• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.719-722
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• 2003

Ferroelectric $Pb(Zr_{1-x}Ti_x)O_3$ (PZT) films were deposited on (001) MgO single crystals using sol-gel method. Structural properties and surface morphologies of PZT films were investigated using an X-ray diffractometer and a scanning electron microscopy, respectively. The dielectric properties of PZT films were investigated with the dc bias field using interdigitated capacitors (IDC) which were fabricated on PZT films using a thick metal layer by photolithography and dry etching process. The small signal dielectric properties of PZT films were calculated by a modified conformal mapping method with low and high frequency data, such as capacitance measured by an impedance gain/phase analyzer at 100 kHz and reflection coefficient (S-parameter) measured by a HP 8510C vector network analyzer at 1 -20 GHz. The IDC on PZT films exhibited about 67% of capacitance change with an electric field of 135 kV/cm at 10 GHz. These PZT thin films can be applied to tunable microwave devices such as phase shifters, tunable resonators and tunable filters.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.358-360
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• 2007

For large scaled solar cells and photosensors CdS thin films of $2{\mu}m$ thickness have deposited on ITO glass substrate by chemical bath deposition methode in $300^{\circ}C$ electric furnace. The surface roughness and resistance of cadmium sulphide(CdS) thin films with different microstructures and morphologies was investigated by using a x-ray diffraction (XRD), a scanning electron microscope (SEM), an atomic force microscope (AFM), and a near-field scanning microwave microscope (NFMM). As the different substrate heat temperatures, the microwave reflection coefficient $S_{11}$ and intensity of the (002) diffraction peak was changed, and the surface morphology also has shown differently.

• Journal of the Korean Magnetics Society
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• v.18 no.5
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• pp.195-199
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• 2008

Composites of $Fe_{93.5}Si_{6.5}$ powder and epoxy were prepared using a thermal curing process. Scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and network analyzer were used to analyze the structure, electromagnetic properties and microwave absorption of the composites. Results show that the saturation magnetization depends on the fraction of the $Fe_{93.5}Si_{6.5}$ powder in the composite, which affects initial permeability. It is believed that the eddy current loss is a dominant factor over 1 GHz and that the resonance frequency of the composite decreases with increasing fractions of $Fe_{93.5}Si_{6.5}$ powder. Finally, reflection loss was calculated from the permeability and permittivity of these composites. Composite with 50 wt.% $Fe_{93.5}Si_{6.5}$ powder fractions and 5 mm thickness showed reflection loss below -20 dB from 3.66 GHz to 4.16 GHz. Therefore, it is believed that thin Fe-Si/epoxy composites may be a good candidate for microwave absorption application.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.10
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• pp.788-793
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• 2017

This paper presents the verification of accuracies of theoretical models for calculating the microwave reflections from rough sea surfaces. First of all, the Pierson-Moskowitz ocean spectrum was used to generate the rough sea surfaces. Then the relationship between the significant wave heights, root-mean-square(RMS) heights and wind speed was derived by estimating the significant wave heights and RMS heights of the generated sea surfaces according to various wind speeds, and compared the derived relationship with other measurement data sets. The reflection coefficients of the sea surfaces were calculated by using a numerical method(the moment method). Then, the numerical results were compared with Ament model, PO(Physical Optics) model, GO(Geometrical Optics) model and B-M(Brown-Miller) model for various roughness conditions(wind speed) and incidence angles. It was found that the Ament model is not accurate except for a very low roughness conditions($kh_{rms}$<0.4, k is wavenumber and $h_{rms}$ is RMS height). It was also found that at incidence angles lower than $70^{\circ}$, the PO and the GO models agree well with the numerical results, while the B-M model agrees well with the numerical analysis results at incidence angles higher than $80^{\circ}$ for very rough sea surfaces with $kh_{rms}$>10.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.9
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• pp.35-43
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• 2002

In this paper, microstrip ring with a narrow gap is characterized and used as a tunable microwave bandgap (MBG) structure. The center frequency of MBG is mainly determined by the mean circumference of the ring and coincides with odd mode resonance frequency of the ring resonator. The stop band formation by the proposed microstip MBG ring is due to the reflection of electromagnetic waves at the narrow gap introduced in the ring, and the reactive component mounted on the gap makes the stop band vary according to its value. The mounting of capacitor (inductor) is observed to decrease (increase) the center frequency of the stop band. The varactor-mounted microstrip MBG ring is expected to be useful in microwave switches and microwave amplifier circuits.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.1002-1008
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• 2001

The absorbing structure composed of multi-layered fiber reinforced composite materials was designed and microwave absorbing properties are investigated. On the basis of transmission line theory, the theoretical equations to predict the reflection loss and the appropriate composite material for each functional layer are suggested. The most significant result of this study is the successful design and fabrication of triple-layered composite laminates which has the superior microwave absorbing porperties (more than 10 dB in 4∼12 GHz range), without using the ferrite filler in the impedance transforming layer. In the two-layered composite laminate (absorber/substrate), however, the use of ferrite filler (about 40 wt %) in the absorbing layer is necessary to obtain the certain level of microwave absorbance. By combining the glass-fiber composite with ferrite filler and carbon-fiber composite substrate, the microwave absorbing properties more than 10 dB in 4∼12 GHz frequencies than be obtained.

• Composites Research
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• v.29 no.3
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• pp.98-103
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• 2016

This paper deals with the fabrication and verification of the microwave absorbing structure using semiconductive fiber reinforced composite. Two kinds of fiber were used to fabricate composites. Electromagnetic properties of the composites were measured by freespace measurement system over X-band. Two single slab absorbers and a double slab absorber were designed by thickness optimization method. Single slab absorbers did not show good microwave absorption performance because the permittivity is away from non-reflection curve. Double slab absorber complemented the limitations on single slab absorber and it showed good microwave absorption performance. Double slab absorber showed -43.9 dB loss near 10 GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.149-150
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• 2009

In this paper we study on the semiconductor characteristic by calculating the variation of reflection function in microstrip lines, which has open-ended termination containing an optically induced plasma region. The variation of impedances resulting from the presence of plasma has evaluated with time and frequency domain. The responses have been also evaluated theoretically for changing the phase of the variation in the reflection.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.451-454
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• 2002

In this paper, a low-noise amplifier is designed and fabricated using the HJFET for the reception of the Ku-band satellite broadcast signals. The optimum input and output reflection coefficients of each amplifier stage are obtained by the trade-off between the stable gain and the noise figure circle. The amplifier performance is simulated and optimized using a microwave CAD software. The designed amplifier is fabricated and tested. Results of the test show a gain of 17.0 dB, a gain flatness of less than $\pm$2.BdB, the noise figure of less than 1.0 dB, and the input and output reflection coefficient of less than -10 dB.

• Journal of Korea Society of Industrial Information Systems
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• v.6 no.4
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• pp.89-94
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• 2001

A new design method of the microwave multisection impedance transformer is proposed. This method is based on the inverse scattering theory using the frequency domain reflection coefficient of the transformer to be designed. In the first step, the permittivity profile of a virtual one-dimensional dielectric medium is reconstructed using the desired reflection coefficient. In the second step, the transformer which is equivalent to the reconstructed dielectric medium in view of reflection characteristics is synthesized. Theoretically, this method can be used to design the impedance matching transformers with arbitrary passband characteristics within the limit of the Bode-Fano criteria[1]. Our approach is examined for two design examples to show that it is valid.