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In this work, highly selective filters based on periodic arrays of electrically small resonators are pointed out. The highpass filters are implemented in microstrip technology by etching complementary split ring resonators (CSRRs), in the ground plane, and series capacitive gaps, or interdigital capacitors, in the signal strip. The structure exhibits a composite right/left handed (CRLH) behavior and, by properly tuning the geometry of the elements, a high pass response with a sharp transition band is obtained.