• 한국군사과학기술학회지
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• 제25권4호
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• pp.339-346
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• 2022

The importance of stealth technology is increasing in modern warfare, and Radar Cross Section(RCS) is widely used as an indicator of stealth technology. It is useful to measure RCS using an image-based near-field to far-field transformation algorithm in short-range monostatic conditions. However, the near-field measurement system requires a longer measurement time compared to other methods. In this work, it is proposed to reduce the measured data using an interpolation method in azimuth angular domain. The calculated far-field RCS values according to the sampling rate is shown, and the performance of the algorithm applied with interpolation in the angular domain is presented. It is shown that measurement samples can be reduced several times by using the redundancy in the angular domain while producing results similar to the conventional method.

• 한국전자파학회논문지
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• 제24권3호
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• pp.316-323
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• 2013

본 논문에서는 안테나의 원거리장 특성 및 Electromagnetic Compatibility(EMC) testing을 위한 근거리 원거리장 변환에 대한 연구이다. EMC testing은 광대역 신호 및 거대 구조에 대한 원거리장 측정과 같은 복잡한 과정이 필요하다. EMC 측정 문제를 해결하기 위해, Stratton-Chu 공식을 이용하여 간단하고 직접적인 방법으로 원거리장을 예측하였다. 특히 Stratton-Chu 공식을 이용한 예측은 자유 공간상의 평면파를 통해 해석값을 비교하여 유효성을 검증했다. 패치 안테나의 근거리장 추출과 원거리장 확인을 위해, full-wave 시뮬레이션을 이용하여 Stratton-Chu 계산 결과를 비교 및 검증하였으며, 6 % 이내의 오차로 원거리장의 크기를 예측했다.

• 대한전자공학회논문지TC
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• 제39권11호
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• pp.28-33
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• 2002

본 논문에서는 유한 차분 시간영역 해석법을 이용하여 PCS용 임피던스 정합 모노폴 마이크로스트립 안테나를 해석하였다. FDTD 격자를 나누기 위해서 Berenger 가 제안한 완전정합층 흡수경계조건을 사용하였다. 소스 신호로 Gaussian 펄스를 사용하고, 급전부는 내부저항 전압원을 적용시켜 모델링 하였다. FDTD법은 근계 해석 기술이므로 안테나의 방사패턴과 이득을 구하기 위해서는 시간영역과 주파수영역에 모두 적용이 가능한 근계를 원계로 변환하는 것이 필요하다. 따라서 원계 방사패턴을 계산하기 위해 주파수영역 변환을 사용하였다. FDTD법에 의해 얻어진 해석 결과는 HFSS 소프트웨어를 사용한 해석 결과와 비교 분석하였으며, 만족한 결과를 얻었다.

• Structural Engineering and Mechanics
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• 제21권4호
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• pp.437-450
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• 2005

In this study, a complete analysis of soil-structure interaction problems is presented which includes a modelling of the near surrounding of the building (near-field) and a special description of the wave propagation process in larger distances (far-field). In order to reduce the computational effort which can be very high for time domain analysis of wave propagation problems, a special approach based on similarity transformation of the infinite domain on the near-field/far-field interface is applied for the wave radiation of the far-field. The near-field is discretised with standard Finite Elements, which also allows to introduce non-linear material behaviour. In this paper, a new approach to calculate the involved convolution integrals is presented. This approximation in time leads to a dramatically reduced computational effort for long simulation times, while the accuracy of the method is not affected. Finally, some benchmark examples are presented, which are compared to a coupled Finite Element/Boundary Element approach. The results are in excellent agreement with those of the coupled Finite Element/Boundary Element procedure, while the accuracy is not reduced. Furthermore, the presented approach is easy to incorporate in any Finite Element code, so the practical relevance is high.

• 한국전자파학회논문지
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• 제15권5호
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• pp.473-479
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• 2004

본 논문에서는 cellular 이동통신용 기지국 안테나와 같이 사용되는 파장에 비해 비교적 부피가 큰 해석 대상 체의 근거리장에서 전력 밀도를 계산한 내용을 다루었다. 현재 국내에서 cellular 이동통신 기지국용 안테나로 널리 사용되는 판넬형 섹터 안테나를 모델링하고 FDTD 계산법으로 reactive 근거리장의 전자계 분포를 계산하였으며 near to far 변환 통하여 원거리장의 안테나 이득을 구하였다. 그리고 radiating 근거리장의 전력밀도를 계산하기 위하여 원거리장의 이득을 이용하여 gain-based 모델을 적용하였다. 끝으로 radiating 근거리장의 전력밀도 계산 결과와 ICNIRP guideline의 전력밀도에 대한 일반인 및 직업인의 노출 제한 값을 고려하여 인증 거리(compliance distance)를 산출하였다. Gain based 모델을 이용한 계산 결과를 표면주사(surface scanning) 방식을 이용한 전력밀도의 측정 결과와 비교한 결과 주방사 방향의 중심 위치에서 계산된 값은 gain based model을 이용할 경우 -14.55 ㏈m이고, 측정된 값은 -15.75 ㏈m으로 케이블 및 커넥터의 손실을 감안하면 매우 정확한 것으로 나타났다.

• 대한조선학회논문집
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• 제42권2호
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• pp.113-123
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• 2005

A higher order panel method based on B-spline representation for both the geometry and the solution is developed for the analysis of steady flow around marine propellers. The self-influence functions due to the normal dipole and the source are desingularized through the quadratic transformation, and then shown to be evaluated using conventional numerical quadrature. By selecting a proper order for numerical quadrature, the accuracy of the present method can be increased to the machine limit. The far- and near-field influences are shown to be evaluated based on the same far-field approximation, but the near-field solution requires subdividing the panels into smaller subpanels continuously, which can be effectively implemented due to the B-spline representation of the geometry. A null pressure jump Kutta condition at the trailing edge is found to be effective in stabilizing the solution process and in predicting the correct solution. Numerical experiments indicate that the present method is robust and predicts the pressure distribution on the blade surface, including very close to the tip and trailing edge regions, with far fewer panels than existing low order panel methods.

• 정보저장시스템학회:학술대회논문집
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• 정보저장시스템학회 2005년도 추계학술대회 논문집
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• pp.32-37
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• 2005

We developed a numerical simulator in order to study the Super-RENS/ROM (Super REsolution Near-Field Structure, Read Only Memory) using 3-dimensional FDTD (finite difference time domain) method. The simulation can be performed by three steps. In the first step, we utilized the vector-diffraction theory to calculate the characteristics of incident laser beam from the object-lens to the surface of the disk. At the second step, we fed the calculated result as an input for the main FDTD simulations on the optical layers in the disk structure. After performed the FDTD simulations, we took near-to-far field transformation for the reflected signal, from the surface of the disk to the detector. Finally, we can get reflected signal at the photo-diode. Using this developed simulator, we were able to study about the reading signal from various disk structures as a function of a laser beam position. We calculated reading signals for various pit sizes for Super-ROM structure, and it is found that the simple optical diffraction theory can not explain the reading mechanism of Super-ROM, and more complicated temperature dependent physics must be involved.

• 정보저장시스템학회논문집
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• 제2권2호
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• pp.138-143
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• 2006

We developed a numerical simulator in order to study the Super-RENS/ROM (Super REsolution Near-Field Structure, Read Only Memory) using 3-dimensional FDTD (finite difference time domain) method. The simulation can be performed by three steps. In the first step, we utilized the vector-diffraction theory to calculate the characteristics of incident laser beam from the object-lens to the surface of the disk. At the second step, we fed the calculated result as an input for the main FDTD simulations on the optical layers in the disk structure. After performed the FDTD simulations, we took near-to-far field transformation for the reflected signal, from the surface of the disk to the detector. Finally, we can get reflected signal at the photo-diode. Using this developed simulator, we were able to study about the reading signal from various disk structures as a function of a laser beam position. We calculated reading signals for various pit sizes for Super-ROM structure, and it is found that the simple optical diffraction theory can not explain the reading mechanism of Super-ROM, and more complicated temperature dependent physics must be involved.

• 한국항공우주학회지
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• 제33권4호
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• pp.1-6
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• 2005

적대적 환경에서 임무를 수행하는 비행체의 레이다 포착에 관련된 스텔스 기술이 주요 설계 문제로 부각되고 있다. 레이다 회피 기능을 증대시키는 방안들을 분석하기 위해서는 Maxwell 방정식을 해석하는 기법이 필요한데, 본 연구에서는 기본 수치기법으로 다학제 최적설계 연구에 적합한 CFD 기법을 이용하였다. 시간 영역 전자기장 데이터를 DFFT 알고리즘을 이용하여 주파수 영역으로 변환한 후, 근방-원방 변환에 기초한 Green 함수 관계식을 사용하여 RCS 특성을 예측하였다. 검증을 위해 완전전도 실린더 주위 TE 모드를 고려하였으며, CFD 기법을 원용한 CEM 코드의 가능성을 확인하기 위해 비행체 날개단면 주위의 전자기 산란 현상을 계산하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.612-621
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• 2008

For the purpose of improving accuracy in jet noise prediction and investigating its generation mechanism, high subsonic jets were computed by using compressible Large Eddy Simulation(LES), wherein the inflow forcing or disturbance added in the inflow shear layer was incorporated. The far-field Sound Pressure Levels(SPL) as well as the flow field resulted in good agreement with available experimental data by applying only the high azimuthal modes among the inflow forcing parameters. We found that this result was due to an important role of the inflow forcing upon breaking down the axiymmetric vortices that caused high amplitude velocity and pressure fluctuations. In order to examine generation mechanism of the dominant noise component, wavelet transformation was introduced to reveal the presence of a well-organized structure of pressure fluctuations that originated mainly from vortex motions near the end of the jet potential core. This structure took a train of alternately positive and negative wavelet-transformed pressure regions along the jet distance, spreading towards the downstream with advection and propagation. It was concluded that this structure and its dynamic motion are the reason why a high subsonic jet produces the dominant noise with a particular downstream directivity.