Rotman lens beam formers for Army multifunction RF antenna applications

An electronic scanning antenna (ESA) that uses a beam former, such as a Rotman lens, has the ability to form multiple beams for shared-aperture applications. This characteristic makes the antenna suitable for integration into systems exploiting the multi-function radio frequency (MFRF) concept, meeting the needs for a future combat system (FCS) RF sensor. An antenna which electronically scans 45° in azimuth has been built and successfully tested at ARL to demonstrate this multiple-beam, shared-aperture approach at K_a band. Subsequent efforts are focused on reducing the component size and weight while extending the scanning ability of the antenna to a full hemisphere with both azimuth and elevation scanning. Primary emphasis has been on the beamformer, a Rotman lens or similar device, and the switches used to select the beams. Approaches described include replacing the cavity Rotman lens used in the prototype MFRF system with a dielectrically loaded Rotman lens having a waveguide-fed cavity, a microstrip-fed parallel plate, or a surface-wave configuration in order to reduce the overall size. The paper discusses the challenges and progress in the development of Rotman lens beam formers to support such an antenna.