• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.04b
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• pp.79-80
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• 2009

The local oxidation using an atomic force microscopy (AFM) is useful for Si-base fabrication of nanoscale structures and devices. SiC is a wide band-gap material that has advantages such as high-power, high-temperature and high-frequency in applications, and among several SiC poly types, 4H-SiC is the most attractive poly type due to the high electron mobility. However, the AFM local oxidation of 4H-SiC for fabrication is still difficult, mainly due to the physical hardness and chemical inactivity of SiC. In this paper, we investigated the local oxidation of 4H-SiC surface using an AFM. We fabricated oxide patterns using a contact mode AFM with a Pt/Ir-coated Si tip (N-type, $0.01{\sim}0.025\;{\Omega}cm$) at room temperature, and the relative humidity ranged from 40 to 50%. The height of the fabricated oxide pattern ($1{\sim}3\;nm$) on SiC is similar to that of typically obtained on Si ($10^{15}{\sim}10^{17}\;cm^{-3}$). We perform the 2-D simulation to further analyze the electric field between the tip and the surface. Whereas the simulated electric field on Si surface is constant ($5\;{\times}\;10^7\;V/m$), the electric field on SiC surface increases with increasing the doping concentration from ${\sim}10^{15}$ to ${\sim}10^{17}\;cm^{-3}$. We demonstrated that a specific electric field ($4\;{\times}\;10^7\;V/m$) and a doping concentration (${\sim}10^{17}\;cm^{-3}$) is sufficient to switch on/off the growth of the local oxide on SiC.

• Journal of Advanced Navigation Technology
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• v.15 no.4
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• pp.549-555
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• 2011

In this paper, inverted triangle structural planar monopole antenna with Edge for UWB Communication (3.1 ~ 10.6 GHz) is presented. The antenna have broadband property structurally through inverted triangle structural planar monopole which have edge. Monopole and ground of proposed antenna exist on coplanar plane, and excite as CPW. It used FR4 dielectric substrate of ${\epsilon}_r=4.4$, and the size is $20{\times}20{\times}1.6mm$. Return loss is more than - 10dB in 3.1 ~ 10.1 GHz (7.0 GHz). Radiation pattern is about the same that of dipole antenna at all frequency. At measured result, max gain is 8.44 dBi at E - plane.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.830-838
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• 2003

In this paper, TX/RX dual operation microstrip single antenna for satellite communication is designed, analyzed, fabricated and measured. TX/RX frequency ranges are 14.0∼l4.5 GHz, 11.7∼12.75 GHz in respectively and vertical and horizontal polarizations are used for TX and RX. This antenna uses microstrip direct feeding for RX and aperture coupled strip-line feeding for TX and accommodates stacked elements for a high directivity and wide impedance bandwidth. In an analysis of single element, FDTD and MOM was compared and FDTD analysis was more accurate because of the consideration of finite structure and imperfect two ground planes. The proposed structure facilitates generally to an extension of two dimensional array and lower an unwanted radiation by strip-line feed in TX. TX/RX 8${\times}$4 array has a return loss below -10 dB, -14 dB in TX, RX respectively and a gain ranging from 19.1∼20.7 dB in TX, 21.2∼21.8 dB in RX which has a radiation efficiency of 43∼5l %, 52∼57 %.

• Earthquakes and Structures
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• v.8 no.6
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• pp.1363-1386
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• 2015

The October 23 2011 Van Earthquake is studied from an earthquake engineering point of view. Strong ground motion processing was performed to investigate features of the earthquake source, forward directivity effects during the rupture process as well as local site effects. Strong motion characteristics were investigated in terms of peak ground motion and spectral acceleration values. Directiviy effects were discussed in detail via elastic response spectra and wide band spectograms to see the high frequency energy distributions. Source parameters and slip distribution results of the earthquake which had been proposed by different researchers were summarized. Influence of the source parameters on structural response were shown by comparing elastic response spectra of Muradiye synthetic records which were performed by broadband strong motion simulations of the earthquake. It has been emphasized that characteristics of the earthquake rupture dynamics and their effects on structural design might be investigated from a multidisciplinary point of view. Seismotectonic calculations (e.g., slip pattern, rupture velocity) may be extended relating different engineering parameters (e.g., interstorey drifts, spectral accelerations) across different disciplines while using code based seismic design approaches. Current state of the art building codes still far from fully reflecting earthquake source related parameters into design rules. Some of those deficiencies and recent efforts to overcome these problems were also mentioned. Next generation ground motion prediction equations (GMPEs) may be incorporated with certain site categories for site effects. Likewise in the 2011 Van Earthquake, Reverse/Oblique earthquakes indicate that GMPEs need to be feasible to a wider range of magnitudes and distances in engineering practice. Due to the reverse faulting with large slip and dip angles, vertical displacements along with directivity and fault normal effects might significantly affect the engineering structures. Main reason of excessive damage in the town of Erciş can be attributed to these factors. Such effects should be considered in advance through the establishment of vertical design spectra and effects might be incorporated in the available GMPEs.

• Journal of the Korean Society for Railway
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• v.18 no.3
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• pp.223-231
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• 2015

This paper proposes a new wireless backhaul technology based on MHN(Mobile Hotspot Network) which uses a wide frequency band of millimeter wave to provide wideband Wi-Fi services for subway passengers. Performance analysis of MHN up and down links, based on data: up and down links structure analysis of physical layer and simulation study of the MHN wireless backhaul link model, show that the proposed MHN-based wireless backhaul network can transmit data at a 1.2Gbps data rate and provide Internet service 100 times faster than that of conventional WiBro-based wireless backhaul networks. These results indicate that the proposed MHN technology is appropriate for subway mobile networks.

• Journal of Astronomy and Space Sciences
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• v.34 no.4
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• pp.303-314
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• 2017

With increased human activity in space, the risk of re-entry and collision between space objects is constantly increasing. Hence, the need for space situational awareness (SSA) programs has been acknowledged by many experienced space agencies. Optical and radar sensors, which enable the surveillance and tracking of space objects, are the most important technical components of SSA systems. In particular, combinations of radar systems and optical sensor networks play an outstanding role in SSA programs. At present, Korea operates the optical wide field patrol network (OWL-Net), the only optical system for tracking space objects. However, due to their dependence on weather conditions and observation time, it is not reasonable to use optical systems alone for SSA initiatives, as they have limited operational availability. Therefore, the strategies for developing radar systems should be considered for an efficient SSA system using currently available technology. The purpose of this paper is to analyze the performance of a radar system in detecting and tracking space objects. With the radar system investigated, the minimum sensitivity is defined as detection of a $1-m^2$ radar cross section (RCS) at an altitude of 2,000 km, with operating frequencies in the L, S, C, X or Ku-band. The results of power budget analysis showed that the maximum detection range of 2,000 km, which includes the low earth orbit (LEO) environment, can be achieved with a transmission power of 900 kW, transmit and receive antenna gains of 40 dB and 43 dB, respectively, a pulse width of 2 ms, and a signal processing gain of 13.3 dB, at a frequency of 1.3 GHz. We defined the key parameters of the radar following a performance analysis of the system. This research can thus provide guidelines for the conceptual design of radar systems for national SSA initiatives.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.6
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• pp.247-252
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• 2003

In this paper, we have designed and fabricated a broadband 2-stage MMIC amplifier. Broadband characteristics could be obtained by compensated matching networks in a 2-stage amplifier design. This method is compensating low gains at lower frequencies in the 1st-stage with higher gains at lower frequencies in the 2nd- stage and then finally flat gains are obtained in the wide frequency ranges. Also, we have obtained not only broadband characteristics but also high gain using compensation matching network. The fabricated amplifier is measured by attaching on the test PCB(Printed Circuits Board). The measurement results are bandwidth of 1.1~2.8 GHz, S$_{21}$ gain of 11.1$\pm$0.3 ㏈ and P1㏈ of 12.6 ㏈m at 2.4 GHz.

• Journal of electromagnetic engineering and science
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• v.14 no.2
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• pp.61-67
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• 2014

This paper presents a zero-IF CMOS RF receiver, which supports three channel bandwidths of 5/10/40MHz for LTE-Advanced systems. The receiver operates at IMT-band of 2,500 to 2,690MHz. The simulated noise figure of the overall receiver is 1.6 dB at 7MHz (7.5 dB at 7.5 kHz). The receiver is composed of two parts: an RF front-end and a baseband circuit. In the RF front-end, a RF input signal is amplified by a low noise amplifier and $G_m$ with configurable gain steps (41/35/29/23 dB) with optimized noise and linearity performances for a wide dynamic range. The proposed baseband circuit provides a -1 dB cutoff frequency of up to 40MHz using a proposed wideband OP-amp, which has a phase margin of $77^{\circ}$ and an unit-gain bandwidth of 2.04 GHz. The proposed zero-IF CMOS RF receiver has been implemented in $0.13-{\mu}m$ CMOS technology and consumes 116 (for high gain mode)/106 (for low gain mode) mA from a 1.2 V supply voltage. The measurement of a fabricated chip for a 10-MHz 3G LTE input signal with 16-QAM shows more than 8.3 dB of minimum signal-to-noise ratio, while receiving the input channel power from -88 to -12 dBm.

• Journal of the Korean Institute of Intelligent Systems
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• v.27 no.2
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• pp.144-149
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• 2017

In this paper, we developed an intelligent and wideband RF-receiver module to represent a high dynamic range and good linearity characteristics up to 650MHz-2700MHz frequency band. and implemented an intelligent digital-RF- distorted signal measuring system for the RF distortion (intermodulation) signals. Broadband RF-receive module was designed to represent the optimized linear parameters of the receiver to meet the low noise and wide dynamic range. The designed intelligent digital-distortion(intermodulation) signal measument system measured by applying the 1MHz IF of third intermodulation signal of DUT and Measured data was recorded by program on the PC monitor with GUI interface. By variable up to 650MHz-2700MHz measured data showed up to -127.8dBc to -138dBc of the distortion (intermodulation) signal. And developed intelligent digital- distortion signal measurement system can be used to measure intermodulation distortion signal of wireless system widely.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.12
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• pp.171-176
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• 2005

This study designed and fabricated a multi-purpose planar antenna for base stations that are accessible to DCS, WiBro, and ISM. The proposed antenna was designed into an open loop form from the existing monopole structure. The capacitance of the multi-purpose antenna was increased by the coupling of open parts. This makes the use of MMIC and LTCC convenient and the antenna is smaller and has a larger gain than existing antennas. The resonance distance and bandwidth can be adjusted by changing the open gap and the height of the loop of the antenna. The bandwidth of the designed antenna satisfies DCS, IMT-2000, WiBro, Bluetooth, wireless LAN and ISM bands based on VSWR 2. The entire frequency bandwidth is $58.75\%$ of $1.575GHz\~2.985GHz(1.41GHz)$. Also, the radiation pattern of the antenna displayed co-polarization and cross-polarization characteristics at 1.6GHz, 2.3GHz and 2.8GHz.