A 5.8–10.6 GHz UWB filter using novel SIR structure

The paper presents a set of 3 ultra-wideband bandpass filters for the upper UWB band (5.8 GHz to 10.6 GHz). The filters are development versions of a novel multi-mode stepped-impedance resonator (SIR) planar structure with central via to ground. The new SIR is implemented in microstrip technology. It has a single centrally located via to ground which provides a new mechanism for coupling of the SIR modes. The first filter presented in the paper follows the basic concept of the new SIR whereas the other two filters exploit longitudinal symmetry to bisect the SIR and create half-structures. The second filter uses an in-line cascade of two half-structures while the third filter is a folded cascade of the two half-structures. These examples show basic properties with pros and cons of the new SIR. The cascade of the two half-structures is used to easily increase resultant filter order and performance of frequency characteristics. Folding the cascade can be used to build a new filter structure with some potentially interesting properties. One of the benefits of the presented SIR filters is a direct contact port coupling and no need for more problematic very narrow gaps to couple the structure with the input and output lines. This in turn allows for making the new filters on thin substrates. Another benefit is an extended stop band comparing to the classic SIR.