Scattering of electromagnetic waves by periodic stripe grating backed with a layer of metamaterial is considered. The distinguished feature of the structure is the association of periodicity of two scales: Micro scale that is the scale characteristic to metamaterial of the layer, and the scale of periodic metal stripe grating that is of the scale of wavelength of incident electromagnetic field. Such association gives rise to new type of resonant phenomena such as "crowding" of resonant transmission/reflection peaks in the vicinity of characteristic frequencies of the structure. The study of the problem is performed on the base of rigorous and accurate solution to the diffraction and spectral problems, which guarantees the robustness of numerical algorithm; and allows asymptotical analytical analysis of the problem and prediction of various resonant phenomena.
The purpose of this paper is to explain an exact derivation of apparent power in n-sinusoidal operation founded on electromagnetic theory, until now unexplained by simple mathematical models. The aim is to explore a new tool for a rigorous mathematical and physical analysis of power equation from the Poynting Vector (PV) concept. A powerful mathematical structure is necessary and Geometric Algebra offers such a characteristic. In this sense, PV has been reformulated from a Multivectorial Euclidean Vector Space structure (CG_{n}-R^{3}) to obtain a Generalized Poynting Multivector (S). Consequently, from S, a suitable multivectorial form (P and D) of the Poynting Vector corresponds to each component of apparent power. In particular, this framework is essential for the clarification of the connection between a Complementary Poynting Multivector (D) and the power contribution due to cross-frequency products. A simple application example is presented as an illustration of the proposed power multivector analysis.
In this paper, a novel version of the transverse wave approach (TWA) based on two-dimensional non-uniform fast Fourier mode transform (2D-NUFFMT) is presented and developed for full-wave analysis of RF integrated circuits (RFICs). An adaptive mesh refinement is applied in this advanced TWA process and CPU computation time is evaluated throughout 30 GHz patch antenna, application belonging to wireless systems. The TWA in its novel version is favorably compared with the conventional one in presence of AMT technique in the context of EM simulations. Another version of TWA is outlined to illustrate a computationally efficient way to handle an arbitrary mesh for RFICs analysis with high complexity problems.
Linear and circular arrays are optimized using the particle swarm optimization (PSO) method. Also, arrays of isotropic and cylindrical dipole elements are considered. The parameters of isotropic arrays are elements excitation amplitude, excitation phase and locations, while for dipole array the optimized parameters are elements excitation amplitude, excitation phase, location, and length. PSO is a high-performance stochastic evolutionary algorithm used to solve N-dimensional problems. The method of PSO is used to determine a set of parameters of antenna elements that provide the goal radiation pattern. The effectiveness of PSO for the design of antenna arrays is shown by means of numerical results. Comparison with other methods is made whenever possible. The results reveal that design of antenna arrays using the PSO method provides considerable enhancements compared with the uniform array and the synthesis obtained from other optimization techniques.
An E-wave excites longitudinal conductivity currents in a waveguide filled with lossy medium. Total flow of this current through a cross-section is nonzero for odd E-modes; it means that some charge is transported by the pulse along the waveguide. This phenomenon is considered in the paper using analytical approach based on mode expansion of the fields in Time Domain (known as Mode Basis Method) and using Finite Difference in Time Domain method (FDTD). Volume conductivity charges being moved by the pulse wave are determined. In order to set the problem as much physically as possible we consider diffraction of a pulse E-wave on the boundary between a hollow waveguide and a waveguide with conductive medium. Behavior of the transient fields and surface charges at the interface are also examined. It is shown that an incident pulse wave excites a surface wave at the interface that results in transversal resonance with relaxation time much greater than that of the conductive medium. Characteristics of the travelling charge pulse wave are studied based on the obtained closed-form solution.
The patch shape influence on the radar cross section (RCS) of a cylindrical microstrip antenna (CMA) is discussed. The RCS of the CMA is evaluated from a plane wave scattering problem solution to a cylindrical microstrip antenna. The method of moments is employed in the spectral domain using sub-domain basis functions. It is shown that the patch shape has a pronounced effect such that new resonance modes appear at frequencies substantially shifted towards the low-frequency end compared to a cylindrical rectangular patch.
This paper presents a comprehensive location scheme in a rich multipath environment. It is based on the estimation of the distance between two wireless nodes in line-of-sight (LOS) from the best statistical estimator of the round-trip time (RTT), assuming a linear regression as the model that best relates this statistical estimator to the actual distance. As LOS cannot be guaranteed in an indoor environment, the effect of non-line-of-sight (NLOS) is mitigated by a two-step correction scheme. At a first step, the severe NLOS error is corrected from distance estimates applying the prior NLOS measurement correction (PNMC) method. At a second step, a new multilateration technique is implemented together with received signal strength (RSS) information to minimize the difference between the estimated position and the actual one. The location scheme coupled with measurements in a real indoor environment demonstrates that it outperforms the conventional time-based indoor location schemes using neither a tracking technique nor a previous calibration stage of the environment and no need for time synchronization between wireless nodes.
The objective of this paper is all-angle artificial magnetic conductor, i.e., artificial magnetic conductor that has stable magnetic-wall effect with respect to the incidence angle. Furthermore, we seek for a design that would be easy for manufacturing. In order to achieve this we use grounded uniaxial material slabs and we do not constrict ourselves to naturally available materials. Instead, we assume that the desired parameters can be synthesized using the emerging artificial electromagnetic materials. It is found that it is possible to have an all-angle magnetic-wall effect for both TE and TM polarization. Especially for the TM fields the structure would be easily manufacturable. The proposed structure has similar appearance as more well-known artificial impedance surfaces, but the design parameters and the physical properties behind the magnetic wall effect are novel. The performance of the proposed artificial magnetic conductor is verified with numerical simulations. This paper introduces a new approach how to obtain a magnetic-wall effect. It is possible to use this this approach also together with other ways of obtaining the magnetic-wall effect for dual-band operation.
Present paper utilizes the time evolution for estimating the soil moisture and vegetation parameter with Radar remote sensing data. For this purpose, vegetation ladyfinger has been taken as a test field and experimental observations have been taken by bistatic scatterometer at X-band in the regular interval of 10 days for both like polarization (i.e., Horizontal-Horizontal, HH-; Vertical-Vertical, VV-) and at different incidence angles. At this interval, all the vegetation parameters and scattering coefficient have been recorded and computed. Three similar types of field of size 5 x 5 m have been especially prepared for this purpose. The observed data is critically analyzed to understand the effect of incidence angle and polarization effect on scattering coefficient of the ladyfinger. It is observed that VV-polarization gives better result than HH-polarization and incidence angle 55^{ο} is the best suited to observe composite effect of vegetation ladyfinger biomass (Bm) and vegetation covered soil moisture at X-band. This analysis is further used for retrieval of soil moisture and biomass of ladyfinger using Neural Network. The important aspect of the retrieval algorithm is that it includes the time evolution. The retrieval results for soil moisture and Bm are in good agreement with the actual values of the soil moisture and biomass.
Inaccurate range estimates often restrict indoor positioning systems, resulting in a more remarkable drawback when using an already-deployed IEEE 802.11 network. This is the case of the time delay based location system that this paper deals with. The main causes of these inaccuracies are multipath and non-line-of-sight (NLOS) effects. These effects can be solved to a large degree by characterizing arrival times and range estimation errors. For this reason, this paper analyzes multipath and NLOS effects involved in the round-trip time (RTT) discrete measuring process, which is conducted before each range estimate. RTT observations obtained in this process for different real indoor environments provide useful statistical information that allows making the work extendable to other similar scenarios. Moreover, from this statistical information, the nodes in the network can estimate several parameters of the range estimates distribution while performing the location process. These are used to reduce the error caused by multipath components and to predict and correct the NLOS biases produced. In this way, the NLOS error is dynamically estimated and corrected, achieving better results than classical approaches based on static parameters.
Composites containing conducting inclusions are required in many engineering applications, especially, for the design of microwave shielding enclosures to ensure electromagnetic compatibility and electromagnetic immunity. Herein, multilayer shielding structures are studied, with both absorbing and reflecting composite layers. In this paper, fiber-filled composites are considered. For modeling absorbing composites with low concentration of conducting cylindrical inclusions (below the percolation threshold), the Maxwell Garnett theory is used. For reflecting layers, when concentration of inclusions is close to or above the percolation threshold, the McLachlan formulation is used. Frequency dependencies for an effective permittivity are approximated by the Debye curves using a curve-fitting procedure, in particular, a genetic algorithm.
A gas will breakdown in a high electric field and the mechanisms of this breakdown at DC and high frequency fields have been an object of study for the past century. This paper describes a method to induce breakdown in a uniform microwave field using a reentrant sub-quarter wave resonator. Slater's theorem is used to determine the magnitude of the threshold electric field at which breakdown occurs. The breakdown threshold is modeled using the effective electric field concept, showing that breakdown varies with pressure as E_{bd}=CP^{m} (1+(ω/ B·P)^{2})^{1/2} where P is the pressure, B and C are fit parameters, and m was found experimentally to equal 1/2. This function exhibits a minimum at P_{min}=ω/B. Breakdown data from the literature for nitrogen at various microwave frequencies were found to exhibit breakdown minima at the pressure predicted by our own determination of B, further validating the model.
The excitation of metamaterial and non metamaterial, Electromagnetic (EM) modes and fields in an anisotropic, parallel plate waveguide (meeting Dirichlet and Neumann boundary conditions), is studied, using a modified coordinate transformation [3, 4] which reduces Maxwell's equations to the form of a Helmholtz wave equation satisfying Dirichlet and mixed-partial derivative boundary conditions. The EM modes and fields of the system are excited by a novel, slanted electric surface current excitation (Figs. 1 and 2) whose slant angle has been chosen to coincide with the surfaces of constant phase of the anisotropic modes which may propagate in the waveguide. Also presented, for comparison purposes, is the EM field excitation analysis of an isotropic parallel plate waveguide whose dimension, operating frequency, and source is identical to the anisotropic waveguide and whose material parameters are very close to those of the anisotropic waveguide. The analysis consists of several parts. Sections 1 and 2 of the paper describe the Helmholtz wave equation and boundary conditions that arise from use of the modified, coordinate transformation. In Section 3 the modal characteristic equation of the system is derived and in Section 4 this equation is solved to determine the propagating and complex (or non propagating) modes that may exist in the waveguide. For the anisotropic material parameters chosen in the paper, in Section 4, one of the propagating modes of the system was shown to be a metamaterial mode (also called a backward traveling wave, phase velocity and direction of real, positive power flow in opposite directions). An analysis in Section 4 was also presented from which the cutoff frequency of the waveguide could be determined. Sections 5-8 of the paper were concerned with using the complex Poynting theorem and an EM complex power reaction equation to study complex power and energy in the waveguide. The complex Poynting theorem and the reaction equation were also used to derive several power and reaction orthogonality relations that exist between the propagating (including non metamaterial and metamaterial modes) and complex modes of the systems. Using the orthogonality relations derived in Sections 5-8, in Section 9, an efficient matrix analysis based on the reaction equation of Section 8 from which the EM modes excited by a given slanted electric surface current (Section 5) could be determined is presented. The reaction-matrix analysis and the matching of EM boundary conditions near an electric surface current source were shown to be directly related. In Section 10, for comparison to the anisotropic waveguide study under consideration, a Green's function analysis was used to determine the EM fields that would be excited in an isotropic waveguide having EM characteristics similar to that of the anisotropic waveguide. In Section 11 wavenumber and modal orthogonality results were presented and in Section 12 the EM fields corresponding to a specific electric surface current example were calculated for both the anisotropic and isotropic waveguides. In Section 11, six tables of data for the anisotropic and isotropic cases giving numerical examples of the modal wavenumbers that were calculated for the propagating and complex modes of the system (Tables 1 and 2), numerical examples of the modal orthogonality relations that the waveguide modes satisfied (Tables 3 and 4), and numerical examples of the modal power that was transmitted by different propagating modes for anisotropic waveguide case (Table 5) and isotropic waveguide case (Table 6) were presented. In Section 12 for both the anisotropic and isotropic waveguides cases studied, plots of the EM fields near the surface current were shown to meet EM boundary conditions near the electric surface current and near the waveguide walls to a high degree of accuracy. The conservation of complex and reaction power as delivered by and radiated from the electric current source was observed to hold for both the anisotropic and isotropic waveguides studied to a high degree of accuracy.^{}
In this paper, an electromagnetic model based upon the method of auxiliary sources is developed around multilayered structures without any restriction of physical and geometrical macroscopic parameters. Thus, the multilayered structure is considered as a superposition of a finite number of strongly coupled and recovered layers. The extended method of auxiliary sources EMAS is tested for a dielectric shell, a multilayered dielectric cylinder for different medium conductivities and a conducting cylinder coated with a dielectric or a metamaterial. Furthermore, we validate that the coupling between far layers can be neglected for lossy mediums. Numerical results computed in this paper reveal the validity and the accuracy of the aforementioned model in comparison with moment and hybrid methods.
varactor tuned printed planar inverted F antennas (PIFA) are investigated. The lowprofile printed antennas are fabricated together with the layouts of its DC control circuits and other RF/base-band circuit footprints. A surface mounted (SMT) varactor is applied as a frequency-tuning element at the middle of the long radiating arm in PIFA. Passive lumped DC bias circuits are implemented with good isolation. Both single and dual-band varactor tuned PIFA antennas are investigated. For a single-band PIFA, prototype designs show the in-band frequency (return loss is <10 dB) is tunable from 1.6 GHz to 2.3 GHz when the bias voltage varies from 0 V to 9.5 V. Measured results show about 70~75% efficiency and 2~3 dB maximum gain. For a dual band PIFA with two varactor loadings, both the 800~900 MHz and 1.7~2.2 GHz bands are tuned individually by a varactor. By varying low-band capacitance, the operation frequency is tuned from 780 MHz to 1020 MHz, with little change on the higher frequency band. By varying high-band capacitance, the operation frequency is tuned from 1700 MHz to 2140 MHz, with little change on the lower frequency. Measurement shows antenna radiation efficiencies within operation bands are about 55% at the low band and about 45% at the high band. The proposed frequency reconfigurable antennas could be useful for personal mobile terminal applications.
Two planar monopole antennas with wide impedance bandwidth are designed. A full-wave method of moment (MoM) based on the electric field integral equation (EFIE) is applied to analyze the impedance bandwidth and radiation performance of the monopoles. Meanwhile, the multilevel fast multipole algorithm (MLFMA) is employed to reduce the memory requirements and computational time. Experimental results such as the impedance bandwidth and radiation patterns are also presented. The good agreement between the experimental and numerical results well demonstrates the efficiency and accuracy of the MLFMA code. Both the experimental and numerical results show that the two planar monopole antennas possess good input impedance and radiation performance over the AMPS, GSM900, and DCS band. As the proposed antennas can achieve such wide impedance bandwidth with relatively low profile, they are very suitable for multi-band mobile communication systems.
An exact form for the equivalent edge current is derived by using the axioms of the modified theory of physical optics and the canonical problem of half-plane. The edge current is expressed in terms of the parameters of incident and scattered rays. The analogy of the method with the boundary diffraction wave theory is put forward. The edge and corner diffracted waves are derived for the problem of a black half-strip.
High frequency field expressions are derived at the focal points of a paraboloidal reflector placed in a homogenous and reciprocal chiral medium. Firstly Geometrical Optics (GO) field expressions are derived for the paraboloidal reflector placed in chiral medium. As the GO fails at the focal points, so Maslov's method has been used to find the field expressions which are also valid around the focal point. By using hybrid space, Maslov's method combine the simplicity of ray theory and the generality of Fourier Transform method. Some numerical results including contour plots and line plots around the focal region of paraboloidal reflector placed in chiral medium are obtained using the derived expressions.
In a dual-plane compact electromagnetic band-gap (CEBG) microstrip structure, patches are etched periodically in the ground plane to prohibit the propagation of electromagnetic waves in certain frequency bands so as to provide filtering functionality. However, the existence of the etched patches in the ground plane becomes a natural concern for the reason that these structures might be more prone to electromagnetic interference from nearby radiating components as compare to a microstrip filter with a perfect ground plane. In this paper, an investigation into the electromagnetic susceptibility of a C-EBG filter structure is presented. This study examines the effects of the the interference source on the performance of a C-EBG structure in terms of the relative frequency, power level, position, and polarization. From the study, useful guidelines are drawn for the applications of EBG microstrip structures in an environment rich in electromagnetic interference.
This paper presents an efficient and simple approach of implementing the Landau-Lifshitz-Gilbert (LLG) equation of magnetisation motion within the Finite-Difference Time-Domain (FDTD) method. This combined electromagneticmicromagnetic simulation technique is particularly important for modeling electromagnetic interaction with lossy magnetic material in the presence of current and magnetic sources, particularly at very high frequencies. The efficient implementation involves simple two-point spatial interpolations that are applicable to two and three-dimensional FDTD grids, and uses a stable iterative algorithm for the time integration of the LLG equation. A ferromagnetic resonance numerical experiment on a rectangular Permalloy prism excited through its cross-section by a non-uniform pulse field from a transmission line was carried out for the purpose of verifying the combined FDTD-LLG computations. The numerical results were in good agreement with linearised analytical solutions of the LLG equation for uniform and non-uniform precession modes. This paper also presents a brief investigation on the use of non-staggered FDTD grid schemes to model magnetic material using the LLG equation, and indicates that the classical FDTD staggered scheme offers simplicity in implementation and more accuracy for modeling wave interaction with lossy magnetic material than the non-staggered schemes based on Maxwell's equations formulation.