Two focus-scanning schemes, viz. lens-fixed scanning scheme and lens-combined scheme, are proposed for near-field target detection and imaging. Specific lens size must be determined for future lens building in order to achieve desired imaging resolution and convenient data acquisition. Influence of LHM lens size on the performance of two different focus-scanning schemes are investigated and compared by simulating the detection of a perfect electric conductor target of diameter of 2 mm. Numerical simulations indicate that the lens-combined scanning system using thick LHM lens of thickness of two wavelengths requires at least a length of one wavelength to achieve resolution better than 0.4 wavelengths, while the lens-fixed scanning system requires a lens of lengthof approximately 3 wavelengths. When a thin LHM lens is used, high imaging resolution is not a consequent result for the focus-scanning approaches, although thin lens generally yields high focusing resolution. Some guidelines on the selection of length and thickness of flat LHM lens are reported.
Spectrum sharing between wireless systems becomes a critical issue due to emerging new technologies and spectrum shortage. Recently, IMT-Advanced system has been allocated in the same frequency band (3500 MHz) along with fixed services on co-primary basis, which means that harmful interference probability may be transpired. Channel bandwidths (BW) and natural of deployment areas of wireless systems are of the main effective factors in spectrum sharing. Spectrum Emission Mask (SEM) model will be used to study these factors effects beside the interference to noise ratio (I/N) as a fundamental criterion for coexistence and sharing between systems. The frequency and distance separation and antenna high effects are essential to be investigated to achieve spectrum sharing.
Experimental study and SPICE simulation of CMOS digital circuits latch-up effects due to high power microwave interference are reported in this paper. As a traditional inherent destruction phenomenon, latch-up effect may jeopardize the correct function of the circuits, and could be triggered in various ways such as ESD pulse, cosmic ray, heavy ion particles etc. Through the directly injected experimental investigation of CMOS inverters, it is shown that the single short high power RF pulse not only could disturb and upset the inverters output logic voltage, but also might trigger CMOS latch-up effects. It is observed that the RF pulse leading to inverters latch-up effects have energy threshold characteristics, which means that the injected RF pulse power is inversely proportional to the pulse width. SPICE simulations indicated that the inverters maximum static consumption current in latch-up state will increase up to 6600 multiples compared to the normal value when input logic state is high. With the device scaling down, higher integration and higher working frequency, the power consumption problem plays a significant role, which makes CMOS logic circuits more vulnerable due to the latch-up effects under high power microwave threats.
This paper presents a new method to counter Anti Radiation Missiles (ARM) threats, which is effective against advanced ARM. By using random phase and amplitude active decoys in the specified optimum positions and network implementation we show that the ARM threats will be removed dramatically. Also, iterative methods are presented to cancel the internal interference effects in the proposed structure.
Time Reversal Mirror (TRM) technique, in the virtue of its high resolution in the heterogeneous media, has been widely applied in the area of acoustics and electromagnetics. In this paper, the technique is developed to imaging targets in the contest of ultra-wideband (UWB) through wall radar (TWR) through numerical simulation. We firstly consider the technique to image targets behind a single-layered wall and then extend to the multi-layered wall. The simulation results have reported the imaging capability of the algorithm and its powerful use for TWRimaging. For concerning the image stability, we investigate the TRM images for the case in which there is a mismatch between the walls associated with the forward and inverse phases of time reversal. The back projection imaging algorithm is compared here at the same time for a contrast of the imaging quality. Finally, some conclusions are drawn.
This paper links the polarization-sensitive-array signal detection problem to quadrilinear decomposition model. Exploiting this link, it generates a deterministic blind quadrilinear decomposition-based signal detection algorithm, which doesn't require DOA (direction of arrival) and polarization information and has blind and robust characteristics. The proposed algorithm fully utilizes the polarization, spatial and temporal diversity. The simulation results reveal that the performance of blind quadrilinear decomposition-based signal detection algorithm for polarization sensitive uniform square array is close to nonblind MMSE method, and even works better than trilinear decomposition algorithm.
A comparison between two recently developed methods for antenna diagnostics is presented. On one hand, the Spherical Wave Expansion-to-Plane Wave Expansion (SWE-PWE), based on the relationship between spherical and planar wave modes. On the other hand, the Sources Reconstruction Method (SRM), based on the application of the equivalence principle and the integral equations relating fields and sources. In order to compare the results provided by these methods, a reflector antenna has been measured and analyzed.
In this paper the discontinuity problems of the junction of two different dielectric rectangular waveguides has been studied, both for two dimensional (2D) and three dimensional (3D) cases. The technique used, is to obtain expressions for the z-directed complex power due to all modes (propagating and non propagating) present at the step junction for a normalized incident field. The expressions for junction parameters like admittance and susceptance have been derived for the structures with step junctions in x direction, in y direction and for the 3D case where the step is both x and y directed. The numerical results have then been computed for different step ratios of these three cases.
An efficient iterative method is presented for the fast analysis of cylindrically conformal microstrip structures. Based on the transmission line modeling (TLM) method and the fast modal transform (FMT) theory, this technique accelerates the process of the calculation by introducing the concept of the transverse electromagnetic waves instead of the transverse fields considered in the traditional algorithm. Within cylindrically stratified media, the transverse electromagnetic waves are represented by the hybrid modal basis functions. Ultimately, the specific form of the modal admittance and the spectral reflection matrix are deduced. Further more?the surface electric fields and electric currents of the cylindrically conformal microstrip antenna fed by means of a microstripline are calculated via the iterative process. On this basis, the input impedance of the antenna can also be obtained. And the results gained by utilizing iterative approach are compared with those from the published references to demonstrate the accuracy or efficiency of this method.
A well known property of large circular closed-loop arrays is that when the dimensions and the distance of the cylindrical dipoles are properly chosen, the arrays possess very narrow resonances. As far as single isolated loop arrays are concerned, the phenomenon has been predicted and analyzed in the past in the framework of ``two-term" theory. In the present paper the same methodology is, for the first time, applied to investigate the system of two coupled identical circular arrays. It is found that the spectral profile of this new array is characterized by the coupling-induced splitting of the resonances of the single loop array into symmetric and antisymmetric supermodes, in direct analogy with other types of coupled electromagnetic cavities. Due to the circular symmetry of the individual arrays, the phenomenon is strongly correlated to the optical counterpart of two coupled traveling-wave optical resonators, such as whispering gallery or microring resonators. By borrowing the resonance splitting model from optical resonators, this analogy connection is investigated and interesting conclusions are reached.
This paper presents a dispersive finite difference time domain (FDTD) method suitable for the analysis of electromagnetic field rotator (and cloaking) devices. The method employs a coordinate transformation which accurately accounts for the radial dependence of the permittivity and permeability tensors, with Drude material models applied to the respective diagonal elements. The key aspect of the present formulation is the inclusion of the radial dependence of the plasma frequency, which makes this formalism quite attractive for the modeling of a general class of cloaking and field rotator geometries. Firstly, the method is validated by comparing its results with a previously published simulation of a cloaking device. Then, it is applied for the first time to the analysis of dispersive effects on the performance of field rotators.
In this paper, a statistical approach to evaluate randomly rough surfaces (RRS) in an inverse scattering problem is presented. Whereas in these investigations the roughness criterions possess random variables, the use of deterministic techniques such as the target decomposition (TD) can not be useful by itself as a tool of analysis. In these conditions, a statistical approach is essentially required to evaluate the target parameters. The goal of this study is the estimation of the polarimetric signatures, such as the scattering mechanism α and the entropy H, via a novel approach including the combination of TD and a new statistical model. To validate our work, SAR data sets, provided by the European Space Agency (ESA), are analyzed and compared with the simulation results.
We describe an experimental set-up for exposure of small animals to radiofrequency standing waves that allows direct measurement of the power absorbed by the animal. Essentially, the set-up consists of a metallic box containing an antenna and experimental animal immobilized in a methacrylate holder; a signal generator feeding the antenna; and a power meter. In addition, the box can also contain a video camera to record the animal's behaviour, and a receiving antenna (connected externally to a power meter and a spectrum analyser) to detect alien radiation and harmonics. The absorbed power measurement trivially allows calculation of whole-body mean SAR from the animal's weight; and assuming local SARs to be proportional to whole-body mean SAR, the latter can be used to adjust organ-specific SAR predictions obtained by simulation using a commercial FDTD program with a numerical phantom. The use of the system is illustrated by application to rats given subconvulsive doses of picrotoxin to induce a seizure-prone state analogous to epilepsy: levels of the neuronal activity marker c-Fos in the frontal and piriform cortex of picrotoxin-treated rats exposed to 900 MHz GSM radiation were twice as high as those of unexposed animals.
In this paper, a high performance phased antenna array is designed. Compared with the traditional ones, this antenna array has a lower sidelobe characteristic of down to -16 dB. At different scanning angles, the comparison between calculated and measured results of S-parameters and E- and H-plane antenna patterns is made and a very good agreement is found. Moreover, the precorrected fast Fourier transform method is employed to accelerate the entire computational process to reduce significantly both the memory requirement and computational time, but to increase the design accuracy and optimization efficiency.
An analysis of the modal propagation characteristics of a Bragg fiber having asymmetric loop boundary is made, using a simple matrix method. The boundary condition is replaced by matrix equation andthe modal eigen value equation is obtained under weak guidance condition. The computed results are shown in the form of dispersion curves and cutoff frequencies andare compared with the dispersion curves of a standard Bragg fiber having circular core cross section. It is seen that the proposed Bragg fiber with a small number of claddings (two of four) shows comparable or even better performance than the standard Bragg fiber with respect to a few mode-guidance properties.
An axicon, which images a point source into a line along the optic axis, is used widely to generate an approximation to a Bessel beam. More recently many novel axicons, such as Fresnel axicons, Fractal axicons and fractal conical lenses (FCLs), have been proposed. Understanding the properties of Bessel beams generated by these axicons is very helpful to research their applications. However, in optical region, all of them are calculated approximately by the scalar theory. To accurately analyze FCLs when illuminated by a plane wave at millimeter wavelengths, the rigorous electromagnetic analysis method, which combines a two-dimension finite-difference time-domain (2-D FDTD) method and Stratton-Chu formulas, is adopted in our paper. By using this method, the properties of approximate Bessel beams generated by FCLs are analyzed and the conclusions are given.
This paper deals with the possibilities of cancellation of unwanted signals by steering nulls of the pattern in the direction of arrival of signal while keeping the main beam to the desired direction. New iterative adaptive digital beam forming technique is presented here to enhance the conventional effectiveness of beam forming in common commercial application. Simulation and measurement results confirm that this algorithm can achieve effective Co-Channel Interference (CCI) suppression, while increasing the strength of the desired signal.
The 3D probability tomography theory is developed to image polar and dipolar sources of a geophysical field dataset. The purpose of the method is to improve resolution power of buried geophysical targets, using probability as a suitable paradigm allowing all possible equivalent solutions to be included within a single 3D image. The new approach is described by assuming a geophysical field dataset as caused by a discrete number of source poles and dipoles. A few tests are given to show how the combined polar and dipolar tomography can provide a reliable core-and-boundary resolution of the most probable sources of anomalies. An application to the Vesuvius volcano (Naples, Italy) is finally illustrated by analyzing self-potential and geoelectrical datasets collected within the whole volcanic area. A gravity dataset is also analyzed for completeness. The purpose is to get new insights into the Vesuvius shallow structure and hydrothermal system and to outline the features of the deep tectonic depression within which the volcano grew.
The position perturbations of linear antenna elements are used for designing non-uniformly spaced reconfigurable antennas radiating with multiple pattern such that the same amplitude distribution and perturbed positions produces either a pencil or a flat topped beam, the difference being dependent upon phase distribution of the array. The perturbation method consists of inducing small perturbations in the element positions of a linear array to obtain the desired patterns and offer the flexibility of simple design and is similar to other adaptive techniques like phase only or phase/amplitude synthesis. The problem of finding the element position perturbations is treated as a non linear problem and has been solved using a the generalized generation gap steady state genetic algorithm (G3-GA) using parent centric crossover. In the G3-GA approach the population diversity versus selection pressure problem considers both the parent selection and the replacement plans of GA. The positionphase synthesis method using the G3-GA approach is compared with the G3-GA phase-only synthesis technique. It is seen that, an optimal set of element-perturbed positions in a constrained position range with uniform amplitude, unequally spaced elements with unequal phases has the potential to overcome the design challenge of phase only syntheses that uses a larger number of elements to get the same desired side lobe level. Further when the main beam is scanned it is found that the proposed method can maintain a sidelobe level without distortion during beam steering for the angular positions studied.
For maneuvering target Doppler-bearing tracking with signal time delay, a novel approach called ISE-IMM is proposed in this paper. The iterative state estimation (ISE) method is designed to eliminate the negative influence of time delay effect and an interacting multiple model (IMM) filter is embedded to estimate the state according to the measurements of the delayed signal. The nonlinear filter preferred in this paper is a particle filter (PF) with an improved resampling procedure. Performance of our proposed method is evaluated in Monte Carlo simulations. Results show the effectiveness and stability of ISE-IMM-PF in combating the negative effect of signal time delay.
A time domain integral equation approach for analysis of transient responses by 3D composite metallic-dielectric bodies is proposed, which is formulated using the surface equivalent polarization and magnetization as unknown functions. The time domain electric field integral equation is adopted for the metallic part, while the time domain Piggio-Miller-Chang-Harrington-Wu integral equations are adopted for the dielectric part. The spatial and temporal basis functions are the Rao-Wilton-Glisson functions and quadratic Bspline functions, respectively. Numerical examples are provided to demonstrate the stability and accuracy of the proposed method. No late-time instability is encountered, and the results are found in good agreements with analytical or moment method solutions.