• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.12
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• pp.41-46
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• 2008

We report a high gain D-band(110 - 140 GHz) MMIC drive amplifier based on $0.1{\mu}m$ InGaAs/InAlAs/GaAs metamorphic HEMT technology. The amplifier shows an excellent $S_{21}$ gain characteristic greater than 10 dB in a millimeterwave frequency of 110 GHz, Also the amplifier has good reflection characteristics of a $S_{11}$ of -3.5 dB and a $S_{22}$ of -6.5 dB at 110 GHz, respectively The high performances of the MMIC drive amplifier is mainly attributed to the characteristics of the MHEMTs exhibiting a maximum transconductance of 760 mS/mm, a current gain cut-off frequency of 195 GHz and a maximum oscillation frequency of 391 GHz.

• Korean Journal of Optics and Photonics
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• v.18 no.1
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• pp.56-65
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• 2007

The effect of gain dispersion on the self-pulsation (SP) characteristics due to the mode beating of two modes emitted in a multisection DFB laser composed of two complex-coupled DFB sections and a phase control section is investigated. When the peak wavelength, ${\lambda}_{p}$, of the gain spectrum of the DFB section is positioned in the center of the lasing wavelengths or the Bragg wavelengths of the two DFB sections, the maximum SP frequencies are higher and the modulation index has better characteristics compared to those cases for ${\lambda}_{p}$ fixed at the lasing wavelength or Bragg wavelength of one DFB section, when the difference between the Bragg wavelengths of the two DFB sections, ${\Dalta}{\lambda}_{B}$, is varied. When ${\lambda}_{p}$ is positioned in the renter of the Bragg wavelengths of the two DFB sections, the maximum SP frequency is higher and of the modulation index has better characteristics compared to those of the case for ${\lambda}_{p}$ positioned in the center of the lasing wavelengths of the two DFB sections.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.2
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• pp.114-125
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• 2009

Effect of a finite square substrate plane on the radiation characteristics of a microstrip patch antenna is investigated. Effect of a finite square substrate plane on the resonance frequency and bandwidth is very small, while that on the radiation pattern is very large. The gain of front radiation and the direction of the maximum gain vary almost periodically with the length of a square substrate plane. The length of a square substrate plane for the maximum gam and the minimum gain of front radiation decrease as the electrical thickness of a substrate increases. The variation of the gain of front radiation with the length of a square substrate plane increases as the electrical thickness of a substrate increases. The variation of the radiation pattern with the length of a square substrate plane is almost determined by the electrical thickness of a substrate.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.40 no.6
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• pp.68-77
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• 2003

An improved negative capacitance circuit that cancels out input impedance of a front-end in a bioimpedance measurement and operates stably with a low gain margin has been proposed. Since the proposed circuit comprises wide-band operational amplifiers, selecting operational amplifiers is easy, while an operational amplifier of prefer bandwidth should be chosen to apply conventional circuit. Also, since gain margin can be controlled by a feedback resistor connected serially with a feedback capacitor, gain margin is tuneable with a potentiometer. The input impedance of the proposed circuit is two times larger than that of the conventional circuit and 40-times than that without a negative capacitance circuit. Furthermore, closed-loop phase response of the proposed circuit is better than that of the conventional circuit or without a negative capacitance circuit. Above all, for the proposed circuit, the frequency at which a gain peaking occurs is higher than the frequency at which the loop gain becomes a maximum. Thus, the proposed circuit is not affected by a gain peaking and can be operated with a very low gain margin.

• Journal of the Korean Solar Energy Society
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• v.36 no.3
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• pp.53-61
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• 2016

Solar assisted heat pump system uses solar thermal energy as a heat source of evaporator of heat pump. So, COP can be enhanced as well as collector efficiency. For improving performance of this system, some research about hybrid solar collector that has fin-and-tube heat exchanger has been conducted. This collector can get a thermal energy from ambient air for liquid heating, so heated liquid can be used as a heat source of evaporator in heat pump even the solar radiation is not enough. In this study, numerical analysis was conducted for confirming heat gain of liquid according to fin height and pitch of fin-and-tube heat exchanger in collector. As a result, higher heat gain was obtained on lower fin height and narrow fin pitch, but the pressure drop also increased with increment of heat gain. Thus the JF factor considering both heat transfer enhancement and pressure drop was investigated and the maximum value was shown when the fin height and pitch were 40mm and 45mm. So it is considered that this installation condition has a highest heat transfer improvement when comparing with pressure drop. However heat gain of liquid at this condition was less than the other installation conditions of fin pitch on same height. Then, after establishing a proper minimum heat gain of liquid, actual production and experiment of collector will be conducted with fin height and pitch showing maximum JF factor and satisfying selected minimum heat gain of liquid on the basis of results of this study.

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.1464-1468
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• 1997

We propose a decentralized state estimation method in the multisensor state estimation problem. The proposed method bounds teh maximum energy gain from uknown external disturbances to the estimation errors in the suboptimal case. And we formulate aternative H/sip .inf./ filter gain equatiions with teh idea that the suboptimal H.$^{\infty}$ filter is the special form of Kalman filter filter whose state equations are defined in indefinite inner product spaces. Using alternative filter gain equations we design the decentralized $H^{\infty}$ state estimator which is composed of local filters and central fusion filter that are suboptimal in the $H^{\infty}$ sense. In addition, the proposed update equations between global and local data can reduce unnecessary calculation burden efficently.y.

• Proceedings of the Optical Society of Korea Conference
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• 2009.02a
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• pp.509-510
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• 2009

The optical gain of InGaN/GaN multi quantum well (MQW) resonant-cavity light-emitting diode (RC-LED) with different Indium composition and well width in the multi-quantum well was investigated. The optimized optical gain was obtained by simulating active region InGaN/GaN with some test values of well width and Indium composition. By simulation tool, we could simulate on several cases, and then we got exact well width and Indium composition that makes optical gain maximum due to the short wavelength of 470 nm for blue light emission.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.9
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• pp.1064-1072
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• 1999

The basic concepts, which are related to the PSS tuning conditions and performance conditions for the safe of determination of PSS gain and compensation of phasor lagging, are thoroughly investigated in this first part. The performance conditions, where the power system has the lowest inherent damping torque and PSS should provide maximum damping torque, are examined by analysing synchronizing torque and damping torque supplied by the voltage control loop at the oscillation frequency. PSS tuning conditions are also investigated by observing the phasor lagging and the gain, resulted from power system-generator-excitation system depending on operating conditions, such as generator active power, reactive power, transmission impedance and AVR gain. The basic concepts developed in this PartImake it possible to lay foundation for the discussion of PSS tuning in Part II.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.41-45
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• 1997

To design a control system, it is a elementary point that the stability of the system should be guaranteed. Also, the phase of the system plays an important role for its frequence performance. In this paper, we present two stability criterion of repetitive control system with phase-lead and lag compensator. First, the stability criterion for the servo control system with phase-lead and lag compensator is shown by using small-gain theorem. Second, for the repetitive control system with the compensator, the stability criterion, also, is determined by using small-gain theorem. Two stability criterions show the same results that the stability depends on a coefficient of the phase-lead and lag compensator under some condition in servo control system and repetitive control system.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.3
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• pp.76-85
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• 1998

In this paper, a fuzzy tuning method of a control gain in the discrete-time repetitive controller is proposed for precise tracking control of a system whose reference signal is repetitive. The control gain is modified by fuzzy rules which use the magnitude and the variation ofthe maximum output error in the previous repetitive period. The proposed method is applied to a direct drive 2-axis SCARA-type robot and, it is illustratedby computer simulations and real-time experimentation that better performance can be obtained that the fixed gain-based repetitive controller.