Design of multiband antennas with low volume is of practical interest for the ever growing wireless communication industry. In this regard, the design of a small multi band microstrip patch antenna (MPA) for GSM900 (880-960 MHz), GSM1800 (1710-1880 MHz), GSM1900 (1850-1990 MHz), UMTS (1920-2170 MHz), LTE2300 (2305-2400 MHz), and Bluetooth (2400-2483.5 MHz) applications by using a genetic algorithm (GA) is proposed. The proposed GA method divides the overall patch area into different cells taking into account that cells have a small overlap area between them. This avoids optimized geometries with certain cells having only an infinitesimal connection to the rest of the patch. Therefore, the proposed method is robust for manufacturing. A shorting pin is also included for impedance matching. GA optimization combined with finite element method (FEM) is used to optimize the patch geometry, the feeding position and the shorting position. A prototype has been built showing good agreement with the simulated results. The optimized MPA has a footprint of 46 mm × 57 mm (0.138λ x 0.171λ at 900 MHz) and an air gap of 10 mm. It shows a reflection coefficient less than -10 dB at all six bands and can be useful for a base station antenna.
The element failure of antenna arrays increases the sidelobe power level. In this paper, the problem of antenna array failure has been addressed using Firefly Algorithm (FA) by controlling only the amplitude excitation of array elements. A fitness function has been formulated to obtain the error between pre-failed (original) sidelobe pattern and measured sidelobe pattern and this function has been minimized using FA. Numerical example of large number of element failure correction is presented to show the capability of this flexible approach.
A compact 90° bent equal output ports of photonic crystal (PC) beam splitter (BS) with complete band gap (CPBG) based on the effect of defect resonance interface (DRI) in PC waveguides is designed and analyzed. The finite-difference time-domain method is adopted to simulate the relevant structures of defect mode in a two dimensional square lattice circular dielectric rods of anisotropic PC. The device size reduction and flexibility in polarization dependence compared with the conventional PCBS can be attributed to the same resonant frequency for both transverse-magnetic and transverse-electric polarization, because the PC structures designed here have a CPBG. The merit of our proposed PCBSs with identical lights at the output ports possess the short coupling length with direct coupling (the coupling length is the same as that of the width of DRI, 3a) and the short distance without cross-talk among the output ports (only three lattice constant, 3a), thus helping the design flexibility of the PCBSs in IOCs.
A simple and nonlinear LDMOS transistor model with multi-bias consideration has been proposed. Elements of the model are optimizes using particle swarm optimization (PSO) algorithm to fit the measured RF specifications of a typical transistor. The developed model is used then to design a high efficiency power amplifier with 55% power added efficiency (PAE) at 33 dBm output power with 12 dB power gain. This amplifier has a novel topology with optimized BALUN and microstrip matching network which makes it unconditionally stable and extensively linear over UHF frequency range of 100 MHz to 1 GHz with 163% fractional bandwidth. This power amplifier is fabricated and realized with 12-V supply voltage. A good agreement between simulated and measured values observed, indicating high accuracy of either the model and the amplifier design approach.
The beneficial effects of chronic/repeated magnetic stimulation on humans have been examined in previous studies. Although pain relief effects have been reported several weeks after magnetic treatment, no report is available regarding the prompt effect of magnetic stimulations. In this study, a novel apparatus was developed to generate time-varying magnetic fields with rotating magnets. Adult, conscious rats were exposed to the rotating magnets in a posture in which their spines were parallel to the induced electric current. The magnetic field suppressed the paw withdrawal reflex in the anesthetized rats, and the suppression effect disappeared 5 minutes after magnets stopped rotating. The tail flick (TF) latency and mechanic withdrawal thresholds (MWT) of the rats were significantly increased by the rotating magnets; the increases positively correlated with the velocity and period of the magnet rotating. These analgesia effects recovered to the baseline level 30 minutes after magnets stopped rotating. A biophysics model was proposed to qualitatively understand the mechanism of pain inhibition by the rotating field. The prompt analgesia effect of the rotating magnets and its rapid recovery encourage the application of this technique as a promising new analgesia and anesthesia method.
This paper presents comparison of two measurement techniques for ultra wideband (UWB) off-body radio channel characterization. A measurement campaign was performed in indoor environment using UWB wireless active tags and reader installed with the tag antenna and same set of measurement was repeated in the frequency domain using Vector Network Analyser (VNA) and cable connecting two standalone tag antennas for comparison/with a view to finding out the cable effects. Nine different off-body radio channels were experimentally investigated. Comparison of path loss parameters and path loss model for nine different off-body radio channels for the propagation in indoor environment both measurement cases are shown and analyzed. Results show that measurement taken by VNA connecting two standalone antennas through cables experiences lower path loss value for all nine different off-body channels. Least square fit technique is obtained to extract the path loss exponent. Increase of 12.96% path loss exponent is noticed when measurements are made using UWB tags and reader, i.e., without cable measurement scenario.
Liao's absorbing boundary condition (ABC) is a classic ABC algorithm. It has the advantages of better absorption effect, easy programming and needless to split field. However its numerical stability is poor, especially for the higher-order ones, which greatly limits the scope of its application. To solve this problem, a weighting method for improving the stability of Liao's higher-order ABC is presented in this paper. This method is simple and effective, and it can be implemented easily compared with other improvement methods before. It improves the stability of Liao's higher-order ABC remarkably, and extends its application range.
This paper addresses the application of measurement on goodness-of-fit (GoF) for amplitudes of radar clutter sample data against reference/theoretic parameterized probability density function (PDF). In general, various existing methods for this problem highly depend on empirical PDF parameters. This makes GoF assessments with these methods less perceivable and their accuracies are hard to control. A new method based on chi-squared type of measurement is proposed to overcome these difficulties. This method evaluates GoF by estimating the distance between the true PDF of the clutter data amplitude and the reference PDF. Hence the distance is statistically approximately independent with empirical PDF parameters. The new method has higher accuracy and symmetric property. It is especially useful for GoF comparison over multiple radar clutter data sets.
Conventional Far-field decomposition of the scattered electromagnetic (EM) field in the [EH] plane in terms of the horizontal and vertical components (i.e., h, v), introduces ambiguity for multi-static, multi-platform and/or scene-centric polarimetric synthetic aperture radar (SAR) image exploitation. This is due to the fact that a 2-dimensional (2D) vector field can not constitute a complete space capable of modeling 3-dimensional (3D) field transformations. To address this, extension of the Stokes vector, target scattering vectors and coherency parameters' analytic descriptions to 3D is explored and presented. The results are also applicable to compact polarimetry (CP) where mathematically consistent 3D Stokes parameters can be defined.
An 8 mm-band two-dimensional Synthetic Aperture Interferometric Radiometer (SAIR) called BHU-2D has been developed by Electromagnetics Engineering Laboratory of Beihang University. The radiometer could obtain images in realtime benefiting from the adoption of a 1bit/2level FPGA-based correlator array. The correlator array requires a group of Power Measurement Units (PMUs) to denormalize the correlation coefficients into visibility function samples. The design and implementation of the PMU in BHU-2D is presented in this paper. The PMU adopts a novel method based on probability statistics. The principle and quantitative error analysis of this power measurement method is presented. In order to verify the principle of the design, a sample board is manufactured and a series of validation experiments have been conducted. Measurement results have proved that the performance of the PMU could meet the requirements of SAIR systems. The PMU has been applied to BHU-2D and the result is satisfactory.
The particle swarm optimization (PSO) algorithm, a global optimization technique based on cooperative swarming strategy, has been used to solve inverse scattering problem for red flood cells (RBCs) and detect possible anomalies. The inverse scattering problem is recast as an iterative optimization one by definiing a suitable cost function.With this method is possible to estimate the morphological parameters of a red blood cell and to distinguish healthy RBCs from diseased ones. This work lays the basis for a new approach to make diagnosis. Preliminary numerical experiments show the potential effectiveness and the reliability of the proposed method as diagnostic tools.
We present an accurate, efficient numerical analysis for vector modes of dielectric optical waveguide structures with an arbitrary refractive index profile using a quadratic spline collocation method (QSCM). The unknown weights of the polynomials are determined by forcing the errors at the collocation points to be zero. Consequently, the original second order differential equation is converted to a set of algebraic equations which can be solved by matrix techniques. The proposed QSCM method demonstrates better performance than the standard finite-difference method of the same convergence rate in terms of grid size with the same degree of computational complexity.
In this paper, a polarization-independent wide-angle planar metamaterial absorber exhibiting dual directional absorption is proposed. Measurement results indicate that the planar metamaterial absorber achieves absorptivities of 86.87% and 91.48% to the normally incident electromagnetic waves propagating in forward (+z) and backward (-z) directions, respectively. Due to geometry's fourfold rotational symmetry, the absorber is polarization-independent. Additionally, the absorber works well for a wide range of incident angles for both transverse electric and transverse magnetic polarizations. Besides its impressing performance, this planar metamaterial absorber is also extremely thin that it's thickness is approximately 1/32 of the working wavelength.
This paper presents a generalized volume-surface integral equation (GVSIE) to solve electromagnetic (EM) scattering of high contrast inhomogeneous materials. Then the method of moments (MoM) is employed to solve the GVSIE. The GVSIE technique where the domain is represented by a corresponding uniform background medium coupled with a variation, together representing the overall inhomogeneity, is solve by the method of moments (MoM) using Schaubert-Wilton-Glisson (SWG) and Rao-Wilton-Glisson (RWG) basis functions. The adaptive cross approximation (ACA) algorithm combined with the equivalent dipole-moment (EDM) method are extended to reduce memory and CPU time. A highly effective preconditioning strategy is presented to solve the system of equations without any increase in the computational complexity. Experiments on several problems representative of scattering simulations are given to illustrate the potential of the above proposed techniques for solving EM scattering involving high contrast applications.
We carried out measurements of optical transmission through a Frequency Selective Surface (FSS) on a silicon substrate perforated periodically with square cavities of 1 mm2. The substrate is covered on one side with a thin film (1 μm thick) of silicon-nitride, thus forming a membrane for each cavity. The measurements were taken using a Martin-Puplett Interferometer over a spectral range from 100 to 650 GHz, providing a maximum transmission value of around 40% at 480 GHz. Analytical and computed results are also presented for comparison purposes.
The paper introduces the use of Non-Uniform Fast Fourier Transform (NUFFT) routines in ``complex'' (i.e., amplitude and phase) and phaseless Near-Field/Far-Field transformations. The use of those routines results computationally very convenient when non-regular field sampling prevents the use of standard FFTs. The attention is focused on a plane-polar acquisition geometry. Numerical and experimental results show the effectiveness of the developed algorithms.
Recently, referring to a homogeneous background, a new technique estimating the minimum convex hull of a source/scattering system from the radiated/scattered electromagnetic field data has been presented. In this paper, the approach is extended to the inhomogeneous background case by considering the source/scattering system and the observation domain embedded in two different homogeneous media. The underlying theory has been properly reformulated to account for the refraction phenomenon arising at the electromagnetic discontinuities boundaries by considering a 2D geometry. The performances of the technique have been estimated by means of a numerical analysis whose main representative results are presented and discussed in the paper.
The application of the finite-difference time-domain method with rectangular periodic boundary conditions to the analysis of a hexagonal photonic crystal results in a folded bandgap diagram. The aim of this paper is to introduce a new unfolding method, which allows unambiguously determining the position of the modes in a wave-vector space by taking the advantage of the fast Fourier transform of modal field distributions. Unlike alternative solutions, it does not require any modifications of the FDTD method and is based solely on the postprocessing of the simulation results. The proposed method can be applied to any non-rectangular lattice types, such as hexagonal, face-centered cubic or body-centered cubic.
In design phase of naval ships, the effectiveness of RCS reduction means such as shaping, shielding and applying radar absorbing materials is assessed quantitatively via several times of numerical analyses. During the process, in general, the numerical analyses have been carried out only for the static case not considering ship motions in actual ocean environments in spite that ocean waves induce the ship motion of the object naval ship and distort RCS measures. In this study, the dynamic RCS characteristics of the naval ship considering the ocean wave-induced motion have been numerically investigated. For this purpose, a dynamic RCS analysis procedure so called ``quasi-static approach'' has been adopted for considering the time varying ship motion. The results for two types of naval ships, a stealthy and a non-stealthy ship, show that the RCS of the object naval ships could be reduced or increased in mean value by the ship motion due to the ocean wave, compared to the static RCS value, and also the measures are considerably affected by the various parameters, type of object ship, significant wave height and incident angle of ocean wave, and incident angle of radar wave.
The radar backscatter from complex targets, such as aircrafts and ships, tends to vary rapidly with aspect or time. To describe the radar cross section distribution characteristics of such targets, statistic terms are often used. In this paper, we first give a brief introduction of distribution and lognormal distribution model. And complete form of lognormal distribution is proposed which can be used when ratio of mean to median is less than 1 as stealth targets. The significance of the parameters is discussed in detail aiming to find a characterization standard. As an example, the statistic characteristics of the radar cross section data of a stealth aircraft are analyzed with Swerling 1, 3 distribution, distribution and lognormal distribution. The applicability of the distributions is shown with error-of-fit and test of goodness of fit.