8 October 2004 Bandwidth characteristics of corrugated waveguide-horn feeds for CMB experiments
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Because of their special properties profiled corrugated waveguide-horn structures are popular as both single-moded and multi-moded bolometer feeds in CMB experiments (e.g. PLANCK, Archeops, QUaD). Although optimised at a spot frequency the horns are usually employed over a relatively wide bandwidth and for single-moded horns the waveguide itself acts as the high pass filter. The horns can be profiled to reduce the horn length and sometimes also a front flared section is added to provide minimum edge taper and spill-over levels (e.g. on PLANCK). In this paper we report on our detailed analysis of the bandwidth properties of such corrugated horns. In the case of multi-moded horns an important issue is how the number of modes varies across the band with the resulting impact on the beam patterns. The so-called "phase centre" location 3 is also an issue. For polarisation selective systems we probe the polarisation purity of the relayed signal across the band and also investigate waveguide details that determine the exact location of band edges. Furthermore any leakage below the expected cut-off will lead to non-idealised cross-polar effects. We have also undertaken a series of laboratory measurements of bandwidth effects in corrugated waveguides to verify the models used.
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Emily Gleeson, William Lanigan, J. Anthony Murphy, Creidhe O'Sullivan, Bruno Maffei, Sarah E. Church, Eoin Cartwright, "Bandwidth characteristics of corrugated waveguide-horn feeds for CMB experiments", Proc. SPIE 5498, Millimeter and Submillimeter Detectors for Astronomy II, (8 October 2004); doi: 10.1117/12.550934; https://doi.org/10.1117/12.550934


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