Previously derived asymptotics for diffraction by strongly elongated body is generalized to the case of nonaxial incidence. By applying "parabolic" equation method the asymptotics of the field in the boundary layer near the surface is constructed. This asymptotics takes into account the rate of elongation of the body and is applicable both to not too much elongated objects, where it reduces to Fock formulae, and to very elongated bodies.
In high power applications of wireless power transfer systems as Maglev, both a high transferred power and a high efficiency are essential. However, these two requirements usually show dissimilar profiles over a range of operating conditions. Magnetic and electric models for a capacitor compensated system are used to analyze the problem. Using the analysis outcome, a compromise is made to come to an acceptable design, achieving both requirements. In particular, appropriate design parameters and resonance frequency are obtained. The analytical results are confirmed by 3D FEM analysis.
A method is presented for computing aperture-radiated fields in terms of complex-source type beams. These beams are generated in a natural way by expanding the aperture field spectrum in a sum of complex exponentials. The latter are obtained by using the 2D-GPOF method. Inverse transformation in spatial domain leads to an analytical form in terms of complex source points. Fields radiated by apertures obtained via this approach are validated by direct near field integration and compared with those calculated with spectral-based beam expansion which starts from the Hankel spectrum and uses a 1D-GPOF approach.
In this paper, reflection and transmission coefficients at dielectric fractal-fractal interface are discussed. The ratio of permittivity of the two dielectric fractal media is kept constant, while the dimension is varied in order to get the desired results. Conventional results are recovered for the integer dimensions. The proposed expressions are useful to study the behavior of electromagnetic waves for non-integer dimensions, multiple fractal interfaces and waveguides. Moreover, it is also helpful to understand the variation in the magnitudes of reflection and transmission coefficients with the difference in dimensionality at interface of the two fractal media.
Dynamical stability of a system of bilaterally coupled periodic Gunn oscillators (BCPGO) has been studied employing Melnikov's global perturbation technique. In the BCPGO system, a fractional part of the output signal of one oscillator is injected into the other through a coupling network. The injected signal is considered as a perturbation on the free running dynamics of the receiving oscillator and the amount of perturbation is quantified by a parameter named coupling factor (CF). The limiting values of CFs leading to chaotic dynamics of the BCPGO system are predicted analytically by calculating the Melnikov functions (MFs) in the respective cases. Also the effect of the frequency detuning (FD) between the Gunn Oscillators (GOs) on the computed values of MFs has been examined. A thorough numerical simulation of the BCPGO dynamics has been done by solving the system equations. The obtained results are in qualitative agreement with the analytically predicted observations regarding the roles of the system parameters like CF and FD.
This paper presents a multiconductor reduction method for modeling electromagnetic crosstalk of complex cable bundles in the vicinity of a 60 degree corner. Based on the image theory and wide separation assumption, the per-unit-length parameters of the cable bundle can be obtained analytically. A modified six-step procedure is established to define the electrical and geometrical characteristics of the reduced cable bundle model compared with the original equivalent cable bundle method (ECBM). Numerical simulations are performed to demonstrate the viability and effectiveness of the method. This work can find wide applications in real environments.
Multi Populations Rate Equations (MPREs) model is used to analyze the dynamic characteristics of the InAs/InP (113) B self assembled quantum dot laser. The resulting system of differentaial equations is solved using fourth-order Runge-Kutta method taking into consideration homogeneous and inhomogeneous broadening of optical gain. The effects of the injected current, Full Width at Half Maximum (FWHM) of the homogenous broadening, and initial relaxation time (phonon bottleneck) on the rise time, fall time, and hence the maximum allowable bit rate of the optical signal are investigated.
In this work two model selection criteria, i.e., Akaike's information criterion (AIC) and minimum description length (MDL), are applied to measurements in a RC with Rayleigh, Rician, Nakagami, Bessel K, and Weibull distributions as the distribution candidate set. In spite of small differences of the AIC and MDL tests (due to their different penalty terms on distribution parameters), both criteria result in similar conclusions. Results show that the Rayleigh distribution provides the overall good fit to the Cartesian field amplitude, especially for an overmoded RC, and that the Weibull distribution provides good fit to the Cartesian field amplitude in an undermoded or loaded RC. In addition, it is found that both the Rician and Weibull distributions provide improved approximations of the Cartesian field amplitude in a loaded RC with non-negligible unstirred components and that the transition from undermoded RC to overmoded RC depends not only on the operating frequency and mode-stirrer efficiency (as it is commonly believed) but also on source stirring and RC loading.
This paper mainly deals with the detection problem of the target in the presence of the Compound-Gaussian (CG) distribution clutter with the unknown Power Spectral Density (PSD). Traditionally, the CG distributions, in particular the K distribution and the complex multivariate t distribution, are the widely used models for the clutter measurements from the High Resolution (HR) radars. Recently, the CG distribution with the Inverse Gaussian (IG) texture, the specific class of CG clutter, is represented as the IG-CG distribution and validated to provide the better fit with the recorded clutter data than the mentioned two competitors. Within the IG-CG framework, the detector is here proposed in terms of the two-step Generalized Likelihood Ratio Test (GLRT) criterion, and the empirical estimation method is resorted to estimate the unknown PSD in order to adapt the realistic scenario. The proposed detector is tested on the real-life IPIX radar data, in comparison with the existing Adaptive Normalized Matched Filter (ANMF) processor, and the detection results illustrate that it outperforms ANMF.
This paper deals with the application of a meta-heuristic optimization algorithm, namely the Cuckoo Search Algorithm in design of the Electromagnetic band gap (EBG) structures. These EBG structures are employed for the purpose of suppressing power/ground noise in printed circuit boards. A design example of 2D planar EBG structure in the specified frequency band is presented and implemented. The measured results are found to be in good agreement with the simulation as well as the analytical results.
This paper presents the antenna design parameter dependency on the impedance and radiation characteristics of a terahertz coplanar stripline dipole antenna. The antenna response is numerically investigated by applying a semi-infinite substrate and by generating a constant voltage source to drive a signal on the antenna. In this way, we can analyze the antenna characteristics without the photoconductive material response and the substrate lens geometrical effects. Further, we explain the mechanism underlying the preferable uses of several millimeter length DC bias striplines in a typical THz coplanar stripline dipole antenna design. The antenna, consisting of a center dipole connected to long bias striplines, has a traveling wave characteristic supporting an attenuated current, rather than a resonant characteristic supporting a standing wave of current. The traveling wave behavior produces stable antenna input impedances and minimal changes in the antenna radiation patterns. We also found that the length of the center dipole has a prominent effect on the antenna gain response.
In this paper, a method for increasing bandwidth of metamaterial structures is presented. The metamaterial structures used in this study are based on Split Ring Resonators (SRRs), the most recognized structures for realization of metamaterials with negative magnetic permeability coefficients. To increase the frequency bandwidth of such metamaterials, two different methods, 1) rotating the inner ring of SRR with different angles in a hybrid structure, which is herein called unit cell, 2) changing dimensions of SRR, are presented. Moreover, the effect of SRR arrangement in unit cell on bandwidth is investigated. The idea of bandwidth enhancement is verified via simulations, which are performed via full-wave method and measurements, which are done using a built strip-line setup.
The authors propose two 1×N all optical switches by taking the advantage of the accelerating behaviour of a spatial soliton in a Mach-Zehnder waveguide and the soliton's oscillating behaviour while propagating inside the nonlinear waveguide. The proposed switches consist of asymmetric and symmetric Mach-Zehnder waveguides followed by a homogenous Kerr medium, which is terminated by N parallel trapezoidal waveguides. In these switches, the signal is dropped from one of the desired output channels by changing the input pulse of wavelength or power. The numerical results confirm the switching application and show that the proposed 1×N switches can be used for wide ranges of wavelength and power, which are suitable for optical communication networks and optical data processing systems.
The thickness measurement of concrete is one of the most important commercial applications of ground-penetrating radar (GPR) technique. This paper describes a procedure for estimating the thickness of concrete slab for different moisture contents (MCs) in frequency domain, as in Impulse-Response (IR) Method, over the radar frequency band 100 MHz-2 GHz). The method is based on predicting the reflected frequency spectrum through a concrete slab using Jonscher model. The procedure is explained and examples of results are presented.
To simulate the beam and wave interaction (BWI) of various types of traveling wave tube amplifiers (TWTAs), a digitized nonlinear theory has been developed with two features. Firstly, the digitized RF field profiles obtained from electromagnetic simulation software are applied to replace the analytical RF field profiles in TWTAs. Secondly, the relationship of energy conservation between the beam and RF fields is used to derive the RF field equations. Based on this nonlinear theory, onedimensional code has been constructed to predict the performances of TWTAs. Comparisons between the simulations and the experimental results for a K-band helix TWTA, a V-band coupled cavity (CC) TWTA and a W-band folded waveguide (FWG) TWTA are made and discussed to prove the validation of this nonlinear theory.
We propose a combination chaotic map (CCM) signal model to resolve the limited-word-length problem in digitally realizing chaotic signals used for noise radar. The proposed CCM has approximated infinite dimension, much more complicated phase space structure as well as better chaotic properties. The radar signal based on CCM presents much lower PSLR of auto-correlation as well as much flatter power spectrum, so it is very suitable for generating wide-band radar signal. Simulation experiments are conducted to show the good performance of the signal.
This paper presents the novel theoretical design, CAD modeling, and performance analysis of a compact and reliable microwave beamforming network (MBFN) which has been developed based on the RF Rotman lens switched-beam steered array for operation in Ku frequency band. The objective of this investigation is to develop a passive beam steering microwave network device intended for the potential suitable use in satellite communications beam scanning electronically scanned arrays. A thorough Ku-band satellite microwave network system has been theoretically designed and simulated along with the analysis of its output RF characteristics. The antenna array feeding network is capable of multi-beams generation and wide-band operation in terms of the true-time-delay (TDD) and low dispersive properties in order to allow simultaneous operation of multiple RF beams. The Rotman lens demonstrates the potential appropriateness in order to develop a high-performance and well-established design for advanced satellite microwave systems, services, and devices.
This paper describes a novel permittivity measurement technique using dual open ended coaxial sensors. The magnitude reflection coefficients from two open ended coaxial sensors were used to determine complex reflection coefficients and permittivity of a sample under test.
Concrete walls reinforced with rebars have poor shielding effectiveness for telecommunication frequencies (frequencies above 0.5 GHz). An effective method to increase the shielding effectiveness of the walls is to increase the complex permittivity of the concrete. This can be done by mixing in thin filaments of a material with high conductivity. One such material is carbon. In this paper the Maxwell Garnett mixing rule is used to model a concrete material with carbon filaments. The shielding effectiveness computed with the mixing rule is found to agree with previously published measurement results.
We report results continuing the research which looks at the influence of two different magnetic materials in a core construction on the transformation errors of a current transformer . In this paper we consider the behaviour of two different magnetic materials in a core. They are joined in a different way to the previous study; not axially (one-by-one), but also radially (one inside the second). We have conducted 3D analyses of the electromagnetic field distribution for different cases of current transformers and carried out computations based on the finite-element numerical method. We compare the results with tests of real-life models.