An approach is proposed to obtain some exact explicit solutions in terms of elliptic functions to the Novikov-Veselov equation (NVE[V(x, y, t)] = 0). An expansion ansatz V → ψ = Σ2j=0 ajfj is used to reduce the NVE to the ordinary differential equation (f')2 = R(f), where R(f) is a fourth degree polynomial in f. The wellknown solutions of (f')2 = R(f) lead to periodic and solitary wave like solutions V. Subject to certain conditions containing the parameters of the NVE and of the ansatz V → ψ the periodic solutions V can be used as start solutions to apply the (linear) superposition principle proposed by Khare and Sukhatme.
It has been observed that localized solution modes provide sparse factored representations of the discrete integral equations encountered in the simulation of electromagnetic phenomena at low frequencies. This paper extends these results by incorporating overlapped localizing modes. For TMz scattering from a rectangular array of perfectly conducting obstacles, it is observed that the complexity scaling of the resulting factorization is significantly reduced relative to previously reported results. The memory complexity of the resulting factored representation scales approximately as O(N) for electrically small arrays. Limitations and possible extensions of these results are discussed.
n this paper, we measured what influence the sinusoidal transmission characteristics of the electric power line with various forms gave to the transmission characteristic of OFDM (Orthogonal Frequency Division Multiplexing) signal through PLC (power line communication system) modem. The electric power line transmission line with various forms in a real environment is classified into two basic elements, which are an outlet type branch and a switch type branch. Next, PHY rate (Physical rate) is measured for each basic element connected with the PLC modem. At this time, the transmission characteristics of the electric power line are simulated from measured data. OFDM sending and receiving systems are composed on the computer, and the PHY rate is simulated. By comparing with measured and calculated values, it is revealed that PHY rate of PLC modem is most affected in the case of the power line transmission characteristics having broad band and high level attenuation and is not affected in the case of that having narrow band group delay variation.
Oblique coordinates are introduced into the method of lines. For the purpose of analysis, suitable equations are derived. The formulas are applied to compute the transmission in a waveguide device consisting of straight waveguides connected by a tilted one. Furthermore, the band structure of a hexagonal photonic bandgap structure was computed using these oblique coordinates.
This paper presents the design and implementation of an Active Integrated Antenna (AIA) using a Voltage Controlled Oscillator (VCO) for applications in the Industrial Scientific Medical band (2.4 ÷ 2.4835 GHz). Surface Mounting Device (SMD) technology has been applied in the realization of the passive and active components, and low cost FR-4 dielectric slabs have been employed for the integration of the antenna and the active/transmissive circuits, residing, respectively, on the opposite faces of a Personal Computer Memory Card International Association (PCMCIA) card. The proposed layout makes use of a properly corrugated ground plane, i.e., a High Impedance Ground Plane (HIGP), to improve the antenna performances and to minimize the coupling between the radiating component and other possible radiating elements and/or electronic circuits residing nearby. The analysis and the design of the radiating element with the HIGP are based on a rigorous full wave Method of Moment (MoM) formulation developed in the Spectral Domain (SD), while the design of the active circuitry is developed through the commercial tool AWR Microwave Office. The final design of the component is obtained hybridizing the two methods and applying a Genetic Algorithm (GA) optimization tool in order to take advantage of the HIGP, while keeping the geometrical dimensions of the antenna suitable for mounting on a PCMCIA card, and maintaining the antenna performances acceptable. The measured results show the performances of the VCO, an antenna gain of 19.4 dBi and an increased front-to-back radiation ratio compared to the one of the same antenna mounted on a standard Perfect Electric Ground Plane (PEGP). This result, thus, demonstrates the minimization of the interferences between the designed antenna and other possible radiating and transmissive devices residing nearby.
A new methodology has been developed, based on moment method; for analyzing a class of rectangular waveguide based circuits and radiators. The methodology involves in modeling the given structure using tetragonal bricks or cavities and then replacing all the apertures and discontinuities with equivalent magnetic current densities so that the given structure can be analyzed using only the Magnetic Field Integral Equation (MFIE). As it is necessary to use a number of such cavities in order to study these complicated waveguide structures, the present method is named as Multiple Cavity Modeling Technique (MCMT). The ma jor advantage for using the MCMT in rectangular waveguide based structures is the fact that since only the magnetic currents present in the apertures are considered the methodology involves only solving simple magnetic field integral equations rather the coupled integral equation involving both the electric and magnetic currents. Further it is possible to consider both co and cross polarization and also the thickness of the waveguide discontinuities like diaphragm thickness or window thickness in the analysis. Due to this, it is possible to get highly accurate result. It is also possible to extend the method to any number of resonators, cavities or irises regardless of the polarization. To demonstrate, the methodology has been applied to analyze an open end of a waveguide with dielectric plug, both in transmitting and receiving mode, and a waveguide step discontinuity. Even mode and odd mode admittances of interacting identical inductive diaphragms have also been calculated using this methodology. Data obtained using this technique has been compared with measured, CST microwave studio simulation and literature available data. The theory has been validated by the reasonable agreement obtained between experimental data, simulated data and literature available data with numerical data
In this paper, the effect of Electromagnetic Bandgap (EBG) Superstrates on return loss of the Probe-Fed Microstrip Antenna (PFMA) has been examined. Originally the EBG superstrate layer made by Frequency Selective Surface (FSS) layers is used to increase the directivity of the PFMA, but to increase the efficiency of the whole structure including the PFMA and EBG superstrate it is necessary to have suitable impedance matching. In this paper the EBG superstrate as a resonance load to the primary radiation source (PFMA) and then by choosing the appropriate geometrical parameters of the structure we can obtain suitable impedance matching beside the directivity enhancement of the primary radiation source.
In this paper, the theoretical foundations of near-field-far- field transformations with spiral scannings are revisited and a unified theory is provided. This is accomplished by introducing a sampling representation of the radiated electromagnetic field on a rotational surface from the knowledge of a nonredundant number of its samples on a spiral wrapping the surface. The obtained results are general, since they are valid for spirals wrapping on quite arbitrary rotational surfaces, and can be directly applied to the pattern reconstruction via near-field-far-field transformation techniques. Numerical tests are reported for demonstrating the accuracy of the approach and its stability with respect to random errors affecting the data.
This paper presents an improved approach for the propagation of electromagnetic (EM) fields along a helical dielectric waveguide with a circular cross section. The main ob jective is to develop a mode model for infrared (IR) wave propagation along a helical waveguide, in order to provide a numerical tool for the calculation of the output fields, output power density and output power transmission for an arbitrary step's angle of the helix. Another objective is to apply the inhomogeneous cross section for a hollow waveguide. The derivation is based on Maxwell's equations. The longitudinal components of the fields are developed into the Fourier- Bessel series. The transverse components of the fields are expressed as functions of the longitudinal components in the Laplace plane and are obtained by using the inverse Laplace transform by the residue method. The separation of variables is obtained by using the orthogonal- relations. This model enables us to understand more precisely the influence of the step's angle and the radius of the cylinder of the helix on the output results. The output power transmission and output power density are improved by increasing the step's angle or the radius of the cylinder of the helix, especially in the cases of space curved waveguides. This mode model can be a useful tool to improve the output results in all the cases of the hollow helical waveguides (e.g., in medical and industrial regimes).
Abstract-The backscattered field of an illuminated sphere with diameter Ø = 30.5 cm above a perfect conducting plate is measured in an anechoic chamber at different heights for a varying incidence angle φ in the range 5° to 75°. A high frequency field λ « Ø is transmitted, so that two significant transitions from lit to shadow regions are given over the entire incidence angle range for the considered ray field. The polarimetric behavior of the measured scattering matrix [S] is investigated by using the common coherent and incoherent decomposition theorems used by the radar polarimetry scientific community. Close to the shadow boundaries the polarimetric behavior of the sphere significantly changes. Representing the different decomposition parameters used in radar polarimetry over the incidence angle range, the transition zones are related to local maxima or minima. Hence, the extreme values of the polarimetric parameters give information about the geometrical parameters e.g target size and its height above the plate.
Based on the Mie theory, the light scattering properties of clouds consisting of pure water, pure ice spheres and concentric water- ice spheres are studied in the near-infrared regions, respectively. We computed the single scattering albedo, phase function, and asymmetry parameters of water clouds, ice clouds, and ice-water mixed clouds. The near infrared reflectivity of the ice-water mixed clouds is computed by using the adding-doubling method and compared to the other two types of clouds. It is shown that it is possible to use the near infrared reflectivity to derive the microphysical characteristics of the clouds.
Electromagnetic inverse scattering problems are compu- tation intensive, ill-posed and highly non-linear. When the scatterer lies in an inaccessible domain, the ill-posedness is even more severe as only aspect limited data is available. Typical algorithms employed for solving this inverse scattering problem involve a large scale non-linear optimization that generates values for all pixels in the investigation domain including those that might not contain any useful information about the ob ject. This communication is concerned with the local- ization in the investigation domain prior to inverse profiling of buried 2-D dielectric pipelines having circular cross section. A custom defined degree of symmetry is computed for each transmitter position, which is a measure of the symmetry of the measured (synthetic) scattered field vector. The degree of symmetry vector computed for a scat- terer is found to exhibit unique features for the geometric and electric properties of the dielectric pipeline. A probabilistic neural network is trained with the degree of symmetry vectors computed for different ob ject configurations. It classifies the test degree of symmetry vec- tor of the unknown scatterer presented to it into one of the classes that indicate the localized region in the investigation domain in which the pipeline is located. The Distorted Born Iterative procedure is em- ployed for imaging the pipeline that has been localized. The reduction in the investigation domain reduces the degrees of freedom of the in- verse scattering problem and the results are found to be much superior to those when the entire investigation domain is employed.
This research concerns offline identification of acoustic characteristics of enclosures with second-order resonant dynamics and their modeling as linear dynamic systems. The applied models can be described by basis function expansions. The practical problem of acoustic echo in enclosures is used as the target problem to be addressed. It has been found out that the classical filters are ineffective filter structures for approximating an echo generating system, due to their many required parameters. In order to reduce the number of estimated parameters, alternative methods for modeling the room impulse response need to be investigated. Out of various available techniques impulse response identification is utilized. With the help of given experimental data, the enclosures' impulse response is modeled using special orthonormal basis functions called Kautz functions. As another improved approximation, hybrid multistage system identifiers have been used in which the simplicity of classical filter structures and fast convergence of orthonormal structures is utilized as an advantage.
This second part will be devoted to the development of a bistatic synthetic aperture processing method for radar imaging. Indeed, we establish various process that the received signal must undergo in order to estimate the target reflectivity in the bistatic case. High resolution image is obtained by two treatments on the table image of the bistatic received signal developed in the companion paper. The detail of the image reconstructing by a BISAR will be presented in this paper. The interest of this model is important, because it permits for a defined scenario generation of radar data which can be used in signal processing algorithms for target detection, identification and mapping. We present the simulation results for various scenes. These results are obtained by using two algorithms developed for BISAR imagery. Then we present the experimental results.
Bistatic Synthetic Aperture Radar (BISAR) is an active imaging system for which the transmitting and the receiving antennas are located on separate platforms. During its motion, the transmitting antenna emits towards the ground a burst of pulses at a frequency called Pulses Repetition Frequency. Every pulse affects an area of the ground after a propagation time proportional to the distance transmitter-scene. The bistatic receiving antenna receives a signal from the ground after a propagation time proportional to the distance scene-receiver. A communication link between the transmitter and the receiver is necessary to measure the phase of the received signal with respect to that of the transmitted signal. This paper presents, initially, the modeling of a moving polarimetric radar working in bistatic configuration. We propose to write the received signal as a function of time for the general case where the transmitter, the target and the receiver are moving. As BISAR and MONOSAR (Monostatic Synthetic Aperture Radar) geometry differ substantially, the BISAR temporal requirements are examined in detail. The radiolink is completely modeled. The companion paper is devoted to the development of two processing methods for bistatic radar imaging. Simulation and experimentation will be presented.
This paper investigated comparatively the characteristics of four types of artificial magnetic conductor (AMC) surface, including a mushroom-like (electromagnetic band gap) EBG, uniplanar compact EBG (UC-EBG), Peano curve, and Hilbert curve, as a ground plane for a low-profile antenna. The AMC surface structures are designed to have an in-phase reflection property for a plane wave of normal incidence in the vicinity of 2.45 GHz. The bandwidths of the in-phase reflection for the AMC surfaces and return losses, radiation patterns, and gains of the horizontal wire antennas on the AMC ground planes are all measured and compared with each other. The measured data show that all the AMC surfaces act as good ground planes for a low- profile antenna, yet the bandwidth and gain of the mushroom-like EBG structure are broader and larger, respectively, than those of the other structures.
The paper is concerned with the development and mathematical justification of the methodology for applying the time- domain methods in the study of spectral characteristics of open electrodynamic resonant structures.
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