Triple-passband bandpass filter with wide stopband based on microstrip-to-defected stepped impedance resonator (SIR) structure

In this paper, we proposed the new triple-passband bandpass filter (BPF) with wide stopband based on the microstrip-to-defected stepped impedance resonator (SIR) structure. The proposed filter is composed of the coupled stub-loaded stepped impedance resonators (SL-SIR) on the top layer and the defected SIR structures etched off on the ground plane. By using the proposed structure, the center frequencies of the filter are designed to 1.575 / 1.8 / 2.45 GHz and the wide stopband range can be obtained around -30 dB from 3 to 11 GHz. The improved passbands selectivity is obtained since the transmission zeros are located at each passband edges. The simulated and measured results have a good agreement with the proposed design concept.