• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.28 no.10
• /
• pp.761-768
• /
• 2017

In this paper, to implement the electromagnetic wave environment and solve electromagnetic compatibility(EMC) problem, miniaturization of ultra-wide band log periodic dipole antenna for measurement was investigated. In addition, in oder to improve the signal-to-noise ratio in high frequency band, balun was connected to the antenna to stabilize the operation of the differential mode antenna and the single mode coaxial cable. To minimize the total size and to increase bandwidth of the antenna, a fat dipole structure was used for the resonance frequency band below 4 GHz and a general dipole shape was used for that above 4 GHz. The bandwidth of the proposed antenna was represented from 0.6 GHz to 8.0 GHz with a ratio bandwidth of 12.3 : 1. Measured peak gain varies from 5.7 dBi to 9.1 dBi, and a half power beamwidth was presented from $29.4^{\circ}$ to $100.2^{\circ}$ in operating range.

• Journal of Korean Society of Steel Construction
• /
• v.18 no.6
• /
• pp.793-804
• /
• 2006

Various PSC and steel-concrete composite railway bridges are being developed for short-medium spans with structural and economic efficiency. According to the design concept, the prestressed composite girder bridge has the advantages of being lightweight and having low girder depth, with the capacity for long spans. However, the dynamic behavior under a passing train is one of the critical issues concerning these railway bridges designed with more flexibility. Therefore, it is very important to evaluate the modal parameters before performing dynamic analyses. In this paper, real-scale prestressed composite girders were fabricated as a test model and modal testing was carried out to evaluate modal parameters including natural frequency and modal damping ratio. During the modal testing, a digitally controlled vibration exciter as well as an impact hammer was applied to obtain frequency-response functions, and the modal parameters were also evaluated after the fracture of test models. With application of reliable properties from modal tests, the estimation of dynamic performances of prestressed composite girder railway bridges can be obtained from various parametric studies on dynamic behavior under the passage of a moving train.

• Proceedings of the KSR Conference
• /
• 2007.11a
• /
• pp.1370-1378
• /
• 2007

High speed railway bridge is affected on safety of bridge by dynamic amplification effect, when dynamic response of bridge is equal to effect cycle load for rolling stock axle according to high speed operation train. And excessive deformation of structure has negative effect on operation safety of train and comfort of passenger due to fluctuation of wheel load by torsion of track etc. and decrease of contact force on vehicle wheel-rail. To ensure the safety of track and train operation safety, it is have to perform the study on resonance and deformation of structure. That criteria and requirement of railway bridge is limitation of vertical acceleration on deck for dynamic behavior of structure, contact of vehicle wheel and rail, limitation of face distortion and rotation angle of end deck, and limitation of vertical displacement by train. Unlike KYEONGBU High Speed Railway, New constructed HONAM High Speed Railway have to applied the new requirement for dynamic behavior safety according to change of condition which is type of ballast (slab ballast), interval of track, and actual rolling stock load. Therefore, in this paper, it was conformed the dynamic characteristic due to parameter, which related with above mentioned criteria, for steel composite bridges.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.2
• /
• pp.62-66
• /
• 2010

In this article, a oscillator at X-band with a double H-shape metamaterial resonator (DHMR) based on high-Q is proposed with metamaterial structure to improve Ihe phase noise and output power. The proposed oscillator is required low phase noise and high output power for the high performance frequency synthesizer. DHMR is designed to be high-Q at resonance frequency through strong coupling of E-field. This character makes phase noise excellent. The oscillator using DHMR is oscillated in X-band so as to apply frequency synthesizer of radar systems. The output power is 4.33 dBm and the phase noise is -108 dBc/Hz at 100 kHz offset of carrier frequency.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.7 no.1
• /
• pp.116-125
• /
• 1995

Higher order nonlinear transfer functions are applied to model the nonlinear responses obtained Inn dynamic analysis of single degree of freedom systems (SDOF) subjected to wave and current loadings. The structural systems are subjected to single harmonic, two wave combination and irregular wave loading. Three different sources of nonlinearities are examined for each of the wave loading condition and it is shown that the nonlinear response appear at the resonance frequencies of the SDOF even when virtually no wave energy exists at those resonance frequencies. Higher order nonlinear transfer functions based on Volterra series representation are used to model the nonlinear responses mainly f3r the flexible systems and clearly shows the degrees of nonlinearity either as quadratic or cubic.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.7 no.2
• /
• pp.50-55
• /
• 2008

In this paper, multi-band internal antenna which can adjust both resonant frequency and input impedance of antenna as using lumped inductor between shoring plate and ground plane is proposed. The structure of proposed antenna consists of PIFA (Planar Inverted F Antenna) structure and half-wavelength loaded line structure and has two shorting plates and one feeding plate. One shorting plate is shared. The operating frequency bands of designed antenna are GSM, GPS in the PIFA structure and DCS, US-PCS, W-CDMA in half-wave loaded line structure as varying the inductor value in 2.2nH, 3.3nH, and 4.7nH. As varying the inductor value in the shared shorting plate, input impedance of antenna is varied. To minimize the gain variation of antenna as adding lumped element, the inductor value is restricted at maximum of 6.8nH. The maximum gain of proposed antenna is measured as -1.60dBi in the GSM band, -1.16dBi in the GPS band, and 1.41dBi in the DCS/US-PCS/W-CDMA band.

• Journal of the Korean Ceramic Society
• /
• v.40 no.1
• /
• pp.81-86
• /
• 2003

Microwave dielectric properties have been investigated in the$(1-x)CaTiO_3-xYAlO_3$ (x=0.1~1.0) solid solution system. The mixtures of $CaTiO_3$ and $YalO_3$using solid state method were sintered at various temperatures. Their dielectric constants and related temperature coefficients were strongly depend on the composition of the solid solution. The optimum properties were recorded as for ${\varepsilon}_r=47,$ $Q{\times}f_0$=35000 and ${\tau}_f=+11ppm/^{\circ}C$ without sintering agent. Even at $1200^{\circ}C$ full densification has been achieved with addition of $CaB_2O_4$ in the $0.75CaTiO_3-0.25YalO_3$ composition. The sample of $0.3 wt%-CaB_2O_4$ added $ 0.75CaTiO_3-0.25YalO_3$ sintered at $1300^{\circ}C$ for 3 h showed optimum microwave dielectric properties of ${\varepsilon}_r=47$, $Q{\time}f_0=37000$ and ${\tau}_f=+17ppm/^{\circ}C$, which demonstrates the promising candidates for microwave dielectric materials covering 5~7 GHz range.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.2 no.4
• /
• pp.103-114
• /
• 1998

The floors of building structures equipped with vibrating machines can be susceptible to large vibration as a result of resonance or beating. Such a vibration can be reduced efficiently by using tuned mass dampers. However, the effectiveness of the damper depends greatly on the location and the natural frequency of the damper. To determine the optimum damper location is especially important since the dynamic behavior of a building structure varies with the location of the input loading. To this end, it is intended to decide the location and natural frequency of tuned mass dampers for reducing vibration of both loaded floors and floors located nearby the loaded floors considering the location and frequency components of the loading. The Vector composition method and the super elements are used th obtain the responses in steady states, and the optimum damper location and natural frequencies were found with the given damper mass.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.46 no.12
• /
• pp.14-21
• /
• 2009

In this paper, a Ka-band 10 W power amplifier module with seven power MMIC bare dies is designed and fabricated using MIC technology which combines multiple MMIC chips on a thin film substrate. Modified Wilkinson power dividers/combiners and CBFGCPW-Microstrip transitions for suppressing resonance and reducing connection loss are utilized for high-gain and high-power millimeter wave modules. A new TTL pulse timing control scheme is proposed to improve output power degradation due to large bypass capacitors in the gate bias circuit. Pulse-mode operation time is extended more than 200 nsec and output power increase of 0.62 W is achieved by applying the proposed scheme to the Ka-band 10 W power amplifier module operating in the pulsed condition of 10 kHz and $5\;{\mu}sec$. The implemented power amplifier module shows a power gain of 59.5 dB and an output power of 11.89 W.

• Journal of Advanced Navigation Technology
• /
• v.13 no.6
• /
• pp.838-845
• /
• 2009

In order to obtain magneto-dielectrics with various permmittivity and permeability which could be used as the antenna substrate, various magneto-dielectrics compounded of dielectric materials(such as silicon and epoxy resin) and magnetic materials(such as carbonyl iron, barium and strontium powder) were fabricated. The relative permittivity and permeability of those were measured by use of HP 4291B impedance analyzer. Based upon the measured results, inverted-F meander monopole antennas(IFA) which were printed on the magneto-dielectric substrates fabricated as film type were designed and fabricated to investigate into variations of antenna characteristics such as the resonant frequency and impedance bandwidth in comparison with use of dielectric substrate. Some simulated and measured results for the designed IFA were presented. Characteristics of magneto-dielectrics which are different according as the choice of magnetic material or the composition ratio between magnetic material and dielectric material is different have been discussed.