Electronic scanning antenna using a nonuniformly-spaced planar array

In a uniformly-spaced planar-array antenna, when the main beam electronically scans a wide angle, the sidelobe near the secondary mainlobe, and even the secondary mainlobe, may emerge from imaginary space to real space. In this paper, a new method for calculating the separation between the elements of a planar array is presented. The employment of this method not only reduces the above wide-angle-scanning problem, it also can result in a reduction of sidelobes as compared with a uniformly-spaced array. Two cases with uniform and nonuniform excitation for a uniformly-spaced planar array with 20 × 20 elements are shown. In both cases, the uniformly-spaced planar array is used as a base from which the related nonuniformly-spaced array is obtained. A comparison of sidelobes, beam broadening and numbers of elements have been done while the main beam moved in elevation between ±50° or ±60°, depending on weightings, and in azimuth from zero to 90°. A sidelobe reduction of about 6.8 dB for an unweighted planar array and about 3.3 dB for a weighted array, as compared with the uniform spacing, between the above angles, have been obtained. These results have been accomplished by increasing the halfbeam broadening by about 1.17, as compared to a uniformly-spaced array scanned through the same region.