IET Microwaves, Antennas and Propagation

Volume 5, Issue 1, January 2011, Pages 1-9  

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ISSN: 17518725

DOI: 10.1049/iet-map.2010.0019

Miniaturisation and electronic tuning techniques for microstrip spurline filters

 Chongcheawchamnan, M.a , Shafique, M.F.b , Robertson, I.D.b  

a Prince of Songkla University, Department of Computer Engineering, Faculty of Engineering, Thailand

b University of Leeds, Institute of Microwaves and Photonics, Leeds LS2 9JT, United Kingdom

Abstract

A new technique for the miniaturisation and electronic tuning of microstrip spurline filters is presented. The technique is based on connecting a reactive component across the end of the coupling gap of the spurline. The circuit is analysed by using a general coupled-line model, leading to the conclusion that, if a capacitance is used, the filter can be miniaturised or electronically tuned. The analysis leads to a set of simple design equations for these applications and a range of simulations are used to investigate the technique further. The validity of the techniques is demonstrated with three different practical circuits. For a miniaturised spurline filter operating at 1.8 GHz, 50% length reduction is achieved. Two varactor-tuned designs are described: a single-section and a cascaded spurline filter. The single-section spurline can be tuned across almost one octave bandwidth, from 580 MHz to 1.06 GHz whereas the cascaded design achieves tuning range of 320-723 MHz. © 2011 © The Institution of Engineering and Technology.

Language of original document

English

Index Keywords

1.8 GHz; Coupled-line models; Design equation; Electronic tuning; Length reduction; Microstripes; Miniaturisation; Octave bandwidths; Reactive components; Spur-lines; Spurline filters; Tuning ranges

Engineering controlled terms: Coupled circuits; Design; Notch filters

Engineering main heading: Tuning