A Novel Frequency-Dependent Coupling With Flexibly Controllable Slope and Its Applications on Substrate-Integrated Waveguide Filters

This letter reports a novel realization of frequency-dependent coupling (FDC) structure, which can realize both the positive and negative slopes. The FDC is constructed by two coupled stepped-impedance grounded coplanar waveguides with opened ends. The characteristics of the FDC are studied, which indicates that the proposed FDC has advantages of the flexibly controllable slope, zero of position, and weak/strong strength. For the verification of the characteristics of the proposed FDC, an inline-line fourth-order substrate integrated waveguide bandpass filter (BPF) with one large positive slope and a third-order triplet BPF with one small negative slope for additional finite transmission zero with controllable position were designed, fabricated, and measured. Measured results agree well with simulated ones.