Fixed-beam L-band array for space-based platforms

A nonuniform amplitude, equal-phase, fixed beam, 19-element circular array is developed for broadband satellite-to-satellite and satellite-to-ground L-band communication systems. Array topology consists of one center element and two concentric rings, inner ring with six and outer ring with 12 elements. To reduce the losses, the extremely low-loss property of air-loaded transmission lines, specifically rectacoax and suspended stripline, are used to design a low-loss beamforming network (BFN). The elements in the array have equal phase and unequal, 3-bit amplitude distributions (center element, inner and outer ring). A nonuniform amplitude distribution is designed to minimize the side-lobe levels (targeted value is 30 dB below the main lobe) and maximize the gain over a main beam beamwidth of plusmn10deg. Several amplitude distributions are considered, beginning with uniform distribution and ending with an array layout that has its spatial dimensions and amplitude distributions determined by a genetic algorithm that computes the array pattern based on element pattern and array factor. Element patterns are measured to validate simulated results using the method of moments (MoM) code, FEKO.