Reflector antenna

Abstract

One aspect of the present invention is a reflector antenna provided with: a rotationally symmetric secondary reflecting mirror that is a secondary reflecting mirror having a shape (360 / n)-degree rotationally symmetric with respect to a prescribed axis serving as an axis of rotational symmetry, the prescribed axis being an axis that is prescribed; and a rotationally symmetric primary reflecting mirror that is a primary reflecting mirror having a shape (360 / m)-degree rotationally symmetric with respect to the prescribed axis serving as an axis of rotational symmetry. As compared with a reference reflector antenna, which is a reflector antenna provided with: a reference secondary reflecting mirror that is a secondary reflecting mirror having a cross-sectional shape coinciding with or substantially coinciding with a quadratic curve; and a reference primary reflecting mirror that is a primary reflecting mirror having a cross-sectional shape coinciding with or substantially coinciding with a quadratic curve, the rotationally symmetric secondary reflecting mirror has a shape obtained by rotating a part of the cross-sectional shape of the reference secondary reflecting mirror n times by (360 / n) degrees each time with respect to the prescribed axis serving as an axis of rotational symmetry, and the rotationally symmetric primary reflecting mirror has a shape obtained by rotating a part of the cross-sectional shape of the reference primary reflecting mirror m times by (360 / m) degrees each time with respect to the prescribed axis serving as an axis of rotational symmetry.

Description

Reflector Antenna

[0001] The present invention relates to a reflector antenna.

[0002] In OAM (Orbital Angular Momentum) multiplexing transmission using a UCA (Uniform Circular Array), it has been proposed to increase the effective UCA diameter by using a reflector in order to improve the transmission distance.

[0003] Q. Wu, X. Jiang and C. Zhang, “Attenuation of orbital angular momentum beam transmission with a parabolic antenna,” IEEE Antennas Wireless Propag. Lett., vol. 20, no. 10, pp. 1849-1853, 2021.MH Hassan et al., “Beam Divergence Reduction of Vortex Waves with a Tailored Lens and a Tailored Reflector,” IEEE Access, vol. 9, pp. 9800-9811, 2021.

[0004] However, the primary antenna (i.e., the primary radiator) of a Multi-UCA or similar device needs to be placed as close as possible to the subreflector, but if the size of the primary antenna is not negligible, it will cause diffuse reflection and disturbance of the electric field distribution due to shielding by the primary antenna itself. Therefore, there is growing expectation for a technology to suppress this disturbance, which will reduce the rate at which radio waves return to the primary radiator.

[0005] In view of the above circumstances, an object of the present invention is to provide a technique for reducing the rate at which radio waves return to a primary radiator.

[0006] One aspect of the present invention is a radar comprising: a primary radiator; a rotationally symmetric sub-reflector which is a sub-reflector having a shape that is rotationally symmetric at (360 / n) degrees (n is an integer of 2 or more) around a predetermined axis that is a predetermined axis as an axis of rotational symmetry and which reflects radio waves radiated from the primary radiator; and a rotationally symmetric main reflector which is a main reflector having a shape that is rotationally symmetric at (360 / m) degrees (m is an integer of 2 or more) around the predetermined axis as an axis of rotational symmetry and which reflects radio waves reflected by the rotationally symmetric sub-reflector, wherein the shape of the rotationally symmetric sub-reflector is a reference sub-reflector which is a sub-reflector having a cross-sectional shape that is identical or approximately identical to a quadratic curve and a rotationally symmetric shape with the focal axis of the quadratic curve as an axis of rotational symmetry; and a reference main reflector which is a main reflector having a cross-sectional shape that is identical or approximately identical to a quadratic curve and a rotationally symmetric shape with the focal axis of the quadratic curve as an axis of rotational symmetry. a reference reflector antenna in which a portion of the cross-sectional shape of the reference subreflector in a reference reflector antenna is rotated n times by (360 / n) degrees around the specified axis as an axis of rotational symmetry, the shape of the rotationally symmetric main reflector is rotated m times by (360 / m) degrees around the specified axis as an axis of rotational symmetry, the focal axis is an axis that passes through the vertex and focus of a quadratic curve, and the specified axis and the focal axis are parallel but do not coincide, the distance between the focal axis of the quadratic curve in the reference subreflector in the reference reflector antenna and the specified axis coincides or approximately coincides with the distance between the focal axis of the quadratic curve in the reference main reflector and the specified axis, and the primary radiator is an array antenna.

[0007] The present invention makes it possible to reduce the rate at which radio waves return to the primary radiator.

[0008] 1 is an explanatory diagram illustrating a reflector antenna according to an embodiment. FIG. 1 is an explanatory diagram illustrating a first example of a subreflector and a main reflector according to an embodiment. FIG. 2 is an explanatory diagram illustrating a second example of a subreflector and a main reflector according to an embodiment. FIG. 1 is an explanatory diagram illustrating an effect achieved by the reflector antenna according to an embodiment. FIG. 2 is an explanatory diagram illustrating an effect achieved by the reflector antenna according to an embodiment. FIG. 3 is an explanatory diagram illustrating an effect achieved by the reflector antenna according to an embodiment. FIG. 4 is an explanatory diagram illustrating an effect achieved by the reflector antenna according to an embodiment. FIG. 1 is an explanatory diagram illustrating a first example of a reflector antenna according to a modified example in which the confocal condition is satisfied. FIG. 2 is an explanatory diagram illustrating a second example of a reflector antenna 100 according to a modified example in which the confocal condition is satisfied. A diagram showing an example of an arrangement of antenna elements according to a modified example. A diagram illustrating enlargement of a primary radiator according to a modified example. A diagram showing an example of a change in radius ratio according to a modified example. A diagram showing an example of a rotationally symmetric subreflector when n=8 according to a modified example.

[0009] (First embodiment) Fig. 1 is an explanatory diagram illustrating a reflector antenna 100 according to an embodiment. Fig. 1 shows an example of a cross section of a reflector antenna 100 in which the main reflector and sub-reflector have rotationally symmetric shapes. The cross section is perpendicular to the Y axis. That is, the cross section is parallel to the XZ plane. The Z axis is parallel to the axis of rotational symmetry of the reflector antenna 100. The reflector antenna 100 is a reflector antenna used for OAM (Orbital Angular Momentum) multiplex transmission. The reflector antenna 100 includes a primary radiator 1, a rotationally symmetric sub-reflector 2, and a rotationally symmetric main reflector 3.

[0010] The primary radiator 1 is an array antenna including a plurality of antenna elements 101. The rotationally symmetric subreflector 2 is a subreflector having a shape that is rotationally symmetric by (360 / n) degrees (n is an integer of 2 or more) around a predetermined axis that is the axis of rotational symmetry, and reflects the radio waves radiated from the primary radiator 1. The rotationally symmetric main reflector 3 is a main reflector having a shape that is rotationally symmetric by (360 / m) degrees (m is an integer of 2 or more) around the predetermined axis that is the axis of rotational symmetry, and reflects the radio waves reflected by the rotationally symmetric subreflector 2.

[0011] Note that n and m may or may not be the same. Also, n or m may be infinite. When n is infinite, the shape of the cross section perpendicular to the predetermined axis of the rotationally symmetric secondary reflector 2 is circular. When m is infinite, the shape of the cross section perpendicular to the predetermined axis of the rotationally symmetric main reflector 3 is circular. Note that axis K1 in FIG. 1 is an example of the predetermined axis. Note that the propagation axis of the radio waves radiated from the primary radiator 1 may coincide with or be parallel to the predetermined axis.

[0012] <<Reference Reflector Antenna>> A reference reflector antenna will be described below to explain the reflector antenna 100. The reference reflector antenna is a reflector antenna that includes a reference subreflector and a reference main reflector.

[0013] The reference subreflector is a subreflector having a cross-sectional shape that is identical or nearly identical to a quadratic curve and a rotationally symmetric shape with the focal axis of the quadratic curve as the axis of rotational symmetry. The reference main reflector is a main reflector having a cross-sectional shape that is identical or nearly identical to a quadratic curve and a rotationally symmetric shape with the focal axis of the quadratic curve as the axis of rotational symmetry.

[0014] The focal axis is an axis that passes through the vertex and the focal point of the quadratic curve. In the example of Fig. 1, each axis K2 is an example of the focal axis.

[0015] In addition, in the reference reflector antenna, the focal axis of the quadratic curve in the reference subreflector coincides with the focal axis of the quadratic curve in the reference main reflector. Note that the quadratic curve in the reference subreflector refers to the quadratic curve that is the cross-sectional shape of the reference subreflector. The quadratic curve in the reference main reflector refers to the quadratic curve that is the cross-sectional shape of the reference main reflector.

[0016] Such a reference reflector antenna is therefore, for example, a Gregorian antenna. The reference reflector antenna may also be, for example, a Cassegrain antenna.

[0017] In the reference reflector antenna, the distance between the focal axis of the quadratic curve in the reference subreflector and the predetermined axis is equal to or approximately equal to the distance between the focal axis of the quadratic curve in the reference main reflector and the predetermined axis. In addition, the predetermined axis and the focal axis are parallel but not coincident.

[0018] The quadratic curve may be a portion of a quadratic curve such as a parabola, hyperbola, or ellipse. Therefore, the cross-sectional shape of the reference secondary reflector may be, for example, identical or approximately identical to a portion of a parabola, identical or approximately identical to a portion of a hyperbola, or identical or approximately identical to a portion of an ellipse. The cross-sectional shape of the reference primary reflector may be, for example, identical or approximately identical to a portion of a parabola, identical or approximately identical to a portion of a hyperbola, or identical or approximately identical to a portion of an ellipse.

[0019] <First Example of Rotationally Symmetric Subreflector 2 and Rotationally Symmetric Main Reflector 3> Figure 2 is an explanatory diagram illustrating a first example of the rotationally symmetric subreflector 2 and the rotationally symmetric main reflector 3 in an embodiment. More specifically, Figure 2 is an explanatory diagram illustrating the relationship between a reflector antenna 910 and a reflector antenna 100. For both the reflector antenna 910 and the reflector antenna 100 shown in Figure 2, an example of a cross section parallel to the XZ plane is shown. The reflector antenna 910 is an example of a reference reflector antenna in which the subreflector is a concave subreflector such as a Gregorian antenna.

[0020] Figure 2 shows that an example of a rotationally symmetric subreflector 2 of a reflector antenna 100 is a rotating body (g is an even number) formed by rotating a part of the quadratic curve of the cross section of the subreflector of a reflector antenna whose focal axis is shifted parallel to a predetermined axis by (360 / g) degrees around the predetermined axis g times.

[0021] In addition, the quadratic curve of the cross section of a reflector antenna in which the focal axis is shifted parallel to the specified axis is a quadratic curve that differs from the quadratic curve of the cross section of reflector antenna 910 only in that the focal axis and the specified axis are not coincident, but are parallel and misaligned.

[0022] FIG. 2 also shows that an example of a rotationally symmetric main reflector 3 is a rotating body (h is an even number) formed by rotating a part of the quadratic curve of the cross section of the main reflector of a reflector antenna, whose focal axis is shifted parallel to a predetermined axis, around the predetermined axis by (360 / h) degrees for h times.

[0023] In this way, the rotationally symmetric subreflector 2 is, for example, a body of revolution obtained by rotating a portion of the quadratic curve of the cross section of the subreflector of a reflector antenna whose focal axis is parallel to but not coincident with a predetermined axis, g times at (360 / g) degrees each, and the rotationally symmetric main reflector 3 in this case is a body of revolution obtained by rotating a portion of the quadratic curve of the cross section of the main reflector of the reflector antenna whose focal axis is parallel to but not coincident with a predetermined axis, h times at (360 / h) degrees each, around the predetermined axis.

[0024] 2, the reflector 911 is an example of a sub-reflector included in the reflector antenna 910, and the reflector 912 is an example of a main reflector included in the reflector antenna 910. In other words, the reflector 911 is an example of a reference sub-reflector, and the reflector 912 is an example of a reference main reflector.

[0025] Although it is clear from the explanation so far, just to be clear, the reflector antenna 100 itself does not include the subreflector and main reflector of the reflector antenna 910.

[0026] <Second Example of Rotationally Symmetric Subreflector 2 and Rotationally Symmetric Main Reflector 3> Figure 3 is an explanatory diagram illustrating a second example of the rotationally symmetric subreflector 2 and the rotationally symmetric main reflector 3 in the embodiment. More specifically, Figure 3 is an explanatory diagram illustrating the relationship between the reflector antenna 920 and the reflector antenna 100. For both the reflector antenna 920 and the reflector antenna 100 shown in Figure 3, an example of a cross section parallel to the XZ plane is shown. The reflector antenna 920 is an example of a reference reflector antenna in which the subreflector is a convex subreflector such as a Cassegrain antenna.

[0027] Figure 3 shows that an example of a rotationally symmetric subreflector 2 of a reflector antenna 100 is a body of revolution formed by rotating a part of the quadratic curve of the cross section of the subreflector of a reflector antenna whose focal axis is shifted parallel to a predetermined axis around the predetermined axis.

[0028] In addition, the quadratic curve of the cross section of a reflector antenna in which the focal axis is shifted parallel to the specified axis is a quadratic curve that differs from the quadratic curve of the cross section of reflector antenna 920 only in that the focal axis and the specified axis are not coincident, but are parallel and misaligned.

[0029] Figure 3 also shows that an example of a rotationally symmetric subreflector 2 of a reflector antenna 100 is a body of revolution formed by rotating a portion of the quadratic curve of the cross section of the subreflector of a reflector antenna whose focal axis is shifted parallel to the propagation axis of the primary radiator 1 around a predetermined axis by (360 / g) degrees g times.

[0030] In this way, the rotationally symmetric subreflector 2 is, for example, a body of revolution obtained by rotating a portion of the quadratic curve of the cross section of the subreflector of a reflector antenna whose focal axis is parallel to but not coincident with a predetermined axis by g times at (360 / g) degrees around the predetermined axis, and the rotationally symmetric main reflector 3 in this case is a body of revolution obtained by rotating a portion of the quadratic curve of the cross section of the main reflector of the reflector antenna whose focal axis is parallel to but not coincident with the axis of rotational symmetry by h times at (360 / h) degrees around the propagation axis of the primary radiator 1.

[0031] 3, the reflector 921 is an example of a sub-reflector included in the reflector antenna 920, and the reflector 922 is an example of a main reflector included in the reflector antenna 920. In other words, the reflector 921 is an example of a reference sub-reflector, and the reflector 922 is an example of a reference main reflector.

[0032] Although it is clear from the explanation so far, just to be clear, the reflector antenna 100 itself does not include the subreflector and main reflector of the reflector antenna 920.

[0033] The examples in Figures 2 and 3 are merely examples. In the examples in Figures 2 and 3, n and m are even numbers, but n may be odd numbers, and m may also be odd numbers. The rotationally symmetric secondary reflector 2 may be any type of rotating body obtained by rotating a portion of the cross section of a reference secondary reflector whose focal axis is parallel to but not coincident with a predetermined axis n times by (360 / n) degrees around the predetermined axis. Furthermore, the rotationally symmetric main reflector 3 may be any type of rotating body obtained by rotating a portion of the cross section of a reference main reflector whose focal axis is parallel to but not coincident with a predetermined axis m times by (360 / m) degrees around the predetermined axis.

[0034] The reference subreflector is, for example, a subreflector of a reflector antenna having a concave subreflector whose focal axis is offset from a predetermined axis in a parallel manner, and the reference main reflector in this case is the main reflector of that reflector antenna. The reference subreflector is, for example, a subreflector of a reflector antenna having a convex subreflector whose focal axis is offset from a rotationally symmetric axis in a parallel manner, and the reference main reflector in this case is the main reflector of that reflector antenna.

[0035] <Effects of the rotationally symmetric subreflector 2 and the rotationally symmetric main reflector 3> Fig. 4 is a first explanatory diagram illustrating the effects achieved by the reflector antenna 100 of the embodiment. Fig. 5 is a second explanatory diagram illustrating the effects achieved by the reflector antenna 100 of the embodiment.

[0036] More specifically, Fig. 4 shows an example of a propagation path of radio waves in a reflector antenna 910 equipped with a concave subreflector, and Fig. 5 shows an example of a propagation path of radio waves in the reflector antenna 100 shown in Fig. 2. For both the reflector antenna 910 shown in Fig. 4 and the reflector antenna 100 shown in Fig. 5, an example of a cross section parallel to the XZ plane is shown.

[0037] Arrow K3 in Fig. 4 indicates an example of a propagation path of radio waves radiated from primary radiator 1 in reflector antenna 910 in Fig. 2. More specifically, arrow K3 indicates an example of a propagation path of radio waves reflected by reflector 911 after being radiated from primary radiator 1. As indicated by arrow K3, in the case of reflector antenna 910, radio waves reflected by reflector 911 are incident on primary radiator 1. Therefore, primary radiator 1 itself blocks the propagation of radio waves.

[0038] On the other hand, this is not the case with the reflector antenna 100 shown in Fig. 2. Arrow K4 in Fig. 5 shows an example of a propagation path of radio waves radiated from the primary radiator 1 in the reflector antenna 100 of Fig. 2. More specifically, arrow K4 shows an example of a propagation path of radio waves that are radiated from the primary radiator 1 and then reflected by the rotationally symmetric subreflector 2. As shown by arrow K4, in the case of the reflector antenna 100 of Fig. 2, the radio waves reflected by the rotationally symmetric subreflector 2 do not enter the primary radiator 1, but enter the rotationally symmetric main reflector 3.

[0039] The same applies to the reflector antenna 920 equipped with a convex sub-reflector. This will be explained with reference to FIGS.

[0040] Fig. 6 is a third explanatory diagram illustrating the effects achieved by the reflector antenna 100 of the embodiment. Fig. 7 is a fourth explanatory diagram illustrating the effects achieved by the reflector antenna 100 of the embodiment.

[0041] More specifically, Fig. 6 shows an example of a propagation path of radio waves in the reflector antenna 920, and Fig. 7 shows an example of a propagation path of radio waves in the reflector antenna 100 shown in Fig. 4. For both the reflector antenna 920 shown in Fig. 6 and the reflector antenna 100 shown in Fig. 7, an example of a cross section parallel to the XZ plane is shown.

[0042] Arrow K5 in Fig. 6 indicates an example of a propagation path of radio waves radiated from primary radiator 1 in reflector antenna 920 in Fig. 3. More specifically, arrow K5 indicates an example of a propagation path of radio waves reflected by reflector 921 after being radiated from primary radiator 1. As indicated by arrow K5, in the case of reflector antenna 920, radio waves reflected by reflector 921 are incident on primary radiator 1. Therefore, primary radiator 1 itself blocks the propagation of radio waves.

[0043] On the other hand, this is not the case with the reflector antenna 100 shown in Fig. 3. Arrow K6 in Fig. 7 shows an example of a propagation path of radio waves radiated from the primary radiator 1 in the reflector antenna 100 of Fig. 3. More specifically, arrow K6 shows an example of a propagation path of radio waves that are radiated from the primary radiator 1 and then reflected by the rotationally symmetric subreflector 2. As shown by arrow K6, in the case of the reflector antenna 100 of Fig. 3, the radio waves reflected by the rotationally symmetric subreflector 2 do not enter the primary radiator 1, but enter the rotationally symmetric main reflector 3.

[0044] In this way, the reflector antenna 100 can reduce the rate at which radio waves return to the primary radiator 1 .

[0045] The reflector antenna 100 configured in this manner includes a rotationally symmetric subreflector 2 and a rotationally symmetric main reflector 3. Therefore, as described in <Effects of the rotationally symmetric subreflector 2 and the rotationally symmetric main reflector 3>, it is possible to reduce the proportion of radio waves returning to the primary radiator.

[0046] (Modification) Note that a parabolic condition may be satisfied in the reflector antenna 100. The parabolic condition is a condition that the cross-sectional shape of the rotationally symmetric subreflector and the cross-sectional shape of the rotationally symmetric main reflector are identical or nearly identical to a part of a parabola.

[0047] Furthermore, the reflector antenna 100 that satisfies the parabolic condition may also satisfy the confocal condition, which is a condition in which the focal point of the reference subreflector and the focal point of the reference main reflector coincide with each other, and the focal axis of the reference subreflector and the focal axis of the reference main reflector coincide with each other.

[0048] Fig. 8 is an explanatory diagram illustrating a first example of a reflector antenna 100 in a modified example in which the confocal condition is satisfied. Fig. 9 is an explanatory diagram illustrating a second example of a reflector antenna 100 in a modified example in which the confocal condition is satisfied. Figs. 8 and 9 show the reflector antenna 100. Figs. 8 and 9 show an example of a cross section of the reflector antenna 100 that is parallel to the XZ plane.

[0049] The reference subreflector of the reflector antenna 100 in Fig. 8 is a convex subreflector. The reference subreflector of the reflector antenna 100 in Fig. 9 is a concave subreflector. Arrow K7 in Fig. 8 indicates an example of the propagation path of radio waves radiated from the primary radiator 1 and then reflected by the rotationally symmetric subreflector 2.

[0050] 9 is the focus of the parabolic cross section of the rotationally symmetric sub-reflector 2, and is also the focus of the parabolic cross section of the rotationally symmetric main reflector 3. In other words, point P1 is the focus of the rotationally symmetric sub-reflector 2, and is also the focus of the rotationally symmetric main reflector 3.

[0051] In Fig. 9, both arrows K8 and K9 show examples of the propagation path of radio waves radiated in the Z-axis direction from the primary radiator 1. Note that arrow K8 shows a propagation path that runs from the start point of arrow K8-1, through arrow K8-2, and to the end point of arrow K8-3. The propagation path shown by arrow K8 in Fig. 9 indicates that radio waves radiated in the Z-axis direction from the primary radiator 1 are reflected by the sub-reflector, pass through point P1, and are reflected by the main reflector before propagating in the Z-axis direction.

[0052] Arrow K8-1 indicates the propagation path of the radio waves radiated in the Z-axis direction from the primary radiator 1. Arrow K8-2 indicates the propagation path of the radio waves that reach the end point of arrow K8-1, are reflected by the sub-reflector, and pass through point P1. Arrow K8-3 indicates the path of the radio waves that reach the end point of arrow K8-2, are reflected by the main reflector, and propagate in the Z-axis direction.

[0053] In FIGS. 8 and 9, f ｓｕｂ represents the focal length of the cross section of the rotationally symmetric secondary reflector 2, which is a quadratic curve (parabola), and f ｍａｉｎindicates the focal length of the quadratic curve (parabola) in the cross section of the rotationally symmetric main reflector 3. a indicates the distance between the focal axis and the propagation path indicated by arrow K7-1. b indicates the distance between the focal axis and the propagation path indicated by arrow K7-3.

[0054] <Effects of Satisfying the Confocal Condition> An example of the effects of satisfying the confocal condition will be described. First, an example of the arrangement of the antenna elements 101 provided in the primary radiator 1 will be described.

[0055] Fig. 10 is a diagram showing an example of the arrangement of antenna elements 101 in a modified example. Fig. 10 shows an example of a view of the primary radiator 1 as seen from the Z-axis direction. The example in Fig. 10 is a 4UCA (Uniform Circular Array). Therefore, the primary radiator in the example of Fig. 10 is configured with four ring arrays, each with eight antenna elements 101 positioned at equal intervals on a circumference, each having the same center but different radii.

[0056] Therefore, in the example of Fig. 10, the primary radiator 1 has a total of 32 antenna elements 101. In Fig. 10, in order not to make the diagram difficult to view, one of the 32 antenna elements is given a reference symbol.

[0057] 10, the center of the ring array is the point through which the axis of rotational symmetry of the reflector antenna 100 passes. The axis of rotational symmetry of the reflector antenna 100 is parallel to the Z-axis. In the example of FIG. 10, the antenna elements 101 on each ring array are arranged at equal intervals on each ring array. In this way, the primary radiator 1 includes an array antenna, and the antenna elements of the array antenna may be positioned at equal intervals on one or more circumferences centered on the axis of rotational symmetry of the reflector antenna 100.

[0058] In the example of FIG. 10, the number of ring arrays is four, but the number of ring arrays is not limited to four.

[0059] Generally, a reflector antenna has a sub-reflector and a main reflector to achieve the effect of a magnifying mirror. The object being magnified here is the primary radiator 1. In the reflector antenna 100, the primary radiator 1 is also magnified by the rotationally symmetric sub-reflector 2 and the rotationally symmetric main reflector 3.

[0060] Fig. 11 is an explanatory diagram illustrating the expansion of the primary radiator 1 in the modified example. In Fig. 11, the expansion ratio is indicated by M. In Fig. 11, the antenna element 102 is the antenna element 101 before expansion, after expansion.

[0061] The magnification ratio M is expressed by the following equation (1).

[0062]

[0063] Equation (1) is derived using geometric optics.

[0064] In the case of the reflector antenna 100, the expansion is not symmetrical about the propagation axis but about the focal axis. Therefore, before expansion, the distance from the axis K1 is r ＵＣＡ The position R of the antenna element 102 after the expansion of the antenna element 101 is ＵＣＡ is expressed by the following equation (2) when the subreflector of the reflector antenna is a rotationally symmetric subreflector 2 whose focal axis is shifted parallel to the propagation axis of the primary radiator 1.

[0065]

[0066] In addition, position R ＵＣＡ More specifically, r is the distance from the nearest focal axis (axis K2). Point P2 in the example of FIG. 11 is a point on the nearest focal axis. ｏｆｆ represents the deviation between the focal axis and the axis K1.

[0067] Furthermore, the position R of the antenna element 102 ＵＣＡ is expressed by the following equation (3) when the subreflector of the reflector antenna is a rotationally symmetric subreflector 2 whose focal axis is shifted parallel to the propagation axis of the primary radiator 1.

[0068]

[0069] Note that equations (2) and (3) are derived using geometrical optics.

[0070] Incidentally, the ring array of the antenna elements 101 in the primary radiator 1 remains a ring array even after expansion. However, in the case of the reflector antenna 100, as shown in equations (2) and (3), the radius of the ring array after expansion is not simply M times the radius before expansion, but is r ｏｆｆ The radius is corrected by

[0071] Therefore, the radius ratio is larger after the expansion than before the expansion, which is the radius of the smallest ring array relative to the radius of the largest ring array.

[0072] 12 is a diagram showing an example of a change in the radius ratio in the modified example. Fig. 12 shows an example of a set of ring arrays 901 before expansion and an example of a set of ring arrays 902 after expansion in the reflector antenna 100. In the example of Fig. 12, the radius of the ring array with the smallest radius in the set of ring arrays 901 before expansion is r ａ The radius of the ring array with the largest radius in the set of ring arrays 901 before expansion is r ｂ is.

[0073] In the example of FIG. 12, the radius of the ring array with the smallest radius in the set of ring arrays 902 after expansion is R ａ The radius of the ring array with the largest radius in the expanded ring array set 902 is R ｂ is.

[0074] In the example of FIG. 12, the radius ratio in the ring array set 901 before expansion is r ａ ÷r ｂ In the example of FIG. 12, the radius ratio of the expanded ring array set 902 is R ａ ÷R ｂ FIG. ａ ÷r ｂ <R ａ ÷R ｂ This indicates that

[0075] A lens or a reflector for correcting aberration of the incident radio wave may be further provided between the rotationally symmetric main reflector 3 and the rotationally symmetric sub-reflector 2 .

[0076] Although the cross-sectional shape has been described as being identical or substantially identical to a quadratic curve, a shape substantially identical to a quadratic curve means that the cross-sectional shape is expressed by a function obtained by adding a perturbation term to a quadratic function. The perturbation term may be, for example, a term of third degree or higher, whose weight is smaller than that of the square of the quadratic function.

[0077] Figure 13 is a diagram showing an example of a rotationally symmetric subreflector when n = 8 in a modified example. Figure 13 shows a rotationally symmetric subreflector 2a and a reference subreflector 931. The rotationally symmetric subreflector 2a is a rotationally symmetric subreflector 2 with n = 8. The reference subreflector 931 is a reference subreflector for the rotationally symmetric subreflector 2a.

[0078] 13 shows an image G1 of the reference sub-reflector 931 being rotated by 360 / 8 degrees around the axis of rotational symmetry K1. Also, FIG. 13 shows an image G2 of the (360 / 8) degree rotationally symmetric body formed by rotating the reference sub-reflector 931 by 360 / 8 degrees around the axis of rotational symmetry K1.

[0079] As mentioned above, the rotationally symmetric subreflector is a part of the cross-sectional shape of the reference main reflector rotated, so it can be said that the rotationally symmetric subreflector is a part of a rotationally symmetric body created by rotating the reference main reflector. Figure 13 shows this, and the rotationally symmetric subreflector 2a is a part of the (360 / 8) degree rotationally symmetric body shown in image G2.

[0080] When n = even, the cross section of the rotationally symmetric secondary reflector 2 is symmetric about the axis of rotational symmetry. When m = even, the cross section of the rotationally symmetric main reflector 3 is symmetric about the axis of rotational symmetry. On the other hand, when n = odd, the cross section of the rotationally symmetric secondary reflector 2 is not necessarily symmetric about the axis of rotational symmetry. When m = odd, the cross section of the rotationally symmetric main reflector 3 is not necessarily symmetric about the axis of rotational symmetry.

[0081] However, in "Regarding the Effects of the Rotationally Symmetric Subreflector 2 and the Rotationally Symmetric Main Reflector 3," the effects were explained using only one side of the cross section on either side of the axis of rotational symmetry, with reference to Figures 4 to 7. Therefore, the effects described in "Regarding the Effects of the Rotationally Symmetric Subreflector 2 and the Rotationally Symmetric Main Reflector 3" actually occur even if the cross section is asymmetric about the axis of rotational symmetry. Therefore, even when n or m is an odd number, the rate at which radio waves return to the primary radiator can be reduced.

[0082] Furthermore, in the section <Regarding the effect of satisfying the confocal condition>, the effect is explained using only one side of a space partitioned by a plane that passes through the axis of rotational symmetry and is parallel to the axis of rotational symmetry, with reference to Figure 11. Therefore, the effect described in <Regarding the effect of satisfying the confocal condition> actually occurs even when n or m is an odd number.

[0083] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0084] REFERENCE SIGNS LIST 100...reflector antenna, 1...primary radiator, 2, 2a...rotationally symmetric subreflector, 3...rotationally symmetric main reflector, 101...antenna element, 910...reflector antenna, 911...reflector, 912...reflector, 921...reflector, 922...reflector, 931...reference subreflector

Claims

1. A device comprising: a primary radiator; a rotationally symmetric sub-reflector that is a secondary reflector having a shape that is rotationally symmetric at (360 / n) degrees (n is an integer of 2 or more) around a predetermined axis that is the axis of rotational symmetry, and that reflects radio waves radiated from the primary radiator; and a rotationally symmetric main reflector that is rotationally symmetric at (360 / m) degrees (m is an integer of 2 or more) around the predetermined axis that is the axis of rotational symmetry, and that reflects radio waves reflected by the rotationally symmetric sub-reflector, the shape of the rotationally symmetric subreflector is a shape obtained by rotating a part of the cross-sectional shape of the reference subreflector n times by (360 / n) degrees around the predetermined axis, in a reference reflector antenna which is a reflector antenna comprising a reference subreflector which is a subreflector whose cross-sectional shape is identical or approximately identical to a quadratic curve and has a rotationally symmetric shape with the focal axis of the quadratic curve as its axis of rotational symmetry, and a reference main reflector which is a main reflector whose cross-sectional shape is identical or approximately identical to a quadratic curve and has a rotationally symmetric shape with the focal axis of the quadratic curve as its axis of rotational symmetry, the shape of the rotationally symmetric main reflector is a shape obtained by rotating a part of the cross-sectional shape of the reference main reflector m times by (360 / m) degrees around the predetermined axis, the focal axis is an axis that passes through the vertex and focal point of the quadratic curve, the predetermined axis and the focal axis are parallel and do not coincide, A reflector antenna, wherein in the reference reflector antenna, a distance between the focal axis of the quadratic curve in the reference subreflector and the predetermined axis coincides or approximately coincides with a distance between the focal axis of the quadratic curve in the reference main reflector and the predetermined axis, and the primary radiator is an array antenna.

2. The reflector antenna according to claim 1, wherein the antenna elements of the array antenna are positioned at equal intervals on one or more circumferences centered on the axis of rotational symmetry.

3. The reflector antenna according to claim 1, wherein the quadratic curve in the reference subreflector and the quadratic curve in the reference main reflector are identical or substantially identical to portions of a parabola.

4. A reflector antenna as described in claim 1, wherein the focal point of the reference subreflector and the focal point of the reference main reflector coincide, and the focal axis of the reference subreflector and the focal axis of the reference main reflector coincide.

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