In this paper, a directional coupler incorporating the bandpass frequency response characteristic is proposed and characterized. This structure is modified from a conventional branch-line coupler. Two wide open-ended coupled lines are used instead of microstrip branch lines. As such, good restraint performance outside the passband can be achieved. The even-odd mode technique is employed to analyze and synthesize such a coupler. After that, frequency tuning is achieved by modifying the electrical length of the open-ended coupled lines with varactors. Measured results validate the correctness of our theory and design.
The microwave power transmission is an approach for wireless power transmission. As an important component of a microwave wireless power transmission systems, microwave rectennais widely studied. A rectenna based on a microstrip dipole antennas and a microwave rectifier with high conversion efficiencywere designed at 2.45 GHz.The dipole antenna achieved a gain of 5.2 dBi, a return loss greater than 10 dB, and a bandwidth of 20%. The microwave to DC (MW-DC) conversion efficiency of the rectifier was measured as 83% with 20 dBm input power and 600 Ω load. There are 72 rectennasto form an array with an area of 50 cm by 50 cm. The measured results show that the arrangement of the rectenna connection is an effective way to improvethe total conversion efficiency,when the microwave power distributionis not uniform on rectenna array. The experimental results show that the highest microwave power transmission efficiency reaches 67.6%.
In this work, a special indefinite medium is used to produce a plane wave beam due to its linear type equifrequency contour resulted by the zero parameter in the permeability tenser. Only one transmitting mode exists in such a medium, composing the plane wave beam propagating along the zero parameter direction. Parameters along the field vectors of the wave are 1, enabling the wave propagation in the medium like in the air, which is totally different from the zero-index medium. A split ring resonator (SRR)-arrays based metamaterial is used to realize such a medium and produce an approximate plane wave beam experimentally. This idea proposes a feasible way to generate a near field plane wave beam with certain beamwidth, which can also be applied in cylindrical coordination or 3D cases.
High-order unconditionally-stable three-dimensional (3-D) four-step alternating direction implicit finite-difference time-domain (ADI-FDTD) methods are presented. Based on the exponential evolution operator (EEO), the Maxwell's equations in a matrix form can be split into four sub-procedures. Accordingly, the time step is divided into four sub-steps. In addition, high-order central finite-difference operators based on the Taylor central finite-difference method are used to approximate the spatial differential operators first, and then the uniform formulation of the proposed high-order schemes is generalized. Subsequently, the analysis shows that all the proposed high-order methods are unconditionally stable. The generalized form of the dispersion relations of the proposed high-order methods is carried out. Finally, in order to demonstrate the validity of the proposed methods, numerical experiments are presented. Furthermore, the effects of the order of schemes, the propagation angle, the time step, and the mesh size on the dispersion are illustrated through numerical results. Specifically, the normalized numerical phase velocity error (NNPVE) and the maximum NNPVE of the proposed schemes are lower than that of the traditional ADI-FDTD method.
Within the generalized Lorenz-Mie theory framework, an analytic solution to the scattering by a conducting spheroid with non-confocal chiral coating, for incidence of an axial Gaussian beam, is presented. To overcome the difficulty of non-confocal boundary conditions, a theoretical procedure is developed by virtue of a transformation between the spherical and spheroidal vector wave functions. Numerical results of the normalized differential scattering cross section are shown for chiral-coated conducting spheroids.
In this paper, analytical field expressions are proposed to determine the electromagnetic fields due to an inclined lightning channel in the presence of a ground reflection at the striking point. The proposed method can support different current functions and models directly in the time domain without the need to apply any extra conversions. A set of measured electromagnetic fields associated with an inclined lightning channel from a triggered lightning experiment is used to evaluate the proposed field expressions. The results indicate that the peak of the electromagnetic fields is dependent on the channel angle, the observation point angle as well as the value of the ground reflection factor due to the difference between channel and ground impedances. Likewise, the effect of the channel parameters and the ground reflection on the values of the electromagnetic fields is considered and the results are discussed accordingly.
In the paper, the analysis of electromagnetic wave scattering from multilayered frequency selective surfaces is presented. The surface is composed of periodically arranged posts with irregular shapes. The multimodal scattering matrix of such structure is derived and the transmission and reflection characteristic for the structure with arbitrary plane wave illumination are calculated. The exact full-wave theory based on the hybrid approach employing mode-matching method and finite-difference frequency-domain (FDFD) technique is applied to develop an efficient theory to analyze such structures. The validity and accuracy of the approach are verified by comparing the results with those obtained from alternative methods and own measurements of manufactured periodic structures.
A rotationally symmetric short-circuited stub-loaded structure is proposed to design a microstrip-line bandpass filter with two transmission zeros near the lower and upper cut-off frequency edges of operating millimeter-wave bands. Furthermore, interdigital coupled-lines and additional resonators are integrated into the proposed rotationally symmetric bandpass filter to improve the out-of-band rejection. as design examples, the in-band and out-of-band performances of two filter prototypes using single layer microstrip-lines are designed and experimentally examined. the measured results show that the filter without any interdigital coupled-lines achieves a passband insertion loss of 0.97 dB at 40 GHz and out-of-band rejection of larger than 23 dB, while the filter with the interdigital coupled-lines realizes the suppressions in lower and upper-bands of, respectively, larger than 30 dB and 19 dB for the overall insertion loss of 2.1 dB at 40 GHz.
In this work, we show that light intensity modulation can be realized in the system of one-dimensional time-variant photonic crystals. Different from conventional light modulators, the functioning of the proposed structure emphasizes on its spatial/temporal structures instead of inherent material properties. Additionally, our system can perform inherent light modulation without introducing external stimuli, thus avoiding direct contacts with electrodes (or other modulation sources), which would be preferable in certain environments. The influences of parameters such as light frequency, structure dimensions, and refractive index contrasts on the modulation performance of the time-variant photonic crystal were investigated by numerical simulations. The results provide a new strategy for light modulation, which may add functionalities in optical communication, integrated-optics or display technologies.
In this paper two typical arrangements of underground single-core high voltage three-phase power cables (flat and trefoil protected by PVC pipes) inside a closed shield of three different materials (low-carbon steel, non-oriented grain steel and aluminium) are analysed. The shield has two components: a U-shaped base and a flat plate (cover) located on top of the base. Whereas most of previous papers on this subject only dealt with the degree of mitigation obtained with each material, this paper, in addition to also addressing this issue, mainly focusses on the effect that electromagnetic losses induced in the shield have on the ampacity of the cable and the cost involved (material and losses). To obtain the numerical results, a high number of simulations by a well-known commercial finite element method software (COMSOL Multiphysics) have been performed. The results obtained in the numerous cases analysed are widely commented and the solutions that enable an important mitigation with no current derating and at a comparatively low cost are highlighted.
The aperture synthesis technology represents a promising new approach to microwave radiometers for high-resolution observations of the Earth from geostationary orbit. However, the future application of the new technology may be limited by its large number of antennas, receivers, and correlators. In order to reduce significantly the complexity of the on-board hardware requirements, a novel method based on the recently developed theory of compressive sensing (CS) is proposed in this paper. Due to the fact that the brightness temperature distributions of the Earth have a sparse representation in some proper transform domain-for example, in terms of spatial finite-differences or their wavelet coefficients, we use the CS approach to significantly undersample the visibility function. Thus the number of antennas, receivers, and correlators can be further reduced than those based on the traditional methods that obey the Shannon/Nyquist sampling theorem. The reconstruction is performed by minimizing the l1 norm of a transformed image. The effectiveness of the proposed approach is validated by numerical simulations using the image corresponding to AMSU-A over the Pacific.
In this paper, a wide slot loop antenna with an adjustable back-reflector is introduced. Five working statuses are defined by simply adjusting the distances between the radiator and the reflector. Measured results show the total available operating band with better than 10 dB return loss ranges from 0.84 GHz to 3.04 GHz (113.4%). The radiation properties of the array are tested in an anechoic chamber. Stable unidirectional radiations with more than 8.3 dB gains are observed in the working band. Apart from that, the straightforward two-portion arrangement of the design provides cost-effective solution for mass production. All these features make the antenna an appropriate substitute for multiple narrowband antennas.
In this paper, the performance analysis of the natural frequency-based radar target recognition in the time domain is considered. We investigate the dependence of the probability of correct classification on a specific threshold value, and determine the optimum threshold value for two targets, and the sub-optimal threshold for multiple targets to maximize the probability of correct classification. Based on the probability density function (PDF) of some quantity consisting of the projections of the late time response onto the column spaces of the matrices constructed using the natural frequencies of the specific targets, we propose how to determine an optimum threshold in the sense that the probability of correct classification of two targets is maximized. By extending the scheme for two targets, we show how to determine a threshold value close to the optimal threshold for multiple targets. The scheme is validated by comparing the performance using the analytic method with that using the Monte-Carlo simulation.
A very compact low temperature co-fired ceramic (LTCC) dual-band filter is designed based on the proposed novel cross-coupling structure in this paper. A six-pole dual-band filter with four transmission zeros is synthesized using an analytical procedure. By incorporating the proposed novel cross-coupling structure and analyzing the coupling characteristic, the dual-band filter is realized with canonical topology in multilayer LTCC. It is demonstrated by the simulation and experiment that the proposed dual-band filter has both compact size and good selectivity.
Geosynchronous synthetic aperture radar (GEO SAR) has the characteristics of long aperture time and large imaging area. Therefore, the conventional imaging algorithm in Low Earth Orbit (LEO) SAR loses effect. In this paper, based on curved trajectory model under an ideal acquisition and not considering some acquisition perturbations (atmosphere, orbital deviations), an accurate two-dimensional frequency spectrum is analytically obtained via series reversion principle and high order Taylor expansion. Then, an improved Nonlinear Chirp Scaling (NCS) algorithm is proposed in GEO SAR, which includes novel range migration correction factor, coupling phase compensation factor, NCS factor and azimuth compression function. Finally, the correctness of the proposed NCS algorithm is verified via imaging results of point array targets and area targets.
An original target identification method using Wave-Coefficients (WCs) as feature vector is proposed. The scattering fields of arbitrary shaped targets are expressed as a sum of spherical waves and the distinctive coefficients are exploited as the target feature. Decision rule based on correlation coefficient is established, and some analyses on the properties of the WCs are conducted. Numerical simulations of four targets are carried out and the recognition performances without and with noise are provided and discussed.
This paper proposes a microwave filter post-production tuning based on an optimization process which finds the vector of deviations of tuning elements that should be applied to tune the filter. To build the system, the coarse set of scattering parameters is collected in such a way that every tuning element is detuned while other elements remain in their proper positions. In the concept, it is assumed that the relation between the positions of tuning elements and filter scattering characteristics can be modelled by the sum of one argument polynomial functions. Each polynomial function depends on the value of only one tuning element. Therefore, the measured filter characteristics can be linearly decomposed to characteristics from the collected coarse set and corresponding tuning element deviations can be found. This is done by way of optimization process. The presented numerical and physical experiments on the 7th order cross-coupled, bandpass filter have verified our approach.
Two new compact planar triple-mode resonators embedded with inductive or capacitive cross coupling are proposed for bandpass filter design. Both resonators consist of a shorted half-wave ring. In the first resonator, two shorted half-wave sections with inductive coupling are connected to the shorted via of the ring. In the second, two quarter-wave sections with capacitive coupling are connected. The inductive coupling is realized by a short grounded high-impedance segment, and the capacitive coupling is implemented by an interdigital capacitor. When both the inductive and capacitive coupling coefficients are properly realized, a transmission zero can be created at designated position in either upper or lower stopband. The shorted ring is accommodated inside the area of the other two resonance sections so that a compact area can be achieved. As compared with a conventional dual-mode ring resonator filter, the proposed resonators use only 46.7% and 22.5% in area. Two triple-mode resonator bandpass filters are fabricated and measured to validate the ideas. Measurement results have good agreement with the simulation responses.
The insertion of vertical slabs in a metallic rectangular waveguide distorts the power distribution of the waveguide, producing new modes and modifying the existing ones. The resulting waveguide, known as E-plane loaded rectangular waveguide, is studied in this paper, focusing the attention on the TE-type modes in a symmetrical case. A quasi-TE10 is found which may confine the energy in the central air region by suitably choosing the dielectric slabs' dimensions. An algorithm to optimize these dimensions is proposed in order to maximize the confinement of power in the air region and minimize the attenuation of the mode. This minimization is specially important at high frequencies, where the ohmic losses and the dielectric absorption become extremely high. This paper includes an example at THz frequencies and presents the design of several devices using the E-plane loaded rectangular waveguide.
The Wave Iterative Process is applied and validated for the study of the scattering of a plane wave by a multiple metallic dipole diffraction structure. The case of a single metallic dipole is treated, at first in normal incidence, than arbitrarily placed with respect to the incident wave. A double dipole scattering structure is studied, mutual influence being taken into account. The diffraction system is further enlarged to 5 randomly placed dipoles, the results issued from the WIP study being compared with those given by the Moments Method. Finally, the possibility of taking into account a very large number of dipoles is examined, by introducing an equivalent dipole distribution. The influence of this approximation on the WIP precision is presented.
We describe the implementations of Drude-critical point model for describing dispersive media into finite difference time domain algorithm using piecewise-linear recursive-convolution and auxiliary differential equation methods. The advantages, accuracy and stability of both implementations are analyzed in detail. Both implementations were applied in studying the transmittance and reflectance of thin metal films, and excellent agreement is observed between analytical and numerical results.
A transformer that uses bonder-wires and printed circuit board (PCB) patterns is proposed for RF circuit applications. The proposed transformer can be constructed without any additional processes. The PCB patterns are implemented using a typical FR4 substrate and gold bonder wires are used. The self-inductance of the transformer can be controlled according to the number of unit-transformers. Although the size of the transformer is larger than that of a fully-integrated transformer, the maximum available gain (MAG) is almost identical to that of other-types of transformers, which require additional cost or bulky size to obtain sufficient inductance. Additionally, we proposed a method to design the transformer with a symmetric structure for differential RF CMOS circuit applications. The transformer can applied to GHz-order RF CMOS circuits as an input and output matching component with low loss characteristics.
A novel slotted helix slow-wave structure (SWS) is proposed to develop high power, wide-bandwidth, high reliability millimeter-wave traveling-wave tube (TWT). This structure, which can improve the heat dissipation capability of the helix SWS, evolves from conventional helix SWS with three parallel rows of rectangular slots made in the outside of the helix. In this paper, thermal stress analysis, the electromagnetic characteristics and the beam-wave interaction of this structure are investigated. The conclusions of this paper will be a great help for the design of millimeter-wave traveling-wave tube.
This work provides the comparison of different methods for the experimental determination of the phase center location of an antenna. The phase center position is determined by means of measured data obtained with a planar scanning system and computed with different methods: a least squares fit method with and without weighting coefficients and a directivity-based plane wave spectrum (PWS) analysis method. A study of the phase center position for different microwave antennas is provided. The results of the different methods are presented and compared, along with the confidence interval of the phase center values due to the uncertainties of the acquisition system.
This work presents an active balanced sub-harmonic mixer (SHM) using InP double heterojunction bipolar transistor technology (DHBT) for Q-band applications. A miniature spiral type Marchand balun with five added capacitances for improved control of amplitude and phase balance is integrated with the SHM. The measured results for the SHM demonstrates a conversion gain of 1.2 dB at an RF frequency of 41 GHz with an associated LO power of 5 dBm. The conversion loss remains better than 3 dB from 38 to 44 GHz. The LO to IF isolation is better than 42 dB within the bandwidth of the mixer and confirms the excellent balance of the integrated spiral type Marchand balun. The DC power consumption of the SHM is only 22.5 mW under normal mixer operation.
This paper presents an implementation of the FDTD-compatible Green's function on a heterogeneous parallel processing system. The developed implementation simultaneously utilizes computational power of the central processing unit (CPU) and the graphics processing unit (GPU) to the computational tasks best suited to each architecture. Recently, closed-form expression for this discrete Green's function (DGF) was derived, which facilitates its applications in the FDTD simulations of radiation and scattering problems. Unfortunately, implementation of the new DGF formula in software requires a multiple precision arithmetic and may cause long runtimes. Therefore, an acceleration of the DGF computations on a CPU-GPU heterogeneous parallel processing system was developed using the multiple precision arithmetic and the OpenMP and CUDA parallel programming interfaces. The method avoids drawbacks of the CPU- and GPU-only accelerated implementations of the DGF, i.e. long runtime on the CPU and significant overhead of the GPU initialization respectively for long and short lengths of the DGF waveform. As a result, the seven-fold speedup was obtained relative to the reference DGF implementation on a multicore CPU thus applicability of the DGF in FDTD simulations was significantly improved.
In this work, a new efficient simplification method is proposed for crosstalk prediction of multicoaxial cable bundles (MCCB). The purpose of the new simplification method is to reduce the simulation time by reducing the complexity of the complete cable bundle model. A modified five-step procedure is established to define the electrical and geometrical characteristics of the reduced cable bundle by making the outer and inner conductor of the coaxial cable participate in the equivalence procedure respectively. After a short presentation of the MCCB coupling problem, the theory fundamentals of the new simplification method and numerical simulations performed on a simple MCCB are presented to demonstrate the efficiency and the advantages of the new simplification method.
In this paper a procedure for sidelobe suppression in the frequency response of a MIM (metal-insulator-metal) plasmonic filter is presented. Using the calculated effective refractive index for various values of the width of dielectric core and Bragg condition, the structural profile of primary filter is obtained. The frequency response for the transmission coefficient of the MIM plasmonic filter is derived by TRC-LOD-FDTD method. The variation in the frequency response of the filter due to changes in the structural parameters is studied. Finally, the usage of Gaussian, sinusoidal and linear types of gratings in suppressing the sidelobes and their effects on the stop-band bandwidth of the MIM plasmonic filter is investigated.
A new type of varactor-tuned microstrip bandpass filter (BPF) based on a single 1/2λ resonator is investigated. The proposed resonator is composed of a transmission line with both ends short-ended and two varactors inserted symmetrically in the middle section. The variation of coupling coefficient can be controlled by using an inductor. With the proposed structure, it is easy to adjust the external quality factor of the filter and to control the bandwidth. Extra dc-block capacitors for the input and output ports are not necessary because the design of the proposed tunable 1/2λ resonator makes the varactor act as both a frequency tuning element and a dc-block circuit. The proposed BPF is found to have the advantages of compact size, low insertion loss, large tuning range and good linearity.
his paper presented a novel unconditional stable FDTD (US-FDTD) algorithm for solving the transient response of uniform or nonuniform multiconductor transmission line with arbitrary coupling status. Analytical proof of unconditional stability and detailed analysis of numerical dispersion are presented. The precise split-time-step scheme has been introduced to eliminate the restriction of the Courant-Friedrich-Levy (CFL) condition. Compared to the conventional USFDTD methods, the proposed approach generally achieves lower phase velocity error for coarse temporal resolution. So larger time scales can be chosen for the transient simulation to achieve accurate results efficiently. Several examples of coupled uniform and nonuniform lines are presented to demonstrate the accuracy, stability, and efficiency of the proposed model.
Current automotive electromagnetic compatibility (EMC) standards do not discuss the effect of the driving profile on real traffic vehicular radiated emissions. This paper describes a modeling methodology to evaluate the radiated electromagnetic emissions of electric motorcycles in terms of the driving profile signals such as the vehicle velocity remotely controlled by means of a CAN bus. A time domain EMI measurement system has been used to measure the temporal evolution of the radiated emissions in a semi-anechoic chamber. The CAN bus noise has been reduced by means of adaptive frequency domain cancellation techniques. Experimental results demonstrate that there is a temporal relationship between the motorcycle velocity and the radiated emission power in some specific frequency ranges. A Multilayer Perceptron (MLP) neural model has been developed to estimate the radiated emissions power in terms of the motorcycle velocity. Details of the training and testing of the developed neural estimator are described.
The high squint diving SAR is widely used to provide the information in advance. Large squint angle deduces the deeper coupling of range and azimuth of SAR echoes which makes SAR imaging more difficult. Especially, the large range migration of the deep couple heavily burdens the imaging processing time and storage units. The diving motion of platform worsens the situation. This paper proposes the varied azimuth sample frequency (Pulse Repeat Frequency, PRF) to implement the high squint diving SAR imaging. Based on the signal model of the diving squint SAR, it is analyzed that the range walk is the prominent component of range migration in the high squint SAR. The varied PRF imaging method dramatically decreases the range walk of echoes by shifting the beginning position of transmitted pulses and received echoes and the shift is implemented by the PRF variation. Then the range migration is decreased and the couple of range and azimuth of SAR echoes is reduced. The PRF variation law is deduced and the applicable condition of varied PRF is presented. The simulation results show that the variable PRF method is efficient to reduce range walk of echoes. Comparison to the traditional constant PRF, the novel variable PRF method for high squint needs less storage and less time expense, which is helpful to real time SAR imaging. The non-uniform FFT can be used for the azimuth compressing of the variable PRF SAR. It will simplify the implementation of the variable PRF SAR imaging.
In this paper, a X-band wideband bandpass filter based on a novel substrate integrated waveguide-to-defected ground structure (SIW-DGS) cell is proposed. In the cell, the DGS is etched on the top plane of the SIW with high accuracy, so that the performance of the filter can be kept as good as possible. Finally, the filter, consisting of three cascaded cells, is designed and measured to meet compact size, low insertion loss, good return loss as well as smooth group delay. There is good agreement between the measurement and simulation results.
In this study, the Artificial Bee Colony Optimization (ABCO) algorithm has been proposed to estimate the atmospheric duct in maritime environment. The radar sea clutter power is calculated by the parabolic equation method. In order to validate the accuracy and robustness of ABCO algorithm, the experimental and simulation study are respectively carried out in the current research. In the simulation study, the statistical analysis of the estimation results in term of the mean squared error (MSE), mean absolute deviation (MAD) and mean relative error (MRE) are presented to analyze the optimization performance with different noise standard deviation, and the comparative study of the performance of ABCO and particle swarm optimization (PSO) algorithm are also shown. The investigation presented indicate that the ABCO algorithm can be accurately and effectively utilized to estimate the evaporation duct and surface-based duct using refractivity from clutter (RFC) technique in maritime environment. In addition, the performance of ABCO algorithm is clearly superior to that of the PSO algorithm according to the statistical analysis results, especially for the four-parameter surface-based duct estimation.
Microwave array 3-D imaging is an emerging technique capable of producing a 3-D map of scattered electric fields. Its all-weather and large scene imaging features make it an attractive powerful tool for target detection and feature extraction. Typically, a microwave array 3-D imaging system based on the classical sampling theory requires a large dense 2-D antenna array, which may suffer from a very high cost. To reduce the number of the antenna array elements, this paper surveys the use of compressed sensing recovery and sparse measurement strategies for microwave array 3-D imaging. Combining with the typical spatial sparsity of the underlying scene, we pose the sparse array microwave 3-D imaging as finding sparse solutions to under-determined linear equations. Further, to reduce the computational of the compressed sensing recovery with the large-scale echoes data, we divide the underlying 3-D scene into a series of equal-range 2-D slices, and deal with these slices separately using the orthogonal matching pursuit (OMP) algorithm. Lastly, the performance of the presented compressed sensing approach is verified by an X-band microwave array 3-D imaging system. The experimental results demonstrate that the compressed sensing approach can produce a better resolution 3-D image of the observed scatterers compared with the conventional method, especially in the case of very sparse activate antenna array.
A broadband circularly polarized patch antenna with suspended structure is proposed. The suspended patch has an indented edge and a gap-coupled feed. By optimizing the geometries of the antenna, a wide impedance bandwidth of 1.26-1.965 GHz and an axial ratio bandwidth of 1.51-1.68 GHz are obtained. The antenna with simple structure is simulated and measured, and the results show that the bandwidth of the patch antenna is successfully broadened by using the suspended configuration, indented edge and gap-coupled feed.
It is difficult to determine the feed radiation center and F/D of the reflector impulse-radiating antenna (IRA) in frequencydomain, due to its ultra-wideband (UWB) property. This paper presents an efficient approach to design the reflector IRAs, via evaluating the transient radiation patterns (TRPs) of the feed for some given different radiation centers. Only one time-domain simulation for the feed is needed in this method. Comparing with the global optimization algorithms, our method is fast and reliable in the design of the reflector IRAs.
The system which enhances wireless power transmission efficiency for bio-medical applications has been proposed in this report. The system that operates at giga-hertz ranges is based on an inductive coupling between a transmitter coil and a receiver coil. A magnetic current source was modeled to a magnetic dipole with magnetic dipole moment m. To increase wireless power transmission efficiency, a high surface impedance ground plane was used and reflection from the ground plane is responsible for constructive interference. For this system, a theoretical study has been performed in this report by solving Sommerfeld integrals. Compared with the result of a system without a ground plane, the system with a high surface impedance ground plane showed enhancement of received power at a given transmitted power.
Synthetic aperture radar (SAR) automatic target recognition (ATR) has been receiving more and more attention in the past two decades. But the problem of how to overcome SAR target ambiguities and azimuth angle variations has still left unsolved. In this paper, a multi-scale local phase quantization plus biomimetic pattern recognition (BPR) method is presented to solve these two difficuties. By applying multiple scales local phase quantization (LPQ) on the observed SAR images, the blur and azimuth invariant features can be extracted, and these features are fusion with consecutive multiple scales to achieve better results. Then PCA method is applied to further reduce the feature dimension and achieve its efficiency. Finally, high dimensional space geometry covering method based on BPR theory is adopted to construct hyper sausage neuron links for target recognition. Experiments on the MSTAR database show that the proposed method can achieve satisfying recognition accuracy compared with other state-of-the-art methods.
The electromagnetic characterization of piezoelectric micro-needle antenna sensors for fully non-invasive detection of cancer-related anomalies of the skin is presented. To this end, a full-wave finite-difference time-domain procedure is adopted to analyze the performance of the considered class of devices in terms of circuital characteristics and near-field radiation properties as a function of the curvature radius of the relevant sensing probe. This analysis is, in turn, useful to gain a physical insight into the processes which affect the behavior of the structure and, hence, the accuracy in the detection of possible malignant lesions of the skin. In particular, by using the mentioned modeling approach, an extensive parametric study is carried out to analyze the effect produced on the sensor response by variations of the complex permittivity of the skin due to the presence of anomalous cells and, in this way, obtain useful discrimination diagrams for the heuristic evaluation of the exposure level to the cancer risk.
The single mode condition of rectangular waveguides is derived by using a simple ray-optics approach, which relies on geometrical ray tracing principles as in classical optics. Light propagation through such a waveguide can be approximately simplified as reflections within two planes of incidence. By employing the mode equations for different polarizations, a relation that shows the single-mode cut-off as a function of the waveguide dimensions is readily obtained.
Vertical electric fields generated by lightning leader channels, the total leader field change and the total leader field change to the total return stroke field change ratio, at a certain distance, were theoretically analysed by varying the angle of orientation of a segment of upper part. Ground was treated as a perfectly conducting horizontal plane. Results were able to discern significantly large differences in the static field due to leader channels which have the same total length but a certain channel segment is oriented at different angles. The outcome of our calculations consistently explains the scatter of the total leader field observed in previous studies. Without considering such channel segment orientation, one has to assume unrealistic charge source heights or unreasonable charge densities to calculate matching values for many observed total leader fields and leader field to return stroke filed ratios, labelled as anomalous observations in the literature. In some cases, irrespective of the charge source height and the charge density, one cannot find a suitable fit for the observed fields with the straight channel model.
Compressive Sensing (CS) is a recently developed technique, which can reconstruct the sparse signal with an overwhelming probability, even though the signal is sampled at highly sub-Nyquist rate. Based on the observation that the electromagnetic scattering structure (ESS) of a metal landmine is composed of two scattering centers, whose geometrical parameters are tightly related to its physical dimensions, a new physics-based landmine discrimination approach is proposed in this paper. Firstly, the approach uses the Multi-Measurement Iterative Pixel Discrimination method to reconstruct the landmine's ESS in noisy environments. Secondly, the geometrical parameters of the landmine's ESS are extracted from the sparse image. Thirdly, landmine discrimination is conducted according to the measured geometrical features and apriori knowledge. Finally, the field experimental results demonstrate the effectiveness of the proposed approach.
The purpose of this paper is to investigate the use of simulation technology for the analysis of wireless propagation channel in medical environments. In this paper, the channel modeling has been carried out by using an effective simulation platform, which combines full-wave Method of Moments and adaptive ray tracing technique. Base on this, the channel characteristics involving both large-scale and small-scale parameters of a wireless network deployed within a hospital environment can be estimated. Also, it is straightforward to predict the levels of electromagnetic field interference produced from the network infrastructure. The simulated results of four scenarios of medical environment, such as the patient room, the operating room, a particular level of the hospital, and the cardiac stress test room, with different wireless technologies used show the advantage and capability of the presented simulation approach.
A vector network analyzer (VNA) with a bulk current injection (BCI) probe is proposed to measure the transmission coefficient of a PCB. The purpose of developing such a measurement techniques is to predict the radiated emission for good correlation with the fully-anechoic chamber measured results. In this study, the proposed method is used to determine the radiated emission from a DC supply loop. Moreover, the proposed method can be further used to accurately predict the reduction of radiated emission from the improved DC supply loop. Electromagnetic simulations is also developed to confirm the accuracy of the proposed techniques.