A portable tracking and communications device (10) comprises a Global Positioning System (GPS) module and a mobile telephony module, the device including at least a first passive, electronic ground plane simulator comprising a pair of essentially grounded antennae (16, 17) that are selectively connectable one to the other via a parallel-connected resistor-capacitance resonator (18, 19), the resonator being tuned to a first predetermined frequency or frequency range.