Synthesis of Reactively Loaded Sparse Antenna Arrays Using Optimization on Riemannian Manifold

This paper introduces a method for computing reactive terminations for scatterer elements in antenna arrays. With the fixed scatterer elements, we shape embedded element patterns of sparse arrays to focus the radiation into a grating-lobe-free limited field of view. The reactive terminations of the scatterer elements are determined by optimizing reflection coefficients on a Riemannian manifold. In addition, we show that widening the grating-lobe-free field of view is possible by tilting the field of view. We design both 5-element linear and 4-by-4-element planar reactively loaded antenna arrays with 1.4-wavelength inter-element distances. The terminations of the scatterer elements are optimized so that the arrays cover either the broadside-located or the tilted grating-lobe-free field of view. The results obtained from the linear array are validated through measurements of manufactured prototypes.