Time-domain Physical Optics Method Research Articles

A Fast, Hybrid, Time-Domain Discontinuous Galerkin-Physical Optics Method for Composite Electromagnetic Scattering Analysis

To accelerate the solution of transient electromagnetic scattering from composite scatters, a novel hybrid discontinuous Galerkin time domain (DGTD) and time-domain physical optics (TDPO) method is proposed. The DGTD method is used to solve the accurate scattering field of the multi-scale objects region, and a hybrid explicit-implicit time integration method is also used to improve the efficiency of multi-scale problems in the time domain. Meanwhile, the TDPO method is used to accelerate the speed of surface current integration in an electrically large region. In addition, the DGTDPO method considers the mutual coupling between two regions, and effectively reduces the number of numerical calculations for the other space of the composite target, thereby significantly reducing the computer memory consumption. Numerical results certified the high efficiency and accuracy of the hybrid DGTDPO. According to the results, in comparison with the DGTD algorithm in the entire computational domain, the DGTDPO method can reduce computing time and memory by 90% and 70% respectively. Meanwhile, the normalized root mean square deviation (NRMSD) of the time-domain, high-frequency approximation method is over 0.2, and that of the DGTDPO method is only 0.0971. That is, compared with the approximation methods, the hybrid method improves the accuracy by more than 64%.

ISAR Image Algorithm Using Time-Domain Scattering Echo Simulated by TDPO Method

In this letter, we propose an inverse synthetic aperture radar (ISAR) imaging method using time-domain (TD) scattering echo simulated by time-domain physical optics (TDPO) method. First, the TD pulse plane wave is taken as the incident wave and the transient scattering echo data matrix is obtained by using the TDPO method under different look angles of the target. Then, demodulation, pulse compression, and azimuth inverse fast Fourier transform (FFT) are performed on the echo data matrix to obtain the ISAR image under small bandwidth small angle. In this letter, considering the fact of TD pulse signals emitted by radar, electromagnetic scattering modeling method is adopted to obtain more accurate TD scattering echoes. This method combines the electromagnetic scattering algorithm and radar imaging algorithm effectively and is closer to practical application. Finally, ISAR images are given to verify the feasibility and fidelity of the presented method.

Analysis of multilayered homogeneous dielectric targets by using time‐domain physical optics method

An improved time-domain physical optics (TDPO) method is proposed to simulate multilayered dielectric structures, in which the characteristic matrix theory of multilayered medium is implemented. In order to accurately calculate the total reflection coefficient on the surface of the multilayered medium, a series of two-dimensional characteristic matrices are established. Based on the characteristic matrices, the total reflection coefficient can be directly derived, instead of summing up the multiple reflected and refracted waves, which is insensitive to the number of the number of the layers and the polarization of the incident wave. Numerical examples are given to validate effectiveness of the proposed TDPO method. It states that this method has much higher computational efficiency, without the loss of accuracy.

Range Distance Requirements for Large Antenna Measurements for Square Aperture With Uniform Field Distribution

Frequency dependences of the field for constant angle of observation measured by different probes at different distances are discussed. We consider the case of the square aperture antenna with the uniform field distribution. The analysis is based on time-domain physical optics method of field calculation. We show and explain the effect of sidelobe reduction when a big square probe is placed at a finite distance from square aperture antenna. Errors of the sidelobe levels of the antenna radiation pattern (ARP) in the cases of different sizes of the probe placed at different distances are shown. We show an optimal probe size and an optimal measurement distance between antennas. We also show and explain the effect of a large distortion of the ARP first zero, measured by the big probe at the finite distance.

Passive inter-modulation scattering analysis of reflector considering contact nonlinearity

Passive inter-modulation (PIM) is a form of nonlinear distortion caused by the inherent nonlinearities of the passive devices and components in RF/microwave system. It will degenerate the performance of communication system with broad-band channel and high-sensitivity receiver. Therefore, it is necessary to construct a model to simulate this process in order to predict the level of PIM. This paper is aimed at constructing some plate models with one-dimensional and two-dimensional contact nonlinearity sections illuminated by two-tone waves, and calculating the scattered field at a fixed-point in space using time-domain physical optics method. By taking fast Fourier transform (FFT), we get the spectrum of the scattered field and then analyze the generated PIM products. At the end of this paper, some numerical examples are presented to show the influence rules of the relative factors on PIM. The results indicate the variation of the level of PIM with the number of the nonlinear regions, the nonlinear spacing, and the incident power levels.

Time-Domain Physical Optics Method for the Analysis of Wide-Band EM Scattering from Two-Dimensional Conducting Rough Surface

Time-domain physical optics (TDPO) method is extended to investigate electromagnetic (EM) scattering from two-dimensional (2D) perfectly electrically conducting (PEC) rough surface in both time domain and frequency domain. The scheme requires relatively small amounts of computer memory and CPU time, and has advantage over the Kirchhoff Approximation (KA) method in obtaining transient response of rough surface by a program run. The 2D Gaussian randomly rough surface is generated by Monte Carlo method and then is partitioned into small triangle facets through the meshing preprocess. The accuracy of TDPO is validated by comparing the numerical results with those obtained by the KA method in both backward and specular directions. The transient response and its frequency distribution of radar cross section (RCS) from rough surface is shown, respectively. The scattering results from rough surface with different size in the specular direction are given. The influence of the root mean square height (σ) and correlation length (l) on electromagnetic scattering from PEC rough surface is discussed in detail. Finally, the comparisons of backscattering results at different incident angles are presented and analyzed.

Time-Domain Analysis of a Rectangular Reflector Antenna

Rectangular reflector antennas have motivated the time-domain analysis of electromagnetic scattering problems. The asymptotic time domain physical-optics (TDPO) is applied to the analysis of a rectangular reflector illuminated by a Gaussian-impulse. The effects of time-delayed mutual coupling between points on the surface will be ignored as a result of utilizing the TDPO method for determining the equivalent surface-current density on the reflector. Finally, in this work the scattered signals at the specular reflection point, at the edges, and at the corners can be clearly distinguished.

A TDIE/TDPO HYBRID METHOD FOR THE ANALYSIS OF TM TRANSIENT SCATTERING FROM TWO-DIMENSIONAL COMBINATIVE CONDUCTING CYLINDERS

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 e-ciency 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 fleld, 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 verifled by comparing with the results obtained from inverse discrete Fourier transform (IDFT) techniques.