Multi‐layered dual‐mode substrate integrated waveguide bandpass filter with input and output ports located on same substrate layer

This study reports a multi‐layered dual‐mode substrate integrated waveguide (SIW) bandpass filter (BPF), in which the input and output ports are located on the same substrate layer (i.e. the upper one). The dual‐mode SIW cavity in the lower substrate layer is coupled to the upper dual‐mode SIW cavity by two crossed slots, which can independently control the inter‐couplings. The proposed filter can be modelled by a dual‐extended doublet coupling scheme with considering bypass couplings between source and load. Based on the proposed structure, single‐ and dual‐band filtering responses with four controllable finite‐transmission zeros (FTZs) are realised and analysed. For the demonstration, a single‐band filter and a dual‐band filter were fabricated and measured. The measured results agree well with simulated ones.