Re-examination of Analytical Models for Microwave Scattering from Deciduous Leaves

Oh, Yi-Sok,Hong, Jin-Young 弘益大學校 科學技術硏究所 2005 科學技術硏究論文集 Vol.16 No.-

본 논문은 활엽수의 잎에 대한 전파 산란 모델들의 정확성을 수치 해석적 방법인 method of moment(mom)로 비교, 검증하였다. 나뭇잎에 대한 전파 산란 모델로는 Rayleigh모델, GRG모델, PO모델이 있으며, PO모델은 나뭇잎을 resistive sheet으로 근사화하여 계산했다. 잎에 대한 전파 산란 모델들의 유효영역을 method of moment의 수치적 결과와 비교하였으며 두께가 얇은 유전율 디스크에 대해서는 전파 산란 모델들의 유효영역을 확장할 수 있음을 알아냈다. 나뭇잎의 두께(0.2∼0.4mm)가 매우 얇기 때문에 GRG모델과 PO모델 둘다 나뭇잎에 대한 마이크로파 해석에 사용할 수 있다.

시간영역 유한차분법을 이용한 안테나 해석에 관한 연구

오이석,손영규 弘益大學校 科學技術硏究所 1995 科學技術硏究論文集 Vol.6 No.-

The input impedance, return loss, wave propagation process, and other characteristics of a microstrip patch antenna have been analyzed using the Finite-Difference Time-Domain (FDTD) method. Among other absorbing boundary conditions(ABC), the Second order dispersive Boundary Condition(DBC) was used for front and end walls and the Mur's first order ABC was used for top, bottom, and side walls in this FDTD computation. The Current distribution on the microstrip antenna was obtained by FDTD and radiation pattern of the antenna could be computed using the current distribution. The effect of the feedign position has been also investigated in this paper.

임피던스 경계 조건을 이용한 바다 표면에서의 전파 산란에 대한 수치적 해석

오이석 弘益大學校 科學技術硏究所 1998 科學技術硏究論文集 Vol.9 No.2

In this paper, electromagnetic wave scattering from the randomly rough sea surfaces was computed using the Method of Moment/ Monte Carlo method. The integral equations of that the electric and the magnetic fields as functions of the surface electric and magnetic currents are formulated using the impedance boundary conditions. Sea surfaces are generated numerically by using the relationship between the wind speed and the surface roughness parameters which is obtained empirically. The directional rough surface generated by computer shows both vertical and horizontal skewness. Then, the electric fields scattered from the nonlinear directional rough surfaces are computed using the method of moments and the Monte Carlo method. A tapered impedance sheet was used to reduce the edge effect to improve the computation of the scatting coefficient at large incidence angles. It was shown that the computation results for sea surface scattering agreed well with the new PO model.

Ku-밴드 전파산란 측정용 레이다의 보정기술

오이석,이원달 弘益大學校 科學技術硏究所 1997 科學技術硏究論文集 Vol.8 No.-

본 논문에서는 network analyzer와 안테나를 이용하여 Ku-밴드 레이다 시스템을 구성하고, 그 레이다 시스템을 이용하여 RCS를 정확히 측정할 수 있는 기술을 개발한다. 정확한 산란 세기를 측정하기 위해서는 레이다 시스템을 정확히 보정하는 기술(calibration technique)이 필요하다. 본 논문에서는 레이다 시스템을 정확히 보정하기 위해서 RCS를 알고 있는 sphere, cylinder, trihedral의 이론적 RCS를 구하고 보정되지 않은 레이다 시스템으로 측정한 RCS와 비교한다. 여기에서 system loss, 거리 보정, 안테나 위치 보정과 같은 오차를 줄이고 산란 특성을 정확히 계산하는 보정기술을 연구하였다.

광대역무선통신(LMDS) 마이크로스트립 패치 안테나 설계 및 제작

吳二錫,弘振榮 弘益大學校 科學技術硏究所 2001 科學技術硏究論文集 Vol.12 No.-

Design, fabrication and measurement of an LMDS microstrip array antenna are presented in this thesis. At first, basic principles for antenna design has been reviewed. Then 8x8 microstrip array antenna was designed using EM simulators at 24.5GHz. The return losses and the patterns of the microstrip array antennas were simulated using CAD tools to get optimum results. For Tx/Rx antenna, The single-fed dual resonance patch antenna drives perpendicular polarizations at two resonant frequencies from a rectangular patch radiator, using aperture coupling via a bended single-feeding line and a cross-shaped slot. The 8 X 8 array antennas were fabricated based on the simulation results and measured using the network analyzer. the measurements show that this 8x8 array antenna has the resonant frequency of 24.6GHz, the return loss of -21.3dB at the frequency, Band width of 720MHz(VSWR < 2), the gain of 25.47dBi. E-plane and H-plane of the side-lobe level are -19dB, -17dB respectively. The HPBWs of the principal E-plane and principal H-plane are 9.5?respectively.

모멘트 기법을 이용한 유전체 거친 표면에서의 전자파 산란 특성 연구

이병훈,오이석 弘益大學校 科學技術硏究所 1996 科學技術硏究論文集 Vol.7 No.2

Electromagnetic wave scattering from a one-dimensional dielectric randomly rough surface is analyzed using the Moment Method which is one of popular numerical methods. At first, a set of coupled integral equations are formulated using the wave equation, the second Green's theorem and the boundary conditions. The coupled integral equations are solved by the Moment Method for a segment of a randomly rough dielectric surface. Then, the scattering coefficients from a given dielectric rough surface is computed suing the Monte Carlo Method. The numerical results are compared with the small perturbation method (SPM) for a surface which roughness is reside in the validity region for the SPM. The numerical method is utilized for prediction of scattering coefficients from various kinds of dielectric rough surfaces.

Effect of Soil Moisture and Surface Roughness on Radar Backscattering from Soil Surfaces

Oh, Yi Sok 대한원격탐사학회 1995 International Symposium on Remote Sensing Vol.11 No.1

A Semi-empirical Model for Microwave Polarimetric Radar Backscattering from Bare Soil Surfaces

Oh, Yi-Sok The Korean Society of Remote Sensing 1994 大韓遠隔探査學會誌 Vol.10 No.2

A semi-empirical model for microwave polarimetric radar backscattering from bare soil surfaces was developed using polarmetric radar measurements and the knowledge based on the theoretical and numerical solutions. The microwave polarimetric backscatter measurements were conducted for bare soil surfaces under a variety of roughness and moisture conditions at L-, C-, and X-band frequencies at incidence angles ranging from 10` to 70`. Since the accrate target parameters as well as the radar parameters are necessary for radar scattering modeling, a complete and accurate set of ground truth data were also collected using a laser profile meter and dielectric probes for each surface condition, from which accurate measurements were made of the rms height, correlation length, and dielectric constant. At first, the angular and spectral dependencies of the measured radar backscatter for a wide range of roughnesses and moisture conditions are examined. Then, the measured scattering behavior was tested using theoretical and numerical solutions. Based on the experimental observations and the theoretical and numerical solutions, a semi-empirical model was developed for backscattering coeffients in terms of the surface roughness parameters and the relative dielectric constant of the soil surface. The model was found to yield very good agreement with the backscattering measurements of this study as well as with independent measurements.

A Semi-empirical Model for Polarimetric Radar Backscattering from Bare Soil Surfaces

Oh, Yi-Sok The Korean Society of Remote Sensing 2001 大韓遠隔探査學會誌 Vol.17 No.2

A semi-empirical polarimetric backscattering model for bare soil surfaces is presented. Based on measurements by using polarimetric scatterometers and the JPL AirSAR, as well as the theoretical models, the backscattering coefficints $\sigma$$^0_w$, $\sigma$$^0_{hh}$ and $\sigma$$^0_{vh}$, and the parameters of the copolarized phase-difference probability density function, namely the degree of correlation $\alpha$ and the copolarized-phase-difference $\zeta$, are modeled empirically in terms of the volumetric soil moisture content m$_v$ and the surface roughness parameters $k_s$ and $k_l$, where k=2$\pi$f/c, s is the rms height and l is the correlation length.

Comparative Evaluation of Two Analytical Models for Microwave Scattering from Deciduous Leaves

Oh, Yi-Sok The Korean Society of Remote Sensing 2004 大韓遠隔探査學會誌 Vol.20 No.1

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.