• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.12
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• pp.73-78
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• 2007

In this paper, the CPW-fed triple-band internal planar monopole antenna which simultaneously meets the three bands such as Cellular, PCS and Wibro is designed. The size of the radiation elements can be reduced to about $\lambda/4$ by designing the CPW-fed monopole antenna and then we can miniaturize the antenna size by meandering the radiation elements. In addition, we design the planar antenna for the slim-type mobile phone. We can obtain the desired antenna properties by controlling the length of each radiation elements. The measured return loss of the antenna is less than -7 dB at the desired bandwidth. And the measured radiation patterns are similar to that of the monopole antenna. The designed antenna has the gains -5.2 dBi. -2 dBi, -0.4 dBi at each resonant frequencies respectively.

• The Journal of the Acoustical Society of Korea
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• v.32 no.3
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• pp.199-207
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• 2013

In this paper, a $64{\times}8$ channel 1.75D ultrasonic transducer made of piezoelectric single crystals was designed, fabricated, and evaluated. First, a structure of the transducer was selected to be suitable for wiring on a planar array, and components were fabricated to correspond to the structure. Detailed structure of the transducer was designed through finite element analyses. As main performance factors, the crosstalk between neighboring elements was reduced through the control of kerf width and material, and desired frequency bandwidth of the transducer was achieved by designing the optimal thicknesses of the piezoelectric single crystal and matching layers. An experimental prototype of the transducer was fabricated following the design, and its performance was measured. Then the experimental results were compared with those of the finite element analysis, which led to the evaluation of the transducer developed in this work.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.7
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• pp.768-773
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• 2012

A branch-line hybrid using microstrip artificial transmission lines(ATLs) with slotted-triangular patches is proposed. The proposed artificial transmission line is compact in structure as well as easy to adjust the characteristic impedance and electrical length of equivalent transmission line by changing the slot's parameters; hence, it is useful for miniaturizing conventional transmission lines. The designed branch-line hybrid, because of the use of the right angled isosceles triangular shaped artificial transmission lines as building blocks, has no useless empty space, and hence optimally miniaturized. A fabricated 3 dB branch-line hybrid shows the coupling variation of ${\pm}0.5$ dB and the phase difference between two output ports of $91^{\circ}{\pm}4^{\circ}$ within 15 % bandwidth at 2.45 GHz center frequency. The size of proposed branch-line hybrid is only 38% of the conventional branch-line hybrid.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.219-226
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• 2000

In this paper, we design and implement a IF(intermediate frequency) module for WLL(wireless local loop) CDMA(code division multiple access) basestation. The implemented IF transceiver is consists of transmitter, receiver and local oscillator. The considered signal bandwidth is 10 MHz and the local carrier frequency is 40 MHz. As test results, the If transmitter output power is -5dBm $\pm3dB$when the baseband input is -10dBm $\pm3dB$, and the IF receiver output power is -10dBm $\pm3dB$when the IF input is -5dBm $\pm3dB$. Also the AGC(automatic gain control) circuit has dynamic range of 9 dB from -7dBm to +2dBm with output power 2dBm. And the group delay characteristic is analyzed by comparing the phase delay from 1 MHz to 5 MHz and the phase distortion is very low. We can conclude that this IF system can be applied to high speed data rate communication system.

• 대한공업교육학회지
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• v.33 no.1
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• pp.233-248
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• 2008

Stream Control Transmission Protocol(SCTP) is a new transport protocol that is known to provide improved performance than Transmission Control Protocol(TCP) in multi-homing environment that is having two and more IP addresses. But currently single-homed computer is used primarily that is having one IP address. To identify whether mean transfer time for SCTP is faster that for TCP in single-homed environment considering packet loss, we make up real testbed regulating the bandwidth, delay time and packet loss rate on router and observe the transfer time. We write server and client applications to measure SCTP and TCP mean transfer time by C language. Analysis of these experimental results from the testbed implementation shows that mean transfer time of SCTP is not better than performance of TCP in single homed environment exceptional case. Main reasons of performance are that SCTP compared to TCP stops transmitting data by timeout and data transmission is often delayed when SACK congestion happens. The result of study shows that elaborate performance tuning is required in developing a new SCTP module or using a implemented SCTP module.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.3
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• pp.149-155
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• 2019

In this paper, phase shifter has been designed and manufactured to apply to passive phase array seeker for Ka-band and its performance was confirmed. It was designed as a key element for conducting electric beam steering by adjusting the phase of the array element. Insertion loss of less than 1.5dB and phase accuracy of less than $10^{\circ}$(RMS) in operation bandwidth of 1GHz were checked. The performance identified by the actual fabrication was further analyzed by applying the beam pattern analysis based on the array synthesis theory. The effect of the final performamnce of the proven phase shifter on the performance and pointing error and angular accuracy of the passive phase array antenna beam pattern was analyzed. Then, the validation of the proposed phase shifter has been made.

• Journal of Software Engineering Society
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• v.26 no.1
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• pp.1-16
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• 2013

Variable length information message is a communication protocol standard in order for computer network systems to provide efficient delivery of information. The variable length information messages were developed for varying and controlling details of information in accordance with message receiver's required information level or information access level. In the previous studies, data compressing techniques have been in use for information message optimization technologies in order to reduce physical sizes of information messages. In optimization technologies for information messages, accuracy of information is considered as the most important factor; therefore, only non-loss compression techniques are applied to the optimization technologies. However, the non-loss compression based information message optimization methods are not efficient in data compression, and these are limited to efficient delivery of information in wireless network environments that have constraint bandwidth. In this paper, we attempt to optimize information in the variable length information messages at message fields in order to reduce physical sizes of messages more efficiently. To demonstrate the efficiency of our approach, we conduct optimization experiments for variable length information messages.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.10a
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• pp.72-73
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• 2016

In this paper, we studied a method for miniaturizing a broadband stacked patch antenna structure which is widely used for bandwidth improvement. Main patch is a rectangular microstrip patch antenna fed by a 50-ohm microstrip line, and a parasitic patch is laid above the main patch. The size of the main patch is designed to be resonated near the center frequency of the desired frequency band. Then parasitic patch longer than main patch is placed above the main patch. The distance between two patches might be adjusted so as to achieve impedance matching using a shunt open stub. The shunt matching stub is inserted underneath the parasitic patch and so it does not require additional space, which enables the proposed antenna structure to be advantageous in miniaturizing antenna. The effects of the various parameters on the antenna performance are examined, and we introduced the design procedure for the proposed antenna to operate in the frequency range of 2.3-2.7 GHz.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.16 no.1
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• pp.55-63
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• 2006

Recently, there is much abnormal traffic driven by several worms, such as Nimda, Code Red, SQL Stammer, and so on, making badly severe damage to networks. Meanwhile, diverse prevention schemes for defeating abnormal traffic have been studied in the academic and commercial worlds. In this paper, we present the structure of a stepwise intrusion prevention system that is designed with the feature of putting limitation on the network bandwidth of each network traffic and dropping abnormal traffic, and then compare the proposed scheme with a pre-existing scheme, which is a True/False based an anomaly prevention scheme for several worm-patterns. There are two criteria for comparison of the schemes, which are Normal Traffic Rate (NTR) and False Positive Rate (FPR). Assuming that the abnormal traffic rate of a specific network is $\beta$ during a predefined time window, it is known that the average NTR of our stepwise intrusion prevention scheme increases by the factor of (1+$\beta$)/2 than that of True/False based anomaly prevention scheme and the average FPR of our scheme decrease by the factor of (1+$\beta$)/2.

• Korean Journal of Optics and Photonics
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• v.31 no.6
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• pp.259-267
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• 2020

We evaluate the degradation of receiver sensitivity induced by direct and indirect exposure to solar irradiance in free-space optical communication systems. For this purpose, we calculate the variances of numerous noise components arising from solar irradiance, and then estimate the receiver sensitivity penalties for intensity-modulation/direct-detection and coherent systems. The results show that the penalties are less than 1.3 dB when indirect sunlight impinges on the detector, regardless of the system. However, the sensitivity penalties are estimated to be larger than 30 dB when the sunlight is directly incident upon the receiver. These penalties are barely reduced if we insert an optical polarizer, or if we adjust the bandwidth of an optical filter at the receiver to be as narrow as the signal's bandwidth.