An octave bandwidth, electronic scanning cylindrical array has been designed, and a demonstration unit has been built and tested. Using a two-dimensional Luneburg lens beamformer with a simple switching network, a cluster of beams is positioned electronically to cover any azimuth sector. By properly weighting the Luneburg lens excitation, low-azimuth sidelobes are obtained, and beam shapes and pointing angles remain substantially invariant over the octave frequency band. The design embodies novel techniques for obtaining high efficiency, high crossover, and low sidelobes on all beams within the cluster using a simple switching circuit. The principles of the design are experimentally demonstrated on a 2048-element electronic scan array. The theoretical basis of the technical approach, including tradeoffs for low sidelobes and wide bandwidth, is presented. The design details and measured performance of the experimental antenna are described. >