A compact tunable dual-band bandpass filter (BPF) based on substrate integrated waveguide (SIW) and defected ground structure (DGS) is investigated in this paper. The second passband can be flexibly controlled by changing the dimensions of the up-down DGSs whereas the first passband is fixed. The proposed filter exhibits improved selectivity due to the introduction of four left-right DGSs generating transmission zeroes. To verify the design method, a compact dual-band filter with the second center frequency switched among 5.4 GHz, 5.8 GHz, 6.4 GHz and 6.8 GHz and the first center frequency fixed at 4.78 GHz, is designed and fabricated. The simulated and measured results are in good agreement with each other.

Invisible cloak with its amazing functions has been turned into reality due to the advent of transformation optics during the past few years. However, the inhomogeneity and singularity of electromagnetic parameters in cloak are still the main bottlenecks for practical realization. In this paper, we propose a scheme of three-dimensional polyhedral invisible cloak to overcome these shortcomings by using a linear homogeneous transformation method. The constitutive parameters of the polyhedral cloak are homogeneous and anisotropic, which are relatively easy for realization. Numerical simulations demonstrate that good invisibility performance can be achieved for any polarization wave. Our work provides a novel approach to simplify three-dimensional cloak in practice.

Scattering characteristics of periodic dielectric gratings can be accurately and efficiently computed via a spectral volume integral equation combined with normal-vector fields defined on the grating geometry. We study the impact of the geometrical discretization on the convergence rate of the scattering characteristics for two-dimensional gratings in both TE and TM polarization and compare these with an independent semi-analytical reference for circular cylinders. We demonstrate that geometrically conforming normal vector fields lead to substantially faster convergence and shorter computation times, as opposed to the commonly applied staircasing or slicing.

This work presents an experimental study in W band about the behavior of a plane Fresnel reflector when the feeder changes its position on the surface of a sphere whose centre is the same of the Fresnel plate zones. For this purpose, an experimental system based on seven Fresnel plate zones and two different levels has been developed. The center frequency of the reflector is 96 GHz, the focal length is 100 mm and height between levels is 0.78 mm. Based on this Fresnel reflector, an experimental set up has been developed. The horn antenna feeder is fixed and situated in far field and the receiver is also a horn antenna located at the Fresnel focal distance. Both the reflector and the receiving antenna have some rotation capability to enable measurements from different angles. The experimental results show a good, stable behavior in gain versus the angular position of the feeder. This special property of Fresnel reflectors is impossible in parabolic reflectors and consequently, Fresnel reflectors could be used in new applications as radar imaging, increasing the radar field of view or improving the resolution by means of several squint feeders working simultaneously on the same lens or reflector. Therefore, the main objective of this paper is to analyze the behavior of this experimental set up for developing new Fresnel reflector-based applications.

In this paper, an efficient wireless power transfer (WPT) system integrating with highly sub-wavelength metamaterials is proposed. The negative refractive index (NRI) and negative permeability (MNG) metamaterials for operation at radio frequencies are designed and applied to WPT system for improvement of power transfer efficiency. A dual-layer design which consists of a planar spiral on one side and a meander line touching with narrow metallic strips on the other side produces the properties of effective negative permittivity and permeability simultaneously, i.e., negative refractive index. In addition, the structure of double spirals produces a negative permeability. The cell size of the NRI and MNG metamaterials is about 253 times smaller than the operation wavelength. By integrating one, two, three or four metamaterial slabs between the two coupling copper rings, the transfer efficiency is improved significantly. The measured results show that the contribution of high transfer efficiency is due to the property of negative permeability which can make the WPT system work in the mechanism of magnetic resonance.

An equivalent circuit based on propagating and evanescent accessible modes is discussed and the numerical values of its elements (susceptances and electrical length) are obtained starting from the knowledge of the generalized scattering matrix S of microwave discontinuities. A database of the circuit elements is then defined in the frequency and geometric ranges of the analyzed discontinuities and is used to evaluate the generalized scattering matrix for values not contained in the database, with very simple formulas for any number of circuit ports. The obtained S matrices can be used to analyze very complex structures such as iris-based filters and manifold filters.

A new structure of coupled-fed loop antenna connected with two branch radiators for eight-band LTE/WWAN (LTE700/GSM850/900/1800/1900/UMTS/LTE2300/2500) operation in the ultra-thin laptop computer is presented. The two branch strips of the antenna are efficient radiators and contributing multi-resonant modes to greatly enhance the bandwidth of the antenna. The proposed antenna on the top shielding metal wall of the laptop display, with a planar and compact size of 12.5×70×0.8 mm³, is suitable to be embedded inside the casing of the laptop computer. The proposed antenna is fabricated and tested, and good radiation performances are obtained. Compared with the existing published antennas, the volume of the planar antenna is quite small.

In multi-input multi-output (MIMO) radar transmit beampattern synthesis, most current literature formulates the problems in steradian space. However, since the beampattern and its parameters are both measured and defined in radian space, from the view point of physical meaning, it will be better to reformulate the problems in radian space rather than in steradian space. In this paper, we propose methods in the radian space to synthesize beampatterns based on minimizing sidelobe level for the two main designs in MIMO radar, i.e. minimum sidelobe beampattern design (MSBD) and beampattern matching design (BMD). For MSBD, the design criteria considering both peak sidelobe level and integrated sidelobe level is proposed. By this we can have a good tradeoff between the intensity and power distribution in beampattern synthesis. After a two-step converting, the formulation of the criteria is transformed into a convex programming, where a global optimal solution can be obtained. For BMD, instead of minimizing mean square error directly as in conventional methods, we propose a power-approximation-based method by minimizing integrated sidelobe level. Finally, numerical comparisons with classical methods demonstrate that the proposed MSBD maintains for all range of main lobe width and the proposed BMD has smoother main lobes with maximal power focused in.

Primary user (PU) signal detection is critical for cognitive radio networks as it allows a secondary user to find spectrum holes for opportunistic reuse. Eigenvalue based detection has many advantages, such as it does not require knowledge on primary user signal or noise power level. However, most of the work on eigenvalue based detection methods presented in the literature rely on multiple sensing nodes or receiving antennas so that they cannot be directly applied to single antenna systems. In this paper, an effective PU signal detection method based on eigenvalue is proposed for a cognitive user equipped with a single receiving antenna. The proposed method utilizes the temporal smoothing technique to form a virtual multi-antenna structure. The maximum and minimum eigenvalues of the covariance matrix obtained by the virtual multi-antenna structure are used to detect PU signal. Compared with the previous work, the presented method offers a number of advantages over other recently proposed algorithms. Firstly, the presented approach makes use of power method to calculate the maximum and minimum eigenvalues, it has lower computational complexity since the eigenvalue decomposition processing is avoided. Secondly, it can reduce system overhead since single antenna is used instead of multiple antennas or sensing nodes. Finally, simulation results show that performance of the proposed method is close to that of maximum-minimum eigenvalue detection using multiple antennas.

This paper proposes an imaging scheme using a random sparse array (RSA) structure for radar target detection using compressed sensing (CS). The array collects sparse measurements with less collection time and data storage. Two schemes of the RSA are considered, random SAR mode and random array mode. Performances of both static and moving target detections are investigated. Performance of RSA with CS is compared with that using full SAR data with conventional back-projection (BP) method for static target detection and full uniform linear array (ULA) data with conventional beamforming (CBF) method for moving target detection. Simulation and real experimental tests are provided to verify the proposed target imaging scheme. Results show that RSA imaging with CS can perform better than normal SAR and ULA with conventional imaging methods. However, when environment is complicated and background too noisy, CS may have degraded performance.

We present an efficient scheme for the analysis of electromagnetic scattering from target and environment composite model. In this scheme, the whole computed domain is divided into a target part and an environment part, and each part is formulated by different integral equations. The two parts are solved one by one until the relative residual error is less than a given value. Compared with conventional solution with pure electric field integral equation (EFIE), the proposed scheme has a better convergence and lower memory requirement. Additionally, the multilevel fast multipole algorithm (MLFMA) is utilized to accelerate the computations of matrix vector product. Simulated radar-cross-section (RCS) results of several examples demonstrate its validity and efficiency.

Based on the method of the vectorial angular spectrum, an analytical expression of the electric field of an elegant Laguerre-Gaussian beam in free space is derived beyond the paraxial approximation, and the corresponding magnetic field is obtained by taking the curl of the electric field. By using the expressions for the electromagnetic fields, the expression of the orbital angular momentum density of the elegant Laguerre.Gaussian beam is derived, which is applicable to both the near and far fields. The effects of the three beam parameters on the distribution of the orbital angular momentum density of the elegant Laguerre-Gaussian beam are studied. The distribution of the orbital angular momentum density of the elegant Laguerre-Gaussian beam is also compared with that of the standard Laguerre-Gaussian beam. The result shows that the distribution of the orbital angular momentum density of the elegant Laguerre-Gaussian beam is more simple and centralized than that of the standard Laguerre-Gaussian beam.

The Omnidirectional reflection characteristics of one-dimensional (1D) superconducting-dielectric binary graded photonic crystals (PhCs) are studied by using transfer matrix method. The influences of thickness changing rate, numbers of periods, incident angles are analyzed. And the omnidirectional photonic band gaps are extended markedly in the 1D thickness-graded superconducting-dielectric PhC.

We create an invisible gateway simply by putting electric and magnetic superscatterers in a metallic waveguide. The characteristics of the electric and magnetic resonators are analyzed in a metallic hollow waveguide, and the dual-mode superscattering property is discussed in detail to broaden the bandwidth of the invisible gateway. Good agreement is achieved between the simulation and measurement for such an invisible gateway. The present work help readers understand easily how an invisible gateway works (or makes sense) in a classical way without using any complex metamaterial or complicated method of transformation optics.

A novel coupled-fed antenna with compact branch-structure for 4G mobile phone is proposed in this paper. In the proposed design, a driven monopole strip and coupled branch-strips are developed to produce different operation band. The prototype of the proposed antenna was fabricated, tested and discussed. Simulation and measurement results reveal that the proposed antenna can provide two wide frequency bands (698~960 MHz, and 1710~2690 MHz), which covers multi-band for LTE700/GSM850/GSM900/DCS1800/PCS1900/UMTS/LTE2300/LTE2500. The proposed antenna with compact size of 34×12×6.5 mm³ is suitable for today's mobile phone application.

In this paper, a complete model structure for propagation inside tunnels is presented by following the segmentation-based modeling thought. According to the concrete propagation mechanism, totally five zones and four dividing points are modeled to constitute three channel structures corresponding to large-size users and small-size users. Firstly, the propagation characteristics and mechanisms in all the zones are modeled. Then, from the view point of the propagation mechanism, the criterion of judging the type of a user is analytically derived. Afterwards, all the dividing points are analytically localized as well. Finally, a panorama covering all the propagation mechanisms, characteristics, models, and dividing pints for all types of users is presented for the first time. This panorama is very useful to gain a comprehensive understanding of the propagation inside tunnels. Validations show that by using the analytical equations in this paper, designers can easily realize a fast network planning for all types of users in various tunnels at different frequencies.

A novel reduced size three band Koch Pentagonal fractal antenna is presented. The proposed antenna uses pentagonal shape for the basic fractalization combined with inner sides etched with Koch fractal pattern of the first iteration providing reduction in the overall size of the antenna. For higher order of iterations, more size reduction is achieved, producing equal number of radiation bands. Optimization is done for achieving radiations in the S, C and X bands. Ansoft HFSS, CST Microwave Studio and Solid Works are used for the 3D Modeling, S11 frequency optimization and radiation pattern calculations. The proposed third iteration fractal configuration is fabricated on Rogers RT5870, and measured results are presented. Size reduction up to 43.26 percent in terms of its overall size and 75.18 percent in terms of copper cladding remaining is achieved for the third iteration proposed fractal antenna in comparison to pentagonal patch antenna operating in the first resonant frequency band.

A simple and analytical design methodology for a novel multi-way Bagley Polygon power divider with arbitrary complex terminated impedances is proposed in this paper. The design parameters including electrical lengths and characteristic impedances can be obtained by the provided closed-form mathematical expressions when complex terminated impedances are known. Moreover, for convenient test, we design an impedance transformer to transform the complex impedance into real impedance using an extension line, and especially a reflection coefficient chart to solve it. Four special cases of 3-way Bagley Polygon power divider operating at 2.4 GHz are fabricated and measured with different condition complex terminated impedances for the purpose of verification. Excellent agreement between simulation and measurement results proves the validity of the design method. The presented Bagley Polygon power divider exhibits 180° phase difference between any two adjacent output ports and 0° phase difference between two symmetrical output ports and is suitable for multi-antenna and differential antenna system. Furthermore, simple layouts lead to convenient design procedure and easy fabrication.

The paper aims to investigate the use of the Finite Element Method for electrical and mechanical faults detection in three-phase squirrel cage, induction machines. The features of Finite Element Method are significant, which consider the physical mapping of stator winding and rotor bar distribution. Therefore, modeling of the faults in stator winding, rotor bars and air-gap eccentricity will be predicated in more accurate way. In comparison with conventional methods such as coupling method, the Finite Element Method considers the complex machine geometry, material type of the bar, current and the flux distributions within the electrical machines. As a result, the air-gap eccentricity and the broken bars can be modeled effectively using this approach. Motor current signature analysis has been used to give a decision about the fault occurrence. For the broken rotor bar, frequency of the sideband components around the fundamental is used to indicate the presence of fault. However, the sideband frequencies cannot be used to recognize the stator winding short circuit and eccentricities faults, where the harmonics have approximately the same frequency over the spectrum. The amplitude of the sideband harmonic components have been used to differentiate between them. It has been found that the inter-turn short circuit faults have a sideband harmonic component with amplitude greater than that in the case of the air-gap eccentricity faults. Also current paper introduce the detection of broken rotor bars based on stator current envelope technique.

Mass-lumped continuous finite elements allow for explicit time stepping with the second-order wave equation if the resulting integration weights are positive and provide sufficient accuracy. To meet these requirements on triangular and tetrahedral meshes, the construction of higher-degree elements for a given polynomial degree on the edges involves polynomials of higher degrees in the interior. The parameters describing the supporting nodes of the Lagrange interpolating polynomials and the integration weights are the unknowns of a polynomial system of equations, which is linear in the integration weights. To find candidate sets for the nodes, it is usually required that the number of equations equals the number of unknowns, although this may be neither necessary nor sufficient. Here, this condition is relaxed by requiring that the number of equations does not exceed the number of unknowns. This resulted in two new types elements of degree 6 for symmetrically placed nodes. Unfortunately, the first type is not unisolvent. There are many elements of the second type with a large range in their associated time-stepping stability limit. To assess the efficiency of the elements of various degrees, numerical tests on a simple problem with an exact solution were performed. Efficiency was measured by the computational time required to obtain a solution at a given accuracy. For the chosen example, elements of degree 4 with fourth-order time stepping appear to be the most efficient.