T-branch waveguide and antenna device

Abstract

This T-branch waveguide includes: a first waveguide (1) having one end serving as an input / output terminal (1a) and the other end serving as a connection terminal (1b); a second waveguide (2) having one end serving as a first input / output terminal (2a) and the other end serving as a second input / output terminal (2b) and having a connection port (2c) on one side surface; and a third waveguide (3) connecting the connection terminal (1b) of the first waveguide (1) and the connection port (2c) of the second waveguide (2). A first waveguide axis of the first waveguide (1) and a third waveguide axis of the third waveguide (3) are aligned, and the first waveguide axis of the first waveguide (1) and a second waveguide axis of the second waveguide (2) are arranged so as to be orthogonal to each other via the third waveguide axis of the third waveguide (3). The waveguide shape of the third waveguide (3) is a point-symmetrical shape with respect to the third waveguide axis of the third waveguide (3), and is a non-line-symmetrical shape with respect to one diagonal line of two diagonal lines passing through the third waveguide axis of the third waveguide (3).

Description

T-branch waveguide and antenna device

[0001] The present disclosure relates to a T-branch waveguide used for power division and combination in the microwave or millimeter wave band, and an antenna device using the T-branch waveguide.

[0002] In a T-branch waveguide having a first waveguide and a second waveguide connected to the other end of the first waveguide at an intermediate portion in the longitudinal direction, an E-plane T-branch waveguide for improving reflection characteristics is proposed in Patent Document 1. In the E-plane T-branch waveguide shown in Patent Document 1, a stepped ridge-shaped spacing adjustment portion is formed on the bottom surface of the second waveguide from a position closer to the center than both ends to the center.

[0003] Japanese Patent Application Laid-Open No. 2020-188375

[0004] The E-plane T-branch waveguide disclosed in Patent Document 1 has a step-like ridge-like spacing adjustment portion formed on the bottom surface of the second waveguide, and therefore has a problem in that it is not easy to manufacture.

[0005] The present disclosure has been made in consideration of the above points, and an object of the present disclosure is to provide a T-branch waveguide that has a simple structure and can obtain good reflection characteristics.

[0006] A T-branch waveguide according to the present disclosure comprises a first waveguide having one end serving as an input / output terminal and the other end serving as a connection terminal; a second waveguide having one end serving as a first input / output terminal and the other end serving as a second input / output terminal and having a connection port on one side surface; and a third waveguide connecting the connection terminal of the first waveguide and the connection port of the second waveguide, wherein a first tube axis of the first waveguide and a third tube axis of the third waveguide are aligned and the first tube axis of the first waveguide and the second tube axis of the second waveguide are orthogonal to each other via the third tube axis of the third waveguide, and the shape of the waveguide of the third waveguide is point-symmetric with respect to the third tube axis of the third waveguide and is line-symmetric with respect to one of two diagonals passing through the third tube axis of the third waveguide.

[0007] According to the present disclosure, a third waveguide is provided which connects the connection terminal of the first waveguide and the connection port of the second waveguide, and which has a waveguide which has a point-symmetric shape with the tube axis as the origin and a non-linearly symmetric shape with respect to one of two diagonals which pass through the tube axis of the third waveguide. This makes it possible to obtain good reflection characteristics with a simple structure.

[0008] 1 is a perspective view showing a T-branch waveguide according to a first embodiment. FIG. 2 is a top view showing the T-branch waveguide according to the first embodiment. FIG. 3 is a cross-sectional view taken along III-III in FIG. 2. FIG. 4 is a horizontal cross-section showing a third waveguide in the T-branch waveguide according to the first embodiment. FIG. 5 is a conceptual diagram showing an electric field of an electromagnetic wave propagating through a first waveguide in the T-branch waveguide according to the first embodiment. FIG. 6 is a conceptual diagram showing an electric field of an electromagnetic wave propagating through a center in the Z-axis direction of a third waveguide in the T-branch waveguide according to the first embodiment. FIG. 7 is a conceptual diagram showing an electric field of an electromagnetic wave propagating through a second waveguide in the T-branch waveguide according to the first embodiment. FIG. 8 is a diagram showing an electromagnetic field analysis result of reflection characteristics, which are one of the transmission line characteristics in the T-branch waveguide according to the first embodiment. FIG. 9 is a diagram showing an electromagnetic field analysis result of pass characteristics, which are one of the transmission line characteristics in the T-branch waveguide according to the first embodiment. FIG. 10 is a longitudinal cross-sectional view showing an antenna device according to a second embodiment.

[0009] Embodiment 1. A T-branch waveguide according to embodiment 1 will be described with reference to Figures 1 to 10. The T-branch waveguide according to embodiment 1 is a T-branch waveguide for propagating electromagnetic waves to, for example, a waveguide slot antenna employed in an antenna device. The T-branch waveguide according to embodiment 1 includes a first waveguide 1, a second waveguide 2, and a third waveguide 3.

[0010] The T-branch waveguide according to the first embodiment can be applied to either an E-plane T-branch waveguide in which the second waveguide 2 is coupled to one E-plane of the first waveguide 1, or an H-plane T-branch waveguide in which the second waveguide 2 is coupled to one H-plane of the first waveguide 1, due to the presence of the third waveguide 3. That is, the T-branch waveguide according to the first embodiment achieves reflection matching between the first waveguide 1 and the second waveguide 2, and can propagate electromagnetic waves with polarization rotation.

[0011] In the following description, an example in which an E-plane T-branch waveguide is applied as the T-branch waveguide according to embodiment 1 will be described. Also, a structure capable of dividing and combining equal amplitudes and opposite phases will be described as an example in which the T-branch waveguide according to embodiment 1 is applied.

[0012] In the first embodiment, a plane perpendicular to the tube axis of the first waveguide 1 is defined as a horizontal plane, and a plane perpendicular to the tube axis of the second waveguide 2 is defined as a vertical plane. The X-axis is defined as an axis that forms a 45-degree angle with the tube axis of the second waveguide 2 in the horizontal plane, the Y-axis is defined as an axis perpendicular to the X-axis, and the Z-axis is defined as an axis parallel to the tube axis of the first waveguide 1. The X-Y plane is a horizontal plane.

[0013] The direction parallel to the Y axis is the Y axis direction, and the Y axis direction is the first direction. The direction parallel to the X axis is the X axis direction, and the X axis direction is the second direction. The direction parallel to the Z axis is the Z axis direction, and the Z axis direction is the third direction. In each of the X axis direction, Y axis direction, and Z axis direction, the direction indicated by the arrow in the figure is the positive direction, and the direction opposite to the positive direction is the negative direction.

[0014] The first waveguide 1 is a hollow waveguide with an input / output terminal 1a at one end and a connection terminal 1b at the other end. The hollow portion of the first waveguide 1 forms a waveguide 1A through which electromagnetic waves propagate. The outer shape of the first waveguide 1 and the waveguide 1A have a rectangular cross section parallel to a plane perpendicular to the axis of the first waveguide 1.

[0015] The first waveguide 1 has a pair of opposing side walls 11, 12 and a pair of opposing side walls 13, 14. In a plane perpendicular to the tube axis of the first waveguide 1, the length of the side walls 11, 12 is longer than the length of the side walls 13, 14. The area surrounded by the four side walls becomes the waveguide 1A. The tube axis of the first waveguide 1 passes through the center of the waveguide 1A and is a central axis parallel to the Z axis. The first waveguide 1 is manufactured by metal cutting or die forming from a metal plate.

[0016] The second waveguide 2 is a hollow waveguide having a first input / output terminal 2a at one end and a second input / output terminal 2b at the other end, and having a connection port 2c on one side surface, which in the first embodiment is the bottom wall 22. In the second waveguide 2, the hollow portion forms a waveguide 2A through which electromagnetic waves propagate. The outer shape of the second waveguide 2 and the waveguide 2A have a rectangular cross section parallel to a plane perpendicular to the tube axis of the second waveguide 2.

[0017] The second waveguide 2 has opposing top and bottom walls 21 and 22 and a pair of side walls 23 and 24. In a plane perpendicular to the tube axis of the second waveguide 2, the lengths of the top and bottom walls 21 and 22 are longer than the lengths of the side walls 23 and 24. The area surrounded by the top and bottom walls 21 and 22 and the pair of side walls 23 and 24 forms the waveguide 2A. The tube axis of the second waveguide 2 passes through the center of the waveguide 2A and is a central axis perpendicular to the Z axis. The second waveguide 2 is manufactured by metal cutting or die forming from a metal plate.

[0018] In the waveguide 2A in the second waveguide 2, the cross section parallel to the plane perpendicular to the tube axis of the second waveguide 2 is uniformly rectangular from the first input / output terminal 2a to the second input / output terminal 2b. However, in the waveguide 2A from the first input / output terminal 2a to the second input / output terminal 2b, the cross section parallel to the plane perpendicular to the tube axis of the second waveguide 2 may have a cross-sectional shape corresponding to the amplitude ratio of the propagating electromagnetic waves.

[0019] The third waveguide 3 is a hollow waveguide that connects the connection terminal 1b of the first waveguide 1 and the connection port 2c of the second waveguide 2. In the third waveguide 3, the hollow portion forms a waveguide 3A that propagates electromagnetic waves. One end of the third waveguide 3 is a first connection terminal 3a, and the other end of the third waveguide 3 is a second connection terminal 3b.

[0020] The waveguide 3A communicates with the waveguide 1A of the first waveguide 1 via the first connection terminal 3a and the connection terminal 1b of the first waveguide 1, and communicates with the waveguide 2A of the second waveguide 2 via the second connection terminal 3b and the connection port 2c of the second waveguide 2. The tube axis of the first waveguide 1 and the tube axis of the third waveguide 3 coincide with each other, and the first waveguide 1 and the second waveguide 2 are arranged and connected so that the tube axis of the first waveguide 1 and the tube axis of the second waveguide 2 are orthogonal to each other via the tube axis of the third waveguide 3. The tube axis of the third waveguide 3 passes through the center of the waveguide 3A and is a central axis parallel to the Z-axis.

[0021] The first waveguide 1 and the third waveguide 3 are connected by a connecting flange (not shown) that extends perpendicularly outward from the periphery of the connection terminal 1b of the first waveguide 1 and has the same outer shape as that of the third waveguide 3, with the outer shape of the connecting flange being aligned with that of the third waveguide 3.

[0022] When the T-branch waveguide according to the first embodiment is used to distribute electromagnetic waves, the third waveguide 3 achieves reflection matching between the waveguide 1A of the first waveguide 1 and the waveguide 2A of the second waveguide 2, and also rotates the electric field of the electromagnetic wave propagating through the waveguide 1A of the first waveguide 1 by 90 degrees, i.e., rotates the polarization by 90 degrees, to propagate the electromagnetic wave to the waveguide 2A of the second waveguide 2, and distributes the electromagnetic wave equally in opposite phase to the waveguide 2A of the second waveguide 2.

[0023] Furthermore, when the T-branch waveguide according to the first embodiment is used to combine electromagnetic waves, the third waveguide 3 achieves reflection matching between the waveguide 2A of the second waveguide 2 and the waveguide 1A of the first waveguide 1, and also rotates the electric field of the electromagnetic wave propagating through the waveguide 2A of the second waveguide 2 by 90 degrees, i.e., rotates the polarization by 90 degrees, before propagating to the waveguide 1A of the first waveguide 1 and combining the electromagnetic wave into the waveguide 1A of the first waveguide 1.

[0024] 4, the external shape of the third waveguide 3 is such that a cross section parallel to a plane perpendicular to the tube axis of the third waveguide 3 is rectangular, and in the first embodiment, is square. The external shape of the third waveguide 3 is constituted by a first outer surface 31, a second outer surface 32, a third outer surface 33, and a fourth outer surface 34, which are positioned in clockwise order, with the first outer surface 31 and the third outer surface 33 facing each other, and the second outer surface 32 and the fourth outer surface 34 facing each other.

[0025] The waveguide 3A is an area surrounded by a first inner flat surface 31A, a second inner flat surface 32A, a first inner inclined surface 35A, a third inner flat surface 33A, a fourth inner flat surface 34A, and a second inner inclined surface 36A, which are positioned in clockwise order. The first inner flat surface 31A and the third inner flat surface 33A face each other, and in a plane perpendicular to the tube axis of the third waveguide 3, the length L1 of the first inner flat surface 31A and the length L1 of the third inner flat surface 33A are the same.

[0026] The second inner flat surface 32A and the fourth inner flat surface 34A face each other, and the length L2 of the second inner flat surface 32A is the same as the length L2 of the fourth inner flat surface 34A in a plane perpendicular to the tube axis of the third waveguide 3. The length L1 of the first inner flat surface 31A and the third inner flat surface 33A is different from the length L1 of the second inner flat surface 32A and the fourth inner flat surface 34A, and in the first embodiment, L1 is longer than L2.

[0027] The first inner slope 35A connects the second inner flat surface 32A and the third inner flat surface 33A, and the second inner slope 36A connects the first inner flat surface 31A and the fourth inner flat surface 34A. The first inner flat surface 31A faces the first outer flat surface 31, the second inner flat surface 32A faces the second outer flat surface 32, the third inner flat surface 33A faces the third outer flat surface 33, and the fourth inner flat surface 34A faces the fourth outer flat surface 34. The first inner slope 35A and the second inner slope 36A face each other, and in a plane perpendicular to the tube axis of the third waveguide 3, the length of the first inner slope 35A and the length of the second inner slope 36A are the same.

[0028] The first inner slope 35A has a first horizontal plane extending vertically inward from the other end of the second inner plane 32A, a first vertical plane extending vertically from the other end of the first horizontal plane toward the third inner plane 33A, a second horizontal plane extending vertically inward from the other end of the first vertical plane, and a second vertical plane whose other end extends vertically from the other end of the second horizontal plane toward the third inner plane 33A to one end of the third inner plane 33A.

[0029] The first inner slope 35A has a stepped shape with varying heights in a direction along the second outer surface 32. In the first inner slope 35A, in a plane perpendicular to the tube axis of the third waveguide 3, the length L3 of the first vertical plane is different from the length L4 of the second vertical plane, and in the first embodiment, L4 is longer than L3. Note that the corners formed by the second inner flat surface 32A and the first horizontal plane, the corners formed by the first horizontal plane and the first vertical plane, the corners formed by the first vertical plane and the second horizontal plane, the corners formed by the second horizontal plane and the second vertical plane, and the corners formed by the second vertical plane and the third inner flat surface 33A are each right-angled, but may be rounded depending on the manufacturing conditions or the matching conditions of the transmission line characteristics.

[0030] The second inner slope 36A has a first horizontal plane extending vertically inward from the other end of the fourth inner plane 34A, a first vertical plane extending vertically from the other end of the first horizontal plane toward the first inner plane 31A, a second horizontal plane extending vertically inward from the other end of the first vertical plane, and a second vertical plane whose other end extends vertically from the other end of the second horizontal plane toward the first inner plane 31A to one end of the first inner plane 31A.

[0031] The second inner slope 36A has a stepped shape with varying heights in a direction along the fourth outer surface 34. In the second inner slope 36A, in a plane perpendicular to the tube axis of the third waveguide 3, the length L3 of the first vertical plane is different from the length L4 of the second vertical plane, and in the first embodiment, L4 is longer than L3. Note that although the corner formed by the fourth inner flat surface 34A and the first horizontal plane, the corner formed by the first horizontal plane and the first vertical plane, the corner formed by the first vertical plane and the second horizontal plane, the corner formed by the second horizontal plane and the second vertical plane, and the corner formed by the second vertical plane and the first inner flat surface 31A are right-angled, they may have rounded corner shapes depending on manufacturing conditions or matching conditions for transmission line characteristics.

[0032] The length L3 of the first vertical plane of the first inner slope 35A is the same as the length L3 of the first vertical plane of the second inner slope 36A. The length L4 of the second vertical plane of the first inner slope 35A is the same as the length L4 of the second vertical plane of the second inner slope 36A. The length L5 of the first horizontal plane of the first inner slope 35A is the same as the length L5 of the first horizontal plane of the second inner slope 36A. The length L6 of the second horizontal plane of the first inner slope 35A is the same as the length L6 of the second horizontal plane of the second inner slope 36A.

[0033] Therefore, the length from the other end of the second inner flat surface 32A to one end of the third inner flat surface 33A on the first inner slope 35A is the same as the length from the other end of the fourth inner flat surface 34A to one end of the first inner flat surface 31A on the second inner slope 36A. The first inner slope 35A and the second inner slope 36A are symmetrical with respect to the tube axis of the third waveguide 3, i.e., the point where two diagonals connecting two opposing corners of the outer shape of the third waveguide 3 intersect (hereinafter referred to as the origin) in FIG. Furthermore, the first inner slope 35A and the second inner slope 36A are non-symmetrical with respect to a diagonal that does not pass through the first inner slope 35A and the second inner slope 36A, i.e., the X-axis.

[0034] As a result, the inner surface (right side in FIG. 4 ) extending from the line segment connecting the other end of the first inner slope 35A and the other end of the second inner flat surface 32A, passing through the second inner flat surface 32A-first inner slope 35A-third inner flat surface 33A, to the line segment connecting the other end of the third inner flat surface 33A and one end of the fourth inner flat surface 34A, and the inner surface (left side in FIG. 4 ) extending from the line segment connecting the other end of the third inner flat surface 33A and one end of the fourth inner flat surface 34A, passing through the fourth inner flat surface 34A-second inner slope 36A-first inner slope 35A, to the line segment connecting the other end of the first inner slope 35A and the other end of the second inner flat surface 32A are point-symmetric with respect to the tube axis of the third waveguide 3, and are non-axisymmetric with respect to the X-axis.

[0035] In short, the shape of the waveguide 3A of the third waveguide 3 is point-symmetric with respect to the tube axis of the third waveguide 3, and is asymmetric with respect to one of two diagonals passing through the tube axis of the third waveguide 3. The length in the tube axis direction of the third waveguide 3, that is, the length from the first connection terminal 3a to the second connection terminal 3b, is one-quarter of the guide wavelength, that is, one-quarter the wavelength (λ / 4) of the propagating electromagnetic wave, in the T-branch waveguide according to the first embodiment, as shown in FIG.

[0036] The length of the third waveguide 3 in the axial direction is set to λ / 4 of the electromagnetic wave propagating therethrough, resulting in good reflected wave characteristics. Note that although the length of the third waveguide 3 in the axial direction is preferably λ / 4 of the electromagnetic wave propagating therethrough, it may be changed to a length other than λ / 4 depending on the transmission path characteristics of the electromagnetic wave in the T-branch waveguide or the design specifications.

[0037] 4, the length of the waveguide 3A in a direction parallel to the tube axis of the second waveguide 2 is half the wavelength (λ / 2) of the propagating electromagnetic wave. In the T-branch waveguide according to the first embodiment, as shown in FIG. 4, the sum of the length L1 of the first inner flat surface 31A, the length L5 of the first horizontal flat surface of the second inner slope 36A, and the length L6 of the second horizontal flat surface of the second inner slope 36A, and the sum of the length L1 of the third inner flat surface 33A, the length L5 of the first horizontal flat surface of the first inner slope 35A, and the length L6 of the second horizontal flat surface of the first inner slope 35A, is λ / 2 of the propagating electromagnetic wave.

[0038] Furthermore, the sum of the length L2 of the second inner plane 32A, the length L3 of the first vertical plane on the first inner slope 35A, and the length L4 of the second vertical plane on the first inner slope 35A, and the sum of the length L2 of the fourth inner plane 34A, the length L3 of the first vertical plane on the second inner slope 36A, and the length L4 of the second vertical plane on the second inner slope 36A, is the λ / 2 length of the propagating electromagnetic wave.

[0039] The length of the waveguide 3A of the third waveguide 3 in the direction parallel to the tube axis of the second waveguide 2 is preferably the length of λ / 2 of the propagating electromagnetic wave, but may be changed to a length other than the length of λ / 2 depending on the transmission path characteristics of the electromagnetic wave in the T-branch waveguide or the design specifications.

[0040] The planar shape of connection port 2c of second waveguide 2 is the same as the cross-sectional shape of waveguide 3A of third waveguide 3, taken along a plane perpendicular to the axis of third waveguide 3. Second waveguide 2 and third waveguide 3 are connected by aligning connection port 2c of second waveguide 2 with second connection terminal 3b (the other end of waveguide 3A) of third waveguide 3.

[0041] The third waveguide 3 is manufactured by metal cutting or die forming from a metal plate. When manufactured by metal cutting, the first waveguide 1, the second waveguide 2, and the third waveguide 3 are each manufactured by cutting from a metal plate, and are stacked so that the tube axis of the first waveguide 1 coincides with the tube axis of the third waveguide 3 and the tube axis of the first waveguide 1 and the tube axis of the second waveguide 2 intersect at right angles via the tube axis of the third waveguide 3, and the first waveguide 1 and the third waveguide 3, and the second waveguide 2 and the third waveguide 3 are connected. Because the T-branch waveguide can be manufactured using three hollow waveguides, the first waveguide 1, the second waveguide 2, and the third waveguide 3, it is easy to manufacture and the T-branch waveguide as a whole can be made smaller and less expensive.

[0042] Furthermore, when manufacturing by mold forming, for the first waveguide 1, the second waveguide 2, and the third waveguide 3, two integral components are divided into two by a plane including the tube axis of the first waveguide 1, the tube axis of the second waveguide 2, and the tube axis of the third waveguide 3, and each of these components is manufactured by aluminum die casting using an upper mold and a lower mold, and the two integral components are then joined together. The two integral components have the same shape, and the T-branch waveguide can be manufactured using the two integral components, which makes manufacturing easy and allows for a smaller size and lower cost for the T-branch waveguide as a whole.

[0043] Next, when the T-branch waveguide according to the first embodiment is used to divide an electromagnetic wave, the electric field of the electromagnetic wave that passes from the first waveguide 1 through the third waveguide 3 to the second waveguide 2 will be described with reference to Fig. 5 to Fig. 7. The arrow in Fig. 5 indicates the direction of the electric field of the electromagnetic wave excited in the first waveguide 1, the arrow in Fig. 6 indicates the direction of the electric field of the electromagnetic wave excited in the second waveguide 2, and the arrow in Fig. 7 indicates the direction of the electric field of the electromagnetic wave excited in the third waveguide 3.

[0044] As an example, as shown in FIG. 5 , the electric field of the electromagnetic wave excited in the first waveguide 1 is directed from side wall 11 to side wall 12, perpendicular to side wall 11 and side wall 12, and the electromagnetic wave excited in the first waveguide 1 propagates in a direction along the tube axis of the first waveguide 1, from input / output terminal 1 a to connection terminal 1 b, that is, in the positive direction of the Z axis shown in FIG. 5 .

[0045] The electromagnetic wave excited in the first waveguide 1 reaches the connection terminal 1b of the first waveguide 1 and the first connection terminal 3a of the third waveguide 3, and the electromagnetic wave that has reached it propagates through the third waveguide 3 in a direction along the tube axis of the third waveguide 3, from the first connection terminal 3a to the second connection terminal 3b, while rotating the electric field of the electromagnetic wave in a counterclockwise direction, i.e., in the positive direction of the Z axis shown in FIG. 5 .

[0046] 6 , the electromagnetic wave that has reached the first connection terminal 3 a of the third waveguide 3 has its electric field rotated 45 degrees counterclockwise and 45 degrees in the positive direction of the Z-axis at the center of the tube axis of the third waveguide 3, and further rotated 45 degrees counterclockwise and 45 degrees in the positive direction of the Z-axis at the second connection terminal 3 b of the third waveguide 3 and the connection port 2 c of the second waveguide 2. As a result, the electromagnetic wave that has reached the first connection terminal 3 a of the third waveguide 3 is rotated in polarization by 90 degrees counterclockwise and 90 degrees in the positive direction of the Z-axis by the third waveguide 3, before reaching the second connection terminal 3 b of the third waveguide 3 and the connection port 2 c of the second waveguide 2.

[0047] The electromagnetic waves that reach the connection port 2c of the second waveguide 2 are equally divided in opposite phases at the connection port 2c of the second waveguide 2 toward the first input / output terminal 2a and the second input / output terminal 2b of the second waveguide 2, and propagate through the second waveguide 2 toward the first input / output terminal 2a and the second input / output terminal 2b, respectively.

[0048] 7, the electric field of the electromagnetic wave propagating in the direction of the first input / output terminal 2a in the second waveguide 2 is directed from the bottom wall 22 to the top wall 21, perpendicular to the bottom wall 22 and the top wall 21, and the electromagnetic wave that reaches the connection port 2c of the second waveguide 2 propagates from the connection port 2c to the first input / output terminal 2a in a direction along the tube axis of the second waveguide 2. As shown in FIG. 7, the electric field of the electromagnetic wave propagating in the direction of the second input / output terminal 2b in the second waveguide 2 is directed from the top wall 21 to the bottom wall 22, perpendicular to the top wall 21 and the bottom wall 22, and the electromagnetic wave that reaches the connection port 2c of the second waveguide 2 propagates from the connection port 2c to the second input / output terminal 2b in a direction along the tube axis of the second waveguide 2.

[0049] Since the shape of the waveguide 3A of the third waveguide 3 is point-symmetric with respect to the tube axis of the third waveguide 3 and is asymmetric with respect to one of two diagonals passing through the tube axis of the third waveguide 3, the electromagnetic wave distributed from the second connection terminal 3b of the third waveguide 3 at the connection port 2c of the second waveguide 2 can be smoothly propagated to the electric field of the electromagnetic wave excited in the second waveguide 2. As a result, the electromagnetic wave excited in the first waveguide 1 can be propagated as an equally distributed signal with an opposite phase to the second waveguide 2 via the third waveguide 3.

[0050] In the T-branch waveguide according to the first embodiment, the reflection characteristic, transmission characteristic, and transmission phase difference characteristic, which are transmission line characteristics with respect to normalized frequency obtained by electromagnetic field analysis, will be described with reference to FIGS. 8 to 10. The electromagnetic field analysis in the T-branch waveguide was performed on a signal when the T-branch waveguide was used to distribute electromagnetic waves, that is, a signal consisting of electromagnetic waves was input to the input / output terminal 1 a of the first waveguide 1, propagated through the first waveguide 1, passed through the connection terminal 1 b of the first waveguide 1 and the first connection terminal 3 a of the third waveguide 3, propagated through the third waveguide 3, passed through the second connection terminal 3 b of the third waveguide 3 and the connection port 2 c of the second waveguide 2, and was distributed in antiphase and equal directions toward the first input / output terminal 2 a and the second input / output terminal 2 b of the second waveguide 2 at the connection port 2 c of the second waveguide 2, and then propagated through the second waveguide 2 in the directions toward the first input / output terminal 2 a and the second input / output terminal 2 b, respectively.

[0051] The electromagnetic field analysis results for a T-branch waveguide are an example of verification results confirming the characteristics of a signal propagating through the T-branch waveguide. Figure 8 shows the verification results showing the reflection characteristics versus normalized frequency obtained by electromagnetic field analysis. In Figure 8, the horizontal axis represents normalized frequency, and the vertical axis represents the reflection coefficient.

[0052] FIG. 9 shows the verification results showing the insertion loss (insertion loss) versus normalized frequency obtained by electromagnetic field analysis. In FIG. 9, the horizontal axis represents the normalized frequency, and the vertical axis represents the insertion loss. FIG. 10 shows the verification results showing the phase difference versus normalized frequency obtained by electromagnetic field analysis. In FIG. 10, the horizontal axis represents the normalized frequency, and the vertical axis represents the phase difference.

[0053] 8 to 10, favorable characteristics were obtained, with a bandwidth of 10% or more, a reflection coefficient of -20 dB or less, a transmission loss of -3 dB (equal distribution), and a transmission phase difference of 180 degrees (opposite phase), centered around the normalized frequency 1. That is, the electromagnetic field analysis results mean that a signal consisting of an electromagnetic wave input from the input / output terminal 1a of the first waveguide 1 propagates through the first waveguide 1 and the third waveguide 3, propagates without reflection to the second waveguide 2, and then propagates with equal amplitude and opposite phase through the second waveguide 2 in the directions of the first input / output terminal 2a and the second input / output terminal 2b, respectively.

[0054] As described above, the T-branch waveguide according to the first embodiment includes the third waveguide 3 that connects the connection terminal 1b of the first waveguide 1 and the connection port 2c of the second waveguide 2, and the shape of the waveguide 3A of the third waveguide 3 is point-symmetric with respect to the tube axis of the third waveguide 3 and is asymmetric with respect to one of the two diagonals that pass through the tube axis of the third waveguide 3, thereby achieving good reflection characteristics with a simple structure. In addition, the T-branch waveguide is easy to manufacture, and the entire T-branch waveguide can be made smaller and less expensive.

[0055] Furthermore, the electromagnetic wave distributed at the connection port 2 c of the second waveguide 2 can be smoothly propagated from the second connection terminal 3 b of the third waveguide 3 to the electric field of the electromagnetic wave excited in the second waveguide 2 by the third waveguide 3 undergoing a 90-degree polarization rotation, and as a result, the electromagnetic wave excited in the first waveguide 1 can be propagated to the second waveguide 2 via the third waveguide 3 as a signal distributed equally in opposite phase.

[0056] In the T-branch waveguide according to the first embodiment, the first waveguide 1, the second waveguide 2, and the third waveguide 3 are each hollow waveguides whose hollow portions form the waveguides, but they may also be waveguides whose hollow portions are filled with a dielectric. That is, the first waveguide 1, the second waveguide 2, and the third waveguide 3 may each be a waveguide that includes a hollow metal tube and a dielectric filled in the hollow portion of the tube, and whose hollow portion forms the waveguide. A waveguide whose hollow portion is filled with a dielectric is manufactured by manufacturing a hollow metal tube in the same manner as the hollow waveguide and filling the hollow portion of the tube with a dielectric.

[0057] Furthermore, the first waveguide 1, the second waveguide 2, and the third waveguide 3 may each be a waveguide having a hollow resin tube body and a metal-plated layer applied to the entire inner surface of the tube body, with the hollow portion surrounded by the plated layer forming the waveguide. A resin-plated waveguide is manufactured by manufacturing a hollow resin tube body by resin injection molding and then applying a metal plating to the entire inner surface of the tube body to form a plated layer. Furthermore, the T-branch waveguide according to the first embodiment may be a waveguide in which the first waveguide 1, the second waveguide 2, and the third waveguide 3 are integrally manufactured using a metal 3D printer with additive manufacturing technology.

[0058] Embodiment 2 An antenna device according to embodiment 2 will be described with reference to Fig. 11. The antenna device according to embodiment 2 is an antenna device equipped with a T-branch waveguide, for example, a T-branch waveguide for propagating electromagnetic waves to an antenna device using a waveguide slot antenna.

[0059] The antenna device according to the second embodiment includes a T-branch waveguide having a first waveguide 1, a second waveguide 2, and a third waveguide 3, and a waveguide slot antenna 4 to which electromagnetic waves are fed from the T-branch waveguide. The T-branch waveguide in the antenna device according to the second embodiment is the same as the T-branch waveguide according to the first embodiment. In Fig. 10, the same reference numerals as those in Figs. 1 to 7 indicate the same or corresponding parts. The waveguide slot antenna 4 includes a radiating waveguide having a plurality of radiating slots 41, 42.

[0060] The waveguide slot antenna 4 is joined to the upper wall 21 of the second waveguide 2, and the plurality of radiation slots 41, 42 in the waveguide slot antenna 4 communicate with the waveguide 2A of the second waveguide 2. The electromagnetic waves propagated through the waveguide 2A of the second waveguide 2 are radiated into the air from the plurality of radiation slots 41, 42.

[0061] The plurality of radiation slots 41, 42 in the waveguide slot antenna 4 may be formed directly in the upper wall 21 of the second waveguide 2. In this case, the waveguide slot antenna 4 is constituted by the upper wall 21 of the second waveguide 2.

[0062] In the antenna device according to the second embodiment, the electromagnetic waves propagated to the waveguide slot antenna through the first waveguide 1, the second waveguide 2, and the third waveguide 3 that constitute the T-branch waveguide are such that, as in the T-branch waveguide according to the first embodiment, the signal consisting of the electromagnetic waves input from the input / output terminal 1 a of the first waveguide 1 has good reflection characteristics, is propagated in the second waveguide 2 with equal amplitude and opposite phase, and is radiated into the air from the plurality of radiation slots 41, 42 in the waveguide slot antenna.

[0063] It should be noted that the embodiments may be freely combined, or any of the components in each embodiment may be modified, or any of the components in each embodiment may be omitted.

[0064] The T-branch waveguide according to the present disclosure is suitable for use as a T-branch waveguide for propagating electromagnetic waves (signals) in a microwave or millimeter wave band antenna device, particularly as a T-branch waveguide used for power distribution and combination in the microwave or millimeter wave band.

[0065] 1 First waveguide, 1A Waveguide, 1a Input / output terminal, 1b Connection terminal, 11-14 Side wall. 2 Second waveguide, 2A Waveguide, 2a First input / output terminal, 2b Second input / output terminal, 2c Connection port, 21 Top wall, 22 Bottom wall, 23, 24 Side wall, 3 Third waveguide, 3A Waveguide, 3a First connection terminal, 3b Second connection terminal, 31A First inner flat surface, 32A Second inner flat surface, 33A Third inner flat surface, 34A Fourth inner flat surface, 35A First inner inclined surface, 36A Second inner inclined surface, 4 Waveguide slot antenna.

Claims

1. A T-branch waveguide comprising a first waveguide having one end as an input / output terminal and the other end as a connection terminal, a second waveguide having one end as a first input / output terminal and the other end as a second input / output terminal and having a connection port on one side surface, and a third waveguide connecting between the connection terminal of the first waveguide and the connection port of the second waveguide, wherein the first axis of the first waveguide coincides with the third axis of the third waveguide, and the first axis of the first waveguide and the second axis of the second waveguide are arranged to be orthogonal to each other via the third axis of the third waveguide, and the shape of the waveguide path of the third waveguide is point-symmetrical with respect to the third axis of the third waveguide and non-line-symmetrical with respect to one of two diagonal lines passing through the third axis of the third waveguide.

2. A first waveguide having one end as an input / output terminal and the other end as a connection terminal, a second waveguide having one end as a first input / output terminal, the other end as a second input / output terminal, and having a connection port on one side surface, and a third waveguide connecting between the connection terminal of the first waveguide and the connection port of the second waveguide, wherein the first axis of the first waveguide coincides with the third axis of the third waveguide, and the first axis of the first waveguide and the second axis of the second waveguide are arranged to be orthogonal to each other via the third axis of the third waveguide; the waveguide path of the third waveguide is a region surrounded by a first inner plane, a second inner plane, a first inner inclined plane, a third inner plane, a fourth inner plane, and a second inner inclined plane that are sequentially positioned in a clockwise direction; the first inner plane and the third inner plane face each other, and on a plane perpendicular to the axis of the third waveguide, the length of the first inner plane is the same as the length of the third inner plane; the second inner plane and the fourth inner plane face each other, and on a plane perpendicular to the axis of the third waveguide, the length of the second inner plane is the same as the length of the fourth inner plane, and the length of the first inner plane and the third inner plane is different from the length of the second inner plane and the fourth inner plane; the first inner inclined plane connects the first inner plane and the fourth inner plane, and the second inner inclined plane connects the second inner plane and the third inner plane; the first inner inclined plane and the second inner inclined plane face each other, and on a plane perpendicular to the axis of the third waveguide, the length of the first inner inclined plane is the same as the length of the second inner inclined plane; a T-branch waveguide.

3. The first inner inclined surface has a first horizontal plane vertically extending inward from the other end of the second inner flat surface, a first vertical plane vertically extending from the other end of the first horizontal plane toward the third inner flat surface, a second horizontal plane vertically extending inward from the other end of the first vertical plane, and a second vertical plane vertically extending from the other end of the second horizontal plane toward the third inner flat surface with the other end extending to one end of the third inner flat surface. The second inner inclined surface has a first horizontal plane vertically extending inward from the other end of the fourth inner flat surface, a first vertical plane vertically extending from the other end of the first horizontal plane toward the first inner flat surface, a second horizontal plane vertically extending inward from the other end of the first vertical plane, and a second vertical plane vertically extending from the other end of the second horizontal plane toward the first inner flat surface with the other end extending to one end of the first inner flat surface. The length of the first vertical plane in the first inner inclined surface is the same as the length of the first vertical plane in the second inner inclined surface, the length of the second vertical plane in the first inner inclined surface is the same as the length of the second vertical plane in the second inner inclined surface, the length of the first horizontal plane in the first inner inclined surface is the same as the length of the first horizontal plane in the second inner inclined surface, and the length of the second horizontal plane in the first inner inclined surface is the same as the length of the second horizontal plane in the second inner inclined surface. The T-branch waveguide according to claim 2.

4. The T-branch waveguide according to claim 3, wherein the length of the first vertical plane in the first inner inclined surface and the length of the first vertical plane in the second inner inclined surface, and the length of the second vertical plane in the first inner inclined surface and the length of the second vertical plane in the second inner inclined surface are of different lengths.

5. The first inner inclined surface is a plane extending from the other end of the second inner flat surface to one end of the third inner flat surface. The second inner inclined surface is a second vertical plane extending from the other end of the fourth inner flat surface to one end of the first inner flat surface. The T-branch waveguide according to claim 2.

6. The first waveguide, the second waveguide, and the third waveguide are each a hollow waveguide, and the hollow portion constitutes a waveguide path. The T-branch waveguide according to any one of claims 1 to 5.

7. The first waveguide, the second waveguide, and the third waveguide each include a tubular body made of a hollow metal material and a dielectric filled in the hollow portion of the tubular body, and the T-branch waveguide according to any one of claims 1 to 5, wherein the hollow portion constitutes a waveguide.

8. The first waveguide, the second waveguide, and the third waveguide each include a tubular body made of a hollow resin and a metal plating layer applied to the entire inner surface of the tubular body, and the T-branch waveguide according to any one of claims 1 to 5, wherein the hollow portion constitutes a waveguide.

9. The T-branch waveguide according to any one of claims 1 to 5, wherein the length of the third waveguide in the axial direction of the tube axis is a length of a quarter wavelength of the electromagnetic wave to be propagated.

10. The T-branch waveguide according to claim 9, wherein the length of the third waveguide in the direction parallel to the tube axis of the second waveguide in the waveguide is a length of a half wavelength of the electromagnetic wave to be propagated.

11. The T-branch waveguide according to any one of claims 1 to 5, wherein a cross section of the waveguide in the second waveguide parallel to a plane perpendicular to the tube axis of the second waveguide is uniformly rectangular from the first input / output terminal to the second input / output terminal in the second waveguide.

12. The T-branch waveguide according to any one of claims 1 to 5, wherein in the waveguide from the first input / output terminal to the second input / output terminal in the second waveguide, a cross section parallel to a plane perpendicular to the tube axis of the second waveguide is a cross-sectional shape corresponding to the amplitude ratio of the electromagnetic wave to be propagated.

13. An antenna device comprising the T-branch waveguide according to any one of claims 1 to 5, and a waveguide slot antenna connected to the T-branch waveguide and fed with electromagnetic waves from the T-branch waveguide.

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