• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.3
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• pp.25-33
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• 1997

In the design of microwave multi-stage amplifiers composed of N amplifier modules, the variation of performances of amplifier as various connection length between modules has been studied. In addition, the methods, equations and conditions for the maximum gain or the most flat gain are presented. The results of sensitivity analysis for the connection length showed that the small change in phase of input, output reflection coefficients(S$_{11}$, S$_{22}$) of module itself is the most important in determination of connection length for the most flat gain. Th egain flatness of 2-module amplifier of which connection length between modules had been determined by presented methods was the best one out of performances with various arbitrary connectio lengths.s.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.12A
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• pp.1346-1353
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• 2007

In this paper, the methods are presented for the calculation of general coupling coefficient matrixes used in the band pass filter design. They are calculated from transmission coefficient($S_{21}$) and reflection coefficient($S_{11}$) with desired characteristics derived from the poles of filter function and return loss(RL). The calculated matrixes from this method are transformed to the folded canonical filter structure using similarity transformation which lends us the practical filter design. Based on the resulting matrix, the folded canonical filter has been designed.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.5 no.4
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• pp.40-46
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• 1994

Design and microwave absorbing properties of ferrite plate are investigated for the application to the radiowave absorbers used in anechoic chamber. The required frequency-dependence of complex permeability is determined on the basis of wave-impedance-matching relationship. The plate thickness and matchingfrequency are determined from the complex permeability and dielectric constant, and then compared with the directly measured reflection loss. A systematic variation of material constants and their influence on the microwave absorbing properties are demonstrated.

• Journal of electromagnetic engineering and science
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• v.12 no.2
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• pp.171-175
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• 2012

In this work, a new microstrip-to-substrate integrated waveguide (SIW) transition using the parallel half-mode substrate integrated waveguide (HMSIW) is proposed. The proposed transition consists of three sections : a microstrip, parallel HMSIWs, and an SIW. By inserting the parallel HMSIWs section between the microstrip section and the SIW section, the proposed transition can improve the return loss characteristics of the near cut-off frequency because the HMSIWs section has a lower cut-off frequency than the SIW section (8.6 GHz). The lower cut-off frequency is achieved through gradual electromagnetic field mode changes for a low reflection. The measured return loss is less than 20 dB in the of 9.1~16.28 GHz freqeuncy range for the back-to-back transition. The measured insertion loss is within 1.6 dB for the back-to-back transition. The proposed transition is expected to play an important role in wideband SIW circuits fed by a microstrip.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.8
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• pp.401-406
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• 2004

In this experimentation, we investigated the characteristics of electromagnetic wave absorption of ferroxplana powder and silicone rubber composite. Ferroxplana was prepared by flux method at low temperature. The crystallization, magnetic properties and particle morphology of the obtained ferroxplana powder were investigated by using XRD, VSM and SEM. The particle size of ferroxplana powder was 2∼4$\mu\textrm{m}$ at the ratio of R=26, The coercivity and saturation magnetization of ferroxplana powder increased slightly with increase of temperature, The magnetic loss was the main factor of electromagnetic wave absorption of ferroxplana powder and silicone rubber composite, The maximum reflection loss of composite was about -l5dB below 4GHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.1042-1045
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• 2004

ITO thin films ($\sim150nm$) are deposited on glass substrates by different deposition condition. The sheet resistance of ITO thin films measured by using a four probe station. The microstructure of these films is determined using a X-ray diffractometer (XRD) and a scanning electron microscope (SEM) and a atomic force microscope (AEM). The sheet resistance of ITO thin films compared $s_11$ values by using a near field scanning microwave microscope.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.556-560
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• 1995

The absorption properties of Cu-Zn ferrite/rubber composite microwave absorbers with PZT(Lead Zirconate Titanate) additive were evaluated. The composite specimens have prepared by molding and curing the mixture of matrix rubber and Cu-Zn ferrite powders which are synthesized by the coprecipitation method using Fe Cl/sub 3/ .center dot. 6H/sub 2/O, CuCl/sub 2/ .center dot. 2H/sub 2/O and Zn Cl/sub 2/ as a starting raw materials. PZT is used as another filler particles to adjust the material constants of Cu-Zn ferrite/rubber composite specimens. We have found that the material constants of specimens could be controlled by various PZT mixing ratio. On the Cu-Zn ferrite/rubber composite specimens with PZT 10[wt%] additive, the reflection losses were larger than 30[dB] in the frequency range from 2.72 to 4.4[GHz]' by adjusing the thickness.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1680-1682
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• 1999

In this study, three kinds of Mn-Zn ferrite/Ni-Zn ferrite/$Ni_2Y$ ferroxplana prepared by the coprecipitation method were compounded with the silicon rubber, and the ring-shaped specimens with various compositional ratio were made. The material constant of ferrite/rubber composite absorbers was obtained by the 2-port method. The material constants of the ferrite/rubber composite microwave absorber made of three kinds of ferrite with various compositional ratio were utilized in design the matching conditions (frequency and thickness) on the impedance matching map. We were able to predict the matching condition from the matching map. On all three kinds of ferrite/rubber composite microwave absorber with less than compositional ratio 60[wt.%] of ferroxplana, we have found that the reflection losses were over than 20[dB] at the S-Band $(2\sim4[GHz])$ and C-Band$(4\sim8[GHz])$.

• Journal of Electrical Engineering and Technology
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• v.10 no.5
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• pp.2120-2125
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• 2015

In this paper, a rectangular waveguide probe with a ridge-loaded straight slot (RLSS) is presented for a near-field scanning microwave microscope (NSMM). The RLSS is located laterally at the end wall of the cavity and is loaded on double ridges in a narrow straight slot to improve the spatial resolution compared with a straight slot. The probe consists of a rectangular cavity with an RLSS and a feed section of a WR-90 rectangular waveguide. When the proposed NSMM is located at distance of 0.1mm in front of a substrate without patches or strips, the simulated full width at half maximum (FWHM) of the probe improve by approximately 31.5 % compared with that of a straight slot without ridges. One dimensional scanning of the E-plane on a sample under test was conducted, and the reflection coefficient of the near-field scanning probe is presented.

• Journal of IKEEE
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• v.20 no.4
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• pp.424-427
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• 2016

A microwave NDI(Nondestructive Inspecting) method, based on SAR(Synthetic Aperture Radar) for inspecting such internal flaws or physical demage of FRP(Fiber Reinforced Polymer), is proposed in this paper. When a microwave is incident perpendicularly toward a multilayer dielectric FRP material, it gives a good response for the interfaces or transverse cracks. Interface depths or defect positions can be presented from the reflection waves, as using SAR imagery technique. As a result, it can be shown that such a SAR system can effectively inspect the type, size, or location of flaws within FRP composite material.