• International Journal of Internet, Broadcasting and Communication
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• v.8 no.2
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• pp.23-30
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• 2016

In this paper, for the pratical building envoronments, the propagation properties of the electromagnetic waves of the sub-1GHz bands, including the 447MHz, 868MHz, and 715MHz, and the 2.4GHz band are experimentally observed in therms of the received signal strength indicator (RSSI) value. The compasion of the frequency bands can be utilized to efficiently construct the wireless sensor networks (WSN) for the building automation control. In order to measure the RSSI values in the building, an RSSI measurement system is first designed, in which the master part can transmit data packets and measure the corresponding RSSI values, and the slave part can respond the received data packets. Using the measurement system, the RSSI values are then experimentally measured at four types of building enviroments. From the experimental result analysis, we could notice that the sub-1GHz, especially the 447MHz band, showd a good communication performance for the building environment and could provide an efficient WSN construction when the data rate is relatively low.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.61.2-61.2
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• 2020

We study the overdensity of near-infrared sources around 508 sub-mm sources classified as dusty galaxies in the SPT-SZ survey catalog observed in 95 GHz (3.15 mm), 150 GHz (2 mm) and 250 GHz (1.2 mm) bands. We used the VISTA hemisphere survey data release 6 (VHS DR6) catalog covering the J, H, Ks bands. The mean number of galaxies within a radius of 60 arcsec (corresponding to about 500 kpc at z=2) from 500 randomly selected positions is 14.4, while the galaxy number distribution is approximated as a Gaussian with a standard deviation of 7.9. From the 2500 deg2 of SPT-SZ survey + VHS DR6 data, there were 27 sub-mm sources that have galaxy overdensity higher than 4σ. We present color-magnitude diagram around 27 selected sub-mm sources with enhanced galaxy surface densities, in order to investigate the presence of structure around sub-mm sources.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.127.1-127.1
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• 2011

Over the past several years the millimeter wave VLBI(Veryl Long Baseline Interferometry) observations have been intensively carried out. However In millimeter and sub-millimeter waves observations for VLBI, it is crucial to calibrate correctly the phase variations of the electromagnetic waves propagation through the troposphere. To do this, KVN(Korean VLBI Network) has a unique multi-frequency bands receiver system which is able to perform the simultaneous observations in up to four bands such as 22, 43, 86, and 129GHz. The phase of a source at 22GHz can be used to calibrate the phase of the same source at higher frequency bands. The phase calibration using multi-frequency bands receiver system is possible because the phase fluctuations from a given amount of waver vapor increase linearly with frequency. That is to say that troposphere is non-dispersive property in terms of tropospheric delay fluctuations. In this talk, We present results of test observation for multi-frequency bands receiver system.

• International Journal of Internet, Broadcasting and Communication
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• v.12 no.1
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• pp.37-44
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• 2020

In this paper, we proposed a compact printed monopole antenna with an inverted L-shaped slot for dual-band operations. Two operating frequency bands are achieved with the use of an inverted L-shaped slot etched on the radiating strip for bandwidth enhancement and a defected ground structure for return loss improvement in the higher frequency band. The measured results showthat the proposed antenna has impedance bandwidths (S₁₁< -10 dB) of 270 MHz (1.81-2.08 GHz) and 340 MHz (2.36-2.70 GHz), covering the required bandwidths for PCS (1850.5-1989.5 MHz), CDMA 2000 (1850-1990 MHz), TD-SCDMA (1880-2025 MHz) and 2.4 GHz WLAN (2400-2484 MHz). The measured return loss of the proposed antenna has a good value of approximately 27.2 dB at 2.4 GHz WLAN. The antenna's peak gains also have a high value of 1.92 dBi at 2 GHz and 2.12 dBi at 2.45 GHz. The proposed antenna shows omnidirectional radiation patterns over the entire frequency range of interest.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.235.1-235.1
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• 2015

Artificially-engineered materials, whose electromagnetic properties are not available in nature, such as negative reflective index, are called metamaterials (MMs). Although many scientists have investigated MMs for negative-reflective-index properties at the beginning, their interests have been extended to many other fields comprising perfect lenses. Among various kinds of MMs, metamaterial absorbers (MM-As) mimic the blackbody through minimizing transmission and reflection. In order to maximize absorption, the real and the imaginary parts of the permittivity and permeability of MM-As should be adjusted to possess the same impedance as that of free space. We propose a dual-wide-band and polarization-independent MM-A. It is basically a triple-layer structure made of metal/dielectric multilayered truncated cones. The multilayered truncated cones are periodically arranged and play a role of meta-atoms. We realize not only a wide-band absorption, which utilizes the fundamental magnetic resonances, but also another wide-band absorption in the high-frequency range based on the third-harmonic resonances, in both simulation and experiment. In simulation, the absorption bands with absorption higher than 90% are 3.93 - 6.05 GHz and 11.64 - 14.55 GHz, while the experimental absorption bands are in 3.88 - 6.08 GHz and 9.95 - 13.84 GHz. The physical origins of these absorption bands are elucidated. Additionally, it is also polarization-independent because of its circularly symmetric structures. Our design is scalable to smaller size for the infrared and the visible ranges.

• Journal of Electrical Engineering and Technology
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• v.7 no.4
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• pp.582-588
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• 2012

In this paper, a highly miniaturized and performed UWB bandpass filter has been newly designed and implemented by embedding all the passive elements into a multi-layered PCB substrate with high dielectric $SrTiO_3$ composite film for 3.1 - 4.75 GHz compact UWB system applications. The high dielectric composite film was utilized to increase the capacitance densities and quality factors of capacitors embedded into the PCB. In order to reduce the size of the filter and avoid parasitic EM coupling between the embedded filter circuit elements, it was designed by using a $3^{rd}$ order Chebyshev circuit topology and a capacitive coupled transformation technology. Independent transmission zeros were also applied for improving the attenuation of the filter at the desired stopbands. The measured insertion and return losses in the passband were better than 1.68 and 12 dB, with a minimum value of 0.78 dB. The transmission zeros of the measured response were occurred at 2.2 and 5.15 GHz resulting in excellent suppressions of 31 and 20 dB at WLAN bands of 2.4 and 5.15 GHz, respectively. The size of the fabricated bandpass filter was $2.9{\times}2.8{\times}0.55(H)mm^3$.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.42.2-42.2
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• 2013

The F-GAMMA (FERMI-GST AGN Multi-frequency Monitoring Alliance) project is a program for the monthly monitoring of the broad-band spectra of currently about 90 selected Fermi-GST AGNs. F-GAMMA utilizes several facilities in cm, mm, sub-mm, infrared and optical bands, achieving an unprecedented coverage for the study of the spectral evolution of powerful relativistic jets in AGNs. The KVN joined the F-GAMMA project in May 2011, aiming to monitor flux density at 22 and 43 GHz. We present the preliminary results of flux density variability, evolution of spectral index, and modulation index.

• Journal of Korea Society of Industrial Information Systems
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• v.23 no.4
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• pp.23-31
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• 2018

This paper presented the implementation and design of the 2T-2R wireless HD video streaming systems over 1.7 GHz frequency band using 3GPP LTE-TDD standard on NI USRP RIO SDR platform. The baseband of the system used USRP RIO that are stored in Xilinx Kintex-7 chip to implement LTE-TDD transceiver modem, the signal that are transmitted from USRP RIO up or down converts to 1.7 GHz by using self-designed 1.7 GHz RF transceiver modules and it is finally communicated HD video data through self-designed 2x9 sub array antennas. It is that communication method between USRP RIO and Host PC use PCI express x4 to minimize delay of data to transmit and receive. The implemented system show high error vector magnitude performance above 32 dBc and to transmit and receive HD video in experiment environment anywhere. The proposed hybrid beam forming system could be used not only in the future 5G mobile communication systems under 6 GHz frequency band but also in the systems over 6 GHz frequency band like ones in mmWave frequency bands.

• Transactions on Electrical and Electronic Materials
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• v.17 no.5
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• pp.257-260
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• 2016

In this paper, two configurations (T-type and Y-type) of dual band Wilkinson Power Divider based upon Hilbert curves are presented. Formerly, the concept of Hilbert Curves was implemented in only designing microstrip antennas. In power dividers, this is the very first attempt of incorporating them for size reduction. In addition to this, an effect of inculcation of high-dielectric constant layer (Hafnium-oxide, HfO₂, ε_r= 25) between a substrate and top metallization in both configurations was investigated. The proposed configurations are designed on a high resistive silicon substrate (HRS) for L and S bands with resonating frequencies of 1.575 and 3.4 GHz. Both configurations have return loss that is better than 20 dB and an insertion loss of around 6 dB; isolation better than 30 dB was achieved for both models.

• Journal of information and communication convergence engineering
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• v.8 no.6
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• pp.635-639
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• 2010

A multi-resonance antenna for wireless communications is reported. By using double inverted-L strips, the antenna demonstrated compact size (15 mm ${\times}$ 14 mm) including the ground, multi-band operation for IEEE 802.11 a/b/g/p applications, and wide bandwidth of 1.7 GHz at 5 GHz band. Good radiation features of omni-directional patterns and 1.98 and 2.29 dBi peak antenna gains for the lower and upper bands, respectively, have been achieved.