Mapping speed for an array of corrugated horns.

I address the choice of horn diameter for millimeter-wave array receivers with corrugated horns. For maximum point-source mapping speed, in both total power and polarization with typical receiver noise contributions and a close-packed horn array that fills the field of view, the optimum horn diameter is 1.6-1.7Flambda, where F is the focal ratio. A +/-25% change in horn diameter gives <10% degradation in mapping speed. Correlated noise from the cold stop, atmosphere, and cosmic microwave background has little effect on the mapping speed and optimum horn diameter.