This paper is aimed at analyzing the electromagnetic (EM) scattering from the two-dimensional (2-D) Gaussian rough surfaces characterized by textures. Visual appearances of the stripe texture can be generated through the angle rotating in Fourier transform when the ratio of the correlation lengths in two directions is large enough. The scattering field is derived in Cartesian coordinate system through the small-slope approximation (SSA) method with plane incident wave. The normalized co-polarized radar cross section (NRCS) from 2-D Gaussian rough surface characterized by textures are calculated. In particular, several numerical results show the influences of incident angle, texture angle, correlation length, and root-mean-square height on the scattering from the textured rough surface. Finally, the validity of the SSA method is verified by comparisons of theoretical value and measured data.
A problem of electromagnetic waves radiation by an impedance vibrator located over finite-dimensional perfectly conducting screen is solved. The vibrator may have surface impedance distributed over its length. The solution is derived using asymptotic expressions for the current in a horizontal impedance vibrator placed over an infinite plane, obtained by averaging method. The problem was solved provided that the diffracted fields from the edges of the screen have little effect on the vibrator current amplitude, i.e. if the screen dimensions are comparable to or larger than the wavelength. Full radiation fields in all observation space in the far zone were found by the uniform geometrical theory of diffraction. The vibrator dimensions, value and type of surface impedance, removing from the screen and screen sizes were used as parameters. The multivariable electrodynamic characteristics of the resonant impedance vibrators placed above an infinite plane and square screen were studied. Characteristics dependences upon the vibrator dimensions, value and type of the surface impedance, removing from the screen, and screen dimensions were obtained.
In the past few years, several satisfying various objectives and designs of reconfigurable integrated microwave filter and antenna have been proposed for wireless communication systems. Several designs are new concepts and techniques, whereas others are inspired from previous works. The improvement concepts of these designs can be reviewed from this compilation of studies. This paper begins with an explanation of the reconfigurable filter, reconfigurable antenna and reconfigurable integrated microwave filter and antenna, followed by discussion on several designs in terms of size, measurement, performance and technology used. Among various designs, reconfigurable on planar structures are extensively used because of their simple design procedures and easy to tune on the desired frequency, bandwidth and attenuation. Most of the existing studies are focusing tunable on single element, i.e. either on filter or antenna side; however, it limits the tunable range and flexibility of the filtering antenna response. An alternative design of filtering antenna can be suggested to produce reconfigurable tuning capabilities on both microwave filter and antenna to produce overall good performance for multifunction operation in RF/microwave applications.
The dyadic Green's functions for magnetic and electric currents immersed in a parallel plate waveguide (PPWG) filled with dielectric-magnetic anisotropic uniaxial media are developed via a field-based approach. First, the principal Green's function is derived from the forced wave equation for currents immersed in an unbounded uniaxial media. Next, the scattered Green's function is developed from the unforced wave equation. Finally, the total Green's function is found by superposition and subsequent application of the appropriate boundary conditions. The Green's functions are derived from Maxwell's equations, using a spectral domain analysis and reveals several key physical insights. First, the expected longitudinal depolarization dyads are observed. The expected depolarizing terms arise through careful application of complex-plane analysis, leading to expressions that are valid both internal and external to the source region. Secondly, the identification and decomposition of the total Green's function into TE^{z} and TM^{z} field contributions is demonstrated. Thirdly, the mathematical forms of the principal and total Green's functions are shown to be physically intuitive. The primary contribution of this research is the development of the Green's functions for a parallel plate waveguide containing a dielectric and magnetic uniaxial medium directly from Maxwell's equations. Prior derivations considered dielectric-only uniaxial media in a parallel-plate waveguide, due to the relative ease of analysis and readily available inverse identities found in \cite{Chen_1983}. Inclusion of magnetic uniaxial characteristics adds considerable complexity (since no simplifying identities are available) and provides additional insight into the field behavior, thus representing a significant contribution to the electromagnetic analysis of complex media. Finally, practical applications of the Green's functions are considered, such as the non-destructive electromagnetic characterization of a variety of anisotropic uniaxial media.
This paper proposes a hybrid multichannel processing method for spaceborne Hybrid Phased-MIMO SAR (HPMSAR) that can achieve different applications of multi-direction swath imaging on the same platform. The method is optimal because it is a combination of two-dimension (2-D) advanced digital beamforming (DBF) technology and multichannel pre-filter technology for high-resolution wide-swath SAR signal processing. Multichannel signal processing technology for future spaceborne SAR will no longer be single and this combination may be the best choice. The proposed method could avoid spectrum aliasing caused by low pulse repetition frequency (PRF), separate the overlapped echoes caused by different subpulses corresponding to multi-direction swathes and remove the range ambiguity and azimuth ambiguity deeply. At first, we build the signal model of HPMSAR system. Furthermore, the pre-filter design is presented by using matrix inversion method. Then, we address different methods applied to 2-D DBF and propose the advanced linearly constrained minimum variance (LCMV) method. Image results on simulated distributed targets validate the proposed hybrid multichannel processing method.
The success of a ground penetrating radar (GPR) signal modeling scheme largely depends on its accuracy and computational efficiency. Most of the modeling schemes suffer from inaccuracy because of unrealistic assumptions of complex GPR environment. In this respect full wave model (FWM) of GPR signal is a promising approach for accurate characterization of multi-layered media. However, large computation time of FWM compared to other simplified models makes the approach inefficient for real time application. In this work an FWM scheme is developed based on electric field equivalent magnetic current density at antenna phase center. The compact analytical expression of Green's function representing response due to layered media is derived. Then a plane wave model (PWM) is proposed by introducing a spreading factor based on simplified expression of the FWM. The model inversion is successfuly carried out by a gradient based algorithm. A stepped frequency continuous wave GPR in off-ground monostatic configuration is implemented in laboratory environment to verify performances of the models. Experimental analysis proves that the proposed PWM is as accurate as FWM, and its computation efficiency is enormous to detect layered media parameters.
Solutions of Maxwell's equations for electromagnetic fields inside a waveguide coated with chiral nihility metamaterial and having one axis fractal are presented in this paper. A two-dimensional line source placed at the center of the waveguide is taken as an excitation. Power of electromagnetic fields inside the waveguide is determined, and results are plotted for various fractal dimension values ranging from 1 < D ≤ 2, and thickness of the chiral nihility coating.
In this paper, a simple-fed, low profile, 9×10 elements quasi-lumped planar antenna array is presented. The proposed resonator employs a quasi-lumped element resonator that uses interdigital capacitor (IDC) in parallel with a straight strip inductor shorted across the capacitor. The array elements were designed and then excited by a feed network of four coaxial probes situated at the bottom plane but separated from the ground plane using a plastic material. The entire array is divided into four sub-array lattices of 5×5 elements and excited by a coaxial probe located at the centre of the sub-arrays antenna structure, thus exciting the centre resonator who in turn excites the neighbouring elements via proximity coupling. The probes are connected based on Wilkinson power divider principle to provide in-phase excitation. An explicit method is introduced to quickly obtain the array factor (AF) characteristics for such proximity coupled rectangular planar array. Radiation pattern and the array factor are presented, and are further compared with those obtained by the simulation and experimental results. The proposed antenna comprises 9×10 elements array, each of which is 5.8×5.6 sq. mm in size, and the entire antenna structure is about 120×80 sq. mm.
The scattering of an obliquely incident H-polarized plane electromagnetic wave by a magnetized plasma column is studied. It is assumed that the column is located in free space and aligned with an external static magnetic field. The emphasis is placed on the case where the angular frequency of the incident wave coincides with one of the surface- or volume-plasmon resonance frequencies of the column. The spatial structures of the field and energy flow patterns in the near zone of the column are analyzed, and the location of the regions with a greatly enhanced magnitude of the timeaveraged Poynting vector is determined. It is shown that the sign reversal of the longitudinal energy-flow component that is parallel to the column axis can occur when passing across the boundary between the inner region of the column and the surrounding medium.
During re-entry into earth's atmosphere, a spacecraft suffers from loss of communication with the ground control station, known as communication blackout, due to formation of plasma around the re-entry spacecraft. This paper presents the theory and analysis of the communication blackout and its mitigation using static magnetic field method. The interaction between electromagnetic waves and plasma in presence as well as absence of magnetic field is described to determine the effects of plasma sheath on the spacecraft re-entering into the atmosphere. An analysis is done to determine the effectiveness of this mitigation technique for a typical re-entry spacecraft and the strength of magnetic field required to establish the communication link between the re-entry spacecraft and the ground station is obtained.
This paper examines the feasibility of LTE-based passive radar for detecting ground moving targets. Specifically, the focus of this paper is to describe the proposed LTE-based passive radar system and to conduct an experiment using a real LTE eNB transmitter as an illumination source. Seven scenarios were carried out to investigate the detection performance of the proposed system on ground moving targets with different speeds, trajectories and range. In addition, multi-target detection was also tested. The experimental results showed that the LTE-based passive radar system has the capability to detect typical ground targets/objects like cars, motorbikes and humans moving at different trajectories. The positive results opened up a new frontier for passive radar systems to be used in many potential applications, including security, border protection, microwave fences, monitor of buildings and others.
We describe a technique to analytically compute the multipole moments of a charge distribution confined to a planar triangle, which may be useful in solving the Laplace equation using the fast multipole boundary element method (FMBEM) and for charged particle tracking. This algorithm proceeds by performing the necessary integration recursively within a specific coordinate system, and then transforming the moments into the global coordinate system through the application of rotation and translation operators. This method has been implemented and found use in conjunction with a simple piecewise constant collocation scheme, but is generalizable to non-uniform charge densities. When applied to low aspect ratio (≤100) triangles and expansions with degree up to 32, it is accurate and efficient compared to simple two-dimensional Gauss-Legendre quadrature.
Two novel microstrip MIMO antennas have been proposed and presented in this paper. The objective is to design a compact and dual-broadband MIMO antenna module appropriate for many wireless devices including WLAN, LTE and WiMax. The presented MIMO antennas have been analyzed, designed, simulated and investigated using CST_MW simulator. They have been fabricated (FR-4 substrate), and their scattering matrices and total efficiencies have been measured. The first MIMO antenna module is composed of four proposed broadband microstrip antennas arranged in two MIMO antenna pairs. The first MIMO pair resonates at 5.2 GHz (5.08-5.313 GHz) while the second pair resonates at 5.8 GHz (5.643-5.96 GHz). This MIMO antenna has a compact size of 40x40 mm^{2}, dual-broadband, minimum mutual coupling below -25 dB, bandwidth greater than 225 MHz and gain of 3.8 dBi. The second MIMO antenna module consists of two proposed and modified dual-broadband microstrip monopole antennas, where, each has a dual resonance at 3.7 GHz (3.46-3.94 GHz) and 5.2 GHz (4.99-5.41 GHz). This MIMO antenna has an overall compact size of 20x50 mm^{2}, minimum coupling below -22 dB, bandwidth greater than 425 MHz and gain of 2.5 dBi. Good agreement has been achieved between measured and simulated results. The proposed MIMO antennas cover many wireless applications with the following specifications: compact size, dual-broadband, moderate gain, good efficiency and high port-to-port isolation.
Since both metamaterials comprised of artificial molecules (inclusions in a host material) and natural molecular materials at optical and greater frequencies can exhibit significant electric quadrupolarization as well as electric and magnetic dipolarization, we determine the passive, causal electric quadrupolarizability for a spherically symmetric molecule, namely a dielectric sphere subject to source-driven applied fields. For source-driven excitations, it is found that two electric quadrupolarizability constants are generally required to characterize the electric quadrupolar response of the sphere, with one of the constants multiplying the divergence of the applied electric field. For source-free fields, such as the fields of the eigenmodes of an electric quadrupolar array, the local electric field illuminating each inclusion is solenoidal. The constitutive relation is characterized by just one quadrupolarizability constant, and the electric quadrupolarization becomes traceless. It is also found that the electric quadrupolarization becomes very large and effectively traceless near the resonant frequencies of electrically small plasmonic spheres with negative permittivity and for somewhat larger spheres with positive permittivity.
Two previously studied classes of electromagnetic media, labeled as those of Q media and P media, are decomposed according to the natural decomposition introduced by Hehl and Obukhov. Six special cases based on either non-existence or sole existence of the three Hehl-Obukhov components, are defined for both medium classes.
The main goal of the present paper is to analyze the structure of the near field radiated by scalar point sources. The motivations for this study are the strong connection with interaction problem and the need for some insights to be utilized in the later, much more involved study of the full-wave vectorial case. We first suggest that the radial direction is the most convenient at the current time for observing the structure of the near field and proceed to derive the radial Green's function of the problem in a simple analytical closed form. The obtained expressions are then studied and their physical features are illuminated, especially in connection with the engineering radiation problem. The overall understanding of the near field problem obtained here will help in guiding the devolvement for the more complicated sources sometimes encountered in applications and theory.
We describe a surface integral-equation (SIE) method suitable for computation of electromagnetic fields scattered by 2D-periodic high-permittivity and plasmonic scatterers. The method makes use of fast evaluation of the 2D-quasi-periodic Green function (2D-QPGF) and its gradient using a tabulation technique in combination with tri-linear interpolation. In particular we present a very efficient technique to create the look-up tables for the 2D-QPGF and its gradient where we use to our advantage that it is very effective to simultaneously compute the QPGF and its gradient, and to simultaneously compute these values for the case in which the role of source and observation point are interchanged. We use the Ewald representation of the 2D-QPGF and its gradient to construct the tables with pre-computed values. Usually the expressions for the Ewald representation of the 2D-QPGF and its gradient are presented in terms of the complex complementary error function but here we give the expressions in terms of the Faddeeva function enabling efficient use of the dedicated algorithms to compute the Faddeeva function. Expressions are given for both lossy and lossless medium parameters and it is shown that the expression for the lossless case can be evaluated twice as fast as the expression for the lossy case. Two case studies are presented to validate the proposed method and to show that the time required for computing the method of moments (MoM) integrals that require evaluation of the 2D-QPGF becomes comparable to the time required for computing the MoM integrals that require evaluation of the aperiodic Green function.
A matrix method which takes into account the probe positioning errors in cylindrical and spherical near-field (NF) measurement techniques is proposed. The near-field irregularities made impossible the determination of the cylindrical or spherical wave expansion from the measured data using classical techniques based on 2D Discrete Fourier Transformation (2D-DFT) in cylindrical case (CC) and orthogonality properties in spherical case (SC). The irregularities can be randomly distributed but known and the matrix method expresses the linear relation between the measured near-field and the corresponding cylindrical or spherical modal expansion coefficients. Once the coefficients of the cylindrical and the spherical wave expansions are known the far-field of the antenna under test (AUT) is easily determined. Accuracy of the matrix method is numerically studied as a function of the irregularities magnitude and for different noise levels (data Signal to Noise Ratio). Also, experimental results have shown the efficiency of the proposed technique.
Cognitive radio is the enabling technology for license-exempt access to the TV White Spaces (TVWS). There is ever increasing demand of users in the broadcasting and communication services. Large portions of unused spectrum in the UHF/VHF bands exist in India which can be used on geographical basis. This paper describes a study on path loss variation in UHF/VHF bands in India. The aim of this study is to develop and optimize a path loss model based on Linear minimum mean square error estimation (LMMSE) for India. We propose the LMMSE based Optimized Perez-Vega Zamanillo propagation path loss model. The measured path loss values, collected across India, are compared with proposed Optimized Perez-Vega Zamanillo path loss model and other existing path loss models. It is found that Optimized Perez-Vega Zamanillo propagation path loss model has the least root mean square Error (RMSE) of 13.98 dB. Other existing path loss models have root mean square Error (RMSE) value greater than 24 dB. Therefore, Optimized Perez-Vega Zamanillo propagation path loss model is best suited for predicting coverage area, interference analysis in India for TVWS.
This paper proposes a burst model of chaotic noise signals with randomly stepped carrier frequencies for velocity estimation and high-resolution range imaging of high-speed moving targets. The random stepping of carrier frequencies is controlled by a combination chaotic map (CCM), which is generated by embedding a Logistic map into a Bernoulli map. The baseband noise signal adopts the CCM based frequency-modulation (CCM-FM) signal, which has good randomness and a thumbtack ambiguity function as well. The velocity estimation includes a coarse search where the coarse search is conducted with a fixed step to makes the velocity deviation less than the velocity resolution, while the precise search adopts the Golden Section Search (GSS) algorithm to get an accurate estimation of velocity. What should be emphasized is that the velocity estimation process can be completed with just a burst of subpulses. Then the spectra are coherently synthesized to obtain ultra-wide bandwidth and high-resolution range imaging. Finally, numerical simulations demonstrate a good performance of the proposed signal model and the processing algorithm.