Abstract:
A coaxial circulator having ferrite members to which a static magnetic field is applied at a junction of a Y-shaped strip conductor, the coaxial conductor including a dielectric substrate, an inner pattern of the Y-shaped strip conductor provided on a center of an upper surface of the dielectric substrate, and ground patterns provided on the upper surface and a lower surface of the dielectric substrate along a periphery of the conductive inner pattern and electrically connected to each other via a plurality of through-holes in the dielectric substrate, the substrate being sandwiched by an upper block and a lower block, the ferrite members being provided adjacent to both the upper side and a lower side of the substrate so as to ground the ground patterns to the upper and lower block surfaces.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a coaxial circulator and an element sharing device, and more particularly, to a coaxial circulator constructed so that a ferrite member to which a static magnetic field is applied is positioned at a junction of a Y-shaped strip conductor and an element sharing device using such a circulator. 
     2. Description of the Related Art 
     Conventionally, an element sharing device used in a wave decoupling device of a multiplex radio communications apparatus, such as an antenna sharing device, is formed from a waveguide component. In recent years, however, as devices have become cheaper and more compact, there is a growing need to make the element sharing device a coaxial component. 
     However, in an element sharing device, in which multiple. transmission frequencies pass through the same point, it is known that harmonic distortion (2f 2 −f 1 , f 1 +f 2 −f 3 ) arises due to arbitrary two waves or three waves of the transmission frequency, and that, if this harmonic distortion enters the reception frequency band, the true reception signal is degraded. Normally, an isolation function of the circulator used on the element sharing device drops the harmonic distortion arising on the transmitting side to a level below which reception is no longer affected. However, harmonic distortion generated inside the element sharing device is transmitted as is to the reception side, creating many problems. Accordingly, it is desirable that no harmonic distortion be generated inside the element sharing device. 
     FIGS. 16,  17 A,  17 B,  18 ,  19 A and  19 B are diagrams illustrating the conventional art. FIG. 16 is a diagram showing an expanded view of a conventional coaxial circulator. As shown in the diagram, coaxial connectors  31   1  through  31   3  are mounted at three openings in the sides of a metal block  11  and a Y-shaped inner conductor  13  (having a circular junction at a center thereof) is fixedly mounted by soldering between the three central conductors  31   1  through  31   3 . On a top side of the inner conductor  13  are mounted, in order, a polytetrafluoroethylene support  15   a  and a ferrite member  17   a  whose position is determined by the polytetrafluoroethylene support  15   a,  a copper disc  19   a,  an aluminum ring  21   a  and a magnet  23   a  whose position is determined by the aluminum ring  21   a,  on top of which a yoke  25   a  is mounted and attached to the block  11  by using a screw. The bottom side of the inner conductor  13  is configured similarly. 
     FIGS. 17A and 17B are second diagrams illustrating the conventional art. FIG. 17A is a plan view of the inner conductor  13  and FIG. 17B is a cross-sectional view of an assembled coaxial circulator along the line a—a of FIG.  17 A. 
     It should be noted that, in order to prevent the occurrence of harmonic distortion in a coaxial circulator of this type, the copper discs  19   a,    19   b  that contact the ferrite members  17   a,    17   b  must be securely electrically grounded. 
     FIG. 18 is a third diagram illustrating the conventional art, and more specifically, shows an expanded view of an upper right portion of FIG.  17 B. Conventionally, ring  21   a  is thickened, so that when a screw  35  is tightened to a screw hole  33  in the block  11 , the yoke  25   a  urges the ring  21   a  downward, pressing the copper disc  19   a  against an inner stepped portion of the block  11  so that the copper disc  19   a  is grounded. The copper disc  19   b  is similarly grounded. 
     However, the problem with the above-described arrangement is that the seating of the copper discs  19   a  and  19   b  against the block  11  becomes partially inadequate if the parts on the inside of the copper discs  19   a,    19   b,  (that is, the ferrite members  17   a,    17   b,  the polytetrafluoroethylene supports  15   a,    15   b,  and so on) are not shaped exactly to the correct dimensions, and this inadequate or incomplete contact generates harmonic distortion. 
     FIGS. 19A and 19B are fourth diagrams illustrating the conventional art. FIG. 19A, for example is a diagram showing output characteristics in the event that harmonic distortion (two-wave and three-wave distortion) is generated. 
     It should be noted that it has been confirmed that the state of the grounding of the copper discs  19   a  and  19   b  to the stepped portion of the block  11  can be improved by inserting copper foil thereinbetween, thus making it possible to improve the output characteristics. FIG. 19 b  shows such improved output characteristic. 
     However, insertion of the copper foil is an unsatisfactory solution to the above-described drawback because it complicates the structure of the device. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general object of the present invention to provide an improved and useful coaxial circulator and element sharing device in which the above-described disadvantages are eliminated. 
     Another and further object of the present invention is to provide an improved and useful coaxial circulator and element sharing device having a simple structure that adequately suppresses harmonic distortion. 
     The above-described objects of the present invention are achieved by a coaxial circulator having ferrite members to which a static magnetic field is applied disposed at a junction of a Y-shaped strip conductor, the coaxial conductor comprising: 
     a dielectric substrate; 
     an inner pattern of the Y-shaped strip conductor provided on a center of an upper surface of the dielectric substrate; and 
     ground patterns provided on the upper surface and a lower surface of the dielectric substrate along a periphery of the conductive inner pattern and electrically connected to each other via a plurality of through-holes in the dielectric substrate, 
     the substrate being sandwiched by an upper block and a lower block, the ferrite members being provided adjacent to both the upper side and a lower side of the substrate so as to ground the ground patterns to the upper and lower block surfaces. 
     According to the invention described above, by providing a,conductive inner pattern on top of the dielectric substrate, together with the peripheral ground patterns a variety of waveguide structures (that is, characteristics) can be achieved. Additionally, changes to the conductive inner pattern can be easily added, thus making it possible to provide a coaxial circulator with the desired characteristics without regard for variations in the characteristics of peripheral components. Additionally, the ground patterns of the dielectric substrate are sandwiched by the ground faces of the blocks together with the upper and lower ferrite members the bringing together of which makes it possible to obtain a full and complete ground plane of the waveguides (specifically, the upper and lower edge surfaces of the ferrite members on the periphery of the conductive inner pattern. 
     The above-described objects of the present invention are also achieved by device comprising: 
     a single dielectric substrate having dielectric substrate portions of a plurality of coaxial circulators, a Y-shaped conductive inner pattern provided on a center of an upper surface of each one of the dielectric substrate portions, ground patterns provided on the upper surface and a lower surface of each of the dielectric substrate portions and electrically connected to each other via a plurality of through-holes formed in each of the dielectric substrate portions along a periphery of the conductive inner pattern, each of the dielectric substrate portions being sandwiched by an upper block and a lower block, ferrite members being provided adjacent to both the upper side and the lower side of each of the dielectric substrate portions so as to ground the ground patterns to the surfaces of the upper and lower block; and 
     the plurality of coaxial circulators directly coupled to each other via the single dielectric substrate. 
     According to the invention described above, by directly coupling a plurality of coaxial circulators via a single dielectric substrate structure, the harmonic distortion generated at the conventional connecting portions can be adequately suppressed. 
     The above-described objects of the present invention are also achieved by a coaxial circulator having ferrite members to which a static magnetic field is applied disposed at a junction of a Y-shaped strip conductor, the coaxial circulator comprising: 
     an intermediate block containing a central conductor and the ferrite members provided at top and bottom sides of the central conductor; and 
     an upper block and a lower block, surfaces of the upper block and the lower block contacting upper and lower surfaces of the intermediate block, respectively. 
     The above-described objects of the present invention are also achieved by a coaxial circulator having ferrite members to which a static magnetic field is applied disposed at a junction of a Y-shaped strip conductor, the coaxial circulator comprising: 
     an upper block and a lower block; 
     a central conductor positioned between the upper block and lower block; and 
     a supporting member positioning the ferrite members within an interior space formed by the upper block and the lower block. 
     According to the invention described above, a secure ground plane can be obtained within the waveguide space of the circulator using a simple structure, so the internal generation of harmonic distortion can be adequately suppressed. 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a first diagram of a coaxial circulator according to a first embodiment of the present invention; 
     FIGS. 2A,  2 B,  2 C and  2 D are cross-sectional views of the coaxial circulator according to a first embodiment of the present invention and front, side and back surfaces of a dielectric substrate of the coaxial circulator according to a first embodiment of the present invention, accordingly; 
     FIGS. 3A,  3 B and  3 C are diagrams showing top, side and bottom surfaces of an upper block of the coaxial circulator according to a first embodiment of the present invention; 
     FIGS. 4A,  4 B,  4 C and  4 D are first diagrams illustrating a variation of the first embodiment of the present invention; 
     FIGS. 5A and 5B are second diagrams illustrating a variation of the first embodiment of the present invention; 
     FIGS. 6A and 6B are third diagrams illustrating a variation of the first embodiment of the present invention; 
     FIGS. 7A and 7B are fourth diagrams illustrating a variation of the first embodiment of the present invention; 
     FIGS. 8A and 8B are fifth diagrams illustrating a variation of the first embodiment of the present invention; 
     FIGS. 9A and 9B are sixth diagrams illustrating a variation of the first embodiment of the present invention; 
     FIG. 10 is a seventh diagram illustrating a variation of the first embodiment of the present invention; 
     FIG. 11 is a diagram illustrating an element sharing device according to the first embodiment of the present invention; 
     FIG. 12 is a first diagram illustrating a coaxial circulator according to a second embodiment of the present invention; 
     FIG. 13 is a second diagram illustrating a coaxial circulator according to the second embodiment of the present invention; 
     FIG. 14 is a first diagram illustrating a coaxial circulator according to the third embodiment of the present invention; 
     FIG. 15 is a second diagram illustrating a coaxial circulator according to the third embodiment of the present invention; 
     FIG. 16 is a first diagram illustrating the conventional art; 
     FIGS. 17A and 17B are second diagrams illustrating the conventional art; 
     FIG. 18 is a third diagram illustrating the conventional art; and 
     FIGS. 19A and 19B are fourth diagrams illustrating the conventional art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will now be given of embodiments of the present invention, with reference to the accompanying drawings. It should be noted that identical reference numbers denote identical or corresponding elements in all drawings. 
     FIG. 1 is a first diagram of a coaxial circulator according to a first embodiment of the present invention. FIGS. 2A,  2 B,  2 C,  2 D and  3  illustrate the coaxial circulator according to the first embodiment of the present invention. 
     FIG. 1 shows an exploded view of the coaxial circulator. As shown in the diagram, the coaxial circulator sandwiches a central dielectric substrate  41  together with upper and lower ferrite members  17   a,    17   b  between upper and lower blocks  11   a,    11   b,  the whole assembly being held together by the fastening of three screws using three screw holes  34 , thus obtaining a secure ground plane at a periphery of a conductive inner pattern  13 . 
     FIG. 2A is a diagram showing a cross-sectional view of a fully assembled circulator. An upper block  11   a  has countersunk holes, or concave portions, in both top and bottom sides thereof, the top concavity directly containing a magnet  23   a  and the bottom concavity containing polytetrafluoroethylene support  15   a  and a ferrite member  17   a,  the position of the ferrite member  17   a  being determined by the polytetrafluoroethylene supports  15   a.  In this state, a top surface of the ferrite member  17   a  securely contacts a ground plane (the floor of the concave portion) of the upper block  11   a,  as a result of which no harmonic distortion is generated. The lower block  11   b  is similarly structured. 
     FIGS. 2B,  2 C and  2 D show front, side and back surfaces, respectively, of the dielectric substrate  41 . The front surface of the dielectric substrate  41  is provided with a Y-shaped conductive inner pattern  13  and a ground pattern  14   a  on a periphery of the conductive inner pattern  13  so as to surround the conductive inner pattern  13 , the ground pattern  14   a  having the same shape as that of the inner diameter of the upper block  11   a.  Additionally, the back surface of the dielectric substrate  41  has the same ground pattern  14   b  as that on the front surface of the dielectric substrate  41 , with both ground patterns  14   a,    14   b  being electrically shorted, that is, coupled to each other by multiple through-holes  16  positioned as near as possible to the conductive inner pattern  13 . 
     In the above-described structure, the conductive inner pattern  13  is stably supported by the dielectric substrate  41 . Additionally, a secure ground plane is formed at the peripheral surface of the conductive inner pattern  13  by the ground patterns  14   a,    14   b  and the through-holes  16 , essentially as if the conductive inner pattern  13  were to be surrounded by an extension of the upper block  11   a.  The back surface of the dielectric substrate  41  is similarly electrically grounded. 
     FIGS. 3A,  3 B and  3 C show the top, side and bottom surfaces of the upper block  11   a,  respectively. 
     As shown in FIG. 3A, a countersunk hole or concavity  24   a  having essentially the same size as that of a magnet  23   a  is provided in the top surface of the block  11   a,  with the magnet  23   a  being fully contained within the concavity  24   a.  Such a construction eliminates the need for the conventional aluminum ring  21   a  and thus reduces the number of component parts, thereby simplifying the structure of the circulator. 
     As shown in FIG. 3B, a slot portion  18   a  for the purpose of forming an opening for coupling an additional coaxial connector  31  to the lower block  11   b  is formed in the side surface of the upper block  11   a.    
     As shown in FIG. 3C, the concavity  16   a  is formed in the bottom surface of the upper block  11   a,  for the purpose of containing the polytetrafluoroethylene supports  15   a  and the ferrite member  17   a  positioned at the center (circular junction) of the conductive inner pattern  13  by the polytetrafluoroethylene supports  15   a.    
     Returning to FIG. 3B, it can be appreciated that the upper and lower countersunk holes  24   a  and  16   a  do not communicate with each other but are instead separated by metallic block material. This border plane contacts the top surface of the ferrite member  17   a  and at the same time forms a single unit with the upper block  11   a  so as to form a complete ground plane for the waveguide portion of the circulator. Accordingly, the conventional circular copper sheet  19   a  can be eliminated, thus reducing the number of component parts and thereby simplifying the structure of the circulator. 
     Returning to FIG. 3C, it can be appreciated that the countersunk hole  16   a  and the slot portion  18   a  do communicate with each other, with all other sections being flat planes, and accordingly, a secure electrical ground contact with the ground pattern  14   a  of the dielectric substrate  41  can be obtained. Lower block  11   b  is structured accordingly. 
     By sandwiching the dielectric substrate  41  between the upper block  11   a  and lower block  11   b  and holding the whole assembly together with screws as described above, the need for the conventional ground reinforcing component such as metallic foil and the like is eliminated because the stable ground plane is securely formed on the periphery of the conductive inner pattern  13 . Additionally, an interface with external circuitry is converted into a connector at each substrate edge of the pattern extending in three directions from the circular junction of the conductive inner pattern  13 . 
     FIGS. 4 through 10 show various variations of the first embodiment of the present invention. 
     FIGS. 4A,  4 B,  4 C and  4 D show a variation of the dielectric substrate  41  shown in FIGS. 2A,  2 B,  2 C and  2 D, in which the dielectric substrate  41  has three layers instead of two. FIGS. 4B,  4 C and  4 D show top, side and bottom views of the dielectric substrate  41  of the present variation. FIG. 4A shows individual patterns on the intermediate layer. In FIG. 4C, it can be appreciated that the dielectric substrate  41  has three layers. In FIG. 4A, the intermediate layer of the dielectric substrate  41  of the present variation has the conductive inner pattern  13  and the ground pattern  14   a.  FIGS. 4B and 4D show that the top surface and bottom surface each have ground patterns  14   c,    14   b  identical to the ground pattern  14   a  of the intermediate layer. These ground patterns  14   a,    14   b  and  14   c  are electrically shorted, that is, coupled to each other by the through-holes  16 . It will be appreciated that conductive inner pattern  13  of the present variation is centrally positioned in the waveguide space formed by the upper and lower blocks  11   a,    11   b,  thereby improving the symmetry (balance) of the waveguide structure. 
     FIGS. 5A and 5B show other variations of the dielectric substrate  41  shown in FIG.  2 . FIG. 5A depicts a case in which a plurality of lands  18  are provided at the periphery of the junction of the Y-shaped conductive inner pattern  13 . In a coaxial circulator of this type, it is not unusual for variations in the ferrite member  17  and fluctuations in characteristic to cause the circulator characteristic to shift toward the higher frequencies. 
     For example, FIGS. 6A and 6B show return loss for this type of coaxial circulator. FIG. 6A shows a terminal  1  return loss S 11 , with the required frequency band range indicated by markers Δ 1 ,Δ 2 . In this case, the return loss minimum point is shifted slightly toward the higher frequencies. FIG. 6B shows a terminal  2  return loss S 22 , likewise with the required frequency band range indicated by markers Δ 1 ,Δ 2 . In this case, the return loss minimum point is shifted slightly toward the higher frequencies. 
     In such cases as described above, as shown in FIG. 5B an enlarged circular copper foil sheet  20  is prepared and soldered to the conductive inner pattern  13  using a multiplicity of lands  18 . The circular copper foil sheet  20  is soldered at a certain height above the conductive inner pattern  13  due to the presence of the lands  18 , so a uniform contact can be obtained with the ferrite member  17   a  as well. In so doing the junction diameter increases and the resonance frequency of the ferrite. member  17   a  decreases, so adjustment to the necessary frequency band can be made without a major change in the component parts. 
     FIGS. 7A and 7B show return loss after adjustment as described above. FIG. 7A shows a terminal  1  return loss S 11 , with the return loss minimum point shifted to within the required frequency band range indicated by markers Δ 1 ,Δ 2 . FIG. 7B shows a terminal  2  return loss S 22 , likewise with the return loss minimum point shifted to within the required frequency band spanning markers Δ 1 , Δ 2 . 
     Further, as shown in FIGS. 8A and 8B, it is relatively easy to perform a variety of processes to the conductive inner pattern  13  on the dielectric substrate  41 . For example, as shown in FIG. 8A, copper foil  51  may be soldered to or a notch  52  may be cut in the conductive inner pattern  13 , by which means the input/output impedance can be easily changed. Preferably, as shown in FIG. 8B, by inserting a screw  53  from the upper block  11   a  into the pattern portion to be used in place of the coaxial circulator  31  within the conductive inner pattern  13 , it is possible to adjust the input/output impedance simply by changing the depth to which the screw is inserted. Additionally, the accuracy of the pattern of the inner conductor can be rough, with final adjustment thereof easily accomplished with the circulator in a fully assembled state without shaving the pattern of the inner conductor or adjusting the foil. 
     Additionally, as shown in FIGS. 9A and 9B, it is easy to form complex patterns such as a LPF with respect to the conductive inner pattern  13  on the dielectric substrate  41 . FIG. 9B shows one such LPF together with its dimensions. In this case, the printed circuit board material is a polytetrafluoroethylene-glass substrate having a thickness of 0.4 mm, the filter pass band being 3.6 GHz-4.2 GHz, the cut-off frequency being 5 GHz, the number of steps being five. 
     FIG. 10 shows LPF pass characteristic, the horizontal axis representing frequency and the vertical axis representing pass characteristic S 21 . If the range indicated by the markers Δ 1 ,Δ 1  is the circulator required band, then, as can be appreciated, in a case in which no LPF is provided the initial pass extends well beyond the required band into the higher frequencies. As a result, if a high-power signal such as a radar signal is present at or near marker Δ 5 , then a low-noise amplifier (LNA) on the reception side can become saturated by this unwanted signal. By providing an LPF on the circulator, passage of the unneeded wave can be adequately suppressed. 
     FIG. 11 is a diagram illustrating an element sharing device according to the first embodiment of the present invention, in which the element sharing device is shown in an exploded or disassembled state. A state in which the element sharing device is fully assembled is not shown but can be easily understood by those skilled in the art. 
     Basically, the element sharing device shown in the diagram comprises a plurality of coaxial circulators according to the first embodiment of the present invention as described above, the plurality of coaxial circulators being directly coupled to each other. However, unlike the conventional art, in which the circulators are simply directly coupled by a coaxial connector, the present invention uses a plurality of dielectric substrates  41  according to the first embodiment of the present invention as described above, the plurality of dielectric substrates. 41  being directly coupled to each other to form a single dielectric substrate structure  43 , via which single dielectric substrate  43  a plurality of coaxial circulators are directly coupled to form a single element sharing device. 
     That is, a terminal  2  side of the conductive inner pattern  13   1  and a terminal  1  side of the conductive inner pattern  13   2  are directly coupled to each other on the single dielectric substrate  43  as shown in the diagram, around the periphery of which a variety of component parts are assembled in the same manner as with the first embodiment of the present invention described above taking the conductive inner patterns  13   1  and  13   2  as a reference. At this time there is no gap in the direct coupling between the two circulators and a complete waveguide coupling is formed on the single dielectric substrate  43 , as a result of which the kind of harmonic distortion that is generated with the conventional connector coupling can be effectively suppressed. 
     Additionally, it is also possible to directly couple not only two but also three or more conductive inner patterns  13 , thus making it possible to form a high-performance element sharing device having .an arbitrary number of sub-units. In this case also, the finished product is economical because the individual component parts of the coaxial circulator can be used as is. Additionally, any necessary adjustments can be carried out independently at each sub-unit stage. Accordingly, it becomes possible to provide a coaxial element sharing device having as many sub-units as desired, without worrying about the harmonic distortion that is generated with the conventional connector coupling. 
     Additionally, by utilizing the LPF having the structure described above it becomes possible to eliminate unnecessary outside high-frequency wave components, and thus it becomes possible to effectively prevent the saturation of the LNA on the receiver side by such unneeded high-frequency components. 
     It should be noted that, with respect to components other than the single dielectric substrate  43 , although, as noted previously, it is possible to use the individual component parts of the coaxial circulator as is when directly coupling a plurality of coaxial circulators as described above, nevertheless the as-is use of component parts is not limited solely to those of the coaxial circulator. For example, two and even three upper blocks  11   a  and lower blocks  11   b  can be combined into single block units. By so doing, both mechanical strength and electrical grounding are improved. 
     FIGS. 12 and 13 are first and second diagrams of a device using coaxial circulators an element sharing device according to a second embodiment of the present invention, showing another structure by which a secure ground plane within the circulator waveguide space can be obtained. FIG. 12 shows an exploded or disassembled view of the coaxial circulator, with coaxial connectors  31   1 ,  31   2  and  31   3  mounted at side openings in each of three sides of an intermediate block  11 , the Y-shaped conductive inner pattern  13  being soldered between central conductors of each of the three coaxial connectors  31   1 ,  31   2  and  31   3 . Further, upper and lower polytetrafluoroethylene supporters  15   a,    15   b  and upper and lower ferrite members  17   a,    17   b,  respectively, are contained above and below the conductive inner pattern  13 . A bottom surface of the upper block  11   a  is a flat plane which covers an upper surface of the intermediate block  11 . Additionally and similarly, a top surface of the lower block  11   b  is a flat plane which pushes against a bottom surface of the intermediate block  11 . By then fastening these three blocks  11 ,  11   a  and  11   b  together with screws a secure ground plane can be obtained within a waveguide space of the circulator FIG. 13 shows a cross-sectional view of one such above-described fully assembled coaxial circulator. 
     FIGS. 14 and 15 are first and second diagrams of a device using coaxial circulators an element sharing device according to a third embodiment of the present invention, showing another and further structure by which a secure ground plane within a circulator waveguide space can be obtained. FIG. 14 shows an exploded or disassembled view of the coaxial circulator, with polytetrafluoroethylene support  15   b  inserted inside a countersunk hole  16   b  of the lower block  11   b.  The polytetrafluoroethylene support  15   b  extends in a height direction so as to encompass the functions of an upper polytetrafluoroethylene support  15   a,  so the need for such upper polytetrafluoroethylene support  15   a  is eliminated and hence the upper polytetrafluoroethylene support  15   a  is omitted. Into the polytetrafluoroethylene support  15   b  are inserted, in order, the ferrite member  17   b,  the Y-shaped conductive inner pattern  13  and the ferrite member  17   b.  Additionally, coaxial connectors  31   1 ,  31   2  and  31   3  mounted at side openings in each of three sides of a block  11   b,  the Y-shaped conductive inner pattern  13  being soldered between central conductors of each of the three coaxial connectors  31   1 ,  31   2  and  31   3 . At this time a vertical notch portion provided on the polytetrafluoroethylene support  15   b  makes it easier to position the conductive inner pattern  13 . A symmetrically shaped block  11   a  is then positioned atop the block  11   b  and the whole assembly tightened by screws. By so doing, a secure ground plane can be obtained within a waveguide space of the circulator. FIG. 15 shows a cross-sectional view of one such above-described fully assembled coaxial circulator. 
     The above description is provided in order to enable any person skilled in the art to make and use the invention and sets forth the best mode contemplated by the inventor of carrying out the invention. 
     The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the spirit and scope of the present invention. 
     The present application is based on Japanese Priority Application No. 11-212841, filed on Jul. 27, 1999, the entire contents of which are hereby incorporated by reference.