Abstract: A broadband antenna includes a center fed active radiating/receiving element formed of two contiguous conductive spirals. The two planar antenna spirals are secured to a cavity loaded with a wave absorbing lossy material such that the antenna is operative only in its front lobe direction opposite the loaded cavity.In accordance with the present invention, the cavity wall is formed of varying pattern of conductive and insulative material. The resultant composite antenna is characterized by a relatively narrow beam pattern for both horizontally and vertically polarized electric waves across a broad spectrum of frequencies.

Abstract: A ferrite sleeve placed about the cavity portion of an antenna reduces back lobe radiation without degrading the antenna's front hemisphere radiation pattern. The thickness of the ferrite sleeve is selected such that the sleeve highly attenuates the surface currents on the cavity at the lower end of the operating frequency range of the antenna.