• Korean Journal of Optics and Photonics
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• v.21 no.5
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• pp.181-184
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• 2010

A simple technique for a flexibly tunable and switchable dual wavelength-switchable erbium-doped fiber (EDF) laser using fiber Bragg gratings is proposed and demonstrated by using both linear cavity loss controlling and homogeneous gain broadening of the EDF. The oscillating wavelength switching is successfully realized by using the modulation of the acousto-optic modulator driven by the RF signal. The wavelength spacing and lasing wavelength of the proposed wavelength-switchable laser can also be controlled by using the bending-induced tension or compression strain. The proposed tunable dual wavelength-switchable fiber laser has a lot of advantages, such as a high extinction ratio larger than 40dB and a high tunability of ~7.2 nm/$m^{-1}$.

• Asian-Australasian Journal of Animal Sciences
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• v.30 no.12
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• pp.1702-1710
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• 2017

Objective: The study examined the effect of condensed tannins (CT) containing Ficus infectoria and Psidium guajava leaf meal mixture (LMM) supplementation on nutrient metabolism, methane emission and performance of lambs. Methods: Twenty four lambs of ~6 months age (average body weight $10.1{\pm}0.60kg$) were randomly divided into 4 dietary treatments (CT-0, CT-1, CT-1.5, and CT-2 containing 0, 1.0, 1.5, and 2.0 percent CT through LMM, respectively) consisting of 6 lambs each in a completely randomized design. All the lambs were offered a basal diet of wheat straw ad libitum, oat hay (100 g/d) along with required amount of concentrate mixture to meet their nutrient requirements for a period of 6 months. After 3 months of experimental feeding, a metabolism trial of 6 days duration was conducted on all 24 lambs to determine nutrient digestibility and nitrogen balance. Urinary excretion of purine derivatives and microbial protein synthesis were determined using high performance liquid chromatography. Respiration chamber study was started at the mid of 5th month of experimental feeding trial. Whole energy balance trials were conducted on individual lamb one after the other, in an open circuit respiration calorimeter. Results: Intake of dry matter and organic matter (g/d) was significantly (p<0.05) higher in CT-1.5 than control. Digestibility of various nutrients did not differ irrespective of treatments. Nitrogen retention and microbial nitrogen synthesis (g/d) was significantly (p<0.01) higher in CT-1.5 and CT-2 groups relative to CT-0.Total body weight gain (kg) and average daily gain (g) were significantly (linear, p<0.01) higher in CT-1.5 followed by CT-1 and CT-0, respectively. Feed conversion ratio (FCR) by lambs was significantly (linear, p<0.01) better in CT-1.5 followed by CT-2 and CT-0, respectively. Total wool yield (g; g/d) was linearly (p<0.05) higher for CT-1.5 than CT-0. Methane emission was linearly decreased (p<0.05) in CT groups and reduction was highest (p<0.01) in CT-2 followed by CT-1.5 and CT-1. Methane energy (kcal/d) was linearly decreased (p<0.05) in CT groups. Conclusion: The CT supplementation at 1% to 2% of the diet through Ficus infectoria and Psidium guajava LMM significantly improved nitrogen metabolism, growth performance, wool yield, FCR and reduced methane emission by lambs.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.1 s.92
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• pp.9-18
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• 2005

This paper presents an antenna for US-PCS band indoor repeaters with enhancement of isolation. In common repeaters require an enough isolation to reduce the interferences between transmitted and received signals. Thus, it is investigated to improve front-to-back ratio of IBD(Integrated Balun Dipole) antenna which has a good linear polarization with a cavity or multi-cavity by using polarization diversity and aperture matching method. From the simulated and measured results, the antenna realized by using polarization diversity and aperture matching method has a VSWR below 1.5, gain over 8 dBi and enhanced isolation of 15$\~$24 dB in US-PCS band.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.3
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• pp.10-14
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• 2017

A reverberation chamber is widely used in mobile handset measurements due to its faster and simpler measurement process compared to traditional anechoic chambers. We propose an ultra-wideband inverse conical antenna design suitable as a reference antenna in a reverberation chamber. Traditionally, multiple discone antennas are needed to cover more than 10:1 operation bandwidth of a reverberation chamber. The proposed inverse conical antenna offers wideband impedance matching bandwidth by virtue of the linear impedance transition along its oblique side. The antenna is feasible to mount on the conductive walls which can be utilized as a ground to improve the matching bandwidth, antenna gain and radiation patterns. The antenna geometry is optimized using a 3D electromagnetic simulation tool and fabricated using a 3D printer. The measured results show that the antenna reflection coefficient lower than -10dB and radiation efficiency more than 70% at the frequency range of 0.65~7 GHz.

• Journal of the Korea Institute of Military Science and Technology
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• v.12 no.6
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• pp.760-767
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• 2009

This thesis focuses on the study of high-power, coupled-cavity traveling-wave tube(CCTWT) for radar applications. The CCTWT employed a reentrant double-slot staggered RF cavity structure. Computational analysis of the X-band, double-slot staggered structures is carried out through the use of HFSS code, which solves Maxwell's equations fully in three-dimensions. The non-linear, large-signal performance of CCTWTs are predicted from numerical simulations using a three-dimensional particle-in-cell code, MAGIC3D. With beam voltage set to 12.7~13kV and beam current at 300mA, the CCTWT produces a saturated radiation power of 350~430W, corresponding to an electronic efficiency of 8.9~11.2% and a gain of 23.7~24.2dB within a frequency range of 7.9~8.4GHz.

• JSTS:Journal of Semiconductor Technology and Science
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• v.16 no.3
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• pp.312-318
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• 2016

This paper presents a 2-6 GHz GaN HEMT power amplifier monolithic microwave integrated circuit (MMIC) with bridged-T all-pass filters and output-reactance-compensation shorted stubs using the $0.25{\mu}m$ GaN HEMT foundry process that is developed by WIN Semiconductors, Inc. The bridged-T filter is modified to mitigate the bandwidth degradation of impedance matching due to the inherent channel resistance of the transistor, and the shorted stub with a bypass capacitor minimizes the output reactance of the transistor to ease wideband load impedance matching for maximum output power. The fabricated power amplifier MMIC shows a flat linear gain of 20 dB or more, an average output power of 40.1 dBm and a power-added efficiency of 19-26 % in 2 to 6 GHz, which is very useful in applications such as communication jammers and electronic warfare systems.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1673-1681
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• 2015

A low dropout (LDO) regulator with a wide-bandwidth is proposed in this paper. The regulator features a Human Body Model (HBM) 8kV-class high robustness ElectroStatic Discharge (ESD) protection circuit, and two error amplifiers (one with low gain and wide bandwidth, and the other with high gain and narrow bandwidth). The dual error amplifiers are located within the feedback loop of the LDO regulator, and they selectively amplify the signal according to its ripples. The proposed LDO regulator is more efficient in its regulation process because of its selective amplification according to frequency and bandwidth. Furthermore, the proposed regulator has the same gain as a conventional LDO at 62 dB with a 130 kHz-wide bandwidth, which is approximately 3.5 times that of a conventional LDO. The proposed device presents a fast response with improved load and line regulation characteristics. In addition, to prevent an increase in the area of the circuit, a body-driven fabrication technique was used for the error amplifier and the pass transistor. The proposed LDO regulator has an input voltage range of 2.5 V to 4.5 V, and it provides a load current of 100 mA in an output voltage range of 1.2 V to 4.1 V. In addition, to prevent damage in the Integrated Circuit (IC) as a result of static electricity, the reliability of IC was improved by embedding a self-produced 8 kV-class (Chip level) ESD protection circuit of a P-substrate-Triggered Silicon Controlled Rectifier (PTSCR) type with high robustness characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.4B
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• pp.298-307
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• 2002

This paper concentrates on developing and analyzing an advanced space-time multiuser receiver for WCDMA forward link. Through exploring the interference caused by co-channel users and delayed multipaths in CDMA, a constrained linear adaptive filter is adopted to cancel the interference. Furthermore, by utilizing the space-time diversity, an optimum diversity receiver, called a constrained adaptive space-time interference canceller (C-ASTIC), is proposed. For comparison, the statistical analysis of multiuser performance for WCDMA system with space-time diversity is described. The result of the simulation showed that C-ASTIC performs better than both the space-time diversity combining maximal ratio combiner (MRC) and the single-antenna adaptive interference canceller in a multipath fading channel. Also, the efficiency of the C-ASTIC in the multimedia communication environment is investigated under the multiuser, multi-transmit antenna, and multirate WCDMA system in a multipath fading channel. From the results, the C-ASTIC was validated to be useful for multi-rate WCDMA system through improving the performance gain by more than 3 dB at BER of 10$\^$-3/ in a half or more loaded system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.6
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• pp.493-500
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• 2014

Nonlinear characteristics of cellular counterflow diffusion flame near the radiative extinction limit at large Damk$\ddot{o}$hler number are numerically investigated. Lewis number is assumed to be 0.5 and flame evolution is calculated by imposing an infinitesimal disturbance to a one-dimensional(1-D) steady state flame. The early stage of nonlinear development is very similar to that predicted in a linear stability analysis. The disturbance with the wavenumber of the fastest growing mode emerges and grows gradually. Eventual, an alternating pattern of reacting and quenching stripes is developed. The cellular flame temperature is higher than that of 1-D flame because of the gain of the total enthalpy. As the Damk$\ddot{o}$hler number is further increased, the shape of the cell becomes circular to increase the surface area per unit reacting volume. The cellular flames do not extinguish but survive even above the 1-D steady state extinction condition.

• Journal of IKEEE
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• v.2 no.1 s.2
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• pp.1-14
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• 1998

In this paper, Antenna, LNA, Mixer, VCO, and Modulation/Demodulation in Baseband processor which are the RF main components in Wireless LAN system for ultra high-speed communications network are studied. Antenna bandwidth and selective fading due to multipath can be major obstacles in high speed digital communications. To solve this problem, wide band MSA which has loop-structure magnetic antenna characteristics is designed. Distributed mixer using dual-gate GaAs MESFET can achieve over 10dB LO/RF isolation without hybrid, and minimize circuit size. As linear mixing signal is produced, distortions can be decreased at baseband signals. Conversion gain is achieved by mixing and amplification simultaneously. Mixer is designed to have wide band characteristics using distributed amplifier. In VCO design, Oscillator design method by large signal analysis is used to produce stable signal. Modulation/Demodulation system in baseband processor, DS/SS technique which is robust against noise and interference is used to eliminate the effect of multipath propagation. DQPSK modulation technique with M-sequences for wideband PN spreading signals is adopted because of BER characteristic and high speed digital signal transmission.