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 is introduced, offering high selectivity and wide stopband. A novel hybrid triple-mode resonator combining microstrip lines with lumped elements is proposed. The resonator is analyzed using even- and odd-mode analysis, demonstrating its capability to enhance miniaturization and broaden the stopband. It generates three transmission poles (TPs) and incorporates transmission zeros (TZs) through source-load coupling, significantly improving selectivity. The fabricated prototype demonstrates a compact size with 60 dB suppression extending up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2.64 f_{0}$</tex>. With its compact structure, self-packaging, wide stopband, and high selectivity, the proposed BPF is well-suited for modern communication systems demanding highperformance filtering solutions.