Large Reflector Antennas Research Articles

Analysis of the Characteristics of Mesh with Complex Knitting Patterns for Spaceborne Reflector Antennas

Metallic mesh with complex woven structures is commonly used as the surface in large aperture spaceborne reflector antennas. To study the electrical properties of mesh surfaces characterized by intricate patterns, this paper presents a method for building models to analyze complex meshes. High Frequency Structure Simulator and Computer Simulation Technology (CST) simulation of the reflection coefficients, with Astrakhan’s formulation as a reference, confirm that applying the wire-grid model in CST using the tetrahedral mesh type provides sufficiently accurate results. Furthermore, the rectangular periodic wire-grid model is simulated in CST, and its results are compared with those of Astrakhan’s formulation. Correlations between reflection characteristics and influence factors, including mesh opening size, wire diameter, nature of wire contact, and wave incident angle, are investigated. To exemplify the applicability of the wire-grid model to complex mesh with irregular pattern shapes, the reflection coefficients of a warp-knitted gold-coated molybdenum mesh woven by multi-wires are measured and compared to the simulated results from the wire-grid model. The results prove that the method proposed in this paper is suitable for modeling metal mesh with complex weave patterns.

Numerical Investigation on the Thermal Characteristics of Lightweight Metal Mesh-Based Reflector Antenna with Various Knitting Conditions

Proper prediction of the temperature variation in a metallic wire mesh for spaceborne large deployable reflector antennas is essential for evaluating the dimensional stability of the antenna under extreme on-orbit thermal environments. However, predicting the temperature of a mesh is difficult because of its complex yarn configuration. To analyze the thermal behavior of the spaceborne mesh antenna reflector, the thermal optical characteristics with various knitting methods of the metallic mesh were obtained experimentally in this study. Subsequently, to analyze the thermal sensitivity of the reflector based on its optical properties, an on-orbit thermal analysis of the mesh reflector was performed based on measurements of the mesh specimen. We also investigated the influence of deployable solar panels on the thermal gradient of the reflector.

The Active Compensation Technique for Large Reflector Antennas Based on Quadratic Curve Fitting

Active reflectors are often used to compensate the surface distortion caused by environmental factors that degrade the electromagnetic performance of large high-frequency reflector antennas. This is crucial for maintaining high gain operation in antennas. A distortion compensation method for the active reflector of a large dual-reflector antenna is proposed. A relationship is established between the surface deformation and the optical path difference for the primary reflector by geometric optics. Subsequently, employing finite element analysis, a polynomial fitting approach is used to describe the impact of adjusting points on the reflector surface based on the coordinates of each node. By standardizing the positions of various panels on the reflector, the fitting ns can be applied to the reflector panels of similar shapes. Then, based on the distribution characteristics of the primary reflector panels, the adjustment equation for the actuators is derived by the influence matrix method. It can be used to determine the adjustment amount of actuators to reduce the rms of the optical path difference. And, the least squares method is employed to resolve the matrix equation. The example of a 110 m aperture dual-reflector antenna is carried out by finite element analysis and the proposed method. The results show that the optical path difference is reduced significantly at various elevation cases, which indicates that the proposed method is effective.

The Adjustment Analysis Method of the Active Surface Antenna Based on Convolutional Neural Network

Active surface technique is one of the key technologies to ensure the reflector accuracy of the millimeter/submillimeter wave large reflector antenna. The antenna is complex, large-scale, and high-precision equipment, and its active surfaces are affected by various factors that are difficult to comprehensively deal with. In this paper, based on the advantage of the deep learning method that can be improved through data learning, we propose the active adjustment value analysis method of large reflector antenna based on deep learning. This method constructs a neural network model for antenna active adjustment analysis in view of the fact that a large reflector antenna consists of multiple panels spliced together. Based on the constraint that a single actuator has to support multiple panels (usually 4), an autonomously learned neural network emphasis layer module is designed to enhance the adaptability of the active adjustment neural network model. The classical 8-meter antenna is used as a case study, the actuators have a mean adjustment error of 0.00252 mm, and the corresponding antenna surface error is 0.00523 mm. This active adjustment result shows the effectiveness of the method in this paper.

A Quick Calculation Method for Radiation Pattern of Submillimeter Telescope with Deformation and Displacement

Radiation pattern captures the electromagnetic performance of reflector antennas, which is significantly affected by the deformation of the primary reflector due to gravity and the displacement of the secondary reflector. During the design process of large reflector antennas, a substantial amount of time is often dedicated to iteratively adjusting structural parameters and validating electromagnetic performance. To improve the efficiency of the design process, we first propose an approximate calculation method of optical path difference (OPD) for the deformation of the primary reflector under gravity and the displacement of the secondary reflector. Then an OPD fitting function based on the modified Zernike polynomials is proposed to capture the phase difference of radiation over the aperture plane, based on which the radiation pattern will be obtained quickly by the aperture field integration method. Numerical experiments demonstrate the effectiveness of the proposed quick calculation method for analyzing the radiation pattern of a 10.4 m submillimeter telescope antenna at its highest operating frequency of 856 GHz. In comparison with the numerical simulation method based on GRASP (which is an antenna electromagnetic analysis tool combining physical optics (PO) and physical theory of diffraction (PTD)), the quick calculation method reduces the time for radiation pattern analysis from more than one hour to less than two minutes. Furthermore, the quick calculation method exhibits excellent accuracy for the figure of merit (FOM) of the radiation pattern. Therefore, the proposed quick calculation method can obtain the radiation pattern with high speed and accuracy. Compared to the time-consuming numerical simulation method (PO and PTD), it can be employed for quick analysis of the radiation pattern for the lateral displacement of the secondary reflector and the deformation of the primary reflector under gravity in the design process of a reflector antenna.

Influence of sunlight on the surface error of a large antenna reflector and its correction method

Influence of sunlight on the surface error of a large antenna reflector and its correction method

An Integrated Structure Analysis Method of Active Surface Antenna by Using the Simplified Actuator

The main surface of a large reflector antenna is composed of thousands of panels, which are inevitably deformed under natural load, leading to a great deterioration of electrical performance of the antenna. The active surface technique is an effective method to compensate antenna deformation error and has been widely used. The actuator is a complex component, it has not been established in the antenna structure analysis model, which limits the theoretical analysis ability of the active surface technology. To solve this problem, an integrated structure analysis method of active surface antenna by using the simplified actuator is proposed. First, according to the supporting characteristics and adjusting function of the actuator, the complex actuator is simplified a simple structure of support beams, support truss and adjustment beam. Second, the finite element model of the active surface antenna including the simplified actuator is established. Then, the relationship between the adjustment value (load) of adjustment beam and the deformation of the antenna structure is deduced, and the integrated analysis method for realizing the active adjustment of panels is established. Finally, the model and adjustment analysis method of the active surface antenna in this paper is applied to an 8 m antenna, and satisfactory structural analysis results are obtained, which shows the effectiveness and universality of the method, and provides a reference for the modeling and adjustment analysis of the active surface antenna.

A Study on Structural Health Monitoring of a Large Space Antenna via Distributed Sensors and Deep Learning

Most modern Earth and Universe observation spacecraft are now equipped with large lightweight and flexible structures, such as antennas, telescopes, and extendable elements. The trend of hosting more complex and bigger appendages, essential for high-precision scientific applications, made orbiting satellites more susceptible to performance loss or degradation due to structural damages. In this scenario, Structural Health Monitoring strategies can be used to evaluate the health status of satellite substructures. However, in particular when analysing large appendages, traditional approaches may not be sufficient to identify local damages, as they will generally induce less observable changes in the system dynamics yet cause a relevant loss of payload data and information. This paper proposes a deep neural network to detect failures and investigate sensor sensitivity to damage classification for an orbiting satellite hosting a distributed network of accelerometers on a large mesh reflector antenna. The sensors-acquired time series are generated by using a fully coupled 3D simulator of the in-orbit attitude behaviour of a flexible satellite, whose appendages are modelled by using finite element techniques. The machine learning architecture is then trained and tested by using the sensors' responses gathered in a composite scenario, including not only the complete failure of a structural element (structural break) but also an intermediate level of structural damage. The proposed deep learning framework and sensors configuration proved to accurately detect failures in the most critical area or the structure while opening new investigation possibilities regarding geometrical properties and sensor distribution.

Rapid Deformation Calculation for Large Reflector Antennas: A Surrogate Model Method

The surface accuracy of the large-aperture reflector antenna has a significant influence on the observation efficiency. Recent researchers have focused on using the finite element (FE) simulation to study the effect of gravity and heat on the deformation distribution of the main reflector. However, the temperature distribution of the antenna is challenging to obtain, and it takes a long time for the FE simulation to carry out FE modeling and post-processing. To address these limitations, this study presents a surrogate model based on Extreme Gradient Boosting (XGBoost) and deep Convolutional Neural Network (CNN) to get the deformation distribution of the main reflector quickly. In the design of the surrogate model, using the XGBoost algorithm and sparse sampling to solve the difficulty of obtaining the entire temperature distribution is first proposed, and then a deep CNN is developed for estimating deformation. Based on the effect of dynamic loads on the antenna structure, a diverse data set is generated to train and test the surrogate model. The results show that the surrogate model reduces the calculating time dramatically and can obtain the indistinguishable deformation compared to the FE simulation. This technique provides a valuable tool for temperature and deformation calculation of large-aperture antennas.

Hybrid-panel-based new design idea for large reflector antenna

Hybrid-panel-based new design idea for large reflector antenna

Form-Finding Method for Large Mesh Reflector Antennas with Flexible Trusses Based on Stiffness Analysis

Form-Finding Method for Large Mesh Reflector Antennas with Flexible Trusses Based on Stiffness Analysis

Review and evaluation of warp-knitted patterns for metal-based large deployable reflector surfaces

A large deployable reflector antenna (LDA) is comprised of numerous components. One of the key components of this reflector antenna is the reflector surface. Several types of reflector surfaces have been developed and used, namely, metal mesh-based reflector surfaces, membrane-based reflector surfaces, etc. The benefits presented by warp-knitted metal mesh-based reflector surfaces are their foldability and light weight structural characteristics. Typical metal mesh-based reflector surfaces are produced using a warp knitting textile manufacturing process. A warp-knitted metal mesh reflecting surface is an elastic, open structured knit with a low bending stiffness produced on a high gauge knitting machine (E26 or higher gauge) consisting of a compatible metal yarn (typically tungsten or molybdenum). This paper gives an overview about the requirements for mesh reflector surfaces stated in the literature. Afterwards, an overview of different patterns currently investigated by the LDA community is given. The names given to the various types of patterns in the literature often differ. The construction of the various patterns is therefore first optical analysed and compared. Subsequently, the different patterns are evaluated on the basis of the requirements. Based on the requirements and the possibilities of the warp knitting machine, new possible patterns are identified and evaluated. For the development of a new reflector surface, the identified patterns are developed as a warp-knitted spacer fabric. This decision increases the stiffness of the knitted fabric. This new concept for an advanced reflector surfaces is introduced by Large Space Structures GmbH (LSS) (concept) and ITA (production technology).

Evaluating a strategy for measuring deformations of the primary reflector of the Green Bank telescope using a terrestrial laser scanner

AbstractAstronomical observations in the molecule rich 3‐mm window using large reflector antennas provide a unique view of the Universe. To efficiently carry out these observations gravitational and thermal deformations have to be corrected. Terrestrial laser scanners have been used to measure the deformations in large reflector antennas due to gravity, but have not yet been used for measuring thermal deformations. In this work, we investigate the use of a terrestrial laser scanner to measure thermal deformations on the primary reflector of the Green Bank Telescope (GBT). Our method involves the use of differential measurements to reduce the systematic effects of the terrestrial laser scanner. We use the active surface of the primary reflector of the GBT to validate our method and explore its limitations. We find that when using differential measurements it is possible to accurately measure deformations corresponding to different Zernike polynomials down to an amplitude of 60 m. The difference between the amplitudes of known deformations and those measured are m when the wind speed is m s. From these differences we estimate that it should be possible to bring the surface error of the GBT down to m. This suggests that using a commercial off‐the‐shelf terrestrial laser scanner it is possible to measure deformations induced by thermal gradients on a large parabolic reflector.

Preliminary Studies on CIMR Antenna Pattern Brightness Temperature Compensation

Spaceborne microwave radiometry provides an essential contribution to monitoring the Earth with varying spatial resolution both related to the reflector dimension and the frequency of operation. The ESA's Copernicus imaging microwave radiometer (CIMR) mission aims at collecting the geophysical observables at a spatial resolution ranging from 60 km in L band to 4 km in Ka band. This goal can be achieved by equipping CIMR with a large unfurlable mesh reflector antenna. A limitation of the antenna design is that the antenna pattern includes grating lobes that contaminate the scene measurement with contributions originated far from the nominal footprint. This effect introduces inaccuracies in brightness temperature measurements, particularly when facing radiometric discontinuities, e.g., near the coastlines and sea ice edges, which can be greater than the mission required maximum of 0.5 K. The aim of this article is to assess a technique which will be able to correct the effects of antenna pattern and obtain reliable <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T_B</i> measurements. The analyzed simple technique is based on a regularized deconvolution of the antenna pattern to reconstruct the actual brightness temperatures. The technique was tested over a synthetic scenario that mimics both steep and smooth variations in spatial and thermal domains.

Influence and experiment of cable-net manufacturing errors on surface accuracy of mesh reflector antennas

Cable-net structures are of substantial importance in the construction of large mesh reflector antennas. Owing to the inevitable errors in their manufacturing process, the reflector surface accuracy deteriorates. This study makes a comprehensive investigation of random manufacturing errors during constructing the mesh reflector antennas, and analyze its influence on reflector surface accuracy. Firstly, the sensitivity of reflector surface accuracy with respect to the random errors of the unstressed cable length is mathematically deducted. Secondly, a non-button connecting method is proposed and analyzed to reduce manufacturing errors. Thirdly, two physical experiment models based on 2.62-meter mesh reflector antenna are made. Finally, numerical examples and experimental tests are given to demonstrate the effectiveness of the proposed method. Compared with the traditional method, the proposed method can effectively reduce the influence of the manufacturing errors on the reflector surface accuracy. Moreover, the reduction in the sizes of the nodes also reduces the risk of entanglement of the mesh reflector antenna during the deployment process, and thereby improves the deployment reliability.

Deformation measurement by single spherical near-field intensity measurement for large reflector antenna

This paper presents a new method to obtain the deformation distribution on the main reflector of an antenna only by measuring the electric intensity on a spherical surface with the focal point as the center of the sphere, regardless of phase. Combining the differential geometry theory with geometric optics method, this paper has derived a deformation-intensity equation to relate the surface deformation to the intensity distribution of a spherical near-field directly. Based on the finite difference method (FDM) and Gauss-Seidel iteration, deformation has been calculated from intensity simulated by geometrical optics (GO) and physical optics (PO) methods, respectively, with relatively small errors, which prove the effectiveness of the equation proposed in this paper. By means of this method, it is possible to measure the deformation only by scanning the electric intensity of a single hemispherical near-field whose area is only about 1/15 of the aperture. The measurement only needs a plane wave at any frequency as the incident wave, which means that both the signals from the outer space satellite and the far-field artificial beacon could be used as the sources. The scanning can be realized no matter what attitude and elevation angle the antenna is in because the size and angle of the hemisphere are changeable.

Analysis and compensation of the reflector antenna pointing error under wind disturbance

A large reflector antenna has been widely used in satellite communications, gravitational wave detection, galaxy origin observation and other fields due to its narrow beam and high gain. With the increase of the antenna aperture and the improvement of the working frequency, the requirements for the pointing accuracy of an antenna are also rising. However, the effect of environmental load on the deformation of the antenna structure, which in turn affects its beam pointing, has become a key problem to be solved urgently in the antenna engineering applications. The key issue to solving this problem involves accurately estimating the pointing error caused by the structural deformation and designing an effective controller that is based on the structural deformation. In this paper, we first establish a dynamic model for antenna structure based on the modal superposition method. The model is then modified by using modal characteristics and the dynamic displacement information of the sampling points to achieve the purpose of accurately estimating the structural deformation. Secondly, by considering the influence of the deformation of the rotating shaft and the reflector surface on the pointing accuracy, a control-oriented pointing error analysis model is established for estimating the pointing error caused by the environmental load in real time. Thirdly, based on considering the influence of the shaft deformation on the error compensation, the feedback error amount is decoupled and corrected to improve the accuracy of the compensation error. Finally, this paper analyzes and verifies the 65 m S/X-band dual reflector antenna with a numerical example. We consider a fluctuating wind with an average wind speed of 10 m s−1 as an example, which results in a maximum pointing error of 55.82″ as calculated by the antenna theoretical model, whereas the maximum pointing error as predicted by our model is 68.27″. The pointing error after compensating for the cause of the environmental load with the modified controller is reduced to 10.57″, which effectively improves the antenna pointing performance.

Relaxing the Small Facet Size Requirement for the Far-Field Calculation of Large Reflector Antennas

The accurate calculation of the far-field of a large reflector antenna based on the set of discrete reflector points resulting from a structural analysis of the antenna is one of the key problems in the integrated structural-electromagnetic optimization of such antennas. In this study, the classical method that extends the discrete set of points into flat triangular facets on the basis of which the far-field is calculated is considerably upgraded. The innovation is that the proposed method makes full use of the exact knowledge of the systematic error between the ideal reflector surface and its faceted counterpart, and uses this known systematic error to upgrade the calculation of the mechanically deformed reflector, whose surface is composed of corresponding planar facets. Two versions are introduced, the single-grid version and the double-grid version. The double-grid version makes use of a double grid to even further refine the description of the systematic error. Based on this, the dichotomy method is used to quickly obtain the maximum size of the facets that still results in the required precision of the far-field calculation. In the examples given, concerning 50 m standard and 33 m offset reflector antennas operated at 60 GHz, the size of the small facets can be relaxed considerably, yielding much larger facets (such as more than 200 times the operating wavelength for the 50-m standard antenna) for a required far-field accuracy of -60 dB with respect to the main lobe level.

Panel Adjustment and Error Analysis for a Large Active Main Reflector Antenna by Using the Panel Adjustment Matrix

Active panels are generally applied in large aperture and high-frequency reflector antennas, and the precise calculation of the actuator adjustment value is of great importance. First, the approximation relationship between the adjustment value and panel elastic deformation is established. Subsequently, a panel adjustment matrix for the whole reflector is derived to calculate the reflector deformation caused by the actuator adjustment. Next, the root mean square (rms) error of the deformed reflector is expressed as a quadratic form in the matrix form, and the adjustment value can be derived easily and promptly from the corresponding extreme value. The solution is expected to be unique and optimal since the aforementioned quadratic form is a convex function. Finally, a 35 m reflector antenna is adopted to perform the panel adjustments, and the effect of the adjustment errors is discussed. The results show that compared with the traditional model, where the panel elastic deformation is not considered, the proposed method exhibits a higher accuracy and is more suitable for use in large reflectors with a high operation frequency. The adjustment errors in different rings exert different influences on the gain and sidelobe level, which can help determine the actuator distribution with different precisions.

Electronic Performance-Oriented Mold Sharing Method and Application in QTT 110 m Large Radio Telescope

The reflector surface of a large reflector antenna may even consist of thousands of panels, and if the panel molds with high-precision requirements are fabricated uniquely for each ring, the overall cost will be very high. Therefore, from a perspective of reducing the cost, the mold sharing design is of particular significance. In order to obtain the minimum number of molds satisfying the given electronic performance index, the electronic performance-oriented mold sharing design is suggested, in which the effective surface accuracy is used to evaluate electrical performance. The smaller the combined effective root-mean-square (rms) error value introduced after sharing the mold, the more preferential these rings should share the mold to reduce the number of molds. Based on such idea, a fast mold reduction process is presented, which can give the minimum number of molds quickly according to the electrical performance requirements. During this process, a combined effective rms value matrix and a mold sharing discriminant matrix are defined and used. To construct these two matrices, the panel normal error induced by mold sharing is derived, and the optimal mold position is determined first. As a test problem, application of the proposed method to mold reduction of a 110 m radio telescope is presented, and the discussions of the results are given.