• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.386-389
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• 2004

Beamforming for underwater acoustic communication is affected by the broadband feature of underwater acoustic communication signal, which has the low center frequency compared to the signal bandwidth. In this paper, the baseband equivalent array signal model is derived and we present computer simulation results for the broadband finite impulse response (FIR) beamformer performance according to the FIR filter order and the tap spacing. If the FIR filter order is increased above the optimum value, the beamformer performance is degraded. Also the tap spacing is related to the optimum FIR filter order.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.527-530
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• 2002

The frequencies for HAPS used in fixed wireless access are allocated in the millimeter wave bands. The systems using these frequencies can have a serious impact on the radio communication qualities due to rain. In this paper, we compare the specific rain attenuation using CM(combined) raindrop size distribution with those using different sevral raindrop size distributions for the frequency bands 28/48㎓. The rain attenuations using CM raindrop size distribution for the path between the earth and HAPS platform according to the elevation angle are described.

• Journal of the Optical Society of Korea
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• v.13 no.3
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• pp.316-320
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• 2009

A novel broadband wavelength-swept Raman laser was used to implement Fourier-domain mode locked (FDML) swept-source optical coherence tomography (SS-OCT). Instead of a conventional semiconductor optical amplifier, this study used broadband optical fiber Raman amplification, over 50 nm centered around 1545 nm, using a multi-wavelength optical pumping scheme, which was implemented with the four laser diodes at the center wavelengths of 1425, 1435, 1455 and 1465 nm, respectively, and the maximum operating power of 150 mW each. The operating swept frequency of the laser was determined to 16.7 kHz from the FDML condition of 12 km optical fiber in the ring cavity. The OCT images were obtained using the novel broadband wavelengthswept Raman laser source.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.3
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• pp.137-147
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• 2020

This paper proposes printed bow-tie antennas with 3 ~ 5 GHz broadband characteristics were proposed for testing the electromagnetic immunity of automotive electrical components in the 5G frequency band. The antenna get -10 dB bandwidth in the 2.75 ~ 6 GHz frequency band and the broadside radiation pattern with S₁₁ characteristic of -16.2 dB at resonant frequency. In testing electromagnetic immunity in the 5G mobile communication frequency band, the VSWR characteristic remained below 2.1, forming a level of 1 W as proposed by international standards. As a result, it is confirmed that the proposed antenna can be applied to antenna testing for electromagnetic immunity verification in the 5G mobile communication frequency band.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.10 s.103
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• pp.1177-1185
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• 2005

This paper investigates the noise radiated by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. At frequencies above the critical frequency, all wavenumber components of turbulence excite propagating cascade modes, and cascade effects are shown to be relatively weak. In this frequency range, acoustic power was shown to be approximately proportional to the number of blades. Based on this finding at high frequencies, an approximate expression is derived for the power spectrum that is valid above the critical frequency and which is in excellent agreement with the exact expression for the broadband power spectrum. The approximate expression shows explicitly that the acoustic Power above the critical frequency is proportional to the blade number, independent of the solidity, and varies with frequency as ${\phi}_{ww}(\omega/W$), where ${\phi}_{ww}$ is the wavenumber spectrum of the turbulence velocity and W is mean-flow speed. The formulation is used to perform a parametric study on the effects on the power spectrum of the blade number stagger angle, gap-chord ratio and Mach number. The theory is also shown to provide a close fit to the measured spectrum of rotor-stator interaction when the mean square turbulence velocity and length-scale are chosen appropriately.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.3
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• pp.135-140
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• 2019

In this paper, a frequency split type broadband drive amplifier operating in the L, S and C bands was designed and fabricated. Transistor is difficult to efficiently use when the fractional bandwidth of the drive amplifier is more than 100%, In particular, the characteristics of the driving amplifier are important for operating the power amplifier in which the characteristics of the output power and the efficiency are sensitively changed according to the frequency band. A frequency split methods was applied to maximize the bandwidth of a drive amplifier and to divide the output of the drive amplifier into low band and high band so that the transistor of the power amplifier located at the rear of the drive amplifier can be efficiently used. The designed drive amplifier was fabricated in GaAs HBT technology and 9-layer SiP, and verified by the measurements. The fabricated drive amplifier shows a gain of more than 8 dB and an output power of more than 15 dBm in the operating frequency range.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.5
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• pp.413-417
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• 2014

In coherent superhigh speed optical transmission link, compensating the system impairments are critical issues. Among these issues, phase noise and carrier frequency offset are the most important impairments which interrupt the signal recovery. This paper suggests a algorithm of digital signal processing that compensates the phase noise and carrier frequency offset and verified its validity. The suggested digital signal processing algorithm has a lower computational complexity compared with the previous algorithms, so it can ease the burden of signal processing at the receiver to provide high speed optical transmission system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.6
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• pp.245-250
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• 2014

This paper presents the broadband printed sleeve-monopole antenna implementing the sleeve monopole structure in the form of PCB. In the proposed antenna, the antenna performance was improved by the diameter variation of the radiator, the length variation of the sleeve, and the variation of the diameter of the sleeve conductor. HFSS simulator of ANSYS corp. was used in order to confirm the antenna parameter characteristic. According to the simulation results, the VSWR was less than 2 for the range of 2.12GHz~3.18GHz. The frequency bandwidth is 1.08GHz. The frequency range of the actual fabricated antenna was 2.0GHz~3.55GHz, the frequency bandwidth is 1.55GHz. The maximum gain was 1.64dBi. The proposed antenna was $56{\times}5{\times}1.6mm$ in size. The utilization possibility of the broadband printed sleeve-monopole antenna could be confirmed according to compare and analyze the simulation and measurement data.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.7
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• pp.719-725
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• 2008

In this paper, we have proposed a printed monopole antenna using parasitic elements. The broadband characteristics of the antenna is obtained by using the printed monopole and parasitic elements. To confirm the broadband characteristics of the antenna, of have designed and fabricated the proposed antenna. The return loss and radiation patterns are measured in the frequency range of$0.8{\sim}1.2\;GHz$. The measured results show that the proposed antenna has return loss less than -10 dB in the operating frequency band and the radiation pattern is the dipole-like patterns. The antenna gain varies from 1.7 to 4.6 dBi in the operating frequency band. Thus, the proposed antenna can be used for the broadband repeater antenna $0.806{\sim}0.960\;GHz$(TRS-800, CDMA and GSM-900).

• Journal of Environmental Science International
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• v.24 no.3
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• pp.353-358
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• 2015

In this study, we analyzed two types of echolocation calls used by the parti-coloured bat, Vespertilio sinensis. Bats were captured in the Naejangsan National Park in October 2013. Call sounds of hand-released bats were recorded at the location of capture within the National Park. We analyzed pulse duration (PD), pulse interval (PI), peak frequency (PF), maximum frequency ($F_{MAX}$), minimum frequency ($F_{MIN}$), and bandwidth (BW). V. sinensis emitted the different types of the echolocation calls depending on the surrounding environment. Frequency modulated-constant frequency (FM-CF) signal of audible range was emitted when they flew in the uncluttered space over the canopy. However, when flying in the cluttered space below the canopy, they only emitted FM signal. FM-CF signal is in the audible range (e.g., low frequency), and FM signal has a harmonic broadband frequency range of two. There were significant differences in PD, PI, PF, FMAX, FMIN, and BW between the calls emitted over and below the canopy. Considering the functional characteristics of FM and CF signals, we conclude that the foraging activity of V. sinensis was observed below the canopy, and recommend the use of FM signal and broadband as echolocation signals.