• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.571-574
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• 2010

Large-eddy simulation has been conducted to simulate turbulent boundary-layer flows over an array of regularly distributed obstacles considering various cases of a wind incident angle. The effect of wind direction was investigated in the square cube array that periodic boundary condition was imposed. Characteristics of the turbulent flow over the obstacle array have been found to be very sensitive to the direction of prevailing wind or of mean wind or of mean pressure gradient but varied with height, specially below the urban canopy. Turbulent statistics are changed sensitively with the direction of mean pressure gradient around 10 degree.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.234.1-234.1
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• 2012

The largest array SKA (Square Kilometre Array) project was proposed by astronomers from 10 countries, and first coordinated by the LTWG (Large Telescope Working Group) formed at the General Assembly of URSI (International Union of Radio Science) in 1993. It enters the pre-construction phase (2012-2015), towards the 10% SKA construction (2016-2019) called SKA1 and the rest of SKA (2019-2023) called SKA 2, under the leadership of the SKA Organisation (SKAO) established on November 23, 2011. I will review the Chinese participation in the SKA project at national, regional and global levels in the past two decades. During such a Long March to the SKA, a number of national Megascience projects have taken root and have been (are being) successfully constructed, with costs at the 100 M US dollar level, including the largest dish FAST (Five-hundred meter Aperture Spherical Telescope), which can be seen as a forerunner of the KARST (Kilometre Area Radio Synthesis Telescope) project, being as one of the two LDSN (Large Diameter Small Number) concepts for realizing the SKA. A close look at the FAST project gives an impressive snapshot of the construction phase in China.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.68 no.1
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• pp.83-89
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• 2019

In this paper, beam forming using moving least squares method (MLSM) is studied. In the previous research, the least squares method (LSM), one of the data interpolation methods, was used to determine the desired beam pattern and obtain a beam pattern that minimizes the square of the error with the desired beam pattern. However, LSM has a disadvantage in that the beam pattern can not be formed to satisfy the exact steering angle of the desired beam pattern and the peak sidelobe level (PSLL) condition. To overcome this drawback, MLSM is used for beam forming. In order to verify, the proposed method is applied in beam forming of Bezier platform array antenna which is one of conformal array antenna platform.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.9
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• pp.155-163
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• 2012

The geometrical and electrical errors of array sensors can severely degrade the performance of array sensor system. Various calibration techniques are developed to alleviate this problem. In this paper, two different calibration methods with respect to location, gain and phase of array sensors are presented. One method applies the first-order Taylor series expansion to approximate the true steering vector from the nominal values of array sensors. Then a set of equations is formed by using the null characteristics of the MUSIC spectrum to estimate errors of location, gain and phase of array sensors. Another method estimates these errors based on the data covariance matrix of pilot sources. From the simulations, it is demonstrated that two calibration algorithms calibrated an array system successfully. In addition to that, Fistas and Manikas's algorithm is more robust against noise than Ng and Lie's one when SNR is from 10dB to 50dB.

• Journal of Satellite, Information and Communications
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• v.10 no.4
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• pp.136-140
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• 2015

In this paper, a comparative studies on the STAP and SFAP were performed, which are known as representative anti-jamming technology for adaptive array antenna. As a method of estimating the weighting vector for simulation, MMSE(Minimum Mean Square Error) algorithm was commonly used and the analyses of the simulation performance in various jamming environments were presented. Especially, performance comparison between STAP and SFAP according to the jamming power J/S(Jamming to Signal Power Ratio), performance comparison in the ratio of jamming bandwidth to signal bandwidth, and performance comparison of BER between STAP and SFAP were presented.

• Journal of Communications and Networks
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• v.10 no.2
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• pp.118-126
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• 2008

The use of beamforming is effective for users in limited power environments. However, when it is applied to the downlink of a cellular system with universal frequency reuse, users near the sector boundary may experience significant interference from more than one sector. The use of a minimum mean square error (MMSE)-type receiver may not sufficiently cancel out the interference unless a sufficient number of receive antennas are used. In this paper, we consider the use of inter-sector beamforming that cooperates with a neighboring sector in the same cell to mitigate this interference problem in time-division duplex (TDD) environments. The proposed scheme can avoid interference from an adjacent sector in the same cell, while enhancing the transmit array gain by using the TDD reciprocity. The performance of the proposed scheme is analyzed in terms of the output signal-to-interference-plus-noise power ratio (SINR) and the output capacity when applied to an MMSE-type receiver. The beamforming mode can be analytically switched between the inter-sector and the single-sector mode based on the long-term channel information. Finally, the effectiveness of the proposed scheme is verified by computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.7
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• pp.431-436
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• 2014

In this paper, we propose a compressive sensing-based channel quantization feedback mechanism that is appropriate for practical massvie multiple-input multiple-output (MIMO) systems. We assume that the base station (BS) has a compact uniform square array that has a highly correlated channel. To serve multiple users, the BS uses a zero-forcing precoder. Our proposed channel feedback algorithm can reduce the feedback overhead as well as a codebook search complexity. Numerical simulations confirm our analytical results.

• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.1
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• pp.23-30
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• 2022

The active phased array antenna system performs beam steering, multi-beam formation and adaptive beam forming by controlling the amplitude and phase of signals fed to each radiating element. In order to obtain the desired radiation characteristics using an active phased array antenna system, the accurate amplitude and phase of the signal must be fed to each radiating element; however, due to various causes, the signal errors occurs in each radiating element. In this paper, a signal error estimation method of each radiating element is proposed. The proposed method simplifies the process of signal error estimation, and can quickly and accurately calculate the signal error.

• Journal of Advanced Navigation Technology
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• v.27 no.6
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• pp.828-834
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• 2023

In this paper, we studied an antenna that forms a wide beam width by applying a horn-shaped reflector to a patch array antenna. To implement a wide beam width, three patches were arranged in each of the four directions on a square microstrip substrate, and a horn-shaped reflector was applied to the rear of the array antenna. Through this structure, the vertical beam pattern formed from the patch was converted to a diagonal direction, and as a result, the beam widths formed in each of the four sectors were added to create a wide beam width close to a hemisphere. The proposed antenna was studied for application to UAV(unmanned aerial vehicle), and the simulation test results confirmed that the 4.5 dBi beam width was 146.8°.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.5
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• pp.12-18
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• 2008

Ag paste was employed for source and drain electrode of OTFTs and for the data metal lines of OTFT-OLED array on PC(polycarbonate) substrate. We tested two kinds of Ag-pastes such as pastes for 325 mesh and 500 mesh screen mask to examine the pattern ability and electrical performance for OTFTs. The minimum feature size was 60 ${\mu}m$ for 325 mesh screen mask and 40 ${\mu}m$ for 500 mesh screen mask. The conductivity was 60 $m{\Omega}/\square$ for 325 mesh and 133.1 $m{\Omega}/\square$ for 500 mesh. For the OTFT performance the mobility was 0.35 $cm^2/V{\cdot}sec$ and 0.12 $cm^2/V{\cdot}sec$, threshold voltage was -4.7 V and 0.9 V, respectively, and on/off current ratio was ${\sim}10^5$, for both screen masks. We applied the 500 mash Ag paste to OTFT-OLED array because of its good patterning property. The pixel was composed of two OTFTs and one capacitor and one OLED in the area of $2mm{\times}2mm$. The panel successfully worked in active mode operation even though there were a few bad pixels.