• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.145.2-145.2
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• 2011

We present the results of simultaneous observations of SiO v = 1, 2, J = 1-0, $^{29}SiO$ v = 0, J = 1-0, and $H_2O$ $6_{16}-5_{23}$ maser lines toward 152 known $H_2O$-only maser sources (the sources which are previously detected only in the 22 GHz $H_2O$ maser emission) using Yonsei and Tamna 21-m radio telescopes of the Korean VLBI Network from 2009 June to 2011 January. Both SiO and $H_2O$ maser emission were detected from 62 sources giving a detection rate of 40.8 %. SiO-only maser emission was detected from 27 sources, while $H_2O$-only maser was detected from 22 sources. We have identified 19 new detections of SiO maser emission for previous non-detection sources and 51 new detections of SiO maser for previously not observed sources. Characteristics of all observed sources in the IRAS two-color diagram is investigated including their evolutionary sequence and mutual relations between SiO and $H_2O$ maser emission. These observational results will be useful for statistical study of asymptotic giant branch (AGB) stars and future VLBI observation.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.1 no.1
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• pp.1-9
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• 2002

In this paper, a DRO (Dielectric Resonator Oscillator) with high stability in DSRC(Dedicated Short Range Communication) is designed and fabricated. The DRO shows the phase noise characteristic of -109.3 dBc/Hz at 100 kHz offset from the fundamental frequency. The output power of 11.53 dBm, and the second harmonic suppression of 55.33 dBc for the DRO are obtained. This DRO with high stability of the phase noise characteristic can be used for the system in DSRC.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.53-53
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• 2013

We present preliminary results of far-infrared(FIR) study of the supernova remnant(SNR)s in the Large Magellanic Cloud using the Herschel HERITAGE (HERschel Inventory of The Agents of Galaxy Evolution) data set. HERITAGE provides FIR data covering the entire LMC at 100,160, 250, 350, and 500 um. In order to confirm FIR emission associated with SNRs, we refer to Magellanic Cloud Emission-Line Survey (MCELS) H-alpha & SII data, Spitzer surveying the Agents of a Galaxy's Evolution (SAGE) Multiband Imaging Photometer (MIPS) 24um & 70um data, Chandra Supernova Remnants Catalog, and ATCA 4.8GHz continuum images of Dickel et al. (2005). Among 47 SNRs in the LMC, 7 SNRs show associated FIR emission. We present multi-wavelength view of 5 SNRs; DEM L249, N49, N63A, N132D, and the SNR in N4. N49 and N132D show morphological correlation in FIR and X-ray, suggesting that the FIR emission is from dust grains collisionally heated by X-ray emitting plasma. The FIR emission of N63A resembles H-alpha emission, which implies that the FIR line radiation could be dominant. The FIR images of the rest two objects, DEM L249 and SNR in N4, show no correlation to the other-waveband images.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1664-1666
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• 2000

The structural and microwave properties of Ba($Mg_{1/3}Ta_{2/3})O_3$-Ba($Co_{1/3}Nb_{2/3})O_3$ ceramics were investigated with composition ratio. The specimens were sintered at 1525$^{\circ}C$ for 5 hours in air. All specimens exhibited superlattice reflection planes of (100), (111), (200), (201), and (112). Increasing mole ratio of BCN ceramics, the peak intensity of superstructure reflection plane were decreased, while dielectric constant was slightly increased. The dielectric constant and quality factor of the 0.8BMT-0.2BCN ceramics were 27.51, 103,681 [at 1GHz], respectively.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.103-105
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• 2015

The 22 m diameter Mopra telescope in Australia is being used to undertake an improved survey of the CO J = 1-0 line at 3mm along the 4th quadrant of the Galaxy, achieving an order of magnitude better spatial and spectral resolution (i.e. 0.6 and 0.1 km/s) than the Dame et al. (2001) survey that is publically available for the Southern Galactic plane. Furthermore, the Mopra CO survey includes the four principal isotopologues of the CO molecule (i.e. $^{12}CO$, $^{13}CO$, $C^{18}O$ and $C^{17}O$). The survey makes use of an 8 GHz-wide spectrometer and a fast mode of on-the-fly mapping developed for the Mopra telescope, where the cycle time has been reduced to just 1/4 of a second. 38 square degrees of the Galaxy, from $l=306-344^{\circ}$, $b=0{\pm}5^{\circ}$ have currently been surveyed, together with additional 9 sq. deg. regions around the Carina complex and the Central Molecular Zone. We present new results from the survey (see also Burton et al., 2013, 2014). The Mopra CO data are being made publically available as they are published; for the latest release see the project website at www.phys.unsw.edu.au/mopraco.

• Journal of Electrical Engineering and Technology
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• v.13 no.1
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• pp.400-405
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• 2018

This paper presents a compact ultra-wideband (UWB) flexible monopole antenna design on a paper substrate. The proposed antenna is made of iterations of a circular slot inside an octagonal metallic patch. This fractal-based geometry has been deployed to achieve compactness along with improved bandwidth, measured reflection coefficient -10 dB bandwidth ranging from 2.7 to 15.8 GHz. The overall size of the antenna is $26mm{\times}19mm{\times}0.5mm$, which makes it a compact one. The substrate used is paper and the main features like environment friendly, flexibility, green electronics applications and low cost of fabrication are the key factors for the proposed antenna. The aforementioned UWB prototype is suitable for many wireless communication systems such as WiMAX, WiFi, RFID and WSN applications. Antenna has been tested for the effect of bending by placing it over a curved surface of a very small radius of 10 mm.

• Journal of information and communication convergence engineering
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• v.16 no.4
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• pp.252-257
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• 2018

A wideband double radiator circular disc annular monopole antenna is proposed is this work. The radiators are etched on the surfaces of two Taconic TLY-5 substrates with a circular hole cut out of each of the radiators initially at the centers of the radiators with subsequent downward displacement of the holes. The antenna is designed with a two-step feeding transformer system for impedance matching between the input power source supplied by a $50-{\Omega}$ SMA connector and the monopole radiators. The transformer system improves the bandwidth performance at higher frequencies. The proposed antenna achieves a wideband having the capability of working between 0.645 and 18.775 GHz, corresponding to a -10 dB bandwidth of 186.7% with gain ranging from 0.95 to 8.26 dBi. In comparison to other metal disc planar monopole antennas, the proposed antenna has a small total size width due to the size of the ground plane, which has a diameter 100 mm. The frequency range of the antenna provides applications in global positioning systems, mobile communications, ultra-wideband short distance communications, and wireless computer networks.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.956-963
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• 2002

A linearly polarized folded type and H-shape slit folded type microstrip patch antenna at GPS(center frequency:1.575 GHz) were designed and fabricated by folding a conventional single $\lambda_{g}/2(\lambda_{g}:wavelength)$ rectangular patch a half along the length direction at the center of patch and inserting ground plane in the middle. As a result, two types of omnidirectional radiation patterns for E-plane (for zx-plane) in the direction of the length of patch and H-plane (for xy-plane) have been acquired. The experimental results show that the average gains of folded type and slit folded type for omnidirectional E-plane and H-plane are -1.5 dBd (-2.4 dBd) and -3.27 dBd(-2.5 dBd). Slit folded type microstrip patch antenna was more miniaturized than folded type microstrip patch antenna by 27.5 %. In case of slit folded type antenna, average gains of omnidirectional radiation pattern for E & H-plane are almost same.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.421-432
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• 2020

This paper proposes a 2-kW solid-state power amplifier (SSPA) developed by employing power amplifier pallets designed using gallium-nitride high electron mobility transistors, which is used in S-band military radars and to replace existing traveling-wave tube amplifier (TWTA). The SSPA consists of a high-power amplifier module, which combines eight power amplifier pallets, a drive amplifier module, a digital control module, and a power supply unit. First, the amplifier module and component were integrated into a small package to account for space limitations; next, an on-board harmonic filter was fabricated to reject spurious components; and finally, an auto gain control system was designed for various duty ratios because recent military radar systems are all active phase radars using the pulse operation mode. The developed SSPA exhibited a max gain of 48 dB and an output power ranging between 63-63.6 dBm at a frequency band of 3.1 to 3.5 GHz. The auto gain control function showed that the output power is regulated around 63 dBm despite the fluctuation of the input power from 15-20 dBm. Finally, reliability of the developed system was verified through a temperature environment test for nine hours at high (55 ℃) / low (-40℃) temperature profile in accordance with military standard 810. The developed SSPA show better performance such as light weight, high output, high gain, various safety function, low repair cost and short repair time than existing TWTA.

• Journal of the Korean Ceramic Society
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• v.39 no.12
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• pp.1190-1196
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• 2002

Microwave dielectric properties and multilayer characteristics $(1-x)BiNbO_4-xCaNb_2O_6$ (0${\le}$x${\le}$1.0) ceramics were investigated as a function of $CaNb_2O_6$ content. In the composition range of 0.25${\le}$x${\le}$0.75, the mixture phases of $BiNbO_4$ with stibotantalate structure and $CaNb_2O_6$ with columbite structure were detected and secondary phase or phase transition were not detected. Dielectric constant (K) of $(1-x)BiNbO_4-xCaNb_2O_6$ ceramics was largely dependent on the existing phase and could be estimated by the dielectric mixing rule calculated from maxwell equation. Typically, dielectric constant (K) of 26, quality factor (Qf) of 4300 GHz and Temperature Coefficient of resonant Frequency (TCF) of -18 ppm/${\circ}C$ were obtained for $0.5BiNbO_4-0.5CaNb_2O_6$ specimens with 0.8 wt% $CuV_2O_6$ sintered at 1000${\circ}C$ for 3h. The deviation of X-Y shrinkage and camber value of the multilayers obtained from $0.5BiNbO_4-0.5CaNb_2O_6$ green sheet sintered at 850∼950${\circ}C$ for 20 min. were smaller than those of $BiNbO_4$ multilayers.