• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.5
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• pp.697-706
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• 2000

In this paper, new bandpass filters that are composed of microstrip ring resonators with the center frequency of 5.775 GHz and the bandwidth of 100 MHz are presented. For the suppression of the unnecessary harmonics, lowpass filters are inserted into the feedlines and ring resonator itself, respectively These bandpass filters show good microwave characteristics with the harmonic suppression ratio of about 39 dB and 35 dB, respectively. Also, the varactor-tuned microstip ring bandpass filter with harmonic suppression is suggested and the tuning bandwidth of more than 450 MHz is obtained.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.7
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• pp.1237-1242
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• 2016

In this paper, the low pass filter with harmonics suppression and rejection using parallel coupled-line and radial type open stub is presented. And the resultant characteristic of the proposed low pass filter is that the harmonics are suppressed and rejected in wide bandwidth due to the parallel coupled-line structure. The open stub of a low pass filter is constructed in radial type which can be used to adjust the size of filter. The size of the proposed low pass filter is $6.98{\times}7.60mm2$ and the cut off frequency is 2.45 GHz. And the filter is economical in unit cost and can be constructed easily and has the merit of mass product because the filter is composed of distributed element. Also, the widely rejected harmonics is 128 % in the bandwidth and the insertion and return losses of the low pass filter are 1.07 dB and 19.5 dB, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.5 s.120
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• pp.547-552
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• 2007

In this paper, the coupled microstrip lines of hairpin type are applied to design a compact microstrip ring hybrid. When the gap decreases, three attenuation poles are created by coupling between the lines. The proposed structure can achieve a significant reduction of size and suppression of the harmonics. And it has the same frequency responses of conventional ring hybrid at 2.55 GHz. The harmonics are suppressed to below -20 dB up to 12 GHz, including the third harmonic. The ring part size of the proposed ring hybrid is reduced to one forth of the conventional ring hybrid. The measured frequency responses agree well with simulated ones.

• Journal of Power Electronics
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• v.19 no.1
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• pp.89-98
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• 2019

This paper analyzes the input side performance of a conventional three-phase to single-phase matrix converter (3-1MC). It also presents the input-side waveform quality under this topology. The suppression of low-frequency input current harmonics is studied using the 3-1MC plus capacitance compensation unit. The constraint between the modulation function of the output and compensation sides is analyzed, and the relations among the voltage utilization ratio and the output compensation capacitance, filter capacitors and other system parameters are deduced. For a 3-1MC without large-capacity energy storage, the system performance is susceptible to input voltage imbalance. This paper decouples the inner current of the 3-1MC using a Lyapunov function in the input positive and negative sequence bi-coordinate axes. Meanwhile, the outer loop adopts a voltage-weighted synthesis of the output and compensation sides as a cascade of control objects. Experiments show that this strategy suppresses the low-frequency input current harmonics caused by input voltage imbalance, and ensures that the system maintains good static and dynamic performances under input-unbalanced conditions. At the same time, the parameter selection and debugging methods are simple.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.2
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• pp.178-182
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• 2004

In this paper, a 90$^{\circ}$ hybrid coupler with both power division and harmonic rejection characteristics is presented by applying a LPF characteristic to a conventional 90$^{\circ}$ hybrid. Since a conventional 90$^{\circ}$ hybrid coupler operates as a power divider/combiner using phase difference, it does not suppress higher order harmonics when it is incorporated with nonlinear amplifier. This requires an additional filter to take into account of the harmonics. The proposed 90$^{\circ}$hybrid coupler power provides the division capability and proper phase difference, as well as harmonic suppression characteristic by integrating LPF characteristic.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.104-109
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• 2012

In this paper, we propose a way to improve the quality of L-band wireless communication from unfriendly influential factors lying in the neighboring RF bands. The UHF-band system has resonator components and they generate harmonics as the spurious in the L-band. Therefore, a metamaterial CRLH bandpass filter is designed for the purpose of system miniaturization and smaller insertion loss, and its spurious phenomenon is observed in the frequency domain. And its harmonics in the L-band are suppressed by a compact bandstop filter whose equivalent circuit is newly developed. The design methodology is validated by the equivalent circuit to be compared with commercial full-wave EM software simulations, where the spurious is dropped by 20dB. Also, the advantage of the proposed design is presented by the comparison where our filter is much smaller than the conventional parallel edge coupled filter by over 50%, with excellent harmonic suppression.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.10
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• pp.1107-1116
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• 2007

In this paper, a broadband open stubs band pass filters which can suppress the second harmonics using Z-transform technique, is designed, fabricated and characterized. The proposed broadband filters integrate the band stop filter with the FSCS structure and ${\lambda}_g/4$ open stub in order to suppress the second harmonics. Due to insertion of BSF at input and output terminal, the size of the filter was increased in the conventional filter, however, in the proposed structure, the position of inverter that connects the stubs can be integrated between those stubs, thereby decreasing the size. So, it can be fabricated in the size of $18.7{\times}16.9mm^2$ which is smaller size than conventional one. The measured results of the proposed filters have center frequency of a 5.8 GHz with bandwidth of 95 %, insertion loss of 0.6 dB, return loss of 14 dB. The simulation results are consistent with measurement results. The filter is designed far X-band satellite communication and ITS applications.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.85-89
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• 2017

This paper proposes an antenna incorporating a bandstop filter to miniaturize the rectenna used for wireless power transmission with the emerging interest these days. To suppress the harmonics that can be re-radiated, this paper proposes a microstrip patch antenna that can suppress the harmonics while maintaining the size of the antenna by inserting a U-slot, which acts as a bandstop filter, on the ground plane of the antenna. As a result, S11 of the second harmonic(4.6GHz) was reduced from -5.61dB to -0.338dB and the efficiency was suppressed significantly from 29.76% to 1.5%. In addition, the maximum gain was reduced to -12dBi from 2.89dBi. On the other hand, at the fundamental frequency (2.45GHz), the S11 value was reduced from -18 dB to -15 dB, and the efficiency was reduced slightly from 68.2% to 60%. In the case of applying a microstrip antenna combined with the proposed bandstop filter to a rectenna, it is believed that the harmonics that degrade the performance of the rectenna can be removed effectively while reducing the large area occupied by harmonic suppression.

• Journal of Power Electronics
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• v.17 no.5
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• pp.1349-1362
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• 2017

In order to further improve the harmonic suppression capability of conventional 12-pulse rectifiers, this paper proposes a low harmonic 12-pulse rectifier using an Active Inter-Phase Reactor (AIPR). Through a detailed analysis of the relationship between the input current, output current and circulating current of the DC side, the mechanism where the AC grid side current harmonics can be suppressed by the DC side circulating current is revealed. On this basis, an interleaved APFC controlled by a DSP is designed and used as an AIPR along with an interphase reactor. A simulation is carried out with MATLAB/Simulink and an experiment is performed on a 9-kVA prototype. The obtained results verify the feasibility and validity of the proposed approach. Compared with a traditional 12-pulse rectifier, the THD can be reduced to 1/5 of the original value, and the capacity of the AIPR is only 2% of the load power. Thus, it is suitable for high-power applications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.9 s.112
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• pp.845-851
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• 2006

Folded lines are applied to design a compact microstrip ring hybrid. Using the proposed structure we achieve both significant size reduction and good harmonic suppression with the same results of conventional ring hybrid at 2.41 GHz. Including the third harmonic frequency, up to 11 GHz band harmonics are suppressed to -20 dB. The size of the proposed ring-hybrid is reduced to one forth of the conventional ring hybrid. The measured frequency responses agree well with simulated ones.