• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37 no.6A
• /
• pp.488-496
• /
• 2012

In this paper, the scheme for designing optimal beamforming matrix for interference control is proposed. The optimal beamforming matrix is found though linear combination of interference alignment conditions and renewal of linear combination coefficient. The proposed scheme has advantages that the complexity is reduced and there is no multiplying operation in matrix calculations even if proposed scheme has the form similar to that of existing least square based scheme. The simulation results show that proposed scheme has about 4bps/Hz higher gain than existing least square scheme. Also there is no additional multiplying calculation and increase of matrix size when the number of transmit and receive antennas is increased.

• The Journal of the Acoustical Society of Korea
• /
• v.26 no.3
• /
• pp.129-135
• /
• 2007

In this paper. we propose a prewhitening method for the km reverberation to enhance the target signal. The proposed algorithm uses the dechirping method which inversely compensates the frequency chirp rate of LFM and transforms the LFM reverberation to have stationary frequency property in each data block. Also, using the left and right adjacent beam signals as reference signals. we model frequency response of each data block by AR coefficients. From these coefficients, we implement inverse filter and prewhiten the LFM reverberation of the center beam efficiently.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.11
• /
• pp.45-54
• /
• 2008

In this paper, we use particle swarm optimization (PSO) to design a randomly excited and randomly spaced linear array with either the lowest side lobe level (SLL) or the narrowest beamwidth. The positions and the excitation amplitudes of the array elements are considered as variables to be controlled. The beam pattern is optimized by controlling the two variables simultaneously and randomly. The best beam patterns are obtained using PSO in the fitness function where performance is improved by the random assignment of weight coefficients to each angular sector of the beam Pattern. The weight coefficients and angles are obtained through several trial runs. Also, an extra term, ${\beta}{\ast}BW$, is added to the fitness function to account for the beamwidth as well as the SLL. Is produces the best result for the beam pattern with either the lowest SLL or the narrowest beamwidth. In the former case, the SLL and beamwidth are about -43dB and $32.2^{\circ}$, respectively, with only 10 elements. In the latter case, the SLL and beamwidth are about -26dB and $24.2^{\circ}$, respectively.

• Korean Journal of Optics and Photonics
• /
• v.31 no.3
• /
• pp.142-147
• /
• 2020

In this paper, we report highly efficient second harmonic generation of continuous-wave Yb fiber lasers incorporating a periodically poled LiTaO₃ device (MgO:PPSLT) as a frequency converter. The seed laser output from a Yb fiber master oscillator using a Fabry-Perot feedback cavity was amplified in a Yb fiber amplifier stage, yielding 28.5 W of linearly polarized output at 1064 nm in a beam with beam quality, M², of ~1.07. Second harmonic generation was achieved by passing the laser beam through MgO:PPSLT. Under optimized conditions, we obtained 11.1 W of green laser output at 532 nm for an incident signal power of 25.0 W at 1064 nm, corresponding to a conversion efficiency of 44.4%. The detailed investigation to find the optimized operating conditions and prospects for further improvement are discussed.

• Journal of the Institute of Electronics Engineers of Korea SP
• /
• v.42 no.4 s.304
• /
• pp.111-118
• /
• 2005

In this paper, we employ the modulation technique for improving the characteristics of beamformer in the low frequencies and thus improving the overall noise reduction performance. In the 1-dimensional uniform linear microphone arrays, we can suppress the narrowband noise component using the delay-and-sum beamforming. But, for the wideband noise signal, the delay-and-sum beamformer does not work well for the reduction of low frequency component because the inter-element spacing is usually set to avoid spatial aliasing at high frequencies. Hence, the beamwidth is not uniform with respect to each frequency and it is usually wider at the low frequencies. In order to obtain the beamwidth independent of frequencies, subarray systems[1][2][3][4] and multi-beamforming[5] have been proposed. However these algorithms need large space and more microphones since they are based on the theory that the size of the array is proportional to the wavelength of the input signal. In the proposed beamformer, we reduce the low frequency noise by using modulation technique that does not need additional sensors or non-uniform spacing. More Precisely, the array signals are split into subbands, and the low frequency components are shifted to high frequencies by modulation and reduced by the delay-and-sum beamforming techniques with small size microphone array. Experimental results show that the proposed technique Provides better performance than the conventional ones, especially in the low frequency band.

• The Journal of the Acoustical Society of Korea
• /
• v.20 no.7
• /
• pp.31-36
• /
• 2001

Passive sonar system forms the various beams in any desired directions to obtain the improvement in Signal-to-Noise (S/N) ratio, bearing detection and localization of targets, and the attenuation of interferences from other directions. The improvement of beamforming is very important to detect modern underwater targets as noise reduction technology leads to considerably low-level acoustic emissions in the long range in complex environmental sea. In this paper, we proposed the spatial cross correlation beamforming (SCCBF) algorithm using cross correlation matrix of individual hydrophone pairs of linear array sensors. By the theoretical analysis and simulation, the proposed SCCBF is demonstrated that its performances compared to conventional beamforming (CBF) output can be obtain above 3dB of array gain and about half of beam width represented the bearing accuracy in target detection. Also, this paper presents sea test result of linear passive sonar system that the proposed algorithm implemented.

• Applied Microscopy
• /
• v.38 no.3
• /
• pp.185-193
• /
• 2008

An experimental comparison of the detection properties between imaging plate and film for recording the electron diffraction pattern was carried out on a radiation-sensitive material, an aluminum trihydroxide(gibbsite, ${\gamma}-Al(OH)_3$), through the electron beam irradiation. Because the imaging plate has a wide dynamic range sufficient for recording extremely low- and high-electron intensities, the range of spatial frequency for the diffraction pattern acquired by the imaging plate was extended to two times larger than the range by the film, especially at a low electron dose condition(${\leq}0.1\;e^-/{\mu}m^2$). It is also demonstrated that the imaging plate showed better resolving power for discriminating fine intensity levels even in saturated transmitted beam. Hence, in the respect of investigating the structures of radiation-sensitive materials and cryo-biological specimens, our experimental demonstrations suggest that the imaging plate technique may be a good choice for those studies, which have to use an extremely low electron intensity for recording.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.27 no.2
• /
• pp.138-146
• /
• 2016

This paper proposes an optimum beam forming of conformal array antenna by using LSM(Least Squares Method) and GA(Genetic Algorithm). The weights which approximate conformal array antenna beam pattern to linear array antenna beam pattern have been evaluated by applying LSM. Also, the optimum locations of conformal array antenna which form wideband optimum beam pattern have been obtained by using GA. The proposed method is applied to a problem of Bezier platform array antenna for a verification purpose.

• Proceedings of the KIEE Conference
• /
• 1999.07f
• /
• pp.2773-2775
• /
• 1999

포항가속기의 선형가속기 buncher 및 prebuncher 시스템은 가속기 건설 시에 중국의 IHEP로부터 도입된 것이다. 전체적인 시스템은 완성되었으나, 그 동안 몇 가지의 문제점이 있어, 제한된 조건하에서 사용해왔다. 이와 같은 문제점을 해결하여 선형가속기 기계장치를 이용한 연구를 활성화하고 보다 나은 전자빔을 공급해주기 위하여 일부 기계장치를 포함한 모터 및 구동부, 제어부등에 대한 성능개선을 하였고 현장 시험과 설치를 완료하였다. 특히 모터는 설치가 간단하고 정밀한 제어를 할 수 있는 5선 식 5상 스텝 모터를 사용하였고, 구동부는 MOSFET을 이용한 정 전류 초핑 방식을 채택하여 크기와 발열량을 줄였다. 그리고, 제어부는 4축의 독립된 유닛이 단일의 RS485 직렬 접속에 의해서 원격으로 제어가 가능하도록 구성하였다.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.40 no.10
• /
• pp.150-158
• /
• 2003

In the beam pattern synthesis problem using line source, the relationship between source distribution function and beam pattern may be represented by Fourier transform pair. In this paper, a general method to synthesize the line source distribution for a desired lobe-like beam pattern is presented by developing the nonlinear inversion method based on an iterative sampling technique. This method can be applied to the synthesis of continuously distributed dielectric constants satisfying the desired inverse scattering coefficient patterns when illuminating by TE-polarized and TM-polarized plane waves to arbitrary dielectric material. Furthermore this method can also be applied to the synthesis of transmission line with arbitrary reflection coefficient patterns. Some bandstop spatial filter and dispersive transmission line filter are illustrated for generality.