A narrowband absorptive bandstop filter with extended upper passband based on lossy step-impedance stubs

In this paper, a novel absorptive planar bandstop filter (ABSF) with extended upper passband is proposed. The filter has an ingenious, compact structure and reliable performance. It is mainly composed of two resistors and microstrip transmission lines. The stepped-impedance stubs are introduced to extend the upper passband. A bandstop filter prototype equipped with absorption and extended upper passband is fabricated for verification. Excellent absorption performance and upper passband extension are demonstrated. The input return loss is maintained above 10 dB over the operating frequency range (from 0 to 6 GHz). The measured results demonstrate that the upper passband is successfully extended up to 5.6f0 without deteriorating the absorption performance. This filter is highly suitable for strong interference, while devices are sensitive to reflection.