An Adaptive Synthesis and Design Approach of Extracted-Pole Filters

This paper proposes an adaptive synthesis and design approach of narrowband bandpass filters with extracted-poles (EP). After performing only one electromagnetic simulation on the physical structure of the EP section, the corresponding equivalent circuit parameters can be extracted. The remaining filter circuit can be adjusted to adapt to the realized EP section. Then accurate mapping relationship between the physical dimensions and the synthesized prototype circuit can be established. In this paper, a five-pole rectangular waveguide filter with one finite transmission zero is designed as an example. In the novel filter synthesis procedure, a generalized equivalent circuit is proposed to process the connection between the EP structure and the adjacent resonator. Finally, the EP section, coupled resonators, and the connecting waveguide can be assembled to get the whole filter. The frequency response of the entire filter is close to the ideal one, verifying that the proposed synthesis and design approach can give high-quality initial dimensions for filter fine-tuning or optimization.