Microwave inverse scattering approaches have shown their effectiveness in imaging inaccessible regions. Unfortunately, the problem at hand is strongly non-linear and ill-posed and therefore it is often solved by seeking for the global minimum of a proper functional. Nevertheless, it is also necessary to introduce suitable regularizations in order to improve the convergence of the reconstruction process toward a reliable solution. In this context, the paper presents a method that exploits an energetic constraint to define a regularization term of the cost functional. A numerical validation with single and multiple inhomogeneous lossless targets demonstrates that an improvement of the reconstruction accuracy is achievable without introducing significant computational complexity to the inverse scattering problem.

Novel complementary split ring resonator (CSRR) is introduced to increase the stop bandwidth. Despite of their exotic behavior due to negative permittivity, their performance is limited by their stop bandwidth. The orientation of CSRR etched on the ground has strong coupling that can be altered for the increased stop bandwidth. The proposed design has measured stop band from 4~7.25 GHz whereas conventional CSRR of same dimension has stop band from 4.1~5.0 GHz.

In this paper, an innovative method for obtaining a pencil beam pattern is presented. Planar arrays of parasitic dipoles are used to modify the pattern of an active dipole above a ground plane, in order to obtain a pencil beam of moderate gain and bandwidth. Only one feed point and one active element provides a very simple feeding network that reduces the complexity of the antenna. The correct configuration of the elements of the parasitic arrays allows to obtain the desired pencil beam pattern. Three designs that use parasitic arrays fed by a λ/2-dipole and synthesize pencil beam patterns are shown: 1) an antenna designed at 1.645 GHz and composed by one layer of 49 parasitic elements; 2) an antenna designed at the same frequency but composed by two layers of 49 parasitic elements; 3) an antenna designed at 5 GHz, composed by one layer of 49 parasitic elements, and taking into account the dielectric substrate and teflon screws.

To analyze resonances in an axisymmetric inhomogeneous cavity, a higher-order finite element method (FEM) is developed. Mixed higher-order node-based and edge-based elements are applied to eigenvalue analysis for the azimuthal component and meridian components of the field, respectively. Compared with the lower-order FEM, the higher-order FEM can improve accuracy with the same number of unknowns and can reduce the CPU time and memory requirement for specified accuracy. Numerical results are given to demonstrate the validity and efficiency of the proposed method.

Analytical formula for the cross-spectral density matrix of a twisted electromagnetic Gaussian Schell-model (TEGSM) beam propagating through an astigmatic ABCD optical system in gain or absorbing media is derived based on the unified theory of coherence and polarization. Generalized tensor ABCD law in media is derived. As an application example, the evolution properties of the degree of polarization of a TEGSM beam in a Gaussian cavity filled with gain media are studied numerically in detail. It is shown that the behavior of the degree of polarization depends on the parameters of the gain media and the TEGSM beam. Our results will be useful for the spatial modulation of polarization properties of stochastic electromagnetic beam.

Electrically small oblate spheroidal and spherical antennas in confocal shells with negative permittivity represent perspective antenna design to combine moderately small size, wide bandwidth, high e±ciency and power of radiation. However, optimization of the antennas performance parameters imposes contradictory restrictions on permittivity of the shells, electrical size of the antennas, shape of the antennas and shells. Simulation results based on method of eigen-functions have shown that the antennas can be tuned on resonance for small magnitudes of negative permittivity of the shells and antiresonance for higher magnitudes. Optimal combination of power and efficiency of radiation of the antenna and the quality factor is obtained in an intermediate range of negative permittivity by combining merits of resonance and antiresonance of the antenna. Antiresonant range of the oblate spheroidal antenna emerges for lower permittivity magnitudes as compared with the spherical antenna. As a result, the optimal size of the shell of oblate spheroidal antenna is comparatively small. However, more gradual emerging of antiresonant properties of the spherical antenna makes spherical design more suitable for higher level of inherent absorption of the shell medium with negative permittivity.

A compact dual-mode open stub-loaded resonator and bandpass filter (BPF) is proposed in this paper. The resonator, which is formed by attaching a disc-shaped open stub and circular open stubs in pairs to a high impedance microstrip line, generates two operating modes in the desired band, and the even-mode resonance frequency can be flexibly controlled by the disc-shaped open stub at central plane, whereas the odd-mode one is fixed. The four transmission zeros are created to sharpen the rejection skirt, suppress two high harmonic resonant modes and deepen upper-stopband, respectively. Experimental results of the dual-mode filter which incorporates this resonator with parallel-coupled feed line with tuning stub at 5.8 GHz show good agreement with the simulated ones. The size for the resonator is only 4.7 × 3.4 mm (0.29λg×0.21λg in which λg is the guided wavelength of 50 Ω microstrip at 5.8 GHz).

This paper proposes a novel compact dual-band bandpass filter (BPF) using four spiral resonators for application in GSM and IEEE 802.11b WLANs for the first time. Since the two passbands can be tuned individually, the filter has more design freedoms. The symmetry coupling structure is realized to achieve a isolation higher than 30 dB between the lower and higher passbands. The full-wave simulator IE3D is used to design the spiral resonators and calculate the coupling coefficients of the basic coupling structures. The designed BPF is fabricated and measured. Good agreement between the simulated and measured results verifies our design concept.

This paper proposes magnetostatic analysis of Switched Reluctance Motor (SRM) under angular misalignment fault to evaluate the performance of the motor under different operating conditions. In this analysis three-dimensional finite element method (FEM) is used to simulate reliable and precise model by considering the complex motor magnetic geometry, end effects, axial fringing effects as well as nonlinear properties of the magnetic materials. The FE analysis is performed to obtain the static magnetic characteristics of SRM including flux density, flux linkages, terminal inductance and mutual inductance profile under different rotor positions for different varying degree of faults. Consequently, it presents assessing the features of mutual inductance in inactive phases to study the variations of diagnosis index. The results obtained present useful information regarding the detection of fault and its direction as well as the amount of angular misalignment fault in the motor. To the best knowledge of the authors, such an analysis has not been carried out previously.

The work is devoted to the problem of scattering of monochromatic electromagnetic waves on heterogeneous dielectric inclusions of arbitrary shapes. For the numerical solution of the problem, the volume integral equation for the electric field in the region occupied by the inclusion is used. Discretization of this equation is carried out by Gaussian approximating functions. For such functions, the elements of the matrix of the discretized problem are calculated in explicit analytical forms. For a regular grid of approximating nodes, the matrix of the discretized problem proves to have the Toeplitz structure, and the matrix-vector product with such matrices can be carried out by the Fast Fourier Transform technique. The latter strongly accelerates the process of the iterative solution of the discretized problem. Electric fields inside a spherical inclusion and its differential cross-sections are calculated and compared with the exact (Mie) solution for various wave lengths of the incident field. Internal electric fields and the differential cross-sections of a cylindrical inclusion are calculated for the incident fields of various directions and wave lengths.

In this paper, a novel compact quintuple-mode UWB bandpass filter (BPF) with sharp rejection skirt and wide upper-stopband performances is realized using stub-loaded multiple-mode resonator (MMR). The proposed resonator is formed by attaching two pairs of circular impedance-stepped open stubs in shunt and a pair of short-circuited stubs to high impedance microstrip line. By simply adjusting the radius of circular impedance-stepped open stubs and the lengths of short-circuited stubs, the first five resonant modes of the resonator can be roughly allocated within the 3.1--10.6 GHz UWB band meanwhile the high resonant modes in the upper-stopband can be suppressed. The short stubs in pairs can generate two transmission zeros near the lower and upper cut-off frequencies, leading to sharper rejection skirt outside the desired passband. Finally, a quintuple-mode UWB BPF is designed and fabricated, and the measured results demonstrate the feasibility of the design process.

In this paper, some common misconceptions in several papers dealing with the optimal design of multilayer microwave absorbers are indicated. Specifically, it is emphasized that Chew's recursive formula for the reflection coefficient of multilayer media for the TM polarization corresponds to the magnetic field, not the electric field. It is also emphasized that both TM and TE polarizations should have the same magnitude of the reflection coefficient for the case of normal incidence. Numerical optimal results are also presented and ompared with those existing in the literature.

Reverberation chambers are widely used in electromag-netic compatibility test facilities because they provide a large working volume and are cheaper than other types of test facilities. In addition, they provide a statistically uniform field and generate a high maximum electric field within a relatively large volume. The volume of the cavity, the structure of the stirrer, and high tested frequency must be used in the reverberation chamber appropriately. Changing a volume of cavity dimensions and test frequency can be difficult in the reverberation chamber because they were determined already in the design process. In these cases, the stirrer should be changed. We investigated of the effects of various stirrer angles and heights on a reverberation chamber. The optimization of the stirrer with respect to various stirrer parameters was investigated; these parameters are related to field uniformity, the quality factor, stirred efficiency, and electric field polarity. Our results suggest that a reverberation chamber can be successfully operated if careful decisions are made regarding the stirrer design.

The study of a planar circular slot antenna for Ultrawideband (UWB) communications is presented. The integration on this antenna of a notch filter, to reduce the possible interferences with the 5 GHz WLAN communications, has been discussed in detail. Four different structures, achieved by etching a suitable pattern on the antenna circular stub, have been considered, and their features have been compared. The antenna with symmetrical and inverted-L cuts shows the best performance, and it has been therefore realized and fully characterized. It shows very good matching features over the UWB band, and notable rejection of the 5 GHz WLAN band.

This paper proposes a novel multi-band monopole antenna for PDA phone. A simple inverted-U-shaped driven element operates frequency bands centered at 1710 and 2350 MHz, which achieve a bandwidth based on 6-dB return loss from 1550 to 2490 MHz sufficient for DCS, PCS, UMTS, and WLAN applications. A low frequency meander path and an impedance matching stub with a truncated slit located at ground plane operates frequency band centered at 910 MHz. The bandwidth from 868 to 995 MHz covers the GSM 900 application band. The design procedures and both simulated and measured results are presented and discussed in this paper.

The paper aims at solving the problem of plane electromagnetic waves scattered by N dielectric coated conducting strips. The method used is based on an asymptotic technique introduced by Karp and Russek for solving scattering by wide slit. The technique assumes the total scattered field from each coated strip as the sum of the scattered fields from the individual element due to a plane incident wave plus scattered fields from factious line sources of unknown intensity located at the center of every element. The line sources account for the multiple scattering effect. By enforcing the boundary conditions, the intensity of the line sources can be calculated. Numerical examples are introduced for comparison with data published in the literature.

Consider a TEM plane wave incident on a spherical multilayer structure, then the following theorem is valid. This theorem reveals a duality between permeability and permittivity of media in a spherical multilayer structure. Theorem: Consider a sphere with arbitrary radius and parameters s (ε₂,μ₂) surrounded by a homogenous medium with parameters (ε₁,μ₁). Then consider the case that each medium is filled by its dual medium according to the interchange ε_i↔μ_i. Then, the forward and backward radar cross sections of the structure are the same for the two dual cases. However, in half planes φ=((2k+1)π)/4;(k=0,1,2,3), the interchange ε_i↔μ_i has no similar effect on the value of the radar cross section.

The coupling between an irradiated aperture and a monopole antenna into a complex enclosure is investigated. The aperture is realized at the one side of the enclosure and the monopole antenna at the other side. The proposed study uses Babinet's principle to extend the Random Coupling Model to determine the radiation impedance of apertures. An experimental study is carried out using a computer box as an enclosure. A high intensity external electromagnetic radiation is applied to the aperture. The induced voltages is measured along the monopole antenna. The simulated probability levels of the induced voltages agree well with the experimental ones.

New formulas are presented for the reflection coefficient at the open end of a rectangular waveguide radiating into air including the effect of wall thickness or flange. Existing formulas require significant amount of numerical calculations and do not cover the practical range of waveguide dimensions. Reflection coefficients of open-ended standard waveguides are simulated using commercial electromagnetic software and curve-fitted to derive new formulas. Proposed formulas include the effects of waveguide wall thickness and broad-to-narrow wall aspect ratio. The accuracy of proposed formulas is compared with existing analytical, numerical and experimental results.

This paper presents a new methodology to model the near-ground short-range propagation loss in forested areas at the VHF and the UHF band. The path loss modeling is performed by an integration of the foliage induced effect and the effect from the radio-wave reflection/reflections. The analysis shows that the reflection from the dense tree canopy is important for short-range propagation at the VHF band and therefore, cannot be ignored. When taking into consideration the contribution from the possible tree-canopy reflection, the modeled path loss is reduced by more than 15 dB in the VHF band. A good agreement of the modeled path loss with the measured loss in tropical forested areas is achieved.