JPWO2019111353A1 - Waveguide directional coupler and polarization separation circuit - Google Patents

Abstract

The first main waveguide (1) and the second main waveguide (2) are arranged so that their respective wide wall surfaces face each other. A branch waveguide (3) is connected between the wide wall surfaces of the first main waveguide (1) and the second main waveguide (2) to connect the openings. The first main waveguide (1) is provided with a first protrusion (4) so that the guide wavelengths of the first main waveguide (1) and the second main waveguide (2) are different from each other. A second protrusion (5) is formed on the wave tube (2).

Description

  The present invention relates to a waveguide directional coupler mainly used in a VHF band, a UHF band, a microwave band, and a millimeter wave band, and a polarization separation circuit using the same.

  As a circuit for separating two orthogonally polarized signals (right-handed, left-handed) or linearly-polarized signals (vertical, horizontal), a circuit called a septum polarizer with a septum phase plate inserted in a square waveguide Are known. The septum polarizer has one square waveguide terminal and two rectangular waveguide terminals whose wide wall faces are adjacent to each other.

  In a septum polarizer, when two orthogonal circularly polarized waves are input from a square waveguide terminal, they are separated into adjacent rectangular waveguide terminals via a septum phase plate and output. On the other hand, when two orthogonal linearly polarized waves are input from the square waveguide terminal, the directions of the same electric field from the two rectangular waveguides or the directions of the opposing electric fields are respectively determined according to the polarization directions. Is output. Therefore, in order to separate linearly polarized waves, it is necessary to connect a directional coupler having a phase difference of 180 degrees to the two rectangular waveguides of the septum polarizer.

  Magic T and rat race are known as general waveguide directional couplers having a phase difference of 180 degrees. When magic T is input to two waveguide terminals in opposite phases, they are combined into one waveguide terminal and output. On the other hand, the rat race is composed of a 90-degree transmission line and a 270-degree transmission line, and when input into two waveguide terminals in opposite phases, they are combined into one waveguide terminal and output.

  In either case, since the two waveguide terminals are separated from each other, a routing transmission line is required to connect the rectangular waveguide terminals to the adjacent septum polarizer. Conventionally, a waveguide directional coupler having a phase difference of 180 degrees by connecting a phase correction circuit to two waveguide terminals as a waveguide directional coupler having no transmission line for such routing. Is known (for example, see FIG. 1 of Non-Patent Document 1).

F. Arndt et al, “Rigorous Modal-S-Matrix Design of A New Class of Broadband 180-Degree Branch Guide Couplers”, 1990 IEEE MTT-S Digest, pp.577-580, IEEE, 1990.

  However, the conventional waveguide directional coupler described in Non-Patent Document 1 has a problem that the size is increased because a general branch line type directional coupler and a phase correction circuit are connected. there were.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a waveguide directional coupler that can be downsized as a waveguide directional coupler having a phase difference of 180 degrees. I do.

  The waveguide directional coupler according to the present invention has a first main waveguide having a rectangular input / output cross-sectional shape, and a rectangular input / output cross-sectional shape, and has a wide wall surface on the long side of the cross section. In the case, the second main waveguide in which the wide wall surface is arranged to face the wide wall surface which is the surface on the long side of the cross section of the first main waveguide, the first main waveguide and the second main waveguide A branch waveguide connecting the openings of the wide wall surfaces of the first main waveguide and the second main waveguide, and the first main waveguide has a tube axis. The second main waveguide has a cross-sectional shape different from the input / output cross-sectional shape in a part of the direction, and the input / output cross-sectional shape of the second main waveguide and the first main waveguide in a part of the tube axial direction. The cross-sectional shape is different from a cross-sectional shape of a part of the tube.

  A waveguide directional coupler according to the present invention connects a first main waveguide and a second main waveguide with a branch waveguide, and forms a first main waveguide and a second main waveguide. The tube wavelengths are different. Thus, it is possible to reduce the size of the waveguide directional coupler having a phase difference of 180 degrees.

FIG. 2 is a perspective view showing a waveguide directional coupler according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view of the waveguide directional coupler according to Embodiment 1 of the present invention. FIG. 2 is an equivalent circuit diagram of the waveguide directional coupler according to Embodiment 1 of the present invention. FIG. 3 is an explanatory diagram illustrating characteristics of the waveguide directional coupler according to Embodiment 1 of the present invention. FIG. 3 is an explanatory diagram illustrating external dimensions of the waveguide directional coupler according to Embodiment 1 of the present invention. FIG. 6 is a sectional view of a waveguide directional coupler according to Embodiment 2 of the present invention. FIG. 8 is an explanatory diagram illustrating characteristics of the waveguide directional coupler according to Embodiment 2 of the present invention. FIG. 13 is a sectional view of a waveguide directional coupler according to Embodiment 3 of the present invention. FIG. 13 is a sectional view of a waveguide directional coupler according to Embodiment 4 of the present invention. FIG. 13 is a sectional view of a polarization separation circuit according to a fifth embodiment of the present invention. FIG. 15 is a perspective view showing a septum polarizer used in the polarization separation circuit according to the fifth embodiment of the present invention. FIG. 14 is an explanatory diagram illustrating external dimensions of a polarization separation circuit according to a fifth embodiment of the present invention.

Hereinafter, in order to explain this invention in greater detail, the preferred embodiments of the present invention will be described with reference to the accompanying drawings.
Embodiment 1 FIG.
FIG. 1 is a perspective view showing the configuration of the waveguide directional coupler according to the present embodiment.
The illustrated waveguide directional coupler includes a first main waveguide 1, a second main waveguide 2, and a plurality of branch waveguides 3. The first main waveguide 1 and the second main waveguide 2 are waveguides each having a rectangular input / output cross-sectional shape. The input and output cross-sectional shapes of the first main waveguide 1 and the second main waveguide 2 are formed to be the same, and the cross-section in the tube axis direction has a long side (hereinafter referred to as a wide wall surface). They are arranged to face each other. The first main waveguide 1 has a first terminal P1 and a second terminal P2, and the second main waveguide 2 has a third terminal P3 and a fourth terminal P4. The plurality of branch waveguides 3 are waveguides for connecting the first main waveguide 1 and the second main waveguide 2, and include the first main waveguide 1 and the second main waveguide 2. Connect the openings on the wide wall surfaces.
A plurality of first protrusions 4 are provided periodically along the tube axis direction on the wide wall surface inside the first main waveguide 1 opposite to the wide wall surface where the branch waveguide 3 opens. On the other hand, a plurality of second protrusions 5 are periodically formed along the tube axis direction on each of the short-side surfaces (hereinafter referred to as narrow wall surfaces) in the tube axis cross section inside the second main waveguide 2. Is provided.

  FIG. 2 is a cross-sectional view of the waveguide directional coupler, in which a cross section 101 is a plane cutting the wide wall surface along the tube axis direction, and a cross section 102 is narrow in parallel with the wide wall surface of the first main waveguide 1. The surface that cuts the wall surface, the cross section 103 is a surface that cuts the narrow wall surface in parallel with the wide wall surface of the second main waveguide 2, and the cross section 104 is parallel to the projection forming direction of the first projection 4 and the second projection 5 Plane.

  As shown in FIG. 2, the first protrusions 4 and the second protrusions 5 have a distribution in which the heights (projection amounts into the waveguide) increase in the central portion in the tube axis direction. By providing such a first projection 4 and a second projection 5 in the first main waveguide 1 and the second main waveguide 2, the first main waveguide 1 is arranged in the tube axis direction. The second main waveguide 2 has a cross-sectional shape different from the input / output cross-sectional shape in a part, and the input / output cross-sectional shape and a part of the first main waveguide 1 in a part in the tube axis direction. It has a cross-sectional shape different from the cross-sectional shape. Here, a part of the cross section of the first main waveguide 1 in the tube axis direction and a part of the cross section of the second main waveguide 2 in the tube axis direction have smaller outer shapes than the input / output cross section.

Next, the operation of the waveguide directional coupler according to the first embodiment will be described.
The first main waveguide 1 provided with the plurality of first protrusions 4 and the second main waveguide 2 provided with the plurality of second protrusions 5 are different because the manner in which the protrusions are provided is different. A waveguide having a guide wavelength is obtained. Therefore, the passing phases are different even for the same physical length. When such main waveguides are connected to each other by the branch waveguide 3, an equivalent circuit is as shown in FIG.

  Here, Port1 is the first terminal P1, Port2 is the second terminal P2, Port3 is the third terminal P3, Port4 is the fourth terminal P4, and Θ1 is the electrical length of the transmission line of the first main waveguide 1. , Θ2 represent the electrical length of the transmission line of the second main waveguide 2, and Θ3 represents the electrical length of the transmission line of the branch waveguide 3. Further, an arrow schematically shows a path of a signal output to the fourth terminal P4 when a signal is input from the first terminal P1 as an example. Since the signal input from the first terminal P1 and output to the fourth terminal P4 is a superposition of the signals of the respective paths, a signal is output at a desired center frequency by appropriately setting each electrical length. And good isolation characteristics can be obtained. Similarly, good reflection, transmission and coupling characteristics can be obtained.

  Regarding the above principle, for the sake of simplicity, the result of an equivalent circuit calculation will be described. FIG. 4 shows the calculation results. In the drawing, respective characteristics of reflection (S11, S44), isolation (S41), passage (S21), and coupling (S31) are shown. It can be seen that good isolation is obtained at the center frequency, and good characteristics are obtained although the reflection characteristics are shifted from the center frequency at the pass terminal and the coupling terminal. Further, the characteristics of the passage and the coupling have the same distribution ratio at the center frequency. Further, it can be seen that a phase difference of 180 degrees is obtained (see S24 and S34).

  As described above, in the present embodiment, the first main waveguide 1 and the second main waveguide 2 are provided with the plurality of different first projections 4 and second projections 5 so that the first main waveguide 1 and the second main waveguide 2 are longer in the tube axis direction. There is an effect that a phase difference of 180 degrees can be obtained without performing.

  Further, as shown in FIG. 5, when the width of the wide wall surface of the input / output waveguide is A, the width of the narrow wall surface is B, and the length of the branch waveguide is C, the present waveguide directional coupler has The outer shape fits within the width A and the width 2B + C, which also has the effect of contributing to miniaturization.

  Further, when the waveguide directional coupler is connected to another component such as a septum polarizer and configured as a polarization separation circuit, the input / output cross-sectional shapes of the first main waveguide and the second main waveguide are used. In the case where is different, it is necessary to match the input and output waveguide dimensions using a transformer or the like, but in this embodiment, since the dimensions of the first main waveguide and the second main waveguide are the same, It is not necessary to provide such a member as a metamorphic unit, and as a result, it is possible to reduce the size of a device such as a polarization separation circuit.

  In FIG. 1, the heights of the plurality of first protrusions 4 and the plurality of second protrusions 5 are shown to have a distribution that increases in the central portion in the tube axis direction, but depending on desired characteristics. The distribution may be different. Further, the numbers of the first projections 4 and the second projections 5 may be set according to desired characteristics. Further, the width of the first protrusion 4 and the second protrusion 5 may be set according to desired characteristics.

  As described above, according to the waveguide directional coupler of the first embodiment, the first main waveguide having the rectangular input / output cross-sectional shape, the rectangular main input / output cross-sectional shape, and the sectional length When the side surface is a wide wall surface, the second main waveguide, which is disposed so as to face the wide wall surface that is the surface on the long side of the cross section of the first main waveguide, includes a first main waveguide. A branch waveguide that connects the openings of the wide wall surfaces of the waveguide and the second main waveguide, wherein the guide wavelengths of the first main waveguide and the second main waveguide are different, and One main waveguide has a cross-sectional shape different from the input / output cross-sectional shape in a part of the tube axis direction, and the second main waveguide has a cross-section of the second main waveguide in a part of the tube axis direction. Since the output cross-sectional shape and the cross-sectional shape of a part of the first main waveguide are different from each other, the waveguide directional coupler has a 180-degree phase difference. It can be miniaturized by.

  Further, according to the waveguide directional coupler of the first embodiment, the first main waveguide and the second main waveguide have the same input / output cross-sectional shape, so that other components are connected. In this case, no special configuration is required, and the size can be reduced when other components are connected.

  Further, according to the waveguide directional coupler of the first embodiment, a partial cross section of the first main waveguide in the tube axis direction and a partial cross section of the second main waveguide in the tube axis direction are formed. Since the outer shape is smaller than the input and output cross sections, desired characteristics can be easily realized.

  Further, according to the waveguide directional coupler of the first embodiment, the first main waveguide has a first projection on the wide wall surface opposite to the wide wall surface to which the branch waveguide is connected. A plurality of second protrusions are provided periodically along the direction, and the second main waveguide has a plurality of second protrusions periodically provided along the tube axis direction on the two surfaces on the short side, Desired characteristics can be easily realized.

  According to the waveguide directional coupler of the first embodiment, the plurality of first protrusions provided on the first main waveguide and the plurality of second protrusions provided on the second main waveguide are provided. The height of the projections has a distribution that increases in the central portion in the tube axis direction, so that desired characteristics can be easily realized.

Embodiment 2 FIG.
In the second embodiment, a space is provided between the connection surface between the branch waveguide 3 and the second main waveguide 2 and the second protrusion 5.
FIG. 6 is a cross-sectional view of the waveguide directional coupler according to the second embodiment. Similar to FIG. 2 according to the first embodiment, a cross section 101 is a plane that cuts a wide wall surface along the tube axis direction. Reference numeral 102 denotes a surface that cuts the narrow wall surface in parallel with the wide wall surface of the first main waveguide 1, cross section 103 denotes a surface that cuts the narrow wall surface in parallel with the wide wall surface of the second main waveguide 2, and cross section 104 denotes the first surface. 2 shows a plane parallel to the direction in which the projections 4 and the second projections 5 are formed.

As shown in FIG. 6, the waveguide directional coupler according to the second embodiment has a space between the second protrusion 5 and the connection surface between the branch waveguide 3 and the second main waveguide 2. A part 6 is provided. Other configurations are the same as those of the first embodiment, and corresponding portions are denoted by the same reference numerals and description thereof will be omitted.
Also in the present embodiment, the first main waveguide 1 and the second main waveguide 2 have different guide wavelengths, so that the same effect as in the first embodiment can be obtained. Further, in the second main waveguide 2, the space 6 is located between the surface to which the branch waveguide 3 is connected and the second protrusion 5, so that the branch waveguide 3 can be easily connected and manufactured. Has the effect of being easier. Furthermore, the size of the space 6 can also be used as a parameter, which has an effect that adjustment for obtaining desired characteristics is easily performed.

  Here, a description will be given of an electromagnetic field calculation result confirmed as to the effectiveness of the present configuration. The electromagnetic field calculation was performed using a commercially available electromagnetic field simulator ANSOFT_HFSS. FIG. 7 shows the calculation results. Here, S11, S41, etc. are the same as those shown in FIG.

  As in the case of the equivalent circuit calculation result shown in FIG. 4, it can be seen that good reflection, isolation, transmission, and coupling characteristics are obtained even in the physical structure. The phase difference is 180 degrees. This characteristic is approximately the same as that of the conventional literature. Therefore, it was confirmed that the length in the tube axis direction can be reduced to about half with the same characteristics as the conventional one.

  As described above, according to the waveguide directional coupler of the second embodiment, the space is provided between the second protrusion and the connection surface between the branch waveguide and the second main waveguide. Since it is provided, there is an effect that manufacturing becomes easy in addition to the effect of the first embodiment. In addition, since the size of the space can be a parameter, there is an effect that adjustment for obtaining desired characteristics can be easily performed.

Embodiment 3 FIG.
In the third embodiment, the length of the branch waveguide in the width direction of the wide wall surface of the first main waveguide and the second main waveguide is set to the length of the first main waveguide and the second main waveguide. It is smaller than the width of the wide wall.
FIG. 8 is a cross-sectional view of the waveguide directional coupler according to the third embodiment. Similar to FIG. 2 in the first embodiment, a cross section 101 is a plane that cuts a wide wall surface along the tube axis direction. Reference numeral 102 denotes a surface that cuts the narrow wall surface in parallel with the wide wall surface of the first main waveguide 1, cross section 103 denotes a surface that cuts the narrow wall surface in parallel with the wide wall surface of the second main waveguide 2, and cross section 104 denotes the first surface. 2 shows a plane parallel to the direction in which the projections 4 and the second projections 5 are formed.

As shown in FIG. 8, the waveguide directional coupler according to the third embodiment has a branch waveguide 7 in the width direction of the wide wall surface of the first main waveguide 1 and the second main waveguide 2. The length (indicated by D in the figure) is smaller (D <A) than the width (indicated by A in the figure) of the wide wall surfaces of the first main waveguide 1 and the second main waveguide 2. Other configurations are the same as those of the first embodiment, and corresponding portions are denoted by the same reference numerals and description thereof will be omitted.
Also in the present embodiment, the first main waveguide 1 and the second main waveguide 2 have different guide wavelengths, so that the same effect as in the first embodiment can be obtained. Furthermore, since the lengths of the branch waveguides 7 in the first and second main waveguide width directions are short, intersections between the branch waveguides 7 and the second protrusions 5 of the second main waveguide 2 can be reduced, There is an effect that manufacturing is easy.

  As described above, according to the waveguide directional coupler of the third embodiment, the length in the width direction of the wide wall surfaces of the first main waveguide and the second main waveguide of the branch waveguide is described. Is smaller than the width of the wide wall surfaces of the first main waveguide and the second main waveguide, so that an effect that manufacturing is easy can be obtained in addition to the effect of the first embodiment.

Embodiment 4 FIG.
In the fourth embodiment, a third projection is provided on a wide wall surface of the first main waveguide 1 or the second main waveguide 2 opposite to the wide wall surface to which the branch waveguide 3 is connected.
FIG. 9 is a cross-sectional view of the waveguide directional coupler according to the fourth embodiment. Similar to FIG. 2 according to the first embodiment, the cross section 101 is a plane that cuts a wide wall surface along the tube axis direction. Reference numeral 102 denotes a surface that cuts the narrow wall surface in parallel with the wide wall surface of the first main waveguide 1, cross section 103 denotes a surface that cuts the narrow wall surface in parallel with the wide wall surface of the second main waveguide 2, and cross section 104 denotes the first surface. 2 shows a plane parallel to the direction in which the projections 4 and the second projections 5 are formed.

As shown in FIG. 9, the waveguide directional coupler according to the fourth embodiment includes a first main waveguide 1 having a wide wall surface facing the wide wall surface to which the branch waveguide 3 is connected in the axial direction of the tube. A third projection 8 is provided along the second projection. Further, the first main waveguide 1 and the second main waveguide 2 are not provided with the first projection 4 and the second projection 5 in the first to third embodiments. The branch waveguide 3 connects the first main waveguide 1 and the second main waveguide 2 as in the first and second embodiments.
Also in the present embodiment, the first main waveguide 1 and the second main waveguide 2 have different guide wavelengths, so that the same effect as in the first embodiment can be obtained. Furthermore, there is an effect that the manufacture is easy as compared with the case where the first projection 4 and the second projection 5 are provided on the first main waveguide 1 and the second main waveguide 2.

  In the above example, the third protrusion 8 is provided on the first main waveguide 1 side, but may be provided on the second main waveguide 2 side.

  As described above, according to the waveguide directional coupler of the fourth embodiment, the wide area of the first main waveguide or the second main waveguide that faces the wide wall surface to which the branch waveguide is connected is connected. Since the third protrusion is provided on the wall surface along the tube axis direction, an effect that manufacturing is easy is obtained in addition to the effect of the first embodiment.

Embodiment 5 FIG.
Embodiment 5 is an example showing a polarization separation circuit in which a septum polarizer and a waveguide directional coupler are connected.
FIG. 10 is a cross-sectional view illustrating a polarization separation circuit according to the fifth embodiment. Similar to FIG. 2 according to the first embodiment, the cross section 101 is a surface that cuts a wide wall along the tube axis direction, and the cross section 103 is a cross section. A plane which cuts the narrow wall surface in parallel with the wide wall surface of the second main waveguide 2, and a cross section 104 shows a plane parallel to the projection forming direction of the first projection 4 and the second projection 5.

As shown in FIG. 10, in the polarization separation circuit of the fifth embodiment, a septum polarizer 9 and a waveguide directional coupler 10 are connected. FIG. 11 is a perspective view showing the septum polarizer 9. As shown, the septum polarizer 9 has a configuration in which a septum phase plate 12 is inserted into a square waveguide 11. The septum polarizer 9 has a square waveguide terminal P5 at one end, and rectangular waveguide terminals P6 and P7 divided by a septum phase plate 12 at the other end. Such a septum polarizer 9 is directly connected to the waveguide directional coupler 10 without using a routing line. That is, the rectangular waveguide terminals P6 and P7 of the septum polarizer 9 are directly connected to the first terminal P1 and the fourth terminal P4 of the waveguide directional coupler 10. Here, the waveguide directional coupler 10 is the waveguide directional coupler in the first embodiment, and the corresponding portions are denoted by the same reference numerals and description thereof will be omitted. Further, as shown in FIG. 12, when viewed from the direction of the cross section 104, all of the septum polarizers 9 are formed so as to fit within the outer shape (A ₁ × A ₁ ).

  In the polarization separation circuit of the fifth embodiment configured as described above, when two orthogonal linear polarized waves are input from the square waveguide terminal P5 of the septum polarizer 9, the rectangular waveguide terminals P6 and P7 are connected to the rectangular waveguide terminals P6 and P7. The signal is further separated by the waveguide directional coupler 10 and output to the second terminal P2 or the third terminal P3 depending on the direction of polarization.

  In the above example, the waveguide directional coupler according to the first embodiment is used as the waveguide directional coupler 10, but similarly, the waveguide directional coupler according to any one of the second to fourth embodiments is used. A waveguide directional coupler may be used.

  As described above, according to the polarization separation circuit of the fifth embodiment, the septum polarizer includes the waveguide directional coupler of any one of the first to fourth embodiments and the septum polarizer. Has one square waveguide terminal and two rectangular waveguide terminals, the two rectangular waveguide terminals of the septum polarizer, the first main waveguide in the waveguide directional coupler, and the second Is connected to the respective waveguide terminals of the main waveguide, the size of the polarization separation circuit can be reduced, and good polarization separation characteristics can be obtained.

  In the present invention, any combination of the embodiments, a modification of an arbitrary component of each embodiment, or an omission of an arbitrary component in each embodiment is possible within the scope of the invention. .

  As described above, the waveguide directional coupler and the polarization separation circuit according to the present invention relate to a circuit that separates two orthogonal circularly polarized signals or linearly polarized signals, and includes a VHF band and a UHF band. It is suitable for separating polarized signals in the microwave band and the millimeter wave band.

  1 first main waveguide, 2 second main waveguide, 3, 7 branch waveguide, 4 first protrusion, 5 second protrusion, 6 space, 8 third protrusion, 9 septum polarizer, Reference Signs List 10 waveguide directional coupler, 11 square waveguide, 12 septum phase plate, P1 first terminal, P2 second terminal, P3 third terminal, P4 fourth terminal, P5 square waveguide terminal , P6, P7 Rectangular waveguide terminal, 101 A surface cutting a wide wall along the tube axis direction, 102 A surface cutting a narrow wall parallel to the wide wall of the first main waveguide, 103 Second main waveguide A plane that cuts the narrow wall surface in parallel with the wide wall surface of the tube, 104 A plane parallel to the direction in which the first and second protrusions are formed.

Claims (9)

A first main waveguide having a rectangular input / output cross-sectional shape,
When the input / output section has a rectangular input / output cross-sectional shape and the long side surface of the cross section is a wide wall surface, the wide wall surface is disposed so as to face the wide wall surface which is the long side surface of the first main waveguide. A second main waveguide,
A branch waveguide that connects the openings of the wide wall surfaces of the first main waveguide and the second main waveguide,
The guide wavelengths of the first main waveguide and the second main waveguide are different, and the first main waveguide has a cross-sectional shape different from the input / output cross-sectional shape in a part of the tube axis direction. The second main waveguide has a cross-sectional shape different from the input / output cross-sectional shape of the second main waveguide and the cross-sectional shape of a part of the first main waveguide in a part in the tube axis direction. A waveguide directional coupler, comprising:   2. The waveguide directional coupler according to claim 1, wherein the input and output cross-sectional shapes of the first main waveguide and the second main waveguide are the same.   The cross section of a part of the first main waveguide in the tube axis direction and the cross section of a part of the second main waveguide in the tube axis direction are each smaller in outer shape than the input / output cross section. Item 2. A waveguide directional coupler according to item 1.   The first main waveguide is provided with a plurality of first protrusions periodically along a tube axis direction on a wide wall surface opposite to a wide wall surface to which the branch waveguide is connected, and the second main waveguide is provided. 2. The waveguide directional coupling according to claim 1, wherein the waveguide has a plurality of second projections periodically provided along two or more tube axial directions on two narrow wall surfaces having short sides. vessel.   The height of the plurality of first protrusions provided on the first main waveguide and the plurality of second protrusions provided on the second main waveguide is such that the distribution increases in the central portion in the tube axis direction. The waveguide directional coupler according to claim 4, wherein   The waveguide directional coupler according to claim 4, wherein a space is provided between the second protrusion and a connection surface between the branch waveguide and the second main waveguide. .   The length in the width direction of the wide wall surface of the first main waveguide and the second main waveguide of the branch waveguide is equal to the width of the first main waveguide and the second main waveguide. The waveguide directional coupler according to claim 1, wherein the width is smaller than a width of a wall surface.   A third projection is provided along a tube axis direction on a wide wall surface of the first main waveguide or the second main waveguide facing the wide wall surface to which the branch waveguide is connected. The waveguide directional coupler according to claim 1, wherein A waveguide directional coupler according to any one of claims 1 to 8 and a septum polarizer,
The septum polarizer has one square waveguide terminal and two rectangular waveguide terminals, and the two rectangular waveguide terminals of the septum polarizer and the first in the waveguide directional coupler. A polarization separation circuit for connecting a main waveguide and respective waveguide terminals of the second main waveguide.

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