New approach to design a compact triband bandpass filter using a multilayer structure

In this paper, a triband bandpass filter is presented using a dual-layer structure. Three H-shaped resonators are utilized in the proposed structure. The first and third resonators are placed at the top and bottom layers, respectively. The second resonator is divided into two parts: one half is on the top and the other half is at the bottom. The effective permittivity at the first and second layers is different, resulting in different resonant frequencies. The fabricated triband bandpass filter operates at 5.44/6.98/8.36 GHz, with fractional bandwidths of 6.6%/6%/2.9% and measured minimal insertion losses of 1.9/1.7/2 dB.