Low-cost dual-band circularly polarized multi-beam coverage antenna based on single-layer structure and design method thereof

Abstract

The invention discloses a low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure and a design method thereof. According to the antenna, a parabolic antenna and a reflective array antenna are combined, so that the original excellent radiation performance of the parabolic antenna is reserved, and coverage of a plurality of circularly polarized beams in two different frequency bands is successfully realized; the antenna structure is composed of a double-frequency double-circular-polarization horn feed source and a paraboloid type reflection array, wherein a plurality of reflection units specially customized for a K wave band and a Ka wave band are regularly embedded in the array surface of the reflection array. The antenna designed by the invention can respectively radiate two circularly polarized wave beams with different rotation directions in the K and Ka wave bands, and effectively realizes effective isolation of the transmitting and receiving circularly polarized wave beams in frequency and polarization dimensions.

Description

Technical Field

[0001] The present invention belongs to the technical field of antennas, and in particular relates to a low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure and a design method thereof. Background Art

[0002] Satellite communications for broadband services, such as Internet access, rely on the core technology of high-throughput satellites (HTS) systems in geostationary orbit. These HTS systems can accurately subdivide the target service area into numerous small coverage areas through the advanced multi-beam antenna technology deployed on them. The multi-point coverage strategy follows a beam four-color (i.e. dual-frequency dual-beam) multiplexing scheme, where the spot beams are generated at two different frequencies and two orthogonal polarizations. Two adjacent beams at the same frequency and polarization (same color) will never overlap, thereby achieving effective spatial isolation of beams of the same color and greatly reducing the potential interference between adjacent beams.

[0003] Ka-band four-color coverage usually consists of about 50 or 100 overlapping spot beams with a beam diameter of about 0.65° and a spacing of 0.56° between adjacent beams. To avoid the interweaving of spot beams, the most mature and reliable antenna system is based on four single-beam per feed (SFB) reflectors, one for each color of the transmit / receive (Tx / Rx) band. However, conventional reflectors have difficulty in producing the required separation beam angles (0.56°) between them, because the distance between adjacent feeds will be less than the feed size required to illuminate the antenna aperture, which will lead to feed overlap problems. At the same time, this system structure based on four reflectors means limitations in the accommodation and loading of satellite payloads. Therefore, a new structural solution is needed that can not only significantly reduce the number of apertures of the reflective surface and optimize the payload configuration of the satellite, but also solve the problem of feed overlap and ensure the smooth implementation of the four-color coverage of the beam. Such a design will simultaneously meet the multiple requirements of reducing hardware complexity, improving system efficiency and ensuring communication quality. Summary of the invention

[0004] The purpose of the present invention is to provide a low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure and a design method thereof. The communication system using this design scheme can meet the needs of multi-region signal coverage in satellite communications; the parabolic antenna can accurately focus the beam from the feed source at the focal point due to its unique ability, and by carefully deploying a dual-frequency reflection unit structure on the parabolic antenna, and equipping it with a high-performance feed horn with dual-band and dual circular polarization characteristics, it is successfully achieved that only one feed source and a parabolic reflector array antenna are needed to complete half of the beam requirements in the beam four-color coverage scheme.

[0005] The technical solution for achieving the purpose of the present invention is: a low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure, including a dual-band dual circularly polarized feed and a parabolic reflector array; the parabolic reflector array is composed of a plurality of K and Ka band metal reflector units arranged in a periodic nested scheme.

[0006] Furthermore, the dielectric material used in the parabolic reflective array is Arlon 880D, the metal reflective unit is made of copper, and the back of the parabolic reflective array is also covered with a copper layer.

[0007] Furthermore, the low-frequency structure of the parabolic reflectarray unit is composed of a circular ring, a rectangular microstrip line and an arc microstrip line. The arc microstrip line is connected to the circular ring microstrip line through a rectangular microstrip line, and the arc microstrip line and the circular ring microstrip line are concentrically arranged. Under the condition of an operating frequency of 19.5 GHz, the gap between the two arc microstrip lines is initially set to 0.7 mm to ensure that the phase difference between the two orthogonal linear polarizations is 180°. The unit rotation technology is used to ensure that the polarization direction of the generated beam is consistent with the polarization direction of the circularly polarized feed.

[0008] Furthermore, the high-frequency structure of the parabolic reflector array unit includes a circular patch with four notches, and each notch is connected to a spiral microstrip line, and the calculation formula of the spiral line is:

[0009] x=(a+b·θ)·cos(θ)

[0010] y=(a+b·θ)·sin(θ)

[0011] Wherein, a is the initial radius of the helix, b is the rate of change of the helix radius with angle θ, x and y are the position coordinates of the ends of the helix, and the change of angle θ controls the length of the helix. Under the condition of an operating frequency of 29.5 GHz, the angle reflecting the length of the helix in the X direction is initially set to 130°, and the angle reflecting the length of the helix in the Y direction is initially set to 37°, ensuring that the phase difference between the two orthogonal linear polarizations is 180°, and then compensating the phase in the manner of a rotation unit to achieve a beam output consistent with the polarization direction of the circularly polarized feed source.

[0012] Furthermore, the circularly polarized feed source is a corrugated horn capable of operating in a dual-frequency dual circular polarization state.

[0013] Furthermore, the phase center of the circularly polarized horn antenna is placed at the focus of the parabolic antenna.

[0014] Furthermore, the antenna can radiate a right-hand circularly polarized beam in the direction of (1.3°, 90°) and a left-hand circularly polarized beam in the direction of (-1.3°, 90°) in the K band; and can radiate a left-hand circularly polarized beam in the direction of (1.3°, 90°) and a right-hand circularly polarized beam in the direction of (-1.3°, 90°) in the Ka band, ultimately achieving frequency and polarization isolation of transmitting and receiving circularly polarized beams.

[0015] A design method for a low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure includes a deployment and optimization strategy for a parabolic reflector array unit, specifically: firstly, based on the beam pointing requirement, the target phase distribution of right-hand circular polarization and left-hand circular polarization at 19.5GHz and 29.5GHz is calculated; in the deployment stage, each unit on the reflector array is initially set to be the same, that is, to have a consistent physical structure and initial phase; then, according to the technical requirements of the unit rotation compensation phase, each unit on the reflector array is rotated; then, according to the actual incident angle of the unit at different positions, the gap width of two arc microstrip lines in the low-frequency structure and the length of four spiral lines in the high-frequency structure are optimized to suppress the growth of cross-polarization values ​​at two center frequencies; finally, the reflection coefficient and radiation pattern of the reflector array unit are evaluated.

[0016] Compared with some existing parabolic reflector array antennas that realize four-color beam coverage solutions, the dual-band circularly polarized multi-beam coverage antenna of the present invention has the advantages of effectively reducing the mutual coupling performance between the high and low frequency structures of the unit through a unique dual-frequency unit structure design and optimization strategy, so that the designed parabolic reflector array antenna can realize frequency and polarization isolation of the transmit and receive beams in the K and Ka bands. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a structural diagram of the dual-band circularly polarized multi-beam coverage antenna in the present invention.

[0018] Figure 2 It is a schematic diagram of the dual-frequency reflection unit structure in the present invention.

[0019] Figure 3 This is the projection mode of the reflective array unit in the present invention on the parabola.

[0020] Figure 4 It is a right-hand circular polarization phase distribution diagram of the unit on the array surface of the present invention at a frequency of 19.5 GHz, and a schematic diagram of the corresponding low-frequency structure rotation angle distribution.

[0021] Figure 5 It is a right-hand circular polarization phase distribution diagram of the unit on the array surface of the present invention at a frequency of 29.5 GHz, and a schematic diagram of the corresponding high-frequency structure rotation angle distribution.

[0022] Figure 6 This is the gain pattern of the reflectarray antenna in the present invention operating at a frequency of 19.5 GHz.

[0023] Figure 7 It is the gain pattern of the reflect array antenna in the present invention working at a frequency of 29.5 GHz.

[0024] Figure 8 This is the gain pattern of the antenna in the present invention when the feed source is laterally defocused at 19.5 GHz.

[0025] Fig. 9 This is the gain pattern of the antenna in the present invention when the feed source is laterally defocused at 29.5 GHz. DETAILED DESCRIPTION

[0026] The present invention proposes a design method for a low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure, comprising a dual-band dual-circularly polarized feed and a parabolic reflectarray, wherein the circularly polarized feed is a corrugated horn; the parabolic reflectarray is composed of periodically arranged dual-frequency units, wherein the high-frequency unit is nested inside the low-frequency unit, the aperture D of the parabolic reflectarray antenna is 400 mm, the focal diameter ratio F / D is 1.65, and the height H of the parabolic antenna is 340 mm.

[0027] The low-frequency structure and high-frequency structure of the parabolic reflector array antenna unit operate at 19.5 GHz and 29.5 GHz respectively. On the circular aperture projection of the parabola, the layout period of the unit is 5.7 mm. The dual-frequency unit is printed on a single-layer dielectric board with a thickness of 1.57 mm. The dielectric material is Arlon 880D, and the dielectric board adopts a dielectric constant ε r =2.2 is made of a material with a loss of 0.0009. The metal reflection unit is made of copper, and the back of the parabolic reflection array is also covered with a copper layer.

[0028] The parabolic reflector array antenna includes a low-frequency unit and a high-frequency unit, both of which are phase-compensated by unit rotation technology. Specifically, when the circularly polarized horn feed source is in a low-frequency right-hand circular polarization state, the low-frequency unit radiates a right-hand circular polarization beam in the direction of (1.3°, 90°); and when the circularly polarized horn feed source works in a low-frequency left-hand circular polarization state, the low-frequency unit radiates a left-hand circular polarization beam in another direction of (-1.3°, 90°). Similarly, when the circularly polarized horn feed source is in a high-frequency left-hand circular polarization state, the high-frequency unit radiates a left-hand circular polarization beam in the direction of (1.3°, 90°); and when the circularly polarized horn feed source works in a high-frequency right-hand circular polarization state, the high-frequency unit radiates a right-hand circular polarization beam in the direction of (-1.3°, 90°).

[0029] The deployment and optimization strategy of the parabolic reflector array unit first calculates the target phase distribution of RHCP (right-hand circular polarization) and LHCP (left-hand circular polarization) at 19.5GHz and 29.5GHz based on the beam pointing requirements. In the deployment stage, each unit on the reflector array is initially set to be the same, that is, to have a consistent physical structure and initial phase. Subsequently, each unit on the reflector array is rotated in accordance with the technical requirements of the unit rotation compensation phase. Next, the gap width of the two arc microstrip lines in the low-frequency structure and the length of the four spiral lines in the high-frequency structure are optimized according to the actual incident angle of the unit at different positions to suppress the growth of the cross-polarization value at the two center frequencies. Finally, the reflection coefficient and radiation pattern of the reflector array unit are evaluated.

[0030] The low-frequency structure of the parabolic reflectarray unit is composed of a circular ring, a rectangular microstrip line and an arc microstrip line. Under the condition of an operating frequency of 19.5 GHz, the gap between the two arc microstrip lines is initially set to 0.7 mm to ensure that the phase difference between the two orthogonal linear polarizations is 180°. The unit rotation technology is used to ensure that the polarization direction of the generated beam is consistent with the polarization direction of the circularly polarized feed.

[0031] The high frequency structure of the parabolic reflector array unit includes a patch with four notches, and each notch is connected to a spiral microstrip line. The calculation formula of the spiral line is:

[0032] x=(a+b·θ)·cos(θ)

[0033] y=(a+b·θ)·sin(θ)

[0034] Among them, a is the initial radius of the helix, which is 1.18mm, b is the rate of change of the helix radius with the angle θ, which is 0.18, x and y are the position coordinates of the ends of the helix, and the change of angle θ controls the length of the helix. Under the condition of an operating frequency of 29.5GHz, the angle reflecting the length of the helix in the X direction is initially set to 130°, and the angle reflecting the length of the helix in the Y direction is initially set to 37°, ensuring that the phase difference between the two orthogonal linear polarizations is 180°, and then compensating the phase in the manner of a rotating unit to achieve a beam output consistent with the polarization direction of the circularly polarized feed source.

[0035] The antenna combines a parabolic antenna with a reflectarray antenna, which not only retains the original excellent radiation performance of the parabolic antenna, but also successfully achieves the coverage of multiple circularly polarized beams in two different frequency bands (K band and Ka band); the antenna structure consists of a dual-frequency dual-circularly polarized horn feed and a parabolic reflectarray, wherein the reflectarray is characterized in that multiple reflective units customized for the K band and the Ka band are regularly embedded on its array surface. The antenna designed by the present invention can radiate two circularly polarized beams with different rotation directions in the K and Ka bands, respectively, effectively achieving effective isolation of the receiving and transmitting circularly polarized beams in the frequency and polarization dimensions.

[0036] The antenna of the present invention is described in detail below with reference to the accompanying drawings and specific examples.

[0037] Example

[0038] like Figure 1 As shown, this embodiment proposes a dual-band circularly polarized multi-beam coverage antenna, which includes a dual-band dual circularly polarized feed and a parabolic reflector array, wherein the phase center of the circularly polarized horn antenna is placed at the focus of the parabolic antenna.

[0039] like Figure 2 As shown, the unit structure period of the present invention is 5.7 mm, wherein the low-frequency structure is composed of a circular ring, a rectangular microstrip line and an arc microstrip line, and the inner diameter of the circular ring is R k =1.9mm, width W k =0.2mm, the distance between the ring and the arc microstrip line W kd =0.25mm, the spacing between the two arc-shaped microstrip lines is initially set to 0.7mm. The high-frequency structure consists of a circular patch with four notches, and each notch is connected to a spiral microstrip line. The radius of the circular patch R ka =1mm, spiral width W ka =0.15mm, other parameters W s =0.55mm,W c =0.15mm. Reflects the length of the helix in the X direction L x The angle is initially set to 130°, and the length of the helix in the Y direction is L y The angle is initially set to 37°.

[0040] like Figure 3As shown, in the global coordinate system xyz with the focus of the parabola antenna as the origin, two points on the edge of the parabola antenna are taken as point A and point B, whose coordinates are (H+D / 2, 0, (H+D / 2)^2 / 4 / FF) and (HD / 2, 0, (HD / 2)^2 / 4 / FF) respectively. Then, a new three-dimensional coordinate system x'y'z' is established with the midpoint O of points A and B. The coordinate plane x'oy' is also the plane where the aperture surface of the parabola antenna is located. The grid points are evenly divided on the aperture plane with a unit period interval of 5.7mm, and the grid points are projected onto the surface of the parabola along the -z' axis. Finally, the specific positions of a total of 3854 units on the parabola reflect array can be obtained. In the new coordinate system x'y'z', the calculation formula for the z' coordinate of each unit on the array surface is as follows:

[0041]

[0042] N=-2*sin(α)*cos(α)*x'(i)-2*C 2 *sin(α)-4*F*cos(α)

[0043]

[0044] Where D is the aperture of the parabola antenna, F is the focal length of the parabola antenna, H is the offset height of the parabola antenna, A(3) and B(3) refer to the z coordinates of point A and point B, and A(1) and B(1) refer to the x coordinates of point A and point B. α is the angle between the two coordinate systems. x'(i) and y'(j) are the x' and y' coordinates of the (i, j)th unit on the array surface in the new coordinate system x'y'z'. Finally, the coordinates of each unit on the array surface in the global coordinate system xyz can be obtained through appropriate coordinate transformation.

[0045] Reference Figure 3The coordinates of each unit on the parabolic reflectarray in the global coordinate system are obtained by the unit projection method. The deployment and optimization strategy of the parabolic reflectarray unit is first based on the beam pointing requirements. The low-frequency right-hand circularly polarized beam points to the direction of (1.3°, 90°), and the high-frequency left-hand circularly polarized beam points to the direction of (-1.3°, 90°). The target phase distribution of RHCP (right-hand circular polarization) and LHCP (left-hand circular polarization) at 19.5GHz and 29.5GHz is calculated according to the phase compensation formula of the reflectarray antenna. In the deployment stage, it is initially set that each unit on the reflective array is the same, that is, it has a consistent physical structure and initial phase. Subsequently, each unit on the reflective array is rotated according to the technical requirements of the unit rotation compensation phase, that is, there is a 2-fold functional relationship between the unit's rotation angle and the required compensation phase. Next, based on the actual incident angle of each unit at its specific position, the spacing between the two arc-shaped microstrip lines in the low-frequency structure and the extension length of the four spiral lines in the high-frequency structure were finely adjusted to effectively control and reduce the increase in the cross-polarization level at the two center frequency points. The final step involves a comprehensive evaluation of the reflection performance and radiation pattern of the reflective array unit to ensure the effectiveness of the design. After the unit parameters are optimized, the antenna is assembled and a dual-frequency dual circularly polarized feed is used to illuminate the antenna array.

[0046] Figure 4 , Figure 5 The right-hand circular polarization phase distribution of the unit on the reflection front at 19.5GHz and the left-hand circular polarization phase distribution of the unit at 29.5GHz are given. The parabolic antenna can collimate the beam emitted by the feed source. If a circularly polarized beam deviates from the collimation direction, when another circularly polarized feed source is used, the beam will deviate in the opposite direction. At this time, the left-hand and right-hand circular polarization phase distributions satisfy φ LHCP =-φ RHCP The beam pointing designed by the present invention deviates from ±1.3°, the phase change of the circularly polarized beam at 19.5GHz is ±100°, and the rotation angle of the low-frequency structure is ±50°; similarly, the phase change and rotation angle change of the high-frequency structure are ±150° and ±75° respectively.

[0047] Figure 6 , Figure 7The main polarization and cross-polarization gain variation curves of the parabolic reflectarray antenna at 19.5GHz and 29.5GHz are given. Combining the two figures, the antenna designed by the present invention can radiate a right-hand circularly polarized beam in the direction of (1.3°, 90°) and a left-hand circularly polarized beam in the direction of (-1.3°, 90°) in the K band; it can radiate a left-hand circularly polarized beam in the direction of (1.3°, 90°) and a right-hand circularly polarized beam in the direction of (-1.3°, 90°) in the Ka band, and finally achieve frequency and polarization isolation of the receiving and transmitting circularly polarized beams.

[0048] Figure 8 , Fig. 9 The curves of the main polarization and cross-polarization gain changes of the beam when the feed source is horizontally defocused are given. When the beam direction deviates from an angle of one beam width, the parabolic reflector array antenna can achieve frequency and polarization isolation of the transmitted and received circularly polarized beams in the directions of (-5.2°, 90°), (-2.6°, 90°), (2.6°, 90°), and (5.2°, 90°). The good radiation pattern performance proves the superiority of the technical effect.

[0049] The above examples are only used to illustrate the basic principles and effects of the present invention, and are not intended to limit the boundaries of its practical application. Under the premise of ensuring that it does not deviate from the core concept and scope of application of the present invention, relevant professionals have the right to make appropriate adjustments and innovative practices. Therefore, any equivalent modification or change under the guidance of the spirit and technical ideas of the present invention belongs to the protection scope of the present invention.

Claims

1. A low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure, characterized by: It comprises a dual-band dual circular polarization feed source (1) and a parabolic reflective array (3); the parabolic reflective array (3) is composed of a plurality of K- and Ka-band metal reflective units arranged in a periodic nesting scheme, with the high-frequency unit nested inside the low-frequency unit.

2. The low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure according to claim 1, characterized in that: The dielectric material used in the parabolic reflective array (3) is Arlon 880D, the metal reflective unit (2) is made of copper, and the back of the parabolic reflective array is also covered with a copper layer.

3. The low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure according to claim 1, characterized in that: The low-frequency structure of the parabolic reflector array unit is composed of a circular ring, a rectangular microstrip line and an arc-shaped microstrip line. The arc-shaped microstrip line is connected to the circular ring microstrip line through the rectangular microstrip line, and the arc-shaped microstrip line is concentrically arranged with the circular ring microstrip line. Under the condition of an operating frequency of 19.5 GHz, the gap between the two arc-shaped microstrip lines is initially set to 0.7 mm to ensure that the phase difference between the two orthogonal linear polarizations is 180°. The unit rotation technology is used to ensure that the polarization direction of the generated beam is consistent with the polarization direction of the circularly polarized feed.

4. The low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure according to claim 3, characterized in that: The high frequency structure of the parabolic reflector array unit includes a circular patch with four notches, and each notch is connected to a spiral microstrip line. The calculation formula of the spiral line is: x=(a+b·θ)·cos(θ) y=(a+b·θ)·sin(θ) Wherein, a is the initial radius of the helix, b is the rate of change of the helix radius with angle θ, x and y are the position coordinates of the ends of the helix, and the change of angle θ controls the length of the helix. Under the condition of an operating frequency of 29.5 GHz, the angle reflecting the length of the helix in the X direction is initially set to 130°, and the angle reflecting the length of the helix in the Y direction is initially set to 37°, ensuring that the phase difference between the two orthogonal linear polarizations is 180°, and then compensating the phase in the manner of a rotation unit to achieve a beam output consistent with the polarization direction of the circularly polarized feed source.

5. The low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure according to claim 1, characterized in that: The circular polarization feed is a corrugated horn that can operate in a dual-frequency dual circular polarization state.

6. The low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure according to claim 5, characterized in that: The phase center of the circularly polarized horn antenna is placed at the focus of the parabolic antenna.

7. The low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure according to claim 4, characterized in that: The antenna can radiate a right-hand circularly polarized beam in the direction of (1.3ο, 90ο) and a left-hand circularly polarized beam in the direction of (-1.3ο, 90ο) in the K band; it can radiate a left-hand circularly polarized beam in the direction of (1.3ο, 90ο) and a right-hand circularly polarized beam in the direction of (-1.3ο, 90ο) in the Ka band, ultimately achieving frequency and polarization isolation of transmitting and receiving circularly polarized beams.

8. A design method for a low-cost dual-band circularly polarized multi-beam coverage antenna based on a single-layer structure as claimed in any one of claims 1 to 7, characterized in that: It includes the deployment and optimization strategy of parabolic reflectarray units, specifically: first, based on the beam pointing requirements, the target phase distribution of right-hand circular polarization and left-hand circular polarization at 19.5GHz and 29.5GHz is calculated; in the deployment stage, each unit on the reflectarray is initially set to be the same, that is, to have a consistent physical structure and initial phase; then, according to the technical requirements of the unit rotation compensation phase, each unit on the reflectarray is rotated; then, according to the actual incident angle of the unit at different positions, the gap width of the two arc microstrip lines in the low-frequency structure and the length of the four spiral lines in the high-frequency structure are optimized to suppress the growth of the cross-polarization value at the two center frequencies; finally, the reflection coefficient and radiation pattern of the reflectarray unit are evaluated.

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