Non-orthogonal beam steering commands for array antennas

The steering of a phased-array antenna requires the generation of specific calculated values of phase for each active radiating element in the array. These phase values are generally derived by a special-purpose computer which receives basic steering data from a general-purpose system computer. The system computer transfers two basic steering commands which permit positioning the beam in two dimensions. Typically, these two commands consist of the phase increments required for each row and column in the array for steering in the basic azimuthal and elevation direction. The calculations performed by the beam steering computer then derive the phase for each row and each column in the array. However, on the basis of the angular coverage requirements of a typical array, it turns out that the optimum placement of the elements does not fall on a rectangular grid but on apices of triangles. The use of X-Y addressing of the elements consequently requires superfluous rows or columns, some of which access only 50 percent of the elements. By selecting a non-orthogonal set of axes in the array, related to the element pattern, considerable savings in equipment and computation can be realized. This paper derives the relationship between the steering commands used in a non-orthogonal or skewed-axis system and those normally used in an X-Y-oriented system. Reduction in equipment and time are computed and effects on pointing accuracy discussed.