A Lightweight Ultra-Wideband Lens TEM Horn with Low Sidelobes and Low Radar Cross Section

Ultra-Wideband radar systems could contribute significantly to the detection and identification of unknown objects. UWB radars have been shown to work well in environments where conventional radars fail, such as looking through foliage or soil. However,UWB radars suffer from the lack of an antenna with low sidelobes, while still maintaining the ability to radiate a clean impulse. Currently available UWB antennas, such as the reflector Impulse Radiating Antenna, have a problem with sidelobes that aredifficult to treat. In addition, antennas fabricated from lenses are often too heavy to be practical. Finally, UWB antennas, when mounted on an airborne platform, present a large radar cross section (RCS) to X-band radars. To address the problem ofsidelobes in UWB antennas we propose to develop Lens TEM horns. These devices have more uniform aperture fields than more traditional reflector IRAs, so they are expected to have lower sidelobes. In order to keep the weight of the antenna to a minimum,artificial dielectric (AD) materials will be used to fabricate the lens. Since commercially available AD materials are too heavy, we will develop our own materials, consisting of a uniform array of discs embedded into a lightweight foam. Such a materialwill have a density one-sixteenth that of polyethylene. To reduce the RCS of the antenna, we will place it behind a radome covered with a Frequency Selective Surface (FSS). Such a surface can be designed to be transparent to UWB signals below 2 GHz, and tobe opaque to X-band signals. By this method, X-band radar signals reflect off the aircraft skin as if the radome were covered with a continuous perfect electric conductor.