Dual‐/triple‐wideband microstrip bandpass filter using independent triple‐mode stub‐loaded resonator

Abstract A dual‐wideband and a triple‐wideband microstrip bandpass filters (BPFs) using independent triple‐mode stub‐loaded resonators are presented in this letter. The resonator consists of a half‐wavelength transmission line, which resonates at the first resonant mode, and two identical quarter‐wavelength loaded stubs generating the other two resonant modes. The dimensional adjustments of a particular resonator only affect itself without influencing the other two resonators, which results in good independent property. The measurement results verify that the fabricated dual‐wideband BPF possesses the central frequencies of 2.39 GHz (return loss: 18.2 dB) and 5.13 GHz (return loss: 30.1 dB), and the fractional bandwidth (FBW) of 16.2% (insertion loss: 0.25 dB) and 16.6% (insertion loss: 0.31 dB) were obtained. For the fabricated triple‐wideband BPF, the FBW was 16.7% (insertion loss: 0.24 dB) at 2.50 GHz (return loss: 22.8 dB), 14.4% (insertion loss: 0.33 dB) at 3.68 GHz (return loss: 19.7 dB), and 13.2% (insertion loss: 0.40 dB) at 5.04 GHz (return loss: 21.5 dB).