• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.21 no.6
• /
• pp.617-626
• /
• 2010

In this paper, we have proposed and experimentally performed a polarization and phase control method of an optical signal which has same wavelength with the optical carrier to improve phase characteristics of a continuous wave(CW) generated by the double sideband-suppressed carrier(DSB-SC) as one of the famous photomixing technique for making sub-millimeter and terahertz waves. A polarization and phase controlled optical signal has been coupled with the general DSB-SC on an optical coupler. The output of the optical coupler is then photomixed by a photomixer. From our analysis and measurement results, we have found that the amplitude of the generated sub-mm and terahertz CW signal is higher 1.5 dB and the phase noise is lower about 3 dB@10 kHz offset frequency than the general DSBSC. Consequently, since our proposed method has improved the amplitude and phase noise of CW signals in the sub-mm and terahertz bands, it can be helpful results to make low cost CW generator in sub-millimeter and subterahertz bands.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.16 no.4
• /
• pp.1330-1350
• /
• 2022

As a preprocessing operation of transmitter antennas, the hybrid precoding is restricted by the limited computing resources of the transmitter. Therefore, this paper proposes a novel hybrid precoding that guarantees the communication efficiency with low complexity and a fast computational speed. First, the analog and digital precoding matrix is derived from the maximum eigenvectors of the channel matrix in the sub-connected architecture to maximize the communication rate. Second, the extended power iteration (EPI) is utilized to obtain the maximum eigenvalues and their eigenvectors of the channel matrix, which reduces the computational complexity caused by the singular value decomposition (SVD). Third, the Aitken acceleration method is utilized to further improve the convergence rate of the EPI algorithm. Finally, the hybrid precoding based on the EPI method and the Aitken acceleration algorithm is evaluated in millimeter-wave (mmWave) massive multiple-input and multiple-output (MIMO) systems. The experimental results show that the proposed method can reduce the computational complexity with the high performance in mmWave massive MIMO systems. The method has the wide application prospect in future wireless communication systems.

• Journal of Powder Materials
• /
• v.16 no.1
• /
• pp.33-36
• /
• 2009

In order to increase the magnetic loss for electromagnetic(EM) wave absorption, the soft magnetic $Fe_{73}Si_{16}B_7Nb_3Cu_1$(at%) alloy strip was used as the basic material in this study. The melt-spun strip was pulverized using an attrition mill, and the pulverized flake-shaped powder was crystallized at $540^{\circ}C$ for 1h to obtain the optimum grain size. The Fe-based powder was mixed with 2 wt% $BaTiO_3$, $0.3{\sim}0.6$ wt% carbon black, and polymer-based binders for the improvement of electromagnetic wave absorption properties. The mixture powders were tape-cast and dried to form the absorption sheets. After drying at $100^{\circ}C$ for 1h, the sheets of 0.5 mm in thickness were made by rolling at $60^{\circ}C$, and cut into toroidal shape to measure the absorption properties of samples. The characteristics including permittivity, permeability and power loss were measured using a Network Analyzer(N5230A). Consequently, the properties of electromagnetic wave absorber were improved with the addition of both $BaTiO_3$ and carbon black powder, which was caused by the increased dielectric loss of the additive powders.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.37 no.2
• /
• pp.195-201
• /
• 2024

The low-temperature deposition of BaNi_(2-x)Co_xFe₁₆O₂₇ thin films with a Ba hexaferrite structure for electromagnetic shielding was studied. The BaNi_(2-x)Co_xFe₁₆O₂₇ thin films produced through the spin spray process were suitable for thin film deposition on a flexible substrate because it crystallized well at low temperature below 90℃. The change in shielding characteristics depending on the Co content of the BaNi_(2-x)Co_xFe₁₆O₂₇ thin film was investigated, and excellent shielding characteristics with S21 of -1 dB were obtained in a wide frequency range of 26~40 GHz when the Co content was 0.4 or more. The purpose of this study is to analyze changes in shielding properties caused by change in Co content in relation to phase changes in BaNi_(2-x)Co_xFe₁₆O₂₇ and obtain basic data for developing excellent flexible electromagnetic wave shielding materials.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.40 no.9
• /
• pp.644-650
• /
• 2003

In this paper, we have studied characteristics of PHEMT's fabricated by two difference types of gate recess for improving performance of the device in millimeter wave applications. PHEMT's were fabricated using wide and narrow recesses. Maximum transconductance(g$_{m}$) of PHEMT's using the wide recess was 332.7 mS/mm, and that of PHEMT's using narrow recess was 504.6 mS/mm. From small signal performance measurements, cutoff frequency(f$_{T}$) and maximum stable oscillation frequency(f$_{max}$) of PHEMT's using wide recess were 113 GHz and 172 GHz, respectively. f$_{T}$ and f$_{max}$ of PHEMT using narrow recess were 101 GHz and 142 GHz, respectively. The measured data of the fabricated PHEMTs' were carefully studied and analyzed.d.tudied and analyzed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.24 no.4
• /
• pp.357-365
• /
• 2013

The 4 by 4 series slot sub-array antenna is proposed using substrate integrated waveguide(SIW) technology for 35 GHz of Ka band application. The proposed antenna is realized with multi-layered structure for compact size and easy integration features. 4 by 4 radiating slots are arrayed on top PCB with equal spacing and the feeding SIWs are arranged on middle and bottom PCBs for uniform power distribution. The multi-layered antenna is realized using RT/Duroid 5880 that has dielectric constant of 2.2 and the total antenna size is $750.76mm^2$. The individual parts such as radiators and feeding networks are simulated using full-wave simulator CST MWS. Furthermore, the total sub-array antenna also fabricated and measured the electrical performances such as impedance bandwidth under the criteria of -10 dB(490 MHz), maximum gain(18.02 dBi), sidelobe level(SLL)(-11.0 dB), and cross polarization discrimination (XPD)(-20.16 dB).

• Journal of the Korean Magnetics Society
• /
• v.16 no.1
• /
• pp.28-33
• /
• 2006

La substituted perovskite $BiFeO_3$ have been prepared by a sol-gel method. Magnetic and structural properties of the powders were characterized with Mossbauer spectroscopy, XRD, SEM, and TG-DTA. The crystal structure is found to be a rhombohedrally distorted perovskite structure with the lattice constant $\alpha=3.985{\AA}\;and\;\alpha=89.5^{\circ}.\;Bi_{2/3}La_{1/3}FeO_3$ powders that were annealed at and above $600^{\circ}C$ have a single-phase perovskite structure. However, powders annealed at $900^{\circ}C$ have a typical perovskite structure with small amount of $Bi_2O_3$ phase. The Neel temperature of $Bi_{2/3}La_{1/3}FeO_3$ is found to be $680\pm3K$. The isomer shift value at room temperature is found to be 0.27 mm/s relative to the Fe metal, which is consistent with high-spin $Fe^{3+}$ charge states. Debye temperature far$Bi_{2/3}La_{1/3}FeO_3$ is found to be $305\pm5K$. The average hyperfine field $H_{hf}(T)$ of the $Bi_{2/3}La_{1/3}FeO_3$, shows a temperature dependence of $[H_{hf}(T)-H_{hf}(0)]/H_{hf}(0)=-0.42(T/T_N)^{3/2}-0.13(T/T_N)^{5/2}$ for $T/T_N<0.7$ indicative of spin-wave excitation.

• Proceedings of the IEEK Conference
• /
• 2002.07b
• /
• pp.1137-1140
• /
• 2002

A V-band low-noise amplifiers (LNA) based on the Millimeter-wave monolithic integrated circuit (MIMIC) technology were fabricated using high performance 0.1 $\mu\textrm{m}$ $\Gamma$-shaped pseudomorphic high electron mobility transistors (PHEMT＇s), coplanar waveguide (CPW) structures and the integrated process for passive and active devices. The low-noise designs resulted in a two-stage MIMIC LNA with a high S$\sub$21/ gain of 14.9 dB and a good matching at 60 ㎓. 20 dBm of IP3 and 3.9 dB of minimum noise figure were also obtained from the LNA. The 2-stage LNA was designed in a chip size of 2.3 ${\times}$1.4 mm$^2$by using 70 $\mu\textrm{m}$ ${\times}$2 PHEMT’s. These results demonstrate that a good low-noise performance and simultaneously with a high gain performance is achievable with GaAs PHEMT's in the 60 ㎓ band.

• ETRI Journal
• /
• v.39 no.2
• /
• pp.255-263
• /
• 2017

This paper proposes a graph-theatrical approach to optimize spatial reuse by adopting a technique that quantizes the channel information into single bit sub-messages. First, we introduce an interference graph to model the network topology. Based on the interference graph, the computational requirements of the algorithm that computes the optimal spatial reuse factor of each user are reduced to quasilinear time complexity, ideal for practical implementation. We perform a resource allocation procedure that can maximize the efficiency of spatial reuse. The proposed spatial reuse scheme provides advantages in beamforming systems, where in the interference with neighbor nodes can be mitigated by using directional beams. Based on results of system level measurements performed to illustrate the physical interference from practical millimeter wave wireless links, we conclude that the potential of the proposed algorithm is both feasible and promising.

• Journal of the Korean Society of Industry Convergence
• /
• v.23 no.2_2
• /
• pp.245-254
• /
• 2020

This study investigated the so far little-researched characteristics of the behaviors of rock slopes at the time of an earthquake. For the selection of the rock block, a proper model was formed by applying the similarity in consideration of the roughness and strength of the rock slope(10m) on the site, and shaking table tests were carried out according to seismic excitement acceleration, and seismic waves. In the case of the inclination angle of the joint plane of 20°, the long period wave at 0.3g or more at the time of the seismic excitement surpassed the length of 100mm, the permissible displacement (0.01H, H:slope height), which brought about the collapse of the rock; the short period wave surpassed the permissible displacement at 0.1g, which caused the collapse of the slope. The rock slope was close to a rigid block and a structure more vulnerable to the long period wave than to the short period wave. It collapsed in the short period wave even at the seismic amplitude smaller than the maximum design acceleration in Korea.