Impedance helical antenna forming Π-shaped directional diagram

A helix antenna comprising:

• a cylindrical support;
• a plurality of spiral conductors wrapped helically on the cylindrical support from a feed end to a remote end;
• a circular ground plane perpendicular to the cylindrical support;
• and
• each of the spiral conductors including a plurality of gaps, with the gaps having capacitors between conducting portions of the spiral conductors,
• wherein values of the capacitors of each spiral conductor are inversely related to a height z above the ground plane according to
• C
• n
• =
• 1
• 2
• ⁢
• π
• ⁢
• ⁢
• f
• 0
• ⁡
• (
• b
• *
• z
• +
• B
• )
• ⁢
• L
• ,
• where
• Cn is a capacitance of the n-th capacitor;
• z has discrete values z=nL, where n is the number of capacitor position,
• L is a constant distance (center to center) between adjacent capacitors of the spiral antenna element, and B and b are constants, and
• f0=1575±40 MHz,
• wherein a winding angle α of the helix varies linearly with the height z, and
• wherein the antenna exhibits a Down-Up ratio of DU(10°)=−20 dB or better.