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A simple method for improving the stopband response for unequal‐length microstrip coupled‐line filters with stubs
Author(s) -
Lee SangHo,
Ha Jungje,
Yoon Hobyung,
Lee Yongshik
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.30080
Subject(s) - stopband , microstrip , band pass filter , spurious relationship , microwave , bandwidth (computing) , center frequency , topology (electrical circuits) , prototype filter , electronic engineering , materials science , physics , low pass filter , engineering , mathematics , telecommunications , electrical engineering , statistics
This work demonstrates a simple method for improving the stopband response of microstrip coupled‐line bandpass filters in an extremely wide bandwidth. Substantial enhancement in the stopband response is achieved by constituting a filter with reduced‐length coupled lines of unequal length, which are loaded with open stubs. The lengths of these stubs are optimized to compensate for the reduction the reduction in the lengths of the coupled lines, and at the same time, to provide transmission zeros for further suppression of spurious responses. A rigorous mathematical analysis demonstrates a systematic method is verified experimentally with the experimental results obtained with third‐order Chebyshevy‐type bandpass filters that maintain the transmission level below −30 dB up to 17.8 f 0 , where f 0 is the center frequency. Even further enhancement can be achieved simply by increasing the filter order. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2477–2481, 2016