• 전자공학회논문지
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• 제54권2호
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• pp.146-150
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• 2017

OFDM 시스템 앙상블의 대역외 방사는 인접 앙상블의 수신성능에 영향을 주기 때문에 대역외 방사 완화기법의 적용은 매우 중요한 기술에 해당한다. 본 논문에서는 DAB 계열 OFDM시스템 스펙트럼의 대역외 방사 완화 기법과 관련하여 시간영역 윈도윙 방식을 적용한 대역외 방사 완화 기법 적용을 고찰하여 보았으며, 해당 기법을 T-DMB (DAB 모드-1) 및 AT-DMB 향상계층 B-모드 및 Q-모드에 대하여 적용한 결과 약 3dB 정도의 대역외 방사 완화 이득을 얻었다. 또한 BER 성능 측정에서도 해당 기법을 적용함에 따른 성능 저하가 매우 미미함을 확인하였다.

• Nuclear Engineering and Technology
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• 제54권1호
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• pp.255-261
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• 2022

A reliable and well-characterized dosimetry system which is traceable to the international measurement system, is the key element to quality assurance in radiation processing with cobalt-60 gamma rays, X-rays, and electron beam. This is specifically the case for health-regulated processes, such as the radiation sterilization of single use medical devices and food irradiation for preservation and disinfestation. Polyethylene is considered to possess a lot of interesting dosimetric characteristics. In this work, a detailed study has been performed to determine the dosimetric characteristics of a commercialized high-density polyethylene (HDPE) film using Fourier transformed infrared spectrometry (FTIR). Correlations have been established between the absorbed dose and radiation induced infrared absorption in polyethylene having a maximum at 965 cm^-1 (transvinylene band) and 1716 cm^-1 (ketone-carbonyl band). We have found that polyethylene dose-response is linear with dose for both bands up to1000 kGy. For transvinylene band, the dose-response is more sensitive if irradiations are made in helium. While, for ketone-carbonyl band, the dose-response is more sensitive when irradiations are carried out in air. The dose-rate effect has been found to be negligible when polyethylene samples are irradiated with electron beam high dose rates. The irradiated polyethylene is relatively stable for several weeks after irradiation.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
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• pp.560-564
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• 2003

In this paper, we carried out performance analysis of mobile station with built-in antenna for PCS(Personal Communication System) band. The radiation patterns for antenna and mobile phone were simulated by using 3D simulation program, HFSS(High Frequency Structure Simulator) and SEMCAD(Simulation Platform for Electromagnetic Compatibility Antenna Design Dosimetry). We observed radiation pattern variation according to installation of LED(Light Emitting Diode) circuit and ground pattern. The radiation pattern of prototype mobile phone was measured, and the radio sensitivity was measured by using Agilent E5515C and chamber. The measured maximum antenna gain at 1.87GHz was 0.21dBi. The measured radio sensitivity of prototype mobile phone shows proper performances comparable to other models with external antennas.

• 대한기계학회논문집B
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• 제20권10호
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• pp.3371-3380
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• 1996

각종 노(furnace)를 포함하여 보일러, 가스터빈, 우주선 추진기구, 원자로 및 연료전지 등 고온이 열전달 문제를 다루는데 있어서 복사 열전달 연구는 매우 중요하다. 이러한 복사열전달에 대한 연구동향은 최근 복사 물성치(특히 가스에서의)를 예측하기 위한 이론 모델의 개발 및 측정분야와 복사전달 방정식의 해를 비교적 간단하게 구하기 위한 근사해법에 대한 연구로 크게 대별되고 있다. 이러한 두가지 연구방햐은 완전히 분리, 독립되어 있는 것은 아니며 서로 많은 연관성을 가지고 있다. 특히, 비회체가스(nongray gas)의 복사 성질에 대한 모델링은 근사 해법의 계산결과에 큰 영향을 미치게 되므로 가스의 복사 성질의 예측은 매우 중요한 연구 과제가 된고 있다. a Low resolution spectral modeling of water vapor is carried out by applying the weighted-sum-of-gray-gases model (WSGGM) to a narrow band. For a given narrow band, focus is placed on proper modeling of gray gas absorption coefficients vs. temeprature relation used for any solution methods for the Radiative Transfer Equation(RTE). Comparison between the modeled emissivity and the "true" emissivity obtained from a high temperatue statistical narrow band parameters is made ofr the total spectrum as well as for a few typical narrow bands. Application of the model to nonuniform gas layers is also made. Low resolution spectral intensities at the boundary are obtained for uniform, parabolic and boundary layer type temeprature profiles using the obtained for uniform, parabolic and boundary layer type temperature profiles using the obtained WSGGM's with 9 gray gases. The results are compared with the narrow band spectral intensities as obtained by a narrow band model-based code with the Curtis-Godson approximation. Good agreement is found between them. Local heat source strength and total wall heat flux are also compared for the cases of Kim et al, which again gives promising agreement.

• Journal of Communications and Networks
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• 제1권3호
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• pp.166-181
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• 1999

The object of this paper is to investigate the influence of antenna pattern on indoor radio channel characteristics. Different from previous works where this analysis was carried out at a fixed frequency using different antennas, in the present paper (where measurements were taken in a wide frequency range) the variation of the radiation pattern was caused by two factors: the change of the radiation pattern when the same antenna was used at different frequenicies and the use of different type of antennas. To carry out this analysis, frequency domain measurements of the indoor radio channel at 1 GHz, 5.5 GHz, 10 GHz and 18 GHz were collected. Measurements were taken using a network analyzer. Serveral re-alizations of the channel transfer function were obtained varying, for each measurement, the positon of the transmitter and keep-ing the receiver fixed. Estimate of the channel impulse response was obtained from the Inverse Fourier Transform (IFT) of the fre-quency response. The measurements were performed in an office enviroment with mostly metallic walls and inner separations. The obtained data were elaborated to obtain the power versus distance relationship, the Cummulative Distribution Functions(CDFs) of rms Delay Spread(DS) and of the 3 dB frequency correlation band-width. Finally, the 3 dB width of the frequency correlation func-tion has been empirically related to the inverse of the rms DS of the impulse response.

• Journal of electromagnetic engineering and science
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• 제5권2호
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• pp.97-103
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• 2005

This paper describes the measured results of sonobuoy transmitting antenna system for anti-submarine warfare (ASW). Since radiation pattern and power density depend on impedance matching between transmitting RF part and antenna with termination resistance, design of matching circuit is very important for sonobuoy system performance. Matching circuit is designed by Smith chart using control of L and C. In standing wave ratio(SWR) measurement using Network Analyzer, SWR of antenna with matching circuit observed 1.5 below at the assigned VHF band. It shows very excellent performance comparison with conversional product that is used for the same object. The measured vertical and horizontal radiation patterns are also shown the satisfaction of military specifications. A drop out of sonobuoy system on the sea is happened when angle of elevation direction is over 10 degrees, and it is conformed that it takes less than I second return to original signal level. The required electric power density is $83\;mW/m^2$ in the military specification, and measured electric power density is observed over average $110\;mW/m^2$ at all frequency bands.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 추계종합학술대회 B
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• pp.693-696
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• 2008

4세대 이동 통신 서비스를 위한 시스템들은 멀티미디어 서비스를 지원하기 위해 대용량 데이터 전송이 가능한 OFDM(Orthogonal frequency Division Multiplexing) 방식을 이용하고, 서비스의 질을 높이기 위해 통신 영역을 세분화하여 Macro Cell, Pico Cell, Femto Cell 등으로 구성하고 있다. 통신 영역의 세분화로 인해 기존에 단일 Cell 을 사용하는 것과 달리 동일한 채널에서 Cell을 중첩시켜 서비스해야 하므로 시스템들 간의 대역간 간섭이 문제가 된다. 특히, OFDM 신호는 독립적으로 변조된 많은 부반송파들로 구성되므로 이들이 동위상으로 더해질 때 신호의 진폭이 증가하여 PAPR (Peak-to-Average Power Ratio) 문제가 발생한다. 높아진 PAPR은 전력 증폭기와 같은 비선형 소자를 통과하면서 신호의 왜곡이 발생하여 대역 외 스펙트럼 방출이 발생하므로 대역간 간섭으로 작용한다. 본 논문에서는 대역간 간섭을 최소화하기 위해 PAPR 감소기법을 적용한 후 전력증폭기와 같은 비선형 소자를 통과하면서 발생하는 대역 외 스펙트럼 방출에 대하여 분석하였다.

• 한국위성정보통신학회논문지
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• 제9권3호
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• pp.104-108
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• 2014

한국형발사체의 표면에 장착되는 UHF-대역 안테나의 표면에 발생하는 결빙을 모델링하고, 이러한 결빙이 안테나의 공진주파수, 반사손실 및 방사패턴 등의 주요 특성에 미치는 영향을 분석하였다. 안테나 표면결빙을 모델링하기 위해 $-180^{\circ}C$의 얼음층에 대한 비유전율을 추출하였고 추출된 비유전율을 이용하여 안테나 표면결빙 모델을 제안하였다. 중심주파수가 UHF-대역인 안테나 표면에 1mm의 결빙이 되었을 경우의 표면결빙 모델을 적용하여 시뮬레이션 한 결과, 표면결빙에 의해 안테나의 공진주파수가 21MHz 하향 되었고, 방사패턴도 전 방향에 대해 전체적으로 10dB 이상의 성능저하가 발생되었다. 따라서 실제 안테나 표면에 결빙이 발생할 경우 안테나 성능에 심각한 영향을 미칠 것으로 판단된다.

• 한국전자파학회논문지
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• 제15권4호
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• pp.397-405
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• 2004

본 논문에서는PCS대역 안테나내장형 단말기의 성능에 관하여 살펴보았다. 안테나와 안테나 내장형 단말기의 방사패턴을 3차원 전산모의실험 프로그램인 HFSS(High Frequency Structure Simulator)와 SEMCAD(Simulator Platform for Electromagnetic Compatibility Antenna Design and Dosimetry)를 이용하여 전산모의실험하였다. 단말기에 장착된 LED(Light Emitting Bi여e) 회로와 접지판의 형태에 따른 방사패턴의 변화를 살펴보았으며, 외장형안테나 단말기와 내장형 안테나 단말기의 안테나 방사패턴을 원거리장 측정 시스템을 사용하여 전자파 무반사실에서 측정하였다. 측정결과 내장형 안테나는 전산모의실험 결과와 유사한 패턴을 보였다. 그리고 전자파 무반사실에서 Agilent E5515C를 사용하여 안테나 외장형 단말기와 안테나 내장형 단말기의 무선감도를 측정하여 비교하였다. 측정된 안테나내장형 단말기의 무선감도는 안테나 외장형 단말기의 무선감도와 비교해 유사한 성능을 보였으며 수평면상의 동일편파 무선감도 평균치의 경우 차이가 0.12 ㏈로 나타났다.

• 플랜트 저널
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• 제14권1호
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• pp.42-46
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• 2018

The flow and heat transfer characteristics inside a solar chimney power plant system are analyzed in this article. 3-D model with the $k-{\varepsilon}$ turbulence closure was developed. In this model, to solve the radiative transfer equation the discrete ordinates radiation model was implemented, using a two-band radiation model. To simulate radiation effects from the sun's rays, the solar ray tracing algorithm was coupled to the calculation via a source term in the energy equation. Simulations were carried out for a system with the geometry parameters of the Manzanares power plant. Based on the numerical results, the velocity and temperature distributions were illustrated and the results were validated by comparing with experimental data of the Manzanares prototype power plant. Moreover, temperature profile of the ground surface of the system was illustrated.