conversion part is provided to a plurality of peripheral coaxial lines  15  respectively so that characteristic impedance of an output end of the peripheral coaxial line  15  is set higher than characteristic impedance of an input end of the peripheral coaxial line  15  thus overcoming the above-mentioned drawback. The constitutions of the third embodiment are substantially equal to the constitutions of the first embodiment (and the second embodiment) except for the constitution that the impedance conversion part is provided to the plurality of peripheral coaxial lines  15  respectively. 
     To be more specific, in the power combiner/divider W 1  of the first embodiment (and the second embodiment), the characteristic impedance of the peripheral coaxial line  15  connected to the input end of the radial line  13  is set to the same value as the characteristic impedance of the peripheral coaxial connector  14  connected to the input end of the peripheral coaxial line  15 . To the contrary, in the third embodiment, the impedance conversion part (¼ wavelength multi-stage-type impedance conversion part or the like) is provided to the peripheral coaxial line  15  so that characteristic impedance of the output end of the peripheral coaxial line  15  is set higher than characteristic impedance of the input end of the peripheral coaxial line  15  and hence, impedance of the input end of the radial line  13  can be set to a high value thus overcoming the above-mentioned drawback. 
     The reason such a constitution is adopted is that, as expressed in the above-mentioned (formula 1), the height (H) of the radial line  13  and impedance (Z) of the radial line have the proportional relationship. That is, by adopting the constitution of the third embodiment, the height of the input end of the radial line  13  can be set higher and hence, it is possible to prevent a manufacturing (working) error from influencing the characteristic of the radial line  13 . 
     In this manner, the third embodiment can acquire advantageous effects substantially equal to the above-mentioned advantageous effects of the first embodiment. Further, according to the third embodiment, even when the number of combining (N) of the power combiner/divider W 1  becomes large, the height of the input end of the radial line  13  can be set high and hence, the occurrence of a manufacturing (working) error can be prevented. 
     &lt;&lt;Fourth Embodiment&gt;&gt; 
     Next, the fourth embodiment of the present invention is explained in conjunction with  FIG. 3 .  FIG. 3  is a schematic view showing a cross section of a power combiner/divider according to the fourth embodiment of the present invention. The fourth embodiment is an embodiment obtained by partially modifying the constitution of the first embodiment and hence, for the sake of convenience of explanation, the constitutions of this embodiment identical to (and corresponding to) the constitutions of first embodiment are explained using the same symbols. Further, in the explanation of the fourth embodiment, parts which make this embodiment differ from the first embodiment are explained mainly, while the explanation of the constitution of this embodiment similar to the constitution of the first embodiment is simplified. 
     As shown in the drawing, in a power combiner/divider W 2  of the fourth embodiment, in the vicinity of an outer peripheral portion of an upper surface of a box body portion  11  constituting a body portion  10 , a gap portion (high impedance portion)  17  which extends toward a bottom portion from the upper surface is formed at a connecting portion between a peripheral coaxial line  15  and a radial line  13 . The constitutions of the fourth embodiment are substantially equal to the constitutions of the first embodiment except for the gap portion  17 . 
     To be more specific, in the power combiner/divider W 2  of the fourth embodiment, a height size (h) of the gap portion  17  is set odd times as large as “¼ wavelength” of a microwave or a millimeter wave. Further, an opening portion of the gap portion  17  is in an electrically open state. By constituting the gap portion  17  in this manner, a high impedance part which can ignore impedance at a grounded portion can be formed at a connecting portion with the radial line  13 , and the generation of undesired reactance can be prevented since the opening portion of the gap portion is in an electrically open state. Accordingly, by adopting the constitution of the fourth embodiment, the influence (irregularities in performance) exerted by a manufacturing error can be suppressed. 
     Here, the present invention is not limited to the above-mentioned embodiments (the first embodiment to the fourth embodiment), and various modifications are conceivable without departing from the gist of the present invention. 
     For example, in this embodiment, although the impedance conversion part is constituted of ¼ wavelength portions in 3 stages in the radial line  13 , the impedance conversion part is not limited to such a constitution. For example, in the radial line  13 , an impedance conversion part constituted of ¼ wavelength portions in 4 stages or more may be provided, or an impedance conversion part constituted of a ¼ wavelength portion in 1 stage may be provided. Further, although “the ¼ wavelength multi-stage-type impedance conversion part” is provided to the coaxial lines (the center coaxial line  12 , the peripheral coaxial lines  15 ) in this embodiment, this arrangement of the impedance conversion part merely constitutes one example. The impedance conversion part may be formed of a ¼ wavelength portion in 1 stage, for example. 
     Further, the gap portion  17  of the fourth embodiment may be added to the constitution of the second embodiment, or the gap portion  17  of the fourth embodiment may be added to the constitution of the third embodiment. 
     REFERENCE SIGNS LIST 
     
         
         W 1 ,W 2  . . . power combiner/divider 
           10  . . . body portion 
           10   a  . . . lid body portion(body portion) 
           10   a   1  . . . projecting portion(lid body portion(body portion)) 
           10   b  . . . box body portion(body portion) 
           11  . . . center coaxial connector 
           12  . . . center coaxial line 
           13  . . . radial line 
           14  . . . peripheral coaxial connector 
           15  . . . peripheral coaxial line 
           17  . . . gap portion(high impedance portion)