Abstract:
A feed line in the form of a trip late line that runs from a waveguide/triplate-line converter coupled to a radio to a plurality of patch antennas in a cluster pattern. The width and length of a section of said feed line between the waveguide/triplate-line converter and the branch point nearest thereto are set such that the impedance of said section directly matches the parallel combination of the impedances of branches beyond said branch point and the loss in said section is kept to or below a predetermined upper limit.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a feed line formed as a triplate line that runs from a waveguide/triplate-line converter coupled to a radio to a plurality of patch antennas in a cluster pattern. 
         [0002]    Priority is claimed on Japanese Patent Applications No. 2013-127068, filed on Jun. 18, 2013, the contents of which are incorporated herein by reference. 
       BACKGROUND ART 
       [0003]    In satellite communication systems and fixed wireless access (FWA) systems in which wireless transmission is performed in microwave bands and millimeter wave bands over a 10 GHz band, a planar antenna made up of many patch antennas is often employed, and a feed line for these patch antennas is formed as a triplate line in which a structure thereof is simple, parallel feeding can be precisely realized at low cost, and furthermore, gain and efficiency can be highly secured. 
         [0004]    As illustrated in  FIG. 4 , a conventional triplate feed-type planar antenna is made up of, for example, a ground plane  41 , a foam sheet  42 - 1 , a flexible substrate  43 , a foam sheet  42 - 2 , and a slot plate  44  that are laminated. 
         [0005]    Also, the elements laminated in this way are constituted as follows. 
         [0006]    (1) The ground plane  41  is formed with a pattern corresponding to a plane ground on an upper surface thereof. 
         [0007]    (2) The foam sheets  42 - 1  and  42 - 2  are constituted as cushion material, an insulator, and a dielectric that sandwich the flexible substrate  43  from opposite surfaces thereof. 
         [0008]    (3) Along with an array of rectangular patch antennas  43 A 1,1  to  43 Am,n arranged in a lattice pattern, a feed line  43 F implementing tournament feeding for these patch antennas is formed at the flexible substrate  43  as a circuit pattern. 
         [0009]    (4) Lattice-patterned slot openings  44 S 1,1  to  44 Sm,n are formed in a top surface of the slot plate  44  at regions individually corresponding to the patch antennas, and a plane ground pattern is formed on an overall surface other than these regions. 
         [0010]    For example, as illustrated in  FIG. 5 , a feed system of this triplate feed-type planar antenna is constituted as follows. 
         [0011]    A waveguide/triplate-line converter (hereinafter referred to simply as “converter”)  43 C is disposed at a predetermined region surrounded by the patch antennas  43 A 1,1  to  43 Am,n on the flexible substrate  43 . 
         [0012]    Furthermore, a main line  43 B is formed on the flexible substrate  43 . In the main line  43 B, one end thereof continues to a probe  43 CP inserted from a sidewall into a pipe of a waveguide  43 C WC  constituting the converter  43 C, the other end thereof continues to a bus bar  43 FM of a feed line  43 F implementing the aforementioned tournament feeding, and a width thereof is identical to that of the bus bar  43 FM. 
         [0013]    Also, a transformer  43 T, a width of which is set to be narrower than that of the bus bar  43 FM, is formed as a circuit pattern in the vicinity of a connection point with the main line  43 B on the bus bar  43 FM. 
         [0014]    As illustrated in  FIG. 6 , among the constituent elements of the converter  43 C, the waveguide  43 C WC  paired with the aforementioned probe  43 CP is made up of the following elements. 
         [0015]    (1) A waveguide flange  43 CF that corresponds to (is coupled to) one end of a rectangular waveguide connected to a radio (not illustrated) has a rectangular opening continuing into a pipe of the rectangular waveguide, and is disposed in a state in which the opening is in contact with a region corresponding to the ground plane  41 . 
         [0016]    (2) An annular member  43 CR that is formed at the foam sheet  42 - 1 , the flexible substrate  43 , and the foam sheet  42 - 2 , which are laminated, is inserted into a through-hole equivalent to a virtual extension part of the opening, and is formed as a dielectric cylinder having a through-hole through which the aforementioned probe  43 CP passes. 
         [0017]    (3) An annular member  43 Cr that is stacked on the annular member  43 CR via the slot plate  44  and causes the inside of the pipe of the waveguide flange  43 CF to extend to the outside of the slot plate  44  along with the annular member  43 CR. 
         [0018]    (4) A short plate  43 Cs which is installed across a top including an opening of the annular member  43 Cr, and in which holes, through which screws  43 S- 1  to  43 S- 5  to be described below pass, are formed in the top. 
         [0019]    (5) The screws  43 S- 1  to  43 S- 5  that are screwed to screw holes formed in the waveguide flange  43 CF in correspondence with these holes, and thereby clamp the ground plane  41 , the annular member  43 CR, the slot plate  44 , and the annular member  43 Cr between the waveguide flange  43 CF and the short plate  43 Cs. 
         [0020]    The ground plane  41 , the annular member  43 CR, the slot plate  44 , and the annular member  43 Cr are previously formed with holes (not illustrated) into which the screws  43 S- 1  to  43 S- 5  are inserted and have inner walls of dimensions and shapes to stably come in contact with sidewalls of these screws  43 S- 1  to  43 S- 5 . 
         [0021]    In the triplate feed-type planar antenna having this constitution, the waveguide  43 C WC  is sandwiched between the aforementioned waveguide flange  43 CF and the short plate  43 Cs by the screws  43 S- 1  to  43 S- 5 , and is defined by inner walls of the ground plane  41 , the annular member  43 CR, the slot plate  44 , and the annular member  43 Cr that are electrically connected by these screws  43 S- 1  to  43 S- 5 . 
         [0022]    Furthermore, in  FIG. 5 , the probe  43 CP converts a transmission wave, which is output by a transmitter (not illustrated) and is handed over as a basic mode of an electromagnetic field propagated in the pipe of the waveguide  43 C WC , into an “electromagnetic field of the triplate line.” 
         [0023]    On the flexible substrate  43 , the “electromagnetic field of the triplate line” is handed over to the bus bar  43 FM via the aforementioned main line  43 B and the transformer  43 T, and is subjected to the tournament feeding to the patch antennas  43 A 1,1  to  43 Am,n. 
         [0024]    In the this feeding process, as the width of the transformer  43 T is set to be narrower than that of the bus bar  43 FM, the transformer  43 T performs impedance matching between the bus bar  43 FM and the main line  43 B, the widths of which are equally formed. 
         [0025]    Therefore, the tournament feeding to the patch antennas  43 A 1,1  to  43 Am,n is inexpensively realized without damage to the triplate line, which makes high gain and efficiency possible. 
         [0026]    The prior art related to the present invention includes Patent Literature 1 shown below. 
         [0027]    Patent Literature 1 discloses a planar antenna that has a constitution of a triplate in which strip lines formed in a board are sandwiched with a space of about 2 mm from opposite sides by ground boards, a radiation element is formed at one of the ground boards, and power is supplied to respective radiation elements by feed lines of the strip lines, and is characterized in that a stripline/waveguide converter is formed in which the strip lines have final feed points whose widths are about 1.7 mm and are inserted from both sides of a waveguide having a size of 19.05 mm×9.525 mm, an interval between the two strip lines is set to about 0.5 to 1.0 mm, and a phase difference between power input into the waveguide from both of the strip lines is set to 180°, thereby making it possible to supply power using a wavelength capable of achieving good power combining (branching) efficiency. 
       CITATION LIST 
     Patent Literature 
       [0028]    Patent Literature 1 
         [0029]    Japanese Examined Patent Application, Second Publication No. H07-52803 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0030]    Incidentally, in the aforementioned triplate feed-type planar antenna, if the transmission wave has power of about 50 watts, which is considerably greater than conventional power of 25 watts, a loss converted into heat by the main line  43 B increases. 
         [0031]    Furthermore, the main line  43 B is sandwiched between the foam sheets  42 - 1  and  42 - 2  having heat insulating properties, and is also sandwiched again by the ground plane  41  and the slot plate  44 , and hence is heated up to about 150° C. 
         [0032]    Also, as mentioned above, the transformer  43 T is narrow in width compared to the main line  43 B and the bus bar  43 FM, and hence is heated up to, for instance, about 115° C. 
         [0033]    However, the foam sheets  42 - 1  and  42 - 2  have low heat-resistant temperatures of 90° C. to 130° C., and hence regions abutting the main line  43 B and the transformer  43 T are melted. In this state, characteristics such as characteristic impedance suitable for the triplate line are degraded, and hence transmission of a desired high-power transmission wave is impeded. 
         [0034]    That is, in the conventional example, since a heat radiation characteristic of the triplate line constituting the feed line is fundamentally low, as transmission power is increased, securing of the characteristic and stability may be damaged, and overall performance and reliability may be remarkably damaged. 
         [0035]    An object of the present invention is to provide a feed line capable of inexpensively adapting to large power without being accompanied by a change in basic constitution and an increase in physical size. 
       Solution to Problem 
       [0036]    According to a first aspect of the present invention, a feed line is provided, which is formed as a triplate line that runs from a waveguide/triplate-line converter coupled to a radio to a plurality of patch antennas in a cluster pattern, wherein a width and a length of a section interposed between the waveguide/triplate-line converter and a branch point closest to the waveguide/triplate-line converter on the feed line are set to values at which impedance of the section directly matches a parallel combination of impedances of branches ahead of the branch point and a loss of the section is suppressed to or below a preset upper limit. 
         [0037]    That is, the width and the length of the section running from the waveguide/triplate-line converter to the branch point on the feed line are set to values at which impedance mismatching and a loss do not occur unnecessarily. 
         [0038]    According to a second aspect of the present invention, in the feed line according to the first aspect, the width and the length may be set to values at which both or any one of a temperature and a calorific value of the feed line is suppressed within a preset limit in an environment to which the feed line is exposed under power supplied via the waveguide/triplate-line converter. 
         [0039]    That is, the width and the length of the section running from the waveguide/triplate-line converter to the branch point on the feed line are set to values at which a temperature and a calorific value caused due to the impedance mismatching and the unnecessary loss are within a preset limit. 
         [0040]    According to a third aspect of the present invention, in the feed line according to the first or second aspect, the feed line may be formed as the triplate line that realizes tournament feeding from the waveguide/triplate-line converter to the plurality of patch antennas. 
         [0041]    That is, in the feed line according to the present invention, without being accompanied by a considerable disparity in a width of any path individually running from the waveguide/triplate-line converter to the plurality of patch antennas, a level and a phase of a radio signal whose power is supplied to these patch antennas may be precisely set to desired values. 
       Advantageous Effects of Invention 
       [0042]    As the feed line according to the present invention is formed as the triplate line, heating and degradation of characteristics caused by the heating are avoided even in the case in which heat radiation efficiency is structurally low and power supplied from the radio via the waveguide/triplate-line converter is large. 
         [0043]    Also, in the feed line according to the present invention, as it is formed as the triplate line, a calorific value attributed to heating and the heating are suppressed within a limit within which no characteristics are degraded even in the case in which the heat radiation efficiency is structurally low and the power supplied from the radio via the waveguide/triplate-line converter is large. 
         [0044]    Accordingly, in an antenna system to which the present invention is applied, supply of power to the individual patch antennas is simply realized with high precision in a desired mode, and furthermore, characteristics and reliability are kept high. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0045]      FIG. 1  is a view illustrating an embodiment of the present invention. 
           [0046]      FIG. 2  is a view illustrating temperature distribution of a feeding system in the present embodiment. 
           [0047]      FIG. 3  is a view illustrating an appearance of a triplate feed-type planar antenna in which polarized waves are shared and to which the present invention is applied. 
           [0048]      FIG. 4  is a view illustrating a constitution example of the triplate feed-type planar antenna. 
           [0049]      FIG. 5  is a view illustrating a constitution of a feeding system of a conventional triplate feed-type planar antenna. 
           [0050]      FIG. 6  is a sectional view of the conventional feeding system. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0051]    Hereinafter, embodiments of the present invention will be described in detail based on the drawings. 
         [0052]      FIG. 1  is a view illustrating an embodiment of the present invention. 
         [0053]    In  FIG. 1 , elements having the same function as those illustrated in  FIGS. 4 and 5  are given the same signs, and description thereof will be omitted here. 
         [0054]    In the present embodiment, a constitution of a flexible substrate  43  differs from a conventional example illustrated in  FIGS. 4 and 5  in the following respect. 
         [0055]    (1) A converter  43 C is disposed at a point close to a bus bar  43 FM. 
         [0056]    (2) Thus, a length of a main line  43 B is set to be short. 
         [0057]    (3) In addition, a width of the main line  43 B is set to a value of about 2.5 times (impedance becomes one half times) compared to the conventional example. 
         [0058]    (4) Also, the main line  43 B is formed as a circuit pattern that directly continues to the bus bar  43 FM. As indicated in  FIG. 1  by a dotted line frame, a transformer  43 T is not formed at a connecting point between the main line  43 B and the bus bar  43 FM. 
         [0059]    Hereinafter, an operation of the present embodiment will be described with reference to  FIG. 1 . 
         [0060]    Similar to the conventional example, a probe  43 CP converts a transmission wave, which is output by a transmitter and is handed over as a basic mode of an electromagnetic field propagated in a pipe of a waveguide  43 C WC , into an “electromagnetic field of a triplate line.” 
         [0061]    On the flexible substrate  43 , the “electromagnetic field of the triplate line” is handed over to the bus bar  43 FM via the aforementioned main line  43 B. 
         [0062]    The transmission wave output by the transmitter in this way is handed over to the bus bar  43 FM, and is subjected to tournament feeding to patch antennas  43 A 1,1  to  43 Am,n in the same way as the conventional example. 
         [0063]    Also, since a thickness of the main line  43 B is set to a value of about 2.5 times (impedance becomes one half times) compared to the conventional example, an electric signal is handed over to the bus bar  43 FM without being accompanied by impedance mismatching caused by branching of the bus bar  43 FM from the main line  43 B in two directions although the transformer  43 T does not intervene. 
         [0064]    Furthermore, since the converter  43 C is disposed at the point close to the bus bar  43 FM, a length of the main line  43 B is set to be considerably shorter than that of the conventional example. 
         [0065]    That is, electric resistance of the main line  43 B intervening between the probe  43 CP and the bus bar  43 FM is considerably reduced compared to the conventional example. 
         [0066]    In this way, according to the present embodiment, although the transmission wave has power of about 50 watts, which is considerably greater than that of the conventional example, a percentage of the power converted into heat by the main line  43 B has a considerably smaller value than the conventional example. 
         [0067]    Therefore, as illustrated in  FIG. 2 , a temperature of each part is suppressed to a smaller value than, for example, heat-resistant temperatures (90° C. to 130° C.) of foam sheets  42 - 1  and  42 - 2 . 
         [0068]    (1) A temperature of the main line  43 B becomes about 60° C. 
         [0069]    (2) Since no region whose width is narrow like the transformer  43 T intervenes, there are no places that exceed the heat-resistance temperatures of the foam sheets  42 - 1  and  42 - 2 . 
         [0070]    (3) A temperature of the bus bar  43 FM becomes 80° C. or less. 
         [0071]    That is, none of shapes, dimensions, and dispositions of the feed line and the patch antennas  43 A 1,1  to  43 Am,n is considerably changed, and an adjustment to large transmission power is made possible with a low heat radiation characteristic specific to the triplate line constituting the feed line. 
         [0072]    Furthermore, since the length of the main line  43 B is reduced, for instance, from 76 millimeters to 19 millimeters, a loss converted into heat is reduced, and thereby a total gain of the patch antennas  43 A 1,1  to  43 Am,n is improved by about 0.1 dB. 
         [0073]    Therefore, according to the present embodiment, even when the transmission power is large, or is widely changeable, characteristics and reliability of an antenna system are stably secured. 
         [0074]    In the present embodiment, the foam sheets  42 - 1  and  42 - 2  are not limited to plate-like formed materials, and may be formed of any material as long as they function as a suitable dielectric at a desired frequency. 
         [0075]    Also, in the present embodiment, a material of the flexible substrate  43  may be any material as long as a desired characteristic is obtained. For example, when a wavelength should be adjusted for a balance between a frequency and a physical size, the material of the flexible substrate  43  may be a ceramic in which values of effective Q and specific dielectric constant are preferable. 
         [0076]    Furthermore, in the present embodiment, the bus bar  43 FM branches off at the connecting point with the main line  43 B in the two directions. However, if impedance matching is achieved between the main line  43 B and the bus bar  43 FM, and a heat value generated by the two is suppressed below a desired threshold value, the bus bar  43 FM may branch off at the connecting point in three or more directions. 
         [0077]    Also, in the present embodiment, the present invention is applied only to the connecting point between the main line  43 B and the bus bar  43 FM. 
         [0078]    However, the present invention is not limited only to this connecting point, and may also be equally applied, for instance, to a subsequent branch point that is contiguous to the bus bar  43 FM and is formed for the tournament feeding. 
         [0079]    Furthermore, the present invention may be equally applied if there is a KU band (13.75 GHz to 14.5 GHz) as well as a frequency band (mainly 10 GHz to 80 GHz) in which the triplate feed-type planar antenna can be constituted. 
         [0080]    Also, the present invention may be applied if there is an antenna in which the feed line, the main line  43 B, and the patch antennas  43 A 1,1  to  43 Am,n including the bus bar  43 FM are formed on a circuit board as a pattern. 
         [0081]    Moreover, the present invention may also be equally applied to a polarized wave-dedicated planar antenna in which a wireless transmission line is formed at an uplink and a downlink by common polarized waves as well as a planar antenna in which the polarized waves are shared and in which a wireless transmission line is formed at these links by mutually orthogonal polarized waves, for example, as illustrated in  FIG. 3 . 
         [0082]    In addition, the present invention is not limited to the aforementioned embodiment. Various embodiments can be constituted within the scope of the present invention, and any improvements may be carried out for all or some of the components. 
       INDUSTRIAL APPLICABILITY 
       [0083]    The present invention can be widely applied to a feed line formed as a triplate line that runs from a waveguide/triplate-line converter coupled to a radio to a plurality of patch antennas in a cluster pattern. 
         [0084]    As the feed line according to the present invention is formed as the triplate line, heating and degradation of characteristics caused by the heating are avoided even in the case in which heat radiation efficiency is structurally low and power supplied from the radio via the waveguide/triplate-line converter is large. 
         [0085]    Also, in the feed line according to the present invention, by being formed as the triplate line, a calorific value attributed to heating and the heating are suppressed within a limit within which no characteristics are degraded even in the case in which the heat radiation efficiency is structurally low and the power supplied from the radio via the waveguide/triplate-line converter is large. 
         [0086]    Accordingly, in an antenna system to which the present invention is applied, supply of power to the individual patch antennas is simply realized with high precision in a desired mode, and furthermore, characteristics and reliability are kept high. 
       REFERENCE SIGNS LIST 
       [0087]      41  Ground plane 
         [0088]      42  Foam sheet 
         [0089]      43  Flexible substrate 
         [0090]      43 A Patch antenna 
         [0091]      43 B Main line 
         [0092]      43 C Waveguide/triplate-line converter 
         [0093]      43 CF Waveguide flange 
         [0094]      43 CP Probe 
         [0095]      43 CR Annular member 
         [0096]      43 Cr Annular member 
         [0097]      43 Cs Short plate 
         [0098]      43 C WC  Waveguide 
         [0099]      43 F Feed line 
         [0100]      43 FM Bus bar 
         [0101]      43 T Transformer 
         [0102]      44  Slot plate 
         [0103]      44 S Slot opening