We apply the method of the Broadband Green's Functions with Low wavenumber extraction (BBGFL) to calculate band diagrams in periodic structures. We consider 2D impenetrable objects placed in a 2D periodic lattice. The low wavenumber extraction is applied to the 2D periodic Green's function for the lattice which is used to formulate the surface integral equation. The low wavenumber extraction accelerates the convergence of the Floquet modes expansion. Using the BBGFL to the surface integral equation and the Method of Moments gives a linear eigenvalue equation that gives the broadband (multi-band) solutions for a given point in the first Brillouin zone. The method only requires the calculation of the periodic Green's function at a single low wavenumber. Numerical results are illustrated to show the computational efficiency and accuracy of the method. Because of the acceleration of convergence, an eigenvalue problem with dimensions 49 plane wave Floquet modes are sufficient to give the multi-band solutions that are in excellent agreement with results of the Korringa Kohn Rostoker (KKR) method. The multiband solutions for the band problem and the complementary band problem are also discussed.

In the past few years, several satisfying various objectives and designs of reconfigurable integrated microwave filter and antenna have been proposed for wireless communication systems. Several designs are new concepts and techniques, whereas others are inspired from previous works. The improvement concepts of these designs can be reviewed from this compilation of studies. This paper begins with an explanation of the reconfigurable filter, reconfigurable antenna and reconfigurable integrated microwave filter and antenna, followed by discussion on several designs in terms of size, measurement, performance and technology used. Among various designs, reconfigurable on planar structures are extensively used because of their simple design procedures and easy to tune on the desired frequency, bandwidth and attenuation. Most of the existing studies are focusing tunable on single element, i.e. either on filter or antenna side; however, it limits the tunable range and flexibility of the filtering antenna response. An alternative design of filtering antenna can be suggested to produce reconfigurable tuning capabilities on both microwave filter and antenna to produce overall good performance for multifunction operation in RF/microwave applications.

In this manuscript, a reduced size, ground slotted monopole antenna, operating in the range of 3.1-10.6 GHz is designed and implemented for breast cancer detection using time reversal MUSIC. A homemade breast mimicking phantom has been experimentally designed to facilitate the detection implementation. The simulated and measured results are in good agreement. The slots and blending edges of the ground, along with the feed step are some techniques applied to the designed antenna in order to achieve a broad bandwidth and reduce considerably the reflection coefficient. The resulting dielectric constant from the breast phantom is relatively close to the real normal breast tissues. After the design has been completed, some techniques of time reversal MUSIC were employed to mimic the breast cancer detection. The experimental results show that both temporal and spatial images of the cancer (tumor) are well represented here.

In this work, a numerical solution of nonlinear ferromagnetic problems is formulated using the three-dimensional time-domain finite element method (TDFEM) combined with the inverse Jiles-Atherton (J-A) vector hysteresis model. After a brief introduction of the J-A constitutive model, the second-order nonlinear partial differential equation (PDE) is constructed through the magnetic vector potential in the time domain, which is then discretized by employing the Newmark-β scheme, and solved by applying the Newton-Raphson method. Different Newton-Raphson schemes are constructed and compared. The capability of the proposed methods is demonstrated by several numerical examples including the simulation of the physical demagnetization process, the prediction of the magnetic remanence in the ferromagnetic material, and the generation of higher-order harmonics.

In this article, the design and analysis of a compact asymmetrical coplanar strip (ACS) feed multiband monopole antenna operating over the frequency range of Bluetooth/IMT-E (2.4-2.484/2.5-2.6 GHz), worldwide interoperability for microwave access (WiMAX: 3.3-3.6 GHz) and wireless local area network (WLAN: 5.15-5.825 GHz) for Personal Wireless Communication Systems (PWCS) applications has been investigated. The proposed antenna consists of a semi-circular arc and L-shaped stub which forms a vertically flipped G structure that facilitates the multi-band operation at 2.4 GHz and 3.5/5.5 GHz respectively. The antenna is fabricated on a low cost FR-4 substrate having thickness of 1 mm and has compact dimensions of 24 × 10 mm². The proposed antenna yields a highly isolated measured impedance bandwidth of 2.3-2.7 GHz, 3.25-3.65 GHz and 5.1-6 GHz for Bluetooth/IMT-E, WiMAX and WLAN bands respectively and exhibits symmetrical radiation pattern, stable gain across all operating frequency bands which makes the antenna a suitable candidate for PWCS applications.

An approach is proposed for determination of the complex permittivity and permeability of low-loss materials, eliminating half-wavelength resonances occurring in transmission/reflection (T/R) measurements. To this end, we apply the time-domain smoothing for removing resonant artifacts from the wave impedance obtained with the conventional T/R method, with an assumption that we do not have such artifacts in the refractive index. Accordingly, the permittivity and permeability are found from the smoothed wave impedance and conventional refractive index. In this paper, our method is validated by measurements for two different low-loss materials, nylon and lithium ferrite, and those results are discussed. Further, results from the present approach are compared to those from the approximate approach derived in our previous work.

This paper presents a new non-rare-earth axial-field magnetic variable gear (MVG). By real-time changing the numbers of permanent magnet (PM) pole-pairs in the input and output rotors, the gear ratio becomes controllable. The key is to propose a new stationary ring integrated with magnetizing windings in such a way that various PM pieces can be independently magnetized to form different pole-pair numbers. After introducing the unique features of the non-rare-earth PM material aluminum-nickel-cobalt (AlNiCo), the proposed topology and design principle are discussed. By using finite element analysis, the electromagnetic performances of the proposed MVG under different gear ratios are analyzed. In particular, the corresponding torque transmission capability is assessed, and the influence caused by the introduction of the magnetizing windings is discussed. Hence, the validity of the proposed MVG can be verified.

The finite-element method (FEM) is applied to solve the EEG forward problem. Two issues related to the implementation of this method are investigated. The first is the singularity due to the punctual dipole sources and the second is the numerical errors observed near the interface of different tissues. To deal with the singularity of the punctual dipole sources, three source modeling methods, namely, the direct, the subtraction and the Saint Venant's methods, are examined. To solve the problem of numerical instability near the interface of different tissues, a modification on the Saint Venant's method is introduced. The numerical results are compared with analytical solution in the case of the multilayer spherical head models. The advantages of the proposed method are highlighted.

A subreflector system in the parabolic antenna of a 65 m radio telescope has been installed for compensating the gravitational deformation of the supporting frame in the antenna. This paper investigates the influence caused by the displacement of subreflector on the performance of the antenna and the corresponding compensation method. The investigation focuses on Ku-band frequencies and a new fitting formulation which is different from that of low-frequency bands is proposed to reduce the fitting error in the Y direction. In addition, the pointing deviation caused by the offset of the subreflector is analyzed and the model of pointing deflection caused by the displacement of subreflector is established, which can be used to improve the pointing accuracy. The model can determine the position and attitude of the subreflector with elevation and an extensive test shows that it can effectively improve the efficiency of the antenna at each elevation.

Time reversal techniques are based on the time reversal invariance of the wave equation. They use time-reversed fields recollected by an array antenna to perform imaging and focusing on the source of received signals. Two widely used time reversal techniques are DORT and time reversal MUSIC which are based on eigenvalue decomposition of the time reversal operator. We introduce a new time reversal technique based on independent component analysis (ICA). Time reversal ICA (TR-ICA) exploits the independence of scattered signals of the well-resolved targets to perform imaging. It breaks the mixed backscattered received signals to independent components by maximizing the non-Gaussianity of basic signals. The main advantage of this method is that imaging and focusing are achieved using only one transmitting antenna which simplifies the physical implementation drastically. We have simulated the performance of the introduced method in different scenarios such as selective focusing in the presence of scatterers with different materials, sizes and distances. In addition, the effect of noise on TR-ICA and through-the-wall imaging (TWI) are studied. Some of the results are compared to the DORT method. Finally, the validity of this algorithm is verified by performing physical measurements.

A novel design of wideband, ultra-thin, wide-angle metamaterial microwave absorber has been presented. The unit cell of the proposed structure is designed by using parametric optimization in such a way that absorption frequencies come closer and give wideband response. For normal incidence, the simulated FWHM bandwidth of the proposed structure is 1.94 GHz, i.e. from 5.05 GHz to 6.99 GHz and -10 dB absorption bandwidth is 1.3 GHz from 5.27 GHz to 6.57 GHz. The proposed structure has been analyzed for different angles of polarization, and it gives high absorption (more than 50%) for oblique angles of incidence up to 60˚. The designed absorber is in low profile with a unit cell size of λ₀/6 and ultrathin with a thickness of λ₀/32 at the center frequency of 5.92 GHz corresponding to 10 dB absorption bandwidth. The current and electromagnetic field distributions have been analyzed to understand the absorption mechanism of the absorber. An array of the proposed absorber has been fabricated and experimentally tested for various polarization angles and oblique incidences of electromagnetic wave. The proposed absorber is well suited for surveillance and other defense applications.

The dyadic Green's functions for magnetic and electric currents immersed in a parallel plate waveguide (PPWG) filled with dielectric-magnetic anisotropic uniaxial media are developed via a field-based approach. First, the principal Green's function is derived from the forced wave equation for currents immersed in an unbounded uniaxial media. Next, the scattered Green's function is developed from the unforced wave equation. Finally, the total Green's function is found by superposition and subsequent application of the appropriate boundary conditions. The Green's functions are derived from Maxwell's equations, using a spectral domain analysis and reveals several key physical insights. First, the expected longitudinal depolarization dyads are observed. The expected depolarizing terms arise through careful application of complex-plane analysis, leading to expressions that are valid both internal and external to the source region. Secondly, the identification and decomposition of the total Green's function into TE^z and TM^z field contributions is demonstrated. Thirdly, the mathematical forms of the principal and total Green's functions are shown to be physically intuitive. The primary contribution of this research is the development of the Green's functions for a parallel plate waveguide containing a dielectric and magnetic uniaxial medium directly from Maxwell's equations. Prior derivations considered dielectric-only uniaxial media in a parallel-plate waveguide, due to the relative ease of analysis and readily available inverse identities found in \cite{Chen_1983}. Inclusion of magnetic uniaxial characteristics adds considerable complexity (since no simplifying identities are available) and provides additional insight into the field behavior, thus representing a significant contribution to the electromagnetic analysis of complex media. Finally, practical applications of the Green's functions are considered, such as the non-destructive electromagnetic characterization of a variety of anisotropic uniaxial media.

Waveguide geometry is one of the most critical frequency Dispersive Scattering Centres (DSCs) in actual complex radar targets. Because of the occurrence of nonlinear dispersive scattering phase or range extension phenomena the nearby scatterers may be hidden in such cases. So, degradation of spatial resolution occurs in corresponding range profiles. According to a relatively simple parametric scattering model, a computationally efficient technique is introduced to analyze the complex range profiles including both backscattering field intensity and phase. The group delay of each scatterer is used as a criterion for discriminating the dispersive and non-dispersive ones. The wideband measured data samples are used for evaluating the technique, and the comparison is performed relative to Fourier-based results.

A Circularly Polarized (CP) high efficiency wide band Reflectarray (RA) antenna is designed for Ka-band using cross bow-tie elements. The reflected wave phase curve is obtained by anti-clockwise bowtie rotation. The linear phase curve with complete 360° degree is obtained when left-hand circularly polarized (LHCP) is incident normally in unit cell environment. The proposed method provides high gain, high aperture efficiency, wideband axial ratio (AR), in circularly polarized bow-tie RA using multiple copies of unit cell to form 25*25 antenna array. Before designing RA, the unitcell is analyzed, for oblique incidence to predict its bandwidth. The proposed antenna provided good performance in terms of Half Power Beam width HPBW, Side Love Level (SLL), cross polarization, gain bandwidth and AR bandwidth. A 25*25 bow-tie RA antenna provides the highest aperture efficiency of 57%, HPBW of 9.0 degrees, SLL -19 dB, cross polarization -27 dB. A 1-dB gain bandwidth of 32.5%, 3-dB gain bandwidth of 51.4% and 1.5-dB AR bandwidth of 32.9% while 3-dB AR bandwidth of 48.7% is achieved in simulation. These results are validated through fabricated cross bow-tie RA, and the measurements make good agreement with simulation results.

The eikonal equation for inhomogeneous anisotropic metamaterials with equal relative permittivity and permeability tensors (ε(r) = μ(r)) is derived from a free boundary variational principle. An original approach is proposed considering the wavefront as a moving discontinuity surface in an extended continuous media described by the Lagrangian density of electromagnetic fields. The eikonal equation arises as natural (non prescribed) boundary conditions for variational problems.

As we all know, traditional transmission electromagnetic pulse simulator has restricted test space problem. This paper proposes a new directed radiation fast rising time electromagnetic pulse (FREMP) simulator scheme which is based on transverse electric magnetic (TEM) wave antenna of a wire edge curl structure. Through numerical simulation, we study the influence of the parameters of wire edge curl TEM horn antenna and the effect of absorption resistance on radiation field. The simulation results show that the wire edge curl TEM horn antenna can effectively improve the ability of low frequency radiation. It can provide a theoretical support for developing FREMP simulator. We also demonstrate the feasibility of developing FREMP simulator using wire edge curl TEM horn antenna through experiments. Finally, the experimental results show that the radiation field of FREMP simulator developed by wire edge curl TEM horn antenna can meet high-altitude nuclear electromagnetic pulse (HEMP) requirements.

An improved mutual coupling calibration approach based on the element pattern reconstruction (EPR) method is proposed in this paper. Compared to previous calibration methods in which the calibration is carried out in the entire space, the space angle ranges to be calibrated in this method is partitioned according to the interested directions. Through the partition of the space angle region, the angle ranges to calibrate are narrowed, and thus more accurate calibration matrix can be obtained in corresponding angle regions. With the employment of the calibration matrix on 2-D DOA estimation, more effective mutual coupling calibration and more accurate DOA estimations are achieved by alternate iteration in each angle region. The validity of this method is verified by an L-shaped microstrip antenna array, and the performance of mutual coupling calibration is presented by the better accuracy in 2-D DOA estimations.

A new formulation of the Wave Concept Iterative Process (WCIP) method is presented in this work. This approach uses an analysis with the longitudinal components instead of the transverse components. This approach includes decomposing the transverse TM modes into two longitudinal terms: the TM and TEM modes. This approach is applied to model a Vertical Interconnect Access VIA hole. The current density behavior is studied in the two cases with and without VIA hole. Also this method is used to study a SIW slot antenna. Compared to those obtained by available published data, our results show that the proposed method gives convincing results.

A terahertz (THz) antenna is proposed that offers high input resistance and gain in the presence of an electrically thick GaAs substrate. The antenna is centrally fed using two vertical probes connected to a photomixer on a thin low temperature grown gallium arsenide (LTG-GaAs) film which is supported by the GaAs substrate. An input impedance of ~3.3 kΩ has been achieved using a dipole antenna that is printed on a thin dielectric slab, and isolated from the supporting substrate using a metal ground plane. A square aperture has been introduced to facilitate the illumination of the photomixer with two laser beams. Furthermore, a frequency selective surface (FSS) has been incorporated in the configuration, which results in a broadside gain of ~19 dBi at a resonance frequency of 0.97 THz.

In this paper, a frequency-domain-based transient electromagnetic model of grounding system in horizontally stratified multilayer medium is presented. The basis of the model is an improved version of the time-harmonic electromagnetic model of grounding system. Using the originally developed continuous numerical Fourier transform algorithm, the results obtained by the time-harmonic model are synthesized into a complete time domain solution. The presented model features very high accuracy and fast execution speed and is validated through several numerical examples.