CN114156651B - Satellite-borne mesh-shaped reflector antenna beam forming method based on memory alloy actuator - Google Patents
Satellite-borne mesh-shaped reflector antenna beam forming method based on memory alloy actuator Download PDFInfo
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Abstract
The invention relates to a satellite-borne mesh-shaped reflector antenna beam forming method based on a memory alloy actuator. The defects of the existing satellite-borne mesh antenna reflecting surface supporting structure form and the existing shaping technology are overcome, part of vertical cables needing to be pressed are replaced by the actuator, the flexible reflecting surface antenna can realize the shape of a convex-concave undulated shaped reflecting surface without greatly increasing the complexity of the structure, and the reflecting surface shape required by a shaped wave beam and the supporting structure mechanical state required by supporting the shape are obtained by solving through an optimized design method based on electromechanical integration design.
Description
Technical Field
The invention relates to the technical field of satellite antennas, in particular to a method for shaping satellite-borne mesh reflector antenna beams.
Background
The satellite-borne mesh-shaped reflector antenna has limited shaping capability because the reflector is formed by stretching a cable-rod structure and the shape of the convex-concave fluctuated reflector required by shaped beams cannot be generally realized.
In the aspect of beam forming design of a satellite-borne mesh reflecting surface antenna, the patent numbers provided by inventors such as Zhang Tree et al are as follows: 201210510289.2, with a patent name: in the text of the shaping method of the cable net reflector antenna profile based on sensitivity information, the reflector is shaped based on the sensitivity information, and the supporting capability of the cable net supporting structure is not taken into consideration. In the text of A Novel continuous Beam Synthesis Method for the control of Electromagnetic-Structural Design published in 2017 of Yang Decheig, the traditional pure cable rod structure is shaped, the constraint cable force must be a positive value, but the reflecting surface of the traditional pure cable rod structure cannot meet the requirement of a rugged shaped reflecting surface, so the shaping capability of the traditional pure cable rod structure is greatly limited.
In order to solve the problem of realizing the uneven shaped reflecting surface, the inventor of Zhang-Yi group provides the following patent numbers: 201610638630.0, with the patent name: the patent numbers provided by the inventor of the invention, such as the design method of a novel mesh antenna structure with shaped beams and the Yankee antenna structure, are as follows: 201510144508.3, patent names: a satellite-borne mesh antenna forming beam design method based on electromechanical integration adopts a three-layer cable rod structure to realize an uneven reflecting surface, improves the forming capability of a satellite-borne mesh reflecting surface antenna, but increases a layer of cable rod structure compared with the traditional antenna design scheme, thereby leading to the complication of the antenna structure and the great increase of the dead weight, leading to the failure of the spreading because the more complicated the cable rod structure of the antenna is, the more easily the cable rod structure of the antenna is hooked with other structures in the process of spreading on the track, and leading to the great increase of the dead weight of the antenna, thereby leading to the great rise of the satellite transmission cost.
Disclosure of Invention
The invention aims to avoid the defects of the prior art and provides a satellite-borne mesh reflecting surface antenna beam forming method based on a memory alloy actuator, which can realize the shape of an uneven formed reflecting surface required by a formed beam without increasing the self weight of the antenna.
In order to realize the purpose, the invention adopts the technical scheme that: a satellite-borne mesh-shaped reflector antenna beam forming method based on a memory alloy actuator comprises the following steps:
the method comprises the following steps of constructing a satellite-borne mesh-shaped reflector antenna supported by a cable-strut structure, wherein the cable-strut structure comprises an upper cable-strut surface (1), a lower cable-strut surface (2), a plurality of adjusting cables (3) for connecting the upper cable-strut surface and the lower cable-strut surface and a memory alloy actuator (4), and the method comprises the following steps: the nodes arranged on the upper cable net surface and the lower cable net surface of the reflecting surface antenna aperture surface are boundary supporting nodes (5); the nodes on the upper cable net surface and the lower cable net surface are cable net free nodes (6); the upper cable mesh surface divides the metal reflecting surface of the reflecting surface antenna into a plurality of plane surface patches;
then according to the topological relation of the cable-pole structure, defining a line segment between two connected nodes in the cable-pole structure as a line unit;
secondly, giving position coordinates of the boundary support nodes, giving a force density value of the line unit, and establishing a mathematical relationship model between the force density of the line unit and the cable net free node by adopting a force density method, so as to obtain a connection relationship matrix of all nodes forming the cable rod structure and cable net free node coordinates, and obtain the overall shape S of the reflecting surface supported by the cable rod structure;
step three, generating a beam coverage area of the satellite-borne mesh-shaped reflector antenna according to the coverage area required by the ground, sampling in the beam forming area according to a Nyquist criterion, and marking out sampling points;
step four, giving incident waves of the feed source, and calculating the directivity coefficient of a sampling point in a beam forming area corresponding to the integral shape of the current reflecting surface according to the integral shape S of the reflecting surface supported by the cable-strut structure obtained in the step two;
fifthly, establishing an optimized design model of the electromechanical integrated beam forming design by taking the force density value of the line unit as a design variable and taking the minimum value of the directivity coefficient at the maximized sampling point as a target function;
solving the optimized design model in the fifth step until the optimized design model meets the convergence conditions of the design variables and the objective function, and obtaining the overall shape S of the shaped cable-pole structure and the reflection surface supported by the cable-pole structure and the mechanical state of the cable-pole structure;
step seven, judging the positive and negative of all force density values in the shaped final cable-strut structure determined in the step six: if the line unit corresponding to the force density is a regulating cable structure and named as a cable unit, otherwise, the line unit corresponding to the force density is a rod structure formed by replacing a regulating cable with a memory alloy actuator and named as a rod unit, and the satellite-borne mesh reflector antenna cable-rod structure model is completed.
Further, the second step is specifically as follows:
giving the position coordinates of the supporting point of the boundary of the cable-strut structure as、Andgiven the force density value of the thread unitq i (i=1,2,…,b),q i The value is a positive value or a negative value,bestablishing the force density of the wire units and the coordinates of the free nodes of the cable net on the cable rod structure for the total number of the wire units、Andthe mathematical relationship model comprises the following specific steps:
wherein the content of the first and second substances,is linear unit force densityq i The diagonal matrix is formed by the two groups of the diagonal matrix,is a connection relation matrix of the free nodes of the cable network,for the connection relation matrix of the cable-strut structure boundary support nodes, superscriptWhich represents the transpose of the matrix,andconnection relation matrix of all nodes capable of forming cable pole structureIs that is
Is provided withAndfirst, theiThe nodes at both ends of each cell are numbered and specifiedMatrix of rulesThe element in (A) is
Through the steps, the free node coordinates of the cable-strut structure can be obtained、Andobtaining the spatial positions of a series of plane surface patches of the reflecting surface of the antenna according to the coordinates of the free node and the boundary supporting node of the cable-strut structure, and finally obtaining the spatial positions of the reflecting surfaceThe overall shape S.
Further, the third step is specifically:
31 The map boundaries that the ground needs to cover are expressed in longitude and latitude;
32 Convert the longitude and latitude coordinate values to a Cartesian Earth coordinate system;
33 Convert coordinate values in a rectangular coordinate system of the earth into coordinates in a spherical coordinate system of the satellite-borne mesh reflector antenna;
34 Sampling within and at the boundaries of the coverage area to obtain coordinate values of the sampling points of,,NIs the total number of sampling points;
the density of sampling points depends on the aperture of the satellite-borne mesh reflector antennaDOn the antenna apertureDWhen the radiation field is far field, the longitude and latitude interval between the sampling points is as follows from Nyquist criterionIn whichIs the wavelength;
the coordinate value of the sampling point of the map to be covered under the spherical coordinate system of the satellite-borne mesh reflector antenna is obtained through the steps。
Further, the longitude and latitude intervals between the sampling points should beIn whichIs the wavelength.
Further, the fourth step specifically comprises:
41 The overall shape S of the reflecting surface supported by the cable-strut structure obtained in the step two is the shape of the reflecting surface spliced by the triangular patchS;
42 By antenna apertureDThe center of the surface is the origin O and the aperture of the antennaDEstablish rectangular coordinate system O on the facexyzWhich iszThe axis coincides with the axis of the paraboloid;
43 Given feed source incident wave magnetic fieldIn whichr' is the position vector of any point on the reflecting surface;
44 Given cable net free node coordinates、Andand coordinates of the supporting point position of the boundary of the cable-strut structure、Andthe formula for calculating the directivity coefficient at the sampling point in the beam forming region corresponding to the current reflecting surface shape by using a Physical optical transmission (PO) method is as follows:
wherein the content of the first and second substances,rthe surface current at' is,jIs a plurality of, and,is the impedance of the wave in free space,kin order to be a free-space propagation constant,is taken as a unit of a dyadic vector,for far field observation point vectorrThe unit vector of (a) is,as vectorsIn the direction of the vector (c) of (a),is composed ofr' the unit normal vector of the reflecting surface,representing the antenna radiating surface being integrated,an integral surface element on the aperture surface of the antenna is represented;
coordinates of each sampling point,Substituting the formula into the formula to obtain the electric field strength value of each sampling point;
the directivity coefficient value of the map to be covered at the sampling point under the spherical coordinate system of the satellite-borne mesh reflector antenna is obtained through the steps.
Further, the fifth step is specifically:
combining the relationship between the directivity coefficient of the sampling point obtained in the third step and the force density of the line unit, the beam forming of the satellite-borne mesh antenna can be expressed as a mathematical model of electromechanical integration optimization design as follows:
wherein the content of the first and second substances,das a design variable, a vector consisting of the force densities of the line elements,andrespectively the lower and upper limits of the design variable,Nthe number of sampling points in the service area,for the far field related objective function,the amount of directivity required for beam coverage within the service area,andare respectively the firstiThe stress of the individual wire units and their allowable stress, which is related to the force density, can be expressed as
Wherein, the first and the second end of the pipe are connected with each other,is a cross-sectional area of the wire unit,the length of the ith line unit can be determined by nodes at two ends of the ith line unitAndthe calculation formula is as follows:
thus obtaining the electromechanical integrated optimization design model of the beam forming design.
Further, the sixth step is specifically:
selecting an optimization design method, setting design variables and convergence conditions of the objective function, and solving the optimization design model in the step four:
the convergence condition is set asAndwhereinkFor optimizing the designkThe steps of the method are repeated for the second time,andtaking convergence precision values of design variable and objective function respectively(ii) a When the convergence condition is satisfied, the iteration stops, the design variable at this timeNamely the optimal solution, and the corresponding antenna surface is the optimal shaping surface.
Further, the specific analysis step of the seventh step is as follows:
in the mesh reflector antenna, takeiIndividual line unit of force densityq i Can be adjusted by cable forceIs shown as
Wherein the content of the first and second substances,is a firstiA length between two end points of each of the line units;
when the final cable-strut structural shape after shaping determined in the step six is: can be only in tension, not in compression, andthe cable unit of (1), i.e. the cable unit, is, on the contrary, only compressible, not tensionable, andthe wire unit of (2), using the rod unit.
The invention has the beneficial effects that: based on the existing memory alloy actuator which is used, the invention replaces part of vertical cables which need to be pressed with the actuator, and the actuator can enable the flexible reflecting surface antenna to realize the shape of a shaped reflecting surface which is convex-concave and fluctuant, and further, by the calculation method, the shape of the reflecting surface required by a shaped beam and the mechanical state of a supporting structure required for supporting the shape can be accurately obtained, the coordination of the beam shaping of the satellite-borne mesh reflecting surface antenna and the mechanical state of a cable-rod supporting structure is realized, and the realization of the shaped reflecting surface by the supporting structure is ensured.
Drawings
FIG. 1 is a schematic view of a cable support structure incorporating a temperature controlled shape memory alloy actuator;
FIG. 2 is a diagram illustrating cable-rod internal forces of a cable-rod support structure supporting a shaped reflective surface shape.
Detailed Description
The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.
In order to overcome the defects that the shape of a concave-convex shaped reflecting surface cannot be realized in the conventional satellite-borne mesh antenna reflecting surface supporting structure and the defects of the conventional shaping technology, the beam shaping design method of the satellite-borne mesh antenna reflecting surface provided by the invention has the advantages that the shape of the concave-convex reflecting surface can be realized by the satellite-borne mesh expanded antenna by applying the temperature-controlled shape memory alloy actuator, the beam shaping of the satellite-borne mesh expanded antenna is realized by adopting the method provided by the invention, the antenna design efficiency is improved, and the stable realization of the matching structure of the antenna and the cable-rod supporting structure is ensured.
In order to achieve the above object, the present invention provides the following embodiments:
example 1: as shown in fig. 1 to fig. 2, a method for forming a beam of a satellite-borne mesh reflector antenna based on a memory alloy actuator includes the following steps:
the method comprises the following steps of constructing a satellite-borne mesh-shaped reflector antenna supported by a cable-strut structure, wherein the cable-strut structure comprises an upper cable-strut surface (1), a lower cable-strut surface (2), a plurality of adjusting cables (3) for connecting the upper cable-strut surface and the lower cable-strut surface and a memory alloy actuator (4), and the method comprises the following steps: the nodes arranged on the upper cable net surface and the lower cable net surface of the reflecting surface antenna aperture surface are boundary supporting nodes (5); the nodes on the upper cable net surface and the lower cable net surface are cable net free nodes (6); the upper cable mesh surface divides the metal reflecting surface of the reflecting surface antenna into a plurality of plane surface patches;
then according to the topological relation of the cable-pole structure, defining a line segment between two connected nodes in the cable-pole structure as a line unit; the memory alloy actuator is disclosed in the patent numbers: 202110373436.5, patent name: a large space-borne mesh reflector antenna memory alloy actuator is provided.
Secondly, giving position coordinates of the boundary support nodes, giving a force density value of the line unit, establishing a mathematical relationship model between the force density of the line unit and the cable net free node by adopting a force density method, further obtaining a connection relationship matrix of all nodes forming the cable rod structure and cable net free node coordinates, and simultaneously obtaining the overall shape S of the reflecting surface supported by the cable rod structure;
the second step is specifically as follows:
giving the position coordinates of the supporting point of the boundary of the cable-strut structure as、Andgiven the force density value of the thread unitq i (i=1,2,…,b),q i The value is a positive value or a negative value,bestablishing the force density of the wire units and the coordinates of the free nodes of the cable net on the cable rod structure for the total number of the wire units、Andthe mathematical relationship model comprises the following specific steps:
wherein the content of the first and second substances,is linear unit force densityq i The diagonal matrix is formed by the two groups of the diagonal matrix,is a connection relation matrix of the free nodes of the cable network,for the connection relation matrix of the cable-strut structure boundary support nodes, superscriptWhich represents the transpose of the matrix,andconnection relation matrix of all nodes capable of forming cable pole structureIs that is
Is provided withAndfirst, theiThe nodes at both ends of each cell are numbered and specifiedMatrix of timeThe element in (A) is
Through the steps, the free node coordinates of the cable-strut structure can be obtained、Andand obtaining the spatial positions of a series of plane surface patches of the antenna reflecting surface according to the coordinates of the free node and the boundary supporting node of the cable-strut structure, and finally obtaining the overall shape S of the reflecting surface.
Step three, generating a beam coverage area of the satellite-borne mesh-shaped reflector antenna according to the coverage area required by the ground, sampling in the beam forming area according to a Nyquist criterion, and marking out sampling points;
the third step is specifically as follows:
31 The map boundaries that the ground needs to cover are expressed in longitude and latitude;
32 Convert the longitude and latitude coordinate values to a Cartesian Earth coordinate system;
33 Convert coordinate values in a rectangular coordinate system of the earth into coordinates in a spherical coordinate system of the satellite-borne mesh reflector antenna;
34 Sampling within and at the boundaries of the coverage area to obtain coordinate values of the sampling points of,,NIs the total number of sampling points;
the density of sampling points depends on the aperture of the satellite-borne mesh reflector antennaDOn the antenna apertureDWhen the radiation field is far field, the longitude and latitude interval between the sampling points is as follows from Nyquist criterionWhereinIs the wavelength;
the coordinate value of the sampling point of the map to be covered under the spherical coordinate system of the satellite-borne mesh reflector antenna is obtained through the steps。
Step four, giving incident waves of the feed source, and calculating the directivity coefficient of a sampling point in a beam forming area corresponding to the integral shape of the current reflecting surface according to the integral shape S of the reflecting surface supported by the cable-strut structure obtained in the step two;
the fourth step is specifically as follows:
41 The overall shape S of the reflecting surface supported by the cable-strut structure obtained in the step two is the shape of the reflecting surface spliced by the triangular patchesS;
42 By antenna apertureDThe center of the plane is the origin O at the aperture of the antennaDEstablish rectangular coordinate system O on the facexyzWhich iszThe axis coincides with the axis of the paraboloid;
43 Given the incident wave magnetic field of the feed sourceWhereinr' is the position vector of any point on the reflecting surface;
44 Given cable net free node coordinates、Andand coordinates of the supporting point position of the boundary of the cable-strut structure、Andthe formula for calculating the directivity coefficient at the sampling point in the beam forming region corresponding to the current reflecting surface shape by using a Physical optical transmission (PO) method is as follows:
wherein the content of the first and second substances,rthe surface current at' is,jIs a plurality of, and,is the impedance of the wave in free space,kin order to be a free-space propagation constant,is taken as a unit of a dyadic vector,for far field observation point vectorrThe unit vector of (a) is,as vectorsIn the direction of the vector (c) of (a),is composed ofr' the unit normal vector of the reflecting surface,representing the antenna radiating surface being integrated,an integral surface element on the aperture surface of the antenna is represented;
coordinates of each sampling point,Substituting the formula into the above formula to obtain the electric field strength value at each sampling point;
the directivity coefficient value of the map to be covered at the sampling point under the spherical coordinate system of the satellite-borne mesh reflector antenna is obtained through the steps.
Fifthly, establishing an optimized design model of the electromechanical integrated beam forming design by taking the force density value of the line unit as a design variable and taking the minimum value of the directivity coefficient at the maximized sampling point as a target function;
the fifth step is specifically as follows:
combining the relationship between the directivity coefficient of the sampling point obtained in the third step and the force density of the line unit, the beam forming of the satellite-borne mesh antenna can be expressed as a mathematical model of electromechanical integration optimization design as follows:
wherein the content of the first and second substances,das a design variable, a vector consisting of the force densities of the line elements,andrespectively the lower and upper limits of the design variable,Nthe number of sampling points in the service area,for the far field related objective function,the amount of directivity required for beam coverage within the service area,andare respectively the firstiThe stress of the individual wire units and their allowable stress, which is related to the force density, can be expressed as
Wherein the content of the first and second substances,is a cross-sectional area of the wire unit,the length of the ith line unit can be divided into two end nodesAndthe calculation formula is as follows:
thus obtaining the electromechanical integrated optimization design model of the beam forming design.
Solving the optimized design model in the fifth step until the optimized design model meets the convergence conditions of the design variables and the objective function, and obtaining the overall shape S of the shaped cable-pole structure and the reflection surface supported by the cable-pole structure and the mechanical state of the cable-pole structure;
the sixth step is specifically as follows:
selecting an optimization design method, setting design variables and convergence conditions of the objective function, and solving the optimization design model in the step four:
the convergence condition is set asAndwhereinkFor optimizing the designkThe steps are repeated for the next time,andtaking convergence precision values of design variable and objective function respectively(ii) a When the convergence condition is satisfied, the iteration stops, the design variable at this timeNamely the optimal solution, and the corresponding antenna surface is the optimal shaping surface.
Step seven, judging the positive and negative of all force density values in the shaped final cable-strut structure determined in the step six: if the line unit corresponding to the force density is a positive value, the line unit corresponding to the force density is an adjusting rope structure and is named as a rope unit, otherwise, the line unit corresponding to the force density is a rod structure formed by replacing an adjusting rope with a memory alloy actuator and is named as a rod unit, and the satellite-borne netted reflecting surface antenna rope-rod structure model is completed;
the concrete analysis steps of the seventh step are as follows:
in the mesh reflector antenna, takeiIndividual line unit of force densityq i Can be adjusted by cable forceIs shown as
Wherein the content of the first and second substances,is as followsiA length between two end points of each of the line units;
when the final cable-strut structural shape after shaping determined in the step six is: can be only in tension, not in compression, andthe cable unit of (1), i.e. the cable unit, is, on the contrary, only compressible, not tensionable, andthe wire unit of (2), using the rod unit.
Experimental example: the advantages of the present invention can be further illustrated by the following simulation experiments:
1. simulation parameters
The working frequency of the antenna is 3GHz, and the caliber D is 25Focal length 25Offset distance of 15.5The feed source is a Gaussian feed source, and the taper pin is-12 dB. This case takes a typical chinese map as the coverage target area.
2. Simulation result
Interval according to Nyquist criterionSampling is carried out, the final sampling result is that 24 sampling points exist on the map boundary, the whole map has 97 sampling points, and the corresponding cable-rod unit internal force distribution is shown in figure 2.
3. Analysis of results
Conclusion 1: the directivity coefficient values in the shaped area are all above the required values, the design requirements are met, the shape of the isoline with the directivity coefficient of 27.82 is matched with the shaped area, and the interference to adjacent areas is reduced.
Conclusion 2: as can be seen from the results in fig. 2, there are 6 units with negative force densities, i.e. a temperature controlled shape memory alloy actuator that can withstand pressure needs to be used at these 6 units.
Conclusion 3: simulation data show that the optimized forming result meets the expected target, and the feasibility and the effectiveness of the theory and the method provided by the patent are verified.
Example 2: the same as in example 1, except that: the longitude and latitude interval between the sampling points isWhereinIs the wavelength. The sampling interval is taken to ensure the sampling precision without greatly increasing the number of sampling points.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (6)
1. A satellite-borne mesh reflector antenna beam forming method based on a memory alloy actuator is characterized by comprising the following steps:
the method comprises the following steps of constructing a satellite-borne mesh-shaped reflector antenna supported by a cable-strut structure, wherein the cable-strut structure comprises an upper cable-strut surface (1), a lower cable-strut surface (2), a plurality of adjusting cables (3) for connecting the upper cable-strut surface and the lower cable-strut surface and a memory alloy actuator (4), and the method comprises the following steps: the nodes arranged on the upper cable net surface and the lower cable net surface of the reflecting surface antenna aperture surface are boundary supporting nodes (5); the nodes on the upper cable net surface and the lower cable net surface are cable net free nodes (6); the upper cable mesh surface divides the metal reflecting surface of the reflecting surface antenna into a plurality of plane surface patches;
then according to the topological relation of the cable-pole structure, defining a line segment between two connected nodes in the cable-pole structure as a line unit;
secondly, giving position coordinates of the boundary support nodes, giving a force density value of the line unit, establishing a mathematical relationship model between the force density of the line unit and the cable net free node by adopting a force density method, further obtaining a connection relationship matrix of all nodes forming the cable rod structure and cable net free node coordinates, and simultaneously obtaining the overall shape S of the reflecting surface supported by the cable rod structure;
step three, generating a beam coverage area of the satellite-borne mesh-shaped reflector antenna according to the coverage area required by the ground, sampling in the beam forming area according to a Nyquist criterion, and marking out sampling points;
step four, giving incident waves of the feed source, and calculating the directivity coefficient of a sampling point in a beam forming area corresponding to the integral shape of the current reflecting surface according to the integral shape S of the reflecting surface supported by the cable-strut structure obtained in the step two;
fifthly, establishing an optimized design model of the electromechanical integrated beam forming design by taking the force density value of the line unit as a design variable and taking the minimum value of the directivity coefficient at the maximized sampling point as a target function;
solving the optimized design model in the fifth step until the optimized design model meets the convergence conditions of the design variables and the objective function, and obtaining the overall shape S of the shaped cable-pole structure and the reflection surface supported by the cable-pole structure and the mechanical state of the cable-pole structure;
step seven, judging the positive and negative of all force density values in the shaped final cable-strut structure determined in the step six: if the line unit corresponding to the force density is a positive value, the line unit corresponding to the force density is an adjusting rope structure and is named as a rope unit, otherwise, the line unit corresponding to the force density is a rod structure formed by replacing an adjusting rope with a memory alloy actuator and is named as a rod unit, and the satellite-borne netted reflecting surface antenna rope-rod structure model is completed;
the second step is specifically as follows:
giving the position coordinates of the supporting point of the boundary of the cable-strut structure as、Andgiven the force density value of the thread unitq i (i=1,2,…,b),q i The value is a positive value or a negative value,bestablishing the force density of the wire units and the coordinates of the free nodes of the cable net on the cable rod structure for the total number of the wire units、Andthe mathematical relationship model comprises the following specific steps:
wherein, the first and the second end of the pipe are connected with each other,is linear unit force densityq i The diagonal matrix is formed by the two groups of the diagonal matrix,is a connection relation matrix of the free nodes of the cable network,for the connection relation matrix of the cable-strut structure boundary support nodes, superscriptWhich represents the transpose of the matrix,andconnection relation matrix of all nodes capable of forming cable pole structureThat is to say that
Is provided withAndfirst, theiThe nodes at both ends of each cell are numbered and specifiedMatrix of rulesThe element in (A) is
Through the steps, the free node coordinates of the cable-strut structure can be obtained、Andobtaining the spatial positions of a series of plane surface patches of the antenna reflecting surface according to the coordinates of the free nodes and the boundary supporting nodes of the cable-strut structure, and finally obtaining the overall shape S of the reflecting surface;
the fourth step is specifically as follows:
41 The overall shape S of the reflecting surface supported by the cable-strut structure obtained in the step two is the shape of the reflecting surface spliced by the triangular patchS;
42 By antenna apertureDThe center of the surface is the origin O and the aperture of the antennaDEstablish rectangular coordinate system O on the facexyzWhich iszThe axis coincides with the axis of the paraboloid;
43 Given feed source incident wave magnetic fieldWhereinr' is the position vector of any point on the reflecting surface;
44 Given a cable net fromFrom node coordinates、Andand coordinates of the supporting point position of the boundary of the cable-strut structure、Andthe formula for calculating the directivity coefficient at the sampling point in the beam forming region corresponding to the current reflecting surface shape by using a Physical optical transmission (PO) method is as follows:
wherein the content of the first and second substances,rthe surface current at' is,jIs a plurality of, and,is the impedance of the wave in free space,kin order to be a free-space propagation constant,is taken as a unit of a dyadic vector,for far field observation point vectorrThe unit vector of (a) is,as a vectorThe vector of (a) is a vector of (b),is composed ofr' the unit normal vector of the reflecting surface,representing the antenna radiating surface being integrated,an integral surface element on the aperture surface of the antenna is represented;
coordinates of each sampling point,Substituting the formula into the formula to obtain the electric field strength value of each sampling point;
the directivity coefficient value of the map to be covered at the sampling point under the spherical coordinate system of the satellite-borne mesh reflector antenna is obtained through the steps.
2. The method for forming a beam of a space-borne mesh reflector antenna based on a memory alloy actuator according to claim 1, wherein the third step is:
31 The map boundaries that the ground needs to cover are expressed in longitude and latitude;
32 Convert the longitude and latitude coordinate values to a Cartesian Earth coordinate system;
33 Convert coordinate values in a rectangular coordinate system of the earth into coordinates in a spherical coordinate system of the satellite-borne mesh reflector antenna;
34 Sampling within and at the boundaries of the coverage area to obtain coordinate values of the sampling points,,NIs the total number of sampling points;
the density of sampling points depends on the aperture of the satellite-borne mesh reflector antennaDOn the antenna apertureDWhen the radiation field is far field, the longitude and latitude interval between the sampling points is as follows from Nyquist criterionWhereinIs the wavelength;
4. The method for forming a satellite-borne mesh reflecting surface antenna beam based on a memory alloy actuator as claimed in claim 1, wherein the fifth step is specifically as follows:
combining the relationship between the directivity coefficient of the sampling point obtained in the third step and the force density of the line unit, the beam forming of the satellite-borne mesh antenna can be expressed as a mathematical model of electromechanical integration optimization design as follows:
wherein the content of the first and second substances,das a design variable, a vector consisting of the force densities of the line elements,andrespectively the lower and upper limits of the design variable,Nthe number of sampling points in the service area,for the far field related objective function,the amount of directivity required for beam coverage within the service area,andare respectively the firstiThe stress of the individual wire units and their allowable stress, which is related to the force density, can be expressed as
Wherein the content of the first and second substances,is a cross-sectional area of the wire unit,the length of the ith line unit can be divided into two end nodesAndthe calculation formula is as follows:
thus obtaining the electromechanical integrated optimization design model of the beam forming design.
5. The method for forming a beam of a space-borne mesh reflector antenna based on a memory alloy actuator according to claim 1, wherein the sixth step comprises:
selecting an optimization design method, setting design variables and convergence conditions of the objective function, and solving the optimization design model in the step four:
the convergence condition is set asAndwhereinkFor optimizing the designkThe steps are repeated for the next time,andtaking convergence precision values of design variable and objective function respectively(ii) a When the convergence condition is satisfied, the iteration stops, the design variable at this timeNamely, the optimal solution, and the corresponding antenna surface is the optimal forming surface.
6. The method for forming a satellite-borne mesh reflecting surface antenna beam based on a memory alloy actuator as claimed in claim 1, wherein the concrete analysis steps of the seventh step are as follows:
in the mesh reflector antenna, takeiIndividual line unit of force densityq i Can adjust the cable forceIs shown as
Wherein the content of the first and second substances,is as followsiA length between two end points of each of the line units;
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