• Current Optics and Photonics
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• v.2 no.1
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• pp.96-100
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• 2018

A tunable low-phase-noise microwave generation structure that utilizes an optoelectronic oscillator (OEO) and a fiber Bragg grating (FBG) is proposed and experimentally demonstrated in this article. This structure has no particular requirement for the band width of the laser, and its tunability is realized through adjusting the central frequency of the tunable FBG. A detailed theoretical analysis is established and confirmed via an experiment. A high-purity microwave signal with a frequency tunable from 6 to 12 GHz is generated. The single-sideband phase noise of the generated signal at 10.2 GHz is -117.2 dBc/Hz, at a frequency offset of 10 kHz.

• Current Optics and Photonics
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• v.2 no.1
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• pp.53-58
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• 2018

A novel X-band high speed frequency sweep signal generator based on a tunable optoelectronic oscillator (OEO) incorporating a frequency-swept laser is presented and the theoretical fundamentals of the design are explained. A prototype of the generator with tuning range from 8.8552 GHz to 10.3992 GHz and a fine step about 8 MHz is achieved. The generated radiofrequency signal with a single sideband (SSB) phase noise lower than -100 dBc/Hz@10KHz is experimentally demonstrated within the whole tunable range, without any narrow RF band-pass filters in the loop. And the tuning speed of the frequency sweep signal generator can reach to over 1 GHz/s benefiting from applying a novel dispersion compensation modular instead of several tens of kilometers of optical fiber delay line in the system.

• ETRI Journal
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• v.29 no.4
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• pp.437-444
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• 2007

A CMOS frequency synthesizer block for multi-band orthogonal frequency division multiplexing ultra-wideband systems is proposed. The proposed frequency synthesizer adopts a double-conversion architecture for simplicity and to mitigate spur suppression requirements for out-of-band interferers in 2.4 and 5 GHz bands. Moreover, the frequency synthesizer can consist of the fewest nonlinear components, such as divide-by-Ns and a mixer with the proposed frequency plan, leading to the generation of less spurs. To evaluate the feasibility of the proposed idea, the frequency synthesizer block is implemented in 0.18-${\mu}m$ CMOS technology. The measured sideband suppression ratio is about 32 dBc, and the phase noise is -105 dBc/Hz at an offset of 1 MHz. The fabricated chip consumes 17.6 mA from a 1.8 V supply, and the die-area including pads is $0.9{\times}1.1\;mm^2$.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.350-353
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• 2000

In this paper, we designed the microstrip patch antenna with L-shaped aperture, which greatly enhances its bandwidth. We optimized to get a maximum bandwidth. The microstrip patch antenna with L-shaped aperture has the widest bandwidth of the conventional aperture coupled microstrip patch antenna. This antenna also has the low-cross polarization level. The effects of changing several key design parameters of the antenna are investigated. We calculated the VSWR, input impedance, and radiation pattern.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.377-380
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• 2000

본 논문에서는 개구 결합 방식의 마이크로스트립 안테나에 U 슬롯과 turning stub를 동시에 사용하여 넓은 대역폭을 갖는 안테나를 설계 및 제작하였다. 상대 유전율이 2.2이고 두께가 61mil인 duroid 5880기판을 사용하여 ITS(Intelligent Transport System)대역인 5.77GHz에서 동작하는 안테나를 설계하였고, VSWR$\leq$2를 기준으로 하여 약 12.4%의 대역폭을 얻을 수 있었다. 그리고 약 7GHz에서 동작하는 안테나에서는 상대 유전율이 2.2이고 두께가 31mil인 5880기판과 1.6mm인 form을 사용하여 VSWR$\leq$1.5를 기준으로 약 11.7%의 대역폭을 얻을 수 있었다. 각각의 경우 U 슬롯만을 사용한 경우와 비교할 때 5.77 GHz에서는 5.7% 7GHz대역에서는 약 4%의 대역폭 개선 효과를 확인할 수 있었다.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.413-414
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• 1996

A 230 GHz SIS tunnel junction receiver has been being developed for radio astronomy in Nagoya University. In this heterodyne receiver, we use a $\~$1/3 reduced hight rectangular waveguide SIS mixer with two tuning elements as front end. The mixer block with SIS junction was cooled to 4K with a closed cycle He-gas refrigerator. So far, a double sideband receiver noise temperature lower than l00K in 222-237 GHz is obtained. The receiver exhibits a best DSB noise temperature of 69K at 236 GHz as well as 228 GHz.

• Journal of IKEEE
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• v.19 no.1
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• pp.27-32
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• 2015

A flexible and tunable microwave photonic filter based on adjustable optical frequency comb source is demonstrated. We use a combination of a dual parallel Mach Zehnder modulator and an intensity modulator to generate fifteen comb lines with proper weights to implement a desired filter. The optical comb weights, corresponding to the tap coefficients of the filter, are flexibly changed by adjusting the operation parameters of the modulators. The achieved bandwidth and stopband attenuation of the tunable filter are 0.7 GHz and 20 dB, respectively. In addition, we overcome the undesired low frequency suppression appeared in a conventional scheme by applying a dual parallel Mach Zehnder modulator for single sideband suppressed carrier modulation.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1391-1392
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• 2008

The modulation quality of the I/Q modulator in a wireless transmitter usually affects system performance and it mostly depends on both a nonlinearity and a distortion, from the third order intermodulation(IM3) signal and the imperfection features such as an input amplitude error and a local phase error, respectively. This paper focused on how much the Single Sideband Ratio(SSR), which indicates the signal distortion, changes according to the variation of the imperfection features. Since a desired signal, side band and IM3 signals at the I/Q modulator output are also represented with those power series coefficients and the imperfection features, the effects of the imperfection features on SSR can be clearly analyzed.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.655-656
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• 2015

In this paper, diagnosis for 85 high voltage induction motors which have operated for more than 20 years in 18 wide area water supply offices were applied and the results of diagnosis were analysed. Furthermore, main factors that would be affecting rotor defects were selected and correlations between dependent variables which was magnitude for sideband frequency on current during operation and independent variables such as starting characteristic, operating time, number of operation, load factor, maker, rotation speed, capacity were analysed. It was clear that factors including starting characteristic, number of operation, maker, rotation speed caused break by correlation analysis. From this, regression equation was deduced through regression analysis. Based on suggested regression equation, it is applied usefully that we can estimate the condition of rotor without onsite diagnosis and plan the schedule of diagnosis.

• Journal of the Korean Magnetic Resonance Society
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• v.2 no.1
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• pp.59-65
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• 1998

The correction of image artifacts due to misadjustment in tuning of RF coils (tip angle) and in the RF single sideband spectrometer was investigated using phase cycling of the $\pi$/2 and $\pi$ pulses in spin-echo sequences. A general procedure was developed for the systematic design of phase cycles that select desirable coherence transfer pathways. To analyze a phase cycling sequence, changes in the coherence level and phase factor for each RF pulse in the spin-echo cycle must be determined. Four different phase cycling schemes (FIXED, ALTERNATE, FORWARD, REVERSED) to suppress unwanted signal components such as mirror and ghost images were evaluated using two signal acquisitions. When the receiver phase factor is cycled counter-clockwise (REVERSED), these artifacts are completely removed.