Spurious pass band suppression in microwave filters by means of sub-wavelength resonant structures

This work is devoted to the design of spurious free planar microwave filters based on the rejection hand properties of a kind of resonators that are electrically very small, namely, split ring resonators (SRRs), complementary split ring resonators (CSRRs) and spiral resonators (SRs). If properly coupled to the host transmission line medium (CPW, microstrip,...), these particles are able to produce the rejection levels required in most practical applications (i.e. > ZOdBs). In comparison to other approaches, the use of sub-wavelength resonators neither complicates the design procedure, nor increases final device area. The proposed design examples, corresponding to different technologies and fiter responses, are illustrative of the potentiality of the technique to improve the performance of planar microwave fiters.