Circularly polarized wave generator and method for producing same

Abstract

A circularly polarized wave generator (100) comprises a circular waveguide (10), the inner peripheral surface (10a) of which has a circular opening cross-sectional area, and irises (23) which each form an ellipsoidal opening cross-sectional area by having an ellipsoidal inner peripheral surface (23a) that protrudes from the inner peripheral surface (10a) toward the tube axis (C) of the circular waveguide (10). The irises (23) are periodically disposed in the tube axis direction.

Description

Circular polarizer and its manufacturing method

[0001] The present disclosure relates to a circular polarizer and a method for manufacturing the same.

[0002] A circular polarizer converts an input linearly polarized wave into a circularly polarized wave and outputs it. For this reason, some circular polarizers have a corrugated structure applied to the inner wall surface of the square waveguide that constitutes the circular polarizer. The corrugated structure is a structure in which multiple irises are provided on opposing inner wall surfaces so as to narrow the opening of the square waveguide. The irises are protrusions that protrude from each inner wall surface and are periodically arranged in the tube axial direction.

[0003] When two linearly polarized components that are orthogonal to each other are input to the above-mentioned circular polarizer, the linearly polarized component that is orthogonal to the iris and the linearly polarized component that is parallel to the iris have different phase characteristics. Therefore, by optimally selecting the shape of the iris, a phase difference of approximately 90 degrees occurs between the two linearly polarized components, and a circularly polarized wave is output as a composite wave of these.

[0004] Therefore, the circular polarizer can obtain the desired axial ratio characteristics and reflection characteristics by designing the shape of the iris, i.e., the installation interval, thickness, and width of the iris, so that a predetermined phase difference is achieved in the desired frequency band.

[0005] Such a conventional circular polarizer is disclosed in, for example, Non-Patent Document 1.

[0006] “Design and optimization of dual and wide band polarizer for low cost Ka band applications,” 2006 IEEE

[0007] The circular polarizer disclosed in Non-Patent Document 1 includes a square waveguide. Therefore, when attempting to connect the circular polarizer disclosed in Non-Patent Document 1 to a horn antenna having a circular waveguide terminal, a converter is required between them to connect the different cross-sectional shapes, because the square waveguide and the circular waveguide terminal have different opening cross-sectional shapes.

[0008] Therefore, it is conceivable to apply a circular waveguide to the circular polarizer disclosed in Non-Patent Document 1. Therefore, the circular waveguide and the circular waveguide terminal have the same cross-sectional shape of the opening, and therefore can be connected without using a converter.

[0009] However, when an iris is provided in a circular waveguide, the electric field distribution of the linearly polarized component may be disturbed depending on the shape of the iris, which may result in a deterioration in the axial ratio and reflection characteristics of a circular polarizer equipped with a circular waveguide.

[0010] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a circular polarizer that can suppress disturbance of the electric field distribution of linearly polarized components caused by an iris.

[0011] The circular polarizer according to the present disclosure comprises a circular waveguide whose inner circumferential surface has a circular opening cross section, and an iris having an elliptical inner circumferential surface protruding from the inner circumferential surface toward the tube axis of the circular waveguide, thereby forming an elliptical opening cross section, and the irises are arranged periodically in the tube axis direction.

[0012] According to the present disclosure, it is possible to suppress disturbance of the electric field distribution of the linearly polarized component caused by the iris.

[0013] 1 is an external perspective view of a circular polarizer according to a first embodiment. FIG. 1 is a side view of the circular polarizer according to the first embodiment when viewed from outside in the major axis direction of the elliptical inner peripheral surface of the iris. FIG. 2 is a side view of the circular polarizer according to the first embodiment when viewed from outside in the minor axis direction of the elliptical inner peripheral surface of the iris. FIG. 3 is a plan view of the circular polarizer according to the first embodiment when viewed from one terminal side. FIG. 4 is an external perspective view of a portion of a corrugated portion. FIG. 5 is a side view of a portion of the corrugated portion when viewed from outside in the major axis direction of the elliptical inner peripheral surface of the iris. FIG. 6 is a side view of a portion of the corrugated portion when viewed from outside in the minor axis direction of the elliptical inner peripheral surface of the iris. FIG. 7 is a tube axis direction cross-sectional view of the corrugated portion when viewed from outside in the major axis direction of the elliptical inner peripheral surface of the iris. FIG. 8 is a diagram showing the electric field directions when two linearly polarized wave components that are orthogonal to each other are input to one terminal. 11A is a cross-sectional view of a position in the tube axis direction where irises are provided. FIG. 11B is a cross-sectional view of a position in the tube axis direction where no irises are provided. FIG. 12A is a cross-sectional view of a position in the tube axis direction where irises are provided. FIG. 12B is a cross-sectional view of a position in the tube axis direction where no irises are provided. FIG. 12A is a cross-sectional view of a position in the tube axis direction where irises are provided. FIG. 12B is a cross-sectional view of a position in the tube axis direction where no irises are provided. FIG. 13A is a cross-sectional view of a position in the tube axis direction where irises are provided. FIG. 13B is a cross-sectional view of a position in the tube axis direction where no irises are provided. 1A and 1B are side views of a circular polarizer according to a second embodiment, as viewed from the outside in the major axis direction of the elliptical inner peripheral surface of the iris; FIG. 1C are side views of a circular polarizer according to a second embodiment, as viewed from the outside in the minor axis direction of the elliptical inner peripheral surface of the iris; and FIG. 1D are plan views of a circular polarizer according to a second embodiment, as viewed from one terminal side.1 is an external perspective view of a portion of a corrugated portion; FIG. 2 is a side view of a portion of the corrugated portion as viewed from outside in the major axis direction of the elliptical inner peripheral surface of the iris; FIG. 3 is a side view of a portion of the corrugated portion as viewed from outside in the minor axis direction of the elliptical inner peripheral surface of the iris; FIG. 4 is a plan view of a portion of the corrugated portion as viewed from one of the terminal sides; FIG. 5 is a view of two adjacent irises as viewed from the tube axis direction; FIG. 6 is a cross-sectional view of the corrugated portion as viewed from outside in the major axis direction of the elliptical inner peripheral surface of the iris; FIG. 7 is a diagram showing changes in the minor axis length of each elliptical inner peripheral surface in the tube axis direction; FIG. 8 is an external perspective view of a circular polarizer according to a third embodiment; FIG. 9 is a side view of the circular polarizer according to the third embodiment as viewed from outside in the major axis direction of the elliptical inner peripheral surface of the iris; FIG. 10 is a side view of the circular polarizer according to the third embodiment as viewed from outside in the minor axis direction of the elliptical inner peripheral surface of the iris; FIG. 11 is a plan view of the circular polarizer according to the third embodiment as viewed from one of the terminal sides; FIG. 12 is an external perspective view of a portion of the corrugated portion; 1 is a side view of a portion of the corrugated portion as seen from the outside in the major axis direction of the elliptical inner peripheral surface of the iris. FIG. 2 is a side view of a portion of the corrugated portion as seen from the outside in the minor axis direction of the elliptical inner peripheral surface of the iris. FIG. 3 is a plan view of a portion of the corrugated portion as seen from one terminal side. FIG. 4 is a cross-sectional view of the corrugated portion in the tube axis direction as seen from the outside in the major axis direction of the elliptical inner peripheral surface of the iris. FIG. 5 is an external perspective view of a circular polarizer according to a fourth embodiment. FIG. 6 is a side view of the circular polarizer according to the fourth embodiment as seen from the outside in the major axis direction of the elliptical inner peripheral surface of the iris. FIG. 7 is a side view of the circular polarizer according to the fourth embodiment as seen from the outside in the minor axis direction of the elliptical inner peripheral surface of the iris. FIG. 8 is a plan view of the circular polarizer according to the fourth embodiment as seen from one terminal side. FIG. 9 is an external perspective view of a portion of the corrugated portion. FIG. 10 is a side view of a portion of the corrugated portion as seen from the outside in the major axis direction of the elliptical inner peripheral surface of the iris. FIG. 11 is a side view of a portion of the corrugated portion as seen from the outside in the minor axis direction of the elliptical inner peripheral surface of the iris. 1 is a plan view of a part of the corrugated portion as seen from one terminal side, and FIG. 2 is a cross-sectional view of the corrugated portion as seen from the outside in the major axis direction of the elliptical inner peripheral surface of the iris.

[0014] In order to explain the present disclosure in more detail, embodiments of the present disclosure will be described below with reference to the accompanying drawings.

[0015] First Embodiment A circular polarizer 100 according to a first embodiment will be described with reference to FIGS.

[0016] First, the configuration of a circular polarizer 100 according to the first embodiment will be described with reference to FIGS. 1 to 9. FIG.

[0017] FIG. 1 is an external perspective view of a circular polarizer 100 according to a first embodiment. FIG. 2 is a side view of the circular polarizer 100 according to the first embodiment, as seen from outside in the major axis direction of the elliptical inner peripheral surface 13a of the iris 13. FIG. 3 is a side view of the circular polarizer 100 according to the first embodiment, as seen from outside in the minor axis direction of the elliptical inner peripheral surface 13a of the iris 13. FIG. 4 is a plan view of the circular polarizer 100 according to the first embodiment, as seen from one terminal 11a side. FIG. 5 is an external perspective view of a portion of the corrugated portion 12. FIG. 6 is a side view of a portion of the corrugated portion 12, as seen from outside in the major axis direction of the elliptical inner peripheral surface 13a of the iris 13. FIG. 7 is a side view of a portion of the corrugated portion 12, as seen from outside in the minor axis direction of the elliptical inner peripheral surface 13a of the iris 13. FIG. 8 is a plan view of a portion of the corrugated portion 12, as seen from one terminal 11a side. FIG. 9 is a cross-sectional view of the corrugated portion 12 in the tube axis direction when viewed from the outside of the elliptical inner peripheral surface 13 a of the iris 13 in the major axis direction.

[0018] The circular polarizer 100 according to the first embodiment shown in FIG. 1 converts an input linearly polarized wave into a circularly polarized wave and outputs the converted wave. Specifically, when the circular polarizer 100 decomposes the input linearly polarized wave into two linearly polarized wave components that are orthogonal to each other, it can delay the passing phase of one linearly polarized wave component relative to the passing phase of the other linearly polarized wave component. This allows the circular polarizer 100 to output the input linearly polarized wave as a circularly polarized wave. The circular polarizer 100 has a corrugated structure in the waveguide as a means for generating a phase delay in the linearly polarized wave component. Details of this corrugated structure will be described later.

[0019] Circular polarizer 100 is connected to, for example, a horn antenna (not shown) having a circular waveguide terminal. The circular waveguide terminal of this horn antenna is a standard waveguide with a circular cross section. Circular polarizer 100 is primarily used in frequency bands such as the VHF (Very High Frequency) band, the UHF (Ultra High Frequency) band, the microwave band, and the millimeter wave band.

[0020] As shown in FIGS. 1 to 4 , the circular polarizer 100 includes a circular waveguide 10 having a corrugated structure. The circular waveguide 10 is cylindrical. The tube axis C of the circular waveguide 10 is the central axis of the circular waveguide 10. The inner circumferential surface 10a and the outer circumferential surface 10b of the circular waveguide 10 form a circle centered on the tube axis C. That is, the opening cross section formed by the inner circumferential surface 10a of the circular waveguide 10 and perpendicular to the tube axis direction is circular. The inner circumferential surface 10a, together with the surface of an iris 13 described below, constitutes a waveguide that propagates electromagnetic waves. The electromagnetic waves are, for example, linearly polarized waves that can propagate through the circular waveguide 10 in a predetermined frequency band.

[0021] As shown in FIGS. 1 to 9, the circular waveguide 10 has terminals 11 a and 11 b, a corrugated portion 12 , and a plurality of irises 13 .

[0022] One terminal 11a constitutes one end of the circular waveguide 10. The other terminal 11b constitutes the other end of the circular waveguide 10. Terminal 11b can be connected to, for example, a circular waveguide terminal of a horn antenna. Therefore, in the circular waveguide 10, when a linearly polarized wave is input to terminal 11a, a circularly polarized wave is output from terminal 11b. Next, the circularly polarized wave output from terminal 11b is propagated to the horn antenna via the circular waveguide terminal of the horn antenna. The circularly polarized wave propagated to the horn antenna is then radiated into the air as an electromagnetic wave.

[0023] The corrugated portion 12 is provided at the center of the circular waveguide 10 in the tube axis direction. The corrugated portion 12 is arranged between the terminals 11a and 11b in the tube axis direction of the circular waveguide 10. The corrugated portion 12 has a plurality of irises 13 that protrude from the inner circumferential surface 10a that serves as a waveguide in the tube axis direction. All of the irises 13 in each stage have the same size and shape. It is sufficient that the corrugated portion 12 has at least one iris 13.

[0024] As shown in FIGS. 1 to 3 , the irises 13 are periodically arranged in the tube axis direction on the inner circumferential surface 10a of the circular waveguide 10 that corresponds to the corrugated portion 12. As shown in FIG. 4 , the irises 13 are formed to protrude from the inner circumferential surface 10a toward the tube axis C so that the shape of the inner circumferential surface is elliptical. The center of this elliptical inner circumferential surface 13a is coaxial with the tube axis C. The elliptical inner circumferential surface 13a is a single, continuous surface without any steps. Therefore, in the corrugated portion 12, the opening cross section at the tube axis position where the irises 13 are arranged is elliptical. In this case, the elliptical shape of the elliptical inner circumferential surface 10a does not include a linear shape, and therefore the elliptical opening cross section also does not include a linear shape.

[0025] 1 to 3, the irises 13 are disposed at positions symmetrical on the left and right sides with respect to the axial center of the corrugated portion 12. Also, as shown in Fig. 9, the circumferential cross section of the iris 13 is rectangular.

[0026] In addition, if the inner surface 10a side of the iris 13 is the base end side of the iris 13 and the tube axis C side of the iris 13 is the tip side of the iris 13, the elliptical inner surface 13a of the iris 13 is an elliptical surface formed at the tip of the iris 13.

[0027] As shown in Fig. 8, the major axis length of the elliptical inner circumferential surface 13a is equal to or shorter than the diameter of the inner circumferential surface 10a of the corrugated portion 12. The minor axis length of the elliptical inner circumferential surface 13a is shorter than the diameter of the inner circumferential surface 10a of the corrugated portion 12. Therefore, the opening cross sections of the elliptical inner circumferential surfaces 13a of all the irises 13 are inscribed in the opening cross section of the inner circumferential surface 10a or are located radially inward of the opening cross section of the inner circumferential surface 10a. Note that Fig. 8 shows an example in which the opening cross section of the elliptical inner circumferential surface 13a is inscribed in the opening cross section of the inner circumferential surface 10a.

[0028] Furthermore, in the circular polarizer 100 according to the first embodiment, the length of the major axis of the elliptical inner peripheral surface 13 a is not longer than the diameter of the outer peripheral surface 10 b, which prevents the circular waveguide 10 from becoming larger in the radial outward direction and also makes it easier to manufacture the circular waveguide 10.

[0029] In the circular waveguide polarizer 100 according to the first embodiment, when the iris 13 is provided, the portion of the outer peripheral surface 10b corresponding to the iris 13 is formed in a concave shape along the circumferential direction, but it is not necessary to form such a concave portion in the outer peripheral surface 10b.

[0030] Here, let us consider the case where two linearly polarized components are input to terminal 11a using Fig. 10. Fig. 10 is a diagram showing the electric field directions when two linearly polarized components that are orthogonal to each other are input to one terminal 11a. In Fig. 10, one linearly polarized component is indicated by a solid arrow, and the other linearly polarized component is indicated by a dotted arrow.

[0031] One linearly polarized wave component shown by a solid line is a linearly polarized wave having an electric field direction in the minor axis direction of the elliptical inner circumferential surface 13 a, and the other linearly polarized wave component shown by a dotted line is a linearly polarized wave having an electric field direction in the major axis direction of the elliptical inner circumferential surface 13 a.

[0032] The transmission phases of one linearly polarized component and the other linearly polarized component are different from each other. Therefore, a phase difference of approximately 90 degrees is generated between one linearly polarized component and the other linearly polarized component by optimally setting the shape of the elliptical inner peripheral surface 13a of the iris 13 and the installation interval in the tube axis direction. The shape of the elliptical inner peripheral surface 13a refers to, for example, the thickness in the tube axis direction, the radius of curvature, the major axis length, and the minor axis length. Therefore, when one linearly polarized wave is input from the terminal 11a, it is considered that the one linearly polarized wave is decomposed into one linearly polarized component and the other linearly polarized component. As a result, a circularly polarized signal that is a composite wave of one linearly polarized component and the other linearly polarized component is output from the other terminal 11b.

[0033] Next, the effects of the circular waveguide polarizer 100 according to the first embodiment will be described in comparison with a conventional example with reference to Figures 11 to 13. Figures 11 to 13 are views as viewed from the tube axis direction.

[0034] 11 is a diagram showing the electric field distribution and electric field direction when a linearly polarized component orthogonal to the tip faces 51 a of a pair of irises 51 provided in a square waveguide 50 of a conventional circular polarizer (not shown) is input. In Fig. 11, multiple solid arrows indicate the electric field distribution of the linearly polarized component, and the direction of the arrows indicates the electric field direction of the linearly polarized component.

[0035] 11A and 11B, the square waveguide 50 has a square opening cross section perpendicular to the tube axis direction. As shown in Fig. 11A, a pair of irises 51 are provided on opposing inner wall surfaces of the square waveguide 50. The pair of tip surfaces 51a are both formed linearly. The opening cross section formed by the pair of tip surfaces 51a is rectangular.

[0036] 11A and 11B, the electric field distributions shown in both Fig. 11A and Fig. 11B are linear, and therefore there is almost no difference between the electric field distributions and electric field directions.

[0037] 12 is a diagram showing the electric field distribution and electric field direction when linearly polarized components orthogonal to the tip faces 61 a of a pair of irises 61 provided in a circular waveguide 60 of a conventional circular polarizer (not shown) are input. In Fig. 12, multiple solid arrows indicate the electric field distribution of the linearly polarized components, and the direction of the arrows indicates the electric field direction of the linearly polarized components.

[0038] 12A and 12B, the circular waveguide 60 has a circular opening cross section perpendicular to the tube axis direction. As shown in Fig. 12A, a pair of irises 61 are arranged to be point-symmetrical with respect to the tube axis C of the circular waveguide 60. The pair of tip surfaces 61a are both formed linearly. The opening cross section formed by the pair of tip surfaces 61a is elliptical. This elliptical opening cross section includes a linear shape corresponding to the linear tip surfaces 61a.

[0039] Comparing the electric field distribution and electric field direction between Figures 12A and 12B, the electric field distribution shown in Figure 12A is formed linearly. On the other hand, the electric field distribution shown in Figure 12B is formed linearly in the center of the distribution direction, but is curved on both sides. Therefore, there is a large difference between the electric field distributions and electric field directions. In other words, the electric field distribution corresponding to the pair of irises 61 shown in Figure 12A is formed linearly, and can be said to be distorted compared to the electric field distribution not corresponding to the pair of irises 61 shown in Figure 12B.

[0040] 13 is a diagram showing the electric field distribution and electric field direction when a linearly polarized signal is input that is orthogonal to the major axis direction of the elliptical inner circumferential surface 13a of the iris 13 provided in the circular waveguide 10 of the circular polarizer 100 according to embodiment 1. In Fig. 13, multiple solid arrows indicate the electric field distribution of the linearly polarized component, and the direction of the arrows indicates the electric field direction of the linearly polarized component.

[0041] The electric field distribution shown in Figure 13A is linear in the center of the distribution direction, with curved portions on both sides. The electric field distribution shown in Figure 13B is linear in the center of the distribution direction, with curved portions on both sides. Therefore, there is almost no difference between the electric field distributions and electric field directions. As a result, although the circular polarizer 100 according to the first embodiment includes the iris 13, the iris 13 has an elliptical inner peripheral surface 13a, which can suppress disturbance in the electric field distribution of the linearly polarized component. Therefore, the circular polarizer 100 according to the first embodiment can obtain good axial ratio characteristics and reflection characteristics.

[0042] Second Embodiment A circular polarizer 200 according to a second embodiment will be described with reference to Figures 14 to 24. Components having the same functions as those described in the first embodiment above will be assigned the same reference numerals, and descriptions thereof will be omitted.

[0043] FIG. 14 is an external perspective view of a circular polarizer 200 according to the second embodiment. FIG. 15 is a side view of the circular polarizer 200 according to the second embodiment, as seen from outside in the major axis direction of the elliptical inner peripheral surface 23 a of the iris 23. FIG. 16 is a side view of the circular polarizer 200 according to the second embodiment, as seen from outside in the minor axis direction of the elliptical inner peripheral surface 23 a of the iris 23. FIG. 17 is a plan view of the circular polarizer 200 according to the second embodiment, as seen from one of the terminals 11 a. FIG. 18 is an external perspective view of a portion of the corrugated portion 22. FIG. 19 is a side view of a portion of the corrugated portion 22, as seen from outside in the major axis direction of the elliptical inner peripheral surface 23 a of the iris 23. FIG. 20 is a side view of a portion of the corrugated portion 22, as seen from outside in the minor axis direction of the elliptical inner peripheral surface 23 a of the iris 23. FIG. 21 is a plan view of a portion of the corrugated portion 22, as seen from one of the terminals 11 a. Fig. 22 is a diagram of two adjacent irises 23 as viewed in the tube axis direction. Fig. 23 is a cross-sectional view of the corrugated portion 22 as viewed from the outside in the major axis direction of the elliptical inner peripheral surface 23a of each iris 23. Fig. 24 is a diagram showing the change in the minor axis length of each elliptical inner peripheral surface 23a in the tube axis direction.

[0044] The circular polarizer 200 according to the second embodiment includes a circular waveguide 20 instead of the circular waveguide 10 of the circular polarizer 100 according to the first embodiment.

[0045] As shown in Figures 14 to 17, the circular polarizer 200 includes a circular waveguide 20 having a corrugated structure. The circular waveguide 20 is cylindrical. The tube axis C of the circular waveguide 20 is the central axis of the circular waveguide 20. The inner circumferential surface 20a and the outer circumferential surface 20b of the circular waveguide 20 form a circle centered on the tube axis C. In other words, the opening cross section formed by the inner circumferential surface 20a of the circular waveguide 20 and perpendicular to the tube axis direction is circular. The inner circumferential surface 20a, together with the surface of an iris 23 described below, constitutes a waveguide that propagates electromagnetic waves. The electromagnetic waves are, for example, linearly polarized waves that can propagate through the circular waveguide 20 in a predetermined frequency band.

[0046] As shown in FIGS. 14 to 23, the circular waveguide 20 has terminals 11a and 11b, a corrugated portion 22, and a plurality of pairs of irises 23.

[0047] The corrugated portion 22 is provided at the center of the circular waveguide 20 in the tube axis direction. The corrugated portion 22 is disposed between the terminals 11a and 11b in the tube axis direction of the circular waveguide 20. The corrugated portion 22 has a barrel-shaped cylindrical shape. One end of the corrugated portion 22 is an end on the terminal 11a side. The other end of the corrugated portion 22 is an end on the terminal 11b side.

[0048] The diameter of the inner peripheral surface 20a of the corrugated portion 22 gradually increases from one end and the other end of the corrugated portion 22 toward the center in the axial direction of the tube. That is, the opening cross section of the corrugated portion 22 gradually increases from one end and the other end of the corrugated portion 22 toward the center in the axial direction of the tube. Also, the diameter of the outer peripheral surface 20b of the corrugated portion 22 gradually increases from one end and the other end of the corrugated portion 22 toward the center in the axial direction of the tube.

[0049] The diameters of the inner peripheral surface 20a and the outer peripheral surface 20b at one end of the corrugated portion 22 are the same as those of the inner peripheral surface 20a and the outer peripheral surface 20b of the terminal 11a, and the diameters of the inner peripheral surface 20a and the outer peripheral surface 20b at the other end of the corrugated portion 22 are the same as those of the inner peripheral surface 20a and the outer peripheral surface 20b of the terminal 11b.

[0050] The corrugated portion 22 has a plurality of irises 23 protruding from the inner circumferential surface 20a, which serves as a waveguide, in the tube axis direction. The corrugated portion 22 is required to have at least one iris 23.

[0051] As shown in Figures 14 to 16, the irises 23 are periodically arranged in the tube axis direction on the inner circumferential surface 20a of the circular waveguide 20 corresponding to the corrugated portion 22. As shown in Figure 21, the irises 23 are formed to protrude from the inner circumferential surface 20a toward the tube axis C so that the shape of the inner circumferential surface is elliptical. The center of this elliptical inner circumferential surface 23a is coaxial with the tube axis C. The elliptical inner circumferential surface 23a is a single, continuous surface without any steps. Therefore, in the corrugated portion 22, the opening cross section at the tube axis position where the irises 23 are arranged is elliptical. In this case, the elliptical shape of the elliptical inner circumferential surface 23a does not include a linear shape, and therefore the elliptical opening cross section also does not include a linear shape.

[0052] 14 to 16, the irises 23 are disposed at positions symmetrical on the left and right sides with respect to the axial center of the corrugated portion 22. In addition, as shown in Fig. 23, the circumferential cross section of the iris 23 is rectangular.

[0053] As described above, the diameters of the inner peripheral surface 20a and the outer peripheral surface 20b of the corrugated portion 22 gradually increase from one end to the other toward the center in the axial direction of the tube. Correspondingly, the shape of the iris 23 also gradually changes from one end to the other toward the center in the axial direction of the tube.

[0054] For example, the major axis length and the minor axis length of the elliptical inner peripheral surface 23a of the iris 23 gradually increase from one end and the other end of the corrugated portion 22 toward the center in the axial direction of the tube. Therefore, the elliptical opening cross section formed by the elliptical inner peripheral surface 23a of the iris 23 gradually increases from one end and the other end of the corrugated portion 22 toward the center in the axial direction of the tube.

[0055] As shown in Figure 21 , the major axis length of the elliptical inner circumferential surface 23a is equal to or shorter than the diameter of the inner circumferential surface 20a of the corrugated portion 22. The minor axis length of the elliptical inner circumferential surface 23a is shorter than the diameter of the inner circumferential surface 20a of the corrugated portion 22. Therefore, the opening cross sections of the elliptical inner circumferential surfaces 23a of all irises 23 are inscribed in the opening cross sections of the corresponding inner circumferential surfaces 20a or are located radially inward of the opening cross sections of the corresponding inner circumferential surfaces 20a. Note that Figure 21 shows an example in which the opening cross sections of the elliptical inner circumferential surfaces 23a are inscribed in the opening cross sections of the inner circumferential surfaces 20a.

[0056] Therefore, there is almost no difference between the electric field distribution on the elliptical inner peripheral surface 23a of the iris 23 and the electric field distribution on the inner peripheral surface 20a of the corrugated portion 22. For this reason, the circular polarizer 200 according to the second embodiment can suppress disturbance of the electric field distribution of the linearly polarized wave component due to the elliptical inner peripheral surface 23a of the iris 23. Therefore, the circular polarizer 200 according to the second embodiment can obtain good axial ratio characteristics and reflection characteristics.

[0057] Furthermore, in the circular polarizer 200 according to the second embodiment, the elliptical opening cross section formed by the elliptical inner peripheral surface 23a of the iris 23 can be gradually enlarged from one end and the other end of the corrugated portion 22 toward the center in the tube axis direction. Therefore, the circular polarizer 200 according to the second embodiment can lower the cutoff frequency of the propagating linearly polarized wave component. As a result, the circular polarizer 200 according to the second embodiment can obtain a wide frequency band.

[0058] Furthermore, circular polarizer 200 according to the second embodiment can be used as is without increasing the inner and outer diameters of terminals 11 a and 11 b. Therefore, in circular polarizer 200 according to the second embodiment, terminal 11 b can be connected to a circular waveguide terminal that serves as a standard waveguide in a horn antenna.

[0059] Furthermore, as shown in FIG. 24 , the circular polarizer 200 according to the second embodiment may vary the minor axis length of each elliptical inner circumferential surface 23 a in the tube axis direction. Curve L shown in FIG. 24 indicates the change in the minor axis length of each elliptical inner circumferential surface 23 a in the tube axis direction. This curve L varies like a trigonometric function, with its apex at the center of the corrugated portion 22 in the tube axis direction. The minor axis length at the apex is the longest. Therefore, the circular polarizer 200 according to the second embodiment can gradually vary the minor axis position of the elliptical inner circumferential surface 23 a of the iris 23. As a result, the circular polarizer 200 according to the second embodiment can achieve even better axial ratio characteristics and reflection characteristics.

[0060] Embodiment 3 A circular polarizer 300 according to embodiment 3 will be described with reference to Figures 25 to 33. Note that components having the same functions as those described in the above-mentioned embodiments 1 and 2 will be given the same reference numerals, and their description will be omitted.

[0061] FIG. 25 is an external perspective view of a circular polarizer 300 according to the third embodiment. FIG. 26 is a side view of the circular polarizer 300 according to the third embodiment, as seen from outside in the major axis direction of the elliptical inner circumferential surface 23 a of the iris 23A. FIG. 27 is a side view of the circular polarizer 300 according to the third embodiment, as seen from outside in the minor axis direction of the elliptical inner circumferential surface 23 a of the iris 23A. FIG. 28 is a plan view of the circular polarizer 300 according to the third embodiment, as seen from one terminal 11 a side. FIG. 29 is an external perspective view of a portion of the corrugated portion 22A. FIG. 30 is a side view of a portion of the corrugated portion 22A, as seen from outside in the major axis direction of the elliptical inner circumferential surface 23 a of the iris 23A. FIG. 31 is a side view of a portion of the corrugated portion 22A, as seen from outside in the minor axis direction of the elliptical inner circumferential surface 23 a of the iris 23A. Fig. 32 is a plan view of a part of the corrugated portion 22A as seen from one terminal 11a side. Fig. 33 is a cross-sectional view of the corrugated portion 22A in the tube axis direction as seen from the outside in the major axis direction of the elliptical inner peripheral surface 23a of the iris 23A.

[0062] Circular polarizer 300 according to embodiment 3 includes an iris 23A in corrugated portion 22A instead of iris 23 in corrugated portion 22 of circular polarizer 200 according to embodiment 2. Corrugated portion 22A has the same configuration as corrugated portion 22 except for iris 23.

[0063] 25 to 31, the iris 23A is provided on the inner circumferential surface 20a of the circular waveguide 20 corresponding to the corrugated portion 22A. As shown in Fig. 32, the iris 23A is formed to protrude from the inner circumferential surface 20a toward the tube axis C so that the shape of the inner circumferential surface is elliptical. The center of this elliptical inner circumferential surface 23a is coaxial with the tube axis C. The elliptical inner circumferential surface 23a is also a single, continuous surface without any steps. Therefore, in the corrugated portion 22A, the opening cross section at the tube axis direction position where the iris 23A is arranged is elliptical.

[0064] As shown in Figures 25 to 27, the iris 23A is disposed at positions symmetrical on the left and right sides with respect to the axial center of the corrugated portion 22A. Also, as shown in Figure 33, the cross section of the iris 23A in the circumferential direction is trapezoidal. Details of the cross-sectional shape of the iris 23A will be described later.

[0065] As described above, the diameters of the inner peripheral surface 20a and the outer peripheral surface 20b of the corrugated portion 22A gradually increase from one end to the other toward the center in the axial direction of the tube. Correspondingly, the shape of the iris 23A also gradually changes from one end to the other toward the center in the axial direction of the tube.

[0066] For example, the major and minor axis lengths of the elliptical inner peripheral surface 23a of the iris 23A gradually increase from one end and the other end of the corrugated portion 22A toward the center in the axial direction of the tube, so that the elliptical opening cross section formed by the elliptical inner peripheral surface 23a of the iris 23A gradually increases from one end and the other end of the corrugated portion 22A toward the center in the axial direction of the tube.

[0067] As shown in Figure 32, the major axis of the elliptical inner circumferential surface 23a is equal to or shorter than the diameter of the inner circumferential surface 20a of the corrugated portion 22A. The minor axis of the elliptical inner circumferential surface 23a is shorter than the diameter of the inner circumferential surface 20a of the corrugated portion 22A. Therefore, the cross sections of the openings of the elliptical inner circumferential surfaces 23a of all irises 23A are inscribed in the cross sections of the openings of the corresponding inner circumferential surfaces 20a or are positioned radially inward of the cross sections of the openings of the corresponding inner circumferential surfaces 20a. Note that Figure 32 illustrates an example in which the cross sections of the openings of the elliptical inner circumferential surfaces 23a are inscribed in the cross sections of the openings of the inner circumferential surfaces 20a.

[0068] Therefore, there is almost no difference between the electric field distribution on the elliptical inner circumferential surface 23 a of the iris 23A and the electric field distribution on the inner circumferential surface 20 a of the corrugated portion 22A. Therefore, the circular polarizer 300 according to the third embodiment can suppress the disturbance of the electric field distribution of the linearly polarized component caused by the elliptical inner circumferential surface 23 a of the iris 23A. Therefore, the circular polarizer 300 according to the third embodiment can obtain good axial ratio characteristics and reflection characteristics.

[0069] 30 and 33 , the iris 23A has a trapezoidal cross section in the circumferential direction. Specifically, the iris 23A has a right-angled trapezoidal cross section. The iris 23A has an elliptical inner circumferential surface 23a corresponding to the upper side of the trapezoid, and an orthogonal surface 31a and an inclined surface 31b corresponding to a pair of legs of the trapezoid. The orthogonal surface 31a is disposed on the terminal 11a side and is perpendicular to the elliptical inner circumferential surface 23a. The inclined surface 31b is disposed on the terminal 11b side and is inclined at an inclination angle θ with respect to the elliptical inner circumferential surface 23a. The circular polarizer 300 according to the third embodiment can improve the rigidity of the circular waveguide 20 by providing the iris 23A having a trapezoidal cross section in the corrugated portion 22A of the circular waveguide 20.

[0070] Next, a method for manufacturing the circular polarizer 300 according to the third embodiment will be described.

[0071] When the circular waveguide 20 is formed of a conductive metal, the circular polarizer 300 can be manufactured using a 3D printer. For example, the circular polarizer 300 is manufactured using a metal 3D printer with additive manufacturing technology, from the ground-side terminal 11b toward the sky-side terminal 11a, so that the tube axis C is perpendicular to the ground. In this case, the inclination angle θ of the inclined surface 31b is set to a value greater than or equal to 45 degrees and less than 90 degrees. Therefore, in a manufacturing method using a metal 3D printer with additive manufacturing technology, the corrugated portion 22A can be manufactured while preventing collapse by stacking the orthogonal surface 31a and the inclined surface 31b so that the inclined surface 31b is positioned on the ground side.

[0072] Furthermore, the circular polarizer 300 according to the third embodiment may be manufactured using a resin 3D printer with additive manufacturing technology, similar to additive manufacturing using a metal 3D printer. In this case, after the circular waveguide 20 is additively manufactured, a conductive metal plating is applied to the surface to form a plating layer.

[0073] Fourth Embodiment A circular waveguide polarizer 400 according to a fourth embodiment will be described with reference to Fig. 34 to Fig. 42. Components having the same functions as those described in the first and second embodiments above will be assigned the same reference numerals, and descriptions thereof will be omitted.

[0074] FIG. 34 is an external perspective view of a circular polarizer 400 according to the fourth embodiment. FIG. 35 is a side view of the circular polarizer 400 according to the fourth embodiment, as seen from outside in the major axis direction of the elliptical inner circumferential surface 23 a of the iris 23B. FIG. 36 is a side view of the circular polarizer 400 according to the fourth embodiment, as seen from outside in the minor axis direction of the elliptical inner circumferential surface 23 a of the iris 23B. FIG. 37 is a plan view of the circular polarizer 400 according to the fourth embodiment, as seen from one of the terminals 11 a. FIG. 38 is an external perspective view of a portion of the corrugated portion 22B. FIG. 39 is a side view of a portion of the corrugated portion 22B, as seen from outside in the major axis direction of the elliptical inner circumferential surface 23 a of the iris 23B. FIG. 40 is a side view of a portion of the corrugated portion 22B, as seen from outside in the minor axis direction of the elliptical inner circumferential surface 23 a of the iris 23B. Fig. 41 is a plan view of a portion of the corrugated portion 22B as seen from one terminal side, and Fig. 42 is a cross-sectional view of the corrugated portion 22B in the tube axis direction as seen from the outside in the major axis direction of the elliptical inner peripheral surface 23a of the iris 23B.

[0075] Circular polarizer 400 according to embodiment 4 includes iris 23B in corrugated portion 22B instead of iris 23A in corrugated portion 22A of circular polarizer 300 according to embodiment 3. Corrugated portion 22B has the same configuration as corrugated portion 22A except for iris 23A.

[0076] As shown in Figures 34 to 42, the iris 23B is provided on the inner circumferential surface 20a of the circular waveguide 20 corresponding to the corrugated portion 22B. As shown in Figure 41, the iris 23B is formed to protrude from the inner circumferential surface 20a toward the tube axis C so that the shape of the inner circumferential surface is elliptical. The center of this elliptical inner circumferential surface 23a is coaxial with the tube axis C. Furthermore, the elliptical inner circumferential surface 23a is a single, continuous surface without any steps. Therefore, in the corrugated portion 22B, the opening cross section at the tube axis direction position where the iris 23B is arranged is elliptical.

[0077] As shown in Figures 34 to 36, the iris 23B is disposed at positions symmetrical on the left and right sides with respect to the axial center of the corrugated portion 22B. Also, as shown in Figure 42, the cross section of the iris 23B in the circumferential direction is trapezoidal. Details of the cross-sectional shape of the iris 23B will be described later.

[0078] As described above, the diameters of the inner peripheral surface 20a and the outer peripheral surface 20b of the corrugated portion 22B gradually increase from one end to the other toward the center in the axial direction of the tube. Correspondingly, the shape of the iris 23B also gradually changes from one end to the other toward the center in the axial direction of the tube.

[0079] For example, the major and minor axis lengths of the elliptical inner peripheral surface 23a of the iris 23B gradually increase from one end and the other end of the corrugated portion 22B toward the center in the axial direction of the tube, so that the elliptical opening cross section formed by the elliptical inner peripheral surface 23a of the iris 23B gradually increases from one end and the other end of the corrugated portion 22B toward the center in the axial direction of the tube.

[0080] As shown in Figure 41, the major axis length of the elliptical inner circumferential surface 23a is equal to or shorter than the diameter of the inner circumferential surface 20a of the corrugated portion 22B. The minor axis length of the elliptical inner circumferential surface 23a is shorter than the diameter of the inner circumferential surface 20a of the corrugated portion 22B. Therefore, the opening cross sections of the elliptical inner circumferential surfaces 23a of all irises 23B are inscribed in the opening cross sections of the corresponding inner circumferential surfaces 20a or are positioned radially inward of the opening cross sections of the corresponding inner circumferential surfaces 20a. Note that Figure 41 illustrates an example in which the opening cross sections of the elliptical inner circumferential surfaces 23a are inscribed in the opening cross sections of the inner circumferential surfaces 20a.

[0081] Therefore, there is almost no difference between the electric field distribution on the elliptical inner circumferential surface 23a of the iris 23B and the electric field distribution on the inner circumferential surface 20a of the corrugated portion 22B. Therefore, the circular polarizer 400 according to the fourth embodiment can suppress the disturbance of the electric field distribution of the linearly polarized component caused by the elliptical inner circumferential surface 23a of the iris 23B. Therefore, the circular polarizer 300 according to the fourth embodiment can obtain good axial ratio characteristics and reflection characteristics.

[0082] Here, as shown in Figures 39 and 42, the circumferential cross section of the iris 23B is trapezoidal. Specifically, the circumferential cross section of the iris 23B is an isosceles trapezoid. The iris 23B has an elliptical inner circumferential surface 23a corresponding to the upper side of the trapezoid and inclined surfaces 41a and 41b corresponding to a pair of legs of the trapezoid. The inclined surface 41a is disposed on the terminal 11a side and is inclined at an inclination angle θ with respect to the elliptical inner circumferential surface 23a. The inclined surface 41b is disposed on the terminal 11b side and is inclined at an inclination angle θ with respect to the elliptical inner circumferential surface 23a. The circular polarizer 400 according to the third embodiment can improve the rigidity of the circular waveguide 20 by providing the iris 23B having a trapezoidal circumferential cross section in the corrugated portion 22B of the circular waveguide 20.

[0083] Next, a method for manufacturing the circular polarizer 400 according to the fourth embodiment will be described.

[0084] When the circular waveguide 20 is formed of a conductive metal, the circular polarizer 400 can be manufactured using a 3D printer. For example, the circular polarizer 400 is manufactured using a metal 3D printer with additive manufacturing technology, from the ground-side terminal 11b toward the sky-side terminal 11a, so that the tube axis C is perpendicular to the ground. In this case, the inclination angle θ of the inclined surfaces 41a, 41b is set to a value greater than or equal to 45 degrees and less than 90 degrees. Therefore, in a manufacturing method using a metal 3D printer with additive manufacturing technology, by providing the inclined surfaces 41a, 41b on the iris 23B, collapse of the corrugated portion 22A can be prevented during manufacturing.

[0085] Furthermore, the circular polarizer 400 according to the fourth embodiment may be manufactured by a resin 3D printer with additive manufacturing technology, similar to additive manufacturing using a metal 3D printer. In this case, after the circular waveguide 20 is additively manufactured, a conductive metal plating is applied to the surface to form a plating layer.

[0086] It should be noted that within the scope of the present disclosure, the embodiments may be freely combined, or any component in each embodiment may be modified, or any component in each embodiment may be omitted.

[0087] The circular polarizer according to the present disclosure is suitable for use in a circular polarizer, etc., because it is possible to suppress the disturbance of the electric field distribution of the linearly polarized component caused by the iris by providing an iris that forms an elliptical opening cross section in a circular waveguide.

[0088] 100, 200, 300, 400 Circularly polarized wave generator, 10 Circular waveguide, 10a Inner peripheral surface, 10b Outer peripheral surface, 11a, 11b Terminal, 12 Corrugated portion, 13 Iris, 13a Elliptical inner peripheral surface, 20 Circular waveguide, 20a Inner peripheral surface, 20b Outer peripheral surface, 22, 22A, 22B Corrugated portion, 23, 23A, 23B Iris, 23a Elliptical inner peripheral surface, 31a Orthogonal surface, 31b Inclined surface, 41a, 41b Inclined surface, 50 Square waveguide, 51 Iris, 51 Tip surface, 60 Circular waveguide, 61 Iris, 61a Tip surface, C Tube axis, θ Inclination angle, L Curve.

Claims

1. A circular polarizer comprising: a circular waveguide whose inner circumferential surface has a circular opening cross section; and an iris having an elliptical inner circumferential surface protruding from said inner circumferential surface toward the tube axis of said circular waveguide, thereby forming an elliptical opening cross section, wherein said irises are periodically arranged in the tube axial direction.

2. A circular wave polarizer according to claim 1, characterized in that the length of the major axis of the elliptical inner peripheral surface is equal to or less than the diameter of the inner peripheral surface, and the length of the minor axis of the elliptical inner peripheral surface is equal to or less than the diameter of the inner peripheral surface.

3. A circular wave polarizer according to claim 1 or 2, characterized in that the elliptical shape of the elliptical inner peripheral surface does not include any straight lines.

4. A circular polarizer as claimed in any one of claims 1 to 3, characterized in that the major and minor axis lengths of the elliptical inner peripheral surface gradually increase from one end and the other end of the circular waveguide towards the centre in the tube axial direction.

5. A circularly polarized wave generator according to claim 4, characterized in that the length of the minor axis of the elliptical inner peripheral surface varies in the axial direction of the tube like a trigonometric function with the vertex at the center of the axial direction of the circular waveguide.

6. A circular polarizer as claimed in claim 4 or 5, characterized in that the diameter of the inner circumferential surface gradually increases from one end and the other end of the circular waveguide towards the centre in the tube axial direction.

7. A circular wave polarizer according to any one of claims 1 to 6, characterized in that the circumferential cross section of the iris forms a trapezoid with the inner circumferential surface of the ellipse as its upper edge.

8. A circular waveguide polarizer according to claim 7, characterized in that the iris has an orthogonal surface that is perpendicular to the elliptical inner surface, and an inclined surface that is inclined relative to the elliptical inner surface and faces the orthogonal surface.

9. A circular waveguide polarizer according to claim 7, wherein the iris has a pair of inclined surfaces that are inclined relative to the elliptical inner peripheral surface and that face each other.

10. A circular wave polarizer according to claim 8 or 9, characterized in that the inclined surface is inclined at an angle of 45 degrees or more and less than 90 degrees relative to the elliptical inner peripheral surface.

11. A method for manufacturing a circular polarizer according to any one of claims 1 to 10, characterized in that additive manufacturing is performed using a 3D printer from one terminal of the circular waveguide on the ground side to the other terminal of the circular waveguide on the sky side, so that the tube axis is perpendicular to the ground.

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