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Design of a 170 GHz Notch Filter for the KSTAR ECE Imaging Sensor Application
( Wahab Mohyuddin ),( Dong Sik Woo ),( Sung Kyun Kim ),( Kang Wook Kim ),( Hyun Chul Choi ) 한국센서학회 2016 센서학회지 Vol.25 No.1
A planar, light-weight, and low-cost notch filter structure is required for the KSTAR ECEI (Electron Cyclotron Emission Imaging) system to protect the mixer arrays from spurious plasma heating power. Without protection, this heating power can significantly degrade or damage the performance of the mixer array. To protect mixer arrays, a frequency selective surface (FSS) structure is the suitable choice as a notch filter to reject the spurious heating power. The FSS notch filter should be located between the lenses of the ECEI system. This paper presents a 170 GHz FSS notch filter for the KSTAR ECEI sensor application. The design of such an FSS notch filter is based on the single-sided square loop geometry, because that makes it relatively insensitive to the incident angle of incoming wave. The FSS notch filter exhibits high notch rejection with low pass-band insertion loss over a wide range of incident angles. This paper also reviews the simulated and measured results. The proposed FSS notch filter might be implemented in other millimeter-wave plasma devices.
Compact Wideband Antiparallel Diode Frequency Triplers Utilizing Planar Transitions
Mohyuddin, Wahab,Kim, Kang Wook,Choi, Hyun Chul Hindawi Limited 2015 International journal of antennas and propagation Vol.2015 No.-
<P>Two designs of frequency triplers, which use planar transitions as baluns and an antiparallel diode pair to achieve wide bandwidth, are presented. The ultrawideband transitions are utilized for input and output impedance matching of the frequency triplers. The design process and operation principles are described in this paper. The implemented frequency triplers exhibit flat response over wide frequency range of 3 to 9 GHz. The proposed Type A frequency tripler shows conversion loss of ~18 dB with above 30 dB even harmonics suppression. With Type B frequency tripler, conversion loss of ~17 dB and above 25 dB even harmonic suppression are achieved.</P>
Design of A Compact Single-Balanced Mixer for UWB Applications
Wahab Mohyuddin,In Bok Kim,Hyun Chul Choi,Kang Wook Kim 한국전자파학회JEES 2017 Journal of Electromagnetic Engineering and Science Vol.17 No.2
The design and implementation aspects of a new single-balanced mixer for ultra-wideband (UWB) applications are presented in this study. The proposed mixer utilizes a miniaturized UWB ring coupler as a balun, consisting of a pair of in-phase and inverted-phase transitional structures. The well-balanced UWB performance of the ring coupler, aside from the optimized diode matching, results in improved conversion loss and inter-port isolations for a wide bandwidth. The size of the implemented single-balanced diode mixer is reduced to about 60% of the area of the conventional single-balanced ring diode mixer. The measured results of the proposed mixer exhibit an average conversion loss of 7.5 dB (minimum 6.7 dB) and a port-to-port isolation of greater than 18 dB over a UWB frequency range of 3.1–10.6 GHz. The measured results agree well with the simulated results.
Asymmetric Ultra-Wideband Microstrip-to-Coplanar Stripline Transition
Lee, Gwan Hui,Mohyuddin, Wahab,Choi, Hyun Chul,Kim, Kang Wook THE INSTITUTE OF ELECTRICAL ENGINEERS 2018 IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS Vol.28 No.5
<P>A new design method for an asymmetric microstrip-to-coplanar stripline (CPS) transition based on the analytical electromagnetic model is presented. The cross section at each stage of the transition is analyzed through conformal transformation, and the corresponding line impedance is calculated. Then, the ground linewidth on the substrate bottom is adjusted to form an optimal Klopfenstein impedance taper. To demonstrate the design method, a transition between a 50- <TEX>$\Omega $</TEX> microstrip line and a high-impedance CPS line ( <TEX>$147~\Omega$</TEX>) was implemented. Good transition performance with more than 10-dB return loss and less than 1-dB insertion loss was obtained for frequency ranges of 6–40 GHz.</P>
광대역의 고조파 억제가 가능한 헤어핀 SIR을 사용한 협대역 통과 여파기 설계
박주성(Ju-Seong Park),모우딘 와합(Wahab Mohyuddin),최현철(Hyun-Chul Choi),김강욱(Kang-Wook Kim) 한국전자파학회 2018 한국전자파학회논문지 Vol.29 No.3
본 논문에서는 4~6 %의 협대역 필터를 구현함에 있어서 광대역으로 고조파 성분을 억제하기 위하여 suspended-strip 선로 상에 2개의 헤어핀 계단형 임피던스 공진기 구조를 구현한 새로운 설계법을 제시하였다. 제안된 협대역 필터의 구현의 예로, 중심주파수 f0=1.4 GHz에서 5 %의 대역폭의 협대역 필터를 구현하였고, 7.5f0까지 광대역 고조파 억제 대역을 구현할 수 있음을 보였다. 이 결과는 기존 마이크로스트립 선로를 사용한 협대역 필터 설계법에 비해 2배 이상 넓은 고조파 억제가 구현 가능함을 입증한 것이며, 삽입손실 또한 0.9 dB로 우수한 특성을 얻었다. This paper proposes a new design method for narrow bandpass filters using two cascaded hairpin step impedance resonators (SIRs) with wideband harmonic suppression. The proposed bandpass filter utilizes a suspended strip line (SSL) to maximize the characteristic impedance ratio, thereby maximizing the harmonic suppression bandwidth. As an example of the proposed design method, the SSL bandpass filter with a center frequency of f0=1.4 GHz and fractional bandwidth of 5 % was implemented, and proved to suppress harmonics up to 7.5f0 with a passband insertion loss of approximately -0.9 dB. This result implies that the proposed SSL narrow bandpass filter (NBPF) can suppress the harmonic bandwidth more than two times as compared with the filter design on a microstrip line (MSL).
ECEI 장치를 위한 향상된 성능의 100 ㎓ 렌즈 안테나 설계
이관희(Gwan-Hee Lee),김성균(Sung-Kyun Kim),모우딘 와합(Wahab Mohyuddin),최현철(Hyun-Chul Choi),김강욱(Kang Wook Kim) 한국전자파학회 2016 한국전자파학회논문지 Vol.27 No.9
본 논문에서는 KSTAR의 ECEI(Electron Cyclotron Emission Imaging) 장치에 사용되는 100 ㎓ 미니렌즈의 성능을 향상하기 위해 변형된 타원형 렌즈 안테나 설계를 제안하고 있다. 기존 타원형 렌즈 구조의 밑면에 반구형 렌즈를 추가하고, 이 반구형 렌즈의 끝점에 100 ㎓ CPS 다이폴 안테나를 위치하게 하였다. 기하광학적 설계를 통해 안테나에서 방사된 전자파가 반구형 렌즈의 표면에서 전반사가 일어나도록 함으로써 안테나 패턴이 주빔 방향으로 집속되는 효과를 나타나게 하였다. 이 설계의 유효성은 3차원 EM 시뮬레이터로서 확인하였다. 제안된 반구형렌즈가 추가된 타원형 렌즈의 안테나 이득은 23.8 ㏈인데, 기존의 타원형 렌즈에 비해 2.2 ㏈ 향상되었으며, 사이드 로브 레벨은 E-plane과 H-plane에서 2.6 ㏈, 3.4 ㏈ 감소하였음을 확인하였다. In this paper, a modified elliptical lens antenna design is proposed to improve the performance of 100 ㎓ mini-lens antennas used in the ECEI(Electron Cyclotron Emission Imaging) module at KSTAR. A hemispherical lens is added on the bottom plate of the conventional elliptic lens antenna, and a 100 ㎓ dipole antenna is located on the end point of the hemispherical lens. Using geometrical optics, antenna radiated EM fields are designed to be totally reflected from the inner surface of the hemispherical lens, and thereby the antenna patterns are more focused toward the main beam. The validity of the proposed design is confirmed by the 3D EM simulator. The modified elliptical lens antenna provides 23.8 ㏈ maximum gain, which is 2.2 ㏈ gain improvement as compared with the conventional elliptic lens. Also, the side love levels of E- and H-planes are decreased by 2.6 ㏈ and 3.4 ㏈, respectively.