In this paper, it is demonstrated how anisotropic and inhomogeneous magnetic metamaterials may be used for molding the flow of the magnetic field, considering magnetic field shielding as the main application of practical interest. It is shown that using anisotropic materials, magnetic field shielding may be improved, and this anisotropy can be realized by metamaterials. Introducing additional inhomogeneity in the metamaterial can increase the shielding performance even more. The required parameters for inhomogeneity may be obtained by representing the shielding problem in matrix form, using a quasi-static magnetic field approximation. Finally, some comments on the practical implementation of the metamaterial and comparisons with the standard shielding techniques are given.

The influence of random fluctuations in the layer thicknesses in high contrast, one-dimensional Photonic Crystals (PCs) on the transmission spectra and Photonic Band Gaps (PBGs) is investigated. The change in the PBGs depends on the magnitude of the fluctuations and increases with an increase in the order of the PBG. Introducing thickness non-uniformity into the PC of up to 0.004 times the value of lattice constant for different types of fluctuation distributions has a negligible effect on either the position or the shape of the 1st and nearest PBGs. The approach suggested here allows the determination of the tolerances required in the geometrical parameters of PCs during fabrication. It also allows the optimisation of PC structures using high order PBGs.

This paper presents a comparative study of neural network (NN) training. The trained NNs are used as adaptive beamformers of antenna arrays. The training is performed either by a recently developed method called Mutated Boolean PSO (MBPSO) or by a well known beamforming method called Minimum Variance Distortionless Response (MVDR). The training procedure starts by applying the MBPSO and the MVDR to a set of random cases where a linear antenna array receives a signal of interest (SOI) and several interference signals at random directions of arrival (DOA) different from each other in the presence of additive Gaussian noise. For each case, the MBPSO and the MVDR are independently applied to estimate respective excitation weights that make the array steer the main lobe towards the DOA of the SOI and form nulls towards the DOA of the interference signals. The lowest possible value of side lobe level (SLL) is additionally required. The weights extracted by the MBPSO and the weights extracted by the MVDR are used to train respectively two different NNs. Then, the two trained NNs are independently applied to a new set of cases, where random DOA are chosen for the SOI and the interference signals. Finally, the radiation patterns extracted by the two NNs are compared to each other regarding the steering ability of the main lobe and the nulls as well as the side lobe level. The comparison exhibits the superiority of the NN trained by the MBPSO.

This paper presents a novel planar antenna with a reconfigurable radiation pattern. The proposed layout consists of N ≥ 2 monospaced planar bowtie antennas selected one by one by means of a pair of PIN diodes. Experimental results referring to the case of N=2 and N=4 are reported and discussed demonstrating the feasibility and effectiveness of the proposed design approach.

In this paper, a novel approach to design compact multi-band loop antennas is proposed. This type of antennas is composed of coplanar waveguide (CPW)-based composite right/left-handed (CRLH) quarter-wave type resonators, and developed on a vialess single layer. Both size reduction and low frequency ratios have been achieved, profiting from the employment of quarter-wave resonators and the high nonlinearity in the left-handed region of CRLH transmission line (TL) dispersion diagram. A sample prototype operating at three negative modes (1.92/2.15/2.64 GHz) with an overall size of 29 × 21.3 × 1.0 mm³ was manufactured and measured. Measured results show good agreement with EM simulation, exhibiting good impedance matching as well as stably omni-directional radiation patterns at the three operating modes.

Joint time-frequency analysis (JTFA) is applied to micro Doppler signatures generated by jet engine modulation (JEM) effect using a modified Hilbert-Huang transform (HHT). The modified HHT is developed to improve the JTFA results of measured JEM signals. Wavelet decomposition (WD) with Meyer wavelet function is considered as a supplementary process of the HHT. The modified HHT examines a signature obtained from simulation of a jet engine CAD model, and is then applied to the signatures obtained from measurement of two realistic jet engine models. The modified HHT gives more improved JTFA results of the measured JEM signals than those from the simple short-time Fourier transform - (STFT) based analysis. The modified HHT-based JTFA approach is expected to be significantly useful for enabling high-quality radar target recognition in a real environment by complementing other traditional analyses.

Tapered dielectric fibers are widely used in the near field microscopy to focus the incident beam or collect near field signal. Single mode is always required so that the geometrical dimension of the waveguide is smaller than the wavelength. This paper proposes an inexpensive and easy fabrication of multimode tapered Teflon probe which has bigger dimensions than the wavelength. The field distribution in and outside the probe is analyzed by the total internal reflection theorem and solid core circular dielectric waveguide theory. Simulations are carried out in Microwave Studio CST. Novel applications based on focal points in and outside the probe are discussed, especially dielectric permittivity sensing of biomolecules using a capillary tube is emphasized by the simulations and experiments.

Applications of localized surface plasmon resonance (LSPR) such as surface enhanced Raman scattering (SERS) devices, biosensors, and nano-optics are growing. Investigating and understanding of the parameters that affect the LSPR spectrum is important for the design and fabrication of LSPR devices. This paper studies different parameters, including geometrical structures and light attributes, which affect the LSPR spectrum properties such as plasmon wavelength and enhancement factor. The paper also proposes a number of rules that should be considered in the design and fabrication of LSPR devices.

This paper focuses on the electromagnetic compatibility domain, coupling in microwave circuits and wideband (WB) impedance matching in time domain using a purely temporal method, such as the centered-points Finite Difference Time Domain (FDTD). The paper here presents a new approach of WB impedance matching in transient regime and coupling context, of active circuits such as multiple complex nonlinear components (represented here by metal semiconductor field-effect transistors (MESFETs)), using Nonuniform Multiconductor Transmission Lines (NMTL) with frequency dependent losses and FDTD as modeling method. The FDTD method has several positive aspects such as the ease to introduce nonlinear components in the algorithm, the ease to use NMTL and the gain in simulation time and memory space. Also the FDTD method allows the study of WB impedance matching in time domain without recourse to the frequency domain. Systematic comparisons of the results of this method with those obtained by PSpice are done to validate this study. These comparisons show a good agreement between the method presented here and PSpice. The technique presented in this paper shows higher efficiency and ease to implement when compared to PSpice in regard to the treatment of frequency dependent losses, or shapes of transmission lines.

The observation data obtained from 4-D synthetic aperture radar system is sparse and non-uniform in the baseline-time plane. Hence, the imaging results acquired by traditional Fourier-based methods are limited by high sidelobes. Considering the sparse structure of actual target space in high frequency radar application, a novel 4-D imaging scheme based on compressive sensing is proposed in this paper. Firstly, the azimuth-slant range image is acquired by traditional pulse compression. Then, the basis matrix and the measurement matrix are constructed based on the sparse distribution of the radar positions and the signal form after the azimuth-slant range compression. Moreover, a weighted matrix related to the supporting field of the target is introduced to the cost function. Finally, the elevation-velocity image is reconstructed with this new cost function. Simulation results confirm the effectiveness of the proposed method.

The main purpose of this paper is to separately estimate the important surface parameters (soil moisture and roughness) by using full polarimetric bistatic measurements. The results provide a basis for new satellite application of future bistatic measurement systems such as the TanDEM-X satellite mission. Initially, bistatic X-band measurements, which have been recorded in the Bistatic Measurement Facility (BMF) at the DLR Oberpfaffenhofen, Microwaves and Radar Institute, will be presented. The bistatic measurement sets are composed of soils with different well-known statistical roughness scales and different moistures. The BMF has been calibrated using the Isolated Antenna Calibration Technique (IACT). The validation of the calibration was achieved by measuring the reflectivity of fresh water. In the second part, the assessment of the surface parameters (soil moisture and surface roughness) using the well calibrated data introduced in the former related part, will be detailed. The validation of the specular algorithm by estimating the soil moisture of two surfaces with different roughness scales will be reported. Additionally, a new technique using the coherent term of the Integral Equation Method (IEM) to estimate the soil roughness will be presented, as well as the sensitivity of phase and reflectivity with regard to moisture variation and therefore the penetration depth was evaluated. Current results demonstrate a non-linear relationship between the signal phase and the soil moisture, as expected, confirming the possibility of using DInSAR to measure variations in soil moisture.

A four-layer metallization Cr-Cu-NiP-Au with amorphous and nonmagnetic NiP as a barrier layer is one of the promising candidates for use in microwave integrated circuits. Multi-section Wilkinson broadband 1:2 power divider circuits are delineated photolithographically on alumina substrates metallized by Cr, TiW, Ni, NiP, copper and gold using different metallization processes. The adhesion and dc resistivity are compared for different metallization scheme. Testing and evaluation have been carried out for multi-section Wilkinson broadband 1:2 power divider in the 10 MHz-6 GHz frequency range for Cr-Cu-Au, TiW-Ni-Au and Cr-Cu-NiP-Au to see the effect of NiP. Insertion loss, return loss and isolation are measured and compared. The microwave properties do not show any appreciable differences due to the various metallizations.

A low profile CPW fed millimeter wave rectangular slot antenna operating with a wideband; centered at 94 GHz has been designed, fabricated and tested on a 10 μm silicon diaphragm. To improve the bandwidth of the conventional slot antenna a C-shaped tuning stub has been incorporated. Measurement results show that the antenna operates from 75 to 105 GHz with a reflection coefficient better than -10 dB. At its resonant frequency the fabricated slot antennas have a reflection co-efficient ranging from -25 dB to -35 dB. The bandwidth of the antenna with a tuning stub was found to be over 30% at -10 dB. By using the slot antenna with a C-shaped tuning stub the bandwidth has been shown to improve, which could be used for several Millimeter wave applications.

Using a new combined approach, the effect of the uniaxial anisotropic dielectrics on the resonant frequency and radiation field of an equitriangular patch antenna is presented in this paper. The problem is analysed in the spectral domain using the moment method and an electric field integral equation combined with a mathematical approach. However, the dyadic Green's functions corresponding to the proposed structure are separately developed and the Fourier transform of the basis current components are calculated mathematically using ``the reference element" method. Numerical results show that the change in the resonant frequency and the radiation patterns of the antenna is due primarily to a small disturbance of the substrate's nature. Then the effect of the uniaxial anisotropic materials is a significant parameter and most essential on the microstrip antenna characterization.

The Sources Reconstruction Method (SRM) is a non-invasive technique for, among other applications, antenna characterization. The SRM is based on obtaining a distribution of equivalent currents that radiate the same field as the antenna under test. The computation of these currents requires solving a linear system, usually ill-posed, that may be very computationally demanding for commercial antennas. Graphics Processing Units (GPUs) are an interesting hardware choice for solving compute-bound problems that are prone to parallelism. In this paper, we present an implementation on GPUs of the SRM applied to antenna characterization that is based on a compute-bound algorithm with a high degree of parallelism. The GPU implementation introduced in this work provides a dramatic reduction on the time cost compared to our CPU implementation and, in addition, keeps the low-memory footprint of the latter. For the sake of illustration, the equivalent currents are obtained on a base station antenna array and a helix antenna working at practical frequencies. Quasi real-time results are obtained on a desktop workstation.

In this paper, a hybrid method combining equivalence principle algorithm with physical optics is proposed to solve the radiation problem of antenna mounted on electrically large platform. It is based on domain decomposition method which is a scheme for multi-scale problems. Equivalence principle algorithm can simulate antenna accurately, and physical optics is an asymptotical method to obtain current distribution on the electrically large platform. Continuity of currents is considered when the conductor on the platform is decomposed into two parts by the equivalence surface. In addition, a preconditioning for the hybridization of equivalence principle algorithm and physical optics is discussed. Numerical results demonstrate the feasibility of the hybrid method.

In the previous works, based on winding function theory, the calculation of reluctance machine inductances is carried out using numerical integration or inexact analytical equations based on approximated Fourier series expansions of the inverse air gap function. In this paper, development in Fourier series of the inverse air gap function has not been used, but a closed form analytical equation is developed for inductances calculation. This leads to a very precise computation of the inductances of the faulted machine and more accurate results. Moreover, all space harmonics ignored by the Fourier series expansions of the inverse air gap function will be included in the model. Derived comprehensive equation allows calculating time varying inductances of reluctance machines with different static, dynamic and mixed eccentricities in the frame of a single program. Inductances obtained by the proposed method are compared to those obtained from FE results. A satisfactory match was found between them.

In this paper, we use the concept of stub loadings of planar microstrip antennas to convert a single band antenna into a dual-band antenna used for WLAN. We load a planar triangular monopole (PTM) antenna by combline stubs attached to the edges of patch in order to obtain a second resonance frequency. The simple PTM antenna is first designed to produce the lower resonance frequency and the geometry of combline stubs is then optimally designed to generate the higher resonance frequency to realize a dual-band or a wideband antenna. Three prototype models of PTM antennas are designed, fabricated and measured. Their performances verify the concept of inductive loadings of planar antennas by combline stubs for the realization of dual-band and wideband performance for WLAN.

A planar folded dipole antenna with triple-band operation for WLAN and WiMAX applications is proposed. It comprises a pair of symmetrical branch arms, which occupy a compact size of 35(L)x4(W) mm² to be easily embedded inside a portable device as an internal antenna. By properly designing the branch radiating strips, three operating bands covering 2.39-2.5 GHz, 3.3-3.94 GHz, and 5.06-6.06 GHz can be acquired with the antenna. Moreover, the antenna's resonance can be appropriately adjusted to optimize the radiation performance for actual application. A fabricated prototype of the proposed antenna is tested and analyzed. Experiments show that good omnidirectional coverage and stable gain variation to enhance communication quality for WLAN/WiMAX operations can be obtained with the antenna.

Despite its popularity, the conventional Vivaldi antenna has long suffered from some design problems, such as tilted beam, low or inconsistent directivity and gain, complicated design and fabrication methods, and limited size reduction. These setbacks make its progress lag on the fast track of technological demand. Thus, the antenna overall performance is anticipated to improve by incorporating negative index metamaterial (NIM) into the design method, plus, it is also tunable. In this study, the design uses linearly-tapered shape-loading structure, as its projected performance crucially depends on the space in between the antenna arms, a prerequisite to further boost its performance when combined with NIM technology. A unique slitting approach synchronizes the integration between the Vivaldi antenna and NIM where a single layer NIM piece is simply snugged into the slit perpendicular to the middle antenna substrate. The major improvement in the spotlight is the capability of NIM to focus the entire beam so that it can radiate to the targeted direction. The measurement results are similar to the simulations in terms of high gain, where the gain and directivity of the antenna are increased up to 4 dB. The contrast of overall performance between the plain modified Vivaldi antenna and the ones with NIM evidently asserts the expected contribution of snug and boost method applied and attests its significant potentials for a broad range of ultra-wideband applications.