A method for retrieving evaporation duct height (EDH) is introduced in this paper. The proposed technique employs the changes in radar sea clutter power observed at different heights as input information. It identifies the EDH associated with the modeled clutter change pattern that best matches measured change patterns. The performance of the method is evaluated in terms of RMS errors in retrieving actual EDHs that range from 0 to 40 m. The comparison of the proposed method with the conventional clutter pattern matching method shows that the former more effectively retrieves actual EDHs.
In this paper, a new plasma antenna of beam-forming is investigated based upon the interaction of plasma elements due to the electromagnetic wave. It presents a study of the multiple scattering from argon plasma cylinders rigorously applying boundary value method, grounded on the properties of electromagnetic wave transmitted in the argon plasma. Approximate expressions for the total radiation of plasma antenna in the far field are derived briefly. Also presented is a study that this new antenna of beam-forming exhibits interesting performance in terms of radiation efficiency, beam-forming and beam-scanning. Valid results are brought forth to demonstrate the capabilities of such antenna of two scales. Comparisons are given in detail as well.
In this work, a detailed investigation on the effective plasma frequency fp,eff for one-dimensional binary and ternary plasma-dielectric photonic crystals is made. We extract and then analyze the effective plasma frequency from the calculated photonic band structures at distinct conditions. In the binary photonic crystal, it is found that fp,eff in a photonic crystal is usually smaller than the plasma frequency fp of a bulk plasma system. fp,eff will increase when the electron concentration in the plasma layer increases. It also increases as the thickness of the plasma layer increases, but decreases with the increase in the thickness of dielectric layer. In the ternary photonic crystal, fp,eff is shown to be decreased compared to that of in the binary one. Our results are compared with the analytical expression for fp,eff derived from the concept of effective medium. Fairly good consistence has been obtained for both results. Additionally, a discussion on the effect of loss on fp,eff is also given. The study is limited to the case of normal incidence.
Finite element hp-adaptivity is a technology that allows for very accurate numerical solutions. When applied to open region problems such as radar cross section prediction or antenna analysis, a mesh truncation method needs to be used. This paper compares the following mesh truncation methods in the context of hp-adaptive methods: Infinite Elements, Perfectly Matched Layers and an iterative boundary element based methodology. These methods have been selected because they are exact at the continuous level (a desirable feature required by the extreme accuracy delivered by the hp-adaptive strategy) and they are easy to integrate with the logic of hp-adaptivity. The comparison is mainly based on the number of degrees of freedom needed for each method to achieve a given level of accuracy. Computational times are also included. Two-dimensional examples are used, but the conclusions directly extrapolated to the three dimensional case.
An adaptive approach to minimize acquisition time in planar near-field antenna measurements is described. In contrast to the traditional planar near-field scanning, the presented technique acquires the near-field in form of rectangular rings and skips sampling points in smoothly varying near-field regions. Abrupt changes in the near-field are detected by comparing extrapolated and measured near-field values at coarser sampling points. A decision function based on the signal-to-noise ratio (SNR) of the measured value is used to determine the threshold difference between the measured and the extrapolated near-field values for skipping the sampling point. Near-field data thus collected on the resultant irregular grid is processed using the multilevel plane wave based near-field far-field transformation algorithm. The multilevel transformation algorithm is computationally efficient and capable of handling data collected on irregular grids. A rigorous analysis of the adaptive data acquisition approach is then performed in terms of transformed far-field accuracy, decision factor, and test time reduction. Several test cases covering a variety of antennas are shown using synthetic as well as measured data for realistic results. Afterwards the acquisition time for the worst case scenario is compared with the traditional planar near-field measurement technique.
In this paper, a novel idea of reducing numerical complexity of finite difference method using multiple macromodels is presented. The efficiency of the macromodeling technique depends on the number of ports of a model. To enhance the efficiency of the algorithm the field samples at the boundary of the macromodel are replaced with amplitudes of discretized Legendre polynomials. Redefining the problem in such manner results in significant reduction of the analysis time. The validity and efficiency of the proposed procedure are demonstrated by performing the analysis of two microwave filters requiring a high density mesh.
We present a simple architecture for realizing high capacity W-band (75-110 GHz) photonics-wireless system. 42.13 Gbit/s 16QAM-OFDM optical baseband signal is obtained in a seamless 15 GHz spectral bandwidth by using an optical frequency comb generator, resulting in a spectral efficiency of 2.808 bits/s/Hz. Transparent photonic heterodyne up-conversion based on two free-running lasers is employed to synthesize the W-band wireless signal. In the experiment, we program an improved DSP receiver and successfully demonstrate photonics-wireless transmission of 8.9 Gbit/s, 26.7 Gbit/s and 42.13 Gbit/s 16QAM-OOFDM W-band signals, with achieved bit-error-rate (BER) performance below the forward error correction (FEC) limit.
The detection and identification of multi-stationary human targets with IR-UWB radar is a new and important technology. This paper is focused on the detection and identification of two close stationary human targets by using monostatic IR-UWB radar with low center frequency. For this purpose, the characteristics of the radar echoes from two close stationary human targets are processed and analyzed. Furthermore, the effect that the interference behind the anterior target affects the signal of posterior target is represented, and the features of this interference are interpreted. According to the analyses, a method using adaptive cancellation is proposed to attenuate the interference and improve the detection and identification of two close stationary human targets. Series of experiments are done in different scenarios, and the results of the experiments are presented to demonstrate the validity of the method. It has been shown that the proposed method can attenuate the interference and make the detection and identification of multi-human targets more precise.
Koch-like fractal curve and Sierpinski Gasket are syncretized in minor-main way, forming so called Koch-like sided Sierpinski Gasket multifractal dipole (KSSG). Some iterative combinatorial cases of the two monofractals KiSj KSSG have been investigated in free space without feedline for revealing the assumed multifractal property. Then a pragmatical coplanar stripline (CPS) fed K4S1 KSSG multifractal bow-tie dipole with dimension of 61.1mm×34.75mm was designed, fabricated and measured. Six matched bands(S11<-10dB) with moderate gain (2dBi-6dBi) and high efficiency (80%-95%) are obtained within band 1.5GHz-14GHz, of which f1=2.137GHz (1.978-2.287GHz, 309MHz, 14.46%, PCS1900+IMT2000+UMTS), f2=4.103GHz (3.916-4.2GHz, 374MHz, 9.12%, WiMAX), f3=5.596GHz (5.499-5.679GHz, 180MHz, 3.22%, WLAN+WiMAX) are commonly used. Gain patterns of these bands are all almost omnidirectional in H-plane (Phi=0o, XOZ) and doughnut-shaped in E-plane (Phi=90o, YOZ), which suggests that K4S1 KSSG operates as a half-wavelength dipole. It behaviors like the main fractal in low frequency and resembles the minor one in high frequency. The consistent results of simulation and measurement have evinced the multifractal antennas' peculiar properties and superiority over its monofractals in impedance uniformity, gain pattern, efficiency and dimension. So it is attractive to PCS, UMTS, WLAN, WiFi, WiMAX and other communication systems.
An efficient and stable hybrid method, based on the time-domain integral equation (TDIE) and time-domain physical optics (TDPO), is developed for investigating transient radiation and scattering from perfectly electrical conducting (PEC) objects. It at first requires partitioning the PEC object surface into TDIE and TDPO regions, respectively. Then, a set of hybrid TDIE-TDPO equations is derived and solved using an adaptive marching-on-in-order (MOO) method. The fast Fourier transforms (FFT)-based blocking scheme is further implemented into the proposed algorithm so as to reduce N2O dependence of the traditional MOO method to NOlog2(NO), where NO is the highest order of the weighted Laguerre polynomials used for computation. Under such circumstances, its computational cost, in comparison with the full TDIE-MOO solver, is reduced significantly. Several numerical examples are presented to demonstrate its accuracy and efficiency in solving some typical transient electromagnetic problems.
One novel dielectric conformal finite-difference time-domain (FDTD) method is proposed for computing specific absorption rate (SAR) distribution over the human body model in one metallic cabin with some windows on its wall. It is based on the concept of area average, which is different from other traditional conformal FDTD schemes. Our developed algorithm is verified by calculating both point and average SARs of dielectric sphere and human head models illuminated by an intentional electromagnetic pulse (IEMP), respectively, and CST Microwave Studio (MWS) also used for validating its accuracy. Numerical calculations are further performed to show the average SAR distribution over the human body model for different IEMP incidences, where the cabin door is opened or closed. The effects of E-field amplitude, direction and polarization of the incident IEMP on the SAR distributions are characterized in detail. We would like to say that this study will be useful for further electromagnetic protection for some persons working in high power radiation environment.
In this paper, the subaperture approximation (SA) method for 3-D microwave imaging is presented based on the sparsity of 3-D image. The idea is that the sparsity information can be extracted from the lower resolution image obtained using the subaperture of the (virtual) array and be used for high-resolution imaging to reduce the imaging region. Thus, a recursion procedure that can significantly reduce the computational cost is established. Compared with the surface-tracing-based method, the SA method can avoid the loss of isolated scatterers. The feasibility is verified by using experimental data. After analysis, the SA method can reduce the computational cost from two aspects: reducing the array element number needed to be processed and the pixels needed to be processed. The computational cost is mainly related to the target characteristics (the sparsity ratio and the topological structure), and decreases with the increase of the sparsity ratio. When the sparsity ratio is larger than 97.6%, the computational cost can be lower than 10% of the 3-D back-projection (BP) method.
An efficient strategy for reducing the signature of an antenna is to substitute the conventional solid ground plane with a patterned ground plane thus letting the incoming energy to pass through the structure except over the operating band of the antenna. However, in a real environment, the energy flowing through the FSS (Frequency Selective Surface) can be intercepted by eventual scatterers located behind the antenna, so to nullify the RCS (Radar Cross Section) reduction. To overcome this drawback, a novel composite structure is proposed which is able to dissipate such energy by placing a thin absorbing layer below the FSS ground. It is shown that a careful analysis has to be performed to accomplish this goal since the transparent antenna array and the backing absorber strongly interact and thus they cannot be separately designed. The optimal value of the foam spacer thickness between the FSS ground and the absorbing layer is investigated by an efficient equivalent transmission line approach. Criteria for enlarging the low-RCS band with respect to the free space design are also provided. An antenna array prototype backed by the thin multilayer structure is finally manufactured and tested.
In this paper, it is demonstrated how anisotropic and inhomogeneous magnetic metamaterials may be used for molding the flow of the magnetic field, considering magnetic field shielding as the main application of practical interest. It is shown that using anisotropic materials, magnetic field shielding may be improved, and this anisotropy can be realized by metamaterials. Introducing additional inhomogeneity in the metamaterial can increase the shielding performance even more. The required parameters for inhomogeneity may be obtained by representing the shielding problem in matrix form, using a quasi-static magnetic field approximation. Finally, some comments on the practical implementation of the metamaterial and comparisons with the standard shielding techniques are given.
The influence of random fluctuations in the layer thicknesses in high contrast, one-dimensional Photonic Crystals (PCs) on the transmission spectra and Photonic Band Gaps (PBGs) is investigated. The change in the PBGs depends on the magnitude of the fluctuations and increases with an increase in the order of the PBG. Introducing thickness non-uniformity into the PC of up to 0.004 times the value of lattice constant for different types of fluctuation distributions has a negligible effect on either the position or the shape of the 1st and nearest PBGs. The approach suggested here allows the determination of the tolerances required in the geometrical parameters of PCs during fabrication. It also allows the optimisation of PC structures using high order PBGs.
This paper presents a comparative study of neural network (NN) training. The trained NNs are used as adaptive beamformers of antenna arrays. The training is performed either by a recently developed method called Mutated Boolean PSO (MBPSO) or by a well known beamforming method called Minimum Variance Distortionless Response (MVDR). The training procedure starts by applying the MBPSO and the MVDR to a set of random cases where a linear antenna array receives a signal of interest (SOI) and several interference signals at random directions of arrival (DOA) different from each other in the presence of additive Gaussian noise. For each case, the MBPSO and the MVDR are independently applied to estimate respective excitation weights that make the array steer the main lobe towards the DOA of the SOI and form nulls towards the DOA of the interference signals. The lowest possible value of side lobe level (SLL) is additionally required. The weights extracted by the MBPSO and the weights extracted by the MVDR are used to train respectively two different NNs. Then, the two trained NNs are independently applied to a new set of cases, where random DOA are chosen for the SOI and the interference signals. Finally, the radiation patterns extracted by the two NNs are compared to each other regarding the steering ability of the main lobe and the nulls as well as the side lobe level. The comparison exhibits the superiority of the NN trained by the MBPSO.
Joint time-frequency analysis (JTFA) is applied to micro Doppler signatures generated by jet engine modulation (JEM) effect using a modified Hilbert-Huang transform (HHT). The modified HHT is developed to improve the JTFA results of measured JEM signals. Wavelet decomposition (WD) with Meyer wavelet function is considered as a supplementary process of the HHT. The modified HHT examines a signature obtained from simulation of a jet engine CAD model, and is then applied to the signatures obtained from measurement of two realistic jet engine models. The modified HHT gives more improved JTFA results of the measured JEM signals than those from the simple short-time Fourier transform - (STFT) based analysis. The modified HHT-based JTFA approach is expected to be significantly useful for enabling high-quality radar target recognition in a real environment by complementing other traditional analyses.
Tapered dielectric fibers are widely used in the near field microscopy to focus the incident beam or collect near field signal. Single mode is always required so that the geometrical dimension of the waveguide is smaller than the wavelength. This paper proposes an inexpensive and easy fabrication of multimode tapered Teflon probe which has bigger dimensions than the wavelength. The field distribution in and outside the probe is analyzed by the total internal reflection theorem and solid core circular dielectric waveguide theory. Simulations are carried out in Microwave Studio CST. Novel applications based on focal points in and outside the probe are discussed, especially dielectric permittivity sensing of biomolecules using a capillary tube is emphasized by the simulations and experiments.
Applications of localized surface plasmon resonance (LSPR) such as surface enhanced Raman scattering (SERS) devices, biosensors, and nano-optics are growing. Investigating and understanding of the parameters that affect the LSPR spectrum is important for the design and fabrication of LSPR devices. This paper studies different parameters, including geometrical structures and light attributes, which affect the LSPR spectrum properties such as plasmon wavelength and enhancement factor. The paper also proposes a number of rules that should be considered in the design and fabrication of LSPR devices.
The Sources Reconstruction Method (SRM) is a non-invasive technique for, among other applications, antenna characterization. The SRM is based on obtaining a distribution of equivalent currents that radiate the same field as the antenna under test. The computation of these currents requires solving a linear system, usually ill-posed, that may be very computationally demanding for commercial antennas. Graphics Processing Units (GPUs) are an interesting hardware choice for solving compute-bound problems that are prone to parallelism. In this paper, we present an implementation on GPUs of the SRM applied to antenna characterization that is based on a compute-bound algorithm with a high degree of parallelism. The GPU implementation introduced in this work provides a dramatic reduction on the time cost compared to our CPU implementation and, in addition, keeps the low-memory footprint of the latter. For the sake of illustration, the equivalent currents are obtained on a base station antenna array and a helix antenna working at practical frequencies. Quasi real-time results are obtained on a desktop workstation.
In this paper, a hybrid method combining equivalence principle algorithm with physical optics is proposed to solve the radiation problem of antenna mounted on electrically large platform. It is based on domain decomposition method which is a scheme for multi-scale problems. Equivalence principle algorithm can simulate antenna accurately, and physical optics is an asymptotical method to obtain current distribution on the electrically large platform. Continuity of currents is considered when the conductor on the platform is decomposed into two parts by the equivalence surface. In addition, a preconditioning for the hybridization of equivalence principle algorithm and physical optics is discussed. Numerical results demonstrate the feasibility of the hybrid method.
In this work, the linearity of a high gain Harmonic Self Oscillating Mixer (HSOM) is analyzed. In order to obtain high conversion gain, the working point of the HSOM is established close to a Hopf bifurcation point. The traditional figures of merit used to characterize the linearity of conventional mixers cannot be directly applied to characterize the behavior of autonomous circuits, because of the influence of the input RF signal power on the autonomous signal parameters. The 1\,dB compression point and the third order distortion will be analyzed as a function of the harmonic content and maximum gain of the circuit. From the collected data, the optimum harmonic content and the maximum conversion gain of the HSOM can be selected, for a particular application, in order to minimize the output IF signal distortion.
A novel peer-to-peer (P2P) interconnection architecture in a 60-GHz millimeter-wave (mm-wave) radio-over-fiber (RoF) access network is proposed for the first time. In this scheme, the beating of the lightwaves for downlink and P2P transmissions at the photodiode (PD) can provide signal up-conversion for both signals. Phase noise and frequency instability between the two independent lightwaves can be eliminated by a self-heterodyned radio frequency (RF) receiver (envelope detector) located on the user terminal, which can also down-convert simultaneously the two mm-wave signals to their associated intermediate frequencies. No high-frequency clock sources or other high bandwidth devices are required for signal up/down-conversions. A proof-of-concept experimental demonstration has also been carried out. Error-free transmission of the 1-Gb/ signals is achieved over 50-km fiber (downlink) or 25-km fiber (P2P) plus 4-m air link.
This paper presents lumped dual-frequency impedance transformers for frequency-dependent complex loads. According to different dual-frequency allocations of a complex load in Smith chart, three types of impedance matching networks are presented respectively. Several kinds of lumped circuit blocks are used as basic element for constructing these transformers with design formula deduced. Various examples are given for describing the design procedures.~Good features such as big frequency ratio and big matching bandwidths are demonstrated. These lumped dual-frequency impedance transformers have advantage of much compacter dimensions compared to distributive solutions.
This paper proposes and designs a new method of dualband omnidirectional planar microstrip antenna array. A cascade of transposed microstrip lines have been adapted to produce effective antenna structures that radiate omnidirectionally, with high efficiency, low reflection, and useful radiation patterns. In this paper, the antenna structure has been found to have low-pass characteristics due to the periodic discontinuities at the transposed junctions. The analysis and design of the low-pass characteristic are performed according to the filter theory of periodic structures and full-wave simulation. Therefore, a relatively higher frequency radiating array is appropriately designed with a low-pass filtering attribute, which prevents the lower frequency radiators from resonating at the relatively higher frequency. An air gap between adjacent transposed sections is proposed in order to enhance impedance matching, and a fork shape stub at the end is used as a virtual short point to enhance radiation at the higher frequency. Finally a single port dualband omnidirectional antenna array is obtained by locating the higher frequency radiating array with low-pass filtering attribute near the antenna feed and a relatively lower frequency radiating array at the end. An example of a dualband omnidirectional planar array is demonstrated experimentally, which operates at 2.32~2.56 GHz and 5.65~6.10 GHz with S11<-10 dB and a stable radiation pattern, and corresponding gains of 7.0~7.6 dBi and 6.9~7.9 dBi respectively.
An efficient higher order MLFMA is developed by using an ``extended-tree''. With this extended-tree, the size of the box at the finest level is reduced, and the cost associated with the aggregation and disaggregation operations is significantly decreased. The sparse approximate inverse (SAI) preconditioner is utilized to accelerate the convergence of iterative solutions. The Cholesky factorization, instead of the often used QR factorization, is employed to construct the SAI preconditioner for cavity scattering analysis, by taking advantage of the symmetry of the matrix arising from electric field integral equation. Numerical experiments show that the higher order MLFMA is more efficient than its low-order counterpart.
Periodic eigenproblems describing the dispersion behavior of periodically loaded waveguiding structures are considered as resonating systems. In analogy to resonators, their eigenvalues and eigensolutions are determined by solving corresponding excitation problems directly in the domain of the eigenvalue. Arbitrary excitations can be chosen in order to excite the desired modal solutions, where in particular lumped ports and volumetric current distributions are considered. The method is employed together with a doubly periodic hybrid finite element boundary integral technique, which is able to consider complex propagation constants in the periodic boundary conditions and the Green's functions. Other numerical solvers such as commercial simulation packages can also be employed with the proposed procedure, where complex propagation constants are typically not directly supported. However, for propagating waves with relatively small attenuation, it is shown that the attenuation constant can be determined by perturbation methods. Numerical results for composite right/left-handed waveguides and for the leaky modes of a grounded dielectric slab are presented.
Fully integrated printed RFID antennas show potential solution for item level labeling applications. In order to accommodate the antenna during the package printing process, it is vastly preferred that antenna structures are printed on paper substrates. However, the electromagnetic properties and thickness of paper substrates are susceptible to change due to various environmental effects. Thus, adequately consistent in performance and material insensitive printed Quadrate Bowtie RFID antennas are proposed. This paper presents an in-depth efficient optimization for high performance tag antenna designs for operability in frequencies 866-868 MHz & 902-928 MHz. It is demonstrated that the proposed antennas can tolerate a considerable variation in the permittivity on thin paper substrates, and present benchmarking results when n across metal and water containing objects.
In this paper, the classic oscillator design methods are reviewed, and their strengths and weaknesses are shown. Provisos for avoiding the misuse of classic methods are also proposed. If the required provisos are satisfied, the solutions provided by the classic methods (oscillator start-up linear approximation) will be correct. The provisos verification needs to use the NDF (Network Determinant Function). The use of the NDF or the most suitable RRT (Return Relation Transponse), which is directly related to the NDF, as a tool to analyze oscillators leads to a new oscillator design method. The RRT is the "true" loop-gain of oscillators. The use of the new method is demonstrated with examples. Finally, a comparison of NDF/RRT results with the HB (Harmonic Balance) simulation and practical implementation measurements prove the universal use of the new methods.
Deep brain stimulation (DBS) is a well-established treatment for Parkinson's disease, essential tremor and dystonia. It has also been successfully applied to treat various other neurological and psychiatric conditions including depression and obsessive-compulsive disorder. Numerous computational models, mostly based on the Finite Element Method (FEM) approach have been suggested to investigate the biophysical mechanisms of electromagnetic wave-tissue interaction during DBS. These models, although emphasizing the importance of various electrical and geometrical parameters, mostly have used simplified geometries over a tightly restricted tissue volume in the case of monopolar stimulation. In the present work we show that topological arrangements and geometrical properties of the model have a significant effect on the distribution of voltages in the concerned tissues. The results support reconsidering the current approach for modeling monopolar DBS which uses a restricted cubic area extended a few centimeters around the active electrode to predict the volume of activated tissue. We propose a new technique called multi-resolution FEM modeling, which may improve the accuracy of the prediction of volume of activated tissue and yet be computationally tractable on personal computers.