This paper presents an electronically tunable dual-band filtering power divider (TDFPD) with tuning diodes sharing technique. Two dual-mode tunable resonators (DMTRs) are embedded into a conventional power divider to achieve dual-band tunable bandpass filtering response. The two bands of the proposed TDFPD can be tuned independently. Tuning diodes sharing technique is utilized to reduce the number of tunable diodes. A prototype has been designed and fabricated to validate the proposed design as shown by the good agreement between the measured and simulated results. The measurement shows that the center frequencies of the lower and upper bands can be independently tuned from 1.31 to 1.62 GHz and 2.92 to 3.30 GHz, respectively. Within the passbands, isolation between the two output ports is higher than 16 dB with small phase and magnitude imbalance.
We analyze relief graphene gratings by the coordinate transformation method (the C-method). This method is also used for analysis of multilayer gratings with graphene sheets at the interfaces. By using this method, we are able to obtain the eciency of deep graphene gratings with fast convergence rate while previous methods are limited to very shallow graphene gratings. Moreover, a terahertz polarizer is designed by relief graphene grating. Polarization extinction ratio and transmittance of single-layer and double-layer polarizer are simulated by the C-method. Double-layer polarizer gives extinction ratio from 22 dB to 10 dB over a frequency range of 1 GHz to 4 THz.
Solutions to the Maxwell equations for a planar non-integer dimensional perfect electric conductor (NID-PEC) waveguide are obtained. The space within the guide is NID in direction normal to walls of the waveguide. Field behaviour within the waveguide is noted for different values of the parameter, D, describing dimension of the NID space. For D = 2, classical results are recorded. The discussion is further extended by treating propagation in a tunnel within unbounded dielectric medium. The space within tunnel is also NID in direction perpendicular to walls of the tunnel. For different values of Dfield behaviors are also presented. It has been noted that for D = 2 and taking very high values of permittivity (ϵ → ∝) classical results for PEC waveguide are recorded. Whereas for ϵ → ∝, field behavior within tunnel matches with NID-PEC waveguide.
High power amplifier not only causes in-band intermodulation but also causes out-of-band harmonic distortion. For a wideband transmitter, harmonic distortion out of communication frequency can be restrained by a radio-frequency filter, but harmonic distortion in the communication frequency is difficult to restrain. In this paper, we develop harmonic memory proper to model harmonic distortion and then propose a digital harmonic canceling algorithm based on direct learning structure - nonlinear filtered-x ane projection algorithm (NFX-APA). Simulation and measurement results demonstrate that this novel digital canceling method can cancel harmonic effectively.
Eddy current testing (ECT) is known as an effective technology for inspecting surface and near surface defects in metallic components. It is well known that the amplitude of eddy current (EC) density decreases with increasing depth, which is referred to as skin effect. Skin depth is an important parameter that quantifies the speed of attenuation of EC in the depth direction and is closely related to the capability of ECT for detecting deeply hidden defects. It is found that the traditional formula for calculating skin depth derived under the assumption of uniform plane field excitation is not applicable to the cases of ECT with coils. The skin effect in component with flat surface excited by pancake coil has been investigated by the authors. The skin effect in conductive tube tested by bobbin coil and that in conductive bar tested by encircling coil are more complex. The paper studies the skin effect in these two cases. Finite element analysis shows that the attenuation of EC is not only due to the ohmic loss, but also influenced by the diffusion effects, the aggregation effect, and the combined cancellation/diffusion effect of EC. The skin depth of EC associated with bobbin coil is always smaller than that associated with uniform plane field excitation, whereas the skin depth of EC associated with encircling coil can be greater than that associated with uniform plane field excitation under certain conditions.
In the recently published article, Sood et al. (Progress in Electromagnetics Research M, Vol. 44, 3946, 2015) proposed a wide-angle ultra-thin metamaterial absorber structure for wideband applications. The reported unit cell was shown to have simulated wideband absorbivity FWHM bandwidth of 1.94 GHz i.e. from 5.05 GHz to 6.99 GHz. In this article, we prove that the reported structure is not an electromagnetic wave absorber. For the reported structure, we find that absorption is less than 22.3% over a operating bandwidth of 4 GHz to 8 GHz. It is demonstrated that the strong absorption was caused due to ignorance of cross-polarization effect rather than true absorption as they claimed.
The discovery of ``quasi-crystals,'' whose X-ray diﬀraction patterns reveal certain unusual features which do not conform with spatial periodicity, has motivated studies of the wave-dynamical implications of ``aperiodic order.'' This paper discusses various aperiodic configurations generated by Rudin-Shapiro (RS) sequences. These RS sequences constitute ones of the simplest conceivable examples of deterministic aperiodic geometries featuring random-like (dis)order. The scattering properties of aperiodically-ordered thinned 2-D patch arrays based on RS sequences are analyzed by using physical optics approximation. Compared to a periodic case, RS-based antenna array is found to have a substantial reduction in the magnitude of the backscattering component of the scattered signal with half of the elements and the same magnitude of specular reflection. This property is verified by illustrative numerical parametric studies.
This paper presents a broadband planar printed antenna comprising two dipoles with different lengths and a transition structure of microstrip (MS) to coplanar stripline (CPS). These two dipoles are serially connected through CPS. By adding trapezoid and stepped patches, the dipole elements are modified for enhancing the impedance matching of the antenna. In addition, a tapered transition is adopted in the CPS to achieve improved impedance matching. The current work shows a good agreement between measured and simulated results. The measured bandwidth is from 2.43 to 8.04 GHz for VSWR≤2, corresponding to 107.2% fractional bandwidth. Measured peak gain≥4.0 dBi is obtained in the whole operating band.
In this paper, we present a straightforward numerical algorithm for visual image sequential motion detection based on half quadratic minimization method. To solve the optimization problem modeled for sequential motion detection, an auxiliary functional is introduced. The proposed algorithm is more efficient since the iterative computation is operate mainly on the current frame rather than the whole batch of images. As for the standard visual image sequences with RGB color representation, an intuitive way is to convert it to grayscale image to achieve an approximate motion detection with relatively low computational load. Instead, we propose an improved processing scheme for more accurate detection by utilizing the algorithm separately and then perform fusion on a higher level. Experiment results show that the proposed algorithm can successfully detect moving object in practical visual surveillance applications.
This paper describes a method of designing Frequency Selective Absorber (FSA) which has a transmission band between two neighboring absorption bands. The proposed FSA is composed of a lossy layer on the top and a lossless layer at the bottom. The transmission characteristic is produced by the parallel LC resonators embedded in the lossy layer while the absorption ability is realized by the lumped resistors constructed in the lossy layer. An equivalent circuit model (ECM) is developed and discussed for a better understanding of this method. An FSA prototype is fabricated and measured for demonstration. Experiments show that the proposed FSA has a transmission band at the center frequency of 8.14 GHz, which agrees well with simulation. Both transmission and refection coefficients from 4.5 GHz to 7.5 GHz and from 9.1 GHz to 11.3 GHz are under -10 dB, which indicate good absorption in these frequency bands. In addition, the performance of the proposed FSA demonstrates a low sensitivity with respect to the polarization of incident EM waves and is maintained well when the incident angles range from 0˚ to 45˚.
Ground penetrating radar (GPR) may be used to detect cracks in a buried pipe. Using GPR, there are only a few techniques, such as statistical approach robust principal component analysis (RPCA). to detect cracks in buried objects. Buried nonmetallic pipe crack detection is an important application for GPR to analyze the structural health of underground pipelines. The strength of a reflected signal may be feeble from a cracked location as compared to position with respect to that from other positions of the pipe. Currently, crack detection is a challenging task, especially when the buried pipe is nonmetallic, and soil moisture varies. In this paper, the problem of crack detection in a PVC pipe using GPR is attempted. It is a challenge to detect small sized cracks in an underground PVC pipe because the GPR image is flooded with correlated background signal or clutter, and the image patterns are typically irregularly distributed. In order to efficiently detect the crack in a buried PVC pipe, a novel adaptive crack detection algorithm has been developed with the help of covariance of real GPR data and covariance of normal distributed synthetic Gaussian data. Results are evaluated and validated to show the effectiveness of crack detection algorithm.
The study done in this paper focuses on the detection of breast cancer by neuronal approach, by rotating the transmitting antenna from 15°, 30°, 45°, 60°, 75° to 90° relative to its initial position which is of 0° (i.e. to the opposite of the reciving antenna). We have generated our database by using a CST electromagnetic simulator for each antenna location. Then the learning and test phases of our artificial neural network (ANN) are done for seven antennae locations using two learning algorithms which are: the Scaled Conjugate Gradient Back-propagation (Trainscg) and the Gradient Descent with Momentum (Traingdm). A comparative study was conducted for all the seven cases. The results obtained are very satisfying and show that the best location of the transmitter antenna is at 60° and that the learning algorithm Trainscg gives better results than Traingdm.
In this paper, a novel planar waveguide with quasi-TEM mode for periodic structure measurement applications is proposed. Unlike conventional parallel double conductor transmission lines (PDCTL) which suffer from mismatch to 50 ohms, high insertion loss in higher frequency band, the proposed planar waveguide consisting of an F4B substrate, s metal conductor line, and a metal base has easy access to match to 50 ohm through a special transition region and also has a satisfactory insertion loss in a wide band. The metal conductor line etched on one side of the F4B substrate, and the metal base is parallel to mimic a perfect electric wall, where a ``fake'' infinite plane is realized. The proposed planar waveguide has wide measurement bandwidth with the reflection coefficient below -15 dB, which cannot be realized by a standard rectangular waveguide. Good agreements between the simulated and measured results are obtained. In addition, a simple periodic structure is designed as an example. The transmission characteristics of the periodic structure are simulated and compared in two different methods, namely, standard periodic structure simulation method in free space and proposed planar waveguide method. All the measured results demonstrate the validation of our designed planar waveguide, which is convenient and economic for periodic structure measurement applications.
The proposed microstrip antenna is based on fractal techniques and designed for wireless applications. The radiating element is an A-shaped triangle on which fractal concept is applied. Fractal concept is applied on the proposed A-Shaped Fractal Microstrip Antenna (ASFM-Antenna), similar to English alphabet letter A. Further the analysis and verification of result is achieved by testing the fabricated antenna and also comparison of simulated and experimental results. Von Koch's snowflake concept is used in which a single line is divided into four new lines, and it is done at each side of the triangle. This step is repeated. In this paper, a two-iteration Koch generator is used, thus the proposed antenna is designed. Simulations are carried out using commercially available HFSS (High Frequency Structure Simulator) based on finite element method. The antenna is simulated and fabricated, and results are recorded. It is found that simulated and experimental results are in close agreement with each other. The antenna resonates at 11.44 GHz, 13.178 GHz, 15.482 GHz, 19.902 GHz and 23.529 GHz. Hence, X-band [8.2-12.4 GHz], Ku-band [12.4-18 GHz] and K-band [18-26.5 GHz] are the frequencies of operating bands under consideration.
A synthesis problem of a 2D array of thin linear vibrators, whose geometric centers are located at the nodes of a flat rectangular grid with double periodicity solved. The problem can be formulated as follows. A 2D antenna array radiates monochromatic electromagnetic waves into free space. Suppose that the array radiation pattern (RP) can be scanned in space by varying complex surface impedances of separate vibrators. Then, it is necessary to determine vibrator surface impedances to control the direction of the RP maximum. The analytical solution of the impedance synthesis problem, as an alternative to a numerical solution of a two-dimensional equation system, was obtained under two assumptions: the vibrators are excited by electric currents of equal amplitudes, and the RP of each radiator does not differ from that of an isolated radiator. Verification of theoretical formulas will be done by comparing them with relations known for one-dimensional equidistant arrays.
A self-consistent time-domain travelling-wave model for the simulation of self-assembled quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) is developed. The 1-D time-domain travelling-wave model takes into consideration of time-varying QD optical susceptibility, refractive index variation resulting from intersubband free-carrier absorption, homogeneous and inhomogeneous broadening, and QD spontaneous emission noise source. Carrier concentration rate equations are considered simultaneously with the travelling wave model. Effects of temperature on optical susceptibility and carrier density in the active region are taken into account. The model is used to analyze the characteristics of 1.3-μm oxide-confined QD InAs-GaAs VCSEL. The field distribution resulting from time-domain travelling-wave equations, in both the active region and distributed Bragg reflectors, is obtained and used in finding the device characteristics including light-current static characteristics considering the thermal effect. Furthermore, the dynamic characteristics and modulation frequency response are obtained in terms of inhomogeneous broadening.
An annular-ring element for building a miniaturized bandstop frequency selective surface (FSS) structure which possesses a superior performance with respect to electromagnetic wave polarizations and incident angles is introduced in this paper. The proposed element has prominent miniaturization characteristics with a unit dimension of 0.061λ×0.061λ, where λ represents the free-space wavelength corresponding to resonant frequency. Miniaturization of the proposed FSS element is achieved by constructing special meandered strips in geometry and arranging lumped components between the elements. The advantage of this method lies in its great simplicity in tuning the resonant frequency of FSS by adjusting values of the printed capacitors rather than rebuilding the geometry. The obtained FSS also exhibits a stable performance in terms of angle stability and polarization insensitivity. Prototypes of the proposed FSS are fabricated and measured to verify design method. Measurements are well in line with simulation results.
This paper proposes a two-dimensional (2-D) inverse synthetic aperture radar (ISAR) imaging method with nonuniformly obtained angle samples. A one-dimensional (1-D) radar image, a range profile, is obtained using frequency samples within a given bandwidth. 2-D ISAR images are then obtained by acquiring the Doppler spectrum using range profiles obtained from multiple observation angles having a constant interval. However, when ISAR images are obtained by applying the range-Doppler imaging method for a target scattered signal with nonuniform angle samples, a clear image cannot be obtained. In this paper, we propose a method to generate a covariance matrix from a nonuniform angle sample and obtain an ISAR image based on the multiple signal characterization (MUSIC) technique. The proposed method can be applied to the target scattering signal using a search radar, which observes target with nonuniform aspect angles. We present a scattering signal model of a target for the search radar and provide ISAR images obtained by applying the proposed method to simulated and measured data, respectively. Results reveal that the proposed method improves image quality and reduces computation time compared to the conventional method.
A wideband circularly polarized magnetoelectric dipole antenna fed by a Γ-shaped structure is investigated. In the design, a pair of vertical plates connected to ground work as a magnetic dipole, while a pair of rotationally symmetric horizontal plates with strips bent downward work as an electric dipole. And four metallic plates are vertically added on edges of the ground, forming a cavity reflector with four gaps to improve the axial ratio (AR) bandwidth. Measurements show that the antenna has a wide impedance bandwidth of 102% from 1.35 GHz to 4.2 GHz for voltage standing wave ratio (VSWR) ≤ 2 and a 3-dB AR bandwidth of 79.7% from 1.6 GHz to 3.72 GHz, over which the antenna gain varies from 5.4 dBic to 10.6 dBic. Furthermore, the antenna exhibits right-hand circular polarization and has good unidirectional radiation characteristic. The proposed antenna can be applied to wideband wireless applications.