Direct fed spiral antenna

Claim 1

An element antenna comprising: A plurality of electrically conductive spiral arms spaced from each other and having a common axis of rotation, each said arm having inner and outer ends, said inner ends being rotational displaced about said axis relative to each other by a given angle to achieve a given rotational phase progression about said common axis; each of said arms being of a length sufficient that each arm intersects an annular active region essentially coaxial about said common axis and at which electromagnetic energy is efficiently radiated from the antenna element by currents flowing in the respective arms in the same direction and in-phase as they arrive at the active region; phase control means for effectively electrically rotating said spiral arms about said axis to control the phase relationship of electromagnetic energy to be radiated from said element antenna comprising means for interconnecting at least one pair of inner arm ends together to effectively obtain a short circuit therebetween so that electrical signals in the respectively interconnected pair of arms are interchanged from one arm to the other with a relative phase change dependent upon the rotational phase relationship between the interconnected inner arm ends; and, feed means directly connected only to the outer arm ends of said arms for feeding radio frequency energy from a feed source to each arm to cause current to flow in each arm from the outer end thereof toward the inner end thereof, said feed means including means for feeding energy to said outer arm ends such that the currents in said respective arm ends initially flow from the outer arm ends toward the inner arm ends with a phase progression relative to each other so that as the respective inwardly flowing currents enter the active region they are out of phase, preventing efficient radiation from the antenna element.