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Title: An investigation of transmission line switching and frequency shifting in dipole antennas using optically activated silicon switches
Author: Panagamuwa, Chinthana Jayampathi
ISNI:       0000 0001 2412 1315
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2004
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With the rapid expansion of wireless communication services such as Bluetooth and Wireless Local Area Network (WLAN) , the ability of the antenna in a communications device to cover multiple bands is growing in importance. Using many antennas to cover an ever increasing number of bands is becoming impractical '- with restrictions imposed by available space and cross-interfere~ce. It is in this environment that frequency reconfigurable antennas are becoming a more attractiveú option. Much work has already been presented on tuneable antennas using varactor diodes, PIN diodes and more recently MicroElectroMechanical Systems (MEMS) devices, but each of these solutions require metal biasing lines that may interfere with the radiation patterns and can suffer from low power handling capabilities. In this study, a novel approach is presented where near infra-red light delivered through glass fibre optic cables is used to activate simple photoconductive switches embedded in a planar dipole antenna. Engaging the switches, the length of the dipole is changed, forcing the antenna to resonate at a different frequency. The use of glass fibres reduces interference to minor dielectric loading and gives perfect electrical isolation from the switch. The investigation begins by examining the relationship between the free carner density, the complex permittivity and the electrical conductivity of n-type doped silicon. A switched transmission line is then modelled with a silicon switch whose properties are dictated by the derived equations. This allows the various optical powers used in switching to be tabulated against effective conductivity values An equivalent circuit of the switched transmission line is produced to help explain the observed changesú with increasing optical intensity. The switch design is finally transported to a printed dipole antenna where simulations are performed with previously tabulated conductivity values. Good agreement is observed with measured results, giving a resonance frequency shift of nearly 30% and beam scanning capability.
Supervisor: Not available Sponsor: Not available
Qualification Name: Not available Qualification Level: Doctoral
EThOS ID:  DOI: Not available