Simulation and performance prediction for the radiation patterns of few-moded and multi-moded corrugated horns

Corrugated horn assemblies are the most common method of feeding bolometer cavities for power detection on CMB experiments. Traditionally these have been single moded, whether polarised or unpolarised, but if polarisation is not required greater throughput can be obtained from few-moded or multi-moded horns. The simulation of these assemblies is far more computationally intensive than for single moded systems, and the effort is often compounded by the design of the assemblies. Here we show that multi-moded horn assemblies can be modelled reliably and do perform as required, but performance prediction requires attention to manufacturing tolerances as well as the system design.