New approach to multi-stage directional filter based on band-reject filter design

A new structure for realizing multi-stage directional filter is proposed in this paper. Instead of relying on one-stage directional filter as the building block, this approach relies on stand-alone band-reject filters. In this paper we investigate the viability of this idea by developing a three-stage directional filter prototype with elliptic response and 5.5% bandwidth. It is demonstrated that the final directional filter response is very close to the constituting band-reject filter, hence allows us to synthesize the directional filter with various kinds of responses in a more precise way based on the rich legacy from the filter community.