Design of compact and high selectivity TRI‐band wideband microstrip BPF

In this article, a novel tri‐band wideband microstrip bandpass filter (BPF) with compact size and high selectivity is proposed using three sets of resonators, that is, λ/4 resonators, short‐stub loaded resonator, and λ/2 resonators.Each of the resonators can not only separately generate one passband, but also mainly control the passband performance. Due to the extended feed lines, parasitic coupling and intrinsic characteristics of the resonators, multiple transmission zeros can be created to improve the selectivity. A tri‐band wideband microstrip BPF centered at 2.0, 3.6, and 5.5 GHz is designed, and the predicted results are confirmed experimentally. The size is only 0.156 × 0.303 λg in which λg is the guided wavelength at 2.0 GHz.