Negative-order ridge substrate integrated waveguide coupled-resonator filter

A negative-order resonator (NOR) based on a ridge substrate integrated waveguide (RSIW) structure and its application to a coupled-resonator filter (CRF) is investigated. The NOR is realised by etching an interdigital slot on the ridge surface of the original RSIW to achieve the composite right/left-handed (CRLH) characteristics, which makes the resonator exhibit the unique property of negative-order resonances. The -1st-order resonance can be generated with a much lower resonant frequency than that of the original RSIW resonator with the same size. Thus, miniaturisation can be achieved by using this NOR structure. Besides, the non-radiative property of the CRLH RSIW structure would help in avoiding radiation loss and electromagnetic interference to the other circuits, which is a better choice in guided-wave applications than other open radiative CRLH structures. Electric coupling is adopted between the neighbouring resonators in the filter design. This CRF shows the advantages of a low-profile, compact size, non-radiation as well as easy integration with other planar circuits.