Compact balanced bandpass filters based on multilayer dual-mode substrate integrated waveguide cavities

Abstract

To design size-reduced balanced bandpass filters (BPFs) with high selectivity, two new multilayer dual-mode substrate integrated waveguide (SIW) balanced BPFs are proposed. Firstly, the characteristic of dual-mode SIW cavity is analyzed in detail. Then, a balanced SIW BPF with balanced input/output (IO) ports locating on the upper dual-mode SIW cavity is proposed, and the lower dual-mode SIW cavity is coupled to the upper one using two crossed slots. Three transmission zeros (TZs) can be produced at any locations. A balanced SIW BPF with balanced IO ports locating on the upper and lower dual-mode cavities respectively is also proposed, and the two cavities are coupled by a slot. Two symmetrical TZs can be produced. Based on the proposed structures, two filters with center frequency of 10 GHz are designed, fabricated and measured. The measured results agree well with the simulated ones, which indicates the feasibility of the proposed multilayer dual-mode SIW balanced BPFs with compact size and high selectivity.