Spurious harmonic suppression in compact coupled-line bandpass filter with asymmetric perturbations

• Published in: International journal of electronics Vol. 107; no. 4; pp. 576 - 595
• Main Authors: Das, Tarun Kumar, Chatterjee, Sayan
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 02.04.2020; Taylor & Francis LLC
• Subjects: Asymmetry; Bandpass filter; Bandpass filters; Circuit design; compactness; Coupled modes; Equivalent circuits; harmonic suppression; parallel-coupled lines; perturbations; Unit cell
• ISSN: 0020-7217; 1362-3060
• DOI: 10.1080/00207217.2019.1672801

Present article exhibits the design of a third-order compact parallel-coupled line bandpass filter at 5.25 GHz having asymmetric perturbations to suppress the second harmonic. Initially, the effects of compactness on filter characteristics have been studied by synthesising the distributed filter network into its equivalent circuit model. The design has been initiated by computing the unit cell model, which leads to the first-order and third-order design instances with an improvement in compactness over the traditional parallel-coupled line filter. In contrary, compactness in the filter characteristics degrades the second harmonic level subject to enhanced imbalances among the odd- and even-mode velocities at the coupled lines. Subsequently, the improvement in the harmonic suppression of 53 dB and 58 dB has been achieved by incorporating different non-uniform perturbations to the outer and coupled edges of the compact filters. Accordingly, compactness of 58% and 71% have been obtained subject to the folded and in-line designs over the conventional layout.