• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.107-110
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• 2009

Combustion oscillations are caused by a coupling between acoustic waves and unsteady heat release. They can be eliminated using passive controller such as a helmholtz resonator. But, helmholtz resonator is normally only effective over a narrow frequency range. In this work, helmholtz resonator is applied for reducing the combustion oscillations and we vary the helmholtz resonator volume using piston in oder to tune in the wide range of operating conditions. As the result, it is found that the dominant combustion oscillations can be reduced by optimizing the size of resonator volume. Also, from these results, we investigate feasibility of actively tuned passive control

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.9
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• pp.903-911
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• 2014

This paper proposes a high speed frequency synthesizer with dual phase-locked loop(PLL) structure to improve phase noise level and shape in a wideband receiver. To reduce phase noise and fractional spur, a output frequency of $1^{st}$ PLL used as reference frequency of $2^{nd}$ PLL is changed. The frequency synthesizer has been designed with 1 Hz frequency resolution using digital NCO in 6.5~8.5 GHz wide spectrum. The measured results of the fabricated frequency synthesizer show that the output power is about -3 dBm, the maximum lock-in time and phase noise are within 60 us and -95 dBc/Hz at 10 kHz offset, respectively.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.41 no.5
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• pp.37-42
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• 2004

This paper presents an optimal and robust tuning method of decentralized PI controller for the TITO second order systems to be formulated as LQR. The procedure is developed by establishing relationships between the closed-loop state equation including the decentralized PI tuning parameter and the . closed-loop state equation of LQR and by selecting the weighting factors Q and R of the cost function in order to satisfy the design specifications In frequency domain which the stability robustness and satisfied the performance guaranteed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.9 no.3
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• pp.132-139
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• 1984

This paper presents an exant analysis of the class E tuned power amplifier with a shunt inductor. The following performance parameters are determined for optimum operation with any switch duty ratio: the collector current and voltage waveforms, the peak values of collector current and voltage, the output power, the power output capability, and the values of the load network elements. The analysis shows that the maximum power output capability occurs at a duty ratio of 50 percent. The measured collector efficiency of experiments is 93 percent with 0.93W at 1MHz. This amplifier is especially applicable at portable transmitters because its colletor efficiency is extremely high.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.47 no.6
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• pp.1-5
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• 2010

We propose an algorithm which can classify the system should use a PI controller, which have a weak high frequency attenuation characteristics near the critical frequency. To classify the system, we use a time delay element to calculate a gain attenuation rate near the critical frequency. The proposed algorithm also can design PI controller with the given magnitude margin and phase margin specification. The proposed algorithm uses time delay element and saturation function to identify the one point information in frequency domain. We justify the proposed algorithm via the simulation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.599-602
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• 2006

본 논문에서는 변형된 QMSA에 전기력선이 제한되지 않도록 용량을 장하한 MSA를 제안 하였다. 안테나의 크기는 약 $30mm\times86.6mm\times1.575mm$의 크기를 갖는다. 안테나 특성은 듀얼밴드 설계에서 1.93GHz와 2.03GHz의 두 동작 주파수 동조를 수월하게 하였다. 듀얼밴드 동작을 얻기 위한 기술은 양측 평행 평판과 $\lambda/2$ 방사 폐치를 변화시킴으로서 조정할 수 있다. 또한 1.93GHz 와 2.03GHz의 동작 주파수에 대해 E면과 H면에서 시뮬레이션 된 방사 패턴은 비교 분석되었다. 이동 통신을 위한 설계 제작된 듀얼 밴드 안테나 이득은 약 11.394dBi 이고 이득 변화는 아래와 위 공진 주파수에 대해 1.0dBi 보다 작다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.8 no.4
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• pp.151-155
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• 1983

In this paper, it is studied a novel SAW oscillator by applicating SAW delay characteristics, which can be variable its frequencies by consiting of two output IDT(Inter-Digital Transducer) without external filtering and resonating circuits. The results of experiments showed the temperature characteristics of AT-cut quartz which has been used as frequency-determing substrate of SAW oscillator was good. Though the variable frequencies range was narrow but the experiments showed the possibility to broaden its frequencies range by design of SAW device, and also confromed the stability of fundamental wave oscillating in high frequency range.

• Journal of Broadcast Engineering
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• v.24 no.3
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• pp.485-494
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• 2019

A software-driven real-time frequency de-modulator is implemented with the aid of universal-serial-bus (USB) type software defined radio dongle. An analog stereo frequency modulation (FM) broadcast signal is down-converted to the basedband analog signal then converted to digital bit streams in the USB dongle. Computer software such as Matlab, Python, and GNU Radio manipulates the incoming bit streams with the technique of digital signal processing. Low pass filtering, band pass filtering, decimation, frequency discriminator, double sideband amplitude demodulation, phase locked loop, and deemphasis function blocks are implemented using such computer languages. Especially, GNU Radion is employed to realize the real-time demodulator.

• Journal of the Korea Society of Computer and Information
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• v.3 no.4
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• pp.35-43
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• 1998

This study has been experimented the characteristics of synchronous oscillator for clock recovery of Direct Sequence/Spread Spectrum(DS/SS) communication. When external wave is not provided, The Synchronous Oscillator(SO) oscillates at its natural frequency. As soon as external signal is applied, the SO starts tracking the external frequency which can be sinusoidal, pulsed or some other waveform. Thus, the output is synchronized with the range of wide tracking bandwidth to the external frequency Specifically, the SO also posses frequency division and multiplication capability. All of these indicate that the SO can overcome difficulties to get synchronization in coherent digital communication systems. We make a practical application of DS/SS communication with study on the synchronous properties of SO. As the result, we have a good performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.10A
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• pp.971-978
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• 2005

In this paper, we design and fabricate a VCO(Voltage Controlled Oscillator) for radar detector of X/K/Ka band using frequency multiplier. The existing VCO operated in radar detector have many Problems such as narrow bandwidth, slow frequency variable rate, unstable of production due to high frequency. So we design and fabricate a VCO improved such problems using frequency multiplier. As a result of measure, investigated frequency multiple VCO show its output power 3.64 dBm at multiplied operating frequency 11.27 GHz and have wide frequency tuning range of 660 MHz by controlled voltage 0V to 4.50 V applied diode. And also its phase noise is -104.0 dEc at 1 MHz offset frequency so we obtain suitable performance for commercial use.