A novel interpolation scheme based on Adaptive Integral Method (AIM) is presented to solve electrically large radiation problem of conducting surface/surface configurations. For a complex structure that involves wires and surfaces, three basis functions must be assigned to surfaces, wires and wire/surface junctions. To simplify this, the thin strips with no thickness instead of wires are proposed, and the wire/surface junctions can be replaced by surface/surface junctions, thus it is only necessary to define a uniform basis function. The Electric Field Integral Equation (EFIE) is solved using the Method of Moments (MoM) to obtain the equivalent surface current on PEC surfaces. To facilitate the analysis of electrically large radiation problem, the interpolation scheme based on AIM is employed to accelerate the matrix-vector multiplications and reduce matrix storage. Numerical results are presented to demonstrate the accuracy and efficiency of the technique.

This paper describes the alternating-direction implicit finite-difference time-domain (ADI-FDTD) method for physical modeling of high-frequency semiconductor devices. The model contains the semiconductor equations in conjunction with the Maxwell's equations which describe the complete behavior of high-frequency active devices. Using ADI approach leads to a significant reduction of the full-wave simulation time. We can reach over 99% reduction in the simulation time by using this technique while still have a good degree of accuracy compared to the conventional approaches. As the first step in the performance investigation, we use the electrons flow equations in the absence of holes and recombination as semiconductor equations in this paper.

Efficient embedded antennas are needed for future wireless structural health monitoring. The input return loss and transmission losses of a dipole, a planar inverted-F antenna (PIFA), a microstrip patch, and a loop antenna are studied at around 2.45 GHz when these antennas are embedded inside a concrete cylinder. Antenna performance is investigated in free-space, in air dried concrete and in saturated concrete with and without the presence of steel reinforcements. It is observed that the maximum transmission loss for a distance of 250 mm between antennas is around 50 dB which is acceptable for inside the bridge wireless communication between sensors.

In this work, a hybrid method which combines time domain integral equation method (TDIE) with time domain physical optics method (TDPO) is presented for the problem of TM transient scattering from two-dimensional (2-D) combinative conducting targets. The explicit solution of Marching-On-in-Time (MOT) is developed. The high accuracy and efficiency of this hybrid method are demonstrated by comparing the numerical results of this hybrid method with those obtained by TDIE. To obtain 2-D transient far scattered field, a concise algorithm about time-domain near-zone to far-zone transformation without double Fourier transform is presented for TDIE and hybrid method, and its numerical results are verified by comparing with results obtained from inverse discrete Fourier transform (IDFT) techniques.

For an harmonic plane wave impinging on a perfectly reflecting smooth plane the total field, incident and reflected, satisfying on this plane a Dirichlet or Neumann boundaray condition, has an integral representation that we extend to the specular reflection from a perfectly reflecting rough plane. To make this generalization possible, some constraints must be imposed on the wavelength of the incident field and on the rough amplitude to make the diffuse field negligible so that only the coherent field is important and we may use the fact that the coherent power is identical to that of a smooth surface. This generalized integral representation supplies an approximation of the coherent field valid far from the rough plane. We limit the discussion to acoustic, TE, TM electromagnetic wave incident on 1D-perfectly reflecting rough planes with roughness described by zig-zag functions piecewise linear with opposite slop on adjacent intervalls.

In this paper, the problem of designing linear antenna arrays for specific radiation properties is dealt with. The design problem is modeled as a single optimization problem. The objectives of this work are to minimize the maximum side lobe level (SLL) and perform null steering for isotropic linear antenna arrays by controlling different parameters of the array elements (position, amplitude, and phase). The optimization is performed using two techniques: Taguchi's optimization method and the self-adaptive differential evolution (SADE) technique. The advantage of Taguchi's optimization technique is the ability of solving problems with a high degree of complexity using a small number of experiments in the optimization process. Taguchi's method is easy to implement and converges to the desired goal quickly in comparison with gradient-based methods and particle swarm optimization (PSO). Results obtained using Taguchi's method are in very good agreement with those obtained using the SADE technique.

The problem of determining the eigenmodes of a rectangular waveguide with one hard wall formed by longitudinal corrugations with grooves filled with dielectric is considered. The characteristic equation is derived by using the asymptotic boundary conditions for corrugated surfaces. It is shown analytically that if the groove depth is equal to the value 0.25λ/(ε-1)^1/2 corresponding to the hard wall condition, the TE eigenmode spectrum of the waveguide contains an infinite set of new non-uniform quasi-TEM modes with different transverse propagation constants in the empty part and identical longitudinal propagation constants equal to the wavenumber k. Analytical solution for the case of excitation of the waveguide by a specified source is given, and an example of forming local quasi-TEM waves is considered and discussed.

Possibilities for the extension of the operational frequency band of slotted waveguide antennas are studied. It is shown that by using both conventional longitudinal slots and subarraying techniques it is possible to reach the relative bandwidth of about 15%. This result is illustrated by the development of a novel slotted waveguide antenna for high-resolution SAR applications. The antenna operates in the X-band and forms the beam of 4°×6° with the gain of about 30 dB.

By inserting a dielectric layer, covered by a grounded metal plane, into a hollow rectangular waveguide (HRWG), a planar rectangular waveguide (PRWG) is structured. It is a new candidate solution for both MMIC and hybrid planar RF circuit applications. An intensive numerical analysis of the PRWG is conducted by a 2-D FDTD method. The propagation characteristics of the PRWG with different physical dimensions and electrical parameters are presented. This analysis shows that the PRWG can give an alterable single mode working bandwidth for dominant mode compared with the HRWG, and the size of the transverse section of the PRWG is smaller than the HRWG under the same cutoff frequency of dominant mode.

Microwave hyperthermia is a non-invasive treatment for cancer which exploits a selective heating of tissues induced through focused electromagnetic fields. In order to improve the treatment's efficiency, while minimizing side effects, it is necessary to achieve a constrained focusing of the field radiated by the sources. To address this issue, in this paper we present an innovative and computationally effective approach to the field focusing for hyperthermia. The proposed method, after establishing the number of sources to be used, determines the excitations of the given set of sources such to produce a maximum field in a given region of space subject to a completely arbitrary mask for the field amplitude in all other regions. As the approach relies on a formulation of the problem in terms of convex programming, it is able to achieve the globally optimal solution without the adoption of computationally intensive global optimization procedures. A preliminary assessment of the feasibility is given on hyperthermia therapy of breast cancer by means of numerical examples run on realistic 2D phantoms of female breast.

This paper investigates the use of clonal selection principles based on our immune system for optimization applications in electromagnetics. This concept is based on our immune system's ability to respond to an antigen and produce a pool of anti-body secreting cells. In addition to the common implementations of this algorithm where the affinity maturation and cloning principles of clonal selection principles are used, we utilize memory and the cross-over concepts that are common to other bio-inspired methods. The performance of the algorithm is investigated for well known mathematical test functions and its potential is demonstrated in the context of the design of a radar absorbing material and a planar phased array antenna with specific radiation and null characteristics.

An improved Central Force Optimization (CFO) algorithm for antenna optimization is presented. CFO locates the global extrema an objective function to be maximized, in this case antenna directivity, by flying "probes" through the decision space (DS). The new implementation includes variable initial probe distribution and decision space adaptation. CFO's performance is assessed against a recognized antenna benchmark problem specifically designed to evaluate optimization evolutionary algorithms for antenna applications. In addition, summary results also are presented for a standard twenty-three function suite of analytic benchmarks. The improved CFO implementation exhibits excellent performance.

A new miniaturized bandpass fractal frequency selective surface (FSS) with excellent angular stability performa nce is proposed. The minia turization has been achieved by scheming out a symmetric fractal pattern of continuous slots from the surface of a square-shaped patch, in which each periodic cell consists of incurved slot resonator for reducing the cell size. Reduction in FSS size of up to 74% with respect to the conventional square loop aperture FSS operating at the same frequency of 3.3 GHz is obtained. Furthermore, results show excellent angular stability for both vertica land horizontal polarization at different incidence angles because of its fractal configuration. A prototype is fabricated and the FSS measurement, and simulation results are presented and discussed.

To predict the three-dimensional radar cross section (RCS) pattern of an arbitrary shaped perfectly electric conductor objects in both a broad frequency band and angular domains simultaneously, the method of moments (MoM) combined with the Chebyshev polynomial approximation is presented. The induced current is expanded by a bivariate Chebyshev series. Using this function, the induced current can be obtained at any frequency and angle within the desired frequency band and angular domains. Numerical results show that the proposed method is found to be superior in terms of the CPU time to obtain the three-dimensional RCS pattern compared with the direct solution by MoM repeating the calculations at each frequency and angle. Good agreement between the presented method and the direct MoM is observed.

We have proposed a new architecture for an array in which the elements are placed on a spiral curve in order to obtain an ultra wideband (UWB) radiation pattern. In addition, array factor and bandwidth of the proposed spiral array are calculated. Simulated results obtained by SuperNEC and CST software have shown good agreement with the analytic calculations. Although the proposed antenna array is wideband in nature, it lacks desirable efficiency, due to poor front to back ratio (FBR) and sidelobe level (SLL). In this paper, we have chosen three different approaches in order to improve the e±ciency of proposed array. First, the effect of length and thickness tapering of elements has been studied. Second, we have used Genetic Algorithm (GA) to optimized pattern shape. Finally, the influence of metamaterial cover on array performance has been investigated. Although the first and second methods improve the radiation pattern, the array bandwidth is reduced. It is shown that the third method improves array directivity and FBR by 5-7 dB and 15-17 dB respectively within the frequency band of operation.

Holey fibers (HF) with their peculiar properties have been used in fabrication of Erbium doped holey fiber amplifiers (EDHFA) for third optical communication window. In this paper, by using scalar effective index method, the analyses are presented to investigate the effects of HF geometrical parameters on the gain performance of the EDHFAs. The hierarchical variations of the parameters, including the air-hole sizes (AHS), propagating modes of the core and cladding, mode field diameter of the signal and pump, would cause alterations in the maximum gain and the optimum lengths of the EDHFAs. By determining the normalized frequency of the HF in wide range variations of the air-hole diameter, air-hole spacing, and air-filling factor (AFF), the single-mode regions for signal and pump wavelengths are obtained, where the maximum gain and the optimum lengths are evaluated. In addition, the influence of pump power and the dopant concentration in terms of the AFF are investigated. It is shown that by using suitable AHS and AFF, one can obtain a higher gain for a shorter optimum length in the EDHFAs. The obtained results can be a useful tool for design of HF-based optical amplifiers with lesser effects of amplified spontaneous emission and nonlinearities because of shorter optimized length.

In this paper, a folded stepped impedance resonator (SIR), modified by adding an inner quasi-lumped SIR stub, is used as a basis block for a new implementation of dual-band bandpass filters. The main advantage of the proposed filter is to make it possible to independently control the electrical features of the first and second bands. The behavior of the first band basically depends on the geometry of the outer folded SIR. The second band, however, is strongly influenced by the presence of the inner stub. Additional design flexibility is achieved by allowing the inner stub to be located at an arbitrary position along the high impedance line section of the main SIR. The position of the tapped input and output lines can be optimized in order to reach a reasonable matching of the filter at the central frequencies of both passbands. Some designs are reported to illustrate the possibilities of the proposed structure. Experimental verification has been included.

The frequency responses of two widely used active inductor topologies are analyzed and compared using a generalized circuit model for the active devices in the circuits. A very wideband active inductor in CMOS was subsequently fabricated and tested and the inductor exhibits a measured self-resonant frequency of 9.7 GHz.

This work investigates the variation of the real part of the complex magnetic permeability of a Ni-Zn ferrite for application to temperature sensors. Ferrite samples were fabricated by means of the conventional ceramic method. Zinc, nickel and iron oxides were used as raw materials. The samples were sintered at 1200, 1300, and 1400^oC. The complex magnetic permeability of the samples was measured at temperatures ranging from -40^oC to +50^oC. The complex magnetic permeability of the samples was analyzed in the 100 kHz--100 MHz frequency range, and the temperature sensitivity of the magnetic permeability (μr'/T) was analyzed at 100 kHz. The magnetic permeability variation of the ferrite permits to use it as a temperature transducer with a maximum temperature sensitivity of about -119^oC^-1. The highest magnitudes of temperature sensitivity occurred between +30^oC and +50^oC. Therefore, the ferrite could be sensitive enough to allow temperature measurements at the human body temperature level. The results indicate that the temperature range of maximum temperature sensitivity of the ferrite may be adjusted by means of appropriate selection of the fabrication parameters.

In this paper a novel method for crosstalk reduction is proposed. This is achieved through using the step shaped transmission line, which basically attempts to create steps along the transmission lines to decrease the crosstalk, while having negligible variation in return loss. To this end, various simulations are carried out to get an intuition regarding the underlying processes conducted to the far-end crosstalk, thereby enabling to optimize the far-end crosstalk, and simultaneously to yield a small variation in the return loss. Accordingly, a conventional coupled transmission line is employed as a benchmark, enabling to have an idea regarding the impact of the proposed method in terms of the ability to decrease the far-end cross talk. Furthermore, the proposed transmission line and the benchmark structure are fabricated and then evaluated to verify the experimental results to that of the simulation. In addition, comprehensive parametric studies have been carried out to get insight on the effect of various adjustable parameters over the crosstalk. The obtained results show that the crosstalk is decreased more than 4 dB over the entire operating bandwidth. Some advantages such as ease of design and fabrication have made the proposed technique an advisable method when dealing with low crosstalk.