A multi-stage pass-band filter with ultra-compact spiral-based elements

Recently an innovative pass-band filter based on a disk with a pair of spiral slot etched has been presented in literature. Such a filter has an out-of-band steep descent of the transmission coefficient but a relatively poor insertion loss for frequencies far from the pass-band. In this contribution a multi-stage set up of these filters is proposed to ameliorate the rejected bands insertion loss. The proposed filter is still extremely compact if compared to filters with similar behavior.