Abstract: An electromagnetic wave is transmitted from and received by an antenna system having a cavity member, a passive antenna element and a driver element. The cavity member has a back portion and a wall portion which define a substantially cylindrical interior portion. The antenna element has a first end disposed within the interior portion of the cavity member. The driver element is coupled to the interior portion of the cavity member.

Abstract: A communications system in which a communications channel is defined at least in part by an electromagnetic wave having a carrier frequency and an electric field vector, the extremity of which traces a non-linear periodic path at a second frequency between the carrier frequency and zero from the perspective of an observer looking into the axis of propagation of the wave. The transmitter of the communications system launches a wave having such characteristics and modulated with information in a suitable manner. The receiver of the communications system is sensitive to the periodic path and second frequency. Either the periodic path, the second frequency, or both provide selectivity that can be used to define multiple communications channels.