A Compact Dual-Band Quasi-Elliptic Filter Based on Hybrid SIW and Microstrip Technologies

In this brief, by combining substrate integrated waveguide (SIW) and microstrip technologies, a novel dual-band filter is proposed to achieve a quasi-elliptic response for both passbands. The dual-mode characteristics of the SIW cavities, namely TE
₁₀₁
and TE
₂₀₁
modes, are used to create two passbands. Different with the conventional inductive windows, two pairs of uniform impedance resonators (UIRs) with electric mutual coupling, which are etched between the two rectangular SIW cavities, are used to couple the TE
₁₀₁
and TE
₂₀₁
modes, respectively. Good merits are achieved in this way, including: 1) Independent coupling paths are created for TE
₁₀₁
and TE
₂₀₁
modes, which would reduce the complexity of numerical optimization; 2) Since the electric couplings are generated between each pair of the UIRs, it would be easy to realize a cross coupling by only constructing inductive windows between the SIW cavities. A filter prototype with central frequencies operated at 8 GHz and 10 GHz is then designed and fabricated for validation, which shows a compact size and high selectivity with controllable transmission zeros.