• Structural Engineering and Mechanics
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• v.36 no.6
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• pp.697-714
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• 2010

This paper presents an improved version of the Hilbert-Huang transform (HHT) for the modal evaluation of structural systems or signals. In this improved HHT, a well-designed bandpass filter is used as preprocessing to separate and determine each mode of the signal for solving the inherent modemixing problem in HHT (i.e., empirical mode decomposition, EMD, associated with the Hilbert transform). A screening process is then applied to remove undesired intrinsic mode functions (IMFs) derived from the EMD of the signal's mode. A "best" IMF is selected in each screening process that utilizes the orthogonalization coefficient between the signal's mode and its IMFs. Through mode-by-mode signal filtering, parameters such as the modal frequency can be evaluated accurately when compared to the theoretical value. Time history of the identified modal frequency is available. Numerical results prove the efficiency of the proposed approach, showing relative errors 1.40%, 2.06%, and 1.46%, respectively, for the test cases of a benchmark structure in the lab, a simulated time-varying structural system, and of a linear superimposed cosine waves.

• ETRI Journal
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• v.45 no.2
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• pp.338-345
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• 2023

A filtering power divider based on air-filled substrate-integrated waveguide (AFSIW) technology is proposed in this study. The AFSIW structure is used in the proposed filtering power divider for substantially reducing the transmission losses. This structure occupies a large area because of the use of air as a dielectric instead of typical dielectric materials. A filtering power divider provides power division and frequency selectivity simultaneously in a single device. The proposed filtering power divider comprises three AFSIW cavities. The filtering function is achieved using symmetrical inductive posts. The input and output ports of the proposed circuit are realized by directly connecting coaxial lines to the AFSIW cavities. This transition from the coaxial line to the AFSIW cavity eliminates the additional transitions, such as AFSIW-SIW and SIW-conductor-backed coplanar waveguide, applied in existing AFSIW circuits. The proposed power divider with a second-order bandpass filtering response is fabricated and measured at 5.5 GHz. The measurement results show that this circuit has a minimum insertion loss of 1 dB, 3-dB fractional bandwidth of 11.2%, and return loss exceeding 11 dB.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.265-268
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• 2003

In this paper, we introduce the SIR typed bandpass filters in CPW structures for shifting spurious harmonic frequency into higher frequency band. And we proposed the effective feed structures for suppressing spurious frequency in the SIR typed CPW bandpass filters. The designed folded feed structures have lowpass filtering characteristic. They are very effective feed types in the CPW bandpass filters for suppressing harmonics. The measured results of the CPW bandpass filter with folded feed line shows that it has suppressed and wide out-of-band up to 5.8fo.

• Journal of Ocean Engineering and Technology
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• v.24 no.1
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• pp.166-171
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• 2010

In this paper, the front-end of a digital receiver with a 25 kHz carrier frequency, 5 kHz symbol rate, and any excess-bandwidth is designed using two basic facts. The first is known as the uniform sampling theorem, which states that the sampled sequence might not suffer from aliasing even if its sampling rate is lower than the Nyquist sampling rate if the analog signal is a bandpass one. The other fact is that if the sampling rate is 4 times the center frequency of the sampled sequence, the front-end processing complexity can be dramatically reduced due to the half of the sampled sequence to be multiplied by zero in the demixing process. Furthermore, the designed front-end is simplified by introducing sub-filters and sub-sampling sequences. The designed front-end is composed of an A/D converter, which takes samples of a bandpass filtered signal at a 20 kHz rate; a serial-to-parallel converter, which converts a sampled bandpass sequence to 4 parallel sub-sample sequences; 4 sub-filter blocks, which act as a frequency shifter and lowpass filter for a complex sequence; 4 synchronized switches; and 2 adders. The designed front-end dramatically reduces the computational complexity by more than 50% for frequency shifting and lowpass filtering operations since a conventional front-end requires a frequency shifting and two lowpass filtering operations to get one lowpass complex sample, while the proposed front-end requires only four filtering operation to get four lowpass complex samples, which is equivalent to one filtering operation for one sample.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.5
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• pp.36-41
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• 2007

We report the 94 GHz CPW branch-line bandpass filter for planar integrated millimeter-wave circuits. The branch-line coupler operates as a transversal filtering section by connecting the coupling ports to the open load stubs and taking the isolation port as the output node. For design of the 94 GHz branch-line bandpass filter, we built the CPW library and optimized the characteristic impedances and the lengths of the branch-line coupler and the open load stubs. The fabricated 94 GHz bandpass filter exhibits an insertion loss of 2.5 dB with an 11.7 % 3 dB relative bandwidth and the return loss is -18.5 dB at a center frequency of 94 GHz.

• Journal of electromagnetic engineering and science
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• v.10 no.1
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• pp.28-34
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• 2010

This paper introduces a new U.S. ultra-wideband(UWB: 3.1~10.6 GHz) 1:2 power divider based on a single section Wilkinson type configuration. The divider provides very flat in-band power splitting, high isolation, low insertion loss, sharp roll-off bandpass filtering, and DC blocking characteristics. The circuit consists of a $\lambda$/4 Y resonator, three capacitively coupled $\lambda$/2 short-circuited lines, and a resistor between the two output ports. The circuit structure was simulated with ADS and HFSS, and realized with low-temperature co-fired ceramic(LTCC) green tape, which has a dielectric constant of 7.8. $|S_{11}|$ better than 10 dB, $|S_{21}|$ and $|S_{31}|$ less than 3.2 dB, with both $|S_{22}|$ and $|S_{32}|$ measured as better than 12 dB for the whole UWB band. Measurement results agree closely with HFSS simulation results. The power divider has a compact size of $4\times9\times0.6mm^3$.

• Journal of electromagnetic engineering and science
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• v.18 no.1
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• pp.41-45
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• 2018

In this study, a short-ended coupled line with a short-circuit stub transmission line bandpass filtering impedance transformer is presented. The general designed equations are derived on the basis of circuit theory. The design curves are provided to examine the characteristic of the proposed impedance transformer. The proposed circuit is suitable for high termination impedance. To validate the design formulas, a $400-50{\Omega}$ impedance transformer is designed and fabricated at the operating center frequency ($f_0$) of 2.6 GHz. The measured results show a good agreement with the simulation. The measured insertion and return losses are 0.6 dB and 22.5 dB at $f_0$, respectively. The measured return loss is higher than 20 dB within the passband frequency of 2.51-2.7 GHz. Moreover, the stopband attenuation is higher than 25 dB from DC to 1.64 GHz of the lower stopband and from 3.12 GHz to 6.4 GHz of the higher stopband.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.8
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• pp.47-52
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• 2008

In order to enhance the rejection performance of the UWB bandpass filter based on the Composite Right- and Left-Handed Transmission-line(CRLH-TL) Metamaterial cell, we propose the lowpass filtering concept that fits into the design objectives : Keeping metamaterial property and miniaturization. So the bandpass filter itself is made far less than a quarter-wavelength and a pair of symmetric comprises lowpass filtering blocks are placed before and after the center CRLH filter which comprises tile interdigitated coupled lines and short-circuited stob. The design result will show the size of 'guided wavelength/8', the fractional bandwidth over 100%, the insertion loss much less than 1 dB, a flat Group-Delay and a good return loss performance, as expected.

• ETRI Journal
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• v.37 no.1
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• pp.61-65
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• 2015

In this paper, a novel filtering power divider with external isolation resistors is presented. The proposed power divider can be considered as an integration of a bandpass filter and a Gysel power divider. Based on the circuit topology, a high-order filtering power divider can be easily realized. Odd- and even-mode models are employed to analyze the filtering and power splitting functions. For demonstration, a third-order filtering power divider operating at 1.5 GHz is designed and implemented. The measured results exhibit an isolation between the output ports that is better than 20 dB at around the center frequency.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.278-282
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• 2003

The rapid growth of wireless and mobile communications has stimulated the development of multilayer filter technology. In this paper, one type of aperture-coupled microstrip interdigital-loop resonators in a multilayer structure are proposed and investigated for the applications to the design of a new class of compact microstrip bandpass filter. The new filter configuration consists of two arrays of microstrip interdigital-loop resonators that can be coupled through the apertures on the common ground plane. Depending on the arrangement of the apertures, different filtering characteristics can easily be realized. The results of measurement are almost similar to those of simulation.