We introduce a new class of partially coherent beams that can propagate ove
r large distances without changing their transverse profiles and their cohe
rence properties. Such beams are generated by an incoherent superposition o
f identical fully coherent beams of arbitrary form, whose axes lie on a con
e. (C) 2000 Optical Society of America. OCIS codes: 030.1640, 260.1960.