• Korean Journal of Optics and Photonics
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• v.28 no.5
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• pp.229-235
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• 2017

A widely tunable U-shaped SGDBR (Sampled Grating Distributed Bragg Reflector) laser diode is designed and analyzed by means of a time-domain simulation. The U-shaped SGDBR laser diode consists of SGDBR, active, phase, and TIR (Total Internal Reflection) mirror sections, so the coupling losses across the sections should be carefully considered. The tuning range of the designed U-shaped SGDBR laser is about 1525-1570 nm, which is confirmed by the simulation. The simulation results show that the loss in the TIR mirror region should be less than about 2 dB, and the refractive-index difference at the butt coupling between the passive and active regions should be less than 0.1, to provide the complete tuning range.

• Journal of Broadcast Engineering
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• v.23 no.6
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• pp.925-930
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• 2018

In this paper, we present a low profile dual-microstripline-fed double 4-arrayed meander monopole antenna with a cross-type element back by separated four-segments mesh-type reflector. The cross-type element and separated four-segments mesh-type reflector leads to enhance radiation patterns and antenna gain characteristics. The measurement value of the proposed antenna show that it has dipole-like radiation pattern characteristics. The experimental peak gain of fabricated antenna is about 2.89 dBi, which presents relatively high gain characteristics for a low profile(small-size) one. This antenna can be applied mobile RFID(radio frequency identification) readers, small medical instruments, broadcasting and home-networking operations, and other low profile high-gain systems.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.6
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• pp.805-814
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• 1999

In this paper, elliptic function bandpass filters using ceramic coaxial resonators are designed. Since elliptic function filters have better performance of frequency selectivity than those based on Butterworth or Chebyshev, therefore it is possible to make better use of limited frequency resources. Elliptic function bandpass filters using ceramic coaxial resonators are designed for reducing it's size, weight, cost and for easy manufacturing and tuning. From measurements, an accurate resonator model is obtained and the coupling coefficient values are extracted. Based on these results, elliptic function bandpass filters are designed. The experimental results have shown that the 8th order elliptic function filter of 959 MHz center frequency with 28 MHz bandwidth using coaxial ceramic resonators have about more tan 17 dB return loss, 5 dB insertion loss, more than 20 dB attenuation at $f_c\pm$5 MHz.

• Horticultural Science & Technology
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• v.19 no.4
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• pp.585-590
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• 2001

Bulbs of Lilium Oriental hybrids cv. 'Casablanca' and 'Marco Polo' were grown in a plastic house in alpine area of Pyongchang Kangwondo. Saw-dust, black film, reflective film, transparent film, and white/black double film were used as mulching materials to ascertain the growth of foliage, the quality of flower, and the size of bulbs. Foliage weights of both lilies were higher when lilies were grown with mulching materials than control. There were no differences of bulb weight among the control and mulching treatments, except delayed bulb growth in black film and white/black double film. Mulching cultivation with saw-dust and reflective film stimulated foliage growth, root growth and bulb production, but black film delayed the growth and development. Transparent and white/black double films showed no effects on foliage growth and bulb development than the control. As mulching materials tended to delay lily growth, including foliage and bulb, an extension of growing term might be better to produce high quality lilies than common cultivation in alpine area.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.6
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• pp.473-476
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• 2018

Herein, a $2{\times}2$ subarray antenna is designed to implement a VHF band active electronically scanned array. The Yagi-Uda antenna is used as a radiating element. The bandwidth enhancement and miniaturization of the Yagi-Uda antenna are achieved by optimizing the diameter of a driven element and the length of a director. In addition, the grid reflector is utilized to improve the front-to-back ratio(FBR) and to reduce both the wind resistance and overall system weight. The fabricated $2{\times}2$ subarray antenna fully covers the VHF target band($0.98{\sim}1.02f_c$). The measured maximum gain is 10.61 dBi and the FBR is larger than 26 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.9
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• pp.907-915
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• 2002

In this paper, a compact digital phase shifter to be used an active phased array antenna system for satellite communications was proposed. The even and odd mode analysis for a given reflection-type phase shifter, which uses a folded hybrid coupler as a base element, was performed and the design parameters were derived. Also, to verify experimentally the electrical performances of the proposed structure, X-band 4-bit digital phase shifter was designed and fabricated using Teflon soft substrate $({\varepsilon}_r; =\;2.17)$. Its circuit size was less than 3.5 cm $\times$ 3.0 cm, and it exhibited at least 50 % size reduction as compared with the conventional unfolded configuration. The experimental results of the fabricated phase shifter showed that the average insertion loss and insertion loss variation were less than 3.5 dB, $\pm$ 0.6 dB within the operating band, 7.9 ~ 8.4 GHz, respectively. And, input and output return loss were more than 10 dB, respectively. Also, the phase response of the phase shifter showed 4-bit operation with $\pm$3$^{\circ}$ rms phase error.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.12
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• pp.1308-1315
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• 2009

A full-polarimetric scatterometer(HPS: Hongik Polarimetric Scatterometer) for X-band is designed, fabricated, and verified using the theoretically well-known point-targets in this paper. The X-band full-polarimetric scatterometer consists of an OMT(Orthogonal-Mode Transducer)+horn antenna, the angle control part for the OMT+horn antenna, a transmitter/receiver with a network analyzer and a frequency-conversion circuitry, and a movable support of these parts. We use an inclinometer sensor to control the vertical and horizontal incidence angles. The full polarimetric data can be obtained because of the polarization switches and the OMT. The accuracy of the scatterometer system is verified by measuring the polarimetric RCS(Radar Cross Section) of one of the theoretically well-known point-targets, i.e., a corner reflector.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.29-34
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• 2008

We fabricated the 4 channel wave function generator with variable frequency, pulse width, amplitude and rising/falling slope to develop driving method of charged particle type display. The selective sell driving is ascertained by fabricated panel with black and yellow particles. To measure CIE point, reflectivity, contrast ratio and viewing angle, experimental apparatus is integrated with optical circular$(1^{\circ})$ moving emitting/receiving part and spectrometer connected to emitting part. The yellow particles in glass have reflectivity of $35{\sim}40%$ and wavelength of 571.2nm and black one has reflectivity of $15{\sim}20%$ in case of only 1 layer of particle, and the case of 3 layer the optical property is promoted.

• Korean Journal of Optics and Photonics
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• v.23 no.2
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• pp.55-63
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• 2012

We present results of optical design and fabrication of a light guiding plate (LGP) to be used as an illumination system for photobioreactors. Modeling of a light-emitting diode (LED) light source, a reflection film, and LGP patterns was performed. Especially, the LGP patterns were modeled as Lambertian scatterers. The modeling parameters (reflectance, scatterer width) were determined through matching simulations with the experimentally measured illuminance distribution for a test LGP. An LGP for an LED light source was designed with the extracted model parameters, and fabricated using a computerized numerical control machine. Optical characteristics including average illuminance and uniformity of illuminance distribution were measured for the fabricated LGP.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.4
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• pp.672-678
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• 2017

In this paper, we studied a design method for a broadband quasi-Yagi antenna (QYA) for terrestrial digital television (DTV) reception. The proposed antenna is composed of a dipole driver, a rectangular patch type director close to the dipole, and a ground reflector printed on an FR4 substrate. A balun between a microstrip line and a coplanar strip (CPS) line is a rectangular patch inserted along the center of the CPS. The end of the balun is connected to the CPS line through a shorting pin. An antenna, as an design example for the proposed antenna, is designed for the operation in the frequency band of 470-806 MHz for terrestrial DTV, and the characteristics of the designed antenna are examined. The antenna has a good performance such as a frequency band of 430-842 MHz for a voltage standing wave ratio < 2, a gain > 3.7 dBi, and a front-to-back ratio > 7.4 dB.