• 한국통신학회논문지
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• 제32권10A호
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• pp.1065-1071
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• 2007

본 논문은 도심 협곡 환경에서 마이크로파 대역 다중안테나 이용기술의 주파수 이용효율 특성을 파악하기 위한 3.7GHz와 8GHz의 MIMO 측정 데이터 및 채널 용량을 분석한 결과를 기술하였다. 채널 측정 데이터는 분당의 3-4층 빌딩 밀집지역에서 실험된 데이터를 이용하였으며, 3.7 GHz와 8 GHz대역 전파특성 파라미터를 추출하여 비교 분석하였다. 다중안테나 사용에 따른 채널용량을 분석한 결과 3.7 GHz와 8 GHz 대역의 $2{\times}2$ 다중안테나 환경에서 9.1 bps/Hz와 5 bps/Hz으로 분석되었으며, $4{\times}4$ 안테나 이용 시 각각 21 bps/Hz와 12.5 bps/Hz로 분석되었다. 이를 통해 실외 도심협곡 환경의 신호 대 잡음비와 커버리지 특성을 고려해 볼 때 3.7 GHz대역의 주파수 전송효율이 8 GHz 보다 우월한 특성을 보임을 확인하였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.441-444
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• 2008

This paper describes the development of a circularly polarized microstrip antenna, as a part of the Circularly Polarized Synthetic Aperture Radar (CP-SAR) sensor which is currently under developed at the Microwave Remote Sensing Laboratory (MRSL) in Chiba University. CP-SAR is a new type of sensor developed for the purpose of remote sensing. With this sensor, lower-noise data/image will be obtained due to the absence of depolarization problems from propagation encounter in linearly polarized synthetic aperture radar. As well the data/images obtained will be investigated as the Axial Ratio Image (ARI), which is a new data that hopefully will reveal unique various backscattering characteristics. The sensor will be mounted on an Unmanned Aerial Vehicle (UAV) which will be aimed for fundamental research and applications. The microstrip antenna works in the frequency of 1.27 GHz (L-Band). The microstrip antenna utilized the proximity-coupled method of feeding. Initially, the optimization process of the single patch antenna design involving modifying the microstrip line feed to yield a high gain (above 5 dBi) and low return loss (below -10 dB). A minimum of 10 MHz bandwidth is targeted at below 3 dB of Axial Ratio for the circularly polarized antenna. A planar array from the single patch is formed next. Consideration for the array design is the beam radiation pattern in the azimuth and elevation plane which is specified based on the electrical and mechanical constraints of the UAV CP-SAR system. This research will contribute in the field of radar for remote sensing technology. The potential application is for landcover, disaster monitoring, snow cover, and oceanography mapping.

• Journal of Communications and Networks
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• 제18권3호
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• pp.364-374
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• 2016

With vast amounts of spectrum available in the millimeter wave (mmWave) band, small cells at mmWave frequencies densely deployed underlying the conventional homogeneous macrocell network have gained considerable interest from academia, industry, and standards bodies. Due to high propagation loss at higher frequencies, mmWave communications are inherently directional, and concurrent transmissions (spatial reuse) under low inter-link interference can be enabled to significantly improve network capacity. On the other hand, mmWave links are easily blocked by obstacles such as human body and furniture. In this paper, we develop a multi-hop relaying transmission (MHRT) scheme to steer blocked flows around obstacles by establishing multi-hop relay paths. In MHRT, a relay path selection algorithm is proposed to establish relay paths for blocked flows for better use of concurrent transmissions. After relay path selection, we use a multi-hop transmission scheduling algorithm to compute near-optimal schedules by fully exploiting the spatial reuse. Through extensive simulations under various traffic patterns and channel conditions, we demonstrate MHRT achieves superior performance in terms of network throughput and connection robustness compared with other existing protocols, especially under serious blockage conditions. The performance ofMHRT with different hop limitations is also simulated and analyzed for a better choice of the maximum hop number in practice.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.127-130
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• 2002

In this study, development of a new LTCC material using a non-glassy system was attempted with respect to reducing the fabrication process steps and cost down. Lowering the sintering temperature can be achieved by liquid phase sintering. For LTCC application, the starting material must have quality factor as high as possible in microwave frequency range. And also, the material should have a low dielectric constant for enhancing the signal propagation speed. Regarding these factors, dielectric constants of various materials were estimated by the Clausius-Mosotti equation. Among them, CaWO$_4$ was tamed out the suitable LTCC material. CaWO$_4$ can be sintered up to 98% of full density at 1200$^{\circ}C$ for 3 hours. It's measured dielectric constant, quality factor, and temperature coefficient of resonant frequency were 10.15, 62880GHz, and -27.8ppm/$^{\circ}C$, respectively. In order to modify the dielectric properties and densification temperature, 0.5∼1.5 wt% LiF were added to CaWO$_4$. LiF addition reduced the sintering temperature/time down to 800$^{\circ}C$/10∼30min due to the reactive liquid phase sintering. Dielectric constant lowered from 10.15 to 9.38 and Q x fo increased up to 92000GHz with increasing LiF content.

• 한국광학회지
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• 제15권6호
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• pp.563-568
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• 2004

저손실의 높은 편광 소멸비를 갖는 LiNbO$_3$ 도파로를 만들기 위하여 고온 양자교환 방법을 이용하였다. 이 방법으로 제작된 도파로의 굴절률 특성을 분석하기 위하여 프리즘 결합기 방법으로 도파 모드를 측정하고 IWKB(inverse WKB) 방법을 사용하여 표면 굴절률 변화와 깊이에 대한 굴절률 분포 특성을 관찰하였다. 이러한 방법으로 고온 양자교환법의 주요 인자인 양자교환 온도, LS 농도, 양자교환 시간에 대한 굴절률 변화를 분석하였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.348-351
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• 2006

Initial results of processing data from an experiment performed in November, 2005 are given. A microwave Doppler radar with a knife-like beam ($1.5^0$ - $24.5^0$) was installed on a helicopter. Measurements were made during a flight above the Gorky water storage basin. Power and Doppler spectra of the radar reflected signal were analyzed. The processing has shown that the algorithm developed for the retrieval of the slopes of rough water surface enables one to determine the direction of wave propagation and retrieve the variance of the wave slopes.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 하계종합학술대회논문집
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• pp.38-41
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• 1998

Due to the increasing demand to multimedia services over wireless communication network, LMDS(Local Multipoint Distribution Service) has been proposed as an alternate approach for broadband wireless access network. But LMDS, Which uses the mmwavelength radio spectrum, has been limited for unknown microwave frequency characteristics. In this paper, we analyze the parameters related to the system design on 28GHz frequency: Propagation path loss and rainfall attenuation. Based on these analytical results, the proper cell size in Korea is determined. We also analyze the bit error rate and frame loss rate for various kinds of digital modulation schemes(QAM 4, 16, 64, 256). Finally, we apply to ㅍ service to evaluate a call blocking rate, efficiency and channel capacity.

• 마이크로전자및패키징학회지
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• 제12권1호
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• pp.17-20
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• 2005

In this paper, we presented the quasi-static characteristics of novel microstrip lines with anisotropic grooved dielectric in finite metal. A quasi-static mode-matching method has been used to analyze this new structure and the simulation results are validated through comparison with other available results. The results in this paper show that it is possible to control the propagation characteristics of microstrip lines with the use of anisotropic grooved dielectric in finite metal. Also anisotropic grooved dielectric in microstrip line can be newly added to the design parameters of high performance three dimensional monolithic microwave circuits and other microwave applications.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제51권2호
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• pp.85-91
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• 2002

A novel multi-section power divider configuration is Proposed to obtain wide-band frequency performance up to microwave frequency region. Design procedures for the proposed microwave broadband power divider are composed of a Planar multi-section three-Ports hybrid and a waveguide transformer design procedures. The multi∼section power divider is based on design theory of the optimum quarter- wave transformer Furthermore, in order to obtain the broadband isolation performance between the two adjacent output ports, the odd mode equivalent circuit should be matched by using the lossy element such as resistor. The derived design formula for calculating these odd mode∼matching elements is based on the singly terminated filter design theory. The waveguide transformer section is designed to suppress the propagation of the higher order modes such as waveguide modes due to employing the metallic electric wall. Simulation and experiment show excellent performance of multi section power divider.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권6호
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• pp.296-302
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• 2001

In this paper, the vector finite elements are adopted to calculate eigenvalues of RF and microwave components. Simulation results show that spurious are completely avoided because of the divergence free nature of the vector elements. This paper seeks to extend these low-order elements to higher orders to improve the accuracy of numerical solution. Investigation of numerical results for a rectangular waveguide was provided. A vector finite element program was implemented to allow propagation constants and electric field distributions to be directly computed in the rectangular and circular waveguides which are partially filled with the dielectric.