Abstract: A quadrifilar radio frequency antenna intended primarily for receiving signals from an earth orbiting satellite for navigation has four helical wire elements shaped and arranged so as to define a cylindrical envelope. The elements are co-extensive in the axial direction of the envelope and are mounted at their opposite ends in two printed circuit boards lying in spaced apart planes perpendicular to the axis with the end parts of the elements being soldered to conductor tracks on the boards, the tracks constituting impedance elements between the helical elements and between the helical elements and an axially located coaxial feeder. The conductor tracks are such that the effective length of one pair of helical elements and associated impedance elements is greater than that of the other pair and associated impedance elements.