The present invention discloses an extendable antenna for a portable communication device, made of two radiating wires each shaped as an open loop; a first loop fixed and a second loop movable between two positions: in parallel or alternatively vertically to the first loop; the parallel position suitable for compactly carrying the device in non-active mode, and the vertical combination configured to produce a substantially isotropic radiation pattern, particularly instrumental for satellite communications. According to one embodiment, this device is a satellite served Personal Locator Beacon (PLB) for Search and Rescue (SAR) of people in distress, configured to be wrist worn.