Compact Triple-Wideband Bandpass Filter Based on Multi-Mode Stepped-Impedance Stub-Loaded Resonator

A new compact triple-wideband bandpass filter (BPF) using stepped-impedance stub-loaded resonator (SISIR) is investigated. The tri-band BPF is constructed by the combination of a SISIR, inter-digital coupled-lines, and open-ended stepped-impedance stubs. A triple-wideband BPF is achieved by creating extra transmission zeros to split the single ultra-wide passband into three. For the demonstration, a triple-wideband BPF centering at 4 GHz, 7.6 GHz, and 10.6 GHz with fractional bandwidths of 60%, 28%, and 20%, respectively, has been designed and implemented using microstrip technology. The size of the tri-band BPF is only about 0.57 lambda(g) by 0.52 lambda(g). Good agreement is achieved between simulation and measurement.