M.N. Vouvakis

University of Massachusetts Amherst, Amherst Center, MA, United States

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Publications (52)31.49 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Planar Ultrawideband Modular Antenna (PUMA) arrays are low-cost, wide-scan, and low-cross polarization dual-polarized UWB arrays that combine excellent electrical performance with convenient and practical feeding/fabrication processes. Each member of the PUMA array family consists of tightly coupled horizontal dipoles over a ground plane with novel feeding schemes that enable simple PCB fabrication. This feeding eliminates the need for baluns, “cable organizers,” and other external support mechanisms to produce stand-alone, high-efficiency radiators. Additionally, all PUMA arrays consist of dual-offset dual-polarized lattice arrangements for modular, tile-based assembly. This paper will review the basic operation principles of the PUMA arrays followed by the technological evolution of the PUMA array family. Fabricated PUMA arrays and full-wave simulations of structures that can be manufactured with standard fabrication technologies will be shown along with results.
    Electromagnetic Theory (EMTS), Proceedings of 2013 URSI International Symposium on; 01/2013
  • Steven S. Holland, Daniel H. Schaubert, Marinos N. Vouvakis
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    ABSTRACT: The design, fabrication, and measurement of a 16 × 16 dual-polarized planar ultrawideband modular antenna (PUMA) array operating over 7-21 GHz (3:1 bandwidth) are presented. The array is comprised of tightly coupled dipoles printed on a grounded dielectric substrate and are excited by an unbalanced feeding scheme that eliminates external wideband baluns and feed organizers. The array can be assembled modularly, where each low-profile, fully planar, low-cost tile is fabricated using standard multilayer microwave PCB techniques. A unique solderless, modular interconnect mates the array to a dilation fixture that facilitates measurements using standard surface-mount assembly (SMA) connectors and terminations. After presenting the most critical design trends, simulation results of the final array in infinite, infinite × finite, and finite × finite models are compared with measurements. This prototype array exhibits a measured active VSWR <; 2.1 and close to ideal gain at broadside, and VSWR <; 2.8 with low cross-polarization out to θ = 45° in all planes, showing close agreement with simulations.
    IEEE Transactions on Antennas and Propagation 10/2012; 60(10):4589-4600. · 2.33 Impact Factor
  • Steven S. Holland, Marinos N. Vouvakis
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    ABSTRACT: A fully planar ultrawideband phased array with wide scan and low cross-polarization performance is introduced. The array is based on Munk's implementation of the current sheet concept, but it employs a novel feeding scheme for the tightly coupled horizontal dipoles that enables simple PCB fabrication. This feeding eliminates the need for “cable organizers” and external baluns, and when combined with dual-offset dual-polarized lattice arrangements the array can be implemented in a modular, tile-based fashion. Simple physical explanations and circuit models are derived to explain the array's operation and guide the design process. The theory and insights are subsequently used to design an exemplary dual-polarized infinite array with 5:1 bandwidth and ${\rm VSWR}
    IEEE Transactions on Antennas and Propagation 01/2012; 60(1):130-140. · 2.33 Impact Factor
  • Wei Wang, Marinos N. Vouvakis
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    ABSTRACT: A study of various sampling strategies for extracting reduced models from moderate dimension parametric spaces of finite element (FE) models is conducted. Tensor-product, Monte Carlo method and its various quasi-Monte Carlo alternatives (Sobol, Halton) and sparse grid sampling strategies are compared for a doubly infinite antenna array example.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • Wei Wang, Marinos N. Vouvakis
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    ABSTRACT: A finite element method (FEM) model reduction methodology is combined with a reliable mesh warping algorithm for fast geometric parameter sweeps. The approach avoids remeshing and matrix assembling by carefully repositioning mesh nodes via solving Laplace's equation with a nodal FEM in each mesh region. Even on large deformations, this approach maintains high quality meshes that produce robust reduced models. Numerical results on a patch antenna and infinite Vivaldi array demonstrate the accuracy of the proposed method
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • G.N. Paraschos, Marinos N. Vouvakis
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    ABSTRACT: The newly introduced Locally Exact Algebraic Preconditioner (LEAP) is combined with the well established FETI-DP method to provide robust and scalable iterative convergence. This is achieved by adopting a single-level version of LEAP, sufficient to deduce scalable results due to treatment of domain-edges by FETI-DP. It is experimentally shown that the LEAP can significantly improve the order of convergence of FETI-DP to make it more efficient and robust.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • G.N. Paraschos, Marinos N. Vouvakis
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    ABSTRACT: This paper outlines a robust, effective and efficient local preconditioning strategy for Domain Decomposition Methods (DDM) in electromagnetic computations. The multilevel preconditioner is constructed based on a hierarchy of small auxiliary problems on local topological entities. Eigenspectra and convergence history plots on different decomposition strategies showcase the effectiveness and robustness of the method.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • S.S. Holland, M.N. Vouvakis
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    ABSTRACT: A new wideband, wide-scan array is introduced, called the Banyan Tree Antenna (BTA) array, that employs modular, low-profile, low-cost elements fed directly from standard unbalanced RF interfaces. The elements consist of vertically-integrated, flared metallic fins over a ground plane that are excited by a vertical two conductor unbalanced transmission line. The antenna resembles the bunny-ear or balanced antipodal Vivaldi antenna (BAVA) designs, but most importantly uses metallic shorting posts between the fins and the ground plane that suppress a mid-band catastrophic common-mode resonance that occurs in 2D arrays of balanced radiators fed with unbalanced feeds. This work introduces simple circuit models that describe key performance attributes of the BTA array, leading to unique physical insights and design guidelines. Simulations of infinite single- and dual-polarized BTA arrays have achieved approximately two octaves of bandwidth for VSWR <; 2.2 at broadside and VSWR <; 2.8 at scans out to θ = 45°, while maintaining better than 14 dB polarization purity at θ = 45° in the D-plane.
    IEEE Transactions on Antennas and Propagation 12/2011; · 2.33 Impact Factor
  • Wei Wang, Marinos N. Vouvakis
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    ABSTRACT: A finite element method (FEM) model-order re- duction (MOR) methodology for the fast parametric sweep of geometrical features is presented. The proposed method first linearizes the otherwise non-linear FEM matrix dependence with respect to the geometry variation, and then uses a uniformly sampled balanced truncation proper orthogonal decomposition (BT-POD) reduction algorithm to expediently sweep over the parametric geometry space. The approach avoids slow re-meshing and full matrix reassembly by using mesh morphing approaches. Moreover, BT-POD is known to provide close to optimal size reduced problems using only a small number of samples, thus minimizing the the number of full-model solutions. Numerical results on two large-scale filter design examples are used to study the accuracy and efficiency of the proposed method.
    01/2011;
  • Steven S. Holland, Marinos N. Vouvakis
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    ABSTRACT: Measurements and simulations for various Planar Ultrawideband Modular Antenna (PUMA) arrays are presented. The arrays are based on tightly-coupled printed dipoles above a ground plane and are fully planar, where both the radiating aperture and feed lines are fabricated using low-cost multilayer PCB technology. The dipoles are fed with a novel feeding scheme that suppresses a catastrophic common-mode resonance, thus eliminating the use of feed organizers and external baluns. A product of this novel feeding is the modularity of the aperture (tiled assembly). A proof of concept 16×16×2 dual-polarized array prototype operating over 7-21.5GHz (3:1 bandwidth) was fabricated and measured. The results are in very good agreement with simulations, exhibiting a broadside VSWR =2 .1 and low (−15dB) cross-polarization in the diagonal plane out to 45 ◦ . Additionally, an infinite 5:1 PUMA design with broadside VSWR =2 .1, better than 2.9 VSWR at 45 ◦ in the H-plane, and cross- pol less than −15dB out to θ =4 5 ◦ in the D-plane is presented.
    01/2011;
  • Georgios N. Paraschos, Marinos N. Vouvakis
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    ABSTRACT: A global domain decomposition (DD) preconditioner based on the dual-primal idea is presented. The key attribute of the proposed preconditioner is an auxiliary primal coarse problem that is fully overlapping to the original problem at domain interface regions only, and uses entire-domain basis functions to reduce the primal problem size. A two-level reduction solution process that iterates on the Lagrange multipliers is adopted, resulting in an efficient FETI solver. When compared to other dual-primal DD methods, the proposed method is com- putationally more efficient and, more importantly, is applicable to both conforming and non-conforming mesh decompositions. Numerical results on scattering and propagation problems are used to demonstrate its performance. The proposed method is found to outperform existing state-of-the-art FETI variants in all problems studied. I. INTRODUCTION The ever increasing demand to solve larger and more complex EM problems, such as phased arrays, low observable scattering, IC interconnects, etc., has pushed CEM methods to multi-, many-core and cluster parallel processing. Traditional methods such as Finite Element Method (FEM) or Bound- ary Element Method (BEM) are not well suited for parallel processing without penalties in scalability. In recent years, Domain Decomposition (DD) methods have emerged as an excellent parallel processing vehicle for FEM computations. The Finite Element Tearing and Interconnecting (FETI) (1) method is the most successful non-overlapping DD that uses Lagrange Multipliers (LMs) to weakly enforce continuity across sub-domains. Even though FETI is extremely robust and scalable for positive definite problems (2), its iterative convergence for indefinite systems which are encountered in electromagnetic, is unreliable and lacks scalability. In the quest to improve scalability, a number of precon- ditioning strategies have been proposed. These approaches mostly rely on global means of "information" transferring, which are constructed through the solution of a suitable global coarse problem. The challenge here is to maintain a small global problem size, yet accurately represent the physics of the underlying information transferring mechanisms. The Helmholtz FETI (FETI-H) method (3), designed for acoustic problems, was among the first to use plane waves to construct a coarse problem space. An even more efficient precondi- tioning strategy, termed Dual Primal FETI (FETI-DP), was proposed in (2) and is currently considered state-of-the-art for elasticity and fluid problems. The method constructs a global preconditioner by isolating FEM degrees-of-freedom (DoF) associated with domain vertices. At these vertices, inter- domain continuity is enforced directly via the construction of the FEM basis functions and through the solution of the coarse problem by direct solvers. Toselli, in (4), was the first to extend the FETI-DP idea to electromagnetics by recognizing that the coarse problem must be constructed from the FEM DoFs that reside on domain edges, instead of domain vertices. This approach was adopted in the recent work of Li and Jin in (5), leading to impressive results for realistic scattering and radiation problems. Unfortunately, these FETI-DP approaches could result in an unacceptably large coarse problem that ultimately hampers ef- ficiency and parallel scalability. More importantly, all existing FETI-DP schemes are invalid for non-conforming mesh DD. This paper introduces the Dual, Overlapping Primal FETI (FETI-DOP), a 2-level global preconditioning scheme that is applicable to conforming and non-conforming decompositions. It retains the excellent parallelization properties of FETI and maintains a small-size coarse problem that provides an efficient and effective preconditioner. The approach is based on: 1. a coarse (primal) problem that is overlapping to the existing problem, and resides locally around interfaces, 2. the primal problem is discretized with entire-domain basis functions that are associated with domain edges and their support covers the entire domain interfaces. The overlapping characteristic allows the treatment of non- conforming decompositions, and the extended support of the primal basis functions improves the effectiveness of the preconditioner while maintaining a sufficiently small coarse problem size.
    01/2011;
  • Wei Wang, Georgios N. Paraschos, Marinos N. Vouvakis
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    ABSTRACT: A fast frequency sweep method for wideband an- tennas and infinite arrays based on a singular value decomposition (SVD)-Krylov model reduction method for frequency-domain tangential vector finite elements (TVFEMs) is presented. Reduced models are constructed using balanced congruence transfor- mations constructed from the dominant invariant subspace of the system's Hankel matrix. Traditionally, forming such matrix requires the intensive computation of Gramians; the proposed method only forms their low-rank Cholesky factors via a novel adaptive proper orthogonal decomposition (POD) sampling strategy, leading to significant savings. Unlike some other model reduction methods, balanced truncation POD (BT-POD) is di- rectly applicable to lossy and dispersive electromagnetic models. Numerical studies on large-scale wideband antennas and infinite arrays show that the method is stable, error controllable and, without memory overheads capable of up to two orders-of-mag- nitude speed-ups.
    IEEE Transactions on Antennas and Propagation 01/2011; 59(11):4142-4154. · 2.33 Impact Factor
  • R.W. Kindt, M.N. Vouvakis
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    ABSTRACT: Wavelength-scaled array architectures use scaled elements to achieve ultrawideband performance with significantly fewer overall radiators than traditional ultrawideband arrays based on a single element type. Compared to a conventional ultrawideband array with 8:1 bandwidth, a wavelength-scaled array that uses elements of three different sizes creates an aperture with fewer than 16% of the original element count, i.e., 6.4-times fewer elements, and by extension a comparable reduction in electronics required to feed the array. In this paper, a study of an asymmetric wavelength-scaled array architecture is presented for finite arrays of offset-centered dual-polarized flared-notch radiators. The unique element transitions within the finite array structure are modeled via a non-matching grid Domain Decomposition-Finite Element Method that allows for rigorous impedance and radiation pattern prediction of full-sized wavelength-scaled arrays. This design study shows that the wavelength-scaled array has comparable performance to traditional ultrawideband arrays in terms of VSWR, radiation patterns, array mismatch efficiency, and cross-polarization levels.
    IEEE Transactions on Antennas and Propagation 10/2010; · 2.33 Impact Factor
  • Wei Wang, M.N. Vouvakis
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    ABSTRACT: This paper presents an adaptive sampling model order reduction (MOR) methodology for fast frequency sweep of wideband electromagnetic (EM) systems. The proposed algorithm is an automated, more reliable, robust and error-controllable version of the balanced truncation proper orthogonal decomposition (BT-POD) model order reduction [1], [2]. Although the framework in [1] and [2] works quite well, it is based on an ad-hoc uniform POD sampling strategy that is less robust and efficient and it has no stopping criteria. The adaptive BT-POD intelligently chooses POD sampling points according to goal-oriented error estimates and indicators [3], and provides reliable stopping criteria based on a global error indicator. In [4], an adaptive s-parameter rational interpolation is used to perform the fast sweep. In [5], an adaptive multipoint Krylov method using the s-parameter history to decide the next sample location was proposed. These are different than the present method because the error estimates are computed based on goal-oriented residual error indicators that are known to be more reliable. Numerical results on a large-scale waveguide filter model are used to illustrate the validity and performance of the proposed methodology.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
  • Wei Wang, G.N. Paraschos, M.N. Vouvakis
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    ABSTRACT: The design and optimization of high-frequency electronic systems such as antenna and microwave devices requires scanning and searching over various design parameter spaces that include frequency, material permittivity, permeability, or excitation (i.e., scan angles). Such sweeps require repeatedly solving the computational model (FEM or BEM) at various different parameter value combinations, leading to very slow computational design cycles. This paper presents a methodology for performing such sweeps in a fast manner. A multi-parametric model order reduction (MOR) scheme based on the recently developed balanced truncation proper orthogonal decomposition (BT-POD) MOR [1], [2] is introduced to handle such sweeps. In contrast to the previous multi-parameter MOR presented in [3] and [4] that are based on Krylov model reduction, this work adopts the SVD-based reduction paradigm of BT-POD. The multi-parameter space sweep in this work is achieved in a two-step procedure: (1) An off-line (learning) stage where a coarse parameter space POD sampling is used to produce the multi-dimensional balancing transformations, followed by (2) an online (sweep) stage that performs the fine sampled parameter-space sweep via the solution of the reduced model. The system gramians [5] approximation involved in this MOR paradigm is obtained through the use of numerical integration over parameter spaces of interest, therefore such MOR technique can be extended to moderately high-dimensional parameter spaces using specialized Monte-Carlo and sparse grid integration strategies. The POD sampling is straightforwardly parallelizable, leading to farther time savings.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
  • S.S. Holland, M.N. Vouvakis
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    ABSTRACT: This paper presents the Planar Ultrawideband Modular Array (PUMA), a fully planar implementation of Wheeler's current sheet requiring no feed organizers or external baluns, that can be fabricated entirely using standard planar microwave circuit processes. This allows for low-cost aperture fabrication, high volume production and frequency scalability. The unique feed arrangement of PUMA allows for a modular egg-crate construction, with direct connection to standard 50Ω interfaces, and low profile (~ λ/3 at its highest frequency). Predicted dual-polarized infinite array performance has demonstrated a 3:1 bandwidth (7-21GHz) and scanning with VSWR <; 2.2 out to θ = 45° in all planes. Measurements of a 16x16x2 array are currently in progress.
    Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
  • Georgios N. Paraschos, Marinos N. Vouvakis
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    ABSTRACT: This paper presents a study of the accuracy of that FETI DDM with various choices of the Lagrange multiplier space and for conforming and non-conforming discretizations.
    01/2010;
  • R.W. Kindt, M.N. Vouvakis
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    ABSTRACT: Wavelength-scaled array architectures use scaled elements to achieve ultra-wideband array performance with significantly fewer overall radiators than traditional ultra-wideband arrays consisting of a single element type. Given a requirement for an 8:1 bandwidth array of a given aperture size, an array of equivalent aperture and bandwidth is created from scaled elements of three sizes. The proposed wavelength-scaled equivalent architecture has 16% of the original element count with a comparable reduction in electronics required to feed the array, leading to significant cost savings. Because of the complex electromagnetic environment of the wavelength-scaled architecture, infinite array design tools cannot be used - rigorous analysis methods using domain decomposition techniques for finite arrays are necessary to design and validate performance.
    Electromagnetics in Advanced Applications, 2009. ICEAA '09. International Conference on; 10/2009
  • G.N. Paraschos, M.N. Vouvakis
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    ABSTRACT: This paper presents a design methodology that utilizes both infinite periodic cell methods and domain decomposition (DD), but more importantly it introduces a new intermediate stage that requires the analysis of few infinite x finite structures first. This is not a new idea, yet its practical implementation has not been successful because solving infinite x finite structures with conventional methods remains computationally expensive. The present approach combines ideas from DD and infinite periodic cell approaches in order to exploit repetitions within the infinite x finite cell. The combination significantly reduces the computational overhead, making the method suitable for optimization purposes.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
  • Wei Wang, G.N. Paraschos, M.N. Vouvakis
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    ABSTRACT: This paper introduces a hybrid SVD-Krylov technique based on the balanced truncation - proper orthogonal decomposition (BT-POD). The method combines the best features of the two categories, namely offers error controls and indicators while preserving the efficiency of Krylov MOR. The most time consuming step related to the POD sampling is embarrassingly parallel, making the method suitable for multi-core computing. The method is related to the principal component analysis (PCA) of pattern recognition and machine learning, and shares the same spirit with the low-rank POD of Willcox et.al., Phillips' poor-man's TBR. and the Choleski factor -alternating direction implicit (CF-ADI) algorithm.
    Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009

Publication Stats

452 Citations
31.49 Total Impact Points

Institutions

  • 2006–2011
    • University of Massachusetts Amherst
      • Department of Electrical and Computer Engineering
      Amherst Center, MA, United States
  • 2003–2007
    • The Ohio State University
      • Department of Electrical and Computer Engineering
      Columbus, OH, United States
  • 2001–2004
    • Arizona State University
      • School of Electrical, Computer and Energy Engineering
      Mesa, AZ, United States