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A general design method for tunable microstrip devices at microwave frequency based on liquid crystal technology

Lei, M; Nie, Z; Yang, M; Fernández, FA; Poole, C; Day, SE; (2019) A general design method for tunable microstrip devices at microwave frequency based on liquid crystal technology. Liquid Crystals , 46 (6) pp. 846-856. 10.1080/02678292.2018.1530381. Green open access

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Abstract

This paper proposes a general design method for microstrip devices using liquid crystal (LC) at microwave frequencies. The method employs lumped element modelling to first optimise the filter at the working frequency. Then EM simulation is used for the second optimisation and the full-wave simulation. LC is used as the tunable material since the anisotropy can be changed with low voltages. The approach of modelling LC as a homogeneous anisotropy demonstrated with Computer Simulation Technology (CST) Microwave Studio is an acceptable approximation, which accurately predicts the tuning range. A new tunable inverted microstrip filter using nematic LCs at millimetre-wave frequencies is designed to verify the method. The proposed design utilises interdigital capacitors in parallel with two inductive loops to form a bandpass filter. It is fabricated and measured, and shows that the centre frequency varies from 5.01 to 5.51 GHz (10% tunability) and achieves a 3-dB bandwidth of 450 MHz, which is in good agreement with simulation results. A finite element simulation is used to investigate the behaviour of LC directors in the fully switched state; the effective permittivity is extracted from finite-element simulation and used in CST to achieve an even more accurate agreement with experimental results.

Type: Article
Title: A general design method for tunable microstrip devices at microwave frequency based on liquid crystal technology
Open access status: An open access version is available from UCL Discovery
DOI: 10.1080/02678292.2018.1530381
Publisher version: https://doi.org/10.1080/02678292.2018.1530381
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Liquid crystals, frequency-agile, finite element modelling, inverted microstrip structure, tunable bandpass filter
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
URI: https://discovery.ucl.ac.uk/id/eprint/10065744
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