An ultra‐wideband bandstop filter with circularly etched stub resonator

Abstract

In this letter, an ultra‐wide band bandstop filter (BSF) with three transmission zeros and one reflection zero is presented. The role of the circular etched shaped stub as a notch pass response is investigated. Further, a compact size of 13 mm × 24.30 mm (0.219λg× 0.410λg) is achieved by employing an interdigital capacitor to increase coupling between the lines. Furthermore, the transmission line model of the filter is proposed, and consequently even and odd mode impedance is calculated analytically. The proposed filter offers an ultra‐wide bandwidth of 6.1 GHz (3.7 GHz‐9.8 GHz) with a rejection depth of 20 dB over the entire rejection band. Moreover, the upper skirt factor of 47.2 dB per GHz is achieved. A prototype of the proposed BSF is fabricated and measured. Simulated and measured results are in good agreement which validates the proposed design.