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Proceedings Paper

Optical modelling of far-infrared astronomical instrumentation exploiting multimode horn antennas
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Paper Abstract

In this paper we describe the optical modelling of astronomical telescopes that exploit bolometric detectors fed by multimoded horn antennas. In cases where the horn shape is profiled rather than being a simple cone, we determine the beam at the horn aperture using an electromagnetic mode-matching technique. Bolometers, usually placed in an integrating cavity, can excite many hybrid modes in a corrugated horn; we usually assume they excite all modes equally. If the waveguide section feeding the horn is oversized these modes can propagate independently, thereby increasing the throughput of the system. We use an SVD analysis on the matrix that describes the scattering between waveguide (TE/TM) modes to recover the independent orthogonal fields (hybrid modes) and then propagate these to the sky independently where they are added in quadrature. Beam patterns at many frequencies across the band are then added with a weighting appropriate to the source spectrum. Here we describe simulations carried out on the highest-frequency (857-GHz) channel of the Planck HFI instrument. We concentrate in particular on the use of multimode feedhorns and consider the effects of possible manufacturing tolerances on the beam on the sky. We also investigate the feasibility of modelling far-out sidelobes across a wide band for electrically large structures and bolometers fed by multi-mode feedhorns. Our optical simulations are carried out using the industry-standard GRASP software package.

Paper Details

Date Published: 23 July 2014
PDF: 9 pages
Proc. SPIE 9153, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII, 91532V (23 July 2014); doi: 10.1117/12.2055853
Show Author Affiliations
Créidhe O'Sullivan, National Univ. of Ireland, Maynooth (Ireland)
J. Anthony Murphy, National Univ. of Ireland, Maynooth (Ireland)
Ian Mc Auley, National Univ. of Ireland, Maynooth (Ireland)
Daniel Wilson, National Univ. of Ireland, Maynooth (Ireland)
Marcin L. Gradziel, National Univ. of Ireland, Maynooth (Ireland)
Neil Trappe, National Univ. of Ireland, Maynooth (Ireland)
Fiachra Cahill, National Univ. of Ireland, Maynooth (Ireland)
T. Peacocke, National Univ. of Ireland, Maynooth (Ireland)
G. Savini, Univ. College London (United Kingdom)
K. Ganga, Lab. AstroParticule et Cosmologie (France)


Published in SPIE Proceedings Vol. 9153:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII
Wayne S. Holland; Jonas Zmuidzinas, Editor(s)

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