Radiation patterns of multi-moded corrugated horns for far-IR space applications

Multi-moded horn antennas are now being proposed for far-IR space imaging s ystems in which diffraction limited resolution is not required (e.g. the Hi gh-Frequency Instrument (HFI) on the ESA PLANCK Surveyor). In such systems individual modes in the waveguide filter section feeding the horn can coupl e independently to an overmoded detector (such as a bolometer in an integra ting cavity), The number of modes is chosen to optimize the coupling effici ency to the source without compromising any spillover losses. We consider i n detail the case of a cylindrically symmetric corrugated configuration, pr esenting two alternative techniques for modelling such few-moded systems. T he first approach is based on a mode-matching description of propagation in a non-uniform waveguide structure, while the second approach makes use of hybrid mode solutions for a waveguide with corrugated walls assuming a unif orm but non-isotropic impedance. We present practical examples comparing th e radiation patterns predicted by both models. (C) 2001 Elsevier Science B. V. All rights reserved.