Field behavior near the edge of a microstrip antenna by the method of matched asymptotic expansions

International audienceThe cavity model is a wide-spread powerful empirical approach for the numerical simulation of microstrip antennas. It is based on several hypotheses assumed a priori: a dimension reduction in the cavity, that is, the zone limited by a metallic patch and the ground plane in which is fed the antenna, supplied by the additional condition that the open sides of the cavity act as magnetic walls. An additional important assumption of this model consists in an adequate description of the singular field behavior in the proximity of the edge of the patch. A simplified two-dimensional problem incorporating the main features of the field behavior near the edge of the patch and inside the cavity is addressed. The method of matched asymptotic expansions is used to carry out a two-scale asymptotic analysis of the field relatively to the thickness of the cavity. All the empirical hypotheses at the basis of the derivation of the cavity model can thus be recovered. Proved error estimates are given in a simplified framework where the dielectric constants of the substrate are assumed to be 1 in order to avoid some unimportant technical difficulties

Annual Review of Progress in Applied Computational Electromagnetics

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Electromagnetic Scattering in Microwave Remote Sensing and Fluctuation Electrodynamics

Application of the electromagnetic scattering theory to the physical models of microwave remote sensing of natural targets including but not limited to polar ice sheets, soil surface, vegetated area, etc. and fluctuation electrodynamics as well as microwave resonators are presented in this thesis. Advancement of the remote sensing technology led the radar and radiometry measurement to a level of accuracy that correct interpretation of the measurement outcomes and relating those to the unknown parameters under study requires the physical models that are capable of resembling the real life situation as close and accurate as possible. Along with accuracy, the model should be simple enough for the purpose of real time implementation. This is where the analytical solution of the physical problem manifest itself against pure numerical methods in terms of the fast evaluation and more importantly the insight that is not available in a numerical approach. Scattering from random rough interferences is studied throughout the first part of the thesis. Also, beyond the small perturbation method, the T-matrix method is also studied as an alternative approach that works for larger surface heights. Beside these, an alternative partially coherent approach is also introduced to significantly reduce the computational cost of the problem of layered media with random permittivity profile. The finite coherency length of the propagating wave inside the layered media is considered to divide the layered media into smaller blocks and then combine the block's responses afterward. In the second part we consider fast and broad band computation of the Green's function inside the cavity of irregular shape. Conventional way of computing the Green's function of an irregular shaped cavity is the numerical methods such as surface integral equation or finite element methods which can obtain the response at single frequency with intensive computational cost. The proposed method utilizes the imaginary wave number extraction of the Green's function from itself to develop a broad band and at the same time fast converging hybrid spatial-spectral expansion to achieve a highly accurate result for the Green's function whereas in computing the Green's function of cavity using numerical methods, a fine sweep over the frequency band is required to capture individual resonance line, the broad band solution provide the solution thousand times faster than the competitor methods. The last part of the thesis includes a classical electromagnetic treatment of the Casimir self-stress on nano tubes. Although the Casimir force on the parallel plates can be regularized by throwing away the bulk part of the full Green’s function, it is shown that such a regularization does not remove divergence of zero-point energy and the final stress is computed by applying further regularizations.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155155/1/mrsanam_1.pd

Bibliography of Lewis Research Center Technical Publications announced in 1991

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific engineering work performed and managed by the Lewis Research Center in 1991. All the publications were announced in the 1991 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

Bibliography of Lewis Research Center technical publications announced in 1992

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1992. All the publications were announced in the 1992 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Analysis of large antenna systems

The research presented in this thesis has been conducted within the framework of the Square Kilometre Array (SKA) project. SKA is a next generation radio telescope that will have a receiver sensitivity two orders of magnitude larger than the most sensitive radio telescope currently in operation. To meet the specifications, various low-cost low-noise actively beamformed receiving array antennas are being considered. A major problem in designing these systems is that the present-day commercially available electromagnetic solvers need an excessive amount of memory and simulation time to solve electrically large antenna problems. Moreover, it is essential to be able to analyze the receiver sensitivity of large antenna array systems to understand the sensitivity limiting factors. No dedicated commercial software tools exist that can analyze the receiver sensitivity of entire antenna systems specifically for radio astronomy. The thesis subject deals with two major challenges: (i) To accurately compute the impedance and radiation characteristics of realistically large and complex antenna arrays using only moderate computing power, particularly, of single and dual-polarized arrays of 100+ Tapered Slot Antenna (TSA) elements that are electrically interconnected. If the collection of these elements forms a subarray of a larger system, it is also of interest to analyze an array of disjoint subarrays. (ii) To characterize the system sensitivity of actively beamformed arrays of strongly coupled antenna elements. To address the above challenges, a conventional method-of-moments approach to solving an electric-field integral equation is enhanced using the Characteristic Basis Function Method (CBFM) to handle electrically large antenna problems. The generation of the associated reduced matrix equation is expedited by combining the CBFM with the Adaptive Cross Approximation (ACA) technique. Furthermore, because an overlapping domain decom270 Bibliography position technique is employed, Characteristic Basis Functions (CBFs) are generated that partially overlap to ensure the continuity of the current between adjacent subdomains that are electrically interconnected. While generating the CBFs, edge-singular currents are avoided by a post-windowing technique. Finally, a meshing strategy is proposed to optimally exploit the quasi-Toeplitz symmetry of the reduced moment matrix. The numerical accuracy and efficiency has been determined for numerous cases, among which a dual-polarized interconnected TSA array of 112 elements that has been fabricated and subsequently validated by measurements. The receiver system has been modeled by both a numerical and a semi-analytical method. The models account for a nonuniform brightness temperature distribution of the sky, mismatch effects, noise that emanates from amplifiers inputs and re-enters the system coherently through the mutually coupled antennas (noise coupling), beamformer weights, etc. Results are shown for a practical setup and design rules are derived which demonstrate that minimum receiver noise can be reached by noise matching the low-noise amplifiers to the active antenna reflection coefficient, rather than the passive one. Finally, it is demonstrated that the radiation efficiency of antennas is an important quantity that can degrade the system sensitivity severely. Nevertheless, a number of commercial software tools have shown to be inadequate as the computed efficiency exceeds 100%. A method is proposed which is numerically efficient and robust since it guarantees an efficiency below 100%

Terahertz and Millimetric Rectennas

In recent years, the energy market has witnessed increasing demand on green electromagnetic energy resources to meet the next generation devices requirements. While energy harvesting in the lower gigahertz band has witnessed many improvements leading to market-ready solutions, the terahertz harvesting is, still, in an immature state. As will be demonstrated later, the electromagnetic radiation frequency identifies the theory of operation and so the rectifiers are categorised, into lower and upper frequency bands. While the theoretical framework for the lower frequency rectifiers is more "uniform", there are many theories to explain the rectifier operation for upper frequency bands. For the latter case, Simmons and the transfer matrix method models are chosen and elaborated in more details. An optimisation framework that deploys the transfer matrix method to calculate the voltage-current relationship of a tunnelling diode and improve the relevant figures of merit will be also suggested. New and novel techniques leading to optimized wireless energy transmission will be elaborated. In this context, the time-modulated array technique will be considered and studied, for a range of frequencies extending to 28 GHz, as a possible substitution to the lossy linear phased array control circuits. The novel frequency-diverse array technique, leading to distance-dependent radiation pattern behaviour, will be also discovered. A market-ready solution for an efficient 2.4 GHz energy-harvesting device is presented and tailored to work in harsh electromagnetic environments. Starting from a simple and generic rectifier model, the design is upgraded to reach an end-product prototype together with its measurements in a real-world scenario. In the end, an efficient and fast simulation method capable to calculate the received power by wireless sensors is also presented. Thanks to the integral solver simulation, the results are more accurate than typical finite difference simulation and are obtained much faster as demonstrated in the corresponding chapter