• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.7
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• pp.216-222
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• 1996

Since many typical 2.5 Gbps optical transmitter modules use a 50$\Omega$ characteristic impedance, they require relatively high voltage and high power sources compared to the 25$\Omega$ module. However, simple replacement of the 50$\Omega$ internal matching impedance with 25$\Omega$ results in bandwidth reduction and consequent problem of data transmitter module is proposed in order to expand the modulator bandwidth. From the calculated resutls based on accurate 3-dimensional inductance analysis, we have found that the series parasitic inductance is a dominant element limiting the bandwidth and the insertion of a 2.5pF capacitor in parallel to the 20$\Omega$ matching resiter can increase the 3 dB bandwidth about 1.4GHz wider. The time-domain results show the rise time (140 psec) without the compensation is greatly improved to 63 psec with the compensation. This capacitive ocmpensation can be implemented easily and be compatible with common manufacturing process of the optical transmitter module.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.6
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• pp.388-388
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• 2000

A design method for a multisection impedance transforming branch-line hybrid using a genetic algorithm suitable for MMIC applications is proposed. In contrast to the previous design methods, an asymmetric structure is introduced to optimize the hybrid. Optimization is performed within the impedance range to achieve the realizable hybrids with a microstrip line in a desired frequency range. This design method is applicable to the hybrid which has the arbitrary power division ratio, impedance transforming ratio, isolation, directivity and bandwidth. The hybrid designed by the proposed method has 3∼10％ more bandwidth than the previous results.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.6
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• pp.28-35
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• 2000

A design method for a multisection impedance transforming branch-line hybrid using a genetic algorithm suitable for MMIC applications is proposed. In contrast to the previous design methods, an asymmetric structure is introduced to optimize the hybrid. Optimization is performed within the impedance range to achieve the realizable hybrids with a microstrip line in a desired frequency range. This design method is applicable to the hybrid which has the arbitrary power division ratio, impedance transforming ratio, isolation, directivity and bandwidth. The hybrid designed by the proposed method has 3∼10％ more bandwidth than the previous results.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.8
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• pp.119-124
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• 2004

In this paper, we are designed and fabricated circular polarization microstrip patch antenna of 5［GH］z bandwidth for the wireless LAN and the ISM. We are proposed new structure that removed the section which intersected at a right angle and were composed to four separated slots. The antenna of proposed structure could solve parasitic elements from intersected in a right angle and weak coupling efficiency from asymmetry between feed line and a slot. The proposed cross slots antenna is easily impedance matching and increased impedance bandwidth. Also this is increased efficiency and a bandwidth of antenna and reduce back lobe of radiation pattern. We designed 2${\times}$2 array antenna of 5［GHz］ band. It took impedance bandwidth 280［MHz］(VSWR < 1.5) and gam 12.5［dBi］

• Korean Journal of Materials Research
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• v.13 no.10
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• pp.658-662
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• 2003

In this study, we have tried to find the optimized design variables of the matching layer which is important part of thickness mode ultrasonic transducer and finally reach the conclusion that the electrical property of piezo-element must be under consideration when the optimized acoustic impedance is estimated. Proper expression of the effective impedance of front load at free resonant frequency(: $Z_{f}$ $^{(0)}$ /) has been induced by introducing the principle of binomial multilayer transformer and gradient based numerical method is utilized to find the most acceptable value of $Z_{ f}$/$^{(0)}$ . Optimized point of acoustic impedance can be calculated directly from $Z_{f}$ $^{(0)}$ using some simple formula which we propose. We also verify our result by both numerical and experimental method and get a good enhancement especially it concern to the bandwidth of ultrasonic transducer.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.418-422
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• 2003

In this paper a dual-band circularly polarized stacked microstrip antenna for Global Positioning System (GPS) service and Digital Multimedia Broadcasting (DMB) service is designed. By stacking two different corner-truncated square microstrip patches, dual-band, dual polarization characteristic is obtained. Experimental results show impedance bandwidth of 60 MHz (3.8%) and axial ratio bandwidth of 6 MHz (0.4%) in GPS and impedance bandwidth of 126 MHz (4.7%) and axial ratio bandwidth of 30MHz (1.1%) in DMB.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.54 no.3
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• pp.180-185
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• 2005

Microstrip antennas generally have a lot of advantages that are thin profile, lightweight, low cost, and conformability to a shaped surface application with integrated circuitry. In addition to military applications, they have become attractive candidates in a variety of commercial applications such as mobile satellite communications, the direct broadcast system (DBS), global positioning system (GPS), and remote sensing. Recently, many of the researches have been achieved for improving the impedance bandwidth of microstrip antennas. The basic form of the microstrip antenna, consisting of a conducting patch printed on a grounded substrate, has an impedance bandwidth of $1\~2\%$. For improvement of narrow bandwidth of microstrip patch, we were designed U-slot microstrip patch antenna in this paper. This antenna had wide bandwidth for all personal communication services (PCS) and IMT-2000. For the design of U-slot microstrip patch antenna using a finite difference time domain(FDTD) method. This numerical method could get the frequency property of U-slot patch antenna and the electromagnetic fields of slots.

• ETRI Journal
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• v.41 no.3
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• pp.289-297
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• 2019

In this paper, a wideband, circularly polarized patch antenna is proposed that leverages the unidirectional resonant modes of a circular patch mounted on top of a grounded dielectric-ferrite substrate. The proposed antenna is fed via the proximity coupling method and several parasitically coupled patches are placed on a dielectric superstrate to enhance the impedance bandwidth of the antenna. The resonant modes of the structure rotate only in the clockwise or counter clockwise directions. In the frequency range where the effective permeability of the ferrite layer is negative, the resonance frequencies of these modes differ significantly, which produces a large axial ratio (AR) bandwidth. For the proposed antenna, the numerical results show the 10 dB impedance bandwidth to be around 44% and the 3 dB axial ratio bandwidth to be higher than 64%.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.2 no.4
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• pp.10-16
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• 1991

A microstrip bandpass filter using stepped impedance resonators and tapped input / output is realized with Teflon substrate, whose center frequency is 3.5 GHz and fractional bandwidth is 20%. In order to realize a wider bandwidth of 30%, the Crystal's design method and the input / output tapping scheme are used. Another microstrip filter designed as mentioned above is realized with Epsilam-10 substrate. This case shows good agreement between the theoretical responses and the measured ones.

• ETRI Journal
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• v.34 no.3
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• pp.454-457
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• 2012

A miniaturized planar digital video broadcasting terrestrial (DVB-T) antenna, which is composed of a patterned helical line, an open stub, and an impedance matching circuit on an FR4 (${\varepsilon}_r$=4.4) substrate for portable media player applications, is presented in this letter. The antenna has monopole-like, omni-directional radiation characteristics and a wide impedance bandwidth (VSWR<3) in the DVB-T band from 174 MHz to 230 MHz at the VHF band.