• ETRI Journal
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• v.27 no.3
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• pp.243-249
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• 2005

A mobile antenna for multimedia communications with Ku-band geostationary satellite KOREASAT-3 and JSAT-2A is presented. The forward link of the satellite communication is 11.7 to 12.75 GHz, and the return link is 14.0 to 14.5 GHz. The mobile antenna is designed to be a stair structure using 24 active phased array elements in order to provide a low profile, and to be at a non-periodic array distance using the genetic algorithm. Also, the designed antenna uses the double beam forming method for stable satellite tracking. The fabricated mobile antenna is examined using various experiments to confirm its capability for practical application. From the measured results, the fabricated mobile antenna system is confirmed to have a good performance.

• The Journal of the Acoustical Society of Korea
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• v.34 no.5
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• pp.335-342
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• 2015

Phononic crystals are composite materials consisting of a periodic arrangement of scattering inclusions in a host material. One of the most important properties of phononic crystals is the existence of band gaps, i.e., ranges of frequencies at which acoustic waves cannot propagate through the structure. The present study aims to investigate theoretically and experimentally the acoustic band structures in two-dimensional (2D) phononic crystals consisting of periodic square arrays of stainless steel solid cylinders with a diameter of 1 mm and a lattice constant of 1.5 mm in water. The theoretical dispersion relation that depicts the relationship between the frequency and the wave vector was calculated along the ${\Gamma}X$ direction of the first Brillouin zone using the finite element method to predict the band structures in the 2D phononic crystals. The transmission and the reflection coefficients were measured in the 2D phononic crystals with 1, 3, 5, 7, and 9 layers of stainless steel cylinders stacked in the perpendicular direction to propagation at normal incidence. The theoretical dispersion relation exhibited five band gaps at frequencies below 2 MHz, the first gap appearing around a frequency of 0.5 MHz. The location and the width of the band gaps experimentally observed in the transmission and the reflection coefficients appeared to coincide well with those determined from the theoretical dispersion relation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.6022-6026
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• 2012

This article presents a band-stop filter (BSF) by using a periodic structure property of frequency selective surfaces (FSSs) embedded in a microstrip transmission line. The proposed BSF is designed with FSS unit cells modifying the cross-loop slots. The BSF is interpreted with an equivalent circuit model and a dispersion diagram. The center frequency (fo) of the BSF is 6.6GHz. Proposed filter increases the number of unit cell. As a result, 3dB bandwidth is wider and insertion loss is reduced. Also, Facbricated BSF exhibits uniplanar geometry, simple fabrication.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.215-221
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• 2017

An electromagnetic (EM) wave absorber reduces the possibility of radar detection by minimizing the radar cross section (RCS) of structures. In this study, a radar absorbing structure (RAS) was applied to the leading edge of a blended wing body aircraft to reduce RCS in X-band (8.2~12.4GHz) radar. The RAS was composed of a periodic pattern resistive sheet with conductive lossy material and glass-fiber/epoxy composite as a spacer. The applied RAS is a multifunctional composite structure which has both electromagnetic (EM) wave absorbing ability and load-bearing ability. A two dimensional unit absorber was designed first in a flat-plate shape, and then the fabricated leading edge structure incorporating the above RAS was investigated, using simulated and free-space measured reflection loss data from the flat-plate absorber. The leading edge was implemented on the aircraft, and its RCS was measured with respect to various azimuth angles in both polarizations (VV and HH). The RCS reduction effect of the RAS was evaluated in comparison with a leading edge of carbon fabric reinforced plastics (CFRP). The designed leading edge structure was examined through static structural analysis for various aircraft load cases to check structural integrity in terms of margin of safety. The mechanical and structural characteristics of CFRP, RAS and CFRP with RAM structures were also discussed in terms of their weight.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.3 s.357
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• pp.20-25
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• 2007

The periodic domain-inversion in the selective areas of $Ti:LiNbO_3$ Mach-Zender waveguides was performed and band-pass modulators and single sideband (SSB) modulators were fabricated by using domain-reversal. The domain wall velocity was precisely controlled by real-time analysis of a poling-induced response current under an applied voltage. The domain wall velocity was significantly affected by the crystal orientation of the domain wall propagation which influenced the final domain geometry. In a certain case, the decomposition of $LiNbO_3$ crystal was observed, for example, under the condition of too fast domain wall propagation. The fabricated band-pass modulator with a periodic domain-inversion structure showed the maximum modulation efficiency at 30.3 GHz with 5.1 GHz 3dB-bandwidth, and SSB modulator was measured to show 33 dB USB suppression over LSB at 5.8 GHz RF.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.801-808
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• 2004

In this paper, we proposed the grating parallel plate waveguide structure for converting a linearly polarized wave to a circularly polarized wave. For the design of the polarizer, the moment method and Floquet's theorem are applied under two assumptions that the incident wave is a plane wave and the structure is infinitely periodic. In order for the more precise design, we performed the near-field analysis for the finite polarizer structure using MATLAB. By comparing with the measured results obtained by the near-field arrangement, we verified the correctness of our near-field analysis. By taking the ideal assumptions considered in the initial design procedure into account, newly designed modified dimensions for the polarizer was suggested which give improved performance.

• Journal of Power System Engineering
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• v.3 no.1
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• pp.55-59
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• 1999

Generally, T.G(Tacho-generator, Tachometer) sensor is used widely for sensing the angular velocity in rotary machine. By limitation of T.G sensor's structure, the sensed angular velocity include a periodic noise, and the noise is called "ripple" as an electrical term. To reduce the effecting of the ripple, many kinds of filters are designed and installed, but there is necessary a trade off between response time and adapted frequency band. In this paper, we propose a generalized observer to estimate an angular velocity from the output signal of T.G sensor. The generalized observer is proposed firstly for continue systems, and it is applied to DC servo motor with T.G sensor. For simulation, we measure T.G signals at 60, 400, 570 rpm respectively, and analysis those to obtain the resonance frequency of ripple by FFT method. To verify the effectiveness of the proposed algorithm, we compare the results with those of a RC low frequency band filter.

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.2995-3004
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• 2013

The structural, electronic, and optical properties of poly(3-hexylthiophene) (P3HT) have been comprehensively studied by density functional theory (DFT) to rationalize the experimentally observed properties. Rather, we employed periodic boundary conditions (PBC) method to simulate the polymer block, and calculated effective charge mass from the band structure calculation for describing charge transport properties. The simulated results of P3HT are consistent with the experimental results in band gaps, absorption spectra, and effective charge mass. Based on the same calculated methods as P3HT, a series of polymers have been designed on the basis of the two types of building blocks, furofurans and furofurans substituted with cyano (CN) groups, to investigate suitable polymers toward polymer solar cell (PSC) materials. The calculated results reveal that the polymers substituted with CN groups have good structural stability, low-lying FMO energy levels, wide absorption spectra, and smaller effective masses, which are due to their good rigidity and conjugation in comparison with P3HT. Besides, the insertion of CN groups improves the performance of PSC. Synthetically, the designed polymers PFF1 and PFF2 are the champion candidates toward PSC relative to P3HT.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.2
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• pp.151-156
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• 2021

Leakage and Bragg condition of optical waveguide with asymmetric rectangular grating profile are evaluated in detail by using novel and rigorous modal transmission-line theory (MTLT) based on eigenvalue problem. The optical waveguide composed by asymmetric rectangular grating occur leaky-wave stop-bands at Bragg conditions, and anomalies based on Rayleigh-Wood condition near Bragg conditions. Furthermore, DFB properties of the guiding structure at Bragg conditions are analyzed by applying longitudinal equivalent transmission-line with characteristic impedance of periodic grating. The numerical results show that filtering characteristics that maximize the reflected power of DFB waveguide are activated near Bragg conditions, in which leaky-wave stop-bands occur.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.4
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• pp.616-624
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• 2006

In this paper, the transfer characteristics of high frequency transmission line having defected ground structure (DGS) and lumped elements are described. When a DGS, which is a kind of periodic structure, is inserted into a transmission line, its equivalent inductance and capacitance elements are added to the characteristics of the standard transmission line. This generates resonance, 3dB cut-off frequency, low-pass, band rejection, and band pass characteristics, and causes a slow-wave and enlarged electrical length of the transmission line. In addition, if the DGS is combined by a lumped element such as resistor, capacitor, and inductor, the resonant and cut-off frequencies moves up or down and other changes occur in the transmission characteristics. The variation of the transmission characteristics is described with the qualitative prediction and measured data.