Designing Shading Schemes for Microphone Phased Arrays

A technique is proposed for designing sensor weightings, or array shading functions, for microphone phased arrays. The presented method attempts to maintain mathematical simplicity while maximizing array gain for a desired mainlobe beamwidth. It does so using the two-parameter optimization of a family of functions. The shading design process is described and applied to an array used recently in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. Several variants of the method are compared to an existing shading scheme for the array, along with a more general optimization formulation. Results are presented for both an idealized point source and experimental data from the wind tunnel test. The shading schemes are shown to improve the behavior of array operations, but have a stronger impact on visual interpretation of maps than on source level calculations. The study results show that the two-parameter optimization scheme provides favorable characteristics while maintaining implementation simplicity.