| Summary: | <p>Superconductor-Insulator-Superconductor (SIS) mixers are regularly employed as the detectors of choice in sub-millimetre wavelength astronomy receivers due to their unparalleled sensitivity, stable operation and ability to capture both amplitude and phase of incoming signals which is necessary to perform high-resolution spectroscopic observations. With the advent of telescopes such as the Atacama Large Millimetre/sub-millimetre Array (ALMA) which are set to explore the field for the foreseeable future, there is considerable interest in developing the technological capabilities employed by such facilities.</p>
<p>The work presented in this thesis has therefore focused on the development of coherent, heterodyne receiver technology at sub-millimetre wavelengths for potential applications such as the upgrade of current, ground based observatories.</p>
<p>In particular, the harmonic content of Local Oscillator reference sources has been investigated and shown to play an important role in both the noise performance of heterodyne receivers and the spectral content of their output IF band.</p>
<p>Furthermore, successful design, optimisation, fabrication and testing of THz frequency feed horns has led to the demonstration of a novel, smooth walled horn design that presents an attractive alternative to the more complex corrugated feed horn structure for antenna deployment in sub-mm wavelength receivers. A three section horn design operating between 780 − 950 GHz has been shown to exhibit excellent measured far-field beam patterns which closely resemble the predicted performance down to ~ −30 dB and a two section design employed in a four pixel feed horn array has been shown to operate between 1300 − 1500 GHz.</p>
<p>In addition, a novel E-Beam lithography fabrication process has been developed for the production of Schottky barrier diodes to be used in high frequency multiplier and mixer components. This process has demonstrated the ability to create the ohmic pad layer, sub-micron anodes and the suspended air-bridge of the device which are necessary for efficient performance at sub-mm wavelengths. Initial RF testing of the diodes as frequency multipliers has produced excellent results between 225 − 330 GHz.</p>
<p>Finally the development of a prototype, heterodyne receiver, based on double side band SIS mixer with a novel optical design that operates between 800 − 900 GHz has been presented and shown to exhibit very encouraging noise temperature characteristics of ~ 340 K at 880 GHz. This system is due to be tested at even higher frequencies with the aim of pushing its detection capabilities into the supra-Terahertz regime.</p>
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