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Synthesis and design of tunable bandpass filters with constant absolute bandwidth using varactor‐loaded microstrip resonator
Author(s) -
Huang Xiaoguo,
Feng Quanyuan,
Zhu Lei,
Xiang Qianyin,
Jia Dinghong
Publication year - 2014
Publication title -
international journal of rf and microwave computer‐aided engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.335
H-Index - 39
eISSN - 1099-047X
pISSN - 1096-4290
DOI - 10.1002/mmce.20812
Subject(s) - insertion loss , chebyshev filter , band pass filter , varicap , resonator , bandwidth (computing) , microstrip , return loss , prototype filter , materials science , optoelectronics , distributed element filter , electronic engineering , low pass filter , physics , electrical engineering , capacitance , computer science , engineering , telecommunications , electrode , quantum mechanics , antenna (radio)
This article presents two new types of tunable filters with constant absolute bandwidth using varactor‐loaded microstrip resonators. First, the second‐ and third‐order Butterworth tunable filters are designed based on the parallel coupled‐line J inverters. Second, a fourth‐order Chebyshev tunable filter is designed based on the alternative J / K inverters, in this design, two adjacent resonators are coupled with each other through a short‐circuited transmission line as the K inverter. The proposed two topologies can be easily extended to high‐order tunable filter. Three tunable bandpass filters with J and alternative J / K inverters, respectively, are built with a tuning range from ∼1.8 to ∼2.3 GHz. The measured second‐order filter has a 3‐dB bandwidth of 160 ± 6 MHz and an insertion loss of 2.4–3.8 dB. The third‐order filter shows a 3‐dB bandwidth of 197 ± 5 MHz and an insertion loss of 3.8–4.8 dB. The fourth‐order filter shows a 3‐dB bandwidth of 440 ± 5 MHz and an insertion loss of 2.1–2.6 dB. For all the designed filters, the measured results are found in excellent agreement with the predicted and simulated results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:681–689, 2014.