Helical / Helix Definition:
Typically wound in a one wavelength per turn spiral, the Helical/Helix produces a wave front of fixed circular polarization. The sense of
the Circular Polarization matches the clockwise or counter clockwise direction of the spiral. The Circular Polarization field cannot be
reversed. The Helical/Helix typically produces 3 dB less gain than a Yagi for a given 2:1 is possible with this design (200 to 400 MHz).
They are typically rear mounted in front of a 1/2 wave length or larger planar reflector. No balun is required and the 50 Ohm feed point
is easily accessible at the back side of the reflector surface. These antennas can be placed in an array configuration for more gain but
matching over a 2:1 bandwidth is sometimes a drawback.