• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3A
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• pp.171-178
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• 2003

In this paper, We has proposed two DGS(Defected Ground Structure) resonators and designed the low-pass filter using the proposed DGS types. This structure consists of two rectangular slots, a ‘II type’ slot on the ground plane, and the stub at the transmission line. It has strong advantages that can vary the return loss at the passband freely and also can easily tune the attenuation pole frequency at the stopband. For enhancing the poor skirt property at the cutoff frequency of the Single Stub ‘II Type’ DGS cell, we have obtained the steep slope attenuation characteristic by combining the rectangular slot on both sides of the DGS. This type of the LPF with the proposed structure can be made more smaller than the existing filters and be used to find the various applications for eliminating the hamonics and spurious mode at WLL and the 2.4 GHz ISM band systems.

• Journal of electromagnetic engineering and science
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• v.17 no.2
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• pp.57-64
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• 2017

In this paper, an asymmetric compact multiband slot antenna is proposed for global positioning system (GPS), worldwide interoperability for microwave access (WiMAX), and wireless area network (WLAN) applications. The top plane, a ground is composed of a rectangular slot with a trapezoidal-like stub, an inverted U-shaped slot at the right side of the rectangular slot, an inverted L-shaped slot at the left side of the rectangular slot, and three stubs. The proposed antenna is fed by an asymmetric cross-parasitic strip on the bottom plane. By properly designing the slots and stubs, four resonant frequency bands are achieved with -10 dB reflection coefficient bandwidths of 50 MHz, 400 MHz, 390 MHz, and 830 MHz in the 1.57 GHz GPS band, 2.4 GHz WLAN band, 3.5 GHz WiMAX band, and 5.5 GHz WLAN bands, respectively. The antenna has a total compact size of $13mm{\times}32mm{\times}0.8mm$. Simulated and measured results indicate that the proposed antenna has sufficient bandwidth and good radiation performance in each band.

• Steel and Composite Structures
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• v.12 no.1
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• pp.73-92
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• 2012

The effect of element interaction and material nonlinearity on the ultimate capacity of stainless steel plated cross-sections is investigated in this paper. The focus of the research lies in cross-sections failing by local buckling; member instabilities, distortional buckling and interactions thereof with local buckling are not considered. The cross-sections investigated include rectangular hollow sections (RHS), I sections and parallel flange channels (PFC). Based on previous finite element investigations of structural stainless steel stub columns, parametric studies were conducted and the ultimate capacity of the aforementioned cross-sections with a range of element slendernesses and aspect ratios has been obtained. Various design methods, including the effective width approach, the direct strength method (DSM), the continuous strength method (CSM) and a design method based on regression analysis, which accounts for element interaction, were assessed on the basis of the numerical results, and the relative merits and weaknesses of each design approach have been highlighted. Element interaction has been shown to be significant for slender cross-sections, whilst the behaviour of stocky cross-sections is more strongly influenced by the material strain-hardening characteristics. A modification to the continuous strength method has been proposed to allow for the effect of element interaction, which leads to more reliable ultimate capacity predictions. Comparisons with available test data have also been made to demonstrate the enhanced accuracy of the proposed method and its suitability for the treatment of local buckling in stainless steel cross-sections.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.9
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• pp.13-19
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• 1998

It was shown that the bandwidth of T-shaped microstripline fed slot antenna is wider than many of the conventional feeding structures. In this paper, we proposed a new method of enhancing the bandwidth of T-shaped microstripline fed slot antenna with a shunt open stub, and analyzed this antenna by using the FDTD method. We have computed waves and electric field distribution in the time domain, and VSWR, input impedance and radiation pattern in the frequency domaim by Fourier transforming the time domain results. It was found that the bandwidth of this antenna depend on the position(L$_1$) and length(L$_2$) of a shunt open stub. When these parameters are L$_1$=30 mm and L$_2$=33mm, we obtained the maximum bandwidth at the center frequency of 2.3 GHz. From the computed results, the optimum antenna is designed and fabricated. The fractional bandwidth of this antenna was 53.9 %. The measured results were in relatively good accordance with computed values.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.9
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• pp.791-799
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• 2016

This paper presents the design of reconfigurable frequency selective surfaces for X-band bandpass operation with improved isolation. The proposed reconfigurable FSS is composed of a four-legged loaded element, a inductive stub and a bias grid. The PIN diode is located between the four-legged loaded element and the stub, which can control the frequency response of reconfigurable FSS by ON/OFF state. By adjusting the length of the stub, the desired bandpass frequency and the improved isolation between ON and OFF state can be obtained. For validation of simulated results, we have carried out transmission characteristic measurements using rectangular waveguide of WR-90. The measured results are in good agreements with the simulated results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.9
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• pp.888-896
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• 2011

In this paper, we studied characteristics of the bent antenna febricated on Flexible-PCB. Flexible-PCB consisting of a polyimide has dielectric constant 3.5, thickness 0.125 mm. Proposed antennas which operates at Bluetooth band are a rectangular loop antenna and a loop antenna with inverted-L type stub. We compared the input matching and radiation characteristics of the proposed antennas under eight kinds of bending conditions.

• Steel and Composite Structures
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• v.44 no.4
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• pp.489-502
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• 2022

The stiffeners, also known as ribs, are utilized to increase the resistance of T-stubs. The author's previous studies showed that stiffeners can increase plastic capacity by an average of 1.71 times. A combined experimental and numerical study was undertaken to examine the effects of the stiffener configuration on the behavior of T-stubs. A total of 20 stiffened T-stubs where the shape and angle of stiffeners were considered as the main parameters were tested under monotonic loading. Rectangular, triangular and AISC types of stiffener were tested under monotonic loading. The experimental results indicated that when the height of the stiffener is equal to or higher than the length of the stiffener, the shape of the stiffener does not have an influence on the behavior. A numerical study using the finite element tool ABAQUS was carried out in order to further investigate the effects of the stiffener shapes. In this case, the height is considered less than the length of the stiffener. Moreover, the shape of the stiffeners was investigated with the different thicknesses of the stiffener. The simulation findings revealed that when the height of the stiffener is less than the length of the stiffener, the shape of the stiffener significantly affects the plastic capacity. Based on the numerical and experimental results, it is recommended to use the triangular shape of the stiffener when height is equal to or higher than the length of the stiffener while it is recommended to utilize the rectangular shape of the stiffener when height is less than the length of the stiffener.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.7
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• pp.3140-3145
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• 2012

In this paper, a design method for a compact slot antenna fed by a coplanar waveguide (CPW) is studied. A T-shaped tuning stub is inserted inside a narrow rectangular slot and the slot is impedance matched to the CPW feedline by adjusting the width, length, and position of the stub. The resonance frequency is adjustable by the slot length and the antenna size can be reduced by bending the slot. The resonance frequency and impedance matching property of the compact slot antenna are similar to those of the half-wavelength slot antenna, which enables one to design compact antenna of this type with ease. A compact slot antenna for 2.45-GHz ISM band is designed, fabricated on an FR4 substrate (dielectric constant of 4.4 and thickness of 0.8 mm), and experimentally tested. The measured results agree well with the simulations, which confirms the validity of this study. The fabricated compact slot antenna shows an impedance bandwidth of 200 MHz(2.32-2.52 GHz) for a VSWR < 2, which is suitable for 2.45-GHz ISM band (2.4-2.48 GHz). The measured radiation patterns show ${\infty}$-shaped directional pattern in the E-plane and nearly omni-directional pattern in the H-plane with a peak gain of 2.0 dBi, which are similar to those of a monopole antenna. The proposed antenna is expected to be suitable for the applications as antennas for WLAN, RFID, and mobile handset.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.3
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• pp.341-348
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• 2019

In this paper, a monopole type antenna applicable to WLAN and WiMAX standard frequency bands is designed and fabricated. The proposed antenna is designed to have rectangular ring and rectangular patch based on microstrip feeding for triple band characteristics and inserted two stub in the top of the rectangular ring patch to enhance impedance bandwidth characteristics. The proposed antenna has $18.0mm(2W_1+W_2){\times}33.0mm(L_7+L_8+L_9)$ on a dielectric substrate of $27.0mm(W_1){\times}44mm(L_1){\times}1.0mm$ size. From the fabrication and measurement results, impedance bandwidths of 660MHz (2,08 to 2.74GHz) for 2.4/2.5MHz band, 488MHz (3.40 to 3.88GHz) for 3.5MHz band, and 2,180MHz (4.61 to 6.79GHz) for 5,000MHz band were obtained based on the impedance bandwidth. The proposed antenna also obtained the measured gain and radiation pattern in the anechoic chamber.

• Steel and Composite Structures
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• v.18 no.4
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• pp.1023-1044
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• 2015

Concrete-filled tubes (CFT), formed by an outer steel tube filled with plain or reinforced concrete inside, have been increasingly used these recent decades as columns or beam-columns, especially for tall buildings in seismic areas due to their excellent structural response. This improved behavior is derived from the effect of confinement provided by the tube, since the compressive strength of concrete increases when being subjected to hydrostatic pressure. In circular CFTs under compression, the whole tube is uniformly tensioned due to the radial expansion of concrete. Contrarily, in rectangular and square-shaped CFTs, the lateral flanges become subjected to in-plane bending derived from this volumetric expansion, and this fact implies a reduction of the confinement effect of the core. This study presents a numerical analysis of different configurations of CFT stub columns with inner stiffening plates, limited to the study of the influence of these plates on the compressive behavior without eccentricity. The final purpose is to evaluate the efficiency in terms of strength and ductility of introducing stiffeners into circular and square CFT sections under large deformation axial loading.