• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.761-768
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• 2010

This paper presents an effective method to achieve the wideband waveform for high resolution SAR(Synthetic Aperture Radar) using the frequency multiplication technique. And also this paper analyzes the root causes for the spectral regrowth due to 3rd-order intermodulation in chirp bandwidth expansion scheme using quadrature modulator and frequency multipliers. The amplitude and phase imbalance requirement are defined based on the simulation results in terms of quadrature channel imbalance. This minimizes the degradation of range resolution, peak sidelobe ratio and integrated sidelobe ratio. The wideband chirp generator using the frequency multiplier and memory map scheme was manufactured and the compensation technique was presented to reduce the spectral regrowth of SAR waveform by minimizing the amplitude and phase imbalance. After I and Q channel imbalance adjustment, the carrier level reduces －28.7 dBm to －53.4 dBm. Chirp signal with 150 MHz bandwidth at S-band expands to 600 MHz bandwidth at X-band. The sidelobe levels are reduced by about 8 to 9 dB by compensating the amplitude balance between I and Q channels.

• The Journal of the Acoustical Society of Korea
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• v.40 no.1
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• pp.46-54
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• 2021

In this paper, active noise control was performed to reduce radiated noise in the low frequency band of dishwashers. First, through an analysis of the noise environment of the dishwasher, it was confirmed that the pump noise contributed the most to the radiated noise in the low frequency band, From the result of the noise environment analysis, the reference signal was selected to be the vibration signal of the pump body. The reference signal was obtained by using the accelerometer on the pump body, which can prevent acoustic feedback. The error signal sensor was selected as a microphone located at 1 m in front of the dishwasher and 0.5 m in height. And to design the controller, the error signal and the reference signal were measured at the operational rpms of the dishwasher at 2,500 rpm, 2,600 rpm and 2,800 rpm, and the secondary path transfer function was measured. The designed controller was mounted on Digital Signal Processor (DSP) equipment, and the control performance was verified experimentally. As a result of the measurement at the 3 operational rpms, the 7th multiple component of pump operating frequency decreased by 1.93 dB, 4.43 dB, 5.15 dB per rpm, and the 12th multiple component decreased by 6.67 dB, 2.34 dB, 4.28 dB per rpm. And overall Sound Pressure Level (SPL) decreased by 0.84 dB, 2.58 dB, 1.48 dB by rpm.

• Current Photovoltaic Research
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• v.4 no.1
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• pp.25-29
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• 2016

$Eu^{3+}$-activated $MgMoO_4$ phosphor thin films were grown at $400^{\circ}C$ on quartz substrates by radio-frequency magnetron sputter deposition from a 15 mol% Eu-doped $MgMoO_4$ target. After the deposition, the phosphor thin films were annealed at several temperatures for 30 min in air. The influence of thermal annealing temperature on the structural and optical properties of $MgMoO_4:Eu^{3+}$ phosphor thin films was investigated by using X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible spectrophotometry. The transmittance, optical band gap, and intensities of the luminescence and excitation spectra of the thin films were found to depend on the thermal annealing temperature. The XRD patterns indicated that all the thin films had a monoclinic structure with a main (220) diffraction peak. The highest average transmittance of 91.3% in the wavelength range of 320~1100 nm was obtained for the phosphor thin film annealed at $800^{\circ}C$. At this annealing temperature the optical band gap energy was estimated as 4.83 eV. The emission and excitation spectra exhibited that the $MgMoO_4:Eu^{3+}$ phosphor thin films could be effectively excited by near ultraviolet (281 nm) light, and emitted the dominant 614 nm red light. The results show that increasing RTA temperature can enhance $Eu^{3+}$ emission and excitation intensity.

• The Journal of the Korea Contents Association
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• v.9 no.12
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• pp.322-331
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• 2009

In clinical SPECT, FWHM provides quality information of the images obtained under different observing conditions. Therefore, the purpose of this study was to determine the optimum cut off level with comparison of FWHM according to cut off levels in each filter - Band limited, Sheep-Logan, Hanning, Hamming, Low pass cosine, Parazen and Butterworth filter in a SPECT camera. I recorded images along the X, Y, Z-axis with 99mTcO4 point source and measured FWHM with profile curves. In conclusion, all filters showed the longest figures of FWHM with cut off level 0.4, which has the worst image resolution. The images with cut off level 0.7 showed best image resolution. The shortest average of FWHM in MS2 was $11.07\pm0.07mm$ using the Butterworth filter, in MS3 it was $8.44\pm0.19mm$ through using the Hanning filter.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.7
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• pp.635-643
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• 2004

In this paper, dual-polarized 2${\times}$2 array antenna is designed and fabricated for the polarization diversity applications in wireless LAN system. For the improved bandwidth and isolation characteristics, the aperture coupled feeding and the L-shaped probe feeding are employed for each polarization. The measured bandwidths of the fabricated antenna are 210MHz for aperture coupled feeding and 280MHz for L-shaped probe feeding. The isolation for two ports is -40dB and the antenna gain is measured as 14.3${\pm}$0.2dBi in the operating frequency band of wireless LAN.

• Composites Research
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• v.14 no.5
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• pp.20-25
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• 2001

This paper deals with finite element analysis for free vibration and forced sinusoidal vibration of Ka- and Ku- band antenna structures using MSC/NASTRAN. The structures are designed to satisfy minimum resonance frequency requirement in order to decouple the dynamic interaction of the satellite antenna with the spacecraft bus structure. The large mass method was utilized to analyze output acceleration according to the forced sinusoidal vibration inputs in X-, Y- and Z- directions. The analysis results can also be used thor verification experimental planning of satellite antenna.

• Journal of the Korean Institute of Navigation
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• v.22 no.3
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• pp.9-16
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• 1998

Loran C is a low frequently , pulsed. hyperbolic radio aid to navigation system, which operates in the 90 to 110 kHz frequency band. The position accuracy is not excellent but the repeatable and relative accuracy is very good, and it is very useful for fishing vessel in coastal waters. The operation of China north sea chain9GRI 7430) was begun on January, 1996, and in order to evaluate the accuracy of this chain, it was observed with Loran C receiver (LC-90, Furuno) in July 9 and December 30, 1997 at the fixed position of Kunsan national university. The obtained results were as follows : The time difference error of M-X, M-Y pair were $0.5{\mu}s$, $4.4{ \mu}s$ respectively and the mean time difference of M-X, M-Y pair were $15120.4{,\mu}s$ $32085.4{\mu}s$ respectively. The Loran C signals were received steadily and the daily fluctuation of time difference was very small. The longitudinal position error was very much than latitudinal position error, and the mean position error was about 1091.8m.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.7A
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• pp.935-942
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• 2000

In this paper, miniature voltage-controlled oscillator(VCO) for 1.6GHz PCS band is designed and implemented. Colpitts type LC resonating oscillator is designed with multilayer PCB and circuit parameters are optimized using the circuit simulator. Using the optimized design parameters, miniature VCO with 6X6X1.8mm3 (0.065cc)dimensions is fabricated and experimented. Developed VCO has -1.67dBm $\pm$0.5dBm output power level in52.5MHz tunung range, and has -99.33dBc/Hz phase noise performance at 10 KHz frequency offset.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.3
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• pp.49-57
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• 2000

In this paper, lumped-element isolator is analyzed and designed using the scattering matrix approach. Using the designed parameters, compact isolator with 7.0x7.0x2.3 mm$^3$ dimensions is fabricated and tested in 1.765GHz PCS phone band. Implemented isolator shows 29.95dB isolation characteristic at center frequency and has 0.35dB insertion loss in overall 30MHz operating bandwidth. Return losses of input and output port are measured below -19 dB. Experimental results show that the implemented isolator has better performances than the conventional one.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1351-1355
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• 2018

The photocurrent characteristics of zinc-oxide (ZnO) thin-film transistors (TFTs) prepared using radio-frequency sputtering and spin-coating methods were investigated. Various characterization methods were used to compare the physical and the chemical properties of the sputtered and the spin-coated ZnO films. X-ray photoelectron spectroscopy was used to investigate the chemical composition and state of the ZnO films. The transmittance and the optical band gap were measured by using UV-vis spectrometry. The crystal structures of the prepared ZnO films were examined by using an X-ray diffractometer, and the surfaces of the films were investigated by using scanning electron microscopy. ZnO TFTs were prepared using both sputter and solution processes, both of which showed photocurrent characteristics when illuminated by light. The sputtered ZnO TFTs had a photoresponsivity of 3.08 mA/W under illumination with 405-nm light while the solution-processed ZnO TFTs had a photoresponsivity of 5.56 mA/W. This study provides useful information for the development of optoelectronics based on ZnO.