Miniaturized Multilayer and Self-Packaged Triple-Mode Bandpass Filter with High Selectivity and Wide Stopband

A miniaturized, self-packaged triple-mode bandpass filter (BPF) based on multilayer printed circuit board (PCB) technology with high selectivity and wide stopband is proposed. A novel hybrid triple-mode resonator combining strip lines with lumped elements is proposed. The resonator is analyzed using the even- and odd-mode principle, demonstrating its miniaturization and stopband expansion capability. It generates three transmission poles (TPs) and incorporates transmission zeros (TZs) through source-load coupling, which significantly improves selectivity. The fabricated prototype demonstrates a compact size with 60 dB suppression extending up to 2.64f0. With its compact structure, self-packaging, wide stopband, and high selectivity, the proposed BPF is well-poised for modern communication systems demanding high-performance filtering solutions.