• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.6B
• /
• pp.1156-1164
• /
• 1999

In this paper, we have studied the 8 YSB (8 Vestigial Side Band) method which is decided as the standard of modulators for next generation digital TV System. In developing digital TV System, one of the difficult problems is how digital signal can be transmitted to the receiver without any phase distortion. But, phase error is liable to occur by imperfect design, circumstance variation and device degradation. These characteristics result in distortion of 1,0 signal of modulator and interference in adjacent channels. In particular, the interference in modulator of a high power amplifier result in serious problems in adjacent channels. Here we analyzed problems of phase error which are occurred when 8 levels digital signals are modulated to If signal. And we suggested phase error compensation algorithm and discussed the results for adaptation of the algorithm

• Korean Journal of Optics and Photonics
• /
• v.19 no.1
• /
• pp.60-67
• /
• 2008

An all-optical 4-bit Gray code to binary coded decimal (BCD) converter by means of commercially available numerical analysis tool (VPI) was demonstrated, for the first time to our knowledge. Circuit design approach was modified appropriately in order to fit the electrical method on an all-optical logic circuit based on a cross gain modulation (XGM) process so that signal degradation due to the non-ideal optical logic gates can be minimized. Without regenerations, Q-factor of around 4 was obtained for the most severely degraded output bit (least significant bit-LSB) with 2.5 Gbps clean input signals having 20 dB extinction ratio. While modifying the two-level simplification method and Karnaugh map method to design a Gray code to BCD converter, a general design concept was also founded (one-level simplification) in this research, not only for the Gray code to BCD converter but also for any general applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.15 no.9
• /
• pp.826-834
• /
• 2004

In this paper, we fabricated thick film monopole antennas using Bi$_2$O$_3$-doped BaTi$_4$$O_{9}$ ceramics for small size and broadband intenna. In the result, the high permittivity was fixed and the quality factor was also significantly decreased by the formation of secondary phase of Bi$_4$Ti$_3$O$_{12}$ repleced by addtion Bi. The antenna property influenced by the quality value more than the permittivity. The bandwidth of antenna was increased to 33 %. On the other hand, the gain was reduced to -4.3 dBi. Also radiation patterns were showed low dBi value by increasing of dielectric loss. Specially, Measured x-y plane radiation patterns was distorted as the dispersion of wavelength and high permittivity difference. But the result is showed execellent bandwidth because of low quality value in all formation range.nge.

• Journal of the Korean Magnetics Society
• /
• v.19 no.3
• /
• pp.113-119
• /
• 2009

$^{57}Fe_xCu_{1-x}O$(x = 0.0, 0.02) powders were prepared by sol-gel method and their crystallographic and magnetic hyperfine properties have been studied using X-ray diffraction and $M{\ddot{o}}ssbauer$ spectroscopy (MS). The crystal structure of the samples is found to be monoclinic without any secondary phases and their lattice parameters increase with increasing annealing temperature ($T_A$), which is attributed to an increase in oxygen-vacancy content. MS measurements at room temperature indicate that $Fe^{3+}$ ions substitute $Cu^{2+}$ sites and ferromagnetic phase grow with increasing $T_A$. Magnetic hyperfine and quadrupole interactions of $^{57}Fe_{0.02}Cu_{0.98}O$ ($T_A=500^{\circ}C$) in the antiferromagnetic state at 17 K have been studied, yielding the following results: $H_{hf}=426.94\;kOe$, ${\Delta}E_Q=-3.67\;mm/s$, I.S.=0.32 mm/s, ${\theta}=65^{\circ}$, ${\phi}=0^{\circ}$, and ${\eta}=0.6$.

• Journal of the Korean Association of Geographic Information Studies
• /
• v.23 no.2
• /
• pp.53-69
• /
• 2020

The increase of the impermeable area due to industrialization and urban development distorts the hydrological circulation system and cause serious stream drying phenomena. In order to manage this, it is necessary to develop a technology for impact assessment of stream drying phenomena, which enables quantitative evaluation and prediction. In this study, the cause of streamflow reduction was assessed for dam and weir watersheds in the five major river basins of South Korea by using distributed hydrological model DrySAT-WFT (Drying Stream Assessment Tool and Water Flow Tracking) and GIS time series data. For the modeling, the 5 influencing factors of stream drying phenomena (soil erosion, forest growth, road-river disconnection, groundwater use, urban development) were selected and prepared as GIS-based time series spatial data from 1976 to 2015. The DrySAT-WFT was calibrated and validated from 2005 to 2015 at 8 multipurpose dam watershed (Chungju, Soyang, Andong, Imha, Hapcheon, Seomjin river, Juam, and Yongdam) and 4 gauging stations (Osucheon, Mihocheon, Maruek, and Chogang) respectively. The calibration results showed that the coefficient of determination (R²) was 0.76 in average (0.66 to 0.84) and the Nash-Sutcliffe model efficiency was 0.62 in average (0.52 to 0.72). Based on the 2010s (2006~2015) weather condition for the whole period, the streamflow impact was estimated by applying GIS data for each decade (1980s: 1976~1985, 1990s: 1986~1995, 2000s: 1996~2005, 2010s: 2006~2015). The results showed that the 2010s averaged-wet streamflow (Q95) showed decrease of 4.1~6.3%, the 2010s averaged-normal streamflow (Q185) showed decreased of 6.7~9.1% and the 2010s averaged-drought streamflow (Q355) showed decrease of 8.4~10.4% compared to 1980s streamflows respectively on the whole. During 1975~2015, the increase of groundwater use covered 40.5% contribution and the next was forest growth with 29.0% contribution among the 5 influencing factors.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.20 no.5
• /
• pp.25-32
• /
• 2006

This paper proposes a regeneration inverter system, which can regenerate the excessive power form do bus line to ac source for traction system. The proposed regeneration inverter system for dc traction can reduce harmonics which are included to ac current source. The regeneration inverter is operated as two modes. In the regeneration inverter mode, it can recycle regenerative energy caused by decelerating tractions and in the active power filter mode, it can compensate harmonic distortion produced by the rectifier substation. In this paper, the regeneration inverter uses PWM DC/AC inverter algorithm and the active power filter uses p-q theory. From the informative simulation and experimental results, which are performed wiith a prototype rated 3.7[kw], it can expected that the proposed system can be effectively applied in the real traction system rated 100[kw].

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.6
• /
• pp.682-690
• /
• 2012

In this paper, a highly linear self oscillating mixers(SOM) using second harmonic injections are presented. The H-slot defected ground structure(DGS) is designed as a balanced resonator for oscillation in the proposed SOM. Since the H-slot DGS resonator achieves a high Q factor, it is a suitable structure to provide low phase noise for the oscillator. The single balanced mixer is utilized in this work and it provides good LO-RF isolation since balanced LO signals are suppressed at the RF input port. In order to inject the second harmonic of the IF, we propose two different methods using feedback loops. In the first method, IF achieves a 3.08 dB conversion gain at 226 MHz with input power of -20 dBm at 5 GHz RF input signal. The IF achieves 2 dB conversion gain at 423 MHz with the input power of -20 dBm at 5.2 GHz RF input signal in the second method. The measured IMD3s are 61.8 dB and 65 dB for the each method. These SOMs present improved linearity compared to that without the second harmonic injection because IMD3s are improved by 18. dB and 21 dB for each method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.17 no.12 s.115
• /
• pp.1156-1163
• /
• 2006

This paper presents an ultra wideband(UWB) direct conversion mixer for IEEE 802.15.3a applications with simulation and measurement results. Since the direct conversion mixing causes dc-offset and even-order distortion, the proposed mixer adopts an anti-parallel diode pairs(APDPs) to solve these problems. The proposed mixer consists of an in-phase wilkinson power divider over $3.1{\sim}4.8GHz$, a wideband $45^{\circ}$ power divider over $1.5{\sim}2.4GHz$, and miniatured band pass filters(BPFs) for RF-LO isolations. The conversion loss is optimized with impedance matchings between APDPs and wideband components. The measured mixer shows the conversion loss of 13.5 dB, input third-order intercept-point($IIP_3$) of 7 dBm, and 1-dB gam compression point($P_{1dB}$) of -4 dBm. Quadrature(I/Q) outputs have the magnitude difference of about 1 dB and phase difference of ${\pm}3^{\circ}$.

• Journal of radiological science and technology
• /
• v.31 no.1
• /
• pp.55-60
• /
• 2008

Purpose: This study is to decide a quality control and calibration period of LCD display devices used for reading diagnostic images. Materias and Methods: The assessment test of 20 flat panel LCD color display devices used for reading diagnostic images were performed based on AAPM TG 18 protocol over the total six sessions at one month intervals from three months after primary calibration, in terms of geometric distortion, reflection test, luminance response evaluation, luminance uniformity, resolution, noise, veiling glare and chromaticity test. Results: The results of geometric distortion, reflection test, luminance uniformity, resolution, noise, veiling glare and chromaticity test were within the criteria recommended by AAPM TG 18, except for luminance response evaluation. In the measured luminance deviation of luminance response evaluation, 4(25%) of 20 display devices were passed a criterion from four months after calibration, and 11 (55%) were passed from eight months. Also in the contrast response of the luminance response evaluation, 1(5%) display device was passed a criterion from four months after calibration, and 3(15%) were passed from eight months. Conclusion: Considering the passing deviation after calibration, the time required and a manpower, the quality control and calibration period of LCD display devices used for reading diagnostic images should be a three months and six months after calibration.

• Journal of Broadcast Engineering
• /
• v.15 no.1
• /
• pp.122-132
• /
• 2010

AT-DMB system has been developed to increase data rate up to double of conventional T-DMB in the same bandwidth while maintaining backward compatibility. The AT-DMB system adopted hierarchical modulation which adds BPSK or QPSK signal as enhancement layer to existing DQPSK signal. The enhancement layer signal should be small enough to maintain backward compatibility and to minimize the coverage loss of conventional T-DMB service coverage. But this causes the enhancement layer signal of AT-DMB susceptible to fading effect in transmission channel. A turbo code which has improved error correction capability than convolutional code, is applied to the enhancement layer signal of the AT-DMB system for compensating channel distortion. However there is a need for other solutions for better reception of AT-DMB signal in receiver side without increasing transmitting power. In this paper, we propose adaptive array antenna system with Eigen-space beamforming algorithm which benefits beamforming gain along with diversity gain. We analyzed the reception performances of AT-DMB system in indoor and mobile environments when this new smart antenna system and algorithm is introduced. The computer simulation results are presented along with analysis comments.