Program and Abstract Book - SRON

19 th International Symposium on Space Terahertz Technology
12-3
The fabrication and testing of novel smooth-walled feed horns for focal
plane arrays.
Authors:
P. Kittara (*) email: tepcy@mahidol.ac.th
J. Leech (+) , G .Yassin (+), B.K Tan (+),
A. Jiralucksanawong (*) and S. Wangsuya (*).
Affiliations:
(+) Department of Physics, University of Oxford Keble, Oxon OX1 3RH, UK
(*) Department of Physics, Mahidol University, 272 Rama VI Road, Bangkok,
Thailand
Abstract:
Corrugated horns have traditionally been used to give coupling to
sub-mm detectors with low cross polarisation and sidelobe levels over
a large bandwidth. Since they require the fabrication of many
azimuthal grooves per wavelength into the walls of the horn, they can
be difficult and expensive to manufacture at submillimetre
wavelengths. This is a particularly difficult for large focal plane
arrays, which require tens or hundreds of horns. In previous work, we
presented designs for easy-to-machine, smooth walled horns which have
performance comparable to corrugated horns. These horns have a few
discontinuities in flare-angle along the length of the horn. The
positions and magnitudes of the angular discontinuities are
determined using a combination of modal matching analysis and a
genetic algorithm optimisation.
In this paper we present further investigations into these new types
of feed horns including experimental results. In particular, we will
describe a simple fabrication method which employs direct machining
of horns into a block of aluminium using shaped drill bits. This
method is very promising for the fast, inexpensive fabrication of
large format focal plane arrays. We have now successfully used this
fabrication method to manufacture many prototype horns at 230 GHz. We
demonstrate the effectiveness of the manufacturing method by
presenting beam pattern measurements for prototype horns across the
230 GHz band. The method is particularly efficient at THz frequencies
where corrugated horns are awkward to fabricate. To this end we will
also present a horn design and pattern analysis at 1.3 THz.
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