Anglo-Irish Technology Development - Development of millimetre optics components for ALMA

Development of millimetre optics components for ALMA

The University of Manchester Advanced Radio Instrumentation Group (AIG) has won funding from ESO for the design, development and production of extremely sensitive, broadband Low Noise Amplifiers (LNAs) in order to upgrade the capabilities of the ALMA telescope. The expertise and track record established by this work will put the ARIG in a very strong position to bid for further work towards future developments in which the field-of-view of the telescope is dramatically enhanced through deploying Focal Plane Arrays (FPAs) or Phased Array Feeds (PAFs). However, the sensitivity promised by the state-of-the-art LNAs can only be realised if they are well coupled to the sky. Critical to achieving this is the design of the passive optical elements, primarily the feed-horn and ortho-mode transducer (OMT). The design of these components is challenging due to the large fractional bandwidth of operation desired. However, when designing FPAs, additional considerations due to optical effects in the focal plane away from boresight become important. These include: image fidelity issues; reduction in antenna efficiency; additional coupling to ground spill. In addition issues such as cross coupling between elements, physical packing of the optical elements and polarisation leakage must be considered. The purpose of this proposal is to initiate a collaboration between University of Manchester and Maynooth University to explore these issues through full EM simulations with the aim of optimising the design and preparing for a more substantive future application for joint funding.

The Maynooth University group (4 academic staff) has internationally-recognised expertise in millimetre-wave optics, electromagnetics, instrument qualification and astronomical observation. They have been core team members of a number of important astronomical projects such as HFI (High Frequency Instrument) on the ESA Planck Surveyor, HIFI on the Herschel Space Observatory, the QUAD CMB polarisation experiment and ALMA interferometer bands 3 and 5 as well as several ESA TRP contracts. In addition to experience with commercial software (e.g GRASP, CST), they have written their own code for both the electromagnetic modelling of horn antennas and THz physical optics analysis incorporating features not available commercially.

After the 2019 meeting aimed at establishing common Anglo-Irish technology development, the Manchester and Maynooth teams collaborated on full EM simulations of PAF performance. The proposed project will build upon this experience and will as a secondary parallel objective continue the PAF work since long term this is indeed a technology that can be rolled out onto ESO telescopes.