• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.7
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• pp.1543-1551
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• 2011

Dithering scheme has been widely used to improve the resolution of DCO(Digitally Controlled Oscillator) in conventional ADPLLs(All Digital Phase Locked Loop). In this paper a new resolution improvement scheme is proposed where a simple DAC(Digital-to-Analog Converter) is employed to overcome the problems of dithering scheme. The frequencies are controled by varactors in coarse, fine, and DAC bank. The DAC bank consists of an inversion mode NMOS varactor. The other varactor banks consist of PMOS varactors. Each varactor bank is controlled by 8bit digital signal. The proposed DCO has been designed in a $0.13{\mu}m$ CMOS process. Measurement results shows that the designed DCO oscillates in 2.8GHz~3.5GHz and has a frequency tuning range of 660MHz and a resolution of 73Hz at 2.8GHz band. The designed DCO exhibits a phase noise of -119dBc/Hz at lMHz frequency offset. The DCO core consumes 4.2mA from l.2V supply. The chip area is $1.3mm{\times}1.3mm$ including pads.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.321-326
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• 2003

We constructed grating- tuned external cavity semiconductor lasers using Littman and Littrow configuration, for which the wavelengths are tuned by rotation of the grating. This wavelength tunable semiconductor laser is one of the main devices of WDM optical communication. In Littman configuration, the wavelength range of about 60 nm (The C- and L-band range of 1,530~1,590 nm) was obtained by changing the incidence angle of the grating about $\pm$1$^{\circ}$ from the incidence angle of 70$^{\circ}$. In the 40 nm tuning range, the output power variation was less than 1.25 ㏈ and the side mode suppression ratio(SMSR) was 32 ㏈. In Littrow configuration (The incidence angle and the first order diffraction angle is the same, i.e. $\alpha$=$\delta$), the wavelength tuning range was about 80 nm for the same conditions used in Littman configuration except the incidence angle ($\alpha$=49$^{\circ}$). In 60 nm tuning range, the output power variation was less than 1.5 ㏈ and SMSR was 35 ㏈.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.10
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• pp.1008-1016
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• 2013

SAR measurement which was applied only to the mobile phone has been expanded in the Korean radio regulation law to the portable wireless communication equipments within 20 cm from the human body since Jan. 2012. The two-way radio operating at 150 MHz frequency band was newly included following the revised radio regulation in the target equipment of measurement. SAR measurement system at 150 MHz satisfying this regulation is necessary accordingly for SAR conformity assessment. The international SAR measurement standard(IEC 62209-2) includes the evaluation method on frequencies above 300 MHz, and the commercial SAR measurement system can measure SAR above 300 MHz only. The size of the reference dipole antenna(760 mm, return loss: -27.57 dB) and flat phantom ($1,300 mm(L){\times}900 mm(W){\times}200 mm(H)$), targeted SAR values for numerical analysis(1 g: 1.08 W/kg, 10 g: 0.77 W/kg) for SAR validation evaluation at 150 MHz frequency are proposed in this paper. The suggested dipole antenna and flat phantom are assembled and used to verify the conformity assessment of commercial SAR measurement system. The measured SAR values of 1 g and 10 g were obtained respectively to be 1.13 W/kg, 0.81 W/kg, and they satisfied the effective range(within ${\pm}10$ %) of IEC international standard. The standards based on this study are expected to be used for the domestic SAR measurement standard and IEC(International Electrotechnical Commission) international standard.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.3 no.3
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• pp.517-531
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• 1999

This paper presents the development of the 2-mode variable gain high power amplifier for a transmitter of INMARSAT-M operating at L-band(1626.5-1646.5 MHz). This SSPA(Solid State Power Amplifier) is amplified 42 dBm in high power mode and 36 dBm in low power mode for INMARSAT-M. The allowable error sets +1 dBm of an upper limit and -2 dBm of a lower limit, respectively. To simplify the fabrication process, the whole system is designed by two parts composed of a driving amplifier and a high power amplifier, The HP's MGA-64135 and Motorola's MRF-6401 are used for driving amplifier, and the ERICSSON's PTE-10114 and PTF-10021 are used the high power amplifier. The SSPA was fabricated by the circuits of RF, temperature compensation and 2-mode gain control circuit in aluminum housing. The gain control method was proposed by controlling the voltage for the 2-mode. In addition, It has been experimentally verified that the gain is controlled for single tone signal as well as two tone signals. The realized SSPA has 42 dB and 36 dB for small signal gain within 20 MHz bandwidth, and the VSWR of input and output port is less than 1.5:1 The minimum value of the 1 dB compression point gets 5 dBm for 2-mode variable gain high power amplifier. A typical two tone intermodulation point has 32.5 dBc maximum which is single carrier backed off 3 dB from 1 dB compression point. The maximum output power of 43 dBm was achieved at the 1636.5 MHz. These results reveal a high power of 20 Watt, which was the design target.the design target.

• Korean Journal of Remote Sensing
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• v.23 no.2
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• pp.137-144
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• 2007

In KORDI (Korea Ocean Research and Development Institute), the KOSC (Korea Ocean Satellite Center) construction project is being prepared for acquisition, processing and distribution of sensor data via L-band from GOCI (Geostationary Ocean Color Imager) instrument which is loaded on COMS (Communication, Ocean and Meteorological Satellite); it will be launched in 2008. Ansan (the headquarter of KORDI) has been selected for the location of KOSC between 5 proposed sites, because it has the best condition to receive radio wave. The data acquisition system is classified into antenna and RF. Antenna is designed to be $\phi$ 9m cassegrain antenna which has 19.35 G/T$(dB/^{\circ}K)$ at 1.67GHz. RF module is divided into LNA (low noise amplifier) and down converter, those are designed to send only horizontal polarization to modem. The existing building is re-designed and arranged for the KOSC operation concept; computing room, board of electricity, data processing room, operation room. Hardware and network facilities have been designed to adapt for efficiency of each functions. The distribution system which is one of the most important systems will be constructed mainly on the internet. and it is also being considered constructing outer data distribution system as a web hosting service for offering received data to user less than an hour.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.7 s.337
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• pp.63-70
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• 2005

We investigated the phase noise of an oscillator with a extremely high-Q resonator used as the resonant element. A TE$_{011}$ mode rutile-loaded resonator with high-temperature superconductive (HTS) $YBa_2Cu_3O_{7-\delta}$(YBCO) films used as the endplates is prepared for this purpose. At 23.5 K, the unloaded Q and the loaded Q are 863000 and 180000, respectively. The phase noise of -104.8 dBc/Hz at 1 KHz offset was observed for the oscillator having a resonator with $Q_{L}$ =180000 at the $TE_{01\delta$ mode resonant frequency of 8.545 GHz at 23.5 K Such oscillators with very low phase noise are expected to be used for building up communication systems capable of efficient use of the frequency band and high-speed data transmission as well as for Doppler radars. Frequency tuning could be realized for the resonator by using a piezoactuator Applicability of the tunable rutile resonator for fabricating tunable oscillators of high performances is discussed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.9
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• pp.862-876
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• 1991

In this theses, the procedure for finding the equivalent immittance of an n-line coupled structures is presented in terms of the normal mode parameters of the n-line coupled system. The above generalized equations can be applied to the various Coupled structures including directional couplers, DC blocks, bandpass/band elimination filters, and various other uniformly coupled filters. The design equations are based on a simplified TEM(Quasi TEM) mode. The obtained results and the definition of the scattering parameters for a general coupled line four port with arbitrary terminations are used to present the procedure to determine the optimum physical dimensions matching the given load impedances connected to input, output port. Multiple coupled rnicrostrip two-port with three lines circuit designed shows little discrepancy between the conventional method and this one. Four port with five lines were fabricated on teflon substrate($e$r=2.55) with its thickness h=l.588mm designed at the center frequency, 4 GHz. Their measured results are fairly close to the ones by computation.

• Aerospace Engineering and Technology
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• v.12 no.2
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• pp.156-162
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• 2013

In the communication between satellite and ground station, data rate can be determined from the data volume and required transmission time. Increasing data rate can be limited according to the available bandwidth. For the reason, it has been popularly studying on high spectral-efficient modulation scheme in large volume data application such as digital video broadcasting service. This paper presents the conceptual design of UHRIT broadcasting in GEO-KOMPSAT-2A (GK2A) mission by using DVB-S2 standard. Based on the recently determined data rate, UHRIT bandwidth was calculated at the various modulation schemes and code rates of DVB-S2 standard. Receiving performance of global user station was also evaluated thorough link analysis by considering that user station is located at the edge of beam coverage. Finally, maximum data rate was analyzed in a situation that COMS HRIT bandwidth should be alternatively applied for UHRIT downlink.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.12
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• pp.1075-1083
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• 2016

Nowadays, the use of wireless input devices has been increasing on the basis of high convenience and portability. In particular the most widely used wireless keyboard and the mouse to use the 2.4 GHz frequency band, but due to the third party receives the electromagnetic wave from leaking when the radio equipment it is easy to obtain the personal information and the vulnerability is also being reported consistently. In this paper, implement a system to analyze and manipulate the packets of 2.4 GHz wireless keyboard and mouse using USRP device and GNU Radio package for verify the vulnerability of 2.4 GHz wireless keyboard and mouse. Using the construction system has attained a equipment specific address and key information by analyzing the communication protocol and the packet structure of the device was proved that a user can operate the PC to send the random key from long distance.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.1062-1070
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• 2022

In the present communication, pure and stable α-Bismuth Oxide (Bi₂O₃) nanoparticles (NPs) were synthesized by low temperature solution combustion method using urea as a fuel and calcined at 500℃. The synthesized sample was characterized by using powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy dispersive X-ray analysis (EDAX), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and UV-Visible absorption spectroscopy. The PXRD pattern confirms the formation of mono-clinic, stable and low temperature phase α-Bi₂O₃. The direct optical energy band gap was estimated by using Wood and Tauc's relation which was found to be 2.81 eV. The characterized sample was studied for X-ray/gamma ray shielding properties in the energy range 0.081-1.332 MeV using NaI (Tl) detector and multi channel analyzer (MCA). The measured shielding parameters agrees well with the theory, whereas, slight deviation up to 20% is observed below 356 keV. This deviation is mainly due to the influence of atomic size of the target medium. Furthermore an accurate theory is necessary to explain the interaction of X-ray/gamma ray with the NPs.The present work opens new window to use this facile, economical, efficient, low temperature method to synthesize nanomaterials for X-ray/gamma ray shielding purpose.