Dual-frequency dual-beam common-aperture reflector antenna based on FSS subsurface and design method thereof

Abstract

The invention discloses a dual-frequency dual-beam common-aperture reflector antenna based on an FSS subsurface and a design method of the dual-frequency dual-beam common-aperture reflector antenna, relates to the field of satellite antennas, and is used for replacing two large-scale reflectors on a satellite, so that the satellite can perform a plurality of tasks at the same time, and meanwhile, more flexible choices are provided for determining whether the reflectors and a feed source are offset. According to the invention, the Cassegrain-configured antenna is adopted, and the main reflection surface and the FSS auxiliary reflection surface are respectively shaped to meet the shape of a target coverage area of corresponding wave beam reflection and the directivity index of a far-field electric field. According to the invention, a plurality of different shaped beams of a plurality of wavebands are generated to cover different target areas under the condition of avoiding the risk of breakdown sparking caused by convergence of electromagnetic waves at one point, the plurality of beams can be designed to be spatial isolation beams and can also be designed to be spatial overlapping beams, and the flexibility is high.

Description

Technical Field

[0001] The present invention relates to the field of satellite antennas, in particular to a dual - frequency and dual - beam common - aperture reflector antenna based on an FSS sub - reflector, and a design method for a dual - frequency and dual - beam common - aperture reflector antenna based on an FSS sub - reflector. Background Art

[0002] With the application and development of space technologies such as satellite communication, navigation, remote sensing, and deep - space exploration, more challenging requirements are put forward for the performance of satellite antennas. In order to improve satellite communication capacity and meet multi - task requirements, multi - band and multi - beam antenna technologies have received extensive attention and research since the 1960s. In the current development trend, one of the main requirements is that satellite systems can provide multiple coverage areas in multiple frequency bands simultaneously, and increase the compactness of antenna design to reduce the mass and cost of spacecraft.

[0003] However, limited by the space of the satellite launcher fairing, it is difficult to configure a reflector antenna field in each coverage area. At the same time, this will also greatly increase the design cost. For this reason, synthesizing different - shaped beams with a common reflector antenna aperture becomes an option. There are two typical methods for designing a common - aperture reflector antenna. One is to design a feeding system. By introducing a Beam Forming Network (BFN) to optimize the excitation coefficients or the geometric arrangement of array feeding, the formation and directional radiation of different beams are controlled, thereby expanding the coverage of the antenna. However, it is obvious that the feed network designed by this method will be very complex, further increasing the burden on the satellite and the manufacturing cost. Moreover, as the frequency increases, the radio - frequency loss problem brought by this method will become more serious. Another design method is to only change the shape of the reflector. By changing the shape of the reflector, the phase distribution of electromagnetic waves on the aperture plane is adjusted, thereby controlling the formation and directional radiation of different beams. Compared with the first design method, the second design method has the advantages of low cost, light weight, and high system efficiency.

[0004] The Chinese patent document with the publication number CN109885897A proposes a design method for a spaceborne communication hybrid reflector antenna system, which includes the following steps: Step 1: Design feeds F1, F2, and F3 according to the basic geometric dimensions of the shaped main reflector antenna; Step 2: Represent the shaped main reflector using Zernike polynomials, and take the expansion coefficients of the Zernike polynomials characterizing the shape of the shaped main reflector as optimization variables. Use an optimization algorithm to optimize the shaped main reflector so that its radiation pattern can cover the service area, thereby obtaining the expansion coefficients of the Zernike polynomials characterizing the shape of the optimized shaped main reflector, and denote this shaped main reflector as M. Place feed F1 at the excitation position of the shaped main reflector to excite the shaped main reflector M, and a shaped beam can be obtained; Step 3: Use the least squares method to fit the shaped main reflector M obtained in Step 2 to obtain the fitted shaped main reflector M'. On the premise that the corresponding beams of feed F1 and feed F2 do not block each other, determine the position of feed F2, and use the ray tracing method to perform sub-reflector shaping design on the shaped main reflector M' to obtain the shaped sub-reflector denoted as S. Use feed F2 to excite the sub-reflector S to obtain a spot beam, and realize the limited scanning function of the spot beam through the lateral defocusing of the sub-reflector S and feed F2; Step 4: According to the desired beam pointing of the fixed spot beam, use the conjugate matching method of the focal plane field of the shaped main reflector M and the horn aperture field of feed F3 to obtain the optimal feed position of feed F3. Place feed F3 at this position and excite the shaped main reflector M to obtain a fixed spot beam with the desired beam pointing.

[0005] This antenna can be regarded as a combination of a single reflector antenna and a dual reflector antenna, coupled through a common main reflector. An independent feed is used for one coverage area. When one feed feeds the main reflector, a shaped contour beam covering the area will be generated. When the other feed feeds the sub-reflector, another shaped contour beam covering the area will be generated. In this antenna structure, the main reflector aperture is shared by two contour beams, and the shapes of the two contour beams are determined by the main reflector and the sub-reflector respectively. However, as Figure 1 (a) shows, the electromagnetic waves of this antenna will converge at the focal position of the main reflector to form a "real focus", which is more likely to cause breakdown and sparking phenomena. Moreover, since feed 1 needs to avoid the electromagnetic waves reflected by feed 2 through the sub-reflector, a certain offset is required, resulting in a certain spatial isolation between the centers of the two beams generated by it. Summary of the Invention

[0006] The object of the present invention is to: address all or part of the above problems, and provide a dual-frequency and dual-beam common-aperture reflector antenna based on an FSS sub-reflector and its design method, which can realize the independent beam transmission of two frequency bands on the same antenna, avoid the risk of breakdown and sparking caused by the convergence of electromagnetic waves at a point, and at the same time provide more flexible choices for whether the reflector and the feed itself are offset-fed, providing additional design freedom for the beam position.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A dual-frequency and dual-beam common-aperture reflector antenna based on an FSS sub-reflector, comprising:

[0009] A first feed, which emits a first beam;

[0010] A second feed, which emits a second beam with a frequency band different from that of the first beam;

[0011] A main reflector and an FSS sub-reflector arranged with a common aperture; the FSS sub-reflector is located between the first feed and the second feed; the second feed is located between the FSS sub-reflector and the main reflector; the FSS sub-reflector transmits the first beam and reflects the second beam; the main reflector reflects both the first beam and the second beam; the main reflector is shaped to: meet the shape and far-field electric field directivity index requirements of the first target coverage area for the reflection of the first beam; the FSS sub-reflector is shaped to: under the condition that the shape of the main reflector is determined, meet the shape and far-field electric field directivity index requirements of the second target coverage area for the reflection of the second beam.

[0012] Further, the shaping method of the main reflector includes:

[0013] First, initialize the main reflector as a standard reflector, and determine the aperture size of the standard reflector according to the shape and far-field electric field directivity index requirements of the first target coverage area; on the basis of the standard reflector, continuously optimize its surface shape to make it present concave and convex deformation until the first beam reflected by the main reflector meets the shape and far-field electric field directivity index requirements of the first target coverage area.

[0014] When verifying whether the shaping of the main reflector and the FSS sub-reflector meets the shape and far-field electric field directivity index requirements of the first target coverage area and the second target coverage area, sample from both inside and outside the first target coverage area to verify the main reflector, and sample from both inside and outside the second target coverage area to verify the FSS sub-reflector.

[0015] Further, the shaping method of the FSS sub-reflector includes:

[0016] Keep the shape of the main reflector unchanged. First, initialize the FSS sub-reflector to a standard reflector, and determine the aperture size of the standard reflector according to the second feed position and the focal diameter ratio of the main reflector. On the basis of the standard reflector, continuously optimize its surface shape until the second beam satisfies the requirements for the shape and far-field electric field directivity index of the second target coverage area after being reflected by the FSS sub-reflector and the main reflector in sequence.

[0017] When verifying whether the shaping of the main reflector and the FSS sub-reflector meets the requirements for the shape and far-field electric field directivity index of the first target coverage area and the second target coverage area, sample from both inside and outside the first target coverage area to verify the main reflector, and sample from both inside and outside the second target coverage area to verify the FSS sub-reflector.

[0018] Furthermore, the method for determining the aperture size of the standard reflector is as follows:

[0019]

[0020] where D λ is the determined aperture size of the standard reflector in units of wavelength, C c is the perimeter of the target coverage area in degrees, S c is the area of the target coverage area in square degrees, and D min is the minimum directivity requirement value of the target coverage area.

[0021] Furthermore, the standard reflector is initialized in the form of Jacobi-Fourier orthogonal functions.

[0022] Furthermore, optimizing the surface shape of the standard reflector includes:

[0023] Determine the optimization points for optimizing the surface shape of the standard reflector;

[0024] Adjust the optimization coefficients of the determined optimization points;

[0025] Adjust the concave-convex shape of the determined optimization points on the standard reflector with the adjusted optimization coefficients.

[0026] Furthermore, the method for adjusting the optimization coefficients of the determined optimization points is as follows:

[0027] Initialize the optimization coefficients C nm and d nm according to the following formula:

[0028]

[0029] where n and m are constants that control the number of local undulations on the surface of the reflector; refers to the vertical coordinate Z of the initial reflector expressed in terms of the parameters t and for solving the initial optimization coefficients, where t represents the ratio of the polar radius of any point on the aperture of the reflector to the radius of the aperture of the reflector, represents the polar coordinate azimuth angle of that point; represents the optimized Jacobi polynomial, with represents the Jacobi polynomial;

[0030] Keep c 00 unchanged and vary the remaining optimization coefficients near 0.

[0031] Furthermore, the shape and far-field electric field directivity index target for optimizing the shape of the standard reflector are:

[0032]

[0033] where N1 and N2 are the numbers of sampling points inside and outside the target coverage area respectively, i represents the serial number of the sampling point inside the target coverage area, and u represents the serial number of the sampling point outside the target coverage area; D i and D u are the directivity values of a single sampling point inside and outside the target coverage area respectively; Θ() is the Heaviside function; D min is the minimum directivity requirement value of the target coverage area.

[0034] The present invention also provides a design method for a dual-frequency and dual-beam co-aperture reflector antenna based on an FSS sub-reflector. The antenna includes a first feed source for transmitting a first beam, a second feed source for transmitting a second beam, and a main reflector and an FSS sub-reflector arranged with a common aperture; the FSS sub-reflector is located between the first feed source and the second feed source; the second feed source is located between the FSS sub-reflector and the main reflector; the method includes:

[0035] Design a frequency-selective basic unit on the FSS sub-reflector that can transmit the first beam and reflect the second beam according to the frequency bands of the first beam and the second beam;

[0036] Shape the main reflector until it meets the requirements of the shape and far-field electric field directivity index of the first target coverage area for reflecting the first beam;

[0037] Fix the shape of the main reflector and shape the FSS sub-reflector until it meets the requirements of the shape and far-field electric field directivity index of the second target coverage area for reflecting the second beam.

[0038] Further, the method for shaping the reflector according to the shape of the target coverage area and the far-field electric field directivity index includes:

[0039] Initialize the reflector as a standard reflector, and determine the aperture size of the standard reflector according to the shape of the target coverage area and the requirements of the far-field electric field directivity index;

[0040] On the basis of the standard reflector, continuously optimize its surface shape until the reflected beam meets the requirements of the shape of the target coverage area and the far-field electric field directivity index after reflection.

[0041] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0042] The dual-frequency and dual-beam common-aperture reflector antenna of the present invention is based on the Cassegrain antenna as the basic configuration. By designing appropriate frequency-selective basic units and shaping the two reflectors, multiple different shaped beams in multiple frequency bands can be generated by the same antenna to cover different target areas while avoiding the risk of breakdown and sparking caused by the convergence of electromagnetic waves at a point. Compared with the prior art, there is a more flexible choice whether the reflector and the feed itself are offset-fed. The multi-beams can be designed as spatially isolated beams or spatially overlapping beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be described by way of examples and with reference to the accompanying drawings, wherein:

[0044] FIG Figure 1 is a schematic comparison diagram of the electromagnetic wave propagation of the Gregorian antenna and the Cassegrain antenna design schemes;

[0045] FIG Figure 2 is a structural diagram of a dual-frequency and dual-beam common-aperture reflector antenna based on an FSS sub-reflector;

[0046] FIG Figure 3 is a flowchart of the reflector shaping;

[0047] FIG Figure 4 is a comparison diagram before and after shaping of the dual-reflector antenna;

[0048] FIG Figure 5 FSS sub-reflector basic unit and its frequency-selective performance simulation diagram, where (a) is the frequency-selective basic unit and (b) is the frequency-selective performance;

[0049] FIG Figure 6 is a diagram showing the coverage area of the contour beam design result when using the sampling points inside and outside the target coverage area for comparative verification, where (a) is the first beam contour and (b) is the second beam contour.

[0050] FIG Figure 7It is a view showing the first beam coverage area in the contour beam design result when only the sampling points within the target coverage area are used for verification. Detailed implementation mode

[0051] All features disclosed in this specification, or steps in all methods or processes disclosed, except for mutually exclusive features and / or steps, can be combined in any way.

[0052] Any feature disclosed in this specification (including any additional claims, abstract) can be replaced by other equivalent or similar-purpose alternative features unless specifically stated. That is, unless specifically stated, each feature is only an example in a series of equivalent or similar features.

[0053] Embodiment 1

[0054] A dual-band dual-beam common-aperture reflector antenna based on an FSS sub-reflector, as Figure 1 (b) shows that the antenna uses a common-aperture Cassegrain configuration to design the feed source and the reflector. The antenna can operate in two frequency bands and generate different beams from two independent feed sources. Compared with the scheme of arranging multiple antenna fields, this antenna occupies less space and has a more compact structure; compared with a Gregorian antenna, it can avoid the risk of breakdown and sparking caused by electromagnetic waves converging at a point.

[0055] Specifically, as Figure 2 shown, the antenna includes a first feed source, a second feed source, a main reflector, and an FSS sub-reflector. The first feed source emits a first beam in the first frequency band, and the second feed source emits a second beam in the second frequency band, and the frequency bands of the two beams are different. The main reflector and the FSS sub-reflector are arranged with a common aperture, where the FSS sub-reflector is located between the first feed source and the second feed source; the second feed source is located between the FSS sub-reflector and the main reflector. Since both feed sources need to be finally reflected by the main reflector, and the FSS sub-reflector is located between the first feed source and the second feed source, the FSS sub-reflector needs to be able to transmit the first beam and reflect the second beam, while the main reflector reflects both beams. The first feed source is then selected as a feed source operating in the transmission frequency band, and the second feed source is selected as a feed source operating in the reflection frequency band. Therefore, the frequency-selective basic unit of the FSS sub-reflector needs to be selected and designed according to the working frequency band requirements of the target coverage area. The FSS sub-reflector can be designed to transmit low frequencies and reflect high frequencies, or to reflect low frequencies and transmit high frequencies. If the FSS sub-reflector is designed to transmit low frequencies and reflect high frequencies, then the first feed source is a low-frequency feed source, and vice versa. The beam generated by the low-frequency feed source has a larger coverage area.

[0056] After determining the positions of the first feed, the second feed, the main reflector, and the FSS sub-reflector, it is also necessary to shape the main reflector and the FSS sub-reflector according to the target areas to be covered by each feed and the corresponding far-field electric field directivity indices. Among them, the main reflecting surface is shaped to satisfy the shape and far-field electric field directivity index of the first target coverage area for the reflection of the first beam; the FSS sub-reflecting surface is shaped to satisfy the shape and far-field electric field directivity index of the second target coverage area for the reflection of the second beam under the condition that the shape of the main reflecting surface is determined. For the shape and far-field electric field directivity index of the first target coverage area, it is required that the far-field electric field directivity index of the sampling points within the first target coverage area is greater than the design value, and the far-field electric field directivity index of the sampling points outside the target area is less than the design value, so that the energy is as concentrated as possible within the coverage area. Similarly, for the shape and far-field electric field directivity index of the second target coverage area, it is required that the far-field electric field directivity index of the sampling points within the second target coverage area is greater than the design value, and the far-field electric field directivity index of the sampling points outside the target area is less than the design value.

[0057] The shaping processes of the main reflecting surface and the FSS sub-reflecting surface are the same. During the shaping process, the main reflecting surface is shaped first, then the shape of the main reflecting surface is fixed, and then the FSS sub-reflecting surface is shaped.

[0058] The shaping method of the main reflecting surface includes:

[0059] First, initialize the main reflecting surface as a standard reflecting surface, and determine the aperture size of the standard reflecting surface according to the shape and far-field electric field directivity index requirements of the first target coverage area; on the basis of the standard reflecting surface, continuously optimize the surface shape of the standard reflecting surface until the first beam reflected by the main reflecting surface satisfies the shape and far-field electric field directivity index requirements of the first target coverage area; when verifying whether the shaping of the main reflecting surface meets the shape and far-field electric field directivity index of the first target coverage area, sample from both inside and outside the first target coverage area to verify the main reflecting surface at the same time.

[0060] The shaping method of the FSS sub-reflecting surface includes:

[0061] Keeping the shape of the main reflector unchanged, first initialize the FSS sub-reflector as a standard reflector, and determine the aperture size of the standard reflector according to the position of the second feed and the focal diameter ratio of the main reflector; on the basis of the standard reflector, continuously optimize the curved surface shape of the standard reflector until the second beam satisfies the requirements for the shape of the second target coverage area and the far-field electric field directivity index after being reflected by the FSS sub-reflector and the main reflector in sequence; when verifying whether the shaping of the FSS sub-reflector meets the requirements for the shape of the second target coverage area and the far-field electric field directivity index, sample from both inside and outside the second target coverage area to verify the FSS sub-reflector simultaneously.

[0062] As Figure 3 shown in the flowchart of reflector shaping, both the main reflector and the FSS sub-reflector are shaped according to this process.

[0063] Figure 3 The standard reflector described in the first step in [reference] is described in the form of Jacobi-Fourier orthogonal functions, that is, the shape of the standard reflector is initialized using the Jacobi-Fourier orthogonal function form. Then, by changing the optimization coefficients C nm and d nm to adjust the concave-convex deformation of the standard reflector to obtain the shaped surface. The far-field electrical performance of the corresponding beam is calculated for the shaped surface obtained in each round of optimization, and it is judged whether the far-field directivity coefficient of the target coverage area meets the requirements. If not, the optimization coefficients C nm and d nm are changed for the next round of optimization. When the requirements are met, the optimization is stopped, and the shaping design of the reflector is completed.

[0064] Specifically, after initializing the standard reflector using the Jacobi-Fourier orthogonal function form, the optimization process of the surface shape of the standard reflector includes:

[0065] Determine the optimization points for optimizing the surface shape of the standard reflector;

[0066] Adjust the optimization coefficients of the determined optimization points;

[0067] Adjust the shape of the optimization points determined on the standard reflector with the adjusted optimization coefficients.

[0068] The so-called determination of optimization points is to select appropriate parameters n and m to determine the number of optimization coefficients. Here, n and m are constants that control the number of local concave-convex fluctuations on the reflector surface. The larger n and m are, the more concave-convex deformation the shaped reflector has. In some specific embodiments, the values of n and m can be determined to be 4 and 7 respectively. In this way, the optimization coefficients c nm and d nm will have 28 respectively (c 00, c 01 ,......, c 35 , c 36 ; d 00 , d 01 ,......, d 35 , d 36 ).

[0069] The number of optimization coefficients represents the number of optimization variables in the optimization problem. Given the number of optimization coefficients, the optimization coefficients can be calculated and adjusted.

[0070] First, at the mathematical level, the mathematical expressions of the two reflecting surfaces need to be presented first to express the shaped model mathematically. Based on Figure 4 the coordinate system established for the dual-reflector antenna as shown, the vertical coordinates Z (i.e., the points on the reflecting surface) of the main reflector and the FSS sub-reflector are expressed in terms of the parameters t and as variables. For example, Equation (1) represents the position expressions of the main reflector and the FSS sub-reflector in the Figure 4 global coordinate system shown.

[0071]

[0072] In the formula, t represents the ratio of the polar radius of any point on the reflector aperture to the radius of the reflector aperture, with a maximum value of 1, represents the polar coordinate azimuth angle of the point, i.e., the polar angle, ranging from 0 to 2π. R is the aperture radius of the main reflector, f is the focal length of the main reflector, a is the length of the real semi-axis of the FSS sub-reflector, b is the length of the imaginary semi-axis of the FSS sub-reflector, c is the semi-focal length of the FSS sub-reflector, and r is the aperture radius of the FSS sub-reflector.

[0073] On this basis, the optimization coefficients c nm and d nm of the initialized standard reflector can be obtained using Equation (2) to nm and d nm initialize the optimization coefficients C

[0074]

[0075] In the formula, refers to the standard reflector initialized in the form of Jacobi-Fourier orthogonal functions, i.e., the main reflector in Equation (1) or the FSS sub-reflector represents the optimized Jacobi polynomial, and represents the Jacobi polynomial.

[0076] After initializing the optimization coefficients C nm and d nm keep c 00 unchanged, vary the remaining optimization coefficients near 0, and start the solution of the shaping optimization. Using the optimization coefficients C nm and d nm The expression for shaping optimization of the standard reflector is:

[0077]

[0078] Compare with Figure 3 the shaping process in, and when using the optimization coefficients C nm and d nm After each adjustment of the shape of the standard reflector, it is necessary to determine whether the far-field directivity coefficient of the target coverage area meets the requirements. In this embodiment, the shape and far-field electric field directivity index target for optimizing the shape of the standard reflector are:

[0079]

[0080] where N 1 and N 2 are the number of sampling points inside and outside the target coverage area respectively (i.e., the shape has been limited here), i represents the sampling point serial number inside the target coverage area, and u represents the sampling point serial number outside the target coverage area; D i and D u are the directivity values of a single sampling point inside and outside the target coverage area respectively; Θ() is the Heaviside function; D min is the minimum directivity requirement value of the target coverage area. The value of D min can be estimated using Equation (5).

[0081]

[0082] In the formula, D λ is the aperture size of the standard reflector in wavelengths, C c is the perimeter of the target coverage area (in degrees), and S c is the area of the target coverage area in square degrees (in square degrees).

[0083] In addition, according to Equation (5), the antenna aperture can also be calculated when the target coverage area and the minimum directivity requirement value are determined, that is:

[0084]

[0085] According to Equation (6), before shaping, the aperture size of the standard reflector can be calculated first according to the requirements for the shape of the target coverage area and the far-field electric field directivity index.

[0086] The far-field electrical properties of the sampling points inside and outside the target coverage area can be calculated by calling electromagnetic software for planar antennas such as FEKO and GRASP and importing the shaped surface during the optimization process. Of course, it is also possible to write a program by oneself and use the physical optics method or the geometric optics method for calculation. The specific selection can be made according to the design accuracy and time.

[0087] Taking the calculation of the far-field electrical properties by the physical optics method as an example, the calculation of the electrical properties mainly calculates the optical path difference brought by the shaped surface relative to the standard surface, that is Figure 4 the difference between the solid line and the dashed line of the middle beam I (corresponding to the first beam) and beam II (corresponding to the second beam). That is, the standard optimization coefficients c nm and d nm and the optimization coefficients c nm and d nm in the optimization process. Then, the optical path difference τ of the electromagnetic wave from the feed source to the aperture plane is calculated, and then the phase influence δ at the aperture plane after the reflector is deformed is obtained by multiplying the optical path difference by the free space wave constant k, that is, δ = kτ. Then, the far-field electric field value of the observation point during the optimization process can be calculated using Equation (7).

[0088]

[0089] In the formula, I represents the I-th integration unit on the aperture plane, V represents the total number of integration units on the aperture plane, f I () is the amplitude distribution function on the aperture plane, Φ() is the phase distribution function on the aperture plane, ΔS I represents the integration area of the I-th integration unit, ρ′ represents the polar radius of the calculation integration point, φ′ represents the polar angle of the calculation integration point, φ represents the elevation angle of the observation point, and θ represents the azimuth angle of the observation point.

[0090] Taking most land areas in China and Shaanxi Province as examples, two spatially overlapping beams are generated, with operating frequencies of 3.5 GHz and 14.5 GHz respectively, the diameter of the main reflector aperture is 6.5 m, the focal diameter ratio is 0.4, the ratio of the diameter of the FSS sub-reflector aperture to the diameter of the main reflector is 0.1, the feed is Gaussian feed, the radiation angles are 64° and 44° respectively, and the radiation level is 14 dB. According to the aforementioned design steps, the frequency selective basic unit is first selected as the basic square loop double-layer unit, and its structure and performance are as Figure 5 shown, transmitting in the S band and reflecting in the Ku band. The size parameters obtained by HFSS optimization parameter design are shown in Table 1.

[0091] Table 1 FSS Size Parameters (mm)

[0092] W1 W2 W3 W4 W5 H1 H2 3.8 4.5 4.4 4.6 5 12.254 0.254

[0093] Therefore, the S-band feed is determined as the first feed, and the Ku-band feed is determined as the second feed. Select n and m to be 7 and 4 respectively. First, Figure 3 use the process shown in Figure 3 to shape the main reflector with the parameters of the first feed, and obtain a contour coverage beam covering most of the land areas in China. Then, keep the main reflector unchanged, and use Figure 6 the process shown in

[0094] to shape the FSS sub-reflector, and obtain a contour coverage beam covering Shaanxi Province. The contour beams of the two feeds are as shown in Figure 7 Figure 6 (a) Figure 7 By comparison, it can be found that by using the sampling points inside and outside the target coverage area to compare and verify the indicators (i.e., setting the objective function), and then optimizing the shape of the reflector, the boundary of the contour beam obtained after shaping can be more matched with the boundary of the target area to be covered.

[0095] Embodiment 2

[0096] This embodiment proposes a design method of a dual-frequency and dual-beam common-aperture reflector antenna based on an FSS sub-surface in contrast to Embodiment 1. This method is used to design a reflector antenna with a shared-aperture Cassegrain configuration, that is, an antenna including a first feed for transmitting a first beam, a second feed for transmitting a second beam, and a main reflector and an FSS sub-reflector arranged with a common aperture. The FSS sub-reflector is located between the first feed and the second feed, and the second feed is located between the FSS sub-reflector and the main reflector. Obviously, the frequencies of the first beam and the second beam are different.

[0097] The antenna design method includes the following steps:

[0098] According to the frequencies of the first beam and the second beam, design a frequency-selective basic unit on the FSS sub-reflector that can transmit the first beam and reflect the second beam, that is, as​Figure 5 Frequency - selective basic unit of the embodiment shown in (a).

[0099] Shape the main reflector until it meets the requirements of the shape of the first target coverage area for the reflection of the first beam and the far - field electric - field directivity index.

[0100] Fix the shape of the main reflector and shape the FSS sub - reflector until it meets the requirements of the shape of the second target coverage area for the reflection of the second beam and the far - field electric - field directivity index.

[0101] When verifying whether the shaping of the main reflector and the FSS sub - reflector meets the requirements of the shape of the first target coverage area and the second target coverage area and the far - field electric - field directivity index, sample both inside and outside the first target coverage area to verify the main reflector, and sample both inside and outside the second target coverage area to verify the FSS sub - reflector.

[0102] The shaping processes of the main reflector and the FSS sub - reflector are both carried out according to Figure 3 the following process. Briefly, the method for shaping the reflector according to the shape of the target coverage area and the far - field electric - field directivity index includes:

[0103] Initialize the reflector as a standard reflector and determine the aperture size of the standard reflector according to the shape of the target coverage area and the requirements of the far - field electric - field directivity index.

[0104] On the basis of the standard reflector, continuously optimize its surface shape until the reflected beam meets the requirements of the shape of the target coverage area and the far - field electric - field directivity index after reflection.

[0105] For the method of determining the aperture size, refer to the introduction of Equation (6) and related parts in Embodiment 1, which will not be elaborated here. The method for optimizing the surface of the standard reflector can also refer to the corresponding content in Embodiment 1, generally including:

[0106] Determine the optimization points for optimizing the surface shape of the standard reflector;

[0107] Adjust the optimization coefficients of the determined optimization points;

[0108] Adjust the shape of the optimization points determined on the standard reflector with the adjusted optimization coefficients.

[0109] For the specific optimization method and the optimization termination condition, refer to the corresponding parts in Embodiment 1, which will not be elaborated here.

[0110] The present invention is not limited to the foregoing specific embodiments. The present invention extends to any new feature or any new combination disclosed in this specification, as well as to any new method or process step or any new combination disclosed.

Claims

1. A dual-frequency dual-beam common-aperture reflector antenna based on an FSS sub-surface, characterized in that: include: A first feed source, transmitting a first beam; A second feed source transmits a second beam in a frequency band different from that of the first beam; The main reflector and FSS sub-reflector of the common aperture setting; The FSS sub-reflector is located between the first feed source and the second feed source; the second feed source is located between the FSS sub-reflector and the main reflector; the FSS sub-reflector transmits the first beam and reflects the second beam; the main reflector reflects both the first beam and the second beam; the main reflector is shaped to meet the shape of the first target coverage area reflected by the first beam and the far-field electric field directivity index; the FSS sub-reflector is shaped to meet the shape of the second target coverage area reflected by the second beam and the far-field electric field directivity index when the shape of the main reflector is determined.

2. The dual-frequency dual-beam common-aperture reflector antenna based on the FSS sub-surface as claimed in claim 1, characterized in that: The shaping method of the main reflecting surface includes: Initialize the main reflection surface as a standard reflection surface, and determine the aperture size of the standard reflection surface according to the shape of the first target coverage area and the far-field electric field directivity index requirements; on the basis of the standard reflection surface, continuously optimize its surface shape to make it present a concave-convex deformation until the first beam meets the shape of the first target coverage area and the far-field electric field directivity index requirements after being reflected by the main reflection surface; When verifying whether the shaping of the main reflection surface meets the shape and far-field electric field directivity indicators of the first target coverage area, sampling is simultaneously performed from inside and outside the first target coverage area to verify the main reflection surface.

3. The dual-frequency dual-beam common-aperture reflector antenna based on the FSS sub-surface as claimed in claim 1, characterized in that: The shaping method of the FSS sub-reflector comprises: Keeping the shape of the main reflector unchanged, the FSS sub-reflector is first initialized as a standard reflector, and the aperture size of the standard reflector is determined according to the second feed position and the focal ratio of the main reflector; on the basis of the standard reflector, the surface shape is continuously optimized until the second beam meets the shape and far-field electric field directivity index requirements of the second target coverage area after being reflected successively by the FSS sub-reflector and the main reflector; When verifying whether the shaping of the main reflection surface meets the shape and far-field electric field directivity indicators of the first target coverage area, sampling is simultaneously performed from inside and outside the first target coverage area to verify the main reflection surface.

4. The dual-frequency dual-beam common-aperture reflector antenna based on the FSS sub-surface as claimed in claim 2, characterized in that: The method for determining the aperture size of the standard reflecting surface is: Among them, D λ The aperture size of the standard reflective surface in units of wavelength is determined by C c is the perimeter of the target coverage area in degrees, S c is the area of ​​the target coverage area in square degrees, D min is the minimum directivity requirement value of the target coverage area.

5. The dual-frequency dual-beam common-aperture reflector antenna based on the FSS sub-surface as claimed in claim 2 or 3, characterized in that: The standard reflection surface is initialized using the Jacobi-Fourier orthogonal function form.

6. The dual-frequency dual-beam common-aperture reflector antenna based on the FSS sub-surface as claimed in claim 5, characterized in that: Optimize the surface shape of the standard reflective surface, including: Determine the optimal point for optimizing the surface shape of the standard reflecting surface; Adjust the optimization coefficient of the determined optimization point; The concave-convex shape of the optimized point determined on the standard reflection surface is adjusted with the adjusted optimization coefficient.

7. The dual-frequency dual-beam common-aperture reflector antenna based on the FSS sub-surface as claimed in claim 6, characterized in that: The method for adjusting the optimization coefficient of the determined optimization point is: For the optimization coefficient c nm and d nm Initialize according to the following formula: Among them, n and m are constants that control the number of local undulations on the reflector surface; The parameters t and The vertical coordinate Z of the initial reflection surface represented by the variable, where t represents the ratio of the polar diameter of any point on the reflection surface diameter to the reflection surface diameter radius, Indicates the polar coordinate azimuth of the point; Represents the optimized Jacobi polynomial, represents the Jacobi polynomial; Keep c 00 Keep it unchanged and change the other optimization coefficients around 0.

8. The dual-frequency dual-beam common-aperture reflector antenna based on the FSS sub-surface as claimed in claim 7, characterized in that: The shape and far-field electric field directivity index targets of the optimized shape of the standard reflector are: Where N1 and N2 are the number of sampling points inside and outside the target coverage area, respectively; i represents the number of sampling points inside the target coverage area, and u represents the number of sampling points outside the target coverage area; D i and D u are the directional values ​​of a single sampling point within and outside the target coverage area; Θ() is the Heaviside function; D min is the minimum directivity requirement value of the target coverage area.

9. A design method for a dual-frequency dual-beam common-aperture reflector antenna based on an FSS sub-surface, the antenna comprising a first feed source for transmitting a first beam, a second feed source for transmitting a second beam, and a main reflector and an FSS sub-reflector arranged in a common aperture; The FSS sub-reflector is located between the first feed source and the second feed source; the second feed source is located between the FSS sub-reflector and the main reflector; characterized in that, Methods include: According to the frequency bands of the first beam and the second beam, a frequency selective basic unit on the FSS sub-reflection surface is designed, which can transmit the first beam and reflect the second beam; The main reflection surface is shaped until the shape of the first target coverage area reflected by the first beam and the far-field electric field directivity index requirements are met; The shape of the main reflector is fixed, and the FSS sub-reflector is shaped until the shape of the second target coverage area reflected by the second beam and the far-field electric field directivity index requirements are met; When verifying whether the shaping of the main reflecting surface and the FSS sub-reflecting surface meets the shape and far-field electric field directivity indicators of the first target coverage area and the second target coverage area, sampling is performed from both inside and outside the first target coverage area to verify the main reflecting surface, and sampling is performed from both inside and outside the second target coverage area to verify the FSS sub-reflecting surface.

10. The design method of the dual-frequency dual-beam common-aperture reflector antenna based on the FSS sub-surface as claimed in claim 9, characterized in that: Methods for shaping the reflective surface according to the shape of the target coverage area and the far-field electric field directivity index include: Initialize the reflective surface as a standard reflective surface, and determine the aperture size of the standard reflective surface according to the shape of the target coverage area and the far-field electric field directivity index requirements; On the basis of the standard reflecting surface, its surface shape is continuously optimized until the beam to be reflected meets the shape requirements of the target coverage area and the far-field electric field directivity index requirements after reflection.

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