A millimetre wave, quasi-optical complex impedance bridge

[摘要] This thesis describes the work undertaken in the design andconstruction of a millimetre wave, quasi-optical impedance bridge. Theinstrument operates as a nulling complex reflectometer, with nullingbeing implemented at the signal frequency by interferometric opticaltechniques. In principle, the quasi-optical components of thereflectometer are operable in the frequency range 80 GHz to 500 GHz,though the range of continuous coverage is determined by the waveguidecomponents and antennas used to couple sources and detectors into theGaussian beams.Gaussian beam mode theory has been employed in the design andmeasurement of the quasi-optical components, which behaved asexpected. Phase and polarisation effects within the impedance bridgewere modelled and the consequent behaviour of the impedance bridgepredicted. A comparison of these predictions with early results led torefinement of the model. This model is based upon a more completedescription of the transmissivities and reflectivities of the wire gridpolarising beam splitters and accurately predicts the instrumentbehaviour.A data acquisition and control system has been built to facilitateautomated operation of the impedance bridge. This system is interfacedto an Acorn® Archimedes microcomputer and the hardware andsoftware has been developed to enable interrupt driven data acquisition.The reflectivity of a quasi-optical load has been measured at 85 GHzwith an accuracy and standard deviation of better than 0.1 % Inamplitude and a standard deviation of better than 0.10° in phase.The quasi-optical half cube and computer interface componentsdeveloped in this work form the basis of a stock of general purposemodules now in everyday use at St. Andrews.

[发布机构] University:University of St Andrews;Department:Physics & Astronomy (School of)