The transition towards next generation communications has increased the need for fast and accurate propagation models that can predict all aspects of the wireless channel. This paper develops a very accurate approach for indoor propagation modelling based on the volume electric field integral equation (VEFIE). The three-dimensional form of the VEFIE is used to predict frequency domain characteristics. Whilst, a 2D to 3D model is developed based on the 2D VEFIE to perform accurate and efficient time domain predictions. The 2D to 3D model applies correction terms to the solution of the 2D VEFIE to account for three-dimensional propagation. Both models are compared against frequency and time domain measurements as well as popular empirical models for both scenarios.
In the paper, we present a novel PCE-based approach for the effective analysis of worst-case scenario in a wireless telecommunication system. Usually, in such analysis derivation of polynomial chaos expansion (PCE meta-model) of a considered EM field function for one precise set of probability densities of random variables does not provide enough information. Consequently, a number of PCE meta-models of the EM field function should be derived, each for the different joint probability density of a vector of random variables, e.g., associated with different mean (nominal) values of random variables. The general polynomial chaos (gPC) approach requires numerical calculations for each PCE meta-model derivation. In order to significantly decrease the time required to derive all of the PCE meta-models, the novel approach has been introduced. It utilizes the novel so-called primary approximation and the novel analytical formulas. They significantly decrease the number of numerical calculations required to derive all of the PCE meta-models compared with the gPC approach. In the paper, we analyze the stochastic EM fields distributions in a telecommunication system in a spatial domain. For this purpose, analysis of uncertainties associated with a propagation channel as well as with transmitting and receiving antennas was introduced. We take advantage of a ray theory in our analysis. This allows us to provide the novel method for rapid calculation of a PCE meta-model of a telecommunication system transfer function by using the separate PCE meta-models associated with antennas and a propagation channel.
A triple two-level nested array (TTNA) configuration is proposed for direction-of-arrival (DOA) estimation of multiple time-space signals. The proposed TTNA consists of multiple two-level nested arrays, and the distance between two adjacent nested arrays is also given according to a nested array. As traditional nested arrays, it can generate a hole-free different co-array. Compared with some preexisting nested arrays, the proposed nested array can offer more degrees of freedom (DOFs). The closed-form expression of DOFs and the array configuration are given. Moreover, the detailed process for the construction of extended covariance matrix also is obtained. The simulation results show that the proposed method offers improved performance in the precision of DOA estimation due to the increase of virtual sensors.
The High Frequency hybrid radar mode combines sky and surface wave propagation. As all High Frequency radars, it can be impacted by ionospheric instabilities. A behavioral model able to include ionospheric spatial and temporal variations has been implemented to estimate the impact of ionospheric irregularities on radar signal processing and Doppler-distance images. In this work, probabilistic models of the ionospheric fluctuations in the ray tracing have been introduced using the phase path fluctuation only. Based on Shkarofsky's spectral power density, random variations on some parameters of Booker's electron density profile have been performed to generate disturbed electron density profiles. Afterwards, a propagation delay, integrated in the received radar signal, has been calculated in terms of phase path variation. Moreover, the temporal aspect of the ionospheric variations has been macroscopically implemented by a filtering step according to the Total Electron Content variation. Results of this simulation are presented with the corresponding statistics. Doppler and distance distributions have been computed for several filter cut-off frequency values and for different Shkarofsky's spectral power density parameters. At last, the process described above works properly: its results have been successfully compared with actual radar data for this purpose.
A rectangular metallic waveguide with a chiral medium is considered in this article. The field distribution inside a rectangular waveguide is investigated. The task is considered in a full vector setting. The mixed finite element method is used to calculate the rectangular waveguide with a chiral medium.
This paper reports an electric field approximation model of the Coplanar Vivaldi antenna on the E-plane. The study is conducted in three stages, i.e., (i) evaluating the impact of various geometrical parameters to the Vivaldi's element performance at different frequencies, (ii) modeling the electric field patterns, and (iii) applying the model to evaluate the linear total array pattern. The examination of the Coplanar Vivaldi element with fractional bandwidth of 133% in the 2-10 GHz band shows the individual roles of the antenna width, the tapered slot length, the opening width and the slope of the tapered slot in determining the VSWR, resistance, reactance and E-Field performance. The Vivaldi element should be designed with element width more than 0.5λ and less than λ to reach better performance of VSWR and E-field. The longer the tapered slot (>λ) with the high value of opening rate of tapered slot, the smaller the E-field. The E-field increases with increasing opening width of the tapered slot. Knowledge of the influence of each geometry parameter is then used as a reference in developing the E-field pattern approximation model of the Vivaldi element. The derivation of the Vivaldi approximation model is started from the pattern of a horn antenna because both antennas share a similar feature, i.e., the enclosure of the E-field propagation within a tapered slot resulting in a directional radiation pattern. The result of Coplanar Vivaldi modeling is verified against the results of electromagnetic computational simulation and measurement. The Vivaldi element model is useful for total array pattern analysis to save computation time and to provide flexibility in the evaluation of array design.
Electromagnetic scattering from time-varying sea surfaces under right-hand circularly polarized (RHCP) wave incidence is investigated, with emphasis on exploring the influence of nonlinear hydrodynamic interactions on Doppler spectral signatures as well as on examining the polarization difference of Doppler spectra between right-hand and left-hand polarized scattering waves. The choppy wave model (CWM) is adopted for describing nonlinear hydrodynamic interactions between ocean waves, and it is constructed by adding horizontal displacements through performing Hilbert transform for a reference linear surface model. Simulation results show that Doppler spectral signatures are significantly influenced by nonlinear hydrodynamic interactions in particular in low-grazing angle regime. It is also indicated that Doppler spectral signatures show distinct polarization dependence. In addition, numerical simulations show that Doppler shift of left-hand polarized scattering wave increases obviously with wind speed increasing, whereas the Doppler shift of right-hand polarized scattering wave looks less sensitive to wind speed variations. The result is potentially valuable in remote sensing applications with Global Navigation Satellite System-Reflectometry (GNSS-R) signals.
We provide herein open-form, double series formulae describing the diffraction of electromagnetic waves by a dielectric, dissipative wedge of finite radius a: Our procedure bypasses altogether any attempt to enforce boundary conditions at wedge faces, and relies instead on volume self-consistency for the total electric field, incident plus self-consistently radiated by polarization/ohmic currents distributed throughout the wedge interior. Self-consistency of this sort is formulated as an integral equation over the wedge cross-sectional area, an equation wherein are implicitly subsumed all necessary boundary conditions. The crux of the ensuing solution depends upon a decomposition within the wedge interior of both incoming (here taken as plane) wave field and the underlying Green's (Hankel) function into standard functional buildings blocks individually compliant with the Helmholtz equation as adapted to the reference, exterior medium. With such decomposition in hand, the remainder of the solution follows a more or less routine, Ewald-Oseen route, one eased by function orthogonality, by cancellation across the board of the total field when similarly so decomposed throughout the wedge interior, and an almost rote reading off of interior expansion coefficients against those found on the exterior. The incoming field series decomposition across the wedge interior, it should be noted, avoids the pitfall of a naive recourse to Fourier series, and invokes instead a root-mean-square minimization. That such a procedure enjoys a measure of validity is confirmed in Appendix C, wherein it is shown that the present analytic apparatus, when permitted to confront a degenerate wedge having its exterior angle γ tending to zero, γ→0+; which is to say, a bona fide dielectric cylinder, recovers the classical, boundary-value solution as to its every detail. All in all, while we do hope that the present work will serve to broaden the prevailing viewpoint as to permeable wedge scattering, we nevertheless admit to a measure of regret as to the complexity of the resulting formulae, whose numerical implementation bodes ominously to be a formidable task in its own right. It would seem that we reach here a frontier of diminishing returns as to the applications of classical analysis, a point at which its intellectual allure can honorably surrender to direct, computer-driven point matching methods.
We analytically model single-, two-, and three-wires above ground to determine the decay lengths of common and differential modes induced by an E1 high-altitude electromagnetic pulse (HEMP) excitation. Decay length information is pivotal to determine whether any two nodes in the power grid may be treated as uncoupled. We employ a frequency-domain method based on transmission line theory named ATLOG - Analytic Transmission Line Over Ground to model infinitely long and finite single wires, as well as solve the eigenvalue problem of a single-, two-, and three-wire system. Our calculations show that a single, semi-infinite power line can be approximated by a 10 km section of line and that the second electrical reflection for all line lengths longer than the decay length are below half the rated operating voltage. Furthermore, our results show that the differential mode propagates longer distances than the common mode in two- and three-wire systems, and this should be taken into account when performing damage assessment from HEMP excitation. This analysis is a significant step toward simplifying the modeling of practical continental grid lengths, yet maintaining accuracy, a result of enormous impact.
Two unsupervised methods, fuzzy c-means (FCM) and $k$-means, as well as three supervised methods, support vector machine (SVM), neural network (NN), and convolutional neural network (CNN), are applied to classify sea-ice type of first-year ice (FYI), multi-year ice (MYI) and open water, by using L-band polarimetric synthetic aperture radar (PolSAR) images in winter and advanced-melt phases, respectively. Different input vectors, pending on different scenarios, are also proposed to increase the accuracy rate. The efficacy of different algorithms in conjunction with different input vectors are analyzed and related to the underlying physical mechanisms.