Optimum optical limited scan antenna

An optical limited scan antenna system is considered for applications such as spot coverage of a small portion of the earth from a satellite. The optimum criterion relating aperture efficiency, number of control elements, and angular coverage is revisited briefly. The optical scheme advocated utilizes a bootlace aperture lens, a generalized Luneberg lens focused to the near field, and a small array of active elements. The operation of the system is described first in terms of geometrical optics and elementary diffraction principles. The subarray viewpoint is then developed using simplified diffraction concepts. These results form the basis of a design procedure for the synthesis of high performance limited scan systems. An accurate solution necessary for the analysis of small antennas is developed using a modal decomposition and the wave equation. Numerical computations for a case of practical interest verify the expectation of near optimum performance.