Operating frequencies for passive remote sensing have been extended to millimeter and sub-millimeter wave regions in recent years. Due to relatively shorter wavelengths, narrower beam widths can be achieved under antenna size limitations. In turn, better spatial resolution can be achieved, which is especially important for sensors in geostationary orbit. There are several mission proposals for millimeter and sub-millimeter wave payloads in geostationary orbit, e.g., Geostationary Observatory for Microwave Atmospheric Sounding (GOMAS) proposed by European countries, Geosynchronous Microwave (GEM) Sounder/Imager Observation System proposed by USA, the next generation Chinese geostationary orbit meteorological satellite FY-4, etc. The feasibility study of geostationary microwave payloads and simulation of millimeter and sub-millimeter wave atmospheric sounding data is currently underway. Many measures evaluate the efficacy of atmospheric sounding data, one of which is the Degrees of Freedom for Signal (DFS). It is independent of specific regression algorithm thus able to offer an objective measure for performance comparison and channel parameter optimization. In this paper, the DFS of a set of millimeter wave (50~70 GHz, 118 GHz, 183 GHz) and sub-millimeter wave (380 GHz, 425 GHz) sounding channels is analyzed. The DFS improvement with increasing bandwidth is given; results suggest that broader channel bandwidth will improve the efficacy and retrieval performance of the future geostationary orbit millimeter and sub-millimeter wave radiometers.
In this paper, we propose an analytical method for modeling a permanent magnets axial field magnetic coupling. The three-dimensional model takes into account the radial fringing effects of the coupler. The analytical solution requires resolving the Laplace equation in low permeability subdomains. The magnetic field calculation allows the determination of global quantities like axial force and torque. 3D finite element computations as well as measurements validate the proposed model.
The performance of smart antenna greatly relies on the efficient use of direction-of-arrival (DOA) estimation techniques for both coherent and non-coherent signals. In practice, DOA estimation problems and difficulties increase when the signals in multipath propagation environments are highly correlated or coherent. Therefore, exploring an algorithm which is capable of estimating coherent signals is of great importance. To overcome this problem, a new high-resolution modified virtual singular value decomposition (MV-SVD) algorithm for DOA estimation of coherent signals is proposed. It is based on the hybrid combination of the virtual array extension, singular value decomposition (SVD), and modified MUSIC algorithms. The proposed algorithm provides many features such as: decorrelation of the coherence between the signals without reducing the rank of the covariance matrix or losing the array aperture size; high-resolution and more stability especially at low SNR values; and an increase in the maximal number of detectable signals to M-1, where M is the number of antenna elements.
The flux and torque of switched reluctance motor (SRM) have a highly nonlinear functional relationship with rotor position and phase current, as a consequence of the double-salient structure of the stator and rotor pole and highly magnetic saturation, which is difficult to build an accurate analytic model. In order to achieve the SRM high-performance control, it is necessary to build an accurate nonlinear model for SRM. On the basis of the adequate and precise sample data, by taking advantage of neural network that has outstanding nonlinear mapping capability, this paper adopts the Back Propagation (BP) based on Levenberg-Marquardt (LM) algorithm and Radial Basis Function (RBF) neural networkto build offline models for SRM respectively. Under different requirements of model accuracy, two kinds of network are studied and compared with each other on accuracy, scale and other aspects. The research results indicate that the network scale built as SRM nonlinear model by BP neural network based on LM algorithm is smaller than the one built by RBF. Additionally, the model accuracy is higher. In terms of the Switched Reluctance Drive (SRD) which requires real-time controller, reducing the network scale will be beneficial to the online real-time control of the system.
In this paper, extended composite right/left-handed (E-CRLH) transmission line (TL) metamaterial structures, with two left-handed (backward) and two right-handed (forward) pass bands, are investigated. Also, design procedures in order to design dual- and quad-band E-CRLH-TLs are presented in detail and the parameters of these structures are extracted by clean formulas, while satisfying arbitrary phase shifts at the operating frequencies. Finally, the dispersion and characteristic impedances of these transmission lines are derived and plotted. The results of this paper can be applied to any type of TL-based dual- and quad-band microwave component.
An approximate self-consistent solution of the problem of plane electromagnetic wave diffraction on a thick grating of metallic bars with slits between the bars filled a Kerr-type nonlinear dielectric is solved. The bistable operating regime of wave transmission through the grating is studied.
In this paper, different causal sub-domain temporal basis functions are investigated to make the explicit marching-on-in time schemes converge and stable for solving two dimensional time domain EFIE. PEC cylinders with arbitrary cross section are illuminated by a TE-polarized Gaussian plane wave. Two different approximations are used for calculation of the singular elements of the impedance matrix analytically. In the Time Domain Method of Moment (TD-MoM) formulation of the Electric Field Integral Equation (EFIE) of the problem, the free-space two-dimensional Green's function and triangular spatial basis function are used. By employing Galerkin's method in spatial domain and point matching in time domain, all time convolution integrals and self-terms are evaluated analytically to increase the accuracy and stability of the proposed technique. The stability and efficiency of the new technique are confirmed by comparison with literature.
In inverse synthetic aperture radar (ISAR) imaging, micro-motion structures on the target will induce additional time-varying frequency modulations to the radar echoes. Due to the disturbance of these mechanical vibration or rotation parts in the ISAR imaging, it will be difficult to obtain a well-focused ISAR image of the target using conventional translational motion compensation methods. To solve this problem, two improved translational motion compensation techniques have been proposed in this paper. Firstly, the power transform is used in the range bin aligment processing to depress the disturbance of the micro-motion parts. Then, a impreoved autofocusing methods based on range bins selection is presented, which only use the range bins of the radar returns of the main body scatterers for the phase adjustment. The results from the measured data are given to verify the validity of the improved translational motion compensation techniques proposed in this paper.
Among ship detection methods for SAR image, constant false alarm rate (CFAR) is the most important one. However, several factors, such as detector parameter and distribution of ocean clutter, affect the performance of CFAR detection. This paper proposes a novel hierarchical complete and operational ship detection approach based on detector parameter estimation and clutter pixel replacement, which is considered a sequential coarse-to-fine elimination process of false alarms. First, a simple barycentric algorithm is adopted to estimate target-window size, and a morphology method is used to estimate false alarm rate for CFAR detector. Second, a clutter pixel replacement approach based on the statistical features of sea clutter is presented to obtain statistically independent, stationary, and Weibull distributed random data for CFAR detector to remove all false alarms. Experimental results of the detection methods on a SAR image dataset show that the proposed approach is effective in reducing false alarms and obtains a satisfactory ship detection performance.
The adaptive cross approximation is applied to boundary element matrices coming from 2D scattering problems by an infinite periodic surface. This compression technique has the advantage to be applied before the assembly of the matrix. As a result, the computational times for both assembly and solution phases are reduced. Numerical results assess the efficacy of the method on scattering problems with several periodic surfaces.
This paper mathematically models the operation of Arrayed Waveguide Grating (AWG) based multiplexer (MUX) and demultiplexer (DEMUX) used in optical networks. In WDM networks, the optical MUX and DEMUX play a crucial role of managing the aggregation and segregation of wavelengths for networking applications. A simple and intuitive model of AWG based MUX design is discussed in this work. This model assumes that the device is linear, in which the principle of superposition is valid, and the primary emphasis is given to the optical power gain of the individual wavelengths. By using this model, one can exactly estimate the individual and overall power associated with each of the multiplexed wavelengths. The developed model was evaluated with experimental results using AWG based multiplexers. The experiments were repeated for different test cases with various power input levels and multiplexer configurations. It was found that the developed model provided a good approximation to the actual AWG mux/demux.
In present paper, the effect of relativistic hot electron beam for field aligned Whistler mode waves has been studied theoretically in the presence of AC electric field perpendicular to magnetic field. Studies have been performed using perturbative approach along with the method of characteristic solutions and are valid for comparatively small ambient magnetic field of Uranus, of the order of nano Tesla, as observed by Voyager 2. The detailed derivation and calculations has been done for dispersion relation and growth rate for magnetosphere of Uranus. Analyses are done by changing various plasma parameters which are explained in result and discussions section of this paper. Extensive study of wave-particle interactions and numerical calculations concludes that in case of injection of a distribution of particles having a positive slope in v⊥, temperature anisotropy remains the main source of free energy. It is seen that other effective parameters for the growth of whistler mode waves are AC frequency and higher number density of hot electrons. We also learn that even the minimal presence of such energetic particles having a positive slope of distribution function and increasing power of perpendicular thermal velocity can increase the growth rate significantly in the magnetosphere of Uranus. The present work is basically based upon the theoretical investigation and mathematical analysis of the magnetosphere of Uranus, supported by satellite data.
Based on energy injection and free resonant mode, an approach to optimize the startup frequency setting of the voltage-fed inductive power transfer (IPT) system is proposed to mitigate the effects of uncertain system parameters and load conditions. Differential equations of the primary resonant network on the free resonant mode is firstly established, then the free resonant frequency with different parameters and load conditions is calculated and verified with the soft-switching frequency of system based on stroboscopic mapping modeling method and fixed points theory. By controlling the micro-energy injection of system and free resonance, the frequency of free resonant mode is detected, and is regarded as the fixed frequency of startup process. Hence, the proposed strategy solves the uncertainty of the startup frequency and system re-setting to fit with changed system parameters and load conditions. This method also initiates immediate protection when the system operates under zero loads. In sum, our experimental results verify the theoretical implication, effectiveness, and merits of the proposed approach.
Dipole antennas on a substrate without a ground plane are common in wireless sensor networks and RFID applications. This paper reviews a number of theoretical approaches to solving for the effective permittivity when the substrate material is thin. The surface impedance and slab waveguide propagation techniques are compared to a capacitive solution and an insulated wire antenna. The insulated wire method gives most accurate results (< 3.5%) and was verified using numerical modeling and experimental work. Measurements on a planar straight dipole on FR4 (fc = 1.50 GHz) compare favorably with the antenna modelled without the substrate and scaled using the insulated wire technique at (fc = 1.49 GHz). The method can be readily incorporate the effect of an RFID antenna on a thin plastic film placed on a wide variety of lossy and lossless objects.
In this paper, the finite element method (FEM) is applied to the analysis of three-dimensional (3D) electromagnetic structures. The incomplete Cholesky (IC) preconditioner based on shifted operators is used to solve the finite element linear systems. Several strategies are adopted to raise the efficiency and robustness of the preconditioner. Numerical experiments for several microwave devices demonstrate the superior numerical convergence and robustness of the proposed preocnditioner.
An efficient optimization technique for frequency selective surface (FSS) radome with nonuniform wall thickness is proposed to improve the power transmission efficiency and the boresight error (BSE) of FSS radome simultaneously. The high-frequency method based on the approximate locally planar technique is used to evaluate the transmission performance of FSS radome. An efficient multi-dimensional adaptive sampling method combined with spectral domain method of moment (MoM) is employed to analyze transmission performance of FSS structure. The immune clone algorithm (ICA) is applied to the design of a FSS radome, in which the linear combination of the maximizing power transmission efficiency and the minimizing BSE is adopted as the affinity function, and the radome wall thickness is optimized. A design example for the three-dimensional tangent ogive radome with nonuniform thickness is given. The results show that the power transmission efficiency is improved significantly and the BSE of the optimal antenna-radome system is also reduced over the antenna scan volume.
Investigations have been carried out on the convex lens effect of non-ionizing radiation inside the abdomen of a pregnant woman. Focusing property for a plano-convex lens, which is thicker than twice of its focal length and filled with water, is studied for electric and magnetic fields at different microwave frequencies. It is observed that real image of electromagnetic fields are formed inside the lens itself at the focal plane when a microwave source is placed at a distance much greater than the twice the focal length. A three dimensional homogeneous electrical model of pregnant woman abdomen model behaves like plano-convex lens and creates real image of the microwave source inside the abdomen.
In this paper, a rigorous and accurate numerical two-dimensional modeling finite element method 2D-FEM is applied to the analysis and design of substrate integrated waveguide components. The finite element method represents an excellent tool for the analysis and design since it easily allows taking into account all details of each device. The advantages of this method have been proved with the successful design of two SIW waveguide topologies operating in [8-12] GHz and [10.7-12.75] GHz respectively for X-band and Ku-band applications employed in satellite communications. In order to validate the proposed method, a comparison is made between the FEM method implemented in Matlab and CST Microwave Studio® software. Agreements between the finite element method data and the CST software results were achieved. The obtained results show the effectiveness of this method to analyze such types of guides.
The dispersion characteristics (ω-β diagram) of a left-handed material (LHM) loaded helical guide is analytically solved and numerically computed for different metamaterial medium properties as well as helical guide parameters. The modal behaviour of this structure has been studied with an aim to achieve ultra slow wave over wide bandwidth which finds potential applications in optical switches and memories for optical processing. Significant amount of phase velocity reduction has been achieved in comparison to when helix is in free space or loaded with normal dielectric column. Other modal properties such as presence of two fundamental modes - backward and forward wave and their lower cut-off frequency (LCF) as well as bandwidth spectrum are also revealed thoroughly.
This paper investigates the generalized case of scattering from a planar grid, containing an infinite number of axially magnetized ferromagnetic microwires placed parallel to each other in free space. A semi-analytical solution is obtained by calculating the local field at the surface of the reference microwire which is the sum of the scattered field from the other microwires as well as the incident field. Graf's theorem is used to transform the scattered field from one coordinate system to the other. Scattering field coefficients for the reference microwire are obtained by matching the tangential field components at the surface of the reference microwire. Simulated results are expressed in terms of the Reflection, Transmission, and Absorption Coefficients for the (TMz) and (TEz) polarizations. For validation, results of the proposed analysis specialized to the case of normal incidence with TMz polarization are compared with the results available in the literature.