• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.4
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• pp.105-111
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• 2019

In this paper, a performance analysis of waveguide broad-wall slot array antenna for millimeter-wave seeker in Ka-band was performed as using near-field measurement. The measurement of slot array antenna was conducted in both far-field and near-field. And the validation of near-field test in millimeter band was confirmed. It was confirmed that the beam pattern characteristics including beam width and side lobe level of the slot array antenna that performed the verification were the same. Differenced in the side lobe level of azimuth and elevation beam pattern were verified to be less than 1dB. Additionally, the new antenna aperture distribution was extracted as using back-projection method modifying the near-field data and then introduced the method conducting performance analysis of array antenna.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.7 no.2
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• pp.109-114
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• 2009

Absorption spectra for a quantitative analysis of actinide elements such as U(VI) and Pu(V) were measured by using a liquid waveguide capillary cell (LWCC) which has an optical path length of 1.0 meter. In order to investigate radioactive elements, a LWCC is installed in a glove box and is coupled to a spectrophotometer with optical fibers. Limits of detection (LOD) for the system were determined as 0.74 and 0.35 M with molar absorption coefficients of 8.14${\pm}$0.07 (414 nm) and 17.00${\pm}$0.16 (569 nm) $M^{-1}cm^{-1}$ for U(VI) and Pu(V) ions, respectively. The measured LOD values are about 30 times more sensitive when compared to those achievable by using a conventional quartz cell with an optical path length of 1.0 cm. As an application with an enhanced sensitivity, a quantitative analysis for micromolar concentrations of Pu(V) has been performed to decrease the uncertainty in the formation constant of the Pu(VI)-OH complex.

• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2147-2158
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• 2006

The continuous wavelet transform (CWT) has a frequency-adaptive time-frequency tiling property, which makes it popular for the analysis of dispersive elastic wave signals. However, because the time-frequency tiling of CWT is not signal-dependent, it still has some limitations in the analysis of elastic waves with spectral components that are dispersed rapidly in time. The objective of this paper is to introduce an advanced time-frequency analysis method, called the dispersion-based continuous wavelet transform (D-CWT) whose time-frequency tiling is adaptively varied according to the dispersion relation of the waves to be analyzed. In the D-CWT method, time-frequency tiling can have frequency-adaptive characteristics like CWT and adaptively rotate in the time-frequency plane depending on the local wave dispersion. Therefore, D-CWT provides higher time-frequency localization than the conventional CWT. In this work, D-CWT method is applied to the analysis of dispersive elastic waves measured in waveguide experiments and an efficient procedure to extract information on the dispersion relation hidden in a wave signal is presented. In addition, the ridge property of the present transform is investigated theoretically to show its effectiveness in analyzing highly time-varying signals. Numerical simulations and experimental results are presented to show the effectiveness of the present method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.7
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• pp.617-624
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• 2009

In this paper, an electromagnetic analysis methodology using reaction theorem based on reciprocity theorem is presented for the aspheric ogival radome applied to a missile and/or airborne radar. The presented analysis methodology is verified using actual measured data. The type of antenna assumed to develope the methodology is a waveguide slot array antenna, and has the structure of 2 axes monopulse of "X" type. The shape of radome is assumed as Von Karman and the ratio of length to base diameter(L/D) is assumed to be 2:1. The electrical characteristics of the radome are measured using radome measurement system and the results are compared to the values estimated using the presented analysis methodology. It is found that the comparison shows good agreement. It is expected that the presented methodology can be applied for the development of missile and airborne radome.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.1-7
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• 2016

In this paper, the design methodology of a corrugated conical horn antenna is proposed to be obtain wide-band properties over the full range of frequencies in the Ku-band. In order to improve the properties of the corrugated conical horn antenna, such as its gain, VSWR, co-polarization to cross-polarization ratio and wide-bandwidth, two types of mode matching converters are implemented within it. One is located at the end of the circular waveguide, while the other is positioned in front of the horn-flare section. The properties of the antenna are analyzed and compared according to the position of the proposed converters through simulations. In the comparison of the antenna performance in the case where the VSWR, co-polarization to cross-polarization ratio and antenna gain over the Ku band of 12-18 GHz are less than 2, greater than 30dB and 20dB respectively, the former antenna exhibits greater stability and a wider frequency band than the latter from the viewpoint of transmitting and receiving signals simultaneously. Therefore, considering the gain, VSWR, radiation pattern and bandwidth, the horn antenna structure in which the mode matching converter is implemented inside the circular waveguide has better performance than the other.

• Journal of the Korean Ceramic Society
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• v.39 no.5
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• pp.479-483
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• 2002

Silicon dioxide thick film using silica optical waveguide cladding was fabricated by Plasma Enhanced Chemical Vapor Deposition(PECVD) method, at a low temperature ($320^{\circ}$C) and from $(SiH_4+N_2O)$ gas mixtures. The effects of deposition parameters on properties of $SiO_2$ thick films were investigated by variation of $N_2O/SiH_4$ flow ratio and RF power. After the deposition process, the samples were annealed in a furnace at $1150^{\circ}$C, in N2 atmosphere, for 2h. As the $N_2O/SiH_4$ flow ratio increased, deposition rate decreased from 9.4 to 2.9 ${\mu}m/h$. As the RF power increased, deposition rate increased from 4.7 to 6.9 ${\mu}m/h$. The thickness and the refractive index measurements were measured by prism coupler. X-ray Photoelectron Spectroscopy(XPS) and Fourier Transform-infrared Spectroscopy(FT-IR) were used to determine the chemical states. The cross-section of films was observed by Scanning Electron Microscopy(SEM).

• The Journal of the Acoustical Society of Korea
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• v.28 no.4
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• pp.318-327
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• 2009

In this paper, we propose a 3-D geometric localization method for near-field broadband source in shallow water environments. According to the waveguide invariant theory, slope of the interference pattern which is seen in a sensor spectrogram directly proportional to a range of the source. The relative ratio of the range between source and sensors was estimated by matching of two interference patterns in spectrogram. Then this ratio is applied to the Apollonius's circle which shows the locus of a source whose range ratio from two sensors is constant. Two Apollonius's circles from three sensors make the intersection point that means the horizontal range and the azimuth angle of the source. And this intersection point is constant with source depth. Therefore the source depth can be estimated using 3-D hyperboloid equation whose range difference from two sensors is constant. To evaluate a performance of the proposed localization algorithm, simulation is performed using acoustic propagation program and analysis of localization error is demonstrated. From simulation results, error estimate for range and depth is described within 50 m and 15 m respectively.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1744-1753
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• 2016

The main purpose of this article is a complex hyperthermia applicator system design for treatment of head and neck region. The applicator system is composed of four waveguides with a stripline horn aperture and circular water bolus. The specific absorption rate (SAR) and temperature distribution from this applicator in various numerical phantom models was investigated. For used targets, the treatment planning based on the optimization process made through the SEMCAD X software is added to show the steering possibilities of SAR and thereby temperature distribution. Using treatment planning software, we proved that the SAR and temperature distribution can be effectively controlled (by amplitude and phase changing) improving the SAR and temperature target coverage approximately by 20 %. For the proposed applicator system analysis and quantitative evaluation of two parameters 25 % iso-SAR and $41^{\circ}C$ iso-temperature contours in the treatment area with the respect to sensitive structures in treatment area were defined. To verify our simulation results, the real measurement of reflectivity coefficient as well as the temperature distribution in a homogenous phantom were performed.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.6
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• pp.570-578
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• 2009

Excitation and propagation of guided waves are very complex problems in pipes due to their dispersive nature. Pipes are commonly used in the oil, chemical or nuclear industry and hence must be inspected regularly to ensure continued safe operation. The normal mode expansion(NME) method is given for the amplitude with which any propagating waveguide mode is generated in the pipes by applied surface tractions. Numerical results are calculated based on the NME method using different sources, i.e., non-axisymmetric partial loading and quasi-axisymmetric loading sources. The sum of amplitude coefficients for 0~nineth order of the harmonic modes are calculated based on the NME method and the dispersion curves in pipes. The superimposed total field which is namely the angular profile, varies with propagating distance and circumferential angle. This angular profile of guided waves provides information for setting the transducer position to find defects in pipes.

• Korean Journal of Optics and Photonics
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• v.10 no.1
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• pp.40-46
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• 1999

We present a new modified effective index method which can be used to analyze lightwave circuit devices in 3-dimensional structure fast and accruatly using 2-dimensional BPM (beam propagating method). This method can analyze the devices with the cross-section of rectangular, ridge, or similar shapes accurately but more quickly than the 3-dimensional BPM, which is impractical to use on account of long calculating time. As an example, we showed that the calculation error of coupling length in a directional coupler by this method is significantly less than the 2-dimensional BPM using the effective index method.