Compact differential bandpass filter using onesixth mode and novel onethird mode triangular SIW resonators

In this letter, a novel one-third mode triangular substrate integrated waveguide resonator (OTMTSIWR) is presented firstly. Compared with the conventional OTMTSIWR, this novel resonator has a lower resonant frequency (f₀) and acceptable unloaded quality (Q_u) to suppress the common-mode (CM) signals, while has more flexibilities to design balanced coupled topology structures. The novel OTMTSIWR and one-sixth mode triangular SIW resonator (OSMTSIWR) can be creatively cascaded together to further reduce filter size. To validate the properties of the novel OTMTSIWR and the above idea, a compact differential bandpass filter (BPF) with a size reduction over 87% is proposed. The filter can produce symmetrical frequency response with one transmission zero (TZ) on each side of the differential-mode (DM) passband by using cross-coupling technology. Meanwhile, good CM suppression is implemented in the DM passband. The measured results are in good agreement with the simulated ones.