In this paper, an improved L1-SVD algorithm based on noise subspace is presented for direction of arrival (DOA) estimation using the reweighted L1 minimization. In the proposed method, the weighted vector is obtained by utilizing the orthogonality between the noise subspace and the subspace spanned by the array manifold matrix. The presented algorithm banishes the nonzero entries whose indices are inside of the row support of the jointly sparse signals by smaller weights and the other entries whose indices are more likely to be outside of the row support of the jointly sparse signals by larger weights. Therefore, the sparsity at the real signal locations can be enhanced by using the presented method. The proposed approach offers a good deal of merits over other DOA techniques. It not only increases the robustness to noise, but also enhances resolution in DOA estimation. Furthermore, it does not require an exact initialization. Simulation results show that the presented algorithm has better performance than the existing algorithms, such as MUSIC, L1-SVD algorithm.

This work presents results of a comprehensive analysis of the Lenz effect due to motion of artificial heart valves during magnetic resonance imaging. The interaction of rotating metallic heart valves with magnetic fields is studied by performing a time-domain analysis of the corresponding electromagnetic problem. We applied the finite element method (FEM) to solve the T-Ω formulation of Maxwell equations in two cases: first, for metallic disks located in the high intensity homogenous field of the magnet iso-center, and second, disks located in the non-uniform fringe field of the bore entrance. We showed that for valves with full solid disks (such as Starr-Edwards 6500) located in the magnet iso-center, the magnitude of adverse forces can be comparable to the forces applied by the beating heart. However, for rings which consist of multiply connected conductive regions, skin effect and proximity effect counteract, which leads to a diminished magnetic force. Results of this study show that mechanical heart valves with strengthening rings {may} be considered safe even under ultra-high imaging conditions with field intensities as high as 10 T. However, heart valves with full conducting disks should be considered as a contraindication to MR imaging.

In this paper we propose a new algorithm called An Informative Differential Evolution with Self Adaptive Reclustering Technique to find the amplitude-phase excitation of a linear phased array to have the desired far field pattern. Here we consider three problems for three different far field patterns and each problem is optimized with this algorithm. This algorithm has a proper balancing of exploration and exploitation power which is achieved with the help of information exchange among the subpopulations. We also used an elitist local search algorithm for the fine tuning at the suspected optimal position, and that helps us from the unnecessary wastage of Function Evaluations (FEs).

Conical log spiral antennas are famous for being appropriate for tracking, telemetry and command (TT&C) applications in low earth orbit (LEO) satellites. In this work, a conical linear (not log) spiral antenna is introduced and investigated for the same purpose. The electric field integral equation (EFIE) technique is applied to a triangular-patch surface model of the conical equiangular linear spiral antenna. This antenna is optimized to produce the radiation characteristics required for TT&C applications for LEO satellites. The input impedance, polarization and radiation patterns of this antenna are investigated over a wide band of frequencies. Some of the obtained results especially those concerning the input impedance, radiation pattern, polarization and bandwidth are verified experimentally. It is shown that the proposed antenna is quite appropriate for TT&C in LEO satellite applications.

The present paper is a study of adaptive beamforming (ABF) techniques applied to antenna arrays. The structure of these techniques is based on Taguchi's Optimization (TagO) method. The high convergence speed and the ability to reach near-optimal solutions by adjusting only one parameter make the Taguchi's method an attractive choice for real time implementations like the case of ABF. Modifications are proposed in order to enhance the applicability of the TagO algorithm and decrease the computational time needed by the algorithm to terminate. The TagO method is used here to construct an ABF technique that aims at steering the main lobe of a uniform linear array towards a signal of interest, under the constraint of low side lobe level (SLL) or the constraint of placing radiation pattern nulls towards respective interference signals. Properly defined fitness functions must be minimized by the TagO algorithm to satisfy respectively the above mentioned constraints. The TagO-based ABF technique is compared with typical beamforming methods, like the Sample Matrix Inversion (SMI) and Maximum Likelihood (ML) ones, and with two evolutionary ABF techniques based on Particle Swarm Optimization (PSO) and Differential Evolution (DE), respectively. The comparison is performed regarding the convergence speed, the ability to achieve better fitness values in less time, the ability to properly steer the main lobe and finally the null-steering ability or the SLL control depending on the constraint type. The results exhibit the superiority of the TagO-based technique.

Electric permittivity and magnetic permeability of linear passive dispersive medium were defined using the circuit equation of an electrically small antenna (scatterer) with resonant and antiresonant properties. It was shown that the average macroscopic energy stored by the scatterers is proportional to frequency derivative of the input admittance of corresponding antenna. It was found that the average macroscopic energy density of electric and magnetic fields in dispersive lossy medium is a function of frequency derivatives of its effective constitutive parameters in accordance with Poynting's theorem in dispersive lossy medium clarified for this case in the paper.

The one-port cavity resonator method based on the S₁₁ parameter measurement technique for measuring the complex permittivity of dielectric samples has been proposed. A novel dual-loop coupler is developed for avoiding and suppressing the spurious modes in one-port cavity resonator. Through threading the pair of half loop in the opposite direction, the opposite surface currents can be generated and only TE₀₁₁ mode will be excited. The operating principles of the dual-loop coupler are investigated. This technique has the advantages of the coupling. Equivalent electronic circuit model has been set up. Simulation and experimental results show good agreement.

The dynamics of the onset of oscillations in a wave guide cavity based Gunn Oscillator (GO) has been critically examined through numerical simulations and experimental studies.The transition of the GO from a non-oscillatory to an oscillatory state and the same in the reverse direction occurs at different critical values of the dc bias voltage applied to the GO. In presence of a weak RF field in GO cavity, oscillations with broad band continuous spectrum and multiple discrete line spectrum are observed at the GO output for different values of dc bias below the above mentioned critical values. Analysing the numerically obtained time series data, chaos quantifiers have been obtained to prove the occurrence of the chaotic oscillations in the GO. Experimental results and observations of numerical simulation show good qualitative agreement.

In this paper, cellular communications from Stratospheric platforms (SPs) is studied, and the coverage footprint analysis and design is demonstrated. In the analysis, two coverage schemes are introduced; flat-earth and real-earth models and cell footprint are determined in each case. The flat-earth provides simple footprint equations describing the cell dimensions especially for the cells of higher elevation angles while more accurate coverage equations, which well determine the geometry of the cells of lower elevation angles, can be obtained from the real-earth scheme. The design of a cellular system using the proposed coverage models is then introduced through a procedure that determines the cells locations and dimensions on the ground according to the teletraffic information. The procedure takes into considerations the cell broadening when going outwardly from the central cell to the outer lower elevation cells and constructs a cellular layout that has the most proper cells overlap and uniform coverage edges, which helps the linking between different SPs coverage areas.

A novel planar ultra-wideband (UWB) antenna with dual band-notched characteristics is proposed. The antenna is fabricated on a printed circuit board (PCB), having a circular monopole and arc-shaped parasitic strips on one side and a ground plane with a slot aperture on the other side. Two narrow bands at 5.15-5.35 GHz and 5.725-5.825 GHz are notched by using two arc-shaped parasitic strips on the same layer of the radiator. Compared with other band-notched UWB antennas, the proposed antenna exhibits the advantages of simple structure, compact size, simple control of each notched frequency band using separate parasitic strips, and good performance. Surface current distributions and equivalent circuit model are applied to analyze the operating principle of the proposed antenna. To validate the concept, a prototype is fabricated and tested. Both simulated and measured results confirm that the proposed antenna achieves a wide bandwidth from 3.1 GHz to 10.6 GHz with two narrow bands notched successfully. The results of VSWR, radiation patterns and gain response are shown and discussed in detail. The antenna enables the independent control of the notched frequency bands, and the proposed method can be extended for designing planar UWB antennas with multiple band-notched characteristics and reconfigurable notched frequency.

In this investigation, scattering from a circular disk with surface impedance has been studied rigorously. The method of analysis is Kobayashi Potential (KP). The mathematical formulation yields the dual integral equations (DIEs). These DIEs are solved by using the discontinuous properties of Weber-Schafheitlin's integral. After applying the boundary conditions and projection, the resulting expressions, finally, reduce to matrix equations for expansion coefficients. The matrix elements are in the form of infinite integrals with single variable. These are then used to compute the values of expansion coefficients. The far field patterns of the scattered wave are computed for different incident angles and surface impedances for both E- and H-polarizations. To verify the results, we have computed the solution based on the physical optics approximation. The agreement between them is fairly good.

In this work, an electronically tunable large range phase shifter based on a broadband Injection-Locked Third Harmonic Self-Oscillating Mixer (IL3HSOM) is designed and analyzed. This multifunctional circuit generates a down-converted Intermediate Frequency (IF) signal and provides a theoretical 540◦ continuous phase shift range. The conversion gain and the bandwidth of the circuit are optimized through bifurcation control techniques. The IL3HSOM will be used as the core of a broadband phased antenna array with electronic beam-steering capabilities. The use of a multi-harmonic load based on an arbitrarily width modulated transmission line allows the nonlinear optimization of the circuit phase shift frequency response to ompensate the frequency scanning effect, which negatively influences the performance of broadband antenna arrays.

A novel broadband monopole antenna design with wideband circular polarization (CP) characteristic is presented. This antenna consists of a feed line and a step-shaped ground plane which is formed by cutting a notch in the upper left corner of an asymmetric ground plane. The asymmetric ground plane is capable of exciting two orthogonal electric field vectors with equal amplitude and 90° phase difference (PD) for CP. By cutting a notch, the impedance-bandwidth can be enhanced greatly and the 3-dB axial ratio (AR) bandwidth is improved meanwhile. The measured impedance-bandwidth is about 5.96 GHz (84.7%) from 4.06 to 10.02 GHz, and the measured AR-bandwidth is about 2.64 GHz (36.5%) from 5.91 to 8.55 GHz. The results show that the antenna can achieve wide impedance-bandwidth and wide AR-bandwidth simultaneously.

A polarization-dependent mutiband radar absorbing material (PDM-RAM) composed of polarization-dependent multiband AMC (PDMAMC) and perfect electric conductor (PEC) cells is proposed. The PDMAMC is realized by etching a complementary split ring resonator (CSRR) on the patch of a conventional AMC. Around the two/three operational frequencies of the PDMAMC-elements for different electric field polarizations, the reflections of the PDMAMC and PEC have opposite phases, so for any normal incident plane wave the reflections cancel out. The basic principle is discussed, and a sample is measured. The results show that the proposed method is feasible and effective for the polarization-dependent multiband radar cross section (RCS) reduction.

This paper proposes a 10:1 unequal Gysel power divider using a capacitive loaded transmission line (CLTL). For obtaining a high dividing ratio of divider, the CLTL is proposed to realize a low characteristic impedance line below 10 Ω. A design method using a CLTL which consists of a small transmission line with shunt open stub at periodic intervals is newly suggested for power divider with the high power division ratio. For the validation of the CLTL power divider, the high dividing ratio of the fabricated Gysel divider is measured at a center frequency of 1 GHz. The measured performances are in good agreements with simulation results.

A novel miniaturized microstrip dual-mode filter using a half wavelength resonator with centrally loaded open stub and quasi-L shaped feed-lines is proposed. The advantage of using such a resonator is inherently generating a transmission zero by itself. To further improve the selectivity, quasi-L shaped feed-lines are introduced to create additional transmission zeros. Theoretical and simulated analyses of this filter are performed. A demonstration filter centered at 2.33 GHz with a fractional bandwidth of 4.7% is designed, fabricated and measured to validate the design methodology.

Principle component analysis based through wall image enhancement is proposed which is capable of discriminating target, noise and clutter signals. The overlapping boundaries of clutter, noise and target signals are separated using fuzzy logic. Fuzzy inference engine is used to assign weights to principle components. The proposed scheme works well significantly for extracting multiple targets having different range profiles in heavy cluttered through wall images. Simulation results are compared on the basis of mean square error, peak signal to noise ratio and visual inspection.

The research about the so-called \emph{complex beams}, localized solutions of the Helmholtz wave equation, lead to the problem of finding the sources of such solutions, which may be formally expressed as a Dirac delta function of a complex argument. To investigate about the meaning of the Dirac delta distribution of complex argument, the Green's function of the 3D Poisson problem with a point source localized at an imaginary position in free space is considered. The main physical features of the potential created by that source are described. The inverse problem consists in looking for the real source distribution which causes that potential. The sources appear on a disk in the real space. Their physical interpretation requires a regularization process based on including the border of the disk.

The adoption of microwave imaging as a tool for non-invasive monitoring of brain stroke has recently gained increasing attention. In this respect, the paper aims at providing a twofold contribution. First, we introduce a simple design tool to devise guidelines to properly set the working frequency as well as to choose the optimum matching medium needed to facilitate the penetration of the probing wave into the head. Second, we propose an imaging strategy based on a modified formulation of the linear sampling method, which allows a quasi real time monitoring of the disease's evolution. The accuracy of the design guidelines and performance of the imaging strategy are assessed trough numerical examples dealing with 2D anthropomorphic phantoms.

A 16-way radial waveguide power divider with the characteristics of low insertion loss and high power handling capacity is investigated. Its design theory and basic structure are proposed at first; a power divider with the center frequency of 4.0GHz is designed, fabricated, and measured. Good agreement between the simulated and measured results is found for the proposed power divider. The measured 15-dB return loss bandwidth is demonstrated to be 440MHz and the measured 0.5-dB insertion loss bandwidth is demonstrated to be 540MHz. The power handling capacity of the proposed power divider is analyzed through simulation, and the results prove its usability in high power applications.