Patent ID: 8242964

Claim:
A helical antenna comprising: a ground plate; a first helical portion that is wound in a spiral manner generally perpendicular to a plane of the ground plate; a second helical portion that is wound in a spiral manner generally perpendicular to the plane of the ground plate and surrounds the first helical portion on a radially outer side of the first helical portion; and a feeder circuit including: an oscillator; a divider connected to the oscillator; a first phase shifter connected between a first output terminal of the divider and a feeding point of the first helical portion; and a second phase shifter connected between a second output terminal of the divider and a feeding point of the second helical portion, wherein: a length of one turn of the first helical portion is equal to a result of multiplication of a wavelength of oscillation of the oscillator by a first predetermined number; a length of one turn of the second helical portion is equal to a result of multiplication of the wavelength by a second predetermined number; and the second predetermined number is larger than the first predetermined number.