Substrate Integrated Waveguide Balun Bandpass Filter with Controllable Transmission Zeros for C Band Application

This paper presents a novel balun bandpass filter (BPF) based on dual-mode substrate integrated waveguide (SIW) structure. The proposed structure is composed of a single layer SIW cavity in which slits on both sides of feeding lines and a metallic via perturbation are placed. Degenerate modes in the cavity can be excited by the proper positions of the perturbation via. Transmission zeros (TZs) can be controlled from both sides of the passband by virtue of lengths of the slits. The designed balun BPF not only reduce the number of resonators and the circuit size, but also provides flexible frequency response. The dual-mode SIW balun BPF has been fabricated and measured in a good agreement with the simulated results. The measured phase and amplitude differences have been observed as 3 degrees and 0.28 dB at the center frequency of 5.35 GHz and better than 8 degrees and 0.35 dB within the fractional bandwidth (FBW) of 2.45 %, respectively.