With coming base stations using active antenna technology enabling new features such as beam forming and full dimensional Multiple Input Multiple Output (MIMO) transmission, RF characteristics such as Equivalent Isotropic Radiated Power (EIRP) and Equivalent Isotropic Sensitivity (EIS) needs to be measured Over The Air (OTA). In this contribution a method is proposed on how to determine the uncertainty of a Compact Antenna Test Range (CATR) for peak direction gain measurements for passive antennas. The uncertainty of peak direction gain for a passive antenna constitutes a major part of the uncertainty of active measurements such as EIRP and EIS.