Abstract: A collapsible bifilar helical antenna comprises a rigid mast, a pair of flexible helical conductors wound about the mast, and a plurality of support arms spaced along the mast and extending radially outwardly therefrom for supporting the helical conductors, the support arms being movable along the axis of the mast to permit the helixes formed by the conductors to be expanded and contracted. The mast includes multiple sections which permit adjustment of the axial length of the mast. The support arms are mounted on sleeves which are slidable along the mast, each of the support arms has a tubular member mounted on the outer end thereof, and each of the flexible helical conductors comprises a metal cable which passes through the interiors of the tubular members.