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ABSTRACT: We review work relevant to the area covered by the transmission line matrix (TLM) method, including certain historical TLM developments and design parameter sensitivity analysis for time-domain simulations. We consider exact TLM sensitivity analysis, compare it with the finite difference approach, and demonstrate its use in accelerating design optimization. We discuss ways of using space-mapping concepts for modeling and design that exploit the TLM time-domain electromagnetic simulator MEFiSTo as a fine model evaluator.
Microwave Symposium Digest (MTT), 2011 IEEE MTT-S International; 07/2011
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ABSTRACT: The authors present a robust algorithm for extracting the Cauchy interpolation coefficients in a multi-dimensional rational function modelling problem. The model extraction problem is formulated as a linear program, which is efficiently solved using the simplex method. The algorithm overcomes numerical errors in the electromagnetic simulations and rejects spurious solutions of the model. The novel algorithm is illustrated using a number of modelling problems.
IET Microwaves Antennas & Propagation 12/2010; · 0.68 Impact Factor
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ABSTRACT: We present a novel approach for adaptive tuning of receiving antenna impedance matching operating in a time-varying environment. Our approach utilizes perturbations of the tuning circuit to construct a system of two nonlinear equations. This system is then solved to determine the exact input impedance of the antenna. With this, the tuning circuit is then adjusted to match the antenna at the calculated input impedance. This cycle is repeated with a certain rate to take into account the dynamic surrounding environment in real time.
Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
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ABSTRACT: We present a novel numerical approach for solving inverse source problems using time domain TLM. Our algorithm reconstructs the unknown excitation sources in the time domain using the observed field outside the source region. In this work, we apply our algorithm to thin source regions consisting only of boundary cells. The source reconstruction for this case is always unique and does not require any regularization procedures.
Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
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ABSTRACT: In this paper we introduce an effective approach for dynamic impedance tuning of antennas in the transmission mode. The proposed approach is based on an optimization process that solves a system of two non-linear equations. It takes place in real-time and computes the actual input impedance of an antenna that changes in reaction to its environment. Our proposed approach does not limit the number of tunable components as the computational overhead is independent of their cardinality. Hence the proposed approach is efficiently applied for broadband antenna tuning.
Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
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ABSTRACT: We present a novel approach for extracting the modal parameters of high frequency components and the sensitivity of there parameters using only few time iterations of an FDTD simulation. An adapted version of the matrix pencil method is utilized for efficient extraction of the modal parameters. Using our approach, the modal parameters of all the guided and leaky modes are extracted over the frequency band of interest in a very efficient manner.
Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
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ABSTRACT: We present a novel algorithm for adjoint sensitivity analysis of time-varying responses that is based on the transmission line modeling (TLM) method. We show that by using at most one extra electromagnetic (EM) simulation, the sensitivities of the complete time domain EM response can be obtained with respect to all designable parameters regardless of their number and regardless of the number of time steps. The complete time domain signature of a certain structure can thus be efficiently and accurately predicted for perturbed structures. Our sensitivities match those obtained using the accurate and time intensive central finite differences (CFD). The adjoint sensitivities are used in the solution of inverse problems through a number of approaches exploiting surrogate model optimization and direct optimization. Our technique enables efficient identification of object position, dimensions and material properties.
IEEE Transactions on Antennas and Propagation 08/2009; · 2.15 Impact Factor
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ABSTRACT: We introduce a tuning space-mapping technology for microwave design optimization. The general tuning space-mapping algorithm is formulated, which is based on a so-called tuning model, as well as on a calibration process that translates the adjustment of the tuning model parameters into relevant updates of the design variables. The tuning model is developed in a fast circuit-theory based simulator and typically includes the fine model data at the current design in the form of the properly formatted scattering parameter values. It also contains a set of tuning parameters, which are used to optimize the model so that it satisfies the design specification. The calibration process may involve analytical formulas that establish the dependence of the design variables on the tuning parameters. If the formulas are not known, the calibration process can be performed using an auxiliary space-mapping surrogate model. Although the tuning space mapping can be considered to be a specialized case of the standard space-mapping approach, it can offer even better performance because it enables engineers to exploit their experience within the context of efficient space mapping. Our approach is demonstrated using several microwave design optimization problems.
IEEE Transactions on Microwave Theory and Techniques 03/2009; · 1.85 Impact Factor
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ABSTRACT: We propose a new compact optical switch that works over a wide wavelength band. This switch has low cross talk and can be easily integrated with other components of the communication system. The device utilizes the self imaging theory of the parabolic index profile. A new methodology to formulate the design problem as an optimization problem is proposed. Both the response and the gradient of the response are utilized within a gradient-based optimization approach. The adjoint variable method is utilized to extract the gradient of the response using the wide angle BPM method.
Journal of Lightwave Technology 02/2009; · 2.78 Impact Factor
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ABSTRACT: An efficient approach is utilized for extracting the modal parameters of high frequency structures and their sensitivities with respect to all the design parameters. Using one FDTD simulation, the modal parameters of all the guided and leaky modes are extracted over the frequency band of interest. An adapted version of the matrix pencil method is utilized for efficient extraction of the modal parameters. In addition, using no extra simulations, the sensitivities of the propagation constants with respect to all the design parameters of the structure are extracted regardless of their number. The computational time is a small fraction of the cost of similar approaches.
Progress In Electromagnetics Research. 01/2009; 94:197-212.
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ABSTRACT: The Adjoint Variable Method (AVM) is applied for the first time to perform sensitivity analysis for Transmission Line Modeling (TLM) using rubber cells with modified tensor properties. Rubber cells allow the conformal modeling of off-grid boundaries in the TLM domain using modified tensor properties. The scattering matrix of the rubber cell is analytically dependent on the dimensions of the modeled discontinuities. Using this property, an exact adjoint system is derived. The original and adjoint systems supply the necessary field information for the rubber cell based sensitivity calculations. Our technique is illustrated through sensitivity analysis and optimization of a waveguide bandpass filter.
Microwave Symposium Digest, 2008 IEEE MTT-S International; 07/2008
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ABSTRACT: The authors present, for the first time, a comprehensive theory for self-adjoint S-parameter sensitivities of non-homogenous transmission-line modelling problems. They show that wideband S-parameter sensitivities can be efficiently calculated without carrying out any adjoint simulations. The N<sub>p</sub> original simulations used to calculate the S-parameters of an N<sub>p</sub>-port electromagnetic structure supply the sensitivities as well. The authors also present their approach for two different types of nodes utilised in transmission-line modelling. The efficiency and accuracy of their algorithms are illustrated through a number of examples. Good match is obtained between their self-adjoint sensitivities and those calculated using finite differences at the response level.
IET Microwaves Antennas & Propagation 05/2008; · 0.68 Impact Factor
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ABSTRACT: We present a novel approach to the sensitivity analysis of 3D structures using the full vectorial beam propagation method (FVBPM). Using no extra simulations, the sensitivities of the response with respect to all design parameters are obtained regardless of their number. Our approach is exploited to calculate the sensitivities of the propagation constants of multimode waveguides. It is also applied to the 3D imaginary distance FVBPM (ID-FVBPM) and utilized to extract the sensitivities of the mode parameters. The calculated sensitivities are then utilized within a gradient-based optimization algorithm to illustrate the application of the obtained sensitivities. The accuracy of our approach is verified through a comparison with the expensive central finite difference applied directly at the response level.
Journal of Lightwave Technology 04/2008; 26(5):528-536. · 2.78 Impact Factor
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ABSTRACT: Gradient-based optimisation relies on the response Jacobian whose evaluation constitutes a major computational overhead in full-wave numerical analysis. Adjoint-based techniques may offer numerically efficient solutions, but their implementation is too involved in the case of full-wave computations. A simple approach that uses the self-adjoint sensitivity analysis and Broyden's update is proposed. The overhead of the Jacobian computation is greatly reduced because an adjoint system analysis is not needed and because Broyden's update is used to compute the system matrix derivatives. To improve the robustness of the Broyden update in the sensitivity analysis, we propose a switching criterion between the Broyden and the finite-difference estimation of the system matrix derivatives. We illustrate and validate the proposed method using full-wave commercial electromagnetic solvers based on the finite-element method as well as on the method of moments. Different gradient-based optimisation algorithms are exploited in the examples where efficiency is compared in terms of CPU time savings.
IET Microwaves Antennas & Propagation 09/2007; · 0.68 Impact Factor
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ABSTRACT: We propose a novel and simple approach for design sensitivity analysis using the beam propagation method (BPM). It exploits the adjoint variable technique to extract the response sensitivities with respect to all the design parameters, regardless of their number. The associated computational cost is less than that of an extra BPM simulation. The accuracy of the results are comparable to those obtained using the expensive central finite-difference approximations applied at the response level. Our approach is successfully illustrated through a number of examples.
Journal of Lightwave Technology 08/2007; · 2.78 Impact Factor
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ABSTRACT: For the first time, convex optimization is applied to the design of multilayer optical coatings. We present two different approaches to approximate the design problem as a convex optimization problem. This problem is then efficiently solved using interior point methods. Our formulation is fast and flexible, allowing the designer to add any number of constraints. The results show that the used approximation is tight and has a good match with the exact solution
Journal of Lightwave Technology 05/2007; 25(4):1078-1085. · 2.78 Impact Factor
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ABSTRACT: For the first time, full-wave optimization exploiting adjoint Hessian matrices is applied to the design of microwave filters and transitions. The first- and second-order sensitivities of the scattering parameters are computed analytically using the adjoint network method (ANM). The mode-matching-based ANM is applied to the generalized scattering matrices of the different filter/transition components. Analytical gradient and Hessian matrices of differentiable objective functions are expressed in terms of the first- and second-order response adjoint sensitivities. Optimization techniques exploiting second-order information such as the Levenberg-Marquardt method are applied using the adjoint first- and second-order information. Significant acceleration is achieved using these techniques over gradient-based optimization techniques such as the Broyden-Fletcher-Goldfarb-Shanno method. The adjoint-based sensitivities are also exploited in efficient tolerance analysis of microwave filters
IEEE Transactions on Microwave Theory and Techniques 09/2006; · 1.85 Impact Factor
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ABSTRACT: Recently, a self-adjoint method was proposed for the computation of network parameter sensitivities. Here, we propose a modification to this method, which practically eliminates its overhead by using the Broyden update for the computation of the system matrix derivatives. We investigate the feasibility and the efficiency of the Broyden-update self-adjoint sensitivities in gradient based optimization. We compare in terms of CPU time the optimization processes with several well known optimization algorithms. We investigate their performance in two cases: 1) when the response and its sensitivities are provided by our method, and 2) when responses only are provided
Antennas and Propagation Society International Symposium 2006, IEEE; 08/2006
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ABSTRACT: We propose an efficient adjoint-variable approach to the sensitivity analysis of S-parameters obtained from full-wave electromagnetic (EM) time-domain simulations. It allows the computation of the S-parameter derivatives with respect to the design variables with negligible overhead. No solutions of adjoint EM problems are needed. The computation is done as an independent post-process outside the solver. The sole requirement is the ability of the solver to export the field solution at user-defined points. Most commercial solvers have this ability, which makes our approach readily applicable to practical design problems. The approach is verified through the analysis of waveguide and antenna structures using commercial simulators.
IEEE Transactions on Microwave Theory and Techniques 07/2006; · 1.85 Impact Factor
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ABSTRACT: A new practical approach to sensitivity analysis of the network parameters of high-frequency structures with commercial full-wave electromagnetic (EM) solvers is proposed. We show that the computation of the linear-network parameter derivatives in the design-parameter space does not require an adjoint-problem solution. The sensitivities are computed outside the EM solver, which simplifies the implementation. We discuss: 1) features of commercial EM solvers which allow the user to compute network parameters and their sensitivities through a single full-wave simulation; 2) the accuracy of the computed derivatives; and 3) the overhead of the sensitivity computation. Through examples based on FEMLAB and FEKO simulations, comparisons are made with the forward finite-difference derivative estimates in terms of accuracy and CPU time.
IEEE Transactions on Microwave Theory and Techniques 03/2006; · 1.85 Impact Factor
