Single-cavity triangular substrate integrated waveguide bandpass filter with complementary triangular split ring resonator

A novel single-cavity equilateral triangular substrate integrated waveguide (TSIW) bandpass filter (BPF) with a complementary triangular split ring resonator (CTSRR) is designed in this paper. A metallic via-hole is used to split the degenerate modes and adjust the transmission zeros (TZs) properly. Meanwhile, the CTSRR is utilized as a resonator to work together with the degenerate modes of the TSIW cavity. The resonant frequency of the CTSRR can be adjusted by its own size. Meanwhile, a TZ is observed in the lower band due to the CTSRR. Finally, a 16% 3 dB fractional bandwidth (FBW) triple-mode TSIW BPF with three TZs in both lower and upper bands is simulated, fabricated, and measured. There is a good agreement between the simulated and measured ones.