Optimisation‐based design of transversal signal‐interference microwave bandpass and lowpass filters with extended stopband

• Main Authors: Roberto Gómez‐García, Li Yang, José‐María Muñoz‐Ferreras
• Format: Article
• Language: English
• Published: Wiley 2021-05-01
• Series: IET Microwaves, Antennas & Propagation
• Online Access: https://doi.org/10.1049/mia2.12091

Abstract Generalised bi‐path stepped‐impedance‐line signal‐interference bandpass and lowpass transversal filtering sections (TFSs) with increased stopband bandwidth above the main transmission band are presented. They are realised by partitioning the two in‐parallel transmission‐line paths in their related classic spectrally periodic TFS approach into a plurality of line sub‐segments, whose characteristic‐impedance and electrical‐length values are derived through optimisation. It is demonstrated that the stopband range above the transmission band in these generalised non‐frequency‐periodic TFSs can be remarkably broadened with regard to those intrinsic to their conventional bandpass and lowpass TFS counterparts. Furthermore, as added benefits, this is achieved for shorter transmission‐line paths and a sharper cut‐off slope between the transmission band and the extended stopband. For experimental‐validation purposes, three proof‐of‐concept microstrip prototypes are manufactured and characterised. They correspond to a 1‐GHz bandpass TFS, a 1‐GHz two‐TFS‐in‐series‐cascade‐based bandpass filter (BPF) with augmented selectivity and out‐of‐band power‐rejection levels, and one lowpass TFS with a designed 3‐dB cut‐off frequency of 1.25 GHz.