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Proceedings Paper

Efficient algorithms for optimising the optical performance of profiled smooth walled horns for future CMB and Far-IR missions
Author(s): Darragh McCarthy; Neil Trappe; J. Anthony Murphy; Créidhe O'Sullivan; Marcin Gradziel; Stephen Doherty; Colm Bracken; Niall Tynan; Arturo Polegre; Peter Huggard
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Paper Abstract

Astronomical observations in the far-infrared are critical for investigation of cosmic microwave background (CMB) radiation and the formation and evolution of planets, stars and galaxies. In the case of space telescope receivers, a strong heritage exists for corrugated horn antenna feeds to couple the far-infrared signals to the detectors mounted in a waveguide or cavity structure. Such antenna feeds have been utilized, for example, in the Planck satellite in both single-mode channels for the observation of the CMB and the multi-mode channels optimized for the detection of foreground sources. Looking to the demands of the future space missions, it is clear that the development of new technology solutions for the optimization and simplification of horn antenna structures will be required for large arrays. Horn antennas will continue to offer excellent control of beam and polarization properties for CMB polarisation experiments satisfying stringent requirements on low sidelobe levels, symmetry, and low cross polarization in large arrays. Similarly for far infrared systems, multi-mode horn and waveguide cavity structures are proposed to enhance optical coupling of weak signals for cavity coupled bolometers. In this paper we present a computationally efficient approach for modelling and optimising horn character-istics. We investigate smooth-walled horns that have an equivalent optical performance to that of corrugated horns traditionally used for CMB measurements. We discuss the horn optimisation process and the algorithms available to maximise performance of a merit parameter such as low cross polarisation or high Gaussicity. A single moded horn resulting from this design process has been constructed and experimentally verified in the W band. The results of the measurement campaign are presented in this paper and compared to the simulated results, showing a high level of agreement in co and cross polarisation radiation patterns, with low levels of integrated cross polar power. For future Far IR receivers using waveguide bounded bolometers and absorbers, an optimisation of the waveg-uide structures and absorber location within the integrating cavity is critical to maximise coupling performance particularly for multimoded systems. We outline the benefit of using multi-moded horns in focal plane arrays and illustrate the increased optical sensitivity associated with a many-moded approach, which may be optimized for coupling to particular incident beams.

Paper Details

Date Published: 23 July 2014
PDF: 8 pages
Proc. SPIE 9153, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII, 915316 (23 July 2014); doi: 10.1117/12.2056336
Show Author Affiliations
Darragh McCarthy, National Univ. of Ireland, Maynooth (Ireland)
Neil Trappe, National Univ. of Ireland, Maynooth (Ireland)
J. Anthony Murphy, National Univ. of Ireland, Maynooth (Ireland)
Créidhe O'Sullivan, National Univ. of Ireland, Maynooth (Ireland)
Marcin Gradziel, National Univ. of Ireland, Maynooth (Ireland)
Stephen Doherty, National Univ. of Ireland, Maynooth (Ireland)
Colm Bracken, National Univ. of Ireland, Maynooth (Ireland)
Niall Tynan, National Univ. of Ireland, Maynooth (Ireland)
Arturo Polegre, European Space Agency (Netherlands)
Peter Huggard, Rutherford Appleton Lab. (United Kingdom)

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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