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Compact continuous tunable low‐pass filter with high selectivity and wide stopband
Author(s) -
Zhang Bo,
Yu Cuiping,
Liu Yuanan
Publication year - 2016
Publication title -
microwave and optical technology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 76
eISSN - 1098-2760
pISSN - 0895-2477
DOI - 10.1002/mop.29867
Subject(s) - stopband , varicap , microstrip , microwave , materials science , frequency selectivity , transition band , electrical impedance , filter (signal processing) , low pass filter , optoelectronics , cutoff frequency , distributed element filter , electronic engineering , capacitance , physics , electrical engineering , engineering , prototype filter , telecommunications , resonator , electrode , quantum mechanics
ABSTRACT This letter presented a novel compact continuously tunable low‐pass filter (LPF) using varactor‐loaded coupled rhombic stubs. The proposed LPF demonstrated excellent roll‐off selectivity, wide stopband range as well as good cut‐off frequency tunability. This LPF consisted of three varactor‐tuned coupled rhombic stubs loaded on a section of high‐impedance microstrip line symmetrically and two coupled line LPFs which could further improve the stopband performance. A detailed explanation of the tuning mechanism was illustrated by adopting lumped‐element equivalent circuit model. The measured results showed not only a wide cut‐off frequency tuning range of 56% from 350 to 800 MHz, but also an excellent steepness factor of less than 1.14. Additionally, a rejection level of greater than 20 dB up to 8 GHz (>10f c ) was observed in the stopband. The proposed ideas were verified by the measured results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1641–1644, 2016