Improved Section Extraction Technique for Fully-Canonical Filters

The applicability of section extraction synthesis techniques for high-order microwave filters is traditionally hampered by numerical roundoff errors which cumulate at each step and quickly prevent correct extractions. A revisited version of cascade synthesis is instead proposed in this work which, instead of operating iteratively on the polynomial coefficients, requires only their evaluation at the transmission zeros. This technique allows a compact representation suited for extracting phase-shifter-extracted-pole blocks sequentially for fully-canonical filters. Good results are obtained up to order 18.