High performance WR-1.5 corrugated horn based on stacked rings
  We present the development and characterisation of a high frequency (500-750 GHz) corrugated horn based on stacked rings. A previous horn design, based on a Winston profile, has been adapted for the purpose of this manufacturing process without noticeable RF degradation. A subset of experimental results obtained using a vector network analyser are presented and compared to the predicted performance. These first results demonstrate that this technology is suitable for most commercial applications and also astronomical receivers in need of horn arrays at high frequencies. 
Bruno Maffei, Arndt von Bieren, Emile de Rijk, Jean-Philippe Ansermet,   Giampaolo Pisano, Stephen Legg and Alessandro Macor
astro-ph.IM