Encircled power study of focal plane field for estimating focal plane array size

The relationship between the size of a focal plane array in a prime focus dish and achievable scan angle is studied in order to find a starting point for designing such systems. A physical optics model is used to obtain focal plane fields and the radii in the focal plane required to encircle 3 dB and 1 dB below the incident power is calculated for a range of dish diameters and focal length over dish diameter ratios (F/D). The study found the focal plane fields are largely independent of dish size when the scan angle is expressed in beamwidths and gives guidance for the optimal F/D to achieve maximum field of view for a given focal plane array size.