Spaceborne Antenna Research Articles

Active on-orbit surface accuracy adjustment for spaceborne antennas based on multi-fidelity adaptive migration learning strategy

For the large spaceborne synthetic aperture radar antenna, its surface accuracy has a decisive impact on the on-orbit electrical performance, which is affected by manufacturing errors, assembly misalignments, and thermal deformations. Therefore, ensuring the surface accuracy on orbit and reducing its fluctuation are highly concerned issues for the large spaceborne antenna in practice. To this end, this study proposes an active adjustment method based on a multi-fidelity adaptive migration learning strategy to guarantee on-orbit surface accuracy. First, the theoretical surface accuracy model considering space thermal deformation is completely established. Then, the surrogate model of surface accuracy is developed to realize fast prediction and optimization, in which a new dynamic Kriging modeling method is proposed. Furthermore, the surrogate prediction model at other sites on the orbit is efficiently obtained by an innovative multi-fidelity migration learning strategy. On this basis, the active adjustment optimization model is constructed based on the surrogate prediction model, and the corresponding adjustment amounts can be obtained accordingly by solving this optimization problem. Finally, the effectiveness and advantages of the proposed method are comprehensively proven through case studies and experimental verification.

Real-time shape sensing of large-scale honeycomb antennas with a displacement-gradient-based variable-size inverse finite element method

Real-time thermal deformation monitoring plays a crucial role in calibrating phase signals and maintaining satellite performance for large spaceborne antennas. The inverse finite element method (iFEM) represents a promising shape-sensing methodology applicable to monitor the three-dimensional displacement of structures through surface-measured strain. However, the high-accuracy reconstruction of large-scale structures involves a large number of inverse elements, which leads to the low level of computational efficiency. To address this issue, a displacement-gradient-based variable-size iFEM is proposed in this paper. According to the characteristics of deformation, this method optimizes the size of each inverse element to reduce the number of inverse elements required, which improves real-time performance and maintains the high accuracy of reconstruction. The real-time performance of the proposed method is verified by conducting a simulation test on a large-scale honeycomb antenna. According to the simulation results, the variable-size iFEM is applicable to achieve the same accuracy of reconstruction using fewer inverse elements than conventional iFEM. An experimental test is performed and the optimal variable-size discretization that balances accuracy and efficiency is determined. The results show that the maximum error of reconstructed displacement is less than 7.3 % and the reconstruction time is in no excess of 0.1 s.

Configuration Investigation, Structure Design and Deployment Dynamics of Rigid-Reflector Spaceborne Antenna with Deviation-Angle Panel.

Rigid-reflector spaceborne antennas (RRSAs) are well-suited for high-frequency application scenarios due to their high surface accuracy. However, the low stowing efficiency of RRSAs limits the aperture diameters and further deteriorates the electromagnetic (EM) performances in terms of gain, resolution and sensitivity. After conducting systematic feature analysis with respect to several typical RRSAs, we propose a novel type of RRSA to solve the aforementioned problems. Inspired by the pose adjustment process for a higher stowing efficiency of traditional RRSAs, we also propose a new segmentation scheme of a reflective surface consisting of a deviation-angle panel that facilitates a higher stowing efficiency. Based on this scheme, its corresponding folded configuration is implemented by combining Euler's rotation theorem and the idea of parameter identification. In addition, we also compare the stowing efficiency of different schemes to verify the high stowing efficiency of the configuration. Finally, we perform mechanism/structure design and deployment dynamics to demonstrate that the antenna can be successfully deployed and exhibits excellent deployment quality. The results suggest that the proposed antenna possesses higher stowing efficiency than that of the same kind, with a stable deployment and interference-free process.

Shape sensing for thin-shell spaceborne antennas with adaptive isogeometric analysis and inverse finite element method

As the preventive maintenance paradigm transfers to condition-based maintenance, deformation monitoring has become a fundamental system capacity in aerospace engineering. In this study, a novel shape sensing method is proposed for accurate and efficient reconstruction of full-field deformation of thin shell structures from discrete strain measurements. Firstly, a flexible isogeometric approach based on the geometry-independent field approximation is developed for characterizing the geometric and physical domains, which fully unlocks the potential of local refinement while preserving the original exact geometry without re-parameterization. On this basis, a posteriori error estimation algorithm is put forward to automatically drive the adaptive refinement procedure, reducing the discretization error with a fast convergence rate. Subsequently, according to the Kirchhoff-Love theory and the least-squares variational principle, an isogeometric inverse-shell element is created to integrate the inherent advantages of adaptive isogeometric analysis with excellent shape-sensing capabilities of the inverse finite element method. Moreover, a smoothing technique is applied to replenish strain data into each inverse shell element, by which the compatibility between the interpolated and measured strain components is also enforced. Finally, the excellent accuracy and efficiency of the proposed deformation reconstruction framework are verified using both experimental and numerical strain data for two thin-shell spaceborne antennas.

Probing supermassive black hole binaries with orbital resonances of laser-ranged satellites

Coalescing supermassive black hole binaries (SMBHBs) are the primary source candidates for low frequency gravitational wave (GW) detections, which could bring us deep insights into galaxy evolutions over cosmic time and violent processes of spacetime dynamics. Promising candidates had been found based on optical and X-ray observations, which claims for new and ready-to-use GW detection approaches before the operations of space-borne antennas. We show that, satellite laser ranging (SLR) missions could serve as probes of coalescing SMBHBs through the GW-induced resonant effects. Lasting and characteristic imprints caused by such resonances in the residual distances or accelerations from SLR measurements are studied, and the detection SNR is analyzed with both the current and future improved ranging precisions. Within redshift z sim 1, the threshold SNR = 5 requires 1–2 years of accumulated data for the current precision and months of data for improved precision, which are workable for the data processing of SLR missions. Meanwhile, joint detections with multiple SLR missions could further improve the total SNR and the confidence level. Such a detection scheme could fulfill the requirement of a tentative SMBHB probe during the preparing stage of LISA and Taiji, and it requires no further investment to any new and advanced facilities. It is also worthwhile to look back and re-process the archived data from the past decades, in where resonant signals from SMBHBs might be hidden.

Near Field Generated by a VLF Magnetic Dipole With Arbitrary Orientation in an Anisotropic Magnetoplasma

With the increasing importance of space-borne antennas in very low-frequency (VLF: 3–30 kHz) transmitting system, it is essential to study radiation characteristics of a radiator in ionosphere. In this article, with an environment of anisotropic magnetoplasma, the near field of a magnetic dipole is treated. Since two eigenmodes coexist in an anisotropic scenario, i.e., ordinary wave (O-wave) and extraordinary wave (E-wave) with different attenuations, a semi-analytical method is proposed to accurately investigate the near field in an anisotropic plasma. Calculations and analysis show that the primary contribution to the field generated by a magnetic dipole with arbitrary orientation comes from the source projection parallel to the geomagnetic field. The results show that the O-wave maintains an amplitude comparable to that of the E-wave in the near zone. Moreover, the radiation pattern shows that the amplitude of E-waves becomes weaker with increasing tilt angle, while the amplitude of O-waves is not sensitive to the change of the geomagnetic tilt angle.

Active optimization adjustment for the surface accuracy of spaceborne SAR antennas

Inevitable disturbances in the spatial thermal environment will seriously degrade the surface accuracy of satellite antennas. Unfortunately, the ground pre-adjustment cannot adaptively guarantee the antenna performance under alternating thermal loadings. To tackle the challenge, this study proposes an active optimization adjustment method to achieve the required surface accuracy for spaceborne antennas. Starting from the comprehensive analysis of external thermal fluxes in outer space, the heat transfer model is firstly established to acquire the temperature field of the antenna system. Subsequently, considering the thermoelastic effect and the geometrical nonlinearity, the antenna surface accuracy is predicted. In particular, the thermoelastic forces induced from temperature changes and dimensional deviations are precisely determined by the absolute nodal coordinate formulation. Moreover, an efficient computational method with invariant matrices is developed to accelerate the prediction. On this basis, we construct the on-orbit active adjustment model to compensate for the effect of thermally induced deformation on the surface accuracy. A mixed-variable optimization algorithm is further put forward to find the optimal strategy of dimensional adjustment. Finally, a case study with simulation analysis and experiment verification demonstrates the feasibility and superiority of the proposed surface adjustment method.

Design and dynamic analysis of a scissors hoop-rib truss deployable antenna mechanism

As the support mechanism of space-borne antennas, space deployable antenna mechanism belongs to complex multi-closed-loop coupling mechanism, configuration design and dynamic analysis are more difficult than general parallel mechanism. In this paper, an unequal-length scissors mechanism (ULSM) is proposed by changing the position of the internal rotational joint through a basic scissors mechanism. A scissors hoop-rib truss deployable antenna mechanism (SHRTDAM) is constructed by replacing the parabolic rib with the ULSM. Kinematic analysis of SHRTDAM is conducted, and the degree of freedom (DOF) of the whole antenna mechanism is analyzed based on screw theory, the result showed that it has only one DOF. Velocity and acceleration characteristics of SHRTDAM are obtained by the screw derivative and rotation transformation. Based on Lagrange equation, dynamic model of this mechanism is established, the torque required to drive the mechanism is simulated and verified by Adams and MATLAB software. In addition, a ground experiment prototype of 1.5-m diameter was fabricated and a deployment test is conducted, which demonstrated the mobility and deployment performance of the whole mechanism. The mechanism proposed in this paper can provide a good reference for the design and analysis of large aperture space deployable antennas.

A dimensionality reduction and layout optimization scheme for grid-stiffened structures

ABSTRACT When directly solving the layout optimization design problem of grid-stiffened structures with large-scale discrete design variables, gradient-based methods and intelligent optimization algorithms are rendered ineffective owing to multilocal optimal traps and the discrete variable space with extremely large dimensionality. A new layout optimization design scheme for grid-stiffened structures is proposed in this study, based on the continuous representation of discrete variables and a dimensionality reduction method. In this method, first, a discrete stiffener layout is described by a bounded field with space correlation and transformed into continuous design variables using material interpolation. Then, to significantly reduce the dimensionality of the design space, a series expansion approach is adopted. Finally, a sequential optimization strategy combined with the kriging surrogate model is used to successfully solve optimization problems. Layout optimization designs, including a stiffened plate and a space-borne antenna reflector, are proposed to demonstrate the validity and applicability of the proposed method.

An integrated framework of surface accuracy prediction for clearance-affected extendible support structures with dimensional deviations and elastic deformations

The surface accuracy of the extendible support structure (ESS) greatly influences the imaging resolution of spaceborne antennas. Therefore, considering dimensional deviations, joint clearances and elastic deformations comprehensively, this paper proposes an enhanced deterministic prediction framework to analyze the surface accuracy of the spatial overconstrained ESS. On the one hand, unlike the previous studies which neglect the elastic deformations and connection constraints of antenna panels, these factors and the link flexibility are fully incorporated into the constructed deformation analysis model via the absolute nodal coordinate formulation. Meanwhile, the elastic forces triggered by dimensional deviations and structural deformations are also determined with the skills of invariant matrices for the flexible elements. On the other hand, accounting for axial and radial clearances in spatial revolute joints, the contact conditions and contact forces are described comprehensively, and the contact detection strategy is further put forward for all potential contact scenarios. Afterwards, an integrated accuracy prediction framework is developed to quantify the interaction among dimensional deviations, joint clearances and elastic deformations. Finally, the dynamic segmentation modeling is proposed to determine the surface accuracy of the ESS, and the experiments verify that the developed method is of good prediction accuracy.

Electrical Property of 3D Printed Continuous Fiber Reinforced Thermoplastic Composite Mesh Reflecting Surfaces

Continuous fiber reinforced thermoplastic composites have been widely used in modern aerospace and other high-end manufacturing fields because of their light weight, high strength, fatigue resistance, and corrosion resistance properties. Due to the reinforcement of carbon fiber strands, continuous fiber reinforced thermoplastic composites have good conductivity which makes it a potential material for the preparation of space-borne antennas reflecting surfaces. The reflecting surfaces of common mesh antennas are usually prepared by gold-plated molybdenum wire which is expensive and hard to produce. In this study, the continuous fiber reinforced thermoplastic composites mesh reflecting surfaces are prepared by 3D printing technology. The effect of different mesh shape and mesh size on the electrical properties are investigated systematically. The electrical property of the reflecting surface were tested by waveguide method at the S band with the frequency of 1.9 ~ 2.3GHz. The results show that the reflection loss of the 3D printed continuous fiber reinforced thermoplastic composite mesh reflecting surfaces are lower than 0.25 dB, which can well meet the requirement of space-borne antennas in the S waveband. The reflection loss of the 3D printed continuous fiber reinforced thermoplastic composite mesh reflecting surfaces increases with the increase of mesh size accordingly for both the quadrangular and the triangular mesh reflecting surface. The reflecting property of the mesh reflecting surface tends to be better with a higher surface mass density. The results foresee that the continuous fiber reinforced thermoplastic composites can be used to develop the reflector of large mesh antenna in the future work.

Radiation Pattern of a VLF Linear Antenna in an Anisotropic Magnetoplasma

As the importance of spaceborne antennas keeps increasing in contemporary very low frequency (VLF: 3–30 kHz) transmitting systems, figuring out the radiation patterns of VLF spaceborne antennas of different lengths has become a critical issue that needs urgent solution. In this article, we propose an analytical method for calculating the radiation pattern of a VLF linear antenna immersed in an anisotropic magnetoplasma. The core idea of the approach is: 1) to consider the influence of current inhomogeneity to the radiation pattern so that the method is suitable for antennas of arbitrary length and 2) to derive the correction factor of the antenna under the far-zone condition. The results show that the radiation patterns for the extraordinary wave (E-wave) and ordinary wave (O-wave) are quite different, but in the near zone, both modes will contribute to the total field collectively. The radiation in the far zone mainly depends on the E-wave, but unlike isotropic cases, the radiation pattern in the anisotropic environment is always oriented along the geomagnetic field, with the shape of the pattern not influenced by the antenna length anymore. This is because the radiation field of a linear antenna can be regarded as the field excited by an electric dipole multiplying the correction factor, and variations on the correction factor only change the magnitude of the field, instead of the pattern.

Precision estimation of large space-borne parabolic antenna support structure

An accuracy analysis approach – mosaic equivalence approach which is based on the principle of approximate structure substitution, to a large complex spatial mechanism with three-dimensional (3D) paired bearings support joint (PBS-joint) clearance is presented to effectively estimate the support structure precision of large parabolic space-borne antenna. The analysis suggests when all the PBS-joints equipped with Metric 628/6 bearings in standard clearance, the surface precision of support structure can obtain relatively high accuracy with a 99.73% probability that root mean square (RMS) was kept in (0.3275, 0.7673) mm and peak-to-valley (PV) was kept in (0.8806, 1.8178) mm. The solution of deviation configuration under a large complex spatial mechanism using the proposed mosaic equivalence approach can be transformed into that under a mosaiced structure of its simple sub-mechanisms. As a result, the high-dimensional coupling between the deviation configuration decision variables can be effectively avoided. Besides, the constraint equations of large complex mechanisms with the PBS-joint 3D clearance can be simplified. This method lays a foundation for reducing the manufacturing cost and risk of large-diameter, high-precision satellite antennas. It has essential engineering value.

Mechanics Design of Conical Spiral Structure for Flexible Coilable Antenna Array

Limited by the effective launch capacity of a rocket, the deployable antenna is very important in the design of spaceborne antenna array. Compared to traditional deployable antenna, flexible coilable antenna array has higher surface precision and better vibration control and therefore is more suitable for high frequency communication. In order to minimize the weight of satellite and reduce cost of its launch, a design guideline to the geometry parameters of flexible coilable antenna array is crucial. Existing models cannot be directly applied to interaction and large deformation between coilable membrane and conical spiral antenna in the flexible coilable antenna array. Hence, the geometry parameters of the conical spiral structure and the thickness of the coilable membrane in the flexible coilable antenna array have not been optimized yet. In this paper, the interaction between the coilable membrane and the concial spiral antenna is analyzed in the antenna array. A concise formula is derived to predict the critical force that flattens the conical spiral antenna by a coiling scroll. Combined with a theoretical model to predict the deformation of the membrane, the model provides an important theoretical support for the lightweight design and mechanical design of flexible coilable antenna array, such as the thickness of the coilable membrane. The proposed design is validated by experiments. The above findings have potential applications in the effective reduction of antenna array weight and satellite launch costs.

A Novel Real-Time Echo Separation Processing Architecture for Space–Time Waveform-Encoding SAR Based on Elevation Digital Beamforming

Space–time waveform-encoding (STWE) SAR can receive echoes from multiple sub-swaths simultaneously with a single receive window. The echoes overlap each other in the time domain. To separate the echoes from different directions, traditional schemes adapt single-null steering techniques for digital receive beam patterns. However, the problems of spaceborne DBF-SAR, in practice, such as null extension loss, terrain undulation, elevation angle of arrival extension, and spaceborne antenna beam control, make the conventional scheme unable to effectively separate the echoes from different sub-swaths, which overlap each other in the time domain.A novel multi-null constrained echo separation scheme is proposed to overcome the shortcomings of the conventional scheme. The proposed algorithm can flexibly adjust the width of the notch to track the time-varying pulse extension angle with less resource consumption. Moreover, the hardware implementation details of the corresponding real-time processing architecture are discussed. The two-dimensional simulation results indicate that the proposed scheme can effectively improve the performance of echo separation. The effectiveness of the proposed method is verified by raw data processing instance of an X-band 16-channel DBF-SAR airborne system.

A Novel Method for Sensing Local Electron Density via Measuring the VSWR of Spaceborne Antenna

The performance of an antenna is impacted by the electromagnetic characteristics of the media surrounding the antenna. Most antennas work in neutral air. However, the surrounding media for the spaceborne antenna is space plasma, which is dispersive dielectric media. It could significantly change the performance of a spaceborne broadband antenna. In the present study, a broadband dipole antenna was taken for example to investigate the impacts led by space plasma. The working parameters in neutral air and space plasma were compared. The space plasma taken into account in the present study was supposed to be time-varying dispersive media. The study revealed that the space plasma could significantly influence the antenna voltage standing wave ratio (VSWR) and the antenna impedance. For those spaceborne radars working in active mode, there was a minimum detection range which makes it hard to detect the plasma area within the range. Since antenna working parameters vary with the variation of the surrounding plasma, a method to sensing the local plasma electron density based on VSWR of spaceborne broadband antennas was proposed. The method makes the antenna system work as a plasma sensor and could complement the radar minimum detection range. The results show the good performance of the method.

Wave Number and Input Impedance of a VLF Insulated Linear Antenna in an Anisotropic Ionosphere

We report a method to obtain the wave number and input impedance of a very low frequency (VLF) insulated linear antenna in an anisotropic ionosphere. Due to the anisotropy, electromagnetic fields in the ionosphere are decomposed into the ordinary wave and extraordinary wave. Wave equations for the layered structure are applied to access the wave number of the insulated antenna in the ionosphere via the derivation of the eigenvalue equation by using boundary conditions. The expression for the wave number is given based on some approximation formulas. Then, King’s antenna theory is further employed to solve the input impedance and current distribution of the antenna in the anisotropic medium. After the validation of the method is performed, near-field characteristics for an insulated antenna with different medium parameters in the anisotropic ionosphere are discussed. Effects of the electric density and geomagnetic field of the time-and space-varying anisotropic ionosphere on the distribution of normalized current are analyzed. This finding provides a promising avenue for getting electromagnetic characteristics of space-borne antennas.

Review of antenna technologies for very high frequency Data Exchange Systems

SummaryThe Automated Identification System (AIS) was originally developed as a terrestrial system tracking vessels near the coastline. Dedicated channels were allocated within the spectrum historically reserved for maritime applications in the very high frequency (VHF) band, enabling long range communications, up to a few kilometers. There have been various initiatives in the last decade that extended this system with a space segment, enabling global monitoring of vessels beyond the range of terrestrial stations. Recently, the World Radiocommunication Conference has allocated frequencies for the extension of this system to a two‐way VHF Data Exchange System (VDES) via satellite. This requires to adapt spaceborne antenna solutions previously developed for AIS, particularly for missions using small satellites and CubeSats. This paper provides a timely review of existing VHF antenna solutions and new concepts under development which could be applicable to VDES missions. Some key metrics are identified to provide a comparative study between various candidate solutions. Considering the range of possible missions, from secondary payloads on‐board larger satellites to dedicated constellations, it is believed that a number of antenna products can find application in future VDES space‐based infrastructure.

Comparison on the Tribological Properties of Roller and Guide Tribo-Pair Used in Antenna Deployable Structure

The tribological properties of roller and guide tribo-pair are important for the design of deployable structure for space-borne perimeter truss antenna. In this study, carbon fiber epoxy resin composites are used as the guide material; while polyimide and GCr15 steel are used as the roller material. Then, friction coefficient of polyimide ball and GCr15 steel ball against carbon fiber epoxy resin composites disk were compared and investigated on the high-temperature, ball-on-disk tribometer under different operating conditions, respectively. The wear morphology of disk was measured by laser scanning confocal microscope. The results show that the friction coefficient of the polyimide ball against carbon fiber epoxy resin composites tribo-pair has better tribological properties. Meanwhile, the friction coefficients of this pair are mainly depend on abrasive wear under low pressure and velocity conditions while the adhesive wear has dominated influence on the friction coefficient for high pressure and velocity conditions. Besides, the tribological properties of carbon fiber epoxy resin composites are mainly affected by ploughing of surface roughness at low temperature, while by surface debonding at high temperature.

Mutual Coupling Effect on Arbitrarily Oriented VLF Circular Antenna Array in Ionospheric Plasma

Mutual coupling between the space-borne antenna has an essential impact on the communication characteristics of a wireless link to submerged submarines. In this article, the mutual coupling between antennas of a circular array in an anisotropic plasma over a very low-frequency (VLF: 3–30 kHz) range is investigated. An expansion of the currents into phase modes enables us to develop an efficient method to analyze the mutual coupling between antennas. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> -coupled integral equations for antennas of an array are first derived with full consideration of the mutual coupling effect. By making use of the phase modes combined with the method of moment (MoM), the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> -coupled integral equations are decomposed into independent ones and solved for each phase mode. Computations and discussions show that the self and mutual impedances of antennas are increased with the geomagnetic field tilt angle. Moreover, the mutual impedance is decreased with the increasing electrical separation, thereby indicating that the mutual coupling effect is weakened as the separation increases. The accuracy of the proposed method is verified by comparing the computed results with experiments and simulation using commercial electromagnetics software FEKO.