• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.2
• /
• pp.141-146
• /
• 2009

A triangular microstrip antenna with T-shaped slits is proposed for tunable dual-band applications. The proposed antenna is designed using chip capacitors as a prototype. From this result the capacitor can be replaced to a varactor diode to control capacitance value. Since the input impedance of the antenna can be varied with the value of the chip capacitors on the T-shaped slits, the resonant frequency may be changed. The return losses are better than 10 dB at the lower band of $0.78{\sim}1.21$ GHz and 20 dB at the upper band of $1.97{\sim}2.17$ GHz, respectively. This antenna has the bandwidth of about 10 MHz and 50 MHz at each band. The peak gains of the antenna yield 0 dBi at the lower band and 3 dBi at the upper band, respectively. Details of the antenna design are described, and its performances are presented and analyzed.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.7 no.3
• /
• pp.48-55
• /
• 2004

본 연구는 중 저해상도 위성영상을 이용하여 하천주변 습지를 판별해내는 보다 개선된 기법을 개발해 내는데 그 목적이 있다. 중 저해상도 위성영상의 하나의 화소는 일반적으로 하나의 동질한 물체의 분광반사값을 나타내기보다는 다양한 분광값을 가진 물체들의 대표값으로 나타나게 된다. 특히 본 연구에서는 식생, 수문 및 토양요소의 혼합체인 습지의 판별을 위해서, 하나의 화소가 하나의 물체를 대표함을 전제로 하는 기존의 분석방법 보다는, 혼합화소 (mixed pixel)를 대상지 의 토지 피복을 가장 잘 반영 하는 순수한 화소값(endmember)들로 분해함으로써 보다 정확한 판별 및 분류를 가능케 하고자 하였다. 이를 위하여 일반적으로 극세분광 위성영상의 분석에 활용되는 기법인 분광혼합화소분석(Spectral Mixture Analysis)을 이용하였는데, 습지 각 화소의 식생, 수문 및 토양요소의 흔합정도를 분해한 후, 이들의 분할영상 (fraction images)을 추출해내고 이를 분석에 이용하였다. 팔당상수원보호구역의 소택형 습지를 대상으로 봄 가을의 Landsat 영상에 대한 분석을 수행하였으며, 도출된 결과는 다음과 같다. 첫째, 봄 가을 각각의 영상에 대하여 4개씩 endmember를 선정하였으며, 분할영상과 원자료 각각에 대하여 습지판별을 수행한 결과, 가을영상에 대하여 분할영상을 이용한 방법의 소택 형 습지 판별 정확도가 가장 높은 값을 보여주었다(생산자 정확도 : 83.3%, 사용자 정확도 : 86.5%). 둘째, 소택형 습지로 판별된 지역만을 대상으로 보다 세분화된 분류가 가능한 지 알아보기 위하여 소택형 습지로 판별된 지역의 영상에 대해 ISODATA 무감독분류를 수행한 결과 2개의 클러스터로 대별되었다. 현장조사, 기존 연구의 수심자료 및 식생에 대한 조사를 바탕으로 위의 2개의 클러스터를 조사한 결과, 수문조건에 따른 분류인 아계(subsystem) 단계의 '영구적 침수형 소택형 습지'와 '계절적 침수형 소택형 습지'로 분류할 수 있었다.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.20 no.3
• /
• pp.206-212
• /
• 2000

The guided wave mode conversion phenomena were investigated for the NDE of a plate-like structure with thickness variation. The ratios of reflection and transmission (R/T) were measured via the self-calibrating procedure which allows us to obtain experimental guided wave data in a more reliable way regardless of the coupling uncertainty between transducer & specimen. The results on R/T could be used to determine the thickness reduction of the structure. It was shown that not only the incident modes but also the converted ones need to be considered in the self-calibrating guided wave inspection to extract a reasonable correlation between experimental data & the thickness variation. Through this study, the potential of guided wave inspection as a quantitative NDE technique was explored based on the combined concept of self-calibration & multi-mode conversion in guided wave scattering problems.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.2A
• /
• pp.201-206
• /
• 2006

A SPST Switch MMIC which used for Microwave Switch Matrix(MSM) of communications satellite payload with multi-beam function has been designed and fabricated. New RE FET switch configuration has been devised to improve power characteristics and isolation. Input and output return losses are better than another switches reported previously for both On and Off states. The MMIC chips were fabricated in 0.15um GaAs pHEMT process and measured insertion loss less than 2.0dB and isolation more than 63dB in the frequency range of 3GHz$\∼$4GHz. Output 3rd order interceptpoint above 32dBm has been recorded and the value is very high even though the unit pHEMT has gate width of 0.2mm and only four pHEMT are used in the MMTC.

• Korean Journal of Optics and Photonics
• /
• v.15 no.1
• /
• pp.1-5
• /
• 2004

Tunable diode laser absorption spectroscopy was performed for analysis of the H$_2$$^{18}$ O/H$_2$$^{16}$ O isotope ratio of a water sample which was enriched by the membrane distillation method. In order to improve the signal-to-noise ratio, the wavelength modulation spectroscopic method was used with a lock-in amplifier. The fringe noise could be suppressed by using the FFT (Fast Fourier Transform) lowpass filter and the optimization of the modulation depth of the laser frequency. The maximum deviation of $\delta$-value was measured to be$\pm$4$\textperthousand$.

• Korean Journal of Optics and Photonics
• /
• v.19 no.2
• /
• pp.122-126
• /
• 2008

Dual backlight unit incorporating a single light source integrated with a beam splitting reflector was demonstrated, providing a surface light beam for both the keypad and the display section simultaneously. The reflector was realized by aligning a groove substrate with a matching cover, and a light guiding module comprising a stack of light guide panels and prism/diffuser sheets was attached to both sides of the reflector. A light emanating from the light source-placed in the middle of the substrate-undergoes a series of reflections through the reflector to reach the input of the light guiding module. Then it is transformed into a surface light beam, which is used to irradiate the keypad and display sections simultaneously. As for the accomplished dual surface light sources, the measured average luminance and the spatial luminance uniformity were respectively about $420\;cd/m^2$ and 69% for the keypad section, and $640\;cd/m^2$ and 79% for the display section.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.3 s.357
• /
• pp.78-84
• /
• 2007

A multistandard direct-conversion mixer for WCDMA, Wibro, and 802.11a/b/g is designed in 0.18 um CMOS technology To support multistandard and to reduce the chip area the switched inductor is used as the matching method. This switched inductor matching network selects the mixer's operation frequency band by turning on or off the switch transistor. Since the performances of mixer and operation frequency can be affected by the parasitic of switch transistor the mixer should be designed with the optimized size of switch to minimize parasitic effects. Proposed mixer is able to achieve return loss less than -13 dB in $2.1\sim2.5GHz$ and $5.1\sim5.9GHz$ bands with the suitable performance to meet requirements of WCDMA, WiBro, and 802.11a/b/g.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.16 no.1 s.92
• /
• pp.66-77
• /
• 2005

This paper proposed a novel broadband PIFA(Planar Inverted-F Antenna) for IMT-2000/WLAN/DMB terminal. Two branch lines for meander line were utilized in order to improve the characteristics of PIFA which usually has a narrow band. The shorting strip between the ground plane and meander-type radiation elements were used in order to minimize the size of the antenna. The -10 dB return loss bandwidth of a realized antenna was $38.2{\%}$(1.84~2.71 GHz), which contains the broadband bandwidth with triple band. And the simulated and measured values of 1 g and 10 g averaged peak SAR on human head caused by the triple band PIFA mounted on folder-type handsets were analyzed and discussed. As a result, the measured 1 g and 10 g averaged peak SARs of PIFA were similar with the simulated values and were lower than the 1.6 W/kg and 2 W/kg of 1 g and 10 g averaged peak SAR limits.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.3
• /
• pp.440-449
• /
• 1988

Small vibration displacements may be measured by optical interferometers, based on the Michelson method. The standard Michelson interferometer works well when the mirror displacements are relatively large compared to the optical wavelength. But it does not work for displacements less than approximately a quater of optical wavelength. Several multiple reflection laser interferometers, simply modified standard Michelson interferometer, have been developed to decrease the minimum detectable limits. Among these a relatively simple and easy multiple reflection system is used to measure the small vibration displacements. This multiple reflection system is constructed with a right angle prism and a convex lens. Therefore this system makes it possible to measure a vibration displacement of the small area on the vibrating structure. The fringe interpolation method and curve fitting method are used to determine accurately the small vibration displacements from the measured interference fringe patterns. Also computer simulation technique is used to check the accuracies of these method. According to the results of the computer simulation technique, the curve fitting method is more accurate than the fringe interpolation method. The optically measured results are in good agreement with those of the standard accelerometer with high accuracy and it is possible to measure the peak vibration displacement as small as 9.01nm using multiple reflection system and curve fitting method.

• 한국지구물리탐사학회:학술대회논문집
• /
• 2006.06a
• /
• pp.281-284
• /
• 2006

The resistive V dipole (RVD) is a V antenna with both arms loaded with the continuous Wu-King resistive profile. The RVD has many advantages for surface and subsurface probing, such as the ability to radiate a short pulse in a desired direction. The radiated pulse is simply related to the input pulse, e.g., derivative. In addition, it mostly eliminates the multiple reflections between the surface of the ground and the antenna because of its low radar cross section. The drawbacks of the RVD include the high input impedance and the difficulty in implementation. This paper presents ways to improve the accuracy and easiness of the implementation and to improve the low-frequency performance while maintaining the characteristics of the V antenna that are good for probing applications. The implemented antenna is used to form a bistatic radar to scan targets underground, and the result is imaged.