• Title, Summary, Keyword: Lowpass

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Performance Analysis of a Lowpass Filter on a CT Saturation Detection Algorithm (변류기 포화 판단 알고리즘의 저역통과 필터에 대한 성능 분석)

  • Gang, Yong-Cheol;Ok, Seung-Hwan;Yun, Jae-Seong;Gang, Sang-Hui
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.51 no.10
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    • pp.495-501
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    • 2002
  • A difference based current transformer (CT) saturation detection algorithm uses the third difference of a secondary current to detect the instants of the beginning/end of saturation. The third difference of a secondary current contains high frequency components when a CT is saturated. Thus, an effect of an anti-aliasing lowpass filter implemented in digital protection relays on the detection algorithm should be studied. This paper describes performance analysis of a lowpass filter on the CT saturation detection algorithm. The cutoff frequency of the lowpass filter is normally set to be half of a sampling frequency. In this Paper, two sampling frequencies of 3,840 (Hz) corresponding to 64 sample/cycle (s/c) and 1,920 (Hz) corresponding to 32 (s/c) are studied; the cutoff frequencies of the lowpass filters are set to be 1,920 (Hz), 960 (Hz) and 960(Hz), 480(Hz), respectively. And the proposed algorithm is verified by experiment. A 2nd order Butterworth filter is designed as a lowpass filter. The test results and experiment results clearly indicate that the saturation detection algorithm successfully detects the instants of the beginning/end of saturation even though a secondary current is filtered by the designed lowpass filters.

Design of Cascaded Lowpass Filter using Combination of Stopbands (저지대역의 중첩을 이용한 캐스캐이드 저역통과 여파기의 설계)

  • 김경훈;김상인;박익모;임한조
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.15 no.7
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    • pp.644-652
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    • 2004
  • In this paper, we designed a cascaded microstrip lowpass filter using the lowpass filters previously proposed. The previously proposed lowpass filters have a ultra-wide stopband and prominent cutoff sharpness using the combined characteristics of slot and microstrip open stub, respectively, and they are catagorized into 2 types by the method that determining their passband characteristics. The first type is determined its passband characteristics by open stub characteristics and the second is by slot characteristics. By cascading these structures with impedance adjustment of each element, the deeper out-of-band rejection and the sharper skirt response were achieved. The fabricated cascaded lowpass filters have -3㏈ cutoff frequencies at 1.035㎓ and 1.286㎓ respectively and -20㏈ stopband is over 20㎓ for both structures.

Design of the harmonic rejection waveguide lowpass filters by synthesis method (합성설계방법에 의한 고조파 억제용 도파관형 저역통과 여파기의 설계)

  • 박준석;박재봉;이재현
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.33A no.10
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    • pp.81-89
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    • 1996
  • In this paper, a very efficient CAD algorithm is proposedd where rhodes formulae combined with distributed lowpass prototype filter in order to design the corrugated waveguide harmonic rejection filters accurately. The proposed algorithm resolves effectively the problem of proximity effect without any optimiation or iterative design process by using the internally convexed corrugated structure. A 13-section tapered corrugated lowpass filter has been designed by the proposed algorithm and fabricated. The experimental results are in good agreement with the calculated results.

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Iterative Thresholded Lowpass Filter for Blocking Effect Removal (블록화 현상 제거를 위한 반복임계저역여파기)

  • 김상호;정해묵;이병욱;장규환;유시룡
    • Journal of the Korean Institute of Telematics and Electronics B
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    • v.32B no.1
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    • pp.103-109
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    • 1995
  • In this paper, we propose a postprocessing method that neatly removes blocking effect but retains visually important image details and edges. The iterative thresholded lowpass filter is basically a low pass filter whose ouput depends on three variable elements. I.e. iteration number, threshold value and passband width. The threshold value restricts the difference between the output of the proposed filter and the original input independent of the iteration number. With this property, the iterative thresholded lowpass filter can retain most of the image details while smoothing the block boundaries. The other two variable elements, i.e. iteration number and passband width, can determine the convergence speed of the proposed filter. In this paper, we also propose several adaptive filtering techniques based on the iterative thresholded lowpass filter with their simulation results.

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Microstrip Coupled-Line Lowpass Filter with Wide Stopband for RF/Wireless Systems

  • Velidi, Vamsi Krishna;Mandal, Mrinal Kanti;Sanyal, Subrata
    • ETRI Journal
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    • v.31 no.3
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    • pp.324-326
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    • 2009
  • We present the design of a compact microstrip lowpass filter with a wide stopband which is up to ten times the cutoff frequency. The filter is based on a coupled-line configuration and shunt open stubs. The open stubs create additional transmission zeros, which are used to extend the stopband of the filter without any additional components or cascaded units. A prototype lowpass filter with a 3 dB cutoff frequency of 0.428 GHz and a 15 dB stopband extended up to 4.77 GHz is fabricated to validate the theoretical predictions.

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Temperature Dependence of Microwave Properties of HTS Multipole Lowpass Filters Consisting of Microstrip Open-Stub Lines

  • Kim, Je-Ha;Han, Seok-Kil;Kang, Kwnag-Yong;Ahn, Dal
    • ETRI Journal
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    • v.19 no.2
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    • pp.48-58
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    • 1997
  • Using high quality high-$T_c$ superconducting (HTS) YBCO thin films, we designed and fabricated 3-pole, 5-pole, and 7-pole lowpass filters consisting of microstrip transmission lines and open-stub lines. We measured the microwave response of the filters in the temperature range of T=85 K to 27 K. AtT=30 K, the observed inband insertion loss was 0.14dB and 0.02dB for the 5-pole and 7-pole filters, respectively. The cut-off frequency was 4.7 GHz for the 5-pole filter and 7.9GHz for the 7-pole filter. To the authors' knowledge, the measured inband insertion losses are the best values reported so far for the open-stub line type HTS multipole lowpass filters. The skirt property of the 5-pole filter showed a large improvement over that of the 3-pole filter as predicted from the simulation. We found that, to obtain a stable performance, the HTS multipole lowpass filters should be operated at the temperatures between 60% and 70% of $T_c$.

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Reduction of the Blocking Effect in Block Coded Images Using Human Visual Model (인간 시각 모델을 이용한 블록 부호화에서의 경계 현사의 제거)

  • 김근형;박래홍
    • Journal of the Korean Institute of Telematics and Electronics
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    • v.25 no.6
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    • pp.663-671
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    • 1988
  • In this paper, in order to reduce the blocking effect of block coded images, we propose the method considering the lowpass and bandpass components of Granrath's human visual model. This method consists of two-stage enhancement procedure. The first step is lowpass filtering which smooths out the blocking effect, and the second step is a high frequency enhancement procedure to increase the contrast decreased by the lowpass filtering in the first step. In the first step, the one-dimensional Gaussian filter which aligthns parallel to the edge direction is considered to preserve the edge in the block and the two-dimensional Gaussian filter is used to smooth out the blocking effect near the block boundaries. In the second step, the lowpass and bandpass components of the Granrath's model are considered to increase contrast in a restored image. The performance comparison of the proposed method and the existing mehtods is made by a computer simulation with several block coded images. We can see that the enhancement in the subjective quality of images of the proposed method is more significant than the enhancement in the subjective quality of images of the proposed method is more significant than the existing methods, though the proposed method does not show better performance on the PSNR gain, the poor measure of picture quality for block coded images.

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A Compact and High Performance Lowpass Filter using Combined Characteristics of Slot and Open Stub (슬롯과 개방 스터브의 특성을 결합한 소형 저역통과 여파기)

  • 김경훈;김상인;박익모;임한조
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.15 no.1
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    • pp.36-43
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    • 2004
  • In this paper, we proposed a novel compact microstrip lowpass filter with an ultra-wide stopband and prominent cutoff sharpness using slot on the ground plane and microstrip shunt open stub. The microstrip shunt open stub and slot exhibit the different stopband response. The combined characteristics of these structures gives the ultra-wide stopband characteristics and the coupling effect between slots on the ground plane makes the prominent cutoff sharpness. The fabricated microstrip lowpass filter with the size of 20.1 mm ${\times}$ 18.7 mm has -3 ㏈ cutoff frequency at 1.187 ㎓ and -20 ㏈ stopband from 1.33 ㎓ to over 20 ㎓ and the insertion loss in the passband is less than -0.4 ㏈ form DC to 1 ㎓.

Design of Lowpass Filter With the Wide Stopband Characteristics Using Microstrip Line (마이크로스트립 선로를 이용한 광대역 차단특성을 가지는 저역통과 필터 설계)

  • Choi Dong-Muk;Shim Joon-Hwan;Jeon Joongn-Sung;Kim Dong-Il
    • Journal of Navigation and Port Research
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    • v.30 no.5
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    • pp.331-334
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    • 2006
  • In this paper, we designed and fabricated the lowpass filter with the wide stopband characteristics using microp- strip line. Adding the $\lambda_g/4$ open stub at the input and output ports, we developed the L-C ladder type lowpass filter using the open stub which has wide stopband characteristics. In order to reduce the entire size qf this filter, the high impedance microstrip lines were made with the meander structure. The lowpass filter was fabricated with the cutoff frequency 2.3 GHz and its measured frequency responses agree well with the simulation results.

DCT Domain Post-Processing Based on POCS (DCT 영역에서의 POCS에 근거한 후처리)

  • Yim Chang hoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.30 no.3C
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    • pp.158-166
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    • 2005
  • Even though post-processing methods based on projections onto convex sets (POCS) have shown good performance for blocking artifact reduction, it is infeasible to implement POCS for real-time practical applications. This paper proposes DCT domain post-processing method based on POCS. The proposed method shows very similar performance compared to the conventional POCS method, while it reduces tremendously the computational complexity. DCT domain POCS performs the lowpass filtering in the DCT domain, and it removes the inverse DCT and forward DCT modules. Through the investigation of lowpass filtering in the iterative POCS method, we define kth order lowpass filtering which is equivalent to the lowpass filtering in the kth iteration, and the corresponding kth order DCT domain POCS. Simulation results show that the kth order DCT domain POCS without iteration gives very similar performance compared to the conventional POCS with k iterations, while it requires much less computations. Hence the proposed DCT domain POCS method can be used efficiently in the practical post-processing applications with real-time constraints.