On distorted surface analysis and multidisciplinary structural optimization of large reflector antennas

The large reflector antenna structural design is a typical multidisciplinary design mainly involving structural mechanics and electromagnetics. Deformation of the antenna reflector affects antenna’s electrical characteristics. In this paper, an analysis is made of the variation of antenna’s performances under different employment conditions by applying the response surface method and the Coons divided-fitting method with presentation of the mathematical formula. Furthermore, three types of optimization models of the antenna structure are discussed and the main structural variables influencing electrical performances are analyzed. Finally, an example of multidisciplinary optimization design of an 8-m antenna is explored to illustrate the accuracy of the methods and the potential of application to improve the electrical performances of reflector antennas.     

Matched feeds for offset reflector antenna using circular microstrip patch antenna

This article presents two designs of matched feed for an offset fed reflector. Circular microstrip patch antennas are used in the proposed designs. Both the matched feeds achieve conjugate field matching by generating TM₂₁ mode at an appropriate ratio to the fundamental TM₁₁ mode. The first matched feed generates the required dual mode field distributions using a dual layer stacked patch antenna. The second matched feed is a novel design using centered circular array with the central element generating the required TM₂₁ mode and the surrounding circular ring antenna elements operating in the TM₁₁ mode. Both the designs are studied analytically using cavity model and are implemented in High frequency System Simulator (HFSS) and Computer Simulation Technology (CST). The matched feed designs are investigated for an offset reflector with the projected diameter, D = 50λ, focal length, F = 30λ and clearance height, H = 5λ operating at 20 GHz. The secondary field patterns of the offset reflector fed by the matched feeds are evaluated numerically using a MATLAB code based on geometrical optics technique and verified by HFSS‐PO results. Offset reflector performance such as cross‐polarization, ?30 dB cross‐polar bandwidth, gain, and first side‐lobe level are investigated for the both matched feeds.     

Integrated risk and multi-objective optimization of energy systems

This paper presents a risk aware energy planning model with storages as decision makers. The amount of energy bought from generators, stored in storages, and sold to users is set by storages. The paper also provides the optimal risk strategy for each storage considering energy cost, environmental impact, and failure rate as social welfare functions. A robust, simple, and verifiable framework for understanding and measuring risk scenarios for energy systems is introduced. Multiple-objective approach for integrating risk with social welfare functions is also discussed. Application of presented framework in energy industry is discussed by examples.     

Microstrip patch antenna feed for offset reflector antenna for dual band application

In this article, details of a dual band microstrip patch antenna (MPA) array feed for an offset reflector antenna is presented. The main objective of the proposed structure is to achieve low cross‐polarization at Φ = 90° plane in the reflector pattern. Low cross‐polar levels in the reflector pattern are achieved by illuminating the reflector with fields of the proposed dual band feed structure. A centered circular array as the dual band feed structure is proposed in which the central radiating element is a dual mode circular MPA operating at 6 GHz and the surrounding circular ring of eight circular MPA elements operating at 4 GHz in the dominant mode. The dual mode central antenna uses the concept of conjugate field matching for cross‐polarization reduction. TM₂₁ mode is excited at an appropriate ratio with the TM₁₁ mode to achieve the proper field matching at 6 GHz. The radius of the surrounding circular array is varied to obtain cross‐polarization better than ?30 dB at both the resonant frequencies. The offset reflector gain is found to be better than 37 dB with a 2.5 m parabolic reflector and F/D = 0.8 at both the operating frequencies.     

Multicriteria discrete optimization of large scale truss systems

The paper discusses optimization problems in civil engineering structural design. The following questions are discussed: continuous or discrete optimization, single- or multicriteria optimization, one- or multi-level optimization. The paper is illustrated with examples of the multi-criteria discrete optimization of large scale truss systems. The cross-sectional areas of truss bars are taken as design variables. Minimization of mass, labour cost and displacements are chosen as optimization criteria. Optimization constraints concern stresses, displacements and stability, as well as technological and computational requirements. The results of single- and multicriteria optimization of hall structures are presented in the form of diagrams and tables.Presented at NASO ASI Optimization of Large Structural Systems, Sept. 23 – Oct. 4, 1991, Berchtesgarden, Germany     

Investigation of factors contributing depolarization in offset reflector antenna and trimmed‐reflector offset parabolic antenna with lower cross‐polarization

This article outlines impact of various factors on cross‐polarization characteristics of offset reflector antenna for communication spacecraft with smaller sized bus at C band. Effects of different parameters are considered in rigorous analysis of the antenna. Measured and predicted performances are found in agreement. To fulfill specific requirement of higher edge‐of‐coverage gain (>26 dBi) and higher cross‐polarization discrimination (XPD > 30 dB) over a wider coverage and dual linear polarization under the imposed constraints, a novel trimmed‐reflector offset parabolic antenna (TROPA) is devised. This interesting configuration is obtained by trimming both sides parallel to symmetrical plane of a parabolic offset reflector antenna. Parametric study of trimming distance versus its impact on cross‐polarization is also presented. The TROPA acquires wider bandwidth, simplification in its mechanical design and manufacturing, and offers low weight and compactness. It is also shown that trimmed reflector has almost even RF performance in presence of spacecraft body and other antenna. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Two‐dimensional synthesis and optimization of a broadband shaped beam reflector antenna using IWO and PSO algorithms

A new technique for broadband shaped beam reflector antennas synthesis is presented. The surface of the shaped reflector is represented by a set of orthogonal Jacobi–Fourier expansion functions. To achieve a cosecant squared pattern in the elevation plane and a pencil beam in the azimuth plane, the expansion coefficients are optimized using invasive weed optimization and particle swarm optimization algorithms. High accuracy is achieved by combining optimization tools and analysis methods such as physical optics and integral equation. Besides, in the optimization procedures, a complex object function is used to achieve the desired performance over the entire 26–40 GHz operating bandwidth. The simulation results via FEKO and CST Microwave Studio software packages prove the validity and versatility of this technique for solving shaped reflector synthesis problems. There are several features that distinguish this technique from the previous methods. First of all is the wide bandwidth. The second is its ability to shape the radiation patterns in the elevation and azimuth planes simultaneously (two‐dimensional synthesis). Moreover, compared with other techniques, the proposed method allows achieving extra desired features such as high directivity, low sidelobe levels, and small ripples in the shaped beam region. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:129–140, 2015.     

Dynamic optimization of large scale systems: Case study

We present the analysis of the steady state backoff problem with state and dynamic constraints of a non-linear chemical process described by almost 3000 differential algebraic equations. The dynamic optimization is carried out using a new approach based on an SQP algorithm for semi-infinite non-linear programming problems. The system equations are integrated with an implicit Runge-Kutta method and 'reduced' gradients are evaluated by adjoint equations. The high performance of the algorithm is analysed and compared to fully non-linear programming proposals in which discretized system equations are treated as general non-linear equality constraints.     

Sequential stability and optimization of large scale decentralized systems

The notion of sequential stability in the synthesis of decentralized control for large scale systems is introduced in this paper. This notion is concerned with the property of a synthesis technique which allows the decentralized controllers of a large scale system to be connected to the systems one at a time (in a sequential way) such that the controlled system remains stable at all times. The motivation for introducing this constraint is that in practical terms, it is generally impossible to connect all decentralized controllers to a system simultaneously (due to the difficulties of communication etc.). A practical design procedure for the synthesis of a decentralized robust regulator for the servomechanism problem, based on a sequential approach to system design, is then given. The design procedure proceeds in two stages: (1) decentralized controllers are initially connected to the system in a sequential way to guarantee stability; (2) the parameters of the decentralized controllers are then sequentially adjusted, in a way to guarantee stability, so as to optimize a given performance index for the system. Applications of the above procedure are then made to the synthesis of centralized multivariable controllers and to the decentralized robust control of unknown systems.A simple example is given to illustrate the design synthesis.     

A wideband beam shaping reflector antenna using model predictive control

A novel method based on model predictive control (MPC) is presented for synthesis and optimization of a wide band reflector antenna with cosecant squared and flat‐topped radiation patterns. The proposed system is a doubly curved reflector antenna with nonlinear dynamic equation. This article investigates design and optimization of a double ridged horn reflector antenna operating within the frequency range of 8 to 18 GHz. In order to synthesize the proposed reflector antenna, MPC is used to achieve the desired radiation cosecant pattern. This method utilizes system model and tries to find the best control effort for minimizing the cost function by predicting the future behavior. The system differential equation is comprised of first and second order derivatives, so MPC can be a good solution for synthesis of a doubly reflector antenna. MPC optimizer operates based on state space model, so the proposed system is linearized in the operating range. Maximum error, the average error and side lobe level of this method for the radiation pattern of the proposed wideband antenna respectively are 1.4, 0.9, and ?20 dB. Simulation results of the radiation pattern in CST and HFSS software show that the proposed reflector antenna can be used in broadband surveillance radar systems.     

Effects of reflector antenna panel installation errors on average power pattern

A large reflector antenna generally consists of several rings of panels and panel installation errors (PIEs) are inevitable during the panel installation process. In this paper, a mathematical model is developed to analyze the effects of PIEs on reflector's average power pattern. Whether for the PIEs of each ring of panels or for the PIEs of all the panels for the whole reflector, the proposed model can be used to calculate the average power pattern with the root‐mean‐square value of the PIEs, and its correctness is demonstrated by the results calculated by Monte Carlo simulation. For a given paneled reflector, the peak gain losses and the first side lobe level increments caused by different PIEs for the whole reflector are presented. Then, through an analysis for each ring of panels, including the effects of different amplitude aperture distribution functions and different ratios of focal length to diameter (F/D ratios), the results clearly show that the PIEs of the panels for different rings have different effects on the reflector's average power pattern, and valuable results are obtained. The derived results will greatly benefit the panel installation and adjustment of large reflector antennas.     

An ordinal optimization theory-based algorithm for large distributed power systems

In this paper, we propose an ordinal optimization (OO) theory-based algorithm to solve the yet to be explored distributed state estimation with continuous and discrete variables problems (DSECDP) of large distributed power systems. The proposed algorithm copes with a huge amount of computational complexity problem in large distributed systems and obtains a satisfactory solution with high probability based on the OO theory. There are two contributions made in this paper. First, we have developed an OO theory-based algorithm for DSECDP in a deregulated environment. Second, the proposed algorithm is implemented in a distributed power system to select a good enough discrete variable solution. We have tested the proposed algorithm for numerous examples on the IEEE 118-bus and 244-bus with four subsystems using a 4-PC network and compared the results with other competing approaches: Genetic Algorithm, Tabu Search, Ant Colony System and Simulated Annealing methods. The test results demonstrate the validity, robustness and excellent computational efficiency of the proposed algorithm in obtaining a good enough feasible solution.     

控制系统中存在传感器大延迟时的优化研究

传统的Smith预估器较好地解决了前向通道大滞后系统的控制问题,但对于反馈通道中传感器延迟造成的滞后的问题则并不适用。提出了一种改进的Smith预估控制方法,克服了反馈通道中大滞后对于控制系统稳定性的不利影响。仿真结果表明：该方法能够有效地抵消前向通道与反馈通道同时存在的大滞后环节对控制系统稳定性的负面影响。     

Integrated topology and controller optimization of motion systems in the frequency domain

In the precision mechatronics industry the limits of current technology are expanded by a very tight integration of the design disciplines involved, such as structural mechanics and control systems technology. In this article a framework is presented which allows the simultaneous and integrated design of a structure and controller. The structure is designed using topology optimization and the objectives and constraints are related to the closed-loop control performance and defined in the frequency domain. For simple examples it is shown that this approach leads to at least as good performance as a sequential approach consisting of eigenfrequency optimization followed by controller tuning, and leads to lighter designs. The framework allows rapid development of prototype designs, which may save a number of the costly design iterations which are currently made in industrial practice. Examples are found in the semiconductor industry, microscopy, micro–electromechanical devices, medical devices and robotics.     

超高频天线传感器的优化设计

描述了用于检测气体绝缘开关设备 (GIS)中产生的局部放电的超高频天线传感器的结构 ,分析了影响传感器灵敏度的结构参数 ,并研究了为使传感器达到最佳灵敏度进行的优化设计。同时 ,对传感器频率响应进行了实测。     

An efficient method for unconstrained optimization problems ofnonlinear large mesh-interconnected systems

Presents an efficient method for solving unconstrained optimization problems for nonlinear large mesh-interconnected systems. This method combines an approximate scaled gradient method with a block Gauss-Seidel with line search method which is used to obtain an approximate solution of the unconstrained quadratic programming subproblem. The authors prove that their method is globally convergent and demonstrate by several numerical examples its superior efficiency compared to a sparse matrix technique based method. In an example of a system of more than 200 variables, the authors observe that their method is 3.45 times faster than the sparse matrix technique based Newton-like method and about 50 times faster than the Newton-like method without the sparse matrix technique     

新的MOPSO及其在大型复杂系统可靠性优化中的应用

可靠性优化问题是大型复杂系统设计的一个关键问题。针对大型复杂系统多个指标(可靠度、造价和冗余数)同时进行最优分配的结果多样性不好的问题,提出了一种基于杂草克隆的多目标粒子群算法—IWMOP-SO(invasive weed multi-objective particle swarm optimization)的多指标分配方法。该分配方法通过引入杂草克隆机制来改善Pareto最优解的收敛性和多样性。通过对大型复杂系统多个指标进行分配,其分配效果与NSGA-Ⅱ相比,得到的Pareto非劣解集多样性和均匀性好,分布范围更广,更利于设计者进行决策,是一种更有效的复杂系统多指标分配方法。     

Topology optimization of reflector antennas based on integrated thermal-structural-electromagnetic analysis

Structural and Multidisciplinary Optimization - In the area of structural design of reflector antennas, the existing researches mainly focus on size/shape optimization or just optimizing for...