Generalised parallel-coupled line and interdigital filters with unusually broad upper stop bandwidth: synthesis and design in homogeneous media

The synthesis and design of generalised parallel-coupled line and interdigital filters suitable for realisation in a homogeneous media are proposed in this study. The filters comprise novel coupled line sections whose synthesis is discussed in detail leading to the derivation of formulae to evaluate their modal-impedances. It will be shown that the proposed filters comprise asymmetrically coupled stepped-impedance resonators and are capable of realising broad upper stopbands. Filter examples are synthesised and subsequently realised in suspended-substrate stripline technology were simulated utilising High Frequency System Simulator (HFSS) show close correspondence to theoretical predictions.