Dual-band spiral antenna with parasitic element

摘要

Antenna systems for transmitting and receiving electrical signals in two widely separated frequency bands are provided which comprise a helix antenna and a parasitic element which is adjacent to the helix antenna. The parasitic element is positioned so that when radio frequency energy in the higher of the frequency bands is incident on the antenna system, the helix antenna and the parasitic element are capacitively coupled, while when radio frequency energy in the lower of the frequency bands is incident on the antenna system, the helix antenna is substantially isolated from the parasitic element. The effective aperture of the antenna system is preferably substantially the same in both of the frequency bands of operation, and the parasitic element may be positioned either inside or outside of the helix antenna, and may be parallel to the major-axis of the helix, or alternatively, may be positioned diagonally so as to only be adjacent to two or more windings of the helix antenna. Additionally, the antenna system may be implemented in combination with a radiotelephone having a transmitter, a receiver, a user interface, and an antenna feed system.