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This letter presents a high-selectivity compact microstrip bandpass filter (BPF) with a flexibly controllable bandwidth, based on multi-path source-load couplings and a square-type split-ring resonator (STSRR). An STSRR, which is enclosed between the capacitively coupled source and load transmission feed lines, forms the structure of the proposed BPF. The main advantages of the proposed BPF lie in its simple structure and high selectivity due to multiple transmission zeros generated by multipath source-load couplings based on STSRR-enabled magnetic coupling between the feed lines with dual capacitive couplings. In addition, the bandwidth of the proposed BPF can be flexibly controlled by varying the magnetic coupling gap between the STSRR and the feed lines. The measured pass-band insertion and return loss of 0.83 and 27.23 dB, respectively, for a prototype BPF with a central frequency of 3.83 GHz and corresponding bandwidth of 12.98%, demonstrates the validity of the proposed method.

This paper presents a high-selectivity compact microstrip bandpass filter (BPF) with a flexibly controllable bandwidth, based on multi-path source-load couplings and a square-type split-ring resonator (STSRR). An STSRR, which is enclosed between the capacitively coupled source and load transmission feed lines, forms the structure of the proposed BPF. The main advantages of the proposed BPF lie in its simple structure and high selectivity due to multiple transmission zeros generated by multipath source-load couplings based on STSRR-enabled magnetic coupling between the feed lines with dual capacitive couplings. In addition, the bandwidth of the proposed BPF can be flexibly controlled by varying the magnetic coupling gap between the STSRR and the feed lines. The measured pass-band insertion and return loss of 0.83 and 27.23 dB, respectively, for a prototype BPF with a central frequency of 3.83 GHz and corresponding bandwidth of 12.98%, demonstrate the validity of the proposed method. [ABSTRACT FROM AUTHOR]