Dual-Band Recursive Active Filters With Composite Right/Left-Handed Transmission Lines

Unique properties exhibited by metamaterial transmission lines have been previously used to design a large number of dual-band microwave passive devices, but not active ones. In this paper, a novel dual-band active filter scheme based on composite right/left-handed transmission lines is proposed. The inclusion of these types of lines as feedback sections in a first-order recursive topology can be used to generate a filtering response with two arbitrary passbands. Additionally, dual-band couplers are also required. These may be implemented by means of stub-loaded branch-line structures. As an added advantage, these elements produce a strong rejection level at the central stopband that improves the overall response. Theoretical analysis and design procedures are verified by means of manufacturing and measurement of a prototype containing a distributed amplifier.