SHARP REJECTION AND WIDE STOPBAND MICROSTRIP LOWPASS FILTERS USING COMPLEMENTARY SPLIT RING RESONATORS
Keywords:Complementary split ring resonators, Microstrip filters, Microwave, Selectivity
Chebyshev microstrip lowpass filters with improved performance, achieved by means of circular complementary split ring resonators (CSRR), are presented. The CSRR particles exhibit a frequency rejection bandwidth in the vicinity of their resonant frequencies that can be used to meliorate both the selectivity and stopband in microstrip lowpass filters. Two configurations have been used: a stepped-impedance model and a configuration using open-circuited stubs. Microstrip filters having 5, 7 and 9 poles were designed and fabricated. Selectivity values up to 86 dB/GHz and suppression levels reaching 60 dB in the stopband were obtained. The filters have cutoff frequencies around 2 GHz and rejection band up to 10 GHz. The insertion of the designed CSRR resonators in the ground plane of the filters removes all the transmission spurious observed in the analyzed frequency band. No considerable variation in the passband group delay is observed in the CSRR-based lowpass filters. It is also made a comparison among the filters designed in this and other referenced works, considering their number of poles and size. The measured results are in good agreement with the simulated ones.
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