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A microstrip bandpass filter with 2 independently tunable transmission zeros
Author(s) -
Cheng Fei,
Li XuanTan,
Lu Ping,
Huang Kama
Publication year - 2020
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.32275
Subject(s) - band pass filter , center frequency , insertion loss , bandwidth (computing) , prototype filter , varicap , resonator , materials science , microstrip , electronic engineering , distributed element filter , optoelectronics , physics , low pass filter , computer science , telecommunications , engineering , capacitance , electrode , quantum mechanics
This letter presents a new design method for a tunable bandpass filter with independently and widely tunable transmission zeros (TZs). Varactor‐loaded microstrip resonators are introduced to a fixed bandpass filter to realize the continuously tunable TZs. Although the tunable resonators have unloaded Q lower than 100, the insertion loss of the filter is not increased. The coupling matrix with the lossy resonators is synthesized and used to analyze the characteristic of the TZ‐tunable filter. A bandpass filter centered at 2 GHz with a 3‐dB bandwidth of 230 MHz is designed to validate the design concept. The measured results show good agreement with the simulated results. The fabricated filter has 2 TZs ranging from 1.4 to 1.8 GHz and from 2.28 to 3.08 GHz, respectively. The TZ‐tunable filter exhibits insertion losses ranging from 1.62 dB to 1.93 dB at the center frequency. The center frequency and bandwidth keep nearly unchanged when the TZs are tuned.