• 한국전자파학회지:전자파기술
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• 제12권4호
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• pp.13-23
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• 2001

최근, 디지털 통신 기술의 발전과 더불어 소출력 무선설비의 신뢰성이 향상되고, 이동성을 기반으로 한 무선 정보통신 수요가 급증함에 따라 소출력 무선설비의 수요가 폭발적으로 증가하고 있다. 본 연구에서는 국내 소출력무선설비 관리제도를 조명해 보고, 새로운 통신서비스와 기술을 수용하는데 필요한 제도개선 방안을 제시하였다. 주파수 자원 연구, 전파 환경 연구 등 일부 연구가 수반되어야 하는 부분도 있지만, 본 연구에서 논의한 소출력 무선설비 관리제도상의 개선방향이 전파관리 측면에서나 전파 이용기술 개발 및 근거리 전파통신 활성화 측면에서 그 기대를 만족시킬 수 있으리라 기대된다.

• 한국전자파학회논문지
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• 제13권2호
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• pp.217-224
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• 2002

FDTD 해석법에서 공간적 셀의 크기는 해석의 정확도를 결정하는 중요한 요소이다. 하지만 정확도를 향상시키기 위하여 진의 크기를 줄이게 되면, 해석시간과 기억용량의 증가를 초래하게 되는데 서브 그리딩을 사용하여 이를 해결할 수 있다. 본 논문에서는 관심영역만 세밀하게 해석할 수 있는 3차원 서브 그리딩법을 기술하고 이를 응용하여 몇 가지의 구조를 해석하였다. 제안한 방범의 타당성을 화인하기 위하여 균일 그리딩과 서브 그리딩을 적용하여 특성을 해석하고 그 격과를 비교하였다. 제안한 방법을 사용하였을 경우 동일한 정확도에서 균일 그리딩에 비하여 6배의 해석시간의 줄었고 기억용량은 2.5배 정도 줄어들었다.

• Journal of electromagnetic engineering and science
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• 제17권2호
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• pp.65-70
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• 2017

The design and implementation aspects of a new single-balanced mixer for ultra-wideband (UWB) applications are presented in this study. The proposed mixer utilizes a miniaturized UWB ring coupler as a balun, consisting of a pair of in-phase and inverted-phase transitional structures. The well-balanced UWB performance of the ring coupler, aside from the optimized diode matching, results in improved conversion loss and inter-port isolations for a wide bandwidth. The size of the implemented single-balanced diode mixer is reduced to about 60% of the area of the conventional single-balanced ring diode mixer. The measured results of the proposed mixer exhibit an average conversion loss of 7.5 dB (minimum 6.7 dB) and a port-to-port isolation of greater than 18 dB over a UWB frequency range of 3.1-10.6 GHz. The measured results agree well with the simulated results.

• Journal of electromagnetic engineering and science
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• 제19권1호
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• pp.20-30
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• 2019

A wide-band multiple-input multiple-output (MIMO) antenna with dual-band (2.4 and 5 GHz) operation is proposed for premium indoor access points (IAPs). Typically, an omni-directional pattern is used for dipole antennas and a directional radiation pattern is used for patch antennas. In this paper, both antenna types were used to compare their performance with that of the proposed $2{\times}2$ MIMO antenna. We simulated and measured the performance of the MIMO antenna, including the isolation, envelope correlation coefficient (ECC), mean effective gain (MEG) for the IAPs, and the throughput, in order to determine its communication quality. The performance of the antennas was analyzed according to the ECC and MEG. The proposed antenna has sufficient performance and excellent characteristics, making it suitable for IAPs. We analyzed the communication performance of wireless networks using the throughput data of a typical office environment. The network throughput of an 802.11n device was used for the comparison and was conducted according to the antenna type. The results showed that the values of the ECC, MEG, and the throughput have unique characteristics in terms of their directivity, antenna gains, isolation, etc. This paper also discusses the communication performance of various aspects of MIMO in multipath situations.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 C
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• pp.1523-1525
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• 1996

Partial discharges(PD) in air insulated electric power systems cause power loss, produce interfering electromagnetic radiation, and can indicate incipient failure. An understanding of PD in air gap is clearly important. The Wavelet transformation is an extended method of fourier transformation. The fourier method is a powerful tool for signal analysis, but it can't include informations for time. However tile wavelet transformation analysis can include on the informations of time and frequency at the same time. In this paper we apply the wavelet transformation to the PD signals in needle-plane air gap for tile purpose of analysis of developing aspects of PD. We can analyze the developing aspects of PD, namely, PD current, repetition rates, width of pulse distribution region, pulseless region and frequencies distribution of PD pulses.

• 한국환경과학회지
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• 제23권4호
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• pp.543-552
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• 2014

Fixed Electromagnetic Wave Surface Velocimetry (Fixed EWSV) has been started to be used to measure flood discharge in the mountain stream, since it has various advantages such that it works well to continuously measure stream discharge even in the night time as well as very strong weather. On the contrary, the Fixed EWSV only measures single point surface velocity, thus it does not consider varying feature of the transverse velocity profile in the given stream cross-section. In addition, a conventional value of 0.85 was generally used as the ratio for converting the measured surface velocity into the depth-averaged velocity. These aspects could bring in error for accurately measuring the stream discharge. The capacity of the EWSV for capturing rapid flow velocity was also not properly validated. This study aims at conducting error analysis of using the EWSV by: 1) measuring transverse velocity at multiple points along the cross-section to assess an error driven by the single point measurement; 2) figuring out ratio between surface velocity and the depth-averaged velocity based on the concurrent ADCP measurements; 3) validating the capacity of the EWSV for capturing rapid flow velocity. As results, the velocity measured near the center by the fixed EWSV overestimated about 15% of the cross-sectional mean velocity. The converting ratio from the surface velocity to the depth-averaged velocity was 0.8 rather than 0.85 of a conventional ratio. Finally, the EWSV revealed unstable velocity output when the flow velocity was higher than 2 m/s.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 추계학술대회 초록집
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• pp.179.2-179.2
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• 2010

This research has been performed to provide fundamental design aspects of Permanent Magnet Synchronous Generators(PMSGs) for a kilowatt class wind turbine. When it comes to kilowatt class wind turbines, the typical type of generators are Axial Flux Permanent Magnet(AFPM) generators. However, Radial Flux Permanent Magnet(RFPM) generators have been optimally designed to study the output characteristics of a kilowatt class wind turbine in Graduate School of Wind Energy, POSTECH. An existing squirrel-cage rotor has been modified for another newly designed permanent magnet rotor to utilize the commercially existing stator rotor. Electromagnetic analysis utilizing Finite Element Methods tools(ANSYS, MAXWELL 2D) has been applied to analyze the system.

• 전자공학회논문지A
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• 제31A권9호
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• pp.53-63
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• 1994

In indoor radio systems, vehicular communication systems, and land mobile systems, a very important problem is that of maintaining stable communications at all locations. Therefore solutions for the indoor propagation problem are important aspects of the mobile communication system. leaky coxial cables are finding increasing use in communications systesm involving mines, tunnels, tailroads, and highways, and in new obstacle detection, or guided radar, schemes for ground transportation and perimenter surveilance. In this paper a leaky coaxial cable having periodic slots in the outer conductor is described to obtain the propagation modes in the various environments. We use aneccentric cylindrical model to develop the theory for surface-wave propagation on the cable. Numerical Results are also included for the propagation constants, field distribution and current distribution. First, we derive the electromagnetic equation for leaky coaxial cable having symmetrical periodic slots using mode-matching method and Floquet's theorem, and then find various modes, propagation constants, field distribution, etc.

• 한국광학회지
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• 제2권1호
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• pp.36-49
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• 1991

The coherence properties of electromagnetic fields are reviewed, based on both the classical and quantum theories. The elementary concepts, employed frequently in the discussion of interference phenomena, are summarized. The well-known interference phenomena are described in terms of second-order coherences. The coherence theory in space-frequency domain is introduced and the coherent mode representation is presented. The generation and propagation of coherence of light are analysed and it is shown that the coherence of light is developed as light propagates. The quantum theory goes parallel with the classical theory, via the optical equivalence theorem. There are, however, certain nonclassical characteristics of light, which may not be easily understood in classical therms. These nonclassical phenomena are believed to originate from the particle aspects of light. The quantum effect on the interfernce phenomena is analysed and finally the outlook of the future research is briefly mentioned.

• 한국전자파학회논문지
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• 제28권1호
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• pp.42-48
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• 2017

지하에 매설된 관을 탐지하기 위해 지하탐사레이다(GPR) 신호의 특성을 수치해석으로 조사하였다. GPR 시스템의 송수신부, 지하매질, 유전체로 채워진 플라스틱 관을 시간영역유한차분법(FDTD)으로 모델링하였다. GPR 신호의 양상을 관찰하기 위해서 관의 지름과 관 속에 채워진 물질의 유전율 변화에 따른 FDTD 모의계산을 수행하였다. 유전체로 채워진 플라스틱 관에 의해 산란된 GPR 신호는 관 외부의 전방 볼록면 반사파와 관 내부의 후방 오목면 반사파의 중첩으로 나타났다. 두 파의 진폭, 극성, 지연시간은 플라스틱 관 사이즈와 관 내부 충진 물질의 유전율에 종속되어 있음을 알 수 있었다.