A tunable bandpass filter using substrate integrated waveguide resonator

This article presents a compact-size tunable wideband bandpass filter (BPF) design that can operate in the S/C Band. A hybrid approach combining lumped capacitors and the substrate-integrated waveguide (SIW) technique is chosen. The goal is to decrease the size of BPF while improving its ability to shield it from the outside. Then, an electrically tunable version of the filter is enhanced using varactor diodes. This modification results in a minimal enlargement of the filter and negligible power consumption. Circuit representations of the BPFs and their correlation with simulations are also investigated to aid and expedite the design process. Finally, ground capacitors are converted into a distributed form for finely tuned capacitance values. The ideal parallel plate dimensions for the widest band are determined using optimization. Measurements of the manufactured BPFs exhibit a high correlation with the simulations. The developed compact-size tunable filter can be conveniently incorporated into modern wireless RF front-ends for multistandard applications that demand good selectivity, wide stopband, and tunability, enabling efficient spectrum management for 5G applications. The proposed filter also provides independent adjustment of the upper and lower cutoff frequencies with two control voltages, allowing precise operating range customization for asymmetric bandwidth adjustment or dynamic band allocation.