• Electronics and Telecommunications Trends
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• v.32 no.5
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• pp.85-96
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• 2017

The research, design, and development of wireless access technologies using the new 6 to 100GHz band mmWave are actively underway in order to address the frequency shortage problem in the sub-6GHz band and accommodate the 5G technical requirements, such as the increased transmission capacity. Technical elements to efficiently overcome the problems caused by mmWave signal characteristics, support an effective interworking with a conventional communication service, and ensure smooth mobility between mmWave base stations and existing base stations are also being investigated. This paper discusses the technical solutions for an mmWave-based 5G RAN configuration and their considerations under various operational scenarios.

• Proceedings of the IEEK Conference
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• 2000.07b
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• pp.1009-1012
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• 2000

In this paper, we have designed and fabricated power PHEMT’s with an unit gate width of 80$\mu\textrm{m}$ and 4 fingers, and MIMIC power amplifiers using the PHEMT’s as well. The PHEMT’s have a 0.2$\mu\textrm{m}$ gate length and source to drain spacing of 3$\mu\textrm{m}$. The characteristics of the fabricated PHEMT’s are 4.08dB of S$\sub$21/ gain at the 35GHz and 317mS/mm of gm, and 62GHz of f$\sub$T/ and 120GHz of f$\sub$max/. The designed and fabricated MIMIC’s power amplifiers with 6 PHEMT’s and MIN capacitors were fully passivated by 1000 Α of Si$_3$N$_4$ film for higher performance and surface protects. The chips were processed using the MINT processes, and size was 3.25 ${\times}$ 1.8$\textrm{mm}^2$. The fabricated MIMIC power amplifiers have RF characteristics such as 11.25dB of S$\sub$21/ gain, 11.37dB of input return-loss and 12.69dB of output return-loss at the 34.55GHz.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.633-636
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• 1998

In this study, power AlGaAs/InGaAs/GaAs PM-HEMT's for mm wave's were fabricated using Electron beam lithography and air-bridge techniques, and so on. DC and AC characteristics of the fabricated power PM-HEMTs were measured under the various bias conditions. For example, DC and RF characteristics such as S21 gain of 3.6 dB at 35 ㎓, current gain cut-off frequencies of 45 ㎓ and maximum oscillation frequencies of 100 ㎓ were carefully analyzed for design methodology of sub-mm wave power devices.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.7
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• pp.2010-2026
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• 2024

This work investigates the hybrid precoder scheme in a millimeter wave (mmWave) multi-user MIMO system. We study a sum rate maximization scheme by jointly designing the digital precoder and the analog precoder. To handle the non-convex problem, a block coordinate descent (BCD) method is formulated, where the digital precoder is solved by a bisection search and the analog precoder is addressed by the penalty dual decomposition (PDD) alternately. Then, we extend the proposed algorithm to the sub-connected schemes. Besides, the proposed algorithm enjoys lower computational complexity when compared with other benchmarks. Simulation results verify the performance of the proposed scheme and provide some meaningful insight.

• Journal of Aerospace System Engineering
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• v.17 no.1
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• pp.42-50
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• 2023

In this study, hexagonal ferrite powder with chemical formula SrZn_2-xCo_xFe₁₆O₂₇ was synthesized by a solid-state reaction method and its electromagnetic (EM) wave absorption characteristics were evaluated in the frequency range of 0.1-18 GHz with absorber thickness range of 0 - 10 mm. Reflection loss (RL) affecting electromagnetic wave absorption performance was calculated based on the transmission line theory using measured complex permeabilities and permittivities. RL spectra were also directly measured for some samples. They were well matched with calculated results. High-frequency complex permeability characteristics were changed gradually according to the amount of Co substitution (x). The EM wave absorption frequency band could be tuned accordingly. Hexaferrite samples with x = 1.0, 1.25, and 1.5 exhibited remarkable maximum electromagnetic wave absorption performances with minimum RL (RL_min) lowered than -50 dB. They also showed a very broad frequency band (Δf > 10 GHz) in which more than 90% of the EM wave energy absorption occurred (RL ≤ -10 dB).

• Journal of electromagnetic engineering and science
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• v.8 no.3
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• pp.110-113
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• 2008

In this paper, we designed and fabricated an electromagnetic(EM) wave absorber for automotive radar in cars using $TiO_2$ as a dielectric material and chlorinated polyethylene(CPE) as a binder. First of all, we confirmed that the optimum composition ratio of $TiO_2$ was about 70 wt.%. The complex relative permittivity of a sample containing $TiO_2$: CPE=70:30 wt.% was calculated from S-parameter. The EM wave absorption abilities were simulated for the EM wave absorbers of different thickness using the calculated relative permittivity, and the EM wave absorber was manufactured based on the simulated design. A comparison of simulated and measured results is in good agreement. Measurement shows that a 1.85 mm thick absorber has absorption ability higher than 20 dB in the frequency range of $76{\sim}77$ GHz for automotive radars.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.10
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• pp.1136-1141
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• 2007

In this paper, we designed and fabricated EM wave absorbers using Sendust, $Al(OH)_3$ and CPE(Chlorinated Polyethylene). We compared the absorption properties of samples containing 0 wt.%, 3 wt.%, 5 wt.%, 7 wt.% of $Al(OH)_3$. The optimized composition ratio of $Al(OH)_3$ is 5 wt.%, and the absorption property curve just has the tendency to improve at 5 wt.% of $Al(OH)_3$. And we used this characteristics to design the double-layered EM wave absorber. The double-layered EM wave absorber has thickness of 2 mm and has absorption ability more than 18.5 dB at a wireless LAN frequency band using 2.4 GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.11a
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• pp.71-74
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• 1993

In this paper, the permeability(${\mu}$$\sub$r′/, ${\mu}$$\sub$r"/), permittivity($\varepsilon$$\sub$r′/, $\varepsilon$$\sub$r"/) and absorption properties of Ferroxplana/Rubber composites were investigated. The composite specimens were prepared by molding and curing the mixtures of matrix rubber and Ni$_2$Y ferroxplana powders which were synthesized by coprecipitated method. The permeability(${\mu}$$\sub$r′/) of specimen was decreased in the range of 8∼12.5(GHz) and the permeability(${\mu}$$\sub$r"/) and Permittivity($\varepsilon$$\sub$r′/, $\varepsilon$$\sub$r"/) were increased. The optimum thickness of electromagnetic wave absorber (F/R=4, 1,200($^{\circ}C$) ), utilizing the Smith chart, was about 3.0(mm). The Figure of Merit was 93(%).

• ETRI Journal
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• v.38 no.6
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• pp.1031-1041
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• 2016

This paper presents millimeter-wave (mmWave) propagation characteristics and channel model parameters including path loss, delay, and angular properties based on 28 GHz and 38 GHz field measurement data. We conducted measurement campaigns in both outdoor and indoor at the best potential hotspots. In particular, the model parameters are compared to sub-6 GHz parameters, and system design issues are considered for mmWave 5G Giga communications. For path loss modeling, we derived parameters for both the close-in free space model and the alpha-beta-gamma model. For multipath models, we extracted delay and angular dispersion characteristics including clustering results.

• Current Optics and Photonics
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• v.2 no.2
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• pp.179-184
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• 2018

Terahertz (THz) wave generation by periodically poled $BaTiO_3$ (PPBT) with a quasi-phase-matching (QPM) scheme based on cascaded difference-frequency generation (DFG) is theoretically analyzed. The cascaded DFG processes comprise cascaded Stokes and anti-Stokes processes. The calculated results indicate that the cascaded Stokes processes are stronger than the cascaded anti-Stokes processes. Compared to a noncascaded Stokes process, THz intensities from $20^{th}$-order cascaded Stokes processes increase by a factor of 30. THz waves with a maximum intensity of $0.37MW/mm^2$ can be generated by $20^{th}$-order cascaded DFG processes when the optical intensity is $10MW/mm^2$, corresponding to a quantum conversion efficiency of 1033%. The high quantum conversion efficiency of 1033% exceeds the Manley-Rowe limit, which indicates that PPBT is an excellent crystal for THz wave generation via cascaded DFG.