In this paper, a method is proposed to compact waveguide devices at a desired frequency. In this method a previously designed hollow waveguide is filled with several dielectric and ferrite layers alternately so that the characteristic impedance of the waveguide is not changed. First, the permittivity and permeability of a fictitiously mixed material is obtained. Then, the required permittivity and permeability of dielectric and ferrite layers are obtained at desired frequency. The usefulness of the proposed method is verified using some theoretical and simulation examples.
In this paper, some studies on one-dimensional plasma photonic crystal (PPC) containing alternate layers of dielectric and micro-plasma have been presented. The band structures, reflectivity, group velocities and effective group index of such photonic crystals have been studied. For the purpose of computation, we have used transfer matrix method. In this study, we take two PPC structures named PPC1 and PPC2. In PPC1, we take SiO2 as the material for the dielectric layers whereas in PPC2, we take TiO2 as the material for the dielectric layers. It is found that the forbidden band gap(s) can be increased by increasing the thickness of plasma layers. The ranges of 100% reflection is found to be in the higher normalized frequency region in the case of PPC1 whereas in PPC2 the ranges of 100% reflection is found in the lower normalized frequency region. It is also found that for a certain normalized frequency, the group velocity becomes negative in both PPCs. However, the range of normalized frequency for which the group velocity is negative is larger in the case PPC1 than in PPC2. This abnormal behaviour of group velocities of both PPCs results in superluminal propagation (speed of EM wave in PPC greater than speed of light) of electromagnetic waves. Also, because of the abnormal behaviour of group velocity, effective group index becomes negative and possesses ultra high values. uch structures may be considered as a flip flop as there is positive and negative symmetry of effective group velocity. Also, PPC2 exhibits superluminal propagation for wider range of normalized frequency where there is superluminal propagation inside the structure as compared to that of PPC1.
In this paper, analysis of half U-slot loaded patch antenna with shorting wall is presented. The parameters of the antenna significantly depend on slot and notch dimensions. Bandwidth of the proposed antenna is found to be 21.59%. The 3dB beamwidth of the antenna is found to be 90o at the central frequency of 2.6 GHz. The theoretical results are compared with IE3D simulated and experimental ones which are in good agreement.
This paper establishes the extension of the method of auxiliary sources EMAS for the purpose of modeling the electromagnetic scattering response by jacket cylindrical structures constituted by a finite number of dielectric eccentric cylindrical inclusions embedded in a host dielectric one. Appropriate boundary conditions mixed with judicious decomposed domains leads to the prediction of the backscattering cross section. The algorithm also integrates the global electromagnetic coupling between the inclusions. The EMAS is validated by varying the inner cylinders repartitions and fine-tuning the electric permittivity according to different geometries. The EMAS level of accuracy compared with the indirect matching mode method IMM reveals a good agreement between the numerical computation results.
This paper provides a reliable dielectric measurement theory of the open resonator for non-planar objects such as convex-concave objects. It is the first time that the complete analytical formulas of the complex permittivity are presented by means of the second-order theory of the open resonator and field matching method. Furthermore, a measurement system is designed and built at Ka band, and the consistency of the results between planar and non-planar samples verifies the accuracy of the new theory. Finally, the experimental error analysis is investigated.
We propose a general method to determine the material parameters for arbitrary shapes of cloak based on the Poisson's equation to map the coordinate transformation. As a result, we can obtain the diverse deformation material properties and then the field distribution. This method, compared with the previous technique presented in literature, can determine the countless transformation forms, so it may provide the opportunity to choose the optimization transformation and the material parameter map which is easily to be fabricated using the metamaterial technology.
A new beampattern synthesis formulation is proposed to compute the minimum number of array sensors required. In order to satisfy all the prescribed specifications of the beampattern, the proposed method imposes linear matrix inequality (LMI) constraints on the beampattern as developed by Davidson et al., which remove the need to discretize the beampattern region. As the proposed formulation is quasi-convex, an iterative procedure is used to decompose it into a systematic sequence of convex feasibility problems, in order to find the minimum number of sensors. The proposed method guarantees convergence if the globally optimal solution lies in the search interval, which is easily ensured at the start of the search.
In this paper, we present a new electromagnetic modelling analysis based on the Analytical Spatial Method of Moments (AS-MoM) using roof-top basis functions and prove advantages of integrals' resolution in conjunction with technique that permit to reduce the number of unknowns in the MoM matrix and to minimize time and memory consumption. This technique takes into account the existence of TEM zones inside the structure and far from discontinuities. There, we represent the current under an exponential form to analyze wave's propagation inside the structure. The advantages of this contribution will be illustrated by numerical results.
The aim of this paper is to show the interest of using equivalence models for calculating the electric field produced by cylindrical capacitors with dielectrics. To do so, we use an equivalent model, based on the dual Maxwell's Equations for calculating the two electric field components created inside the capacitor and outside it. This equivalent model uses fictitious currents generating a electric vector potential that allows us to determine the electric field components in all points in space. The electric field produced by charge distributions as capacitor with dielectrics is generally determined by using the coulombian model. Indeed, it is well known that the electric field derives from a scalar potential. By using the Maxwell's equations, this scalar potential is in fact linked to the existence of charge distributions that are generally located on the faces of the capacitors. However, this last model does not allow us to obtain reduced analytical expressions since it involves the calculation of charge volume density appearing in the dielectric material for arcshaped cylindrical topologies. Consequently, it is interesting to look for another approach that gives analytical expressions with a lower computational cost. In this paper, we show that the use of fictitious currents instead of charges allow us to obtain 3D analytical reduced expressions with a lower computational cost. This analytical approach is compared to the coulombian model for showing the equivalence between the two approaches.
Two closed form approximations are given for mutual coupling between arbitrarily oriented slots with cosinusoidal distribution, using the known results for dipoles along with a new correction factor to account for the piecewise sinusoidal dipole current. Using these approximations, a scheme has been developed for calculating mutual coupling between practically used slots of arbitrary orientation and useful results are obtained from simple closed form expressions for slot separation of 1.2 × slot length or more depending upon the approximation chosen and the length of the slot. These approximations are found to be more accurate than those available in the literature, with a maximum error of less than 1.6% for slots shorter than 0.5 wavelength and separated by 0.85 × wavelength or more. Simple yet accurate expressions for mutual coupling, like the point dipole approximation developed here, result in efficient evaluation of mutual coupling for the design of large arrays of slots or for Electromagnetic Compatibility analysis.
Many applications of microstrip antenna are rendered by their inherent narrow bandwidth. In this paper a new approach is proposed to design inset feed microstrip antenna with slots in it to improve the antenna bandwidth. This paper deals with the design of slotted microsrip antenna on a substrate of thickness 1.588 mm that gives wideband characteristics using ANN. The illustrated patch antenna gives enhanced bandwidth as compared to antenna with out slots of the same physical dimensions. In the present work an Artificial Neural Network (ANN) model is developed to analyse the bandwidth of the example antenna. The Method of Moments (MOM) based IE3D software has been used to generate training and test data for the ANN. The example antenna is also designed physically with glass epoxy substrate with εr = 4.7 for few results for testing the artificial neural network model. The different variants of training algorithm of MLPFFB-ANN (Multilayer Perceptron feed forward back propagation Artificial Neural Network) and RBF -ANN (Radial basis function Artificial Neural Network) has been used to implement the network model. The results obtained from artificial neural network when compared with experimental and simulation results, found satisfactory and also it is concluded that RBF network is more accurate and fast as compared to different variants of backpropagation training algorithms of MLPFFBP.
An electromagnetic inversion method is proposed for the reconstruction of lossy dielectric slabs. The inversion is done using particle swarm optimization hybridized with Quasi-Newton algorithm. The inversion process is applied to reconstruct dielectric slabs with discrete or continuous profiles. Accurate reconstruction of lossy dielectric slabs is obtained from inversion of reflection coefficient data of normally incident plane waves in the specified frequency range. The proposed algorithm is also tested using noisy data and showed satisfactory performance.
Particle Swarm Optimization algorithm (PSO) is a popular stochastic searching optimization algorithm to solve complicated optimization problems. The approach of retrieving duct parameters from the sea-surface reflected radar clutter is also known as Refractivity From Clutter (RFC) technique. RFC technique provides the near-real-time duct parameters to evaluate the radio system performance, without adding any hardware. Basic principles of PSO and its applications and RFC technique are introduced. Evaporation duct is retrieved based on RFC technique using PSO. The performance of PSO is validated using experiment data launched at East China Sea, and compared with those of genetic algorithm (GA) and ant colony algorithm (ACA). The results indicate that PSO has the advantages of faster convergence and higher retrieval precision than the other two methods.
In this paper, for developing analytical and semi-analytical methods to evaluate band structure in photonic quasicrystals the perturbation theory is examined. It is shown that more isotropic and complete photonic band gap can be observed under low dielectric contrast for photonic quasicrystals in comparison with ordinary crystals and because of this feature of photonic quasicrystals, perturbation theory is suitable for evaluation of these structures. In this work, we show that using perturbation semianalytical method one can obtain complete band structure for quasicrystals that are interesting for terahertz technology especially and microwave and optical engineering too. Also, we investigate that complete band gap is appeared in quasicrystals in low refractive index contrast and with increasing number of fold in quasicrystals gap size and isotropy are increased.
In this paper, we have extended the recently introduced theory of coupled propagation of two coaxially co-propagating and mutually incoherent bright 1-D beams to coupled propagation of two 2-D (cylindrical) bright beams and investigated the propagation behavior and spatial soliton pair formation of such beams by a recently introduced simple approach. We have considered saturable form of the nonlinear medium in this paper as 2-D spatial solitons are unstable in Kerr type media. We found that many of the propagation features of two 2-D beams in saturable media are same that of 1-D beams in Kerr type media. However, many features are different and to the best of our knowledge, reported in this paper for the first time. The present version of the theory is applicable in all possible physical situations and parameters.
A new approach of imaging reconstruction of concealed PEC targets in a dielectric closed box, using azimuth multi-angle measurements, is developed. As the broadband stepped-frequency radar transmits planar wave from different azimuth directions around the target, the backscattered electrical fields in both the amplitude and phase are obtained. The two-dimensional fast Fourier transform (2D-FFT) algorithm for spline interpolation is adopted for uniformly sampled backscattering fields. Then, 2D images of a dielectric box with and without the concealed targets can be numerically simulated. Multi-azimuth backscattering electri- cal fields of complex shaped PEC targets and dielectric surrounding walls are calculated by the method of moments (MoM), which is based on the coupled volume-surface integral equation (VSIE). The concealed targets can be well identified from the imaging reconstruction.
In this paper, the wave propagation and the cutoff frequencies of a rectangular metallic waveguide, partially filled the metamaterial multilayer slabs have been studied. The equations of the TMM method are not complex and the numerical examples show that we can easily obtain the characteristics of the metamaterial multilayer's rectangular waveguide satisfyingly. The cutoff frequencies of the metamaterial waveguide show very different characteristics compared with the usual waveguide.
Photonic band structure and reflection properties of one-dimensional magnetic star wave-guide (MSWG) structure composed of a backbone (or substrate) waveguide along which a finite side branches grafted periodically have been investigated. The dispersion relation and hence the photonic band gaps (PBGs) of the magnetic SWG structure have been obtained by applying the Interface Response Theory (IRT). Investigation of dispersion characteristics shows that the existence of band gaps in magnetic SWG structures does not require the contrast in the wave impedance of the constituent materials, which is unlike the usual magnetic photonic crystal structure, where there must be the contrast in the wave impedance for the existence of the band gaps. Moreover, magnetic SWG structures have wider reflection bands in comparison to normal magnetic photonic crystal (MPC) structure for the same contrast in the wave impedance. Analysis shows that the width of forbidden bands for MSWG structure changes with the change in permittivity and permeability of the backbone, and side branches materials even the ratio of wave impedance is the same, but it remains the same in case of MPC structure. In addition to this, we have studied the effects of variation of number of grafted branches and substrates i.e., number of nodes on the reflection bands of magnetic SWG structure.
In this paper, inhomogeneous planar layers are optimally designed as reflection wave polarizers in a desired incidence angles range. First, the electric permittivity function of the structure is expanded in a truncated Fourier series. Then, the optimum values of the coefficients of the series are obtained through an optimization approach. The validation and the performance of the proposed structure are verified using some examples.
In this paper, the effective skin depth which provides a useful evaluation for field penetration in multilayer coated conductor is proposed. The reflection on the interface between the adjacent conductors is considered in theoretical derivation. It is found that the effective skin depths of the gold and gold-nickel coated copper rapidly vary with the thickness of the outer layer (gold) when the gold thickness is less than twice gold skin depths and achieve stabilization as the gold thickness increases to five times gold skin depths.