The design of highly selective adaptive three-dimensional recursive cone filters

A simple method for the design of highly selective adaptive 3-D recursive cone filters is described. The cone-shaped passband is realized by cascading (multiplying) two 3-D transfer functions having wedge-shaped passbands of different orientations. Each 3-D wedge-shaped function is realized by employing a highly selective 2-D fan filter. The passband of each fan filter can be rotated to permit the design of adaptive 3-D cone filters by a simple rotation of one frequency variable. This method also leads to cone passbands that are more selective than those previously reported in the literature.