• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.1
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• pp.1-8
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• 2006

A linear acoustic analysis is conducted to examine bituning of acoustic resonators for acoustic damping in a combustion chamber of liquid rocket engine. Bituned resonators are tuned to the two principal modes, the first tangential(1T) and the first radial(1R) modes. First, the acoustic-damping effect of monotuned resonators is investigated. The damping capacity is quantified by damping factor as a function of the number of the resonators monotuned to 1T or 1R mode. Next, the damping characteristics of the bituned resonators are investigated. From the numerical data, the number of resonators, to be tuned to 1T and 1R modes, respectively, can be selected properly. Furthermore, the concept of resonator bituning is applied to reduce the degradation of damping effect caused by the mode split and thereby, optimal bituning frequencies are found.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.355-358
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• 2006

A linear acoustic analysis is conducted to examine bituning of acoustic resonators for acoustic damping in a combustion chamber of liquid rocket engine. Bituned resonators are tuned to the two principal modes, the first tangential(1T) and the first radial(1R) modes. First, the acoustic-damping effect of monotuned resonators is investigated. The damping capacity is quantified by damping factor as a function of the number of the resonators monotuned to 1T or 1R mode. Next, the damping characteristics of the bituned resonators are investigated. From the numerical data, the number of resonators, to be tuned to 1T and 1R modes, respectively, can be selected properly.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.281-284
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• 2009

Acoustic tuning frequency of quarter-wave resonators is investigated numerically to suppress combustion instability in a liquid rocket engine. A quarter-wave resonator is adopted, which was designed from the cold acoustic test for optimal damping condition. First, in a model combustion chamber scaled down from a full-scale chamber, reactive flow filed is analyzed numerically and acoustic-pressure responses are examined. Next, thermodynamic properties in the resonators are predicted. Based on the data, frequency tuning method is studied. The optimum tuning length of each resonator is proposed and thereby, sufficient damping is produced.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.36C no.11
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• pp.29-34
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• 1999

In this paper, a current comparative frequency automatic tuning circuit for the CMOS gm-C bandpass filters are designed with the new architecture. And also, when the designed circuit is compared to the typical tuning circuit, the designed circuit has very simple architecture that is composed of the current comparator and charge pump and operating in 3V power supply. The proposed tuning circuit automatically compensates the difference between the operating current of the transconductor and the specified reference Current. Using CMOS 0.8um parameter a biquad gm-C bandpass filter with center frequency($f_\circ$=60MHz) is designed, and according to the transistor size the variation of the center frequency is simulated. As the HSPICE simulation results, the tuning operation of the proposed current comparative frequency automatic tuning circuit is verified.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5A
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• pp.513-518
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• 2010

Improvement of phase noise characteristics in a different approach of HEMT VCO (Voltage Controlled Oscillator) with coupled microstrip lines to tune the oscillating frequency is investigated. Two HEMT VCOs of 9.8GHz are manufactured in the same configuration except for the frequency tuning circuit in order to empirically demonstrate the phase noise reduction. Experimental result shows that phase noise reduction can be enhanced 8dBc/Hz at 100KHz offset frequency from carrier by frequency tuning circuit with coupled microstrip lines over the conventional VCO.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.12
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• pp.1251-1257
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• 2014

In this paper, a 6~13 GHz ultra high speed frequency synthesizer having minimum 30 kHz step size and minimum 500 ns frequency settling time is proposed. In order to obtain fast settling time, fine resolution, and good phase noise performance, wideband output frequencies were synthesized based on DDS(Direct Digital Synthesizer) and analog direct frequency synthesis technology. The phase noise performance of wideband frequency synthesizer was estimated by the superposition theory and its results were compared with measured ones. The measured frequency settling time was below 500 ns, phase noise was below -106 dBc @ 10 kHz at 13 GHz, and frequency accuracy was measured below ${\pm}2kHz$.

• The Journal of the Acoustical Society of Korea
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• v.5 no.3
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• pp.44-49
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• 1986

회로의 간편성에 최대 역점을 두어 PLL을 이용한 정현파 간섭음을 실시간으로 제거하는 방식을 제안하였다. SC 여파기를 이용한 적응 노치 여파기ㅘ 적응 대역 여파기를 자기 동조법으로 구동시킴으 로써 간섭음을 제거하였다. SC 여파기의 구동 스위칭 주파수는 제거하려는 신호 주파수으 L49배가 되 도록 하엿으며 소자의 동작 특성상 4KHz의 간섭음 제거 대역을 갖게 된다. 노치 여파기는 6차 여파기 이고 감쇄도는 중심 주파수에서 약 -56dB이다.

• Electronics and Telecommunications Trends
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• v.22 no.6
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• pp.182-193
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• 2007

본 연구에서는 프랑스, 영국, 핀란드 등 유럽을 대표하는 몇몇 국가와 미국, 일본, 호주 등 주요국을 대상으로 $800{\sim}900MHz$ 대역의 이용현황 및 활용사례를 살펴보았다. 특히, 저대역 주파수에서 상업적 가치가 높은 이동통신용 주파수의 이용현황 및 전개방향을 중심으로 살펴보았다. 그 결과 전세계적으로 이동전화서비스의 성장 및 신규서비스의 도입으로 주파수 수요가 급증함에 따라 주파수 부족현상이 심화되고 있고, 이에 따라 효율적인 주파수 사용을 위해 국가별로 회수 재배치가 중요한 이슈로 부각되고 있음을 알 수 있었다. 본 연구에서는 동조화가 높은 저대역 주파수에 대한 해외 주요국의 이용동향을 살펴봄으로써 향후 부족한 전파자원에 대한 유용한 시사점을 도출하고자 하였다. IMT-2000 주파수의 동조화는 800MHz와 900MHz 대역을 중심으로 이루어지는데 해외의 저대역 주파수에 대한 이용선례는 향후 통신사업자들의 사업방향에 중요한 지표가 될 것으로 기대된다. 이러한 연구는 전파정책을 추진하는 당국과 사업자에게 정책결정을 하는 데 유용한 정보를 제공할 것이라 기대된다.

• Journal of IKEEE
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• v.16 no.2
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• pp.121-126
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• 2012

In this paper, a push-push VCDRO (Voltage Controlled Dielectric Resonator Oscillator) with a modified frequency tuning structure is investigated. The push-push VCDRO designed at 16GHz is manufactured using a LTCC (Low Temperature Co-fired Ceramic) technology to reduce the circuit size. The frequency tuning structure is embedded in intermediate layer of A6 substrate by an advantage of LTCC process. Experimental results show that the fundamental frequency suppression is above 30dBc, the frequency tuning range is 0.43MHz over control voltage of 0 to 12V, and phase noise of push-push VCDRO presents a good performance of -103dBc/Hz at 100KHz offset frequency from carrier.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.1
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• pp.26-35
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• 1996

In this paper, characteristics of the electromagnetically coupled broadband microstrip antennas are analyzed by the Finite Difference Time Domain (FDTD) method, and antenna para- meters are optimized to get maximum bnadwidth. By using short radial tuning stub in microstrip feedline, electromagnetically coupled microstrip antenna shows broadband ($\simeq$13%) characteristics, and the characteristics are varied as a function of radius, radial angle, and position of the radial tuning stub. Operating frequency, return loss, VSWR and input impedance are calculated by Fourier transforming the time domain results. After optimization of the parameters, maximum bandwidth of the radial stub tuning microstrip antenna is about 15% and the ripple char- acteristic of the VSWR is better than the rectangular tuning stub microstrip antenna.