In this paper CSRRs (complementary split-ring resonators) are used to suppress the first spurious response in microstrip hairpin filters. The CSRRs are merged in the filter structure, and therefore the filter size is not increased. The design methodology is presented, and a filter with center frequency at 3 GHz is designed, fabricated and tested as an example. The characterization of this new filter shows the efficiency of the proposed approach to improve filter response with spurious rejection up to 20dB while the size is even slightly reduced.
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