• Journal of the Korean Society for Nondestructive Testing
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• 제21권2호
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• pp.147-151
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• 2001

An optical fiber sensor is capable of nondestructive measurement of a structure and it has an advantage of the immunity to electromagnetic interference because light is not affected by electromagnetic wave. In addition, if optical fibers are buried in an object like a concrete, this sensor tan analyze defects and physical status of the object without disassembling it. Especially, the fiber Bragg grating sensor is a promising optical fiber sensor capable of nondestructive test of such an object. A fiber Bragg grating has the characteristics of reflecting or blotting light of a specific wavelength. If we apply physical quantity like strain to the fiber Bragg grating, the center wavelength of the reflected light is shifted and then we can find the physical quantity applied to the fiber Bragg grating by measuring the center wavelength shift of the reflected light. The fiber Bragg grating sensor capable ot static and dynamic strain measurement is being used in health-monitoring of buildings, structures, etc. Recently increasing is interest in dynamic strain measurement inevitable to the civil structures such as roads and bridges. In this study we implemented the optical fiber sensor system which can measure dynamic strain at multiple points using Fabry-Perot wavelength demodulation. And we measured the static and dynamic strain using this sensor system with a test structure(cantilever). Measurement results were similar to those obtained with the conventional electrical measurement methods.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제20권9호
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• pp.906-913
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• 2009

In this paper, the design concept and implementation method of the X-band 4-bit($22.5^{\circ}$, $45^{\circ}$, $90^{\circ}$, $180^{\circ}$ BIT) diode phase shifter in the parallel plate waveguide are introduced. The simulated results of $11.25^{\circ}$, $22.5^{\circ}$ and $45^{\circ}$ dielectric phase shift layers using CST's MWS and Agilent's ADS are presented, and the measured results are compared with the simulated ones. The simulated phase shift errors at the center frequency are $0.6^{\circ}$, $0.7^{\circ}$, and $3.5^{\circ}$, respectively and the measured phase shift errors at the center frequency are $0.6^{\circ}$, $2^{\circ}$, and $5.5^{\circ}$, respectively. Also, the MWS simulated results of $22.5^{\circ}$ BIT and $45^{\circ}$ BIT phase shifter are presented and compared with the ADS simulated ones to verify the validity of the presented design concept and implementation method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제14권9호
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• pp.904-911
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• 2003

A new method to reduce the size of microwave amplifiers spiral-shaped defected ground structure(Spiral-DGS) is proposed. A microstrip line having Spiral-DGS on the ground plane produces increased slow-wave factor and electrical length for the fixed physical length. In addition, it provides an excellent rejection characteristic for a finite frequency band like band rejection filters. The rejection band is used for rejecting harmonic components of amplifiers. The reduced microstrip line lengths in matching networks by Spiral-DGS are 39 % and 44 % of the original ones in input and output matching networks, respectively. It is shown that the measured S-parameters of the reduced amplifier agree well with those of the original amplifier. The measured second harmonic of the reduced amplifier is much less than that of the original amplifier by at least 10 dB. The same technique is applied to reject the third harmonic using the proper Spiral-DGS for the third harmonic frequency. The measured third harmonic is smaller than that of the original amplifier by 25 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제16권3호
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• pp.300-310
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• 2005

In this paper we propose the compact three-layer EBG structure. The unit cell of the proposed EBG structure is composed of a square patch in the upper layer and a square ring stripline in the lower layer that are connected to the ground plane through conducting vias. Reflection phase analysis method and tangential transmission method were considered to accomplish effective EM simulation and measurement. EM simulation results indicate that bandgap characteristics of the EBG structure using both methods is nearly identical. Parametric studies have been performed with the EM simulator to analyze the properties of the EBG structure by investigating the phase shift of the normally incident plane wave, and the transmission measurements between simple monopole antennas positioned near the EBGstructure have been done. The operating fiefuency bandgap of the proposed EBG structure is about 34 $\%$ lower than the conventional EBG structure with the same size. Measured results show bandgap from 0.930 GHz to 0.945 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제16권10호
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• pp.1050-1058
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• 2005

This paper presents how to design and implement a very compact, cost effective and broad band receiver module for IEEE 802.16 FWA(Fixed Wireless Access) in the 40 GHz band. The presented receiver module is fabricated in a multi-layer LTCC(Low Temperature Cofired Ceramic) technology with cavity process to achieve excellent electrical performances. The receiver consists of two MMICs, low noise amplifier and sub-harmonic mixer, an embedded image rejection filter and an IF amplifier. CB-CPW, stripline, several bond wires and various transitions to connect each element are optimally designed to keep transmission loss low and module compact in size. The LTCC is composed of 6 layers of Dupont DP-943 with relative permittivity of 7.1. The thickness of each layer is 100 um. The implemented module is $20{\times}7.5{\times}1.5\;mm^3$ in size and shows an overall noise figure of 4.8 dB, an overall down conversion gain of 19.83 dB, input P1 dB of -22.8 dBm and image rejection value of 36.6 dBc. Furthermore, experimental results demonstrate that the receiver module is suitable for detection of Digital TV signal transmitted after up-conversion of $560\~590\;MHz$ band to 40 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제10권1호
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• pp.78-89
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• 1999

In this paper, to improve bandwidth amplitude fluctuation for the broadband signal in indoor propagation environment, we measured and analyzed broadband signal using a vertically polarized, horizontally polarized and circularly polarized antenna, conducting by frequency sweeping method in NLOS (Non-Line-of-Sight) environment. And, to investigate the optimum condition for the improvement of broadband propagation characteristics we also examined the effects of both human motions and transmission antenna height in the NLOS environment. As a result, in the case of NLOS environment, it was found that the amplitude deviation characteristics in frequency bandwidth can be improved by polarization diversity reception. Especially, we found that it is the best effective one to make polarization diversity reception branches, which install the circularly polarized antenna at transmitting end and install the polarized diversity branches received vertical or/and horizontal polarized wave at receiving end. The affection of a human motions is not so much in LOS and NLOS environment, but it can lead to the cause of burst error in indoor digital radio communications as the fade of signal strength become more deeper. And also, when raise the transmitting antenna up to the ceiling, the LOS and NLOS environment could be coexisted. In this case, it can be also inferred that frequency bandwidth amplitude deviation must be fundamentally improved by using polarization diversity reception technique to make the possibility of high transmission rate.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제21권11호
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• pp.1324-1333
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• 2010

In this paper, three kinds of beam coupling losses which occur in a quasi-optics circuit for millimeter wave receiver system have been intensively investigated. First, the beam coupling losses which are caused by mismatch of beam waists radii and their positions between those of one and the other have been evaluated. It shows that beam coupling losses due to mismatch of beam waists radii and their positions between two quasi-optics circuits can be minimized if beam waist radius is chosen as larger than 3 times the operation wavelength. Second, the beam coupling losses have been studied when the axis of propagation of one beam is tilted with respect to that of the other beam. It is noted that smaller beam waist radius results in greater tolerance to tilts and angular misalignments. Third, the beam coupling cases in which two beams are offset if their axes of propagation are parallel but one is displaced relative to the other have been investigated. It is confirmed that beam waists radii with larger than 3 times operation wavelength are less sensitive to lateral offsets.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제24권4호
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• pp.366-373
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• 2013

This paper discusses the singly curved phased reflector for reduced RCS pattern, which has minimized RCS level at boresight with a null by phase cancelation and the lowered RCS level of main beam by splitting the main beam into multi directions. Considering the reduced level of boresight and main beam compared to the same sized reference PEC, this proposed multi-beam reflector can be adopted in the mono-static radar and the bi-static radar environment. The proposed reflector is a multi-beam reflector, which has different phase distributions at each row for different steering angle. It is designed through an intermediate stage of a single and dual-beam reflector. The behaviors of the designed reflectors are verified through full-wave simulation and experiment. The reflectors are designed in the frequency of 10 GHz and it has a size $240{\times}180mm^2$($8{\times}6\;{\lambda}^2$) with the curvature k=3.3. From the measured results, the proposed reflectors reduce the reflected power by 17 dB at boresight.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제19권1호
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• pp.15-22
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• 2008

In this paper, we propose a numerical analysis on reversed current of distributed amplifier based on transmission line theory and proposed a theory to obtain optimum transmission line length to minimize the reversed currents by cancelling those components. The reversed current is analyzed as being simply absorbed into the terminal resistance in the conventional analysis. In the proposed analysis, however, they are designed to be cancelled by each other with opposite phase by the optimal length of the transmission lint Circuit simulation and implementation using pHEMT transistor were performed to validate the proposed theory with the cutoff frequency of 3.6 GHz. From the measurement, maximum gain of 14.5dB and minimum gain of 12.3dB were achieved In the operation band. Moreover, measured efficiency of the proposed distributed amplifier is 25.6% at 3 GHz, which is 7.6%, higher than the conventional distributed amplifier. Measured output power Is about 10.9dBm, achieving 1.7dB higher output power than the conventional one. Those improvement is thought to be based on the cancellation of refersed current.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제19권1호
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• pp.7-14
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• 2008

In this paper, we propose VATL(Voltage-controlled Artificial Transmission Line) employing periodically loaded diodes for application to on-chip matching components on MMIC. Compared with conventional microstrip line, the VATL showed a much shorter wave length due to periodic capacitance of diodes, and the characteristic impedance of the VATL was easily controlled bγ changing supplied voltage. Concretely, the characteristic impedance of the VATL was changed from $80{\sim}20{\Omega}$ in a range of $0{\sim}1.05V$ and the VATL showed a wavelength of 1.5mm at 20GHz, while conventional microstrip line showed a wavelength of 5.3mm at the same frequency. Using the VATL, a ${\lambda}/4$ impedance transformer was fabricated on GaAs MMIC for application to on-chip matching components on MMIC. Using the ${\lambda}/4$ impedance transformer made it possible to perform impedance matching between RF components with various characteristic impedance of $30{\sim}100{\Omega}$ by adjusting applied Voltage.