Yeow Beng Gan

Design of a uniform amplitude time modulated linear array with optimized time sequences

A novel approach to realize uniform amplitude time modulated linear arrays with both suppressed sidelobes and sidebands is proposed. The approach utilizes the direct optimization of the switch-on time sequence of each array element via the simple genetic algorithm (SGA). As compared to previous time modulated linear arrays, the new array has the advantages of having low sidelobe level (SLL), low sideband level (SBL) and uniform excitations simultaneously. Experimental results on an experimental prototype of a 16-element printed dipole linear array with the SGA optimized time sequences verified the approach.

Fast Analysis of RCS Over a Frequency Band Using Pre-Corrected FFT/AIM and Asymptotic Waveform Evaluation Technique

The pre-corrected fast Fourier transform (PFFT)/adaptive integral method (AIM) is combined with the asymptotic waveform evaluation (AWE) technique to present fast RCS calculation for arbitrarily shaped three-dimensional PEC objects over a frequency band. The electric field integral equation (EFIE) is used to formulate the problem and the method of moments (MoM) is employed to solve the integral equation. By using the AWE method, the unknown equivalent current is expanded into a Taylor series around a frequency in the desired frequency band. Then, instead of solving the equivalent current at each frequency point, it is only necessary to solve for the coefficients of the Taylor series (called ldquomomentsrdquo) at each expansion point. Since the number of the expansion points is usually much smaller than that of the frequency points, the AWE can achieve fast frequency sweeping. To facilitate the analysis of large problems, in this paper, all the full matrices are stored in a sparse form and the PFFT/AIM method is employed to accelerate all the matrix-vector products on both sides of the matrix equation for the moments. Further, the incomplete LU preconditioner is used at each expansion point to improve the convergence behaviour of the matrix equation for the moments. The present method can deal with much larger problems than the conventional MoM-AWE method since the PFFT/AIM achieves considerable reduction in memory requirement and computation time. Numerical results will be presented to show the efficiency and capability of the method.

Anisotropy of composite materials with inclusion with orientation preference

In this paper, the quasicrystalline model and the differential evolution strategy are applied to analyze the effective electromagnetic properties of composite materials with aligned nonspherical inclusions. The relationship between the effective wave number, volume concentration, direction of wave propagation vector, and aspect ratio of the inclusion particle are numerically studied. It is found that composite materials with small inclusion particles behave like uniaxial material. In addition, we observed general effective anisotropy in composite materials with larger inclusion particles.

Efficient analysis of electromagnetic scattering and radiation from patches on finite, arbitrarily curved, grounded substrates

[1]xa0A precorrected-fast Fourier transform (FFT) accelerated surface integral equation approach formulated using the homogeneous medium Greens function is presented for the analysis of patch arrays on finite, arbitrarily shaped, grounded substrate. The integral equation is solved by the method of moments, and the precorrected-FFT method is applied to reduce the memory requirement and computational complexity of the solution procedure. The memory required for this algorithm is O(N1.5), and the computational complexity is NiterN1.5log N, where N is the number of unknowns and Niter is the iteration number. Numerical results are presented to demonstrate the accuracy and capability of the method.

Precorrected-FFT solution of the volume integral equations for inhomogeneous dielectric bodies

The precorrected-FFT method is applied to the fast solution of the volume integral equation for lossy, inhomogeneous dielectric bodies. The volume of the dielectric body is discretized into tetrahedron elements and the SWG basis functions are employed to expand the unknown electric flux density. The basis functions are then projected onto a uniform grid surrounding the nonuniform mesh, enabling the FFTs to be used to speed up the matrix-vector multipliers in the iterative solution of the matrix equation. The resultant method has a computational complexity and memory requirement of O(N log N) and O(N) respectively.

Efficient analysis of probe-fed microstrip antennas on arbitrarily shaped, finite ground plane and substrate

An efficient method based on the volume-surface-wire integral equation and precorrected-FFT method is presented for the accurate analysis of probe-fed microstrip antennas on arbitrarily shaped, finite sized ground plane and substrate. The method of moments (MoM) is used to solve the integral equation in which three triangular-type basis functions are used to represent the unknown currents on the substrates, surfaces, and wires. The probe feed is rigorously modeled using an attachment mode at the junction, The precorrected-FFT is applied to reduce the memory requirement and computational cost of the MoM to facilitate analysis of large arrays.

Effective wave number of composite materials with oriented randomly distributed inclusions

The design of composite materials with specific electromagnetic properties is important to applications in the aerospace, communications, defense, food, medical, power and transportation industries. In this paper, we follow the T-matrix method (P.C. Waterman, Proc. IEEE, vol. 53, no. 8, pp. 805-812, 1965; and Phys. Rev. D, vol. 3, no. 4, pp. 825-839, 1971), configurational averaging technique (L.L. Foldy, Phys. Rev., vol. 67, nos. 3 and 4, pp 107-119, 1945; M. Lax, Revs. Modern Phys., vol. 23, no. 4, pp. 287-310, 1951) and quasicrystalline approximation (TCQ) approach originated by Varadan et al (Phys. Rev. D, vol. 19, no. 8, pp. 2480-2489, 1979) to predict the effective wave number of composite materials with oriented randomly distributed inclusions. However, it is noted that the vector spherical wave functions translational addition theorems (VSWFTAT) used by Varadan et al were found to be incorrect (A. Qing, Proc. PIERS03, 2003). Here, the corrected VSWFTAT are applied to formulate the problem. The problem of prediction of the effective wave number is cast as an optimisation problem. Due to the simplicity, versatility and strong search ability of the differential evolution strategy (DES) (Qing, IEEE Trans. Antennas Propagat., vol. 51, no. 5), the optimisation problem is solved using DES, instead of Mullers method. Preliminary numerical results have been obtained.

Fast frequency-sweep analysis of RCS using pre-corrected FFT and asymptotic waveform evaluation technique

To facilitate the analysis of large problems, in this paper, all the full matrices are stored in a sparse form and the PFFT method is employed to accelerate all the matrix-vector products appearing in both hand sides of the matrix equation for the moments. The present method can deal with much larger problems than the traditional MoM-AWE method since the PFFT achieves great reduction in memory requirement and computation time.

Parallel FFT Based Fast Algorithms for Solving Large Scale Electromagnetic Problems

This paper presents two parallel schemes of fast algorithms based on the parallel FFT. In the first scheme, the parallel FFT is applied to speed up multiplication of the impedance matrix and a vector directly. In the second scheme, the AIM is parallelized. To demonstrate the efficiency of the parallel schemes, electromagnetic scattering by a very large cylindrical wire array and a conducting sphere are computed

Analysis of antenna arrays with finite frequency selective surfaces

In this paper, a full-wave method based on the volume-surface integral equation is applied to analyze microstrip antenna arrays with finite FSS radome. The volume integral equation is applied to the dielectric region of the composite structure, while the surface integral equation is used on the conductive surface. The integral equations are solved using the method of moments (MoM), with the precorrected-FFT (P-FFT) method used to reduce the memory requirement and accelerate the matrix-vector products in the iterative solution of the equation. With this method, the effects of the FSS on the characteristics of the antenna can be accurately investigated.