The performance of single feed truncated corner circularly polarized microstrip antennas with different substrate thickness is studied by simulation and experiment. It is found that the axial ratio bandwidth could be enhanced considerably when a thicker substrate is used, provided that a U-slot and/or L-probe is used to effect impedance matching. One of the configurations attains an axial ratio bandwidth (< 3 dB) of about 14% within the impedance matching band when the substrate thickness is about 0.2λ_o

Several characteristics of the wire antenna on electrically large composite body are analyzed by an adaptive multilevel fast multipole algorithm (MLFMA). Adaptive MLFMA is applied to the boundary integration of the analysis model. With the basis functions and testing functions expanded with Dirac functions on different position, the calculation of impedance integration can be simplified and all the translation process can be calculated by fast Fourier transformation (FFT). Good agreement between the computed and measured results of antenna characters is obtained.

We present an efficient boundary element method to solve electromagnetic scattering problems relative to an impedance boundary condition on an obstacle of arbitrary shape in the frequency domain. In particular, the technique is based on a Combined Field Integral Equation (CFIE) and is well adapted to treat the partially coated objects. Some methods are then proposed in order to eliminate the magnetic current and to treat correctly the rotation operator n × · (where n is the unit outward normal). After discretization, the final system is solved by an iterative method coupled with the Fast Multipole Method (FMM). Finally, a numerical comparison with a well-tried method to solve this kind of problem proves that we have proposed an attractive technique in terms of memory storage and CPU time.

This paper presents a bacterial foraging algorithm (BFA) for null steering of linear antenna arrays by controlling only the element amplitudes. The BFA is a new evolutionary computing technique based on the foraging behavior of Escherichia (E.) coli bacteria in human intestine. To show the accuracy and flexibility of the proposed BFA, several examples of Chebyshev array pattern with the imposed single, multiple and broad nulls are given. It is found that the nulling method based on BFA is capable of steering the array nulls precisely to the undesired interference directions.

In this paper we introduce general numerical analysis for investigation the performance of avalanche photodiodes (APD) while we change the multiplication region mole fraction. We have found that the gain, breakdown voltage, and performance factor, at a given bias voltage, increase while the excess noise factor decreases through the decreases in fraction of Al in Al_xGa_1−xAs-APDs. For calculation the characteristics of Al_xGa_1−xAs-APDs we use the dead space multiplication theory (DSMT) and width independent ionization coefficient.

A new circular ultra-wideband fractal monopole antenna based on descartes circle theorem (DCT) with elliptical iterations is presented. The proposed fractal design is optimized for return loss below -15 dB. The basic structure is slightly modified to ensure an overall smooth current distribution limited by the junction point nature of the fractal geometries. The measured return loss of the proposed design is below -15 dB within its impedance bandwidth along with omni-directional radiation pattern. Moreover due to the fractal shape, the proposed design has less weight and wind loading effect.

This paper presents a hybrid numerical approach combining an improved Time Domain Finite Element-Boundary Integral (FE-BI) method with Time Domain Physical Optics (TDPO) for calculations of electromagnetic scattering of 3-D combinativecomplex objects. For complex-combined objects containing a small size and large size parts, using TDPO is an appropriate approach for coupling between two regions. Therefore, our technique calculates the objects complexity with the help of FE-BI and the combinatory structures by using of the TDPO. The hybridization algorithm for restrictive object is implemented and the numerical results validate the superiority of the proposed algorithm via realistic electromagnetic applications.

Anew multimodal variational formulation (NVMF) analysis is used for a rigorous analysis of four microwave subsystems with multiple discontinuities: one double-step and one quadruplestep empty-ridged waveguide discontinuity, one iris-coupled cavities filter with four resonators and one impedance transformer. The sparameters of each structure are deduced from its total impedance matrix, without cascading the S-parameters of individual discontinuities as with the most methods based on mode-matching technique; the convergence study versus the accessible modes is no long necessary, which makes this passive microwave circuit's analysis and design tool very efficient.

This paper presents a novel technique for efficiently combining genetic algorithms (GA's) with method of moments (MOM) for planar inverted-F antennas (PIFAs). MOM is applied to analyze rectangular patches fed by a coaxial probe and shorted with a shorted pin. The impedance matrix of such a mother structure is, then manipulated by a GA optimization procedure in order to detect the optimal patch shape matching the required frequency properties. GA adoption enables optimal shape detection among all possible shapes allowed by the mother structure dimensions. The design example of dual-band antenna is presented, and measurement result is compared to numerical results. Excellent agreement between numerical and measured results is observed.

The most common and simple structure to reduce the level of the reflected power from a metallic surface is the single layer structure known as Salisbury screen which is a sheet of porous material impregnated with graphite and spaced a quarter-wavelength off a metallic backing plate. The main disadvantage of this mechanism is the narrow frequency bandwidth. Many techniques have been reported to improve the working frequency bandwidth but with some degradation in the other technical properties of the overall structure. In this paper a novel technique has been introduced based on a spatial kind of material called circuit analog screen. Theoretical analysis shows that the bandwidth of the reflected power will be improved if the graphite sheet of Salisbury screen has been loaded by circuit analog screen with spatial geometry with spatial parameters.

New fractional boundary conditions (FBC) on plane boundaries are introduced. FBC act as intermediate case between perfect electric conductor and perfect magnetic conductor. In certain sense FBC are analogue of commonly used impedance boundary conditions with pure imaginary impedance. The relation between fractional order and impedance is shown. Plane wave diffraction problem by a strip described by FBC is formulated and solved using new method which extends known methods. Numerical results for physical characteristics are presented. Analyzing the scattering properties of the fractional strip new features are observed. FBC has one important special case where the fractional order equals to 1/2. For this special case the solution of diffraction problem can be found in analytical form for any value of wavenumber. Also for small values of wavenumber monostatic radar cross section has new specific resonances which are absent for other values of fractional order.

This paper proposes a displaced sensor array (DSA) configuration for estimating the angles of arrival of narrowband sources arriving at grazing incidence directions. Unlike the conventional uniform linear array (ULA) where all the array elements are aligned along one axis, the proposed DSA configuration comprises two displaced ULAs aligned on two parallel axes in the vertical plane. The steering vectors of the two parallel arrays differ from each other by only two multiplicative phase terms that represent the space factors due to the vertical separation and horizontal displacement of the two arrays. This makes the computational load of using MUSIC algorithm with the proposed DSA configuration identical to that of ULA yet the accuracy is much higher especially for cases involving narrowband sources arriving at grazing incidence angles. Simulation results obtained show that the proposed DSA configuration outperforms the conventional ULA in terms numerical accuracy and angular resolution.

In order to overcome drawbacks of standard particle swarm optimization (PSO) algorithm, such as prematurity and easily trapping in local optimum, a modified PSO algorithm which adopts a global best perturbation, is used to optimize the pattern of cylindrical conformal antenna array for sidelobe level (SLL) suppression and null control in certain directions.The convergence speed and accuracy of the algorithm are improved.Compared with genetic algorithm and simulated annealing, The PSO algorithm is much easier to understand and implement.Firstlypattern formula of conformal array is provided, then, the standard and modified PSO algorithm are introduced, at last, application examples and simulation results are presented.The results show that the Modified PSO algorithm is an effective and efficient method to solve multi-dimension and nonlinear problem.

This paper outlines basic principle of Synthetic Aperture Radar (SAR). Matched filter approaches for processing the received data and pulse compression technique are presented. Besides the SAR radar equation, the linear frequency modulation (LFM) waveform and matched filter response are also discussed. Finally the system design consideration of various parameters and aspects are also highlighted.

Modifications in the measurement of the complex permittivity are described, based on the transmission and reflection coefficients of a dielectric slab. The measurement uses TRL twoport calibration to bring the reference planes accurately to the sample surface. The complex permittivity as a function of frequency is computed by minimizing the difference between the measured and the ideal scattering parameters. An alternative procedure for determining the complex permittivity uses the fractional linear data fitting to a Qcircle of the virtual short-circuit and/or virtual open circuit data. In that case, the sample must be a multiple of one-quarter wavelength long within the measured range of frequencies. Comparison with results obtained by other traditional procedures is provided.

In this paper, a novel wideband directional coupler using coplanar waveguide multilayer slot-coupled technique is presented and implemented. The coupler uses two coplanar waveguide lines etched on two layers and coupled through an hexagonal slot etched on the common ground plane located between these layers. Firstly, conformal mapping techniques were used to obtain analytic closed-form expressions for the even- and odd-mode characteristic impedances. Secondly, using this approach, a new design of the directional coupler was performed. Both simulation and experimental results show a good performance in terms of bandwidth.

This paper outlines the trend of signal generation in synthetic aperture radar particularly chirp (linear FM signal) generation using digital approach. A study in fundamental of FM signal and typical analog FM signal generation is highlighted. Various signal generation in SAR using digital techniques is discussed and finally the some of the digital chirp generators are presented.

The electromagnetic rays might be shaded when an obstacle occurs in its way. In this paper, the close analytic expressions determining whether a ray is shaded by boards, elliptic cylinders, elliptic spheres and elliptic cones are presented based on general principle of Geometrical Optics. In optical methods like GTD or UTD in computational electromagnetics which are based on various rays, what studied in this paper with the advantages of analytical measures can be useful to keep the rays valid. Several examples are given as further proof.

Some new parameters in Vivaldi Notch antennas are debated over in this paper. They can be availed for the bandwidth application amelioration. The aforementioned limiting factors comprise two parameters for the radial stub dislocation, one parameter for the stub opening angle, and one parameter for the stub's offset angle. The aforementioned parameters are rectified by means of the optimization algorithm to accomplish a better frequency application. The results obtained in this article will eventually be collated with those of the other similar antennas. The best achieved bandwidth in this article is 17.1 GHz.

In this paper, the bit-error-rates performance of impulse radio ultra-wideband (IR-UWB) wireless communication system based on time reversal technique is investigated in both single-input singleoutput and multiple-input single-output situations. Simulations indicate that the good result is obtained as we expect it and IR-UWB based on time reversal technique is very promising for high bit rates wireless communication applications.