The design, fabrication, and characterization of an amulti-section impedance transformer using Klopfenstein tapering method is presented. The transformer is employed in a Ka-band traveling-wave tube (TWT)for radar applications. The Klopfenstein tapering provides the shortest length between the two different impedance levels with continuous tapering sections.

This paper proposes and designs a new method of dualband omnidirectional planar microstrip antenna array. A cascade of transposed microstrip lines have been adapted to produce effective antenna structures that radiate omnidirectionally, with high efficiency, low reflection, and useful radiation patterns. In this paper, the antenna structure has been found to have low-pass characteristics due to the periodic discontinuities at the transposed junctions. The analysis and design of the low-pass characteristic are performed according to the filter theory of periodic structures and full-wave simulation. Therefore, a relatively higher frequency radiating array is appropriately designed with a low-pass filtering attribute, which prevents the lower frequency radiators from resonating at the relatively higher frequency. An air gap between adjacent transposed sections is proposed in order to enhance impedance matching, and a fork shape stub at the end is used as a virtual short point to enhance radiation at the higher frequency. Finally a single port dualband omnidirectional antenna array is obtained by locating the higher frequency radiating array with low-pass filtering attribute near the antenna feed and a relatively lower frequency radiating array at the end. An example of a dualband omnidirectional planar array is demonstrated experimentally, which operates at 2.32~2.56 GHz and 5.65~6.10 GHz with S11<-10 dB and a stable radiation pattern, and corresponding gains of 7.0~7.6 dBi and 6.9~7.9 dBi respectively.

An efficient higher order MLFMA is developed by using an ``extended-tree''. With this extended-tree, the size of the box at the finest level is reduced, and the cost associated with the aggregation and disaggregation operations is significantly decreased. The sparse approximate inverse (SAI) preconditioner is utilized to accelerate the convergence of iterative solutions. The Cholesky factorization, instead of the often used QR factorization, is employed to construct the SAI preconditioner for cavity scattering analysis, by taking advantage of the symmetry of the matrix arising from electric field integral equation. Numerical experiments show that the higher order MLFMA is more efficient than its low-order counterpart.

Periodic eigenproblems describing the dispersion behavior of periodically loaded waveguiding structures are considered as resonating systems. In analogy to resonators, their eigenvalues and eigensolutions are determined by solving corresponding excitation problems directly in the domain of the eigenvalue. Arbitrary excitations can be chosen in order to excite the desired modal solutions, where in particular lumped ports and volumetric current distributions are considered. The method is employed together with a doubly periodic hybrid finite element boundary integral technique, which is able to consider complex propagation constants in the periodic boundary conditions and the Green's functions. Other numerical solvers such as commercial simulation packages can also be employed with the proposed procedure, where complex propagation constants are typically not directly supported. However, for propagating waves with relatively small attenuation, it is shown that the attenuation constant can be determined by perturbation methods. Numerical results for composite right/left-handed waveguides and for the leaky modes of a grounded dielectric slab are presented.

Fully integrated printed RFID antennas show potential solution for item level labeling applications. In order to accommodate the antenna during the package printing process, it is vastly preferred that antenna structures are printed on paper substrates. However, the electromagnetic properties and thickness of paper substrates are susceptible to change due to various environmental effects. Thus, adequately consistent in performance and material insensitive printed Quadrate Bowtie RFID antennas are proposed. This paper presents an in-depth efficient optimization for high performance tag antenna designs for operability in frequencies 866-868 MHz & 902-928 MHz. It is demonstrated that the proposed antennas can tolerate a considerable variation in the permittivity on thin paper substrates, and present benchmarking results when n across metal and water containing objects.

In this paper, the classic oscillator design methods are reviewed, and their strengths and weaknesses are shown. Provisos for avoiding the misuse of classic methods are also proposed. If the required provisos are satisfied, the solutions provided by the classic methods (oscillator start-up linear approximation) will be correct. The provisos verification needs to use the NDF (Network Determinant Function). The use of the NDF or the most suitable RR_T (Return Relation Transponse), which is directly related to the NDF, as a tool to analyze oscillators leads to a new oscillator design method. The RR_T is the "true" loop-gain of oscillators. The use of the new method is demonstrated with examples. Finally, a comparison of NDF/RR_T results with the HB (Harmonic Balance) simulation and practical implementation measurements prove the universal use of the new methods.

Deep brain stimulation (DBS) is a well-established treatment for Parkinson's disease, essential tremor and dystonia. It has also been successfully applied to treat various other neurological and psychiatric conditions including depression and obsessive-compulsive disorder. Numerous computational models, mostly based on the Finite Element Method (FEM) approach have been suggested to investigate the biophysical mechanisms of electromagnetic wave-tissue interaction during DBS. These models, although emphasizing the importance of various electrical and geometrical parameters, mostly have used simplified geometries over a tightly restricted tissue volume in the case of monopolar stimulation. In the present work we show that topological arrangements and geometrical properties of the model have a significant effect on the distribution of voltages in the concerned tissues. The results support reconsidering the current approach for modeling monopolar DBS which uses a restricted cubic area extended a few centimeters around the active electrode to predict the volume of activated tissue. We propose a new technique called multi-resolution FEM modeling, which may improve the accuracy of the prediction of volume of activated tissue and yet be computationally tractable on personal computers.

This paper studies the effect of incipient stator faults in salient-pole synchronous generators and its detection using a simple pattern recognition methodology. A theoretical linear model for the synchronous generator is first developed to provide the relationships between stator and rotor harmonic currents and possible incipient faults on stator electric circuits. All theoretical findings were verified by experimental results. The stator currents and its αβ and dq representations have been used to detect incipient faults on salient-pole synchronous generators using a similar pattern recognition technique which have been proposed for induction machines. From our test results, it became clear that the proposed methodology is capable of correctly monitoring incipient stator faults in salient-pole synchronous generators.

The novelty of this letter is that it capitalizes on noise waveform to construct measurement operator at the transmitter and presents a new method of how the analogue to digital converter (ADC) sampling rate in the monostatic multiple-input multiple-output (MIMO) noise radar can be reduced --- without reduction in waveform bandwidth --- through the use of compressive sensing (CS). The proposed method equivalently converts the measurement operator problems into radar waveform design problems. The architecture is particularly apropos for signals that are sparse in the target scene. In this letter, Estimates of both target directions and target amplitudes using CS for monostatic MIMO noise radar are presented. Sparse bases are constructed using array steering vectors. Orthogonal least squares (OLS) algorithm for reconstruction of both target directions and target amplitudes is implemented. Finally, the conclusions are all demonstrated by simulation experiments.

The transmission and reflection of electromagnetic waves at dielectric-fractal interface is studied, the fractal exhibits quasi fractional space properties.~The closed form expressions for transmission and reflection coefficients are formulated for such an interface. The classical results are obtained when integer dimensions, instead of fractional dimension are inserted in the said expressions. This work can be used to study behavior of electromagnetic waves in slabs and waveguides filled with fractal media.

High-resolution wide-swath (HRWS) imaging with spaceborne synthetic aperture radar (SAR) can be achieved by using azimuth displacement phase center antenna (DPCA) technique. However, it will consequently leads to extremely high data rate on satellite downlink system. A novel sparse sampling scheme based on compressed sensing (CS) theory for azimuth DPCA SAR was proposed, by which only a small proportion of radar echoes are utilized for imaging to reduce data rate. The corresponding image formation algorithm for the proposed scheme was presented in the paper. The SAR echo signal of each channel can be reconstructed with high probability by using orthogonal matching pursuit (OMP) algorithm in Doppler frequency domain. The reconstructed echo signals of each channel are jointly processed by means of spectrum reconstructing filter for compensating Doppler spectrum aliasing resulting from non-uniform sampling in azimuth direction. The high quality SAR image can be obtained by using chirp scaling algorithm. The effectiveness of the proposed approach was validated by computer simulations using both point targets and distributed targets.

A GHz Transverse Electromagnetic (GTEM) cell is proposed to investigate the arising of biological effects due to electromagnetic signals at the typical frequencies of mobile phone communications. The proposed GTEM cell, placed within a commercial incubator, has been ad hoc designed and fabricated to expose in vitro samples. The electromagnetic and the thermal analyses of the GTEM cell are reported. In particular, the inner electromagnetic field and the Specific Absorption Rate of the exposed sample (saline solution having 9 g/l concentration) have been evaluated by a home-made computer code based on the transmission line matrix method. Furthermore, the thermal analysis of the exposure arrangement has been carried out by the finite difference time domain algorithm.

A highly compact bandpass filter (BPF) is designed with a capacitively-coupled compact ring resonator. The ground plane is perturbed with a combination of two inter-digital and two spiral defected ground structures (DGSs), which enhance the selectivity and suppress the higher order harmonics of the BPF respectively. The filter has a selectivity of 0.22 dB/MHz, passband insertion loss (IL) of 1.55 dB and bandwidth of 61 MHz at 2.53 GHz. The proposed compact ring resonator yields a size reduction of 70.5% compared to a conventional ring resonator. This BPF is significant for wireless telemetry monitoring systems for physiological parameters including electrocardiogram (ECG), electroencephalography (EEG) and electromyography (EMG) using portable devices.

In this paper, a fully automatic goal-oriented hp-adaptive finite element strategy for open region electromagnetic problems (radiation and scattering) is presented. The methodology leads to exponential rates of convergence in terms of an upper bound of an user-prescribed quantity of interest. Thus, the adaptivity may be guided to provide an optimal error, not globally for the field in the whole finite element domain, but for specific parameters of engineering interest. For instance, the error on the numerical computation of the S-parameters of an antenna array, the field radiated by an antenna, or the Radar Cross Section on given directions, can be minimized. The efficiency of the approach is illustrated with several numerical simulations with two dimensional problem domains. Results include the comparison with the previously developed energy-norm based hp-adaptivity.

With the advancement of technology, the need of antenna arrays with shaped power patterns increases day by day for the purpose of improvement of communication. In this article, we represent a new method for designing optimized linear array with shaped beam radiation pattern of desired specifications. The main objective is to obtain suitable current excitation amplitude and phase distribution for the linear array elements so that it can produce the desired custom shaped radiation pattern as the user demands. The design procedure utilizes an improved variant of a prominent and efficient metaheuristics of current interest, namely the Differential Evolution (DE). In our modified DE algorithm, denoted as DE_rBM_2SX, new mutation and crossover strategies are employed. These modifications help to overcome some drawbacks of classical DE. Two examples of linear array with shaped radiation pattern design problem are considered to illustrate the effectiveness of our algorithm. Our results are also compared with two state-of-the-art variants of DE and Particle Swarm Optimization (PSO) - namely JADE and CLPSO (Comprehensive Learning Particle Swarm Optimization). The comparison clearly reveals that our optimization algorithm is more efficient than JADE or CLPSO in finding optimum element excitation amplitude and phase distribution for the desired shaped pattern.

We propose a 3D-approach of the soil surface height variations, either for the roughness characterization by the mean of the bidimensional correlation function, or as input of a backscattering model. We consider plots of 50\,cm by 50\,cm and two states of roughness of seedbed surfaces: an initial state just after tillage and a second state corresponding to the soil roughness evolution under a rainfall event. We show from stereovision data that the studied surfaces can be modelled as isotropic Gaussian processes. We study the change of roughness parameters between the two states. To discuss the relevance of their differences, we find from Monte-Carlo simulations the bias and variance of estimator for each roughness parameters. We study the roughness and moisture combined influences upon the direct backscattering coefficients by means of an exact method based on Maxwell's equations written in a nonorthogonal coordinate system and by averaging the scattering amplitudes over several realizations. We discuss results taking into account the numerical errors and the precision of radar. We show that the ability of the radar to discriminate the different states of seedbed surfaces is clearly linked to its precision.

The design and full-wave analysis of piezoelectric micro-needle antenna sensors for minimally invasive near-field detection of cancer-related anomalies of the skin is presented. To this end, an accurate locally conformal finite-difference time-domain procedure is adopted. In this way, an insightful understanding of the physical processes affecting the characteristics of the considered class of devices is achieved. This is important to improve the structure reliability, so optimizing the design cycle. In this regard, a suitable sensor layout is described, and discussed in detail. The major benefit of the proposed system stems from the potential for obtaining a superior performance in terms of input impedance matching and efficiency, in combination with an electronically tunable steering property of the near-field radiation intensity which can be profitably used to enhance the illumination and, hence, the localization of possible malignant lesions in the host medium. By using the detailed modeling approach, an extensive parametric study is carried out to analyze the effect produced on the sensor response by variations of the complex permittivity of the skin due to the presence of anomalous cells, and thus useful heuristic discrimination formulas for the evaluation of the exposure level to cancer risk are derived.

A low pass filter with ultra-wide band rejection and compact size using a proposed radial loaded transformed radial stubs is introduced and investigated. The implemented unite cell low pass filter with 1-dB cutoff frequency f_c of 3.2 GHz demonstrates stopband rejection up to 11.8 f_c i.e. 38 GHz. The design is further extended to the high-order LPF through cell cascading. The implemented four-cell LPF with f_c of 3.6 GHz demonstrated 35dB rejection from 4.8GHz to 39GHz, 50 dB rejection from 5.4 GHz to 26 GHz (7.2 f_c) and 20dB rejection from 4.4 GHz to 50 GHz (13.8 f_c). The measured passband insertion loss is less than 1.7 dB, and group delay is from 0.45~0.8 nS. The size of the four-cell low pass filter is only 0.33λg × 0.135λg, (λg is the guide wavelength at center cutoff frequency) without using any lumped elements.

We present an ω-k approach based on the use of a 1D Non-Uniform FFT (NUFFT) routine, of NER (Non-Equispaced Results) type, programmed on a GPU in CUDA language, amenable to real-time applications. A Matlab main program links, via mex files, a compiled parallel (CUDA) routine implementing the NUFFT. The approach is shown to be an extension of an already developed parallel algorithm based on standard backprojection processing to account also for near-field data. The implementation of the GPU-based, parallel NUFFT routine is detailed and the computational advantages of the developed approach are highlighted against other confronted sequential or parallel (on multi-core CPU) procedures. Furthermore, the benefits of the $\omega$-k, NUFFT-based processing are pointed out by both comparing its accuracy and computational convenience against other interpolators, and by providing numerical results. By comparing the computational performance of the algorithm against a multi-core, Matlab implementation, the speedup has been about 20 for a medium size image. The performance of the approach has been pointed out in the applicative case of vegetation imaging against experimental data of a boxtree (Buxus tree), also under a source of temporal decorrelation (wind).

In this work, threshold mode structures of two-dimensional (2D) photonic crystal (PC) lasers are presented. The subjects of this paper are finite photonic crystal structures with circular holes arranged in square and triangular lattices. In each case, both transverse magnetic (TM) and transverse electric (TE) polarization are studied. The analysis is based on the coupled-wave equations and analyzes modes' behavior for the wide range of coupling coefficient values. The laser mode is characterized by threshold gain and frequency deviation, and these quantities depend on coupling constants, which means that the threshold gain of the mode and the mode's frequency deviation depend on the coupling constants. Presented analysis gives an interesting insight into behavior of the modes in photonic crystal lasers.