• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.8
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• pp.904-912
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• 2007

In this paper, a broadband 4-way power divider which can be used from 20 MHz to 500 MHz in the V/UHF band is designed using transmission-line transformer and ferrite toroid. A 4:1 impedance transformer is realized and this 4:1 transformer is connected with bridge-type 2-way dividers to form a 4-way rower divider, Insertion loss of about 6.8dB, isolation of less than -20dB, and return loss of less than -15dB in most band of interest are measured.

• Progress in Superconductivity and Cryogenics
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• v.18 no.1
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• pp.1-5
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• 2016

Field and temperature dependence of the critical current density, Jc, were measured for both un-doped and carbon doped $MgB_2/Nb/Monel$ wires manufactured by Hyper Tech Research, Inc. In particular, carbon incorporation into the $MgB_2$ structure using malic acid additive and a chemical solution method can be advantageous because of the highly uniform mixing between the carbon and boron powders. At 4.2 K and 10 T, Jc was estimated to be $25,000-25,300Acm^{-2}$ for the wire sintered at $600^{\circ}C$ for 4 hours. The irreversibility field, $B_{irr}$, of the malic acid doped wire was approximately 21.0 - 21.8 T, as obtained from a linear extrapolation of the J-B characteristic. Interestingly enough, the Jc of the malic acid doped sample exceeds $10^5Acm^{-2}$ at 6 T and 4.2 K, which is comparable to that of commercial Nb-Ti wires.

• Journal of Magnetics
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• v.16 no.4
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• pp.431-434
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• 2011

The reduction of the Nb content in the $(Fe_{0.75}B_{0.20}Si_{0.05})_{96}Nb_4$ bulk metallic glass (BMG) has been studied. The glass-forming ability (GFA) is reduced by decreasing the Nb content, but it can be enhanced by replacing partially Fe by Co. Furthermore, the saturation magnetization of the $(Fe_{0.8}Co_{0.2})_{76}B_{18}Si_3Nb_3$ BMG is 1.35 T, being with 13% larger than that of the base alloy $(Fe_{0.75}B_{0.20}Si_{0.05})_{96}Nb_4$. $(Fe_{0.8}Co_{0.2})_{76}B_{18}Si_3Nb_3$ BMG exhibits slightly larger $B_{800}$ (the magnetic flux density at 800 A/m) and smaller core losses (20%-30%) compared with the commercial Fe-6.5 mass% Si steel.

• Journal of the Korean Magnetics Society
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• v.10 no.6
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• pp.280-294
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• 2000

[(300nm)Ta/(500nm)NdFeB/(300nm)Ta] thin films were deposited at 5 mTorr Ag gas pressure by RF-DC magnetron sputtering, and their magnetic properties were investigated. The [Ta/NdFeB/Ta] films deposited on heated Si substrates showed high perpendicular anisotropy and excellent hard magnetic properties. The films sputtered at tile substrate temperature of T$\sub$s/=650$^{\circ}C$ and 700$^{\circ}C$ showed (BH)$\sub$max/=20 MGOe and $\sub$i/H$\sub$c/= 18.9 kOe along the perpendicular direction to the film plane, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.4 s.107
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• pp.387-392
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• 2006

In this paper, measurement scheme and uncertainty estimation of the K-band attenuation standard fitted with 3.5 mm coaxial connectors are described. The standard comprises a build-up chain of four steps of power ratio mea-surement and operates in the frequency range of 18 GHz to 26.5 GHz. The nominal attenuation of each step is around 20 dB and total dynamic range is 80 dB. The expanded uncertainty of the overall system is 0.01 dB at the confidence level of approximately 95%.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.2
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• pp.173-181
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• 2011

In this paper, we propose a half mode substrate integrated waveguide(HMSIW) balanced bandpass filter to yield improved isolation between output ports. In order to achieve good isolation, resistive coupling slot is employed in HMSIW filter. The measurement results show that the insertion losses($S_{21}$, $S_{31}$) are $5.4{\pm}0.2$ dB and input return loss($S_{11}$) is more than 10 dB from 5.8 GHz to 6.4 GHz. Moreover isolation between output ports is larger than 18 dB and phase difference of output ports is $180{\pm}10^{\circ}$.

• Journal of The Korean Astronomical Society
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• v.38 no.3
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• pp.345-355
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• 2005

We present a photometric study of the star cluster system in the merging galaxy NGC 1487, based on the BI photometry obtained from the F450W and F814W images in the HST /WFPC2 archive data. We have found about 560 star cluster candidates in NGC 1487, using the morphological parameters of the objects. We have investigated several photometric characteristics of the clusters: color-magnitude diagrams (CMDs), color distribution, spatial distribution, age, size and luminosity function. The CMD of the bright clusters with 18.5 < B < 24 mag in NGC 1487 shows three major populations of clusters: a blue cluster population with $(B-I){\le}0.45$, an intermediate-color cluster population with $0.45<(B-I){\le}1.55$, and a red cluster population with (B - I) > 1.55. The intermediate-color population is the most dominant among the three populations. The brightest clusters in the blue and intermediate- color populations are as bright as $B{\approx}18mag$ ($M_B{\approx}-12mag$), which are three magnitudes brighter than those in the red population. The blue and intermediate-color clusters are strongly concentrated on the bright condensations, while the red clusters are relatively more scattered over the galaxy. The CMD of these clusters is found to be remarkably similar to that of the clusters in the famous interacting system M51. From this we suggest that the intermediate-color clusters were, probably, formed during the merging process which occurred about 500 Myrs ago.

• Journal of IKEEE
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• v.24 no.1
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• pp.238-242
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• 2020

This paper presents a technique using a multilayered dielectric coating to reduce the radar cross section (RCS) value of an integrated mast mounted in a destroyer. The proposed multilayer structure has the advantage of being easy to fabricate because the dielectric constant is defined so that a general dielectric that does not contain a magnetic component that requires high dielectric constant or is frequently used for blocking electromagnetic wave absorption can be used. After applying the proposed multi-layer dielectric structure to the integrated mast shape, the simulation results show that the RCS reduction performance is 10.9dB at 6GHz, 11.95dB at 12GHz, and 11.63dB at 18GHz compared to the structure without the multilayer structure.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.67-76
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• 2000

In this paper, a low noise amplifier has been developed, which is operating at L-band i.e., 1525-1575 MHz. By using resistive decoupling circuits, the resistor dissipates undesired signal in low frequency band. By adopting this design method the stability of the LNA is increased and the input impedance matching is improved. The LNA consists of the low noise GaAs FET ATF-10136 and the internally matched VNA-25. The low LNA is fabricated by both the RP circuit and the self-bias circuits in an aluminum housing. As a result, the characteristics of the LNA implemented show more than 32 dB in gain, lower than 0.5 dB in noise figure, 18.6 dBm output gain in 1 dB gain compression point.

• Bulletin of the Korean Chemical Society
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• v.18 no.10
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• pp.1050-1052
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• 1997

The complexes M(CO)4-1,2-(PPh2)2-1,2-C2B10H10 (M=Cr 2a, Mo 2b, W 2c) have been prepared in good yields from readily available bis-diphenylphosphino-o-carboranyl ligand, closo-1,2-(PPh2)2-1,2-C2B10H10 (1), by direct reaction with Group Ⅵ metal carbonyls. The infrared spectra of the complexes indicate that there is an octahedral disposition of chelate bis-diphenylphosphino-o-carboranyl ligand around the metal atom. The crystal structure of 2a was determined by X-ray diffraction. Complex 2a crystallizes in the monoclinic space group P21/n with cell parameters a = 12.2360(7), b = 17.156(1), c = 16.2040(6) Å, V = 3354.1(3) Å3, and Z =4. Of the reflections measured a total of 2514 unique reflections with F2 > 3σ(F2) was used during subsequent structure refinement. Refinement converged to R1 = 0.066 and R2 = 0.071. Structural studies showed that the chromium atom had a slightly distorted pseudo-octahedral configuration about the metal center with two phosphine groups of o-carborane occupying the equatorial plane cis-orientation to each other. These metal carbonyl complexes are rapidly converted to the corresponding metal carbene complexes, [(CO)3M=C(OCH3)(CH3)]-1,2-(PPh2)2-1,2-C2B10H10 (M= Cr 3a, Mo 3b, W 3c), via alkylation with methyllithium followed by O-methylation with CF3SO3CH3.