Design and Fabrication of an Ultra-Wide Stopband Compact Bandpass Filter

In this brief, we present a novel ultra-wide stopband compact microstrip bandpass filter (BPF) with low insertion loss and compact size. The proposed filter is designed based on two five-stage stepped impedance resonators (SIRs) which are capacitively coupled to each other's. The five-stage SIRs can be used to have miniaturized size as well as suppression of harmonics. In this BPF, by increasing stages of SIRs, multiple transmission zeros are generated. Therefore, a compact BPF with a ultra-wide stopband could be achieved. The bandpass region of the proposed filter is extended from 3.58 GHz up to 10.31 GHz with insertion loss lower than 0.42 dB. The rejection level is better than -26 dB from 11.25 GHz up to 30 GHz and better than -17.5 dB up to 100 GHz. The center frequency of the proposed BPF is located at 6.95 GHz with -3 dB fractional bandwidth (FBW) of 97%. The dimension of the fabricated filter is 0.128 λ g ×0.378 λ g . The simulation results are verified by fabrication and measurement up to 30 GHz that there is a good agreement between them.