The purpose of this paper is to introduce the concept of fractals and its use in antenna arrays for obtaining multiband property. One type of fractals namely, Cantor set is investigated. Cantor set is used in linear array antenna design. Therefore, this array know fractal Cantor linear array antenna. A comparison with conventional non-fractal linear array antenna is made regarding the beamwidth, directivity, and side lobe level. MATLAB programming language version 7.2 (R2006a) is used to simulate the fractal and conventional non-fractal linear array antenna and their radiation pattern.

The transverse electric (TE) field patterns and characteristics are considered for a cylinder with N infinite axialsl ots of arbitrary opening size and position. The cylinder is a thin circular conductor and covered by an eccentric material. Radiations are determined by applying the boundary conditions to the cylindrical wave functions of the fields. The addition theorem of Bessel functions is employed to find an infinite-series solution in Fourier-Bessel series form. Results are achieved by reducing the produced infinite series to a finite number of terms and judged against other published data. Numerical and graphical results for different values are also presented and discussed for small eccentricities.

Kelvin-Helmoholtz instability by parallel flow velocity shear in presence of inhomogeneous d.c. electric field and perpendicular density temperature magnetic field gradient has been studied by using method of characteristic solution and kinetic approach. Effect of in homogeneity of d.c. electric field and gradient have been discussed in result. The growth rates have been calculated for different effects and showing in stabilizing and destabilizing of instability.

An analysis of the modal propagation characteristics of a Bragg fiber having asymmetric loop boundary is made, using a simple matrix method. The boundary condition is replaced by matrix equation andthe modal eigen value equation is obtained under weak guidance condition. The computed results are shown in the form of dispersion curves and cutoff frequencies andare compared with the dispersion curves of a standard Bragg fiber having circular core cross section. It is seen that the proposed Bragg fiber with a small number of claddings (two of four) shows comparable or even better performance than the standard Bragg fiber with respect to a few mode-guidance properties.

Our method that uses current generator operator assumes the current on the entire surface of conducting scatterers. While, Physical Optics (PO) method assumes that the surface current generates only on the illumination region. The effect of the shadow region on the scattering waves is, therefore, proved by comparing our exact method with PO method. In this regard, radar cross-section (RCS) is calculated for smooth concave-convex contour. We work on numerical calculation of the RCS and analyze its characteristics with different target configurations including complexity and size. Concave illumination region is postulated with considering targets are taking large sizes of about five wavelengths. Here, we assume waves propagation and scattering from targets in free space and horizontal polarization (E-wave incidence).

This work is concerned with generating the digital elevation models (DEMs) from the SAR images of the region of interest using multiple sensor arrays that are fixed on the distributed satellites. We present an exact estimate of the unwrapped phase and the relationship between the unwrapped phase and the terrain height. The optimum scheme that jointly processes the signals from all sensors is based on the model of the multibaseline joint block vector. The method can simultaneously coregister the SAR images, phase unwrapping and DEM generation in the presence of the large coregistration errors. The performance of our approach is verified by a series of simulation experiments based on the distributed sensor arrays.

This paper describes a fast pattern synthesis method for a broadband array antenna using the particle swarm optimization (PSO) and cubic spline interpolation (CSI). Being an indispensable part of a high speed space-division communication system, the array antenna operates in a wide frequency band (200-400 MHz) and has stable patterns with 60-degree half power beam width (HPBW) in the whole frequency band. Firstly, by establishing a versatile objective function, the complex excitations of the circular array at the selected seven frequency points are determined via the PSO algorithm. Then, the complex excitations of the circular array at arbitrary frequency points in the whole working frequency band are calculated effectively using the CSI method. A uniform circular array with six broadband dipole elements is examined. The broadband patterns with 60-degree HPBW and the accuracy of the interpolation method are demonstrated.

A novel radiation pattern and frequency reconfigurable microstrip antenna is introduced in this paper. This antenna is designed on a thin substrate for the application of conformal phased antenna future. The proposed antenna make the operating frequency range 6 times larger than that of a simple rectangular microstrip antenna, and make the beam covering from -70^。∼70^。 compared with the traditional rectangular microstrip antenna beam which only covers -50^。∼50^。. It is potential on the application of wide-band and wideangle.

An axicon, which images a point source into a line along the optic axis, is used widely to generate an approximation to a Bessel beam. More recently many novel axicons, such as Fresnel axicons, Fractal axicons and fractal conical lenses (FCLs), have been proposed. Understanding the properties of Bessel beams generated by these axicons is very helpful to research their applications. However, in optical region, all of them are calculated approximately by the scalar theory. To accurately analyze FCLs when illuminated by a plane wave at millimeter wavelengths, the rigorous electromagnetic analysis method, which combines a two-dimension finite-difference time-domain (2-D FDTD) method and Stratton-Chu formulas, is adopted in our paper. By using this method, the properties of approximate Bessel beams generated by FCLs are analyzed and the conclusions are given.

This paper deals with the possibilities of cancellation of unwanted signals by steering nulls of the pattern in the direction of arrival of signal while keeping the main beam to the desired direction. New iterative adaptive digital beam forming technique is presented here to enhance the conventional effectiveness of beam forming in common commercial application. Simulation and measurement results confirm that this algorithm can achieve effective Co-Channel Interference (CCI) suppression, while increasing the strength of the desired signal.

In this paper, we present an improved Coulombianbased analytical calculation of magnetic fields created by permanentmagnetic rings. The 3 dimensional (3D) components of two types of magnetized rings (axially and radially) were analytically evaluated. The obtained components of the magnetic field are expressed over complete elliptical integrals of the first and second kind, as well as by Heuman's Lambda function. These expressions permit fast and accurate calculations of the magnetic field at any point of interest, for both regular and singular cases. The presented method gives an improvement of already known expressions for calculating the magnetic fields of the aforementioned magnetized rings, and we consider that these improved analytical expressions are more extendable to numerical applications.

This paper presents a broad-band technique for measuring the dielectric permittivity of isotropic nonmagnetic film-shaped materials at low microwave frequencies. The material under test is the substrate of an open-end coplanar waveguide (CPW) used as sample-cell. The dielectric permittivity is extracted from S₁₁ reflection parameter measurement of the open-end CPW cell using analytical relationships, which allow to decrease the computation time with respect to any full-wave electromagnetic method. Vector network analyzer (VNA) and high-quality on-coplanar test fixture are used for the measurements between 300 kHz and 3 GHz. Measured ε_r data for several nonmagnetic low-loss materials are presented. This technique shows a good agreement between measured and predicted data for the real permittivity over 0.05 GHz-3GHz frequency range.

With development of communication with integration technology, size reduction of microstrip antennas is becoming an important design consideration for practical applications. Here a new microstrip antenna with Koch shaped fractal defects on the patch surface is presented. Using this method, the overall electric length of the antenna is increased largely and hence the size of antenna is reduced to 85%, compared to an ordinary microstrip antenna with the same resonance frequency. Antenna is simulated using high frequency structure simulator (HFSS) V.10 which is based on finite element modeling (FEM). Finally antenna is fabricated on RO4003 substrate. Measurement results are in good agreement with simulated results.

In this paper, a broadband bandpass filter (BPF) with superior spurious suppression over a wide frequency range at least up to 20 GHz at −20 dB has been designed. The proposed broadband bandpass filter has designed using quarter-wavelength short stubs alternating with branch stubs co-via structure, and inserting the bandstop filters to substitute for redundant connecting lines. Compare with some traditional co-via structure, this work by using the branch stubs to construct the co-via structure, not only reduce the size around 70% but also decrease the radiation loss due to some complex meander configurations occurring in the connecting lines. For the prototype broadband filter, center frequencies around 4 GHz were selected. The bandwidth of passband was between 1.95 GHz and 6.25 GHz, in which the insertion-loss amounts to around −1.5 dB. The suppression range of stopbandis between 8.2-20.3 GHz, in which the insertion-loss amounts to around −20 dB.

The 3D probability tomography theory is developed to image polar and dipolar sources of a geophysical field dataset. The purpose of the method is to improve resolution power of buried geophysical targets, using probability as a suitable paradigm allowing all possible equivalent solutions to be included within a single 3D image. The new approach is described by assuming a geophysical field dataset as caused by a discrete number of source poles and dipoles. A few tests are given to show how the combined polar and dipolar tomography can provide a reliable core-and-boundary resolution of the most probable sources of anomalies. An application to the Vesuvius volcano (Naples, Italy) is finally illustrated by analyzing self-potential and geoelectrical datasets collected within the whole volcanic area. A gravity dataset is also analyzed for completeness. The purpose is to get new insights into the Vesuvius shallow structure and hydrothermal system and to outline the features of the deep tectonic depression within which the volcano grew.

A technique to characterize the fields generated by a cell phone, and projected into an area inside a TEM cell for possible biological interaction studies is described. A double-ended monopole antenna is proposed as the lead signal inducer between the inside and the outside areas of the TEM cell. The coupling voltage at the TEM cell ports and the field distribution within the area under test (AUT) were found to be a function of the phone position, polarization, and dialing type. The measurements for a GSM 850MHz cellular phone showed that the optimum setup is achievable when the phone is placed outside the TEM cell and co-polarized with the signal leader. An improvement of the field uniformity is possible with the use of a shorter signal leader but at the cost of decreased field strength. The proposed setup can be utilized in studies and experiments related to the radio frequency effects on biological cells and organs.

In this paper, we present an adaptive beamforming scheme for smart antenna arrays in the presence of several desired and interfering signals, and additive white Gaussian noise. As compared with standard schemes, the proposed algorithm minimizes the noise and interference contributions, but enforces magnitude-only constraints, and exploits the array-factor phases in the desired-signal directions as further optimization parameters. The arising nonlinearly-constrained optimization problem is recast, via the Lagrange method, in the unconstrained optimization of a non-quadratic cost function, for which an iterative technique is proposed. The implementation via artificial neural networks is addressed, and results are compared with those obtained via standard schemes.

The position perturbations of linear antenna elements are used for designing non-uniformly spaced reconfigurable antennas radiating with multiple pattern such that the same amplitude distribution and perturbed positions produces either a pencil or a flat topped beam, the difference being dependent upon phase distribution of the array. The perturbation method consists of inducing small perturbations in the element positions of a linear array to obtain the desired patterns and offer the flexibility of simple design and is similar to other adaptive techniques like phase only or phase/amplitude synthesis. The problem of finding the element position perturbations is treated as a non linear problem and has been solved using a the generalized generation gap steady state genetic algorithm (G3-GA) using parent centric crossover. In the G3-GA approach the population diversity versus selection pressure problem considers both the parent selection and the replacement plans of GA. The positionphase synthesis method using the G3-GA approach is compared with the G3-GA phase-only synthesis technique. It is seen that, an optimal set of element-perturbed positions in a constrained position range with uniform amplitude, unequally spaced elements with unequal phases has the potential to overcome the design challenge of phase only syntheses that uses a larger number of elements to get the same desired side lobe level. Further when the main beam is scanned it is found that the proposed method can maintain a sidelobe level without distortion during beam steering for the angular positions studied.

For maneuvering target Doppler-bearing tracking with signal time delay, a novel approach called ISE-IMM is proposed in this paper. The iterative state estimation (ISE) method is designed to eliminate the negative influence of time delay effect and an interacting multiple model (IMM) filter is embedded to estimate the state according to the measurements of the delayed signal. The nonlinear filter preferred in this paper is a particle filter (PF) with an improved resampling procedure. Performance of our proposed method is evaluated in Monte Carlo simulations. Results show the effectiveness and stability of ISE-IMM-PF in combating the negative effect of signal time delay.

A time domain integral equation approach for analysis of transient responses by 3D composite metallic-dielectric bodies is proposed, which is formulated using the surface equivalent polarization and magnetization as unknown functions. The time domain electric field integral equation is adopted for the metallic part, while the time domain Piggio-Miller-Chang-Harrington-Wu integral equations are adopted for the dielectric part. The spatial and temporal basis functions are the Rao-Wilton-Glisson functions and quadratic Bspline functions, respectively. Numerical examples are provided to demonstrate the stability and accuracy of the proposed method. No late-time instability is encountered, and the results are found in good agreements with analytical or moment method solutions.