A proximity-fed MIMO (multiple-input-multiple-output) antenna with two printed IFAs (inverted-F antennas) and a wideband T-shaped neutralization line is presented. Each element printed IFA is fed by a proximity-fed structure which provides a parameter to control the return loss without effect on the isolation of the two IFAs. The wideband T-shaped neutralization line, which consists of two meandered branches and a rectangular grounded branch, can enhance the isolation of the two IFAs over a wide operation band (2.35-3.75 GHz). The two meandered branches are connected to the two IFAs, respectively, and the rectangular branch is connected to the ground plane. There are two parameters to adjust the isolation without effect on the return loss. Therefore, the operational bandwidth and the isolation of the proposed antenna can be controlled independently. A bandwidth of 46% with VSWR ≤ 2 and isolation ≥ 20 dB from 2.35 to 3.75 GHz is achieved. The MIMO antenna of compact size 40 x 14 mm2 is suitable for application in mobile phones. Moreover, the ground plane size can be changed for applying the proposed antenna in different handsets. The results, including S-parameters, radiation pattern, mean effective gain (MEG), radiation efficiency, complex correlation coefficient and the effects of human hand and head, indicate the proposed MIMO antenna can provide spatial and pattern diversity.
The excitation of ion azimuthal surface oscillations with extraordinary polarization by light ion beam is studied analytically. Beam-plasma system consists of a cylindrical metal waveguide filled partially by cold magnetized plasma and light ion flow rotating around the plasma column. Dependencies of the beam instability growth rate on the system parameters (plasma and beam densities, value of the external axial magnetic field, radius of the plasma column, width of the gap between the plasma column and the waveguide wall, absolute value and sign of the azimuthal wave number) are analyzed numerically.
Scattering of electromagnetic plane wave from an infinitely long circular DB cylinder placed in chiral and chiral nihility metamaterials is studied, and the results are compared with that of scattering from DB cylinder placed in free space. The discussion is further extended by considering coating of DB cylinder with chiral/chiral nihility metamaterial. For DB cylinder placed in unbounded free space/chiral/chiral nihility metamterial, only co-polarized scattered fields are obtained, whereas, for chiral/chiral nihility metamaterial coated case, both co- and cross-polarized scattered fields are noted. Numerical results are presented for different values of chirality parameter.
A full-wave analysis for determining the resonant frequency, quality factor and far-zone radiation patterns of a circular disk and annular ring microstrip patches, printed on a uniaxial anisotropic substrate is presented. Green's functions of the structure are determined in Hankel transform domain (HTD) using Hertz potential vectors. Galerkin's method, together with parsval's relation in Hankel transform domain is then applied to compute the resonant frequency and quality factor. The far-zone radiation patterns are expressed in terms of Hankel transforms of the tangential fields on the substrate. Wave equation is solved in cylindrical coordinates for the structure to estimate the basis function. The numerical results show that there are substantial deviations in calculated resonant frequency and quality factor when substrate dielectric anisotropy is considered. Furthermore, significant variations are seen in the radiation patterns of the structures due to substrate anisotropy. The variations of resonant frequency, quality factor and radiation patterns of the structure, with respect to anisotropy ratio of the substrate, for several values of substrate thickness and patch radius are presented.
The success of wireless technologies could paradoxically leads to a collapse in their performance: the interference between adjacent networks and the attacks done by users from outside the expected coverage limits are two important enemies to the well function of the networks. The proposal of this paper is simple but efficient: the use of vegetation barriers to create shadowing areas with excess attenuations in the edge of the service area, in order to reduce the coverage distance of each wireless node, reducing the possible interference to other networks as well as improving security aspects by minimizing the signal strength outside the service area.
The dependence of reflectivity on inhomogeneous plasma density for one dimensional plasma photonic crystal is presented. The exponential varying and linear varying plasma density profiles have been chosen in such a way that the volume average permittivity remains constant. The transfer matrix method is used to derive the dispersion relation and reflectivity of the proposed structures by employing the continuity conditions of electric fields and its derivatives on the interface. The exponential varying plasma density profile gives high reflectivity than the linear varying plasma density profile in all considered cases. Also the exponential varying plasma density profile shows perfect reflection in considered volume average permittivity. This profile may be used in sensor applications or in plasma functional devices.
With the increases of the module integration density and complexity in electrical and power electronic systems, serious problems related to electromagnetic interference (EMI) and electromagnetic compatibility (EMC) can occur. For the safety, these disturbing effects must be considered during the electronic equipment design process. One of the concerns on EMC problems is induced by unintentional near-field (NF) radiations. The modeling and measurement of EM NF radiations is one of the bottlenecks which must be overcome by electronic engineers. To predict the unwanted different misbehaviors caused by the EM radiation, NF test benches for the reconstitution of scanning maps at some millimeters of electrical/electronic circuits under test were developed at the IRSEEM laboratory. Due to the difficulty of the design with commercial simulators, the prediction of EM NF emitted by active electronic systems which are usually based on the use of transistors necessitates more relevant and reliable analysis techniques. For this reason, the main focus of this article is on the experimental analysis of EM NF radiated by an MOSFET transistor with changing electrical parameters. Descriptions of the experimental test bench for the EM map scan of transistors radiation are provided. This experimental setup allows not only to detect the EM NF emission but also to analyze the influence of the excitation signal parameters as the cyclic ratio. It is found that the magnetic radiation is maximal when the cyclic ratio is close to 50%. In the future, In the future, the technique introduced in this article can be used to evaluate the EM radiation of embedded electronic/electrical devices in order to improve the safety and security of electronic systems.
The existence of reverse radiation noise in the millimeter-wave (MMW) radiometric imaging system with a superheterodyne receiver seriously affects the imaging experiments carried out at short range, thus leading to the degradation of MMW radiometric images and difficulty in recognizing targets. Based on the generation mechanism of reverse radiation noise, the specific influence on imaging for relative radiometry is investigated in this paper, and some methods of eliminating or reducing this noise are proposed. Then, two series of comparative imaging experiments are conducted with a 3 mm band radiometric imaging system. Both theoretical analysis and experimental results are presented to validate the actual existence of interference-like stripes imposed by the reverse radiation noise. Moreover, it is proved that adopting an isolator in the MMW receiving front-end can effectively reduce the reverse radiation noise and significantly improve the imaging performance.
This paper proposes an algorithm for wide-band microwave imaging for the detection of a hemorrhagic stroke. A realistic head phantom and finite-difference time-domain program are used to estimate back-scattered signals which are subsequently used in the image reconstruction process. The proposed imaging approach can lead to a portable and cost effective system; particularly suitable for rural medical clinics that lack the necessary resources in effective stroke diagnosing.
Up to now, ray-tracing simulations are commonly used with a deterministic approach. Given the input parameters, the ray-tracing algorithm computes a value for the electric field. In this paper, we present a method that aims at computing the mean and standard deviation of the electric field. More precisely, we aim to obtain the probabilistic content of the electric field value and direction. We assume that this uncertainty results from input random variables which we consider uniformly distributed. Since ray-tracing computations have a high computational cost, we use spectral methods in order to optimize the number of simulations. We consider 2D electromagnetic propagation for the multi-path components, which can interact with the environment through four processes: transmission, single reflection, double reflection and diffraction. These are modelled using adequate coefficients. In order to calculate the polynomial chaos expansion coefficients, we use the projection method and Gauss-Legendre quadratures. These coefficients can then be used to determine the Sobol indices of input parameters. This is done in order to neglect variables in practical computation of the uncertainties.
Estimation and mitigation of multipath error improves the positional accuracy of GPS. The objective of this paper is to estimate the effect of multipath interference at the receiver antenna based on both code and carrier phase measurements using Code minus Carrier (CMC) technique, and suggest a suitable method to mitigate it for static applications. Different adaptive filters such as Least Mean Squares (LMS) and various Recursive Least Squares (RLS) are considered to mitigate the error. The estimated multipath error for a typical signal is 0.8 m and 2.1 m on L1 and L2 carriers, respectively. The results due to adaptive filtering methods are encouraging and significant reduction of error (cm level) is observed. It is found that, when compared with experimental static dual frequency GPS receiver data, LMS and RLS filters give better error minimization on L1 and L2, respectively.
The classical problem for diffraction of a plane wave with an arbitrarily oriented wave vector at a strip is considered asymptotically by Wiener-Hopf method. The boundary-value problem has been broken down into distinct Dirichlet and Neumann problems. Each of these boundary-value problems is consecutively solved by a reduction to a system of singular boundary integral equations and then to a system of Fredholm integral ones of second kind. They are solved effectively by a reduction to a system of linear algebraic equations with the help of the etalon integral and the saddle point method.
Based on linear optical transformation method, a diamond shaped reciprocal cloak with perfect invisibility in a certain direction is proposed. Compared with traditional cloaks, the object hidden inside the reciprocal cloak is not blind and can receive information from the outer region. Moreover, the reciprocal cloak is constructed of nonsingular homogeneous material parameters with reduced anisotropy that is relatively easy for practical realization. Full wave simulations validate the performance of the cloak.
There is increasing interest in electromagnetic interference (EMI) shielding due to the serious electromagnetic environment pollution caused by the continuously increased use of the electrical products and electronic devices. Electrical conductivity and EMI shielding effectiveness (SE) of composite materials made from silicone rubber with carbon powder and ferrite powder have been studied in microwaves and terahertz frequency ranges and the results are presented in this paper. In microwaves range, samples with higher electrical conductivity show a small variation of shielding performance with frequency, whereas the performance of samples with lower conductivity falls away with increasing frequency. It is shown that the variation of attenuation with frequency relates to the conductivity of the material.
In this study, refractive index changes associated with intersubband transitions in a spherical quantum dot, GaAs/AlxGa1-xAs, have been theoretically calculated in the presence of impurity. In this regard, the effect of dot radius, stoichiometric ratio, impurity and incident optical intensity on the refractive index changes have been investigated for the transitions between higher energy states, i.e., 1s-1p, 1p-1d and 1d-1f. The results show that these parameters have a great influence on the refractive index changes.
A cylindrical wave expansion method is used to obtain the scattering field for a two dimensional cylindrical invisibility cloak incorporating perfect electromagnetic conductor (PEMC) at perturbed void region. A near-ideal model of the invisibility cloak is set up to solve the boundary-value problem at the inner boundary of the cloak shell. It is confirmed that a cloak with the ideal material is a perfect cloak by observing the change of the scattering coefficients from the near-ideal case to the ideal one. However, because of the slow convergence of the zeroth-order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering. A better convergence rate of the scattering coefficients has been observed for decreasing δ in PEMC case.
A tunable microwave notch filter is developed on magneto-dielectric material having low saturation magnetization to attain low external dc magnetic field for biasing. A simple microstrip line at 10 GHz is developed on nickel ferrite/low density polyethylene nanocomposite system as substrates and its microwave transmission response is studied in X-band. Composite system is developed by dispersing nano sized nickel ferrite (~6.63 nm) in low density polyethylene to obtain a homogeneous flexible substrate. Saturation magnetization of 4% volume fraction of the composite is found to be 1.8745 emu/g. Tunability of Q value and insertion loss is studied with magnitude of external dc magnetic field and at different angles of its orientation with the axial plane. A very low field up to 250 G is sufficient to tune the selectivity. An insertion loss of ~-30 dB and Q ~ 375 at 10.2 GHz is observed. The interaction of magneto static modes with orientation of the applied dc magnetic bias with respect to rf magnetic field is discussed with couple mode theory. Good cut-off behaviour of more than 28 dB is observed at magnetic field angles from 23.52° to 34.21°. The experimental and theoretical couplings show close proximity.
Conventional interferometric ISAR (InISAR) imaging requires a radar system with at least three antennas, and the hardware complexity may be a main obstacle to practical realization. In this paper, we propose an InISAR three-dimensional imaging algorithm using only one antenna. Interferometric processing is carried out among ISAR images obtained during three near measurement intervals. The scatterer position in the range direction is obtained from range cell number in ISAR images, and the azimuth/height information is estimated from interferometric phases and geometrical relationship. Moreover, the target track requirements of the proposed method are also investigated. Simulations have shown the effectiveness of the proposed method.
A miniaturized printed log-periodic fractal dipole antenna is proposed. Tree fractal structure is introduced in an antenna design and evolves the traditional Euclidean log-periodic dipole array into the log-periodic second-iteration tree-dipole array (LPT2DA) for the first time. Main parameters and characteristics of the proposed antenna are discussed. A fabricated proof-of-concept prototype of the proposed antenna is etched on a FR4 substrate with a relative permittivity of 4.4 and volume of 490 mm × 245 mm × 1.5 mm. The impedance bandwidth (measured VSWR < 2) of the fabricated antenna with approximate 40% reduction of traditional log-periodic dipole antenna is from 0.37 to 3.55 GHz with a ratio of about 9.59 : 1. Both numerical and experimental results show that the proposed antenna has stable directional radiation patterns and apparently miniaturized effect, which are suitable for various ultra-wideband applications.
In this paper, we consider a dense array of metallic circular patches printed on a electrically thin metal-backed dielectric substrate. Since the sub-wavelength dimensions, the array and the metal-backed substrate can be described in terms of a lumped capacitance and a lumped inductance, respectively. Around the resonant frequency, the structure, known as high-impedance surface, reflects totally an incident electromagnetic wave with zero shift in phase. Due to this property, it is widely employed in antenna systems as compact back reflector with improved performances with respect to typical metal reflector. Starting from the concept of the grid capacitive reactance of a planar array of squared patches and its related formulas, we investigate on the field distribution on the array plane and properly modify the formulas for the case of the circular patches. We present two new analytical formulas which can be effectively used for the fast design of 2D-isotropic circular HISs. In order to validate the models, we compare the resonant frequency of the array obtained through our approaches to the one resulting from full-wave numerical simulations and from other analytical methods available in the open technical literature.