A procedure based on the analytical model of a lumpedelement, crossover circulator has been developed to maximize its operating bandwidth. The procedure considers the circulator as a network and employs the circulation impedance - the load associated with perfect circulation - as a metric to optimize the bandwidth. Using this procedure, we find that a maximum 194% bandwidth can be obtained for an ideal circulator for any above-FMR range operation. By applying this same procedure to an actual circulator device in 225-400 MHz frequency range, we achieve a 125% bandwidth from a numerical simulation model. We have verified this result from the measurement of a fabricated device; the measured data reveals a bandwidth of 129%.

In this letter, a novel compact tri-band bandpass filter (BPF) with high selectivity is presented. The proposed tri-band performance measure is realized by using eight sets of resonators, i.e., two- and three-section stepped impedance resonators (SIRs). The three-section SIR is designed for determining the three passbands and providing the electric coupling, while the two-section SIR is used for determining each passband respectively and providing the magnetic coupling. Then, coupling structures with two transmission zeros near each passband edge are presented, therefore, the band selectivity of the filter is much improved. The three passband frequencies could be independently designed and tuned. This novel tri-band BPF is fabricated and the measured results are in good agreement with the full-wave simulation results.

A direct near-field - far-field transformation with helicoidal scanning for electrically long antennas is proposed in this paper. Such a transformation, which allows the evaluation of the antenna far field in any cut plane directly from the acquired near-field data without interpolating them, relies on the nonredundant sampling representation of electromagnetic fields and makes use of a prolate ellipsoidal modelling of the antenna under test for determining the number of helix turns, whereas the number of samples on each of them is fixed by the minimum cylinder rule, as in the classical cylindrical scan. Numerical and experimental tests assessing the effectiveness of the approach are shown.

A new scheme for overcoming losses with incoherent optical gain in a quantum-coherent left-handed atomic vapor is suggested. In order to obtain low-loss, lossless or active left-handed media (LHM), a pump field, which aims at realizing population inversion of atomic levels, is introduced into a four-level atomic system. Both analytical and numerical results are given to illustrate that such an atomic vapor can exhibit intriguing electric and magnetic responses required for achieving simultaneously negative permittivity and permeability (and hence a gain-assisted quantum-coherent negative refractive index would emerge). The quantum-coherent left-handed atomic vapor presented here could have four fascinating characteristics: i) three-dimensionally isotropic negative refractive index, ii) doublenegative atomic medium at visible and infrared wavelengths, iii) high-gain optical amplification, and iv) tunable negative refractive index based on quantum coherent control. Such a three-dimensionally isotropic gain medium with negative refractive index at visible and infrared frequencies would have a potential application in design of new quantum optical and photonic devices, including superlenses for perfect imaging and subwavelength focusing.

The Modal Method by Gegenbauer polynomials Expansion (MMGE) has been recently introduced for lamellar gratings by Edee [J. Opt. Soc. Am. 28, (2011)]. This method shows a promising potential of outstanding convergence but still suffers from instabilities when the number of polynomials is increased. In this work, we identify the origin of these instabilities and propose a way to remove them.

Microstrip reflectarrays consisting of rectangular patches are investigated for application in space-based dual-polarized dual-beam radar interferometers. For nadir looking beams the angle of incidence of feed radiation in each patch is nominally 45˚. In such an application, square-patch reflectarrays can be designed for only one polarization with a sacrifice in performance in the other whereas reflectarrays consisting of rectangular patches may be designed for both polarizations, thereby improving their radiation performance. Piecewise planar parabolic reflectarrays consisting of square patches exhibit poor scan performance in tilted configuration. It is shown that with the use of rectangular patches in such a reflectarray one can design two beams of different polarizations for two offset feeds, thereby providing significant improvement in bandwidth and radiation performance.

In this paper, we report experimentally and numerically on coupling effects of dielectric metamaterial dimer (metadimer) which composed of two identical ceramic cubes with high permittivity. The distance dependence of Mie resonance for metadimer is investigated under various polarizations of external wave. By changing the configurations and alignment of dimer resonator, it is revealed that magnetic and electric resonances of metadimer exhibits a red/blue shift, resulting from longitudinal or transverse coupling effects of dipoles. Besides, quasi bound states between tightly stacked dielectric cubes are also been pointed out for electric Mie resonance, which is responsible for an unexpected frequency shift with a reverse variation.

ISAR imaging of maritime targets has greater success than other ISAR applications due to the constant oscillatory motions induced by waves and wind. However, relative target motions are usually unknown, difficult focusing, image interpretation and target classification. Using interferometry to obtain the height information makes possible to obtain a 3-D reconstruction of a target, aiding image focusing, image interpretation and target classification. However, the information and utility of the ISAR image and the interferometric information depends highly on geometry and targets dynamics. In this paper we will study the influence of movement dynamics in interferometric ISAR imaging using a realistic extended moving target simulation, a general geometry and complex dynamics models.

The analysis of an antenna mutual coupling is a significant issue for designing the wireless communication system especially includes an array mutual coupling problem. The accurate analysis of the mutual coupling between antennas is needed. Accordingly, several methods for the mutual impedance calculation of dipoles have been studied in cases of coplanar-skew and nonplanar-skew. This paper proposes an exact and simple method for analyzing the mutual impedance between two arbitrarily located and slanted dipoles using the modified induced EMF method; their expressions and the exact analytic solution. The proposed formula and their closed-form solutions are verified by numerical solution using HFSS and give good agreement.

In this paper an explicit finite-difference scheme is developed in staggered grids for solving the Maxwell's equations in time domain. We are aimed to preserve the discrete zero-divergence condition in the electrical and magnetic fields and conserve the inherent laws in non-dispersive simple media all the time using the explicit second-order accurate symplectic partitioned Runge-Kutta temporal scheme for the time derivative terms. The spatial derivative terms in the semi-discretized Faraday's and Ampere's equations are then approximated to get an accurate numerical dispersion relation equation that governs the numerical angular frequency and the wavenumbers for the Maxwell's equations defined in two space dimensions. To achieve the goal of getting the best dispersive characteristics in the chosen grid stencil, a fourth-order accurate space centered scheme with the ability of minimizing the difference between the exact and numerical dispersion relation equations is proposed. Our emphasis is placed on the accurate modeling of EM waves in the dispersive media of the Debye, Lorentz and Drude types. Through the computational exercises, the proposed dual-preserving Maxwell's equation solver is computationally demonstrated to be efficient for use to predict the long-term accurate wave solutions in a medium belonging either to a frequency independent or to a dependent type.

Step-by-step procedures for designing a third order bandpass filter and a sixth order bandpass filter using a triple-mode resonator are described in this paper. The triple-mode resonator is a square open-loop resonator with an open circuited stepped-impedance stub and a grounding via located at the symmetrical plane of the resonator. The equations for approximating the resonant frequencies of the resonator are obtained from odd- and even-mode analysis. To design a filter, first, the theoretical resonant frequencies for the filter are calculated. Then the basic dimensions of the resonator are approximated using the equations. The filter layouts are fine-tuned by simulation and verified by experiment to conclude the paper. The first spurious response occurs at about 3 times the center frequency of the first passband in both filters. The simulated and measured results are in good agreement.

A novel 3-pole bandpass filter (BPF) based on microstrip loaded ring resonators (LRRs) is proposed. Each resonator is composed by a closed-loop transmission line and a short-circuited stub. By properly adjusting the impedance and the electrical length of each resonator, the proposed circuit may be made compact (over 93.7% smaller than a conventional ring resonator) and its stopband may be extended simultaneously. Each resonator exhibits an area of 0.0727 λ_g x 0.079 λ_g where λ_g is the guided wave length. A BPF at the center frequency of f₀=1.9 GHz with stopband extended up to 7.8 GHz (=4f₀) is developed showing good agreement between simulation and experimental results.

An efficient trans-impedance Green's function that describes the electromagnetic behavior of a ring circulator is presented. A rigorous derivation composed of an infinite summation of modified Bessel functions of the first and second kinds is included. As with more traditional circulator descriptions, the formulation herein contains a weak singularity when the measurement point is located near the impressed source point on the same radius. To accelerate convergence of the series, this singularity is extracted from the formulation and integrated analytically. To complete the formulation, two circulators are presented; the first with ports that emanate at equal angles from the outer radius, and the second with two ports associated with the outer radius and one port that connects to the inner radius. The computation time associated with the proposed analysis lasted approximately 0.25 s, whereas an identical structure simulated via a common full-wave solver lasted approximately 10 hours. Comparison of impedance data between the proposed analysis and full-wave simulation is presented.

A new wideband dual-polarized patch antenna consisting of a magnetically-fed and an electrically-fed is presented in the paper. The two feeds are orthogonal to each other at the center of the ground plane and generate 0° and 90° polarization separately. Two pairs of L-shaped slots are etched in the radiating patch to improve the impedance bandwidth. By using a shorting pin connecting the radiating patch to the ground plane, the coupling between the two feeding ports can be reduced. With the help of circuit simulation and full wave simulation, the equivalent circuit model of the antenna is established. The simulated and measured results show that the impedance bandwidths for VSWR less than 2 of the proposed dual-polarized antenna with a profile of are 27.3% (3.29-4.33 GHz) and 19% (3.05-3.69 GHz) for 0° polarization and 90° polarization, respectively, with a height of 0.08 λ₀ between radiating patch and ground plane. The measured coupling between the two ports is below -20 dB over the operating band. Moreover, the measured gain of the proposed antenna is about 7.9 dBi and 6.1 dBi for port 1 and port 2, respectively, over the operating band. Measured results of the fabricated antenna prototypes are in good agreement with the simulated results.

The numerical calculation of the Specific Absorption Rate (SAR) averaged over a certain tissue mass is a common practice when evaluating the potential health risk due to the human exposure to electromagnetic sources. Nevertheless, SAR values are strongly influenced by many factors such as, for instance, the shape of the volume containing the reference mass, the spatial discretization step, or the treatment of internal air, just to mention some of them: different choices can induce significant discrepancies. In this work an overview on some of the most commonly adopted SAR algorithms is firstly presented, and a discussion on their potential differences reported. Then, based on a spherical volume approach, some new algorithms are proposed. All the algorithms are then used to evaluate the SAR both in artificially generated test cases and in some practical human-antenna interaction problems. The result comparison highlights relevant discrepancies and enforces the necessity of a reasoned standardization of the techniques for the SAR calculation.

In this paper, a planar coupled-fed monopole antenna with eight-band LTE/WWAN (LTE700/2300/2500/GSM850/900/1800/1900/UMTS) operation for mobile handset device application is proposed. It simply consists of a T-shaped driven strip and a coupled radiating structure, which occupy a small PCB area of 50(L)x15(W) mm². This antenna, which is printed on a 0.4 mm FR4 substrate and fed by a 50-Ω coaxial cable, can provide two wide operating bandwidths covering 697-1012 MHz and 1598-2795 MHz for LTE/WWAN communication systems. A prototype of the proposed antenna is fabricated, tested and analyzed. From the measurement results, nearly omnidirectional coverage and stable gain variation across the desired LTE/WWAN bands can be obtained with the antenna.

A study of UWB on-body communication system performance, with the WiMax off-body electromagnetic interference (EMI) existence, is presented. Firstly, a compact UWB antenna with good on-body performance is verified and chosen as our reference antenna. Using this realistic antenna, channel transfer function (CTF) of UWB on-body channel in an indoor room is investigated by measurements. Based on the measured data, the parameters of its pathloss model and its power delay profile (PDP) model are extracted respectively. Secondly, a new body channel communication system model, composed of the on-body and off-body dual-link channel, together with UWB and WiMax signal models are presented. Finally, UWB on-body communication performances under different WiMax off-body EMI levels are studied by simulation. Simulated results show that this on-body system performance is quite limited and easily affected by the off-body WiMax EMI. It is pointed out that the existing UWB on-body communication abilities should be greatly improved when WiMax off-body EMI signals are considered.

This paper mainly deals with the detection problem of the target with low Radar Cross-Section (RCS) in heavy sea clutter with unknown Power Spectral Density (PSD). Since the performance of traditional singlescan detectors degrades as the target of interest is smaller and weaker, three adaptive detectors, based upon a two-step design procedure, are proposed within the framework of the multiple-scan signal model. Firstly, the Multiple-Scan Detectors (MSDs) are derived according to the Generalized Likelihood Ratio Test (GLRT), Rao and Wald tests respectively under the assumption that the PSD of primary data is known. Secondly, three strategies are resorted to estimate the unknown PSD, and their Constant False Alarm Rate (CFAR) properties are assessed. Finally, numerical simulation results show that the adaptive MSDs outperform the traditional single-scan detector using Monte Carlo method.

This article presents an efficient method for characterization of substrate integrated passive circuits. The analysis is based on the wave concept formulation and the iterative resolution of a system of two equations between incident and re ected waves. Simulations obtained are compared with analytical references and HFSS simulations. A good agreement is achieved with computation time saving.

In this paper, a full-wave analysis technique of lossy substrate integrated waveguides, based on the dyadic Green's function of the parallel plate waveguide, is presented. The field inside the waveguide is expressed in terms of cylindrical vector wave-functions and the finite conductivity of the top and of the bottom plates, and of the metallic vias are taken into account. Losses into the dielectric substrate are also included. Coaxial ports are considered as sources and self and mutual admittances are evaluated. Cases of practical structure taken from literature are presented showing a very good agreement with the most used commercial software.