This thesis aims at defining and validating a theoretical model, that approaches the aircraft radiation pattern, whereby the interference power radated by the aircraft UMTS picocell to ground systems can be determined.What is in this thesis analyzes is the dowlink understood as the path between the on-board picocell antenna and on-load user. The chosen manner to achieve this goal relies on deterministic, models specificaly ray-tracing in theinterior of the aircraft and free.space propagation models outside. This thesis show possible models to characterize the radiatio cable, the onland netwoks interference source. Hereafter the immediate surroundings of it ( aircraft interio ) is analyzed using ray tracing tools to determine the illuminating field at aircraft windoes. Knowing its illuminating field, the radiated field by the windows is easily determined, To calculate the aircraft radiatio pattern the windows radiation patterns must be weighed added