• 대한원격탐사학회지
• /
• 제20권1호
• /
• pp.39-46
• /
• 2004

The generalized Rayleigh-Gans (GRG) approximation is usually used to compute the scattering amplitudes of leaves smaller or comparable to a wavelength, while the physical optics (PO) approach with the resistive sheet approximation is commonly used for leaves larger or comparable to the wavelength. In this paper, the scattering amplitudes of an elliptical leaf are computed using those theoretical scattering models (GRG and PO) at different frequencies. The accuracies of the analytical models for microwave scattering from deciduous leaves are investigated by comparison with the precise estimation by the method of moment (MoM). It was found that both the PO approach and the GRG approximation can be used alternatively for computing the scattering matrices of natural deciduous leaves at P-, L-, C- and X-band frequencies.

• 한국전자파학회논문지
• /
• 제25권5호
• /
• pp.601-606
• /
• 2014

IPO(Iterative Physical Optics) 방법은 대규모 물체의 산란파를 효과적으로 계산하는 고주파 근사 방법 중 하나인 PO(Physical Optics) 방법을 반복적으로 적용하는 계산방법이다. IPO 방법은 일차(first-order) PO 방법에서는 고려하지 못하는 다중 반사를 고려할 수 있어, 산란체 표면에 여기되는 전류의 정확도를 높일 수 있다. 그러므로 산란체의 RCS(Radar Cross Section)를 보다 정확하게 예측할 수 있다. 그러나 IPO 방법은 필요한 적분방정식을 정확하게 풀지 않아 수렴성에 문제가 생긴다. 그러므로 본 논문에서는 IPO 방법의 수렴성을 조절하기 위해, 행렬연산에 사용하는 Jacobi, Gauss-Seidel, SOR(Successive Over Relaxation) 그리고 Richardson 방법을 IPO 방법에 적용하였다. 그러므로 대규모 물체의 RCS 계산을 제안된 IPO 방법을 사용하여 효율적으로 계산할 수 있다. 또, 이들의 정확도를 시뮬레이션을 통해 검증하였다.

• 대한원격탐사학회:학술대회논문집
• /
• 대한원격탐사학회 2007년도 Proceedings of ISRS 2007
• /
• pp.369-373
• /
• 2007

This paper presents an examination of theoretical scattering models for radar cross sections (RCS) of lossy dielectric cylinders, such as exact analytical solution, low frequency approximation (Rayleigh) and high frequency approximation (Physical Optics). The validity regions of the PO and Rayleigh models are closely examined with exact solution in terms of various wavelengths and dielectric constants of a circular cylinder. And also this paper examines the PO and Rayleigh models for back and forward scatter RCS of a cylinder at various incidence angles and polarizations. It was found that the PO and Rayleigh model have their validity regions for estimating the RCS of a circular cylinder.

• 한국전산유체공학회지
• /
• 제17권4호
• /
• pp.56-68
• /
• 2012

Nowadays, Unmanned Combat Air Vehicle(UCAV) has become an important aircraft system for the national defense. For its efficiency and survivability, shape optimization of UCAV is an essential part of its design process. In this paper, shape optimization of UCAV was processed for aerodynamic performance improvement and Radar Cross Section(RCS) reduction using Multi Objective Genetic Algorithm(MOGA). Lift and induced drag, friction drag, RCS were calculated using panel method, boundary layer theory, Physical Optics(PO) approximation respectively. In particular, calculation applied Radar Absorbing Material(RAM) was performed for the additional RCS reduction. Results are indicated that shape optimization is performed well for improving aerodynamic performance, reducing RCS. Further study will be performed with higher fidelity tools and consider other design segments including structure.

• Journal of electromagnetic engineering and science
• /
• 제8권3호
• /
• pp.100-109
• /
• 2008

The finite volume time domain(FVTD) technique faces serious limitations in simulating electromagnetic scattering at high frequencies due to requirements related to discretization. A modified FVTD method is proposed for electrically large, perfectly conducting scatterers by partially incorporating a time-domain physical optics(PO) approximation for the surface current. Dominant specular returns in the modified FVTD method are modeled using a PO approximation of the surface current allowing for a much coarser discretization at high electrical sizes compared to the original FVTD scheme. This coarse discretization can be based on the minimum surface resolution required for a satisfactory numerical evaluation of the PO integral for the scattered far-field. Non-uniform discretization and spatial accuracy can also be used in the context of the modified FVTD method. The modified FVTD method is aimed at simulating electromagnetic scattering from geometries containing long smooth illuminated sections with respect to the incident wave. The computational efficiency of the modified FVTD method for higher electrical sizes are shown by solving two-dimensional test cases involving electromagnetic scattering from a circular cylinder and a symmetric airfoil.

• 전자공학회논문지A
• /
• 제32A권1호
• /
• pp.45-52
• /
• 1995

A new Kirchhoff approximation(KA) method was proposed for microwave scttering from randomly rough surfaces. Using the spectral representation of delta function and its sifting theorem, a new KA was formulated directly without any further approximation, and this formulated was used to compute exact backscttering coefficients. The validity of the KA was verified by a numerical method, and this new KA technique was used to evaluate the existing approximated KkA methods; i.t., the zeroth-order and the first-order approximated physical optics(PO) models. It was shown that the first-order approximated PO model has small error than the zeroth-order approximated PO model at low incidence angles and the opposite happens at higher incidence angles. This new KA model can be used to compute exact scattering coefficients in the validity regions of KA and to evaluate other theoretical and numerical models for scattering from randomly rough surfaces.

• 해양환경안전학회지
• /
• 제20권4호
• /
• pp.435-442
• /
• 2014

본 연구에서는 복합 구조물의 레이더 반사면적을 해석하기 위한 프로그램 RACSAN을 개발하였다. 본 프로그램은 물리 광학을 기초로 한 고주파 대역에서의 키르히호프 근사법을 기반으로 하고 있다. 또한, 본 프로그램은 물리/기하 광학 혼합방법을 이용하여 복합 구조물의 다중 반사 효과를 고려 할 수 있다. 즉, 기하 광학을 이용하여 다중 반사 시 유효면적을 계산하고 최종 반사면에서는 물리광학을 이용하여 레이더 반사면적을 해석한다. 개발된 프로그램의 신뢰성 확보를 위하여 이론해가 있는 구조물들의 결과들과 비교하여 본 프로그램이 복합 구조물의 레이더 반사면적 해석에 유용하게 사용될 수 있는 것을 확인하였다.

• International Journal of Ocean System Engineering
• /
• 제3권3호
• /
• pp.158-163
• /
• 2013

The acoustic target strength (TS) is one of the most important parameters for a submarine's stealth design. Because modem submarines are larger than their predecessors, TS must be managed at each design stage in order to reduce it. To predict the TS of a submarine, TASTRAN R1 was developed based on a Kirchhoff approximation in a high-frequency range. This program can present TS values that include multi-bounce effect in the exterior and interior of the structure by combining geometric optics (GO) and physical optics (PO) methods, anechoic coating effect by using the reflection coefficient, and response time pattern for a detected target. In this paper, TS calculations for a submarine model with the above effects are simulated by using this developed program, and the TS results are discussed.

• 한국시뮬레이션학회:학술대회논문집
• /
• 한국시뮬레이션학회 2003년도 춘계학술대회논문집
• /
• pp.15-18
• /
• 2003

전자파 산란해석 방법으로서 유한요소법, 경계요소법 및 모멘트법 등은 임의 구조를 한 산란체의 산란현상을 다룰 수 있다. 그러나 이러한 해석방법들은 정상 파동문제를 다루는데 편중되어 있어 시간영역에서의 비정상 파동문제를 해석하기 위해서는 여러 가지 제약이 따른다. 본 논문에서는 본질적으로 시간영역 해석방법인 TLM(Transmission Line Matrix)법을 이용하여 프레넬 렌즈의 산란특성을 해석하고 키르호프의 근사식과 PO(Physical Optics)법과 비교 검토하여 그 유효성을 검증한다.

• 한국군사과학기술학회지
• /
• 제23권4호
• /
• pp.328-336
• /
• 2020

This paper presents an asymptotic analysis method using the PO(physical optics) approximation technique to analyze the scattering contribution of an electrically large object partially coated with a radar absorbing material(RAM). By using the feature of the PO technique that can calculate the equivalent current value for each mesh independently, instead of analyzing the entire structure, scattering analysis was performed only by calculating the current on the area where the RAM coating is applied. By the numerical examples, the accuracy and the computation time of the proposed method were verified, and the computational efficiency of inverse synthetic aperture radar(ISAR) of the electrically large objects that require enormous resources is improved.