Abstract:
A two-port triplate-line/waveguide converter in one embodiment of this invention is provided with a rectangular waveguide and two probes that connect to central conductors of separate trip late lines via slits, said slits being formed separately on two opposing inside walls of the rectangular waveguide and lying on an imaginary straight line that is perpendicular to said inside walls. The two probes, the tips of which are bent inside the rectangular waveguide, constitute monopole antennas with the aforementioned inside walls functioning as the ground planes thereof.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a two-port triplate-line/waveguide converter which has two ports coupled to an electromagnetic field in a rectangular waveguide and transfers the electromagnetic field to triplate lines connected to these ports. 
         [0002]    Priority is claimed on Japanese Patent Application No. 2013-127069, filed Jun. 18, 2013, the content of which is incorporated herein by reference. 
       BACKGROUND ART 
       [0003]    Satellite communication and fixed wireless access systems (FWA) in which wireless transmission is performed in a microwave band of 10 GHz or above or in a millimeter wave band mostly employ planar antennas consisting of an array of a large number of patch antennas. A feed line for these patch antennas has a simple structure, so that a parallel feed can be precisely realized at low cost. Moreover, the feed line is formed as a triplate line capable of ensuring high gain and high efficiency. 
         [0004]    As shown in  FIG. 6 , a conventional triplate feed type planar antenna includes, 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 . 
         [0005]    The elements stacked in this way are configured as follows.
   (1) On an upper surface of the ground plane  41 , a pattern corresponding to the plane Earth is formed.   (2) The foam sheets  42 - 1  and  42 - 2  are configured as a cushion material, a heat insulating material, and a dielectric with the flexible substrate  43  interposed between both surfaces thereof   (3) On the flexible substrate  43 , an array of rectangular patch antennas  43 A 1,1  to  43 A m,n  arranged in a grid shape and a feed line  43 F which realizes a tournament feed for these patch antennas are formed as a circuit pattern.   (4) Slot openings  44 S 1,1  to  44 S m,n  in a grid shape are formed at positions individually corresponding to the patch antennas in a top surface of the slot plate  44 , and a plane Earth pattern is formed all over the surface other than these positions.   
 
         [0010]    A feed system of such a triplate feed type planar antenna is configured, for example, as shown in  FIG. 7 , as follows. 
         [0011]    A waveguide-triplate line converter (simply referred to as “converter” below)  43 C is disposed at a predetermined position surrounded by the patch antennas  43 A 1,1  to  43 A m,n  on the flexible substrate  43 . 
         [0012]    Also, on the flexible substrate  43 , a main line  43 B is formed to have one end extending to a probe  43 CP inserted from a sidewall of a waveguide  43 C WC  constituting the converter  43 C into the waveguide  43 C WC  and the other end extending to a bus bar  43 FM of the aforementioned feed line  43 F realizing the tournament feed. 
         [0013]    Among the components of the converter  43 C, the waveguide  43 C WC  includes the following elements, as shown in  FIG. 8 .
   (1) A waveguide flange  43 CF that corresponds to (is connected to) one end of a rectangular waveguide connected to a wireless device not shown in the drawings, has a rectangular opening extending into the rectangular waveguide, and is disposed with the opening in contact with the corresponding position of the ground plane  41     (2) An annular member  43 CR that is formed in the stacked foam sheet  42 - 1 , flexible substrate  43 , and foam sheet  42 - 2 , inserted into a through-hole corresponding to an imaginary extended portion of the opening, and formed as a conductive cylinder having a through-hole penetrated by the aforementioned probe  43 CP   (3) An annular member  43 Cr that is stacked on the annular member  43 CR with the slot plate  44  interposed therebetween, and extends from the inside of the waveguide flange  43 CF to the outside of the slot plate  44  together with the annular member  43 CR   (4) A short plate  43 Cs that is laid on a top portion of the annular member  43 Cr including an opening, and has a top portion in which holes (not shown) penetrated by screws  43 S- 1  to  43 S- 5  to be described below are formed   (5) The screws  43 S- 1  to  43 S- 5  that sandwich 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 by being screwed into screw holes which are formed in the waveguide flange  43 CF to correspond to those holes   
 
         [0019]    In the ground plane  41 , the annular member  43 CR, the slot plate  44 , and the annular member  43 Cr, holes (not shown) into which the screws  43 S- 1  to  43 S- 5  are inserted and which have inside walls having a size and a shape with which they stably come in contact with sidewalls of these screws  43  S- 1  to  43  S- 5  are formed in advance. 
         [0020]    In the triplate feed type planar antenna having such a configuration, the waveguide  43 C WC  is sandwiched by the screws  43 S- 1  to  43 S- 5  between the aforementioned waveguide flange  43 CF and the short plate  43 Cs, and formed by inside walls of the ground plane  41 , the annular member  43 CR, the slot plate  44 , and the annular member  43 Cr electrically connected by these screws  43  S- 1  to  43 S- 5 . 
         [0021]    In  FIG. 7 , the probe  43 CP converts transmission waves which are output by a transmitter not shown in the drawings and transferred as an electromagnetic field of the fundamental mode propagating in the waveguide  43 C WC  into an “electromagnetic field of a triplate line.” 
         [0022]    On the flexible substrate  43 , this “electromagnetic field of a triplate line” is guided to a point which is deviated from the center of the bus bar  43 FM by a distance corresponding to a quarter of a wavelength, and is fed to half of the patch antennas  43 A 1,1  to  43 A m,n  and the other half thereof with a phase difference of 180 degrees through the bus bar  43 FM in a tournament manner. 
         [0023]    Also, in such a triplate feed type planar antenna, cross-polarization components become two components having opposite phases and cancel each other out due to the half of the patch antennas  43 A 1,1  to  43 A m,n  and the other half, and thus cross-polarization discrimination is improved. 
         [0024]    As prior art relevant to the present invention, there are Patent Literature 1 to Patent Literature 3 listed below. 
         [0025]    Patent Literature 1 discloses a polarized wave shared planar antenna “obtained by sequentially stacking a ground conductor  11 , a dielectric  10 , a feed substrate  9  having a plurality of radiation elements  7  and a feed line  8  formed therein, a dielectric  6 , a ground conductor  1  having a plurality of slots  12  installed so that the respective slots  12  are disposed right above the radiation elements  7 , a dielectric  2 , a feed substrate  5  having a plurality of radiation elements  3  and a feed line  4  formed therein, a dielectric  13 , and a ground conductor  15  having a plurality of slots  14  installed so that the respective slots  14  are disposed right above the radiation elements  3 , and configured by electromagnetically coupling the radiation elements  3  and the radiation elements  7  together so that the excitation direction of the radiation elements  3  in accordance with the feed line  4  and the excitation direction of the radiation elements  7  in accordance with the feed line  8  cross at right angles, in which radiation elements corresponding to about half the number of array elements of the feed substrate  5  and the feed substrate  9  and a feed line or elements corresponding to about half the number of array elements of any one feed substrate and a feed line are spatially rotated 180 degrees with respect to a reference excitation direction and disposed, and which electrically changes a feeding phase by 180 degrees to be excited,” thus having a characteristic such that “load on a signal-processing circuit is reduced in a planar antenna side as much as possible, and thus a cross-polarization characteristic and a wide band characteristic of isolation are obtained.” 
         [0026]    Patent Literature 2 discloses a waveguide/microstrip line converter “in which a substrate providing a microstrip line so that an antenna probe is disposed toward an opening of a waveguide is sandwiched between a cap corresponding to the opening of the waveguide and a base member, and the microstrip line is connected to both ends of the antenna probe installed on the substrate” thus having a characteristic such that “it also has a function of distributing a feed from the antenna probe in order to reduce removal of antenna elements on the substrate as much as possible.” 
         [0027]    Patent Literature 3 discloses a planar antenna “that has a triplate configuration in which strip lines formed on a substrate are inserted into a ground substrate with gaps left on both sides, has radiation elements formed on one side of the ground substrate, and supplies power to the respective radiation elements in parallel by a feed line of the strip lines, in which strip line-waveguide converters having strip lines of a final feed point inserted from both side surfaces of a waveguide and having a phase difference of 180 degrees between powers input from both strip lines to the waveguide are formed in spaces between radiation elements horizontally and vertically formed at regular spatial intervals,” thus having a characteristic such that “it enables a feed by a waveguide capable of achieving favorable power combining (branching).” 
       CITATION LIST 
     Patent Literature 
     Patent Literature 1 
       [0028]    Japanese Unexamined Patent Application, First Publication No. Hei 09-312515 
       Patent Literature 2 
       [0029]    Japanese Unexamined Patent Application, First Publication No. Hei 11-312909 
       Patent Literature 3 
       [0030]    Japanese Patent No. 2595339 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0031]    In the conventional example described above, the main line  43 B is connected to the point deviated from the center of the bus bar  43 FM by a quarter of a wavelength, so that the aforementioned phase difference of 180 degrees is ensured. 
         [0032]    Therefore, when a frequency of a wireless signal to be transmitted or received has a wide-ranging value or a band occupied by the wireless signal is wide (for example, 2 GHz in a 12 GHz band), it is difficult to set the phase difference with sufficient precision. 
         [0033]    Moreover, an error of such a phase difference in accordance with a frequency is a primary factor that causes degradation of cross-polarization discrimination to shift the direction of a main lobe, and puts a limitation on application of the triplate feed type planar antenna. 
         [0034]    The error of such a phase difference can be reduced by configuring the triplate feed type planar antenna, for example, as shown in  FIG. 9 , as follows.
   (1) A probe  43 CP′ is disposed at a portion on the flexible substrate  43 CP corresponding to a central portion in the waveguide  43 C WC  instead of the probe  43 CP.   (2) The probe  43 CP′ is installed in the central portion of the main line  43 B.   (3) Such a main line  43 B passes through slits (through-holes) formed in opposite sidewalls of the waveguide  43 C WC , and is guided to the outside of the waveguide  43 C WC .   
 
         [0038]    Also, the error of a phase difference can be reduced by configuring the triplate feed type planar antenna, for example, as shown in  FIG. 10 , as follows.
   (1) The probe  43 CP′ is not provided.   (2) The main line  43 B is divided into two parts at its central portion, and tips are formed opposite to each other by a predetermined distance around the central portion in the waveguide  43 C WC  and facing the gap.   
 
         [0041]    However, in these configurations shown in  FIG. 9  and  FIG. 10 , impedance matching is not easily achieved in practice, and it is not possible to ensure a sufficient return loss bandwidth.
   (1) Since there is air around the probe  43 CP′, it is difficult to effectively reduce a wavelength based on a relative permittivity.   (2) In general, a distance b between inside walls of the waveguide  43 C WC  opposite to each other is much smaller than a resonant length (=λ/2).   
 
         [0044]    Therefore, in practice, the configurations shown in  FIG. 9  and  FIG. 10  are obstructed by limitations, such as a frequency, and physical sizes, shapes, dispositions, and the like of components other than the waveguide  43 C WC , and are not applied frequently. 
         [0045]    An object of the present invention is to provide a two-port triplate-line/waveguide converter in which coupling of triplate lines is realized over a wide band in opposite phases, at low cost without drastically complicating the configuration. 
       Solution to Problem 
       [0046]    In accordance with a first aspect of the present invention, a two-port triplate-line/waveguide converter includes a rectangular waveguide, and two probes which connect to central conductors of separate triplate lines through slits separately formed in two opposite inside walls of the rectangular waveguide and having openings on an imaginary straight line crossing the two inside walls at right angles. Tips of the two probes are bent inside the rectangular waveguide, and the two probes constitute monopole antennas with the inside walls functioning as ground planes. 
         [0047]    In other words, the two probes are bent in the rectangular waveguide, so that unnecessary coupling between the two probes is reduced or suppressed. Moreover, the two probes function as the monopole antennas, so that two ports of opposite phases coupled to an electromagnetic field in the waveguide over a wide band are formed between the two probes and the separate triplate lines. 
         [0048]    In accordance with a second aspect of the present invention, a two-port triplate-line/waveguide converter includes a rectangular waveguide, and two probes which connect to central conductors of separate triplate lines through slits separately formed in two opposite inside walls of the rectangular waveguide and having openings on an imaginary straight line crossing the two inside walls at right angles. Tips of the two probes branch in a plurality of directions inside the rectangular waveguide, and the two probes constitute monopole antennas with the inside walls functioning as ground planes. 
         [0049]    In other words, the two probes branch in a plurality of directions in the rectangular waveguide, so that unnecessary coupling between the two probes is reduced or suppressed. Moreover, the two probes function as the monopole antennas, so that two ports of opposite phases coupled to an electromagnetic field in the waveguide over a wide band are formed between the two probes and the separate triplate lines. 
         [0050]    In accordance with a third aspect of the present invention, a two-port triplate-line/waveguide converter includes two probes which connect to central conductors of separate triplate lines through slits separately formed in two opposite inside walls of the rectangular waveguide and having openings on an imaginary straight line crossing the two inside walls at right angles. Tips of the two probes are bent in directions not opposite to each other inside the rectangular waveguide, and the two probes constitute monopole antennas with the inside walls functioning as ground planes. 
         [0051]    In other words, the tips of the two probes are bent in directions not opposite to each other in the rectangular waveguide, so that unnecessary coupling between the two probes is reduced or suppressed. Moreover, the two probes function as the monopole antennas, so that two ports of opposite phases coupled to an electromagnetic field in the waveguide over a wide band are formed between the two probes and the separate triplate lines. 
       Advantageous Effects of Invention 
       [0052]    According to the present invention, transfer of signals having phases opposite to each other is realized in parallel between a rectangular waveguide and two triplate lines without involving a drastic change of the configuration and a heavy dependence on a frequency compared to the conventional example. 
         [0053]    An apparatus or a system to which the present invention is applied does not place serious obstructions or limitations on cost, installation, temperature, power consumption, or the like, and prevents the occurrence of technical problems resulting from a lack of precision in the opposite phases or a change of performance with high precision. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0054]      FIG. 1  is a diagram showing an embodiment of the present invention. 
           [0055]      FIG. 2  is a diagram showing a return loss achieved by the present embodiment. 
           [0056]      FIG. 3  is a diagram ( 1 / 2 ) showing another aspect of a configuration of the present embodiment. 
           [0057]      FIG. 4  is a diagram ( 2 / 2 ) showing another aspect of a configuration of the present embodiment. 
           [0058]      FIG. 5  is a diagram showing a configuration of a polarized wave shared triplate feed type planar antenna to which the present invention can be applied. 
           [0059]      FIG. 6  is a diagram showing an example of a configuration of a conventional triplate feed type planar antenna. 
           [0060]      FIG. 7  is a diagram ( 1 / 2 ) showing a configuration of a feed system of a conventional triplate feed type planar antenna. 
           [0061]      FIG. 8  is a diagram ( 2 / 2 ) showing a configuration of a feed system of a conventional triplate feed type planar antenna. 
           [0062]      FIG. 9  is a diagram ( 1 / 2 ) showing a solution to a conventional example. 
           [0063]      FIG. 10  is a diagram ( 2 / 2 ) showing a solution to a conventional example. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0064]    Hereinafter, an embodiment of the present invention will be described in detail based on the drawings. 
         [0065]      FIG. 1  is a diagram showing an embodiment of the present invention. 
         [0066]    In  FIG. 1 , the same elements as those shown in  FIG. 6  to  FIG. 8  are given like signs, and descriptions thereof will be omitted here. 
         [0067]    The present embodiment and the conventional example shown in  FIG. 7  have the following differences in configuration
   (1) The main line  43 B is not provided.   (2) Instead of the waveguide  43 C WC , a waveguide  11  is provided, and separate through-holes are formed at positions corresponding to one side surface of the flexible substrate  43  in two opposite sidewalls of the waveguide  11 .   (3) The bus bar  43 FM is divided into two parts at a central portion in the longitudinal direction, and tips of the parts are guided into the waveguide  11  through the respective through-holes. The two parts divided from the bus bar  43 FM in this way are denoted by “ 43 FM- 1 ” and “ 43 FM- 2 ” below.   (4) Two probes  12 - 1  and  12 - 2  configured as will be described below are provided instead of the probe  43 CP.   (4-1) The two probes  12 - 1  and  12 - 2  are formed on the flexible substrate  43  as circuit patterns, and as shown in  FIG. 1 , connect to the bus bars  43 FM- 1  and  43 FM- 2 , respectively.   (4-2) The tips are bent in L shapes in directions so that areas of the tips opposite to each other in the waveguide  11  are minimized.   (4-3) The disposition of each of these tips in an inside wall of the waveguide  11  and the size are set as follows.   (4-3-1) In relation to a length L 1  from an inside wall of the waveguide  11  to a bent portion and a length L 2  from the bent portion to a tip, a length L in the waveguide  11  is given by the following equation.   
 
         [0000]      L=L1+L2   (4-3-2) In relation to a wavelength X of a center frequency fin a band of a signal to be transferred from the inside of the waveguide  11  to the bus bars  43 FM- 1  and  43 FM- 2 , the length L is given by the following equation.     
         [0000]      L=λ/4
   (4-3-3) The length L 1  is set based on a balance between the degree of coupling between an electromagnetic field in the waveguide  11  and the probe  12 - 1  ( 12 - 2 ) and isolation to be ensured between the probes  12 - 1  and  12 - 2 .   
 
         [0078]    In the present embodiment configured in this way, both of the probes  12 - 1  and  12 - 2  function as monopole antennas which use a sidewall of the waveguide  11  as a ground plane. 
         [0079]    Here, both of the probes  12 - 1  and  12 - 2  are bent in L shapes, and thus are sufficiently isolated from each other. Also, since both the probes  12 - 1  and  12 - 2  resonate with L=(1/4)λ, the current distribution of each of the probes  12 - 1  and  12 - 2  becomes even, and thus a band is widened. 
         [0080]    Moreover, phases of an electromagnetic field coupled to the probes  12 - 1  and  12 - 2  in the waveguide  11  become opposite to each other, that is, 180 degrees. 
         [0081]    In other words, half of the patch antennas  43 A 1,1  to  43 A m,n  and the other half thereof are fed in parallel with power in opposite phases by the two-port waveguide-triplate line converter which includes the waveguide  11  and the probes  12 - 1  and  12 - 2  as described above. 
         [0082]    Therefore, in the triplate feed type planar antenna to which the present embodiment is applied, slight changes are made as will be described below, and each half of the provided patch antennas is stably fed in an opposite phase.
   (1) A configuration of the waveguide  11     (2) A specific circuit pattern associated with coupling with the waveguide  11  among circuit patterns formed on the flexible substrate  43     
 
         [0085]    As shown in  FIG. 2 , such a feed is efficiently performed over a wide band compared to the conventional example. 
         [0086]    In the present embodiment, a feed by opposite phases is stably realized over a wide band as described above, and thus a shift of a main lobe which is about 0.3 degrees in the conventional example is suppressed to be within 0.1 degrees. 
         [0087]    In the present embodiment, when isolation between the probes  12 - 1  and  12 - 2  and overall feed efficiency are achieved in a desired range, the probes  12 - 1  and  12 - 2  are not limited to the aspect shown in  FIG. 1  and may be configured in any of the forms listed below.
   (1) As shown in  FIG. 3 , the tips are disposed to be opposite to each other within a range allowed by a reduction in isolation between the probes  12 - 1  and  12 - 2 .   (2) As shown in  FIG. 4 , the tips branch not in L shapes but in T shapes so that the probes  12 - 1  and  12 - 2  function as T-shaped monopole antennas.   (3) The tips branch into three or more parts.   (4) A direction in which the tips branch is not limited to the pattern surface of the flexible substrate  43  and is set to cross the pattern surface of the flexible substrate  43  within the limitation of cost or the range of technical feasibility.   (5) The probes  12 - 1  and  12 - 2  are formed on a different surface of the flexible substrate  43  than the bus bars  43 FM- 1  and  43 FM- 2  in a form in which they are connected to the bus bars  43 FM- 1  and  43 FM- 2 , which are central conductors of the triplate lines, outside the waveguide  11 .   (6) The probes  12 - 1  and  12 - 2  are different in both or either one of shape and size.   
 
         [0094]    In the present embodiment, through-holes into which the probes  12 - 1  and  12 - 2  are inserted are formed in a linear shape in two sidewalls of the waveguide  11  opposite to each other. 
         [0095]    However, such a shape of the through-holes may be a shape which is bent in a desired shape and size as long as there is no problem in overall characteristics. 
         [0096]    These through-holes may not necessarily have the same shape or size. 
         [0097]    In the present embodiment, the number of patch antennas to be fed in phases opposite to each other may be any value. 
         [0098]    In addition, the present invention can be applied not only to a triplate feed type planar antenna but also to any apparatus or system in which coupling between a waveguide and two triplate lines should be stably realized over a wide band with high precision in opposite phases. 
         [0099]    Also, the present invention can be applied not only to a polarized wave-dedicated planar antenna that forms a wireless transmission path with polarized waves common in an uplink and a downlink, but also to, for example, a polarized wave shared planar antenna that forms these links with polarized waves orthogonal to each other as shown in  FIG. 5 . 
         [0100]    The present invention is not limited to the embodiment described above. Various embodiments can be made within the scope of the present invention, and any modifications may be made to all or some of the components. 
       Industrial Applicability 
       [0101]    The present invention can be widely applied to two-port triplate-line/waveguide converters that have two ports coupled to an electromagnetic field in a rectangular waveguide, and transfer the electromagnetic field to triplate lines connecting to these ports. 
         [0102]    According to the present invention, transfer of signals having phases opposite to each other is realized in parallel between a rectangular waveguide and two triplate lines without involving a drastic change of the configuration and a heavy dependence on a frequency compared to the conventional example. 
         [0103]    An apparatus or a system to which the present invention is applied does not put serious obstructions or limitations on cost, installation, temperature, power consumption, or the like, and prevents the occurrence of technical problems resulting from a lack of precision in the opposite phases or a change of performance with high precision. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           11 ,  43 C WC  Waveguide 
           12 ,  43 CP Probe 
           41  Ground plane 
           42  Foam sheet 
           43  Flexible substrate 
           43 A Patch antenna 
           43 B Main line 
           43 C Waveguide-triplate line converter 
           43 CF Waveguide flange 
           43 CR Annular member 
           43 Cr Annular member 
           43 Cs Short plate 
           43 F Feed line 
           43 FM Bus bar 
           44  Slot plate 
           44 S Slot opening