• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.9
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• pp.560-562
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• 2014

Broadband power divider operating over the frequency band assigned for all domestic mobile communications is designed and implemented. The implemented power divider with 20Watts power rating has the maximum insertion loss of 3.49dB, input reflection coefficient of below -18.48dB and output reflection coefficient of below -20.2dB, above 24.7dB isolation and -141.2dBc of 3rd PIMD over the operating frequency of 810 ~ 2620MHz.

• 한국정보통신설비학회:학술대회논문집
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• 2004.08a
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• pp.23-26
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• 2004

본 논문은 전력증폭기의 효율을 개선하기 위한 도허티증폭기의 특성 분석에 관한 것이다. 도허티증폭기의 특성을 분석하기 위해 2-tone신호와 WCDMA신호를 사용하였고 180W PEP LDMOSFET을 사용하였다. 제작된 도허티증폭기는 출력 전력 20W에서 약 10%정도의 효율개선을 나타냈지만 선형성이 저하되는 특성을 나타내었다. 저하된 선형성을 개선시키기 위해 carrier 증폭기(Amp. A)와 peaking 증폭기(Amp. B)를 각각 변화하였으며, carrier 증폭기는 높은 PEP(Peak Envelope Power)와 적은 Id(drain current)가 되도록 하였고, peaking 증폭기는 높은 이득과, 낮은 gate bias에서 IMD(Intermodulation Distortion)가 상쇄되도록 하였다. 최종 측정 결과 출력전력 20W에서 선형성은 class AB증폭기와 비교하여 유사한 결과를 얻었으며, 효율은 약 10% 이상의 개선을 얻을 수 있었다.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.5
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• pp.68-75
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• 1994

A new Predistortor that is designed using Feedforward type is proposed to overcome the nonlinearity of HPA (High Power Amplifier). HPA has the nonlinearity of the gain compression and phase distorton, so digital communication system of multi-carrier TDMA needs the linear RF transmitter. Using IMD (Intermodulation Distortion) of drive amplifier, as Feedforward type, the inverse IMD is coupled to the main loop with variable attenuators, phase shifters, and sub-amplifiers well designed. At the input of main amplifier, the over-coupled IMD surpresses the main amplifier 's IMD. Adjusting the level and phase of IMD at the sub loop, C/I of HPA is better than before correction.

• ETRI Journal
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• v.29 no.4
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• pp.533-535
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• 2007

For the purpose of decreasing intermodulation distortion, a new multi-harmonic suppression band-pass filter based on a microstrip radial stub is studied. Compared with traditional resonator filters, the new filter can suppress the second, third, and even fourth harmonics directly. The dimension of the filter is about $0.3\;{\lambda}_{g^0}{\times}0.13\;{\lambda}_{g^0}$ (${\lambda}_{g^0}$ is the guiding wavelength at the resonant frequency). Only one gap was introduced, so lower insertion loss can be obtained. Basic agreement between the measured and simulated results has been achieved.

• Proceedings of the IEEK Conference
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• 2001.06a
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• pp.193-196
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• 2001

To reduce third-order intermodulation distortion(IMD3) generated in the down-conversion process of the mixer, predistortion technique was proposed and its performance was verified fDr Cellular band circuit. This method is based on the fact that down converted IMD3 of a down conversion mixer could be canceled by that of predistortor with a fine tuned vector modulator. Two tone test has been performed at 836 Mhz with 442 KHz separation. The results showed that IM3 level was improved about 16dB and PldB of the mixer was increased 3dB. from the above results, the suggested technique is useful to design the down converters for communication system .

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.87-90
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• 2003

In this paper, A feedforward linear power amplifier is analyzed for imperfect signal cancellation and negative feedback for basestaion of IMT2000 band. the distortion generatied by the error amplifier is reduced using an imperfect signal cancellation for a 1-carrier WCDMA source by 4.3dB at 2.5MHz offset and 6dB at 5MHz offset of IMSR(intermodulation signal power ratio) compared to a perfect signal cancellation system. additionally, An imperfect signal cancellation using negative feedback improved 1.3dB and 8.2dB at 2.5MHz and 5MHz offset of IMSR compared to an imperfect signal cancellation.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.15-18
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• 2006

We have proposed a broadband analog feedforward optical transmitter using a wideband $180^{\circ}$ hybrid coupler instead of conventional frequency-sensitive phase shifter with the narrow bandwidth property using a wideband $180^{\circ}$ hybrid coupler, the wide-band linearization technique enhances the linearity of the feedforward optical transmitter. In two-tone cases, the $3^{rd}-IMD$ products was enhanced more than 10 dB in 385 MHz range(1.375$\sim$l.76 GHz).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12B
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• pp.1754-1757
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• 2001

In this paper, a R-band hybrid amplifier with the coplanar waveguide(CPW) and the photonic bandgap(PBG) structure is designed and fabricated. The PBG and the CPW techniques are simultaneously employed in amplifier to improve the power added efficiency(PAE) and the IMD(Intermodulation Distortion) in R-band. In this paper, the PBG structures are optimized to obtain matching network. The output impedance of amplifier and the input impedance of PBG are matched to minimize the return loss. The PAE and the IMD were improved 15% and 4.5dB compared with the conventional amplifier, respectively.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.6
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• pp.404-411
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• 2001

In this paper, we have measured and analyzed the third-order intermodulation distortion(IMD3) mostly appeared in a laser diode(LD) of an optical link for CDMA signals to characterize the links with an inexpensive way. We analyzed adjacent channel power ratio(ACPR) of CDMA signals as a function of FA, which negatively affects ACPR.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.296-299
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• 2008

최근 통신시스템과 핸드폰, PDA등의 통신기기들의 발전에 따라 사용자들은 높은 데이터 전송률과 고속의 통신서비스를 요구하고 있다. 이러한 상황에서 유 무선 통합 시스템인 Radio-over-Fiber(RoF) 시스템은 그 대안으로 대두되고 있다. 본 논문에서는 광전자소자를 선 왜곡 방식에 적용하여 광 송신기의 선형성을 향상시키는 방법을 제안하였다. 선 왜곡 방식은 두 개의 루프로 구성되어 있으며, 광 부품인 레이저 다이오드와 포토 다이오드 그리고 RF 부품인 위상변위기, 감쇄기, RF 결합/분배기, RF 증폭기를 사용하였다. 메인 루프에서 주 레이저 다이오드의 비선형성에 의해 발생된 왜곡신호성분은 보조 루프에서 부 레이저 다이오드를 이용하여 추출된 선 왜곡신호에 의해서 제거된다. 제안된 선형화 기법을 적용하여 2.4 GHz에서 선형화 기법을 적용하기 전보다 3차 상호변조 왜곡성분이 약 30dB 향상된 결과를 얻었다.