Two-resonance helical antenna capable of suppressing fluctuation in electrical characteristic without restriction in size of a helical coil

摘要

In a two-resonance helical antenna, a single helical coil (3) is made of a conductive material and extends in one axis direction. An annular conductor portion (5) is arranged around the helical coil in a coaxial fashion to be spaced and insulated from the helical coil. The annular conductor portion is positioned in a middle portion of the helical coil in the one axis direction.