The reflectivity of a Spherical Lens Reflector is investigated. The scattering of an electromagnetic plane wave by a Spherical Lens Reflector is treated as a classical boundary value problem for Maxwell's equations. No restrictions are imposed on the electrical size of reflectors and the angular size of the metallic spherical cap. The competitiveness of the Spherical Lens Reflector against the Luneberg Lens Reflector is demonstrated. It has been found that Spherical Lens Reflectors with relative dielectric constant in the range 3.4 ≤ εr ≤ 3.7 possess better spectral performance than 3- or 5-layer Luneberg Lens Reflectors in a wide frequency range.
This work demonstrates an efficient and simple approach for applying high-order extended-stencil FDTD algorithms near planar perfect electric conductors (PEC) boundaries while minimizing spurious reflections off the interface between the high-order grid and the mandated special compact cells around PEC boundaries. This proposed approach eliminates the need for cumbersome subgridding implementations and provides a superior alternative in minimizing spurious reflections without any added modeling complexity or computing costs. The high-order algorithm used in this work is the recently proposed three-dimensional FV24 algorithm and the proposed approach can be easily extended to the standard Fang high-order FDTD algorithm which represents a special case of the highly phasecoherent FV24 algorithm.
This paper presents a method based on adaptive-networkbased fuzzy inference system (ANFIS) to calculate the resonant frequency of a circular microstrip antenna (MSA) with a dielectric cover. The ANFIS is a class of adaptive networks which are functionally equivalent to fuzzy inference systems (FISs). Six optimization algorithms, hybrid learning, least-squares, nelder-mead, genetic, differential evolution and particle swarm, are used to determine optimally the design parameters of the ANFIS. The resonant frequency results predicted by ANFIS are in very good agreement with the results reported elsewhere. When the performances of ANFIS models are compared with each other, the best result is obtained from the ANFIS model optimized by the LSQ algorithm.
Using Bloch formulations, an analysis is presented of the confinement of power in omniguiding photonic band-gap fibers of different dimensional values. Results are compared for four-layer and eight-layer fibers. Power peaks are observed that correspond to different propagation modes. Power patterns are found to be fairly smoothly matched at the different layer interfaces, which confirm the validity of the analytical approach.
Genetic algorithm (GA) is effective for global optimizations, but needs the user to define several parameters. Unless these parameters are defined appropriately, search efficiency drops significantly. There are, however, no clear rules for the defining, and almost all users have considerable difficulty to use GA efficiently. A good algorithm must be use-friendly. It should not, if possible, need the user to define such parameters and can play high performance for any optimization problem. This paper proposes an autonomous GA addressing these problems.
Eddy Current Techniques (ECT) for Non-Destructive Testing and Evaluation (NDT/NDE) of conducting materials is one of the most application-oriented field of research within electromagnetism. In this work, a novel approach is proposed in order to characterize defects on metallic plates in terms of their depth and shape, starting from a set of experimental measurements. The problem is solved by means of a hybrid classification system based on Computation with Words (CWs) and Fuzzy Entropy (FE). They extract information about the specimen under test from the measurements. Main advantages of proposed approach are the introduction of CWs as well as the usage of the FE based minimization module, in order to improve flaw characterization by a low computational complexity system.
High frequency field expressions are derived around feed point of a three dimensional Cassegrain system using the Maslov's method. Maslov's method is a systematic procedure for predicting the field in the caustic region. It combines the simplicity of ray theory and generality of the transform method. Numerical computations are made for the analysis of field pattern around the caustic of a Cassegrain system.
The present study brings together two aspects of electromagnetic theory: the recently discussed low-frequency series expansions based on the concept of Consistent Maxwell Systems, and Einstein's Relativistic Electrodynamics. Combined, this facilitates the analysis of pertinent low-frequency scattering problems involving objects moving with arbitrary constant velocities in free space. The low-frequency series expansions start with leading terms that are prescribed by solutions of the vector Laplace equation, thus significantly simplifying the conventional analysis in terms of the Helmholtz wave equation. The method is demonstrated by deriving relativistically exact explicit results leading terms for perfectly conducting circular-cylindrical and spherical scatterers. The results apply to arbitrary reference frames where the objects are observed in motion. For simplicity of notation expressions are given in terms of spatiotemporal coordinates native to the object's restframe. Subsequent substitution of the Lorentz transformation for the coordinates is then a straightforward matter. Previous exact relativistic results for scattering by moving objects have demonstrated the existence of velocity induced mode coupling. It is shown that the low-frequency expansions used here display the same effects for various orders of the partial fields appearing in the series.
A novel compact ring monopole antenna with double meander lines is proposed for wireless local area networks (WLAN) applications in IEEE 802.11b/g/a systems. The designed antenna, fed by a 50Ω microstrip transmission line, is only 32mm in height and 16mm in width. By introducing a horizontal and a vertical branched strips to a closed rectangular strip ring, the proposed antenna can generate two separate impedance bandwidths. Prototypes of the proposed antenna have been constructed and tested. The obtained impedance bandwidths reach about 12% for the 2.4 GHz band and 45.3% for the 5 GHz band, which meet the required bandwidth specification of 2.4/5 GHz WLAN standard. Also, good radiation performance and antenna gain over the two frequency ranges have been obtained.
With a proper design, the aperture field of a conventional radial waveguide pin-fed non-resonant array antenna (RWPFAA) can be rendered equiphase at a given central frequency. However, when the operating frequency deviates from this central frequency, the aperture field will exhibit an undesired conical phase error. To alleviate this problem, we propose a novel design in which the frequency-dependent aperture phase error distribution is rendered serrated. The gain and side-lobes of an RWPFAA with serrated phase error distributions are studied by resorting a simple model of a line source as well as a more representative model of a circular aperture. The theoretical results are supplemented by numerical data. Schemes of RWPFAAs comprising two and three sections, which render the phase error distribution in the antenna aperture serrated, are suggested.
In this paper, the angular-diversity radar recognition of ships is given by transformation based approaches with noise effects taken into consideration. The ships and sea roughness are considered by simplified models in the simulation. The goal is to identify the similarity between the unknown target ship and known ships. Initially, the angular-diversity radar cross sections (RCS) from a ship are collected to constitute RCS vectors (usually largedimensional). These RCS vectors are projected into the eigenspace (usually small-dimensional) and radar recognition is then performed on the eigenspace. Numerical examples show that high recognition rate can be obtained by the proposed schemes. The radar recognition of ships in this study is straightforward and efficient. Therefore, it can be applied to many other radar applications.
It is well known that planet Jupiter produces strong radio bursts at decametric wavelengths from regions of temporary radio emission in its magnetosphere. Like the man made radio signals, these signals do interfere in the low frequency radio telescope data while observing a different extraterrestrial source. Identification and characterization of this interfering signal is important in radio astronomy. In most of the radio astronomy sites, spectrum monitoring stations are available for such purposes. These instruments record any strong signal within the band and also aim to locate its position. Depending on the properties of different categories of sources, special modules can be attached to these instruments for obtaining a more detailed picture. These modules can be added at the front end of the instrument using a selector switch and can be connected whenever necessary. Construction of one such module for capturing and recording the Jupiter radio bursts has been described with all the engineering details. It consists of an antenna system followed a receiver (connected to a spectrum recorder). An improvement in the antenna system has been made as compared to the contemporarily available single antenna Jupiter radio telescopes, thereby enabling to record the radio emissions over a larger period using a fixed beam. The receiver system has been designed to process the low frequency Jovian signals from 18 to 25 MHz. The back end is that of a spectrum monitoring system which serves as an automated data analyzer and recorder. It offers flexibility and various setup choices to the user. The mathematical analysis of the instrument and computed system characteristics have been produced in detail for ease of reproductions, direct use in radio astronomy and future design developments.
The lowering and raising operators of cylindrical harmonics are used to derive the general fast multipole expressions of arbitrary order Hankel functions. These expressions are then employed to transform the dense matrix in the scattering matrix method (SMM) into a combination of sparse matrices (aggregation, translation and disaggregation matrices). The novel method is referred to as fast multipole accelerated scattering matrix method (FMA-SMM). Theoretical study shows FMA-SMM has lower complexity O(N1.5) instead of SMM's O(N2), where N stands for total harmonics number used. An empirical formula is derived to relate the minimum group size in FMA-SMM to the highest order Hankel functions involved. The various implementation parameters are carefully investigated to guarantee the algorithm's accuracy and efficiency. The impact of the cylinders density on convergence rate of iterative solvers (BiCGStab(2) here), memory cost as well as CPU time is also investigated. Up to thousands of cylinders can be easily simulated and potential applications in photonic crystal devices are illustrated.
Yasuura's mode-matching method is employed in the investigation of plasmon resonance absorption on a metal grating with a gold over-coating and the results are compared with experimental data. Enhancement of TM-TE mode conversion accompanying the plasmon resonance absorption is examined. When a TM wave is incident on a metal grating, enhanced TM-TE mode conversion occurs at angles of incidence at which the surface plasmons are excited. The strength of the mode conversion depends strongly on the azimuth angle of the mounting. This is verified by experiment and an application for refractive index measurement is suggested.
In this paper, circular and hexagonal array geometries for smart antenna applications are compared. Uniform circular (UCA) and hexagonal arrays (UHA) with 18 half-wave dipole elements are examined; also planar (2 concentric rings of radiators) uniform circular (PUCA) and hexagonal arrays (PUHA) are considered. The effect of rotating the outer ring of the PUCA is studied. In our analysis, the method of moments is used to compute the response of the uniform circular and hexagonal dipole arrays in a mutual coupling environment. The particle swarm optimization (PSO) algorithm is used to optimize the complex excitations, amplitudes and phases, of the adaptive arrays elements for beamforming.
A new method is introduced to analyze lossy Inhomogeneous Planar Layers (IPLs). In this method, the equations of IPLs are converted to the equations of homogeneous planar layers, which have been excited by distributed equivalent sources. Then, the electric and magnetic fields are obtained using an iterative approach. The validity of the method is verified using a comprehensive example.
A novel fast and accurate interpolation technique for recovering the uniformly distributed samples from the irregularly spaced samples, collected non-uniformly due to the probe position error in planar near-field antenna measurements, is presented. The technique employs Yen's interpolator and tries to make it as practical as possible for the use in near-field antenna measurements. A comprehensive simulation capability is developed and through out the simulations the speed and precision of this accurate and timely efficient interpolation technique is compared with some other techniques which are also based on Yen's interpolators. The results well demonstrate the advantages of our technique we termed "The Cross-Rail Technique".
A novel band-pass Substrate Integrated Waveguide (SIW) filter based on Complementary Split ring Resonators (CSRRs) is presented in this work. Three different CSRRs cells are etched in the top plane of the SIW for transmission zero control. A demonstration band-pass filter is designed, fabricated and measured. It agreed with the simulated results well.
In this paper, the performance of the separated-aperture sensor working as ground-penetrating radar (GPR) is assessed over the operating frequency band. The capability of the separatedaperture sensor to detect buriedtargets is examinedb y evaluating andcomparing the electromagnetic coupling between the transmitting andreceiving antennas in two cases: (i) when the system is placed over an empty groundand(ii) when it is placedo ver a groundinsid e which a practical target is buriedat the proper depth. The finitedifference time-domain (FDTD) method is used for electromagnetic simulation. The results concerning the coupling between the transmitting andreceiving antennas are presentedconsid ering various practical parameters such as the operating frequency, the electric properties of the groundsoil andthe buriedtarget, andthe depth at which the target is buriedund er the groundsurface. It is shown that target detectability using the separated-aperture sensor is strongly dependent on all of the above parameters.
In this paper, a flat multilayer dielectric reflector antenna has been designed and analyzed. The reflector is made of several sandwiched dielectric layers. The structure is hence an array made of these layers, where the sum of the reflection coefficient of each layer acts as the array factor. By optimizing the permittivity and thickness of each layer, any desired reflection coefficient to shape the reflected pattern can be obtained. It is also possible to synthesize a zero or a maximum in any arbitrary direction. The significance of the reflector is ability to radiate high power and at the same time having small dimensions.