  We introduce a thermal antenna which can be actively switched by phase
transition. The source makes use of periodically patterned vanadium dioxide, a
metal-insulator phase transition material which supports a surface
phonon-polariton (SPP) in the infrared range in its crystalline phase. Using
electrodes properly registred with respect to the pattern, the phase transition
of VO2 can be localy triggered within few microseconds and the SPP can be
diffracted making the thermal emission highly directionnal. This switchable
antenna could find broad applications in the domain of active thermal coatings
or in those of infrared spectroscopy and sensing.
