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Abstract:

Anomalous Microwave Emission (AME) is a component of diffuse Galactic radiation observed at frequencies in the range ≈10–60 GHz. AME was first detected in 1996 and recognised as an additional component of emission in 1997. Since then, AME has been observed by a range of experiments and in a variety of environments. AME is spatially correlated with far-IR thermal dust emission but cannot be explained by synchrotron or free–free emission mechanisms, and is far in excess of the emission contributed by thermal dust emission with the powerlaw opacity consistent with the observed emission at sub-mm wavelengths. Polarization observations have shown that AME is very weakly polarized ( ≲ 1 %). The most natural explanation for AME is rotational emission from ultra-small dust grains (“spinning dust”), first postulated in 1957. Magnetic dipole radiation from thermal fluctuations in the magnetization of magnetic grain materials may also be contributing to the AME, particularly at higher frequencies ( ≳ 50 GHz). AME is also an important foreground for Cosmic Microwave Background analyses. This paper presents a review and the current state-of-play in AME research, which was discussed in an AME workshop held at ESTEC, The Netherlands, June 2016.

Abstract:

We present the design and the measured performance of a compact quad-ridge orthomode transducer (OMT) operating in C-band with more than 100% fractional bandwidth. The OMT comprises two sets of identical orthogonal ridges mounted in a circular waveguide. The profile of these ridges was optimised to reduce significantly the transition length, while retaining the wide operational bandwidth of the quad-ridge OMT. In this letter, we show that the optimised compact OMT has better than -15dB return loss with the cross-polarisation well below -40dB in the designated 4.0-8.5GHz band.