• Proceedings of the Korea Society for Industrial Systems Conference
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• 1997.11a
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• pp.221-233
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• 1997

무선통신 분야에서 다량의 정보전송과 CDMA, PCS 등의 상업화에 의해 광대역 고출력 증폭기의 요구가 증가하고 있다. 제품화된 파워 모듈에 비해 트랜지스터로 구성한 전력증폭기는 비용의 감소와 효율증대, 생산성 향상의 이점이 있다. 3단의 증폭기를 사용하여 VHF(148∼174㎒),UHF(440㎒∼470㎒)대역에서 5W이상의 전력과 45%이상의 효율을 얻었으며, 적정한 바이어스회로와 임피던스 정합회로망을 설계하여 제작, 실험함으로서 기존의 파워 모듈과 동일한 크기, 성능을 나타냈으며, 발진, 방열, 하모닉제거등 전력증폭기에서 요구하는 사항을 만족하였다. 또한 UHF트랜지스터를 사용하여 VHF의 증폭기를 임피던스 매칭을 이용하여 설계할 수 있음을 실험에 의하여 입증하였다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.6
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• pp.99-110
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• 2005

These days, many image processing techniques have been studied for effective image compression. Among those, The 2D image filtering is widely used for 2D image processing. The 2D image filtering can be implemented by performing the 1D linear filter separately in the horizontal and vertical direction. Efficiency of image compression depends on what filtering method is used. Generally, circular convolution is widely used in 2D image filtering for image processing. However it doesn't consider correlations at the boundary region of image, therefore effective filtering can not be performed. To solve this problem. I proposed new convolution technique using loop convolution which satisfies the 'alias-free' and 'error-free' requirement in the reconstructed image. This method could provide more effective compression performance than former methods because it used highly-correlated data when performed at the boundary region. In this paper, Sub-band Coding(SBC) was adopted to analyze efficiency of proposed filtering technique, and the simulator developed by Java-based language was used to examine the performance of proposed method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.5
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• pp.400-409
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• 2017

We have studied a combiner that can withstand high power while minimizing insertion loss in high frequency band. In particularly, because the output power that can be output per unit elements is much lower in the Ku band and above than in the low frequency band, it is necessary to combine many semiconductor elements in order to make a high power SSPA. A planar combiner such as a microstrip, as the number of elements to be combined increases, the insertion loss increases proportionally, resulting in a reduction in the overall system efficiency and an increase heating value also. The planar combiner also have some problems due to the low power handling rate. To improve these problems, we proposed a Cavity Radial Combiner. A Ku band 16-way Cavity Radial Combiner was fabricated and measured. As a result, it was tested 14dB return loss and over 94.5 % output combining efficiency in design band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.8
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• pp.740-747
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• 2015

Recently, mobile communication systems using the millimeter-wave frequency band have been proposed, and the importance of efficient compensation of the nonlinearity caused by 60 GHz high-power amplifiers(HPAs) is increasing. In this paper, we propose a predistorter structure based on multiple coefficient sets which are separately used to different ranges of input power values. These ranges correspond to varying levels of nonlinearity characteristics. The structure is applied to the 60 GHz HPA FMM5715X and the performance of correcting the nonlinearity of LTE signals is evaluated. Evaluation results using a hardware testbed demonstrate that the proposed predistorter structure achieves the maximum of 6 dB gain over the conventional method in terms of the adjacent channel leakage ratio(ACLR).

• Electronics and Telecommunications Trends
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• v.22 no.5
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• pp.86-94
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• 2007

최근까지 태양전지 기술 개발 방향은 발전 단가를 낮추는 저가형 태양전지 개발 연구와 변환 효율을 높이는 고효율 태양전지 개발 연구가 진행되어 왔다. 태양전지의 발전단가를 낮추기 위하여 저가로 대량 생산이 가능하도록 다양한 물질과 공정이 개발되었지만, 변환 효율이 낮아 상용화에 큰 걸림돌이 되고 있다. 또한 변환 효율 향상을 위한 연구는 과거에는 변환 효율이 높은 물질을 찾기 위해 다양한 시도가 이루어졌으며, 현재는 물질 합성과 적층 구조 등을 이용하여 광흡수 대역을 넓혀 변환 효율을 높이는 데 주력하고 있다. 최근에는 양자점과 나노 기술을 이용하여 기존의 광전 변환 메커니즘의 비효율성을 개선한 신개념의 MEG 태양전지에 대한 연구 개발이 추진되고 있다.

• Journal of Advanced Navigation Technology
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• v.10 no.2
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• pp.167-172
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• 2006

In this paper, the 25W power amplifier for UHF band radio transceiver has been designed and realized. The power amplifier was composed of drive, power amplifier and control stages. Feedback topology and coaxial line baluns were used for wide band operation. The VDMOS, which has reliable performance for linearity and efficiency, was used for power device and designed to operate as push-pull amplification at Class AB Bias. The power amplifier designed in such a way was found to show stable AM modulation performance when voice signal was detected at the gate stage, with being designed and realized to meet output specifications of commercial air traffic control transmitter.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.778-780
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• 2001

ATM(Asynchronous Transfer Mode) 망은 사용자의 요구에 의해 대역폭을 할당한 수 있으므로 전송에 필요한 대역폭이 수시로 변화하는 MPEG 비디오를 전송하는데 적합하다. 그러나 MPEG 트래픽(traffic)은 셀(cell) 발생량의 변화가 심한 군집성 (burst)이 큰 트래픽 이기에 전송 품질을 유지하면서 동시에 망의 대역폭을 효율적으로 사용하는 전송을 구현하기가 매우 힘들다. 본 연구에서는 이러한 상반되는 두 가지의 목적을 수행하기 위하여 새로운 대역폭 할당 기법을 제안하였다. 사용자에게 최소한의 품질을 보장하면서 망에 대역폭의 여유가 있는 경우 고품질의 서비스가 가능토록 하는 방안으로 ATM 망의 CBR(Constant Bit Rate) 서비스와 VBR(Variable Bit Rate) 서비스를 복합적으로 사용하는 방법을 제안하였다. 이의 구현을 위하여 2 계층 구조의 MPEG 부호화기를 설계, 구현하였고 모의 실험을 통하여 기존의 단일 계층 CBR 서비스에 비하여 품질과 망의 효율성에 있어 충분히 우수함을 확인하여 그 효용성을 증명하였다.

• Journal of Satellite, Information and Communications
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• v.11 no.1
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• pp.1-5
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• 2016

In this paper, High Power Pulsed Amplifier with wide-band characteristic is implemented for L-band Navigational Aid(NAVAID). Due to the characteristics of L-Band NAVAID, implemented SSPA is demanded characteristics of high RF power, high linearity and high efficiency. Therefore, in this paper, efficiency characteristic is improved by modified class F technique. And linearity characteristic is improved by balance structure using hybrid coupler, $2^{nd}$ & $3^{rd}$ harmonic trap and anti-phase technique using non-linear characteristics of drive amplifier. Implemented SSPA shows that bandwidth of 300MHz, RF Output power of 1.5KW and efficiency of 55%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.11
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• pp.1074-1077
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• 2013

This paper analyzes the benefit of using directional antennas against eavesdropping attack in millimeter wave (mmWave)-based networks. All devices are equipped with a directional antenna or an omni-directional antenna in a single-hop communications. The probability of a device being detected by an eavesdropper is analyzed based on the exposure region of a device. The relative detection rate is introduced to represent the benefit of using directional antenna. Numerical results show that there exists an optimal number of devices that maximizes the detection probability and it varies according to the parameters such as antenna beamwidth. It shows that the use of directional antenna enables to protect the devices from the detection by an eavesdropper for almost the whole situation in mmWave band communication.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.4
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• pp.636-644
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• 2009

This paper presents a compact, low insertion loss, sharp rejection and wide band microstrip band pass filter that is composed rectangular loop resonator and step-impedance-open-stub(SIOS) for wireless data communication. The SIOS can be reduce length about 30% more than general $0.25{\lambda}$ stub. And the stub can the advantage of tuning impedance magnitude. In order to demonstrate agrement of this paper prove, the optimized wide band pass filters are realized and experimented. A transmission line model used to calculate the frequency response of the new filters shows good agreement with measurements. The filter has 3dB fractional bandwith of 52.5%(3.267GHz), an insertion loss of better than 0.33dB from 4.587GHz to 7.854GHz, and two rejection of greater than 30dB within 221MHz$(4.366GHz{\sim}4.587GHz)$ at low frequency band, 181MHz$(7.854GHz{\sim}8.035GHz)$ at high frequency band. Maximum rejection characteristics of the filter are -54dB at low frequency and -60dB at high frequency.