A Helical Antenna for Circular Polarization

A helical coil radiates a wave of circular polarization in a doughnut pattern if the area and pitch of the turns are properly related to the radianlength of the wave. For a coil whose dimensions are less than the radianlength, circular polarization requires that the area A of each turn and the pitch p be related to the radianlength l as follows: A=pl. The simplest form of helical antenna is a self-resonant coil of several turns. To obtain greater radiation power factor and efficiency, a multifilar winding is preferred, having a fractional turn for each of several helical wires connected in parallel with symmetry around the axis. This type of antenna offers television the advantages of circular polarization in suppressing echoes from reflecting surfaces.