• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7B
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• pp.827-833
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• 2011

Directional MAC protocols have drawn great attentions recently in super high speed wireless local/personal area networks due to their higher antenna gain, better spatial reuse, longer transmission range, and lower interference. Despite of these merits, directional MAC protocols suffer from deafness problem. The deafness problem occurs if a node does not answer an RTS frame addressed to it. To overcome this problem, directional MAC protocols have aimed at avoiding the deafness problem using multiple control frames or advance notice techniques or distinguishing deafness from collision. In this paper, we analyze the performance of these schemes in deafness environments with some scenarios. Through performance analysis, we compare the performance of these schemes through evaluating actual network throughput.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.5
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• pp.796-805
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• 2000

A 30GHz band low noise amplifier module, which has linear gain of 30dB and noise figure of 2.6dB, for 30GHz satellite communication transponder was developed by use of MMIC and thin film MIC technologies. Two kinds of MMIC circuits were used for the low noise amplifier module, the first one is ultra low noise MMIC circuit and the other is wideband and high gain MMIC circuit. The pHEMT technology with 0.15$mu extrm{m}$ of gate length was applied for MMIC fabrication. Thin film microstrip lines on alumina substrate were used to interconnect two MMIC chips, and the thick film bias circuit board were developed to provide the stabilized DC bias. The input interface of the low noise amplifier module was designed with waveguide type to receive the signal from antenna directly, and the output port was adopted with K-type coaxial connector for interface with the frequency converter module behind the low noise amplifier module. Space qualified manufacturing processes were applied to manufacture and assemble the low noise amplifier module, and space qualification level of environment tests including thermal and vibration test were performed for it. The developed low noise amplifier was measured to show 30dB of minimum gain, $\pm$0.3dB of gain flatness, and 2.6dB of maximum noise figure over the desired operating frequency range from 30 to 31 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.11
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• pp.1304-1310
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• 2010

This study is to design FMCW radar transceiver of K-band which is used to detect and track approaching high speed targets with low altitude. The transmitter needs high output power due to small RCS targets and wide beamwidth of transmit antenna. Multi-channel receivers are required to detect and track targets by interferometer method. Transmitter consists of high power amplifier, waveguide switch, and frequency up-converter. Receiver is composed of five channel receivers, up and down converters, X-band local oscillator and waveform generator. Before manufacturing it, the proposed architecture of transceiver is proved by modeling and simulation using several parameters. Then, it is manufactured by using industrial RF components. The performance parameters are measured through experiment. In the experiment, transmitting power and receiver gain were measured with 39.64 dBm and 29.1 dB, respectively. All other parameters in the specification were satisfied as well.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.4
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• pp.286-297
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• 2017

This paper is a study of 6~18 GHz wideband high power amplifier which is composed of 10 single amplifier and coaxial type spatial power combiner. The property of this spatial power combiner is on a similar principle to antipodal antenna radiation mechanism. Therefore, the key structure of proposed spatial power combiner is the antipodal finline PCB board and the finline curve shape is numerically synthesized by using Klopfensein's optimum impedance taper. The measured CW output power of spatial combined high power amplifier is nearly 50 W. In conclusion we prove the good combining performance between the spatial power combiner and 10 single amplifier over 6~18 GHz frequency ranges. Also, we developed the key component PA and MFC MMIC which controls the phase and gain of the each amplifier, The main characteristic of MFC MMIC is to maximize combining efficiency of power amplifier.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.8
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• pp.42-50
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• 2007

This paper presents design methods for dual-frequency(2.4/5.8GHz) active receiving antennas. The proposed active receiving antennas are designed to interconnect the output port of a wideband antenna to the input port of an active device of High Electron Mobility Transistor directly and to receive RF signals of 2.4GHz and 5.2GHz simultaneously where the impedance matching conditions are optimized by adjusting the length of $1/20{\lambda}_0$(@5.8GHz) CPW transmission line in the planar antenna The bandwidth of implemented dual-frequency active receiving antennas is measured in the range of 2.0GHz to 3.1GHz and 5.25GHz to 5.9GHz. Gains are measured of 17.0dB at 2.4GHz and 15.0dB at 5.2GHz. The measured noise figure is 1.5dB at operating frequencies.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11B
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• pp.997-1004
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• 2006

There is a growing demand to access the broadband internet while on the very fast move. In order to meet these users needs, much research has been made for providing the broadband internet and HDTV services via satellite broadband internet systems even at top train speeds above 200km/h. In this paper, economic analyses on the satellite broadband internet services for KTX are to be reviewed. Broadband internet to trains in Europe are investigated, and Boeing cases for planes are also examined. In the first step, system configuration which is composed of a hub, terminals, satellite, and gap fillers for the tunnel areas has been proposed. A terminal includes a ultra-fast high gain antenna installed on the roof of the train, and APs inside the coaches. Secondly, cost estimation on the capital expenditures as well as operating expenditures has been performed in the proposed configuration. From the european and Boeing cases, demand and tariff are postulated, consequently, service revenues are derived on the scenario basis. Thirdly, estimated costs and derived revenues make up net present value and internal rate of return in each scenario. Finally, conclusions and contribution of this study are presented.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.308-315
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• 2018

In this paper, we present the basic design results for high-resolution radar development at S-band frequency that can precisely measure the miss distance between two targets. The basic system requirement is proposed for the design of a 3.5 GHz linear frequency-modulated (LFM) radar with maximum detection distance and distance resolution of 2 km and 1 m, respectively, and the specifications of each module are determined using the radar equation. Our calculations revealed a signal-to-noise ratio ${\geq}30dB$ with a bandwidth of 150 MHz, transmission power of 43 dBm for the power amplifier, gain of 26 dBi for the antenna, noise figure of 8 dB, and radar cross-section of $1m^2$ at a target distance of 2 km from the radar. Based on the calculation results and the theory and method of LFM radar design, the hardware was designed using software defined radar technology. The results of the subsequent field test are presented that prove that the designed radar system satisfies the requirements.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.4
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• pp.506-514
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• 1998

The design and fabrication of X-band(11.7~12 GHz) 2-stage monolithic microwave integrated circuit(MMIC) low noise amplifier (LNA) for active antenna are presented using $0.15{\mu}m\times140{\mu}m$ AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (P-HEMT). In each stage of the LNA, a series feedback by using a source inductor is used for both input matching and good stability. The measurement results are achieved as an input return loss under -17 dB, an output return loss under -15dB, a noise figure of 1.3dB, and a gain of 17 dB at X-band. This results almost concur with a design results except noise figure(NF). The chip size of the MMIC LNA is $1.43\times1.27$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.6A
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• pp.642-647
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• 2007

HAP(High Altitude Platform) systems have been proposed due to their unique advantages over terrestrial and satellite systems as the alternative wireless communication system to deliver the third generation IMT-2000 wireless services. It has been required to study for the power control in W-CDMA HAP system as well as the terrestrial mobile system in order to mitigate interference and increase the capacity. In this paper, a new power control has been proposed for HAP system considering the interference profile into the DB(distributed balancing) SIR(signal to interference ratio)-based algorithm which has been considered in terrestrial system, and estimated by the outage performance of the proposed DB algorithm is better remarkably than DBPA(distance-based power allocation) which is proposed for HAP system, and it is the same regardless of the antenna maximum gain and its sidelobe characteristics.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1737-1743
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• 2006

OCR(On channel repeater) provides the high frequency reuse efficiency for allocating frequency bands to repeaters because the frequency of input and output signals of OCRs is the same. However the oscillation probability of OCRs is high due to the same input and output frequency. In order to prevent a repeater from oscillating, we must keep the antenna isolation higher than the gain of the repeater with a some margin. In this paper we simulated the effects of the amplitude, phase and time delay of feedback signals (m the characteristics of non-regeneration OCR. Simulation results show that the highest probability of oscillation is occurred when the gain of a repeater is the same value of the isolation. From the simulation results, we know that the phase of feedback signals can be adjusted to reduce the possibility of oscillation if a non-regeneration repeater has a narrow operation bandwidth or a signal bandwidth is narrow. As the time delay increases, the probability of oscillation and the fluctuation of gain over a certain frequency band increase also. The effects of the amplitude and phase of feedback signals on S/N of 8-VSB signal for generation and non-generation repeater were tested. The measured results show that the set-top can receive 8-VSB signal when the received signal power is $17{\sim}18dB$ higher than the noise power. When the isolation is almost same as the gain of the repeater, then the set-top can not receive 8-VSB signals due to the oscillation of the repeater. And the phase of feedback signals affects S/N at the output of the repeater when the isolation is $11.75{\sim}13.75dB$ larger than the gain of the repeater. In this case the set-top can not receive 8-VSB signal of at $48^{\circ}\;and\;347^{\circ}$ of the phase of feedback signals. However the phase of feedback signals can not affect the S/N of 8-VSB signals of the generation repeater because of the demodulation and modulation process of the generation repenter. The set-top can not receive 8-VSB signals when the amplitude of feedback signals is $12.6{\sim}13.6dB$ larger than the wanted signal power at the input port of the repeater. It's because that the amplitude of feedback signals saturates the front end of the repeater.