Microstrip bandpass filters with wide bandwidth and compact dimensions

In this paper, novel microstrip band-pass filters with small dimensions and wide bandwidth are proposed. The devices are based on a new type of lumped resonators recently reported by the authors: double-slit complementary split-ring resonators (DS-CSRRs). Properly combined with grounded stubs, and coupled by means of variable-width transmission-line sections, these resonators provide the necessary bandwidths for the design of wideband band-pass filters in microstrip technology. To illustrate the potentiality of the proposed approach, a 5th-order prototype device with central frequency fo = 3.8 GHz and 30% fractional bandwidth has been designed and fabricated. The measured frequency response reveals that in-band losses are below 1 dB, while the return losses are larger than 15 dB. High-frequency selectivity has been also obtained, with very sharp cutoff in the upper band edge and 40-dB rejection at 2.3 GHz. These wide bands are not easily obtainable with conventional filter implementations. This fact and the small dimensions, derived from the use of DS-CSRRs, make the proposed approach very attractive for those applications requiring wide bandwidths for data transmission. © 2005 Wiley Periodicals, Inc.