• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.6
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• pp.467-478
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• 2019

This paper describes the development and measurement results of a wide-band planar active phase array antenna system for an electronic warfare jamming transmitter. The system is designed as an $8{\times}8$ triangular lattice array using a $45^{\circ}$ slant wide-band antenna. The 64-element transmission channel is composed of a wide-band gallium nitride(GaN) solid state power amplifier and a gallium arsenide(GaAs) multi-function core chip(MFC). Each GaAs MFC includes a true-time delay circuit to avoid a wide-band beam squint, a digital attenuator, and a GaAs drive amplifier to electronically steer the transmitted beam over a ${\pm}45^{\circ}$ azimuth angle and ${\pm}25^{\circ}$ elevation angle scan. Measurement of the transmitted beam pattern is conducted using a near-field measurement facility. The EIRP of the designed system, which is 9.8 dB more than the target EIRP performance(P), and the ${\pm}45^{\circ}$ azimuth and ${\pm}25^{\circ}$ elevation beam steering fulfill the desired specifications.

• 한국가시화정보학회:학술대회논문집
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• 2001.12a
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• pp.6-13
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• 2001

A new GA-3D-PTV technique has been constructed to measure an impinging jet. The measurement system consists of three CCD cameras, Ar-ion laser, an image grabber and a host computer. GA (Genetic Algorithm) was used based on one-to-one correspondences in order to take advantage of the combinatorial optimization in tracking the pairs of the whole particles of the two images having a time interval. Two fitness functions were introduced in order to enhance the correspondences of the particles. One was based on a concept of the continuum theory and the other one was based on a minimum distance error. The constructed GA-3D-PTV system was applied in success to the measurement of flow characteristics of the impinging jet.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.5
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• pp.2241-2248
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• 2011

This paper describes the design of a palette-type 60watt high power amplifier module using gallium nitride(GaN) devices with high power and efficiency performances for WiMAX and LTE systems. The line-up for the high gain amplifier module consists of the pre-amplifier stage with low power and high gain, 8watt GaN driving amplifier stage, and 60watt GaN high power amplifier stage of Doherty structure with two 30watt GaN devices. The obtained gain is 61.4dB with an excellent gain flatness of ${\pm}$0.075dB over 2.5~2.68GHz. GaN devices and the Doherty structure are adopted for the improvement of high efficiency and output power. The measurement for the fabricated high power amplifier module of palette type is performed using the widely known WiMAX signal all over the world. In the example of RRH(remote radio head) application of the fabricated amplifier module, the measured efficiency is 37~38% with the 10watts of modulated output power. It is shown that when the fabricated amplifier module is activated with a digital predistorter(DPD), the measured ACLR is better than 46dBc under the 10watts of modulated output power.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.249-252
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• 2002

Turbulent properties of the wake of a circular cylinder were measured The diameter of the cylinder is l0mm and the Reynolds number is 420. A new 3D-PTY system was constructed and a genetic algorithm (GA) was introduced in order to increase the number of instantaneous three-dimensional velocity vectors. In the GA two fitness functions were introduced in order to enhance the correspondences of the particles. The measurement system consists of three CCD cameras, Ar-ion laser, an image grabber and a host computer. More than 3000 instantaneous three-dimensional velocity vectors were obtained by the system. The database of the turbulent properties of the circular cylinder was constructed by the constructed 3D-PTV system.

• Journal of the Korean Magnetics Society
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• v.18 no.2
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• pp.67-70
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• 2008

$Tb_2Bi_1Ga_xFe_{5-x}O_{12}$(x=0, 1) fabricated by sol-gel and vacuum sealed annealing process. $Tb_2Bi_1Ga_xFe_{5-x}O_{12}$(x=0, 1) have been studied by x-ray diffraction(XRD), vibrating sample magnetometer, and $M\ddot{o}ssbauer$ spectroscopy. The crystal structures were found to be a cubic garnet structure with space group Ia3d. The determined lattice constants $a_0$ of x = 0, and 1 are $12.497\AA$, and $12.465\AA$, respectively. The distribution of gallium and iron in $Tb_2Bi_1Ga_xFe_{5-x}O_{12}$ is studied by Rietveld refinement. Based on Rietveld refinement results, the terbium and bismuth ions occupy the 24c site, iron ions occupy the 24d, l6a site, and nonmagmetic gallium ions occupy the 16a site. In order to verify the magnetic site occupancy of iron and gallium, we have taken $M\ddot{o}ssbauer$ spectra for $Tb_2Bi_1Ga_xFe_{5-x}O_{12}$(x=0, 1) at room temperature. From the results of $M\ddot{o}ssbauer$ spectra analysis, the absorption area ratios of Fe ions for $Tb_2Bi_1Fe_5O_{12}$ on 24d and 16a sites are 60.8 % and 39.2 %, respectively, and the absorption area ratios of Fe ions for $Tb_2Bi_1Fe_5O_{12}$ on 24d and 16a sites are 74.7 % and 25.3 %, respectively. It is noticeable that all of the nonmagnetic Ga atoms occupy the 16a site by vacuum annealing process.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.5
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• pp.40-47
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• 1998

This paper report sthe design, fabrication and characterization of an AlGaAs/GaAs HBT (heterojunction bipolar transistor) with an air-bridge isolation structure which is made to improve high frequency characteristics for the application to the mobile communication system in the next genration. We found that the size, shape and structure of HBT have an effect on the high frequency operation. The measured dc and ac characteristics of the four type HBTs were compared and analyzed. An E-type HBT with an air-bridge structure by undercut etching exhibited .beta.=56, $V_{off-set}$ = 0.3 V, B $V_{CEO}$=7.0V with $f_{T}$=40 GHz and $f_{max}$=45GHz at a collector current density of 7.1*10$^{4}$ A/c $m^{2}$.>.

• Journal of electromagnetic engineering and science
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• v.4 no.4
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• pp.156-161
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• 2004

The MMIC cascode VCO is designed, fabricated, and measured for Ku-band Low Noise Blcok(LNB) system using InGaP/GaAs HBT technology. The phase noise of -116.4 dBc/Hz at 1 MHz offset with output power of 1.3 dBm is obtained at 11.526 GHz by applying 3 V and 11 mA, which is comparatively better characteristics than compared with the different configuration VCOs fabricated with other technologies. The simulated results of oscillation frequency and second harmonic suppression agree with the measured results. The phase noise is improved due to the use of the smallest value of inductor in frequency determining network and the InGaP ledge function of the technology. The chip size of $830\time781\;{\mu}m^2$ is also achieved.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.11
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• pp.30-36
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• 1997

AlGaAs/GaAs HBTs are developed well enough to be commercialized as an active device in optical transmission system, but there remains the unanswered questions about reliability. In this paper we applied the reverse constant current stress at the high voltage in avalanche region for a long time to find out a new degradation mechanism of junctrion I-V. The unction off-set voltage at which the current vanishes to zero was shifted to the negative direction of applied bias due to the increment of leakage current as the stress time increases. It was identified that the degradation was induced by the hot carriers which were generated at space charge region and trapped at the interface between GaAs base and the passivation nitride enhancing the electric field across the nesa edge.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.3
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• pp.11-17
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• 1998

Although GaAs HBTs are very attractive for high power amplifier because of their power handling capablity, they can't be actively commercialized due to the degradation of current gain occured in hihg current operation. In this paper we analyzed the type of current gain degradation of GaAs HBTs under high constant current stress, and identified the mechanism by using two dimensional numerical simulation. The cause of degradation was found out to be the variation of surface recombination states at the interface between GaAs extrinstic base and the nitride passivating the surface of base. The energy radiated from recombination of carriers in bulk as well as near the surface is estimated to activate the change of the surface states.

• Applied Science and Convergence Technology
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• v.24 no.6
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• pp.257-261
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• 2015

We report on GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) that can cover the spectral range of $3.6-25{\mu}m$. One advantage of the GaAs QWIPs is the wavelength tenability as a function of their structural parameters. We have performed a systematic calculation on the detection wavelength of a typical $GaAs/Al_xGa_{1-x}As$ multi-quantum-well photodetector, with the aluminum mole fraction (x) of $Al_xGa_{1-x}As$ barrier in the range of 0.15-0.43 and the quantum-well width range from 30 to 60 $60{\AA}$. Design and fabrication of a QWIP based on $GaAs/Al_{0.23}Ga_{0.77}As$ structure with $37{\AA}$-thick well width has been carried out. The calculated operation wavelength of the QWIP is in a good agreement with the experimental data taken by photo response and activation energy calculation from thermal quenching of integrated photoluminescence.