A set of initialization parameters are generated for a wireless charging device. Parameters of an antenna circuit connected to an output of the control circuit are measured. The antenna circuit is modelled as first and second virtual antenna portions. The presence of a foreign object is detected by receiving, from a receiver device, characteristics for the antenna circuit and by measuring second parameters of the antenna circuit. The measured second parameters and the initialization parameters are used to determine characteristics for the first virtual antenna portion. A foreign object is detected based upon a comparison of the received characteristics for the antenna circuit and the determined characteristics for the first virtual antenna portion.