Reduction of ground spillover in the Owens Valley 5.5-m telescope

The 5.5-m telescope of the Owens Valley Radio Observatory is used for highly sensitive measurements of the cosmic microwave background radiation, which are easily contaminated by ground spillover. The authors describe the modifications made to the secondary mirror support structure that reduced the total ground pickup of the antenna from 27 to 9 K and decreased the peak differential ground pickup for the observing technique from 43 mK to 140 μK. This was achieved by reducing the physical obstruction, arranging the support leg angles to minimize direct reflections, and installing radiation baffles to control the direction of the reflection or scatter lobes