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[IEEE 2018 15th European Radar Conference (EuRAD) - Madrid, Spain (2018.9.26-2018.9.28)] 2018 15th European Radar Conference (EuRAD) - Analog Beamforming based on Fourier Rotman Lens for Multibeam Applications
摘要： Spatial division represents a popular approach to increasing capacity in modern wireless networks. This paper presents a study of a simplified beamforming network based on a Fourier transform network with the number of output ports lower than the number of the elements in the antenna array. It is shown that connecting the output ports of Fourier transform network via power dividers to several array elements in phase, thus implementing a nearest-neighbor phase interpolation, preserves the gain and width of the beams in a narrow scanning sector. Therefore, in applications where few orthogonal beams are required to span a narrow spatial sector, the proposed approach can offer reduction of the hardware complexity. The simulated radiation patterns for a phase interpolation Fourier beamforming network are demonstrated. The antenna radiation patterns have been measured, using a Fourier Rotman lens with 2-way Wilkinson power dividers, which confirmed the simulated trends.
关键词： Rotman lens,beamforming,Fourier transform beamforming,Antenna arrays
更新于2025-09-04 15:30:14
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On-Line Analysis of Oil-Dissolved Gas in Power Transformers Using Fourier Transform Infrared Spectrometry
摘要： To address the problem of on-line dissolved gas analysis (DGA) of a power transformer, a Fourier transform infrared (FT-IR) spectrometer was used to develop an analysis instrument. Carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), ethane (C2H6), ethylene (C2H4) and acetylene (C2H2) were the analytes for the FT-IR spectrometer while propane (C3H8), propylene (C3H6), propyne (C3H4), n-butane (n-C4H10) and iso-butane (iso-C4H10) were the interferents, which might exist in the dissolved gas but are not currently used as analytes for detecting an internal fault. The instrument parameters and analysis approach are first introduced. Specifically, an absorption spectra reading approach by switching two cone-type gas cells into separate light-paths was presented for reducing the effects of gas in the gaps between gas cells and spectrometers, scanning the background spectrum without clearing the sample cell, and increasing the dynamics. Then, the instrument was tested with a standard gas mixture that was extracted from insulation oil in a power transformer. The testing results show that the detection limit of every analyte component is lower than 0.1 μL/L, and the detection limits of all analytes meet the detection requirements of oil-dissolved gas analysis, which means that the FT-IR spectrometer may be an ideal instrument due to its benefits, such as being maintenance-free and having a high stability.
关键词： power transformer,oil-dissolved gas,gas chromatograph,spectral analysis,Fourier transform infrared spectrometer
更新于2025-09-04 15:30:14
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HIGH-RESOLUTION GRID-INDEPENDENT IMAGING FOR TERAHERTZ 2-D SYNTHETIC APERTURE RADAR WITH SPATIAL UNDER-SAMPLING
摘要： For the purpose of two-dimensional (2-D) imaging in the Terahertz (THz) near field through 2-D synthetic aperture radar technology, Fourier transform (FT) is one of the most popular imaging ways. However, FT-based algorithms would encounter performance loss either when spatial sampling is under Nyquist frequency or there are off-grid scatterers in the scene of interest. Therefore, by exploiting the theory of matrix enhancement and continuous parameter estimation, we propose to use matrix enhancement and matrix pencil (MEMP) method and matched filter to deal with arbitrarily located scatterers when spatial under-sampling is adopted. Through constructing a specifically expanded matrix, the information of the scatterers involved in the small data set can be enhanced. Then, high-resolution grid-independence 2-D imaging can be achieved by the combination of MP and matched filter. Simulation results verify the effectiveness of the proposed algorithm.
关键词： Terahertz,matrix pencil,matrix enhancement,synthetic aperture radar,Fourier transform,grid-independent imaging,under-sampling
更新于2025-09-04 15:30:14
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An inverse problem for one-dimensional diffusion equation in optical tomography
摘要： In this paper, we study the one-dimensional inverse problem for the di?usion equation based optical tomography. The objective of the present work is a mathematical and numerical analysis concerning one-dimensional inverse problem. In the ?rst stage, the forward di?usion equation with boundary conditions is solved using an intermediate elliptic equation. We give the existence and the uniqueness results of the solution. An approximation of the photon density in frequency-domain is proposed using a Splines Galerkin method. In the second stage, we give theoretical results such as the stability and lipschitz-continuity of the forward solution and the Fr′echet di?erentiability of the Dirichlet-to-Neumann nonlinear map with respect to the optical parameters. The Fr′echet derivative is used to linearize the considered inverse problem. The Newton method based on the regularization technique will allow us to compute the approximate solutions of the inverse problem. Several test examples are used to verify high accuracy, e?ectiveness and good resolution properties for smooth and discontinuous optical property solutions.
关键词： Nonlinear inverse problem,Spline basis functions,Fourier transform,Di?usion transport problem,Newton method,Tikhonov regularization,Optical tomography
更新于2025-09-04 15:30:14
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Comparison and Identification for Rhizomes and Leaves of Paris yunnanensis Based on Fourier Transform Mid-Infrared Spectroscopy Combined with Chemometrics
摘要： Paris polyphylla, as a traditional herb with long history, has been widely used to treat diseases in multiple nationalities of China. Nevertheless, the quality of P. yunnanensis fluctuates among from different geographical origins, so that a fast and accurate classification method was necessary for establishment. In our study, the geographical origin identification of 462 P. yunnanensis rhizome and leaf samples from Kunming, Yuxi, Chuxiong, Dali, Lijiang, and Honghe were analyzed by Fourier transform mid infrared (FT-MIR) spectra, combined with partial least squares discriminant analysis (PLS-DA), random forest (RF), and hierarchical cluster analysis (HCA) methods. The obvious cluster tendency of rhizomes and leaves FT-MIR spectra was displayed by principal component analysis (PCA). The distribution of the variable importance for the projection (VIP) was more uniform than the important variables obtained by RF, while PLS-DA models obtained higher classification abilities. Hence, a PLS-DA model was more suitably used to classify the different geographical origins of P. yunnanensis than the RF model. Additionally, the clustering results of different geographical origins obtained by HCA dendrograms also proved the chemical information difference between rhizomes and leaves. The identification performances of PLS-DA and the RF models of leaves FT-MIR matrixes were better than those of rhizomes datasets. In addition, the model classification abilities of combination datasets were higher than the individual matrixes of rhizomes and leaves spectra. Our study provides a reference to the rational utilization of resources, as well as a fast and accurate identification research for P. yunnanensis samples.
关键词： chemometrics,Paris polyphylla Smith var. yunnanensis,Fourier transform infrared,multivariate analysis
更新于2025-09-04 15:30:14