A quadrifilar helix antenna includes a cylindrical support extending along an antenna axis; a plurality of spiral antenna elements wrapped helically on the cylindrical support and along the antenna axis from a feed end to a remote end; a ground plane having a diameter of about 300 mm and perpendicular to the antenna axis; and each of the antenna elements including a plurality of breaks, with the breaks having capacitors between conducting portions of the antenna elements. All capacitors a positioned higher than 60 mm above the ground plane, and capacitance value varies inversely with height. The antenna exhibits a DU(10°)=−20 dB or better at an operating frequency f0=1575 MHz. The diameter of the cylindrical support is 30 +/−5 mm. A total height of the cylindrical support is 300 +/−50 mm. A winding angle of the helix is variable.