Backscattering Radar Cross Section (RCS) of electrically large targets is analyzed using Physical Optics (PO) approximation. The targets are located in a dielectric half-space,and modeled with Nonuniform Rational B-spline (NURBS) surfaces. The influence of the half-space is considered by the "four-path" model approximation. Results show the validity of the method.

An analytical model of a composite dielectric presented in this paper is the extension of Maxwell Garnett formulation. It takes into account the simultaneous statistical (Gaussian) distribution of conductivity and aspect ratio of inclusions. The inclusions are randomly oriented elongated conducting spheroids at concentrations below the percolation threshold. The formulation presented herein is limited to microwave frequencies. However, taking subtle frequencydependent effects that play important part at optical frequencies into account is straightforward. Some results of computations of microwave complex effective permittivity of composites with different input parameters have been obtained using analytical and numerical integration in Maple 10 software. It is shown how the parameters of the distribution laws - mean values and standard deviations of aspect ratio and conductivity - affect the resultant complex effective permittivity. The results of computations demonstrate that the most important factors affecting frequency characteristics of microwave effective permittivity are the mean values of the aspect ratio and conductivity. As for the standard deviations of aspect ratio and conductivity, their effects are the most noticeable in the transition between the static and optical limits of the Debye characteristic for the effective permittivity. There is almost no effect in the static and "optic" regions of the Debye curves.

A new hybrid technique for optimization of a multivariable function is proposed. This method is applied to the problem of complex time Green's function of multilayer media. This technique combines Particle Swarm search algorithm with the gradient based quasi-Newton method. Superiority of the method is demonstrated by comparing its results with other optimization techniques.

An approximate perturbative technique for the analysis of electromagnetic scattering from dielectric bodies of arbitrary shape containing dielectric inclusions, illuminated by an arbitrarily polarized incident plane wave, is investigated. The perturbative approach here presented allows for the efficient computation of the scattering properties of a given body as the inclusions vary, with a formulation solving only for the inclusion bound field component.

In this paper a novel method for ultra-high-resolution, compact and tunable optical displacement sensor using ring resonator and electromagnetically induced transparency (EIT) is proposed. The introduced technique uses ring resonator as an interesting element including high quality factor. We show that the proposed sensor can easily detect well below nanometer ranges. It is shown that the proposed idea of using EIT the resolution of the sensor is so high for displacement below mm range and for ranges larger than mm the sensitivity of the proposed sensor in both EIT and traditional cases is same approximately. Also, the proposed sensor is optically tunable. So, depends on required resolution optical control field can be used to tune the sensitivity of the proposed device.

This paper presents a novel modified Printed Tapered Monopole Antenna (PTMA)for ultra wideband (UWB)wireless communication applications. The proposed antenna consists of a truncated ground plane and two-tapered radiating patch separated by a slot (air gap)of different slopes, which provides a wideband behavior and relatively good matching. Moreover, the effects of a modified T-shaped slot inserted in the first tapered patch, on the impedance matching is investigated. The antenna has a small area of 23 × 26.5mm² and offers an impedance bandwidth as high as 100% at a centre frequency of 7.2 GHz for S₁₁ < −10 dB, which has an area reduction of 15% and a frequency bandwidth increment of 72% with respect to the previous similar antenna. The presented antenna covers the 5.2/5.8 GHz WLAN and 5.5 GHz WIMAX operating bands. Numerical analysis using Ansoft HFSS and measurement results is also presented in the paper.

One of the most important functions of radar remote sensing is to retrieve the soil moisture and surface parameters where surface parameters generally includes soil surface roughness and texture of soil (i.e.,% of coarse sand,silt and clay). Variation of soil moisture and surface parameters changes the soil permittivity, and affects the observation of the radar wave scattering (σ0). How to invert the moisture and surface parameters from radar data has been one of the most interesting problems to be resolved. Still,v ery few reported work is available to retrieve the soil textures with radar data. Therefore,in present paper an attempt has been made to retrieve the soil textures with soil moisture and surface roughness from Synthetic Aperture Radar (SAR) data. In this case number of variables are more and it is difficult to invert and retrieve the various parameters. To overcome this difficulty,an approach based on Genetic Algorithm (GA) with inclusion of empirical modeling has been proposed to retrieve the soil moisture,roughness and soil texture with ERS-2 (European Remote Sensing) SAR (Synthetic Aperture Radar) data of Haridwar region of India. The retrieved surface parameters and moisture content with proposed approach show quite good agreement with observed values of soil moisture and surface parameters. This study infers that modeling with GA has great potential to retrieve several variables simultaneously with good results.

One of most difficult challenges in simulating hybrid RF systems by finite-difference time-domain (FDTD) method is to construct the models for active and lumped elements. In this article, by combining the circuit equations with an integral transform, an enhanced FDTD method is proposed to model the hybrid lumped network which consists of nonlinear and high order linear elements with arbitrary connections. Based on this model, an active radiation system is analyzed. And it shows the application extension of the traditional FDTD method.

A triple-band omni-directional antenna which comprises three pairs of dipoles placed back to back and printed on a dielectric substrate is presented. A prototype is constructed and tested. The experimental results show that the 10 dB return loss bandwidth (VSWR < 2.0) in 2.4 GHz, 5.2 GHz and 5.8 GHz reaches as much as 130 MHz, 500MHz and 200 MHz, respectively. Moreover, the radiation patterns are almost omni-directional in the azimuthal plane. Peak antenna gain is 1.63 dBi, 2.36 dBi and 1.54 dBi, which indicate that the proposed antenna can be used as a triple-band antenna for the WLAN application.

Recently, a marching-on in degree finite difference method (MOD-FDM) was employed in the finite-difference time-domain (FDTD) formulation to obtain unconditionally stable transient responses. The objective of this work is to implement a plane wave excitation in the MOD-FDM formulation for scattering problems for an open region. This formulation has volume electric and magnetic current densities related to the incident field in Maxwell's equations explicitly. Numerical results computed by the proposed formulation are presented and compared with the solutions of the conventional FDTD method.

Besides the return loss and radiation pattern, dispersion characteristic of the antenna is one of the most important factors which should be considered in ultra wideband applications. In this paper, dispersion behavior of two specific Vivaldi antennas has been fully investigated in both frequency and time domains. All simulations are carried out by CST MS software. Moreover, by fabricating the antennas, the simulation results are verified by experimental data.

The transmission line techniques are generalized to measure the permittivity function of one-dimensional inhomogeneous dielectrics. A rectangular waveguide is used and the dielectric slab under test is placed at the input flange of it. Then the measured scattering parameters or the short-circuited reflection coefficient are used to extract the permittivity function of dielectric. To solve the problem an optimization-based procedure is used. The usefulness of the proposed method is verified using a comprehensive example.

A new dual-mode microstrip bandpass filter with wide stop-band is presented using the square loop resonator with treeshaped patches attached to the four inner corners of the loop. The mode splitting is realized by introducing a small cut locating at a 45^◦ offset from its two orthogonal modes. It is shown that the dual-mode filter has a wide stop-band including the first spurious resonance frequency. The center frequency can be tuned. Moreover, the proposed filter has a smaller size compared with conventional dualmode bandpass filters at the same central frequency.

In this paper, we propose two swallow-tailed ultrawideband planar monopole antennas that exhibit notch characteristics in the IEEE802.11a frequency band (5.15-5.825 GHz) by inserting various slots into the antennas. The effects of the lengths of the slots on the notched frequency band are analyzed. The radiation patterns of the proposed antennas are also measured and the gains are shown to be flat, except in the notched frequency band.

Compact spiral artificial magnetic conductors (AMC) have been investigatedin this paper. First, single andd ouble spirals are examinedto achieve an in-phase reflection at a lower frequency comparedto a conventional patch element of the same size. However, these two designs generate a large cross polarization. The cross polarization affects the operating frequency and bandwidth. In order to eliminate the cross polarization effect, a four-arm spiral element is introduced. This geometry does not generate a cross polarization, and an operating frequency that is 49.45% lower than the reference patch element has been achieved.

The characteristics of the guided electromagnetic wave propagation through a slab waveguide of uniaxially anisotropic dispersive metamaterial are investigated. Taking the cold plasma media model with ω_mpz < ω_mp⊥ < ω_ep⊥ as an example,the mode classification established in terms of the operating angular frequency ω₀ of the slab waveguide. The results indicate that the mode properties are closely dependent on the frequency. When ω² _mpz < ω²₀ < ω²_mp⊥ there are infinite guided modes. It is also found that when ω²_em < ω²₀ < ω²_mpz,there may be multiple solutions of the propagating mode with imaginary transverse wave number in a slab waveguide with thickness less than a certain value.

The propagation properties of surface plasmon polaritons (SPP) modes in nanoscale narrow metallic structures: gap, channel, and rectangular-hole waveguides, are analyzed by the complex effective dielectric constant approximation. The results show that all the SPP modes exist below the critical frequency where the real part of metal permittivity is negative unity. It is found that both cutoff frequency and cutoff height exist in channel waveguide and rectangularhole waveguide. The channel and rectangular-hole waveguides have different propagation properties at cutoffs due to their different cutoff conditions. Compared with the gap waveguide, the channel waveguide has shorter propagation length and better confinement when the operation frequency is near the critical frequency, but has longer propagation length and worse confinement when the operation frequency is far from the critical frequency. Among the three waveguides, the rectangular-hole waveguide has the best confinement factor and the shortest propagation length. The comprehensive analysis for the gap, channel, and rectangular-hole waveguides can provide some guidelines in the design of subwavelength optical devices.

The suitable use of an array antenna at the base station of a wireless communication system can result in improvement in signalto- interference ratio (SIR). In the present work, we consider circular array (CA) and concentric circular antenna array (CCAA) that are used for smart antenna systems. The performance criteria for SIR improvement is employed in this paper, is the spatial interference suppression coefficient. We first develop the expression of this figure of merit for CCAA and then analyze and compare the SIR performance for various configurations of eight and nine elements of CA and CCAA, with and without the element in the center by using circular patch antenna are provided. In addition, the effect of mutual coupling (MC) is taken into account.

Some design methods for band-pass filters based on halfwavelength resonators have been proposed. The main feature of these methods is that n or n + 1 transmission zeros can be generated for a structure composed of n resonators. To demonstrate the usefulness of the proposed filter structures, three kinds of two-pole compact microstrip hairpin filters are designed and fabricated. Good agreement between measured and simulated data has been demonstrated.

In this paper, method of moment and modified physical optical hybrid method is used to analyze the scattering from 3-D PEC object buried under rough surface. The random rough ground surface is characterized with Gaussian statistics for surface height and for surface correlation function. The air-earth interface and the object are all replaced by the corresponding equivalent currents and the equivalent current on the ground surface is divided into two parts: the current caused by the incident wave which is named as incident current, and the current caused by buried object which is named as scattered current. The incident currents are obtained by PO approximation and the scattered currents are related to the current on the buried scatter by a modified PO method in this work. Only the current of scatter is considered as unknown and will be solved by MoM. After obtaining the current of scatter, the scattered current on the ground surface is calculated by the modified PO approximation. And the scatter field will be calculated by using the scattered current. In order to validate the hybrid method proposed in this paper, several numerical examples are given and compared with the results of MoM.