Complex FIR Digital Filter Sharpening With Three-Path Structures

The Kaiser & Hamming two-path sharpening structure has long been the primary processing arrangement for using a filter's coefficient set to improve its own performance. Here we study the three-path structure version they proposed, and also introduce a new such structure that makes use of prototype pairing. This expansion, in which we make use of conjugate-reversal of the coefficient set, brings about greatly increased sharpening applicability. Our new structure joins two recently-introduced two-path structures in comparison exercises here. Three of these four offer the option of linear-phase sharpened resultants and comprise what we believe to be the most versatile FIR sharpeners available for effective flattening of two-level gain plateaus in multiband filtering scenarios. All four are compared in complex-valued impulse response example settings, and we arrive at clear ranking of their merits.