Review of radio frequency beamforming techniques for scanned and multiple beam antennas

This state of the art review aims to introduce the topic and to collate and classify types, giving a critical assessment of comparative performance. The fundamental relationship between the number of active control elements and the number of beams is taken as a measure of beamformer performance and this also indicates that, for a limited number of active elements, high gain antennas with narrow beams will have limited scan range whilst low gain systems have a wide angle capability. This deduction is reinforced by the practical results collected at the end of the review. The beamformer types covered include lens based beamformers such as the Ruze, Rotman, R-KR and nonuniform refractive index types together with objective lenses with separate feed arrays. Reflector based multiple beam antennas based on zero, one or two Fourier transform properties are followed by circuit types including the Blass and Butler matrices. The wide range of information presented is clarified by a summary section giving an indication of comparative performance levels.