An ultra-wideband bandpass filter using constructed capacitors

In this paper, a structure of constructed capacitor is presented to enhance the capacitive feeding strength in Ultra-Wideband (UWB) bandpass filters (BPFs). The constructed capacitor can be described as dual-layer broad-side-coupled lines located on each side of the dielectric layer, one line is on the top side and the other one is on the bottom side in the ground plane connecting input/output (I/O) port via metalized hole. Parameters of the structure are extracted by three-dimensional finite element method and simple circuit analysis method. Design method for the proposed UWB BPF is then derived based on triple-mode resonator theory and equivalent circuit of the constructed capacitors. The experimental results of the designed UWB filter show excellent agreements with the simulation results, showing good performances of the proposed filter.