Lumped-Distributed Low-Pass Filters Based on Bragg Hybridization Effect
DOI:
https://doi.org/10.64915/RADAP.2026.104.74-80Keywords:
Bragg hybridization, low-pass filter (LPF), lumped-distributed structures, coherent synchronism, collective transmission zero, stopband enhancementAbstract
This paper proposes and investigates a novel approach to the design of low-pass filters (LPFs) based on the Bragg hybridization (BH) effect implemented in a lumped-distributed configuration. The scientific novelty lies in retaining the structural periodicity, contrary to traditional synthesis methods that introduce periodicity disruption to minimize ripple. It is demonstrated that restoring the coherence of Bragg synchronism and coupling it with the local resonance of low-Q elements resolves the trade-off between stopband suppression and impedance matching. The results show that the synchronization of local and Bragg resonances ensures a continuous stopband, effectively eliminating spurious ripples within the rejection band. A collective transmission zero is formed at the Bragg frequency due to the coherent interaction of the resonators, shifting the first parasitic response to twice the Bragg frequency. For the developed LPF based on four π-sections, the calculated fractional rejection bandwidth relative to the cut-off frequency is 570% at the −60 dB level and 378% at −100 dB, with a passband ripple of 0.2 dB. The lengths of the considered LPFs are approximately twice as small as those of conventional elliptic filters. Utilizing the low-Q BH mode significantly reduces sensitivity to dissipative losses and manufacturing tolerances compared to high-order elliptic filters. Given the use of normalized parameters, the proposed structures serve as generalized templates for the rapid design of miniature LPFs. The findings have direct practical implications for high-performance signal processing systems.
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