A compact dual-band bandpass filter with deep suppression level using transversal signal interaction concepts

This paper proposes a compact dual-band bandpass filter (BPF) based on concepts of transversal signal interaction (TSI). The filter structure is formed by parallel coupled lines loaded with short stubs to create a T-shaped anti-coupling structure (TACS) and microstrip lines loaded with open stubs to form a multimode resonator (MMR). This configuration results in two wide passbands containing eight transmission poles (TPs). The open stubs introduce four transmission zeros (TZs) at 2.4 GHz, 2.65 GHz, 7.1 GHz, and 7.87 GHz. By leveraging TSI, the filter achieves deep rejection levels of 62 dB and 44 dB at the two stop bands, significantly improving out-of-band suppression. The filter operates at center frequencies of 0.93 GHz ( f 1 ) and 5.25 GHz ( f 2 ), with 3-dB fractional bandwidths of 132 % and 55.2 %, respectively. The minimum insertion losses in the passbands are 0.11 dB and 0.28 dB. The filter size is 0.06 λg × 0.14 λg, where λg is the guided wavelength at 0.93 GHz. Good agreement is observed between simulated and measured performances.