15 research outputs found
Computational analysis, design and characterization of periodic metamaterial structures and synthesis of waveguide structures and planar antennas for microwave frequencies and wireless 5G communications
No full textThis doctoral thesis focuses on the numerical analysis of periodic metamaterial structures using the finite element method. A parameter retrieval technique is proposed, which combines the eigenvalue analysis and the field averaging at the unit cell boundaries. In addition, novel waveguide structures and fully planar antennas are designed and optimized in order to operate at wireless and microwave frequencies and potential usage in 5G network frequencies.Στα πλαίσια αυτής της διατριβής πραγματοποιήθηκε υπολογιστική ανάλυση περιοδικών διατάξεων μεταϋλικών με τη μέθοδο των πεπερασμένων στοιχείων. Επίσης, προτάθηκε μία τεχνική εξαγωγής καταστατικών παραμέτρων τεχνητών μέσων που συνδυάζει την ανάλυση ιδιοτιμών και τη μεσοστάθμιση πεδίου στα όρια του μοναδιαίου κελιού. Τέλος, σχεδιάζονται και βελτιστοποιούνται διατάξεις κυματοδήγησης και επίπεδων κεραιών για ασύρματες μικροκυματικές συχνότητες και εν δυνάμει χρήση τους σε συχνότητες δικτύων 5G
Comparison of Split-Ring Resonator Composite Periodic Media based on Numerical Eigensolutions
No full textDispersion diagram reconstruction of effectively bianisotropic composite periodic media
No full textA dispersion diagram reconstruction technique is proposed for arbitrarily bianisotropic composite periodic media, which utilizes a previously introduced parameter retrieval technique based on eigenvalue analysis and field averaging. We initially retrieve the effective electromagnetic parameters of a composite periodic medium consisting of Edge-Coupled Split-Ring Resonators (EC-SRRs) via this homogenization technique using alternative integration approaches for the averaging of the field components. Subsequently, we derive the analytical framework for the wave propagation in a homogeneous medium of arbitrary bianisotropy and extract the appropriate equations which solve for the complex propagation constants. We then involve the retrieved effective parameters in these equations and reconstruct the dispersion diagrams for all three orthogonal directions, thereby spanning the whole irreducible Brillouin zone. An excellent agreement is found between the original dispersion diagrams and the reconstructed ones; a result which further validates the utilized parameter retrieval technique. The reconstruction technique moreover allows one to interpret the slope differences observed in the dispersion diagrams for in-plane and normal incidence modes of the examined composite medium. It may also be used as a tool for the confirmation of the accuracy of other formerly proposed homogenization techniques existing in the literature
Metasurface characterization based on eigenmode analysis and averaging of electromagnetic fields
No full textA fully numerical homogenization technique for the retrieval of the effective surface susceptibilities of a periodic composite metasurface is developed in this work. We utilize the so-called dual field-flux finite element formulation scheme to accurately calculate the eigenmodes of a composite periodic metasurface, a scheme that possesses a crucial advantage: The capability of evaluating all field components and their derivatives accurately and with the same order of approximation is a requirement for our proposed technique. Next, we derive the generalized sheet transition condition equations for a general bianisotropic metasurface, which correlate the field components on either sides of the metasurface with its surface susceptibilities. At this point, we establish a new field averaging scheme for the acquisition of the average field components of the modes supported by the metasurface. Combining this computational information, we derive a set of linear algebraic equations based on the GSTCs and the average electromagnetic fields and numerically solve it, so as to obtain the effective surface susceptibilities of a bianisotropic metasurface. Comparison with the results of other techniques in the literature shows very good agreement, relatively to the resonance behavior of the returned values and their position at the frequency spectrum. The advantages that distinguish the proposed technique over other related methods are its foundation on the intrinsic modal information of the eigenmodes supported by the metasurface and its independence of any wave excitation schemes or involvement of analytical polarizability calculations
Systematic Synthesis of Fully-Planar Antennas Based on Metamaterial-Enhanced SIWs for 5G Communications
No full textA fully numerical process for the systematic design of fully-planar antennas for 5G communications frequencies is presented, utilizing a metamaterial-enhanced SIW as the basis platform. A combined modal analysis and wave propagation Finite Element modeling is proposed for the accurate design of the waveguiding structure towards its leakage loss minimization. Based on this robust numerical scheme, two different types of fully-planar antennas are designed. A leaky-wave fully-planar two-slot antenna and an H-plane end-fire sectoral horn antenna. Both structures are viable candidates for integration in 5G communications platforms, exhibiting attractive characteristics such as optimized gain and bandwidth, low cost, compactness, and ease of fabrication.</p
Field Averaging Techniques in Electromagnetic Problems
No full textIn this work we present two field averaging techniques for structured electromagnetic materials. One is concerned with 3D-periodic composite media, while the other one is concerned with 2D-periodic planar structures. In the first case, the field averaging is prescribed by the integral form of Maxwell’s equations and is carried out along the paths laying at the boundaries of the unit cell. In the second case, the integration regions are prescribed by the Generalized Sheet Transition Conditions. Both techniques are useful in homogenization of structured materials such as metamaterials and metasurfaces, for the extraction of their effective material parameters and surface susceptibilities, respectively
Field-Flux Finite Element Formulation for Wave Propagation in Bianisotropic Media
No full textWe derive a field-flux Finite Element formulation for the inclusion of bianisotropic materials in wave propagation electromagnetic problems. A boundary condition is proposed for the efficient excitation and absorption of the supported modes. Computational results are compared with analytical solutions from the literature for a homogeneous omega bianisotropic medium. Perfect agreement is exhibited, proving the efficiency and robustness of the proposed formulation
Fully Planar CSRR-SIW Slot Antennas of Optimized Gain and Enhanced Bandwidth for Millimeter Wave and 5G Communications
No full textAnalysis and design of fully planar CSRR-enhanced substrate-integrated waveguides and slot antennas for 5G communications
No full text
