Abstract: A self-resonant quadrifilar helix antenna is formed with four helical electrically conductive elements arranged in each of four quadrants about a common central axis. A coaxial feed extends along the common central axis of the four helical electrically conductive elements. Top ends of first and second ones of the four helical electrically conductive elements are connected to a center conductor of the coaxial feed, and top ends of third and fourth ones of the four helical electrically conductive elements are connected to a shield of the coaxial feed. The bottom ends of each of the four helical electrically conductive elements are electrically connected to the shield of the coaxial feed. This provides a very compact structure in which the coaxial feed serves as a support for the antenna.

Abstract: A helical antenna having stubs spaced along the helix curve length and extending toward the central axis of the helix, such that the performance characteristics of the antenna, such as gain and circular polarization, are maintained while the size of the antenna--diameter and length--are reduced.