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Micro-motion feature vectors of space targets are usually unevenly and multicluster distributed, which limits the performance of the traditional radar anomaly detection methods. To solve this problem, a novel detection method of radar space target abnormal motion method via local density peaks (LDPs) and micro-motion feature is proposed in this letter. First, two discriminative micro-motion features are extracted from the radar echoes to construct a 2-D feature space. Then the abnormal motion detector is derived by classifying the feature vectors into different clusters according to the LDPs and minimum spanning tree clustering (LDP-MST) and solving for the decision thresholds of each cluster with the LDPs, neighbors, and some preset false alarm rates. Electromagnetic simulation experiment results demonstrate that the detection rate of the proposed method is 2.49%, 5.26%, 9.63%, 15.37%, 27.99%, and 49.45% higher than six state-of-art methods, respectively, when the false alarm rate is 5%. [ABSTRACT FROM AUTHOR]

The hybrid spectral-element spectral-integral (SESI) method is developed for the electromagnetic (EM) scattering in 1-D Bloch (Floquet) periodic problems with scatterers embedded in multiple regions of 2-D layered media. The periodic layered medium Green’s function (PLMGF) is derived for the SESI method so that it can simulate EM scattering by horizontally periodic scatterers placed in an arbitrary number of layers. The SESI method is a combination of the spectral-element method (SEM) and the spectral-integral method (SIM). The SEM is applied only in regions with scatterers and has the merits of exponential convergence at a low spatial sampling density, while the SIM serves as an exact radiation boundary condition for the bottom and top boundaries of each SEM region. Therefore, there is no need to discretize the regions with pure layered media; furthermore, the inverses of these SIM matrices are given exactly and explicitly with only $O(N\log N)$ CPU time. Three numerical experiments are performed to show the accuracy and efficiency of the SESI method. [ABSTRACT FROM AUTHOR]

In this communication, the sensitivity matrices for the reconstruction of 1-D planarly layered transverse isotropic (TI) media illuminated by electromagnetic wave excited by 3-D electric or magnetic current sources are derived based on the transmission-line network analogy. The elements of the matrices are expressed analytically in the vertical $\textit {z}$ -direction but are in the form of Sommerfeld integration in the horizontal $xy$ -plane. The derived expressions are useful for the inversion of dielectric parameters and boundary positions of 1-D layered TI media. [ABSTRACT FROM AUTHOR]

This communication studies 3-D electromagnetic (EM) scattering and inverse scattering of arbitrary anisotropic dielectric objects embedded in multilayered media. Different from previous work, the scatterer is not only arbitrary anisotropic, but also the arbitrary anisotropy of the layered background media is formed by rotation of the principal axes of uniaxial media. In addition, the scatterers are allowed to be placed across layer boundaries. The forward model is formulated by the electric field integral equation (EFIE), solved by the biconjugate gradient stabilized (BCGS) method, and accelerated by the fast Fourier transform (FFT). The time complexity is analyzed for the BCGS-FFT applied to layered arbitrary anisotropic media. In the inversion model, the variational Born iterative method (VBIM) is employed to reconstruct the arbitrary anisotropic profiles of both the permittivity and conductivity. Numerical simulations are performed to verify the feasibility and antinoise ability of the forward and inverse solvers in the circumstance of layered arbitrary anisotropic background media. [ABSTRACT FROM AUTHOR]

This paper describes a distributed system for the partial discharge (PD) detection and location in the substation. The proposed system is composed of several ultrahigh-frequency (UHF) antennas located dispersedly that form an array. These antennas are connected to the central control room by the optical fiber using the radio over fiber (RoF) technique to decrease the propagation attenuation of the PD signal. The scattered layout increases the coverage of the PD signal sensing and the time difference of arrived PD signals propagating to the antennas. The signal processing part and PD location propose a virtual measurement method based on the statistical simulation. This method only uses a set of measured delay data to simulate and generate multiple sets of delay data by randomly adding the delay error, which follows a specific distribution within the limit range and uses these data to locate the PD source and statistically process the results of location. The actual positioning effect of this method is great, and the positioning accuracy and efficiency of the system are improved. The experimental results of an application case in a 220-kV substation show that this distributed UHF sensor array system can get the location accuracy of 1° when the system error of the time difference is less than 5 ns, which can meet the requirements of the PD detection and location in the entire substation. [ABSTRACT FROM AUTHOR]