In this paper a study is presented to handle the behavior of radar cross section (RCS) of partially convex targets of large sizes up to five wavelengths in free space. The nature of incident wave is an important factor in the remote sensing and radar detection applications. To investigate the effects of incident wave nature on the RCS, scattering problems of plane and beam wave incidences are considered. Targets are taking large sizes to be bigger enough than the beam width with putting into consideration a horizontal incident wave polarization (E-wave incidence). The effects of the target configuration together with the beam width on the laser RCS compared to the case with the plane wave incidence are numerically analyzed. Therefore, we will be able to have some sort of control on radar detection using beam wave incidence.
Spectral domain approach for continuous spectrum of wide class of microwave integrated circuit (MIC) lines is proposed. The continuous spectrum is treated as a continuum of so called hybrid radiation modes. They are the limits of volume modes of line in which lower and/or upper shieldings are moved to infinity. In the preliminary part of analysis a convenient classification of MIC lines into one-side opened and two-sides opened lines is introduced. The spectral domain representation of hybrid radiation modes is discussed in detail and boundary conditions for visible and invisible parts of spectrum are formulated. The normalization conditions in spectral domain are also proposed for both classes of lines. In the next part of paper an iterative approach in spectral domain is proposed for hr modes of one-side opened line. The boundary conditions for hybrid radiation modes are combined with spectral domain approach and the second order equation is formulated for unknown spectral amplitudes of electric or magnetic fields in visible part of spectrum. Two schemes of iteration are presented and they both lead to solutions classified as hybrid EH(y) and HE(y) modes. In the case of two-sides opened lines the solution is a sum of two partial solutions corresponding to symmetrical and unsymmetrical sources distributions. Each partial solution can be found by the iterative procedure proposed for one-side opened lines. The efficiency of proposed procedure was verified for the case of hybrid radiation modes of microstrip line. The results of calculations of amplitudes and phases of spectral amplitudes in visible spectrum part for examplary hybrid radiation modes are shown. As an example of an application of the hybrid radiation modes concept, the advanced cavity model of rectangular patch antenna is proposed. This model allows to calculate the parameters with acceptable precision nearly ten times faster than professional full-wave design tools. In the conclusion other possible applications of this approach are proposed e.g., in modal analysis of discontinuities including the radiation effect or 3D rectangular patch analysis.
Our investigation entailed a thermal analysis of hornets engaging in ventilation activity at the nest entrance. In the hot summer months, between July-October, ventilating worker hornets are seen just outside the nest entrance, where they assume a typical stance, namely, with their feet erect and fastened to the substrate, their abdomen bent downward at a 90o angle to the thorax, their antennae vibrating, and their wings beating rapidly for minutes at a time. Eventually these hornets leave their position, either to retreat into the nest or else to fly off to the field, and are replaced by new hornets that assume the ventilation task. Infra-red (IR) photography reveals that in the course of the ventilation activity, the warmest region in the ventilating hornet body is the anterior upper part of the thorax, and the coolest regions are the wings, limbs, antennae and abdomen. This study involved precise and repeated measurements via IR photography of the temperature in the various body parts of the ventilating hornets, and it also offers a preliminary, tentative explanation for the observed differential body temperature. The communication value of the color of the hornet body when ventilating is discussed.
Observations of L- and C-band backscatter from snow cover are presented at all polarizations. Airborne passive-microwave data was collected in Northern Finland during EMAC'95 (European Multi-sensor Airborne Campaign-95). The measurements cover the 6.8-18.7 GHz frequency range with both verticaland horizontal polarizations. The empirical SAR data were acquired by EMISAR of TechnicalUniv ersity of Denmark over the city of Oulu in Northern Finland during EMAC'95. Airborne measurements were conducted on 22-23 March, and on 2-3 May 1995. The land-use map of the test sites was obtained from the NationalLand Survey of Finland. This study combines the semi-empirical and empirical models that were developed. Applicability of the forest transmissivity formulas developed by using the different data sets of passive and active sensors is shown. Because of the effect of dry snow at C-band is more visible than at L-band. A C-band semi-empiricalbac kscattering modelis developed for the forest-snow-ground system.
The paper presents the application of the hybrid global optimization algorithm, introduced in the companion paper Part I, to reflector antenna power pattern synthesis and reflector antenna surface diagnosis from only amplitude data. The synthesis algorithm determines both the reflector surface and the excitation coefficients of the array of primary feeds to meet the designing specification on the far-field pattern expressed by means of two couple of masks bounding the squared amplitude of both the copolar and crosspolar components. The diagnosis technique allows to find the reflector surface profile from the measurement of the far field power pattern by a proper formulation of the corresponding inverse problem. In both cases we take advantage of the exploring capability of an evolutionary algorithm and of the solution refinement capability of an efficient, quasi-Newton based, local search procedure. The numerical analysis shows that Global Optimization can outperform the standard local approach, by significantly improving the performance of the synthesized antenna in the first case and by enhancing the reliability of the diagnosis procedure in the second one.
This is the first of two companion papers on global optimization and antenna analysis and synthesis. In Part I, an analysis of the problems involved in Global Optimization is presented by critically discussing the basic concepts and tools, the performances to be expected, the required computational complexity and the guidelines to select algorithms solving efficiently the problem at hand. The relevance of stochastic techniques is enhanced and the role of double phase algorithms is stressed. The proof of the convergence property of an idealized version of a simplified evolutionary algorithm is provided. In Part II, the selected algorithm, a hybrid evolutionary algorithm, is tested against two real world problems relevant in electromagnetics, the power synthesis of contoured beam hybrid reflector antennas and the reflector antenna diagnosis from only amplitude data. The results of an extensive numerical analysis are presented.
Wideband printed rectangular slot antennas backed with reflectors for unidirectional radiation patterns are investigated. A U- shaped tuning stub is used to improve the matching. Two different feeding mechanisms are introduced. A rectangular slot excited by microstrip line feed with a U-shaped tuning stub gives an impedance bandwidth of 110% ( |S11| < âˆ’10 dB). When the rectangular slot is excited by a coplanar waveguide (CPW), it gives an impedance bandwidth of 120%. Both slot antennas radiate broadside across the matching band, with front-to-back ratios of 20 dB.
This paper presents a novel broadband, low-profile dielectric resonator antenna using relatively low dielectric constant substrate material. The rectangular DRA is fed with a stepped microstrip feed to ensure efficient coupling. Bandwidths in excess of 17% are obtained. In addition, the paper investigates methods to miniaturize the antenna using metallic strips or patches. Substantial size reduction is demonstrated while maintaining a reasonable bandwidth. Simulations as well as experimental results are presented.
The inverse problem of using an unshielded multiconductor transmission line (MTL) as an distributed sensor is considered. The MTL is analyzed by means of the quasi-TEM mode theory and a propagator formalism. In the inverse problem, the focus is on the problem with intermodal dispersion, due to the possibility of more than one propagating mode. Reconstruction results, from both measured and simulated reflection data, are presented for a three conductor MTL that has been used for diagnosing soil and snow. Both the case when one mode propagates, and the case when two modes propagate are considered. For the latter case it is demonstrated that intermodal dispersion deteriorates the resolution in the reconstruction, due to corruption of the high frequency part of the spectrum.
A radiated susceptibility problem has been identified and solved by means of simulations for a wearable computer system in the frequency range 30 MHz-1 GHz. Simulation strategy is presented for analyzing the effects induced by an electromagnetic plane wave within the system comprising infra-red sensors connected by coaxial cables. A procedure of creating a TLM model of the coaxial cable with controlled electromagnetic coupling characteristics on a coarse grid is proposed. Results are verified by means of theoretical calculations. Different sensor enclosures and filtering circuits are analyzed and implemented to meet the hard electromagnetic compatibility requirements while not interfering with the functionality of the wearable application.
A parallel implementation of an automatic CAD tool based on the parallel virtual machine software package, genetic algorithms and finite element simulators is presented. It is shown that the parallel implementation can be obtained by developing just a few hundred lines of code and a pseudocode description is provided. Finally, selected numerical results are provided in order to show the effectiveness and the reliability of the proposed approach.
Multiple-scale analysis is employed for the analysis of plane wave refraction at a nonlinear slab. It will be demonstrated that the perturbation method will lead to a nonuniformly valid approximation to the solution of the nonlinear wave equation. To construct a uniformly valid approximation, we will exploit multiplescale analysis. Using this method, we will derive the zerothorder approximation to the solution of the nonlinear wave equation analytically. This approximate solution clearly shows the effects of self-phase modulation (SPM) and cross-phase modulation (XPM) on plane wave refraction at the nonlinear slab. In fact, the obtained zeroth-order approximation is very accurate and there is not any need for derivation of higher-order approximations. As will be shown, the proposed method can be generalized to the rigorous study of nonlinear wave propagation in one-dimensional photonic band-gap structures.
The phase of a complex field and its speed of propagation are fundamental concepts of electromagnetic wave motion. Although it seems to be well-known that faster than light propagation of the phase may occur in, e.g., waveguides and certain dispersive media, it is often ignored that a similar phenomenon, in fact a very marked one,presents itself in the near-field of an arbitrary oscillating current in vacuum. Connected herewith is the observation that the phases of the transverse field components of a dipole approach kr - π/2, and not kr, in the radiation zone. This article illustrates these phenomena by theoretical and numerical examples as well as indicates their consequences for broad-band wireless communication over short distances.
Measured equation of invariance in the time domain (TD-MEI) has been used as an FDTD-ABC. The TD-MEI coefficients, are derived using a new technique named "self metron". Unlike the traditional MEI, in this technique there is no need to use metrons to find the MEI coefficients. The real field values of the same FDTD problem but with a PEC surface instead of a radiation boundary condition are sampled and used to find the MEI coefficients. The key is to locate the PEC mesh truncation, farther away than the MEI truncation boundary, such that during the sampling time interval, no wave reflects into the MEI truncation boundary. After the MEI coefficients are found, according to the "time invariance" property of the TD-MEI coefficients, the MEI boundary absorbs the wave for all times. The proposed technique is very fast and the results show that the accuracy is much higher than traditional absorbing boundary conditions and some other ABC's.
The transmission of time-harmonic and transient signals through a complex cylindrical cavity is investigated by methods akin to microwave circuit techniques. The cavity may consist of multiple overlapping cascaded coaxial and circular cylindrical sections whose walls are perfect electric conductors. The sections may have different axial and radial dimensions and may be filled with material having different magnetic and electric properties. The first and last sections of the cavity are coaxial regions where only TEM modes exist, which allows measurements to be performed with proper excitation and termination. The cavity sections may support both a TEM mode and additional higher order modes or may support one or the other. If two sections have a common junction and each supports only one mode, then the junction is modeled by a simple two-port network. When additional modes are present, they are modeled by addition ports at the network junction. Corresponding equivalent transmission lines are associated with each mode at a physical junction. At each junction, scattering parameters are calculated and used to model the interaction of the various modes that exist. The S-parameters at each junction are determined separately by solving a simple integral equation that accounts for the structure of the junction and adjoining sections of coaxial and/or cylindrical guide. The cavity fields are, thus, associated with equivalent currents and voltages on transmission lines. A transmission line network is developed from which the input fields, fields at the cavity termination, and junction fields can be found by microwave circuit techniques or by the BLT transmission line analysis. The results from the transmission line method are compared with results calculated from a coupled integral equation analysis which has been carefully validated experimentally and with measured values on laboratory models.
In the past, coupling capacitances between conductors was extracted using charge distributions directly. In this paper a set of new generalized variational formulas are derived. They are complete since they are valid not only for self-capacitances, but also for mutual capacitances. As for the realistic numerical implementation, elastance matrices become asymmetrical because of numerical method used. Then a more general variational formula is derived to account for the asymmetrical elastance matrix case. By these novel formulas the computational accuracy can be significantly improved compared to the conventional capacitance extraction method.
The resonant frequencies and input impedance of a microstrip-fed third order Hilbert slot antenna are studied as function of antenna and substrate parameters. A distinct dualband characteristic is observed. Findings from HFSS simulation are validated by prototype fabrication and experimental measurement. The two resonant frequencies maintain a ratio of approximately 1.4 for narrow slots. A design parameter, Lax is identified which needs to be about 0.80λg at the lowest operating frequency. The Hilbert slot provides a unidirectional pattern when operated against a metallic ground plane while maintaining dual-band characteristics.