In the present work the radiation of sound from a bifurcated circular waveguide formed by a semi-infinite rigid duct inserted axially into a larger infinite tube with discontinuous wall impedance is reconsidered through an alternative approach which consists of using the mode matching technique in conjunction with the Wiener-Hopf method. By expressing the total field in the appropriate waveguide region in terms of normal modes and using the Fourier transform technique elsewhere, we end up with a single modified Wiener-Hopf equation whose solution involves an infinite system of algebraic equations. This system is solved numerically and the influence of some parameters on the radiation phenomenon is shown graphically. The equivalence of the direct method described in [1] and the present mixed method are shown numerically.

The diffraction by a finite parallel-plate waveguide with four-layer material loading is rigorously analyzed by means of the Wiener-Hopf technique for the H-polarized plane wave incidence. Taking the Fourier transform for the unknown scattered field as well as the Helmholtz equation and applying boundary conditions in the transform domain, the problem is formulated in terms of the simultaneous Wiener-Hopf equations. The Wiener-Hopf equations are solved via the factorization and decomposition procedure together with the use of rigorous approximation procedures leading to an efficient approximation solution. The scattered field in the real space is evaluated explicitly by taking the inverse Fourier transform. Illustrative numerical examples on the radar cross section (RCS) are presented and the far field scattering characteristics of the waveguide are discussed.

The plane wave diffraction by a finite parallel-plate waveguide with four-layer material loading is rigorously analyzed for the case of E polarization using the Wiener-Hopf technique. Introducing the Fourier transform for the scattered field and applying boundary conditions in the transform domain, the problem is formulated in terms of the simultaneous Wiener-Hopf equations, which are solved via the factorization and decomposition procedure together with a rigorous asymptotics. The scattered field is evaluated explicitly by taking the inverse Fourier transform and applying the saddle point method. Representative numerical examples of the radar cross section (RCS) are shown for various physical parameters and the far field scattering characteristics are discussed in detail.

A series of N identical periods of pairs of isotropic and biisotropic layers with defect in j-th basic element is investigated. The universal method that simultaneously allows to taking into account different types of defects in the structure is proposed. The problem is solved using the circuit theory and the transfer matrix methods. The analysis of the dynamic of electromagnetic properties of the investigated structure was carried out for different types of defects.

Main intension is to calculate admittance and radiation pattern of longitudinal shunt slot in rectangular waveguide using Method of Moments (MoM) technique. Resonant length calculation of the slot is a critical parameter in the design of waveguide slot array antenna. All computed results are compared with simulated results. CST Microwave studio is used for the simulation and is totally based on FIT techniques. For computation purpose MATLAB 7.0 is used. The numerical data on transmission and reflection coefficient are evaluated. Method of moment solution is used to calculate resonant length versus slot offset for given waveguide dimension and frequency. E and H field radiation pattern are calculated for different offset in different frequencies.

In this paper, the characteristics of an L probe fed planar rectangular patch antenna mounted on a cylindrical surface for circular polarization is investigated. To obtain a large bandwidth an L probe feed is used which is in the shape of a fork attached to a coaxial cable and is placed under a corner of the patch antenna. Simulation results, obtained via HFSS, on the return loss and radiation pattern of the antenna for circular polarization are presented. Results show an impedance bandwidth of 74.6%, an average gain of 7.5 dBi with stable radiation patterns across the entire passband and a bandwidth of 58% for AR< 3 dB.

Peak to Average Power Ratio (PAPR) is one of the serious problems in any wireless communication system using multi carrier modulation technique like OFDM, which reduces the efficiency of the transmit high power amplifier. In this paper, proposed scheme will be introduced that combine interleaving method with peak windowing. Simulation results show that our technique simultaneously decrease Bit Error Rate (BER), reduce the PAPR by 3.5 dB and improve out-of- band radiation, in presence of nonlinear power amplifier model.

Electromagnetic fields and media can be compactly represented by applying the four-dimensional differential-form formalism. In particular, classes of linear (bi-anisotropic) media can be defined in terms of the medium dyadic mapping between the electromagnetic two-forms. As a continuation to the process started by medium dyadics satisfying linear and quadratic algebraic equations, the class of biquadratic (BQ) media is defined by requiring that the medium dyadics satisfy the bi-quadratic algebraic equation. It is shown that the corresponding four three-dimensional medium dyadics are required to satisfy only two dyadic conditions. After studying general properties of BQ media, a special case is analyzed in detail as an example.

We intend to study two kinds of sources known as Hard Source and Soft Source, which are the simplest kinds of sources used in FDTD. We introduce an exact method to control the direction of propagation of a plane wave which can be either a hard source or soft source. Also we show that a simple implementation of a soft source in the Yee algorithm causes an undesired propagation which can result in incorrect answers. To remove this error we suggest a method for different kinds of sources and modes.

The electromagnetic scattering problem of a short-pulse plane wave by a perfectly-conducting circular cylinder, buried in a dielectric half-space, is solved by means of a cylindrical-wave approach (CWA). The incident plane wave may have a rather general shape in the time domain. The technique is applicable for arbitrary polarization, or any cylinder size and burial depth, and it gives results both in the near- and in the far-field regions. In this work, an application of the technique to a basic but practical detection problem is presented, showing good results.

We designed two type binary 2D subwavelength (wavelength was λ = 10mm) focus diffractive photonic crystal lens and calculated the diffraction of plane TE-wave by use FDTD-method (our program in C++). It has been shown that diffractive photonic crystal lens designs have not an unique solution. Diameter lens was in 5 times more than her width and full width half maximum diameter of focal spot was 0.48λ.

In the analysis, an open-ended rectangular waveguide in an infinite ground plane is used as a near-field probe and the two-element waveguide array in an infinite ground plane is used as a radiator. Moment method analysis is used to find the reflection coefficient of the array element and probe voltage. The reflection coefficient of the array element, which is also an open-end of a rectangular waveguide, is computed and compared with the reflection coefficients, when the probe is at different positions in the near-field. The computations have also been carried out to find the induced probe voltage, when the probe scan in transverse plane (planar scanning) at a distance z₁ from the radiator. Good agreement is obtained between measured and MOM results.

The far field behavior of a small wave size cylindrical microstrip antenna (CMA) has been originally analyzed for a small elevation angle, where a pronounced maximum has been found. Also it has been found that a similar maximum takes place in the far field of an electric dipole taken instead of the patch. It has been shown that the phenomenon originates to the far field behavior of the annular electric current given in the form of n = 1 azimuthally traveling wave harmonic held in the series representation of the electric dipole field. Approximate analytical expressions have been obtained describing the far-field components for two different polarizations. Also, the CMA radiation pattern is shown to bear similarities to the pattern of an electric dipole placed on a dielectric substrate surrounding a circular metal cylinder.

In this paper, a method based on clonal selection algorithm (CLONALG) is proposed for null steering of linear antenna arrays by controlling only the positions of selected elements. The CLONALG is a relatively novel population-based evolutionary algorithm inspired by the clonal selection principle of the human immune system. In order to illustrate the accuracy and flexibility of the proposed algorithm, several numerical examples of Chebyshev pattern with the single and double nulls imposed at the directions of interference are given.

This work reports some recent advances in diffraction theory by canonical shapes like wedges or cones with impedancetype boundary conditions. Our basic aim in the present paper is to demonstrate that functional difference equations of the second order deliver a very natural and efficient tool to study such a kind of problems (For a thorough and up-to-date overview of the scattering and diffraction in general the readers are referred to a special section of the journal ``Radio Science'' edited by Uslenghi [1].). To this end we consider two problems: diffraction of a normally incident plane electromagnetic wave by an impedance wedge whose exterior is divided into two parts by a semi-infinite impedance sheet and diffraction of a plane acoustic wave by a right-circular impedance cone. In both cases the problems can be formulated in a traditional fashion as boundary-value problems of the scattering theory. For the first problem the Sommerfeld-Malyuzhinets technique enables one to reduce it to a problem for a vectorial system of functional Malyuzhinets equations. Then the system is transformed to uncoupled second-order functional difference-equations (SOFDE) for each of the unknown spectra. In the second problem the incomplete separation of variables leads directly to a functional difference-equation of the second order. Hence, it is remarkable that in both cases the key mathematical tool is an SOFDE which is an analog of a second-order differential equation with variable coefficients. The latter is reducible to an integral equation which is known to be the most traditional tool for its solution. It has recently been recognised that reducing SOFDEs to integral equations is also one of the most efficient approaches for their study. The integral equations which are developed for the problems at hand are both of the second kind and obey Fredholm property. In the problem of diffraction by a wedge the generalised Malyuzhinets function is exploited on the preliminary step then ``inversion'' of a simple difference operator with constant coefficients leads to an integral equation of the second kind. The corresponding integral operator is represented as a sum of the identical operator and a compact one [2]. However, in the second problem the situation is slightly different: the integral operator can be represented by a sum of the boundedlyinvertible (Dixon's operator) and compact operators. This situation was earlier considered by Bernard in his study of diffraction by an impedance cone, and important advances have been made (see [3-6]). The Fredholm property is crucial for the elaboration of different numerical schemes. In our cases we exploited direct numerical approaches based on the quadrature formulae and computed the farfield asymptotics for the problems at hand. Various numerical results are demonstrated and discussed.

A new CPW-fed antenna with triple-band is presented for simultaneously satisfying wireless local area network (WLAN) and world interoperability for microwave access (WiMAX) applications. The investigated antenna consists of a T-shaped monopole with a trapeziform ground plane and two parasitic elements to generate triple-band. The design methodology is outlined and the overall size is 32×15×1 mm³. This antenna was numerically designed using Ansoft HFSS simulation software package. The measured 10 dB bandwidth for return loss is from 2.35 to 2.71 GHz and 3.35 to 3.72 GHz and 4.9 to 6.1 GHz, covering all the 2.4/5.2/5.8 GHz WLAN bands and 2.5/3.5/5.5 GHz WiMAX bands.