• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1990.06a
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• pp.813-816
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• 1990

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.5
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• pp.863-871
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• 2003

In this paper, we design a high stable Ku-band phase-locked dielectric resonant microwave oscillator with the gate voltage controls of p-HEMT. By adapting the nonlinear equivalent elements which affects phase noise of microwave oscillator, we optimize the nonlinear elements of p-HEMT to have low phase noise operation. Using the scattering parameters according to bias voltages, we designed the gate voltage control microwave dielectric resonant oscillator and phase-locked loop circuits is applied to have the high stable operations. Designed microwave oscillator as a local oscillator of digital microwave communication shows that output power is 9.17dBm at 10.75GHz and it's phase noise is -88dBc/Hz at 10KHz offset frequency.

• Proceedings of the Optical Society of Korea Conference
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• 2000.08a
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• pp.44-45
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• 2000

Shack-Hartmann 센서로부터 얻어진 기울기 정보로부터 파면을 재구성하고 분석하기 위해서는 각각의 점 영상에 대한 위상 구배로부터 파면의 위상을 재구성할 수 있는 수학적인 알고리즘이 필요하다. 파면의 위상을 재구성하기 위한 알고리즘은 Hudgin, Fried, Southwell이 제시한 세 가지 방법에 대한 연구결과가 가장 많이 알려져 있다. 본 연구에서는 CCD 카메라로부터 전송된 디지털 영상에서 각각의 점 영상의 중심점을 추출하여 점 영상의 이동정보로부터 수평과 수직방향의 기울기를 계산하고, 이를 바탕으로 최소제곱법(least-square fitting)을 사용하여 위상을 재구성하였다. 파면의 기울기 정보로부터 파면을 재구성하기 위해 기존의 이론을 바탕으로 행렬계산법을 사용하여 각각의 경우를 일반화하였고, 위상의 복구와 파면의 보정에 따른 해석적인 오차의 관계를 논의하였다. (중략)

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.39-48
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• 2013

This paper develops a 2-D moving least squares(MLS) difference method for Stefan problem by extending the 1-D version of the conventional method. Unlike to 1-D interfacial modeling, the complex topology change in 2-D domain due to arbitrarily moving boundary is successfully modelled. The MLS derivative approximation that drives the kinetics of moving boundary is derived while the strong merit of MLS Difference Method that utilizes only nodal computation is effectively conserved. The governing equations are differentiated by an implicit scheme for achieving numerical stability and the moving boundary is updated by an explicit scheme for maximizing numerical efficiency. Numerical experiments prove that the MLS Difference Method shows very good accuracy and efficiency in solving complex 2-D Stefan problems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.10
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• pp.1077-1086
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• 2014

We propose a design method of a Rotman lens for curved array antenna applicable to conformal array. In this paper, design equations are derived to obtain an array curve, transmission line lengths of a Rotman lens in conjunction with a curved array antenna, and the phase error of a Rotman lens based on these design equations is minimized through the beam curve optimization procedure and the refocusing procedure. Rotman lenses designed by the proposed design equations and design procedures still maintain 3 focal points, can feed a convex or concave array antenna with circular curve, parabolic curve, V-shaped curve, etc as well as a straight line array antenna, and have minimal phase error.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.11
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• pp.894-901
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• 2017

In the existence of motion, azimuth phase error due to accuracy limitation of GPS/IMU and system delay is unavoidable and it is essential to apply autofocus to estimate and compensate the azimuth phase error. In this paper, autofocus algorithm using MWLS(Modified WLS) is proposed. It shows the robust performance compared with original WLS using new target selection/sorting metric and iterative azimuth phase estimation technique. SAR raw data obtained in a captive flight test is used to validate the performance of the proposed algorithm.

• The Journal of the Acoustical Society of Korea
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• v.26 no.6
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• pp.276-285
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• 2007

In this paper it was discussed and compared measured loudspeaker impedance curve with ones reconstructed by TS parameters estimated using four kinds of parameter estimation methods developed in frequency domain. Frequency dependent parameters were introduced and derived using least square error minimization technique. For known dynamic mass TS parameter estimation methods were reviewed and also proved non-uniqueness of these parameters by simulation method. Minimum phase transformation was adopted to derive phase information from magnitude of loudspeaker electrical impedance curve measured by one channel analyzer.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.855-860
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• 2005

For the accurate measurement of acoustic properties of a surface, efforts have been made to reduce errors caused by external disturbance. If the reflection coefficient is considered as a transfer function between reflected wave and incident wave, causality is required between them and the reflection coefficient should be of minimum phase. In this thesis, the minimum phase condition is applied to measure correct reflection coefficient. The reflection coefficient is approximated as a rational function in the Z domain by minimizing the sum square error. Then the minimum phase reflection coefficient is reconstructed using the distribution of poles and zeros of the reflection coefficient model. The incident wave, the reflected wave and the impulse response function of causality are recalculated from the minimum phase reflection coefficient for further applications.

• Proceedings of the KIEE Conference
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• 2006.07d
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• pp.1773-1774
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• 2006

나노 기술의 급격한 발달에 따라 나노미터 수준의 정밀도를 갖는 초정밀 측정 기술이 여러 분야에서 요구되고 있다. 헤테로다인 레이저 간섭계를 이용하여 초정밀 위치 측정을 하려고 할 때, 광학기기 자체의 불완전함에서 발생하는 비선형성 오차는 주요한 요소로 작용한다. 본 논문에서는 헤테로다인 레이저 간섭계 시스템에서의 비선형성을 보정해주기 위해 적응형 알고리즘을 제안한다. 기준 입력인 정전용량센서와 최소자승법을 이용하여 보정변수를 구한 후, 반복 최소자승법을 이용하여 비선형성에 따른 타원 위상을 비선형성이 보정된 원 위의 위상으로 사상시킨다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.10 s.103
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• pp.1131-1136
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• 2005

For the accurate measurement of acoustic properties of a surface, efforts have been made to reduce errors caused by external disturbance. If the reflection coefficient is considered as a transfer function between reflected wane and incident wave, the causality is required between them and the reflection coefficient should be of minimum phase. In this thesis, the minimum phase condition is applied to measure correct reflection coefficient. The reflection coefficient is approximated as a rational function In the Z domain by minimizing the sum square error. Then the minimum phase reflection coefficient is reconstructed using the distribution of poles and zeros of the reflection coefficient model.