Sun Yu-fa

A Miniaturized GNSS Antenna with Bandwidth Broadening

A miniaturized patch antenna loaded with split-ring resonators (SRRs) and modified reactive impedance surface (RIS) is proposed and present. Four sequentially rotated SRRs around the patch of antenna improve the impedance and the axial ratio bandwidth, the modified RIS which with a balanced slots can miniaturize the antenna size and the circularly polarized radiation is achieved by an asymmetric cross slot cut along the orthogonal directions in the center of patch over RIS. The measured results of the proposed antenna are 3.2% (2.44--2.52 GHz) for 3-dB axial ratio bandwidth, 7.8% (2.40--2.595 GHz) for 10-dB return loss bandwidth, and 2.48 dBi for gain at the boresight. The overall antenna volume is 0.27 λ0 x 0.27 x λ0 0.03 x λ0 on a low cost F4B substrate at 2.49 GHz.

Analysis of Optical Signal Transmission Characteristics

This paper reports the optical signal transmission characteristic in the G.652 fiber based on the software OpticSimu. The simulation results are in agreement with theoretical analysis. Without taking into account the non-linear effect and in the same condition, the longer the transmission distance, the signal distortion caused by the group velocity dispersion is clearer while the bit rate increasing. Through reducing the initial chirp of optical signal, the distortion can be reduced at fiber-optic transmission, and the transmission quality is improved.

Fast calculation of wide-band RCS for three-dimensional PEC objects based on preconditioned AWE technique

The asymptotic waveform evaluation (AWE) technique combined with the method of moments (MOM) is often applied to accelerate the calculation of the wide-band radar cross section (RCS) of the target. However, the technique is still quite time-consuming for solving the inverse of impedance matrix when the objects are electrically large. In this paper, Krylov subspace iterative methods are applied to solve the matrix equation derived from electric field integral equation instead of matrix inverse. The dual threshold incomplete LU factorization preconditioner is adopted to improve the convergence behavior of the Krylov subspace iterative methods. The numerical computation shows that the results in this paper are in good agreement with the results obtained by the method of moments at each frequency, and the computational efficiency is improved greatly.

Fast analysis of wideband electromagnetic scattering from multi-objects based on characteristic basis function method

The asymptotic waveform evaluation (AWE) is an efficient method for analyzing wideband electromagnetic scattering problems. As the number of unknowns increases, the size of MOM impedance matrix grows very rapidly, so it is a prohibitive task for the computation of wideband radar cross section (RCS) from electrically large objects or multi-objects using the traditional AWE technique. The characteristic basis function method (CBFM) is a novel efficient approach for reducing the matrix size to a manageable size for direct matrix inversion. In this paper, the AWE technique based on the CBFM for analyzing electromagnetic scattering from multi-objects over a given frequency band is proposed. Numerical examples are given to illustrate the accuracy and computational efficiency of the proposed method.

Analysis of EM scattering characteristics from 2D electrically large objects using characteristic basis function method

Characteristic basis function method (CBFM) is a novel approach for the efficient solution of electromagnetic scattering problems. In this paper, CBFM combined with the domain decomposition technique is used to calculate the radar cross sections from 2D electrically large conducting cylinder and dielectric cylinder. It is shown that the numerical results presented in this paper are in good agreement with that achieved by the traditional method of moments, while the computational efficiency is improved greatly.

The asymptotic waveform evaluation technique based on lifting wavelet transform

The asymptotic waveform evaluation (AWE) technique based on fast lifting wavelet transform (LWT) was applied to the method of moments to solve combined-field integral equation (CFIE). The wide-band radar cross section of arbitrarily shaped two-dimensional perfect electric conducting objects was calculated. The employment of CFIE eliminates interior resonance problem. The numerical results presented in this paper were compared with the results obtained by the method of moments. It was shown that the computational efficiency was improved greatly.

A new method for solving the induced surface current for arbitrary conducting bodies at resonant frequencies

It is well known that the incorrect surface current is given in the vicinity of the resonant frequencies using the method of moments to solve either the electric or magnetic field surface integral equation. The surface current that produces the correct scattered fields, referred to as the non-resonant mode current, can be obtained by using the singular value decomposition technique or the inverse power method, but it is not the real electric current induced on the object surface. A new method is presented to determine the correct surface current, which is composed of the non-resonant mode current and the normalized resonant mode current multiplied by an unknown complex factor. The unknown complex factor can be obtained by employing the condition that the total field must be zero at specified interior points. A numerical example is given for an infinitely long, perfectly conducting circular cylinder at interior resonance, and the computed surface currents are in good agreement with the analytical ones. The validity and accuracy of the presented method is thus verified.