Synthesis study of a 6-element non-uniform array with tilted elements for CLARREO project

The results of a preliminary study of the gain/pattern properties of a 6-element Radio Occultation (RO) array for the proposed CLARREO (Climate Absolute Radiance and Refractivity Observatory (CLARREO) Project. There are two array antennas at each observatory. Each array is attached to a vertical end of the spacecraft bus with the beam tilted to point towards the Earth´s limb. The requirement is the attainment of a tilted beam with respect to the plane of the array with a maximized uniform coverage over a range of +/-45 degree angles, namely a sector beam. The novelty of this array design is that it is non-uniform and non-planar and falls into the category of spatial arrays where the location and orientation of the array elements are variable. The beam shaping is performed, in general, by variation of a number of spatial and electronic phase and amplitude parameter. We reduce the number of required parameters by taking advantage of various symmetries. Then an overview of the analysis of such arrays is presented. Subsequently we use two approaches to the synthesis problem: one analytic and other a numeric global optimization method using a new evolutionary programming technique. The results for two designs with simultaneous near optimum performance at two different required GPS frequencies of L1 (1.575 GHz) and L2 (1.2 GHz) are presented.