• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.6
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• pp.540-545
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• 2015

This paper presents the design, fabrication and measurement results of a S-band internally-matched power amplifier using Gallium Nitride High Electron Mobility Transistor(GaN HEMT) die. In order to fabricate the S-band internally-matched power amplifier, a high dielectric substrate and alumina were used for input/output matching circuits. The measured output power is 55.4 dBm, the drain efficiency is 78 % and the power gain is 11 dB under pulse operation at the frequency of 3 GHz.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.4 s.346
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• pp.75-80
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• 2006

This paper has proposed a novel dual band transmitter module which can be operating either as an amplifier or as a frequency multiplier according to the input frequency. A conventional dual band transmitter consists of separate amplifiers operating at each frequency band, but the proposed dual band module operates as an amplifier for the IEEE 802.11b/g signal, and as a frequency doubler for the IEEE 802.11a signal according to input frequency and bias voltage. In this paper, we have obtained sharp stop band characteristics by using microstrip DGS(Defected Ground Structure) to suppress the fundamental frequency of the frequency doubler as well as the second harmonic of the amplifier. From measurement result, second harmonic suppression is below -59dBc in the amplifier mode, and fundamental suppression is below -35dBc in the frequency doubler mode. And the designed module has 17.8dBm output P1dB at 2.4GHz and 10.1dBm power for 5.8GHz output, and the output power in the two modes are 0.8dB and 2.8dB larger than the module with ${\lambda}g/4$ reflector, respectively.

• KIISE Transactions on Computing Practices
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• v.20 no.12
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• pp.688-693
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• 2014

With the advent of ubiquitous environments, the smart phone has come into wide use and the demand for various content increases. Thus, in order to efficiently utilize limited resources cognitive radio technology is regarded as a possible solution. Besides spectrum sensing or access schemes, the provision of VoIP traffic service for secondary users with limited spectrum resources is a very important issue. In this paper, a resource allocation and control system for VoIP QoS provision in cognitive radio networks is proposed. Firstly, as the system model, the time structure of the network is addressed and, according to the structure, a bandwidth broker is proposed. In addition, based on available bandwidth estimated by the bandwidth broker, a connection admission control for secondary users is developed. It is demonstrated that the provision of VoIP QoS is greatly affected by channel utilization, the number of channels, and the length of timeslot.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.19 no.3
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• pp.137-147
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• 2020

This paper proposes printed bow-tie antennas with 3 ~ 5 GHz broadband characteristics were proposed for testing the electromagnetic immunity of automotive electrical components in the 5G frequency band. The antenna get -10 dB bandwidth in the 2.75 ~ 6 GHz frequency band and the broadside radiation pattern with S₁₁ characteristic of -16.2 dB at resonant frequency. In testing electromagnetic immunity in the 5G mobile communication frequency band, the VSWR characteristic remained below 2.1, forming a level of 1 W as proposed by international standards. As a result, it is confirmed that the proposed antenna can be applied to antenna testing for electromagnetic immunity verification in the 5G mobile communication frequency band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.11
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• pp.1240-1247
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• 2008

A twisted inverted-F antenna(TIFA) is proposed for a dual-band application. The TIFA features a twisted line for dual bands and a parasitic line for additional resonance. The proposed antenna has wideband characteristics at the high frequency band due to the merge of the resonances of the twisted line and the parasitic line. The electric size of the antenna is $0.109{\lambda}{\times}0.025{\lambda}{\times}0.0025{\lambda}$, whose length is about 44% of that of a conventional inverted-F antenna. The fabricated antenna on a thin FR4 substrate was measured to operate at 960 MHz with a bandwidth of 47 MHz, and at 1.8 GHz with a bandwidth of 289 MHz for $S_{11}$ less than -5 dB; the radiation efficiencies were 49% and 57%, respectively.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.05a
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• pp.449-452
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• 2018

In this paper, we design a Wibro / WiFi dual band microstrip antenna for wireless broadband communication. The proposed antenna is designed to have the characteristics of FR-4 (er = 4.3), size of $40[mm]{\times}40[mm]$, and usable in 2.31[GHz] and 5.8[GHz] bands of Wibro / WiFi. The simulation is performed by CST Microwave Studio 2014 The simulation result shows that the gain is 2.308[dB] at 2.31[GHz] and 2.985[dB] at 5.8[GHz]. S-parameters were also found to be less than -10[dB] (WSWR2: 1) in the desired frequency band, and a small number of parameters and a compact antenna were designed. It is expected that many users will use the mobile communication antenna for accurate and fast communication for smooth wireless broadband communication.

• Journal of Broadcast Engineering
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• v.13 no.6
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• pp.905-914
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• 2008

The paper studied the scheme of applying the MPEG-4 SVC signal to the Ka band satellite broadcasting system through the JSCC system to resolve the rain fading problem generated when providing the Ka band HDTV satellite broadcasting service. The Ka band satellite broadcasting system is based on the VCM mode of the DVB-S2, and the SVC signal is considered as one of the spatial scalability, the SNR scalability and the temporal scalability. The JSCC system jointed all the layers of the source coding system and the channel coding system, and allocated bit rate to source coding and channel coding for each layer to get the optimum receiving quality. The layers are consists of a base layer and an enhancement layer, and the bit rate of each layer is affected by the SVC signal. The applicability of the three SVC signals to the Ka band satellite broadcasting service is analyzed with respect to the rain fading, and the scheme of applying the most excellent SVC to the service is considered.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.4 s.316
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• pp.70-77
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• 2007

Two kinds of QMF(Quadrature Mirror Filter) pairs are used in JPEG2000 standard, which don't have QMF distortions. However, the QMF pairs have the main disadvantages such that there are gentle roll-off rate, ripples in the passband and unequal band decomposition. In this paper, Maxflat(maximally flat) QMF pairs with a half-band gain are proposed for overcoming these problems. Maxflat QMF pairs are realized due to generalized closed-form formulas, and the filters have maximally flat response in the passband/stopband as well as sharp roll-off rate in the transition band. Comparing proposed filters and JPEG2000's filters in frequency domain, it is found that proposed filters have better performance JPEG2000's filters. Moreover, Maxflat QMF pairs show stopband-attenuation exceeding 200 dB almost everywhere.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.320-323
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• 2018

Herein, an ultrawideband spinning direction finding (DF) antenna was designed and fabricated for airborne applications. The proposed antenna is designed by dividing the low-band (UHF - L band) and high-band (S - Ka band) antennas to cover the ultrawideband frequency range (UHF - Ka band). For the high-band antenna, an LPDA antenna fed offset-parabolic-reflector antenna is applied. In the low-band antenna, two LPDA antenna elements are arrayed in front of the reflector of the high-band antenna without increasing to the full antenna size. The low- and high-band gains of the fabricated antenna were measured as 8.76 dBi and 24.55 dBi on average, respectively. The antenna was fabricated with the dimensions of 437 mm in diameter and 358 mm in height. Consequently, we confirmed that the designed antenna is appropriate for the spinning DF antenna in terms of the affordable size for installing on an airplane, as well as the high gain and narrow beamwidth.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.461-466
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• 2012

This paper describes the development and test result of X-band Transmitter flight model(FM) of STSAT-3 by satellite research center(SaTReC), KAIST. The communication sub-system of STSAT-3 is consist of two different frequency band channels. S-band frequency is used for Telemetry & Command, and X-band frequency is used for mission data. Payload observations data in Mass Memory Unit (MMU) is modulated by QPSK modulator in X-band Transmitter, and then QPSK modulation signal is transmitted to antenna through transfer switch. In this Paper, we described the results of modulation, low-pass filter design, power amp development, and switch test. The FM XTU is delivered Spacecraft Assembly, Integration and Test(AIT) level through the completion of functional Test and environmental(vibration, thermal vacuum) Test successfully.