Miniaturized Quad‐Wideband Bandpass Filter With Multiple Transmission Zeros

ABSTRACT In this paper, a miniaturized quad‐wideband bandpass filter (QWB‐BPF) with low insertion loss (IL), high band‐to‐band isolation (Iso), and multiple transmission zeros (TZs) is proposed. The presented QWB‐BPF is exploited based on a multiple‐mode resonator. The proposed QWB‐BPF is analyzed and interpreted by the parity technique. Notably, 14 resonant modes are excited by presented multiple‐mode resonator (MMR), where the first passband is comprised of the first two modes, and the remaining triple passbands are all sequentially formed by quadruple modes. Besides, 11 TZs are yielded to obtain high band‐to‐band Iso characteristics up to 44 dB, 36 dB, and 37 dB. The QWB‐BPF is compact with an overall size of 0.066 λg × 0.093 λg. To validate the proposed filter, a prototype QWB‐BPF with 3‐dB fraction bandwidths ( fbw s) of 27.8%, 33.4%, 30.6%, and 14.9% is designed, fabricated, and measured.