Benchmarking Overlapped Subarrays in Direct Radiating Arrays for GEO Broadband Satellite Communication Systems

Direct radiating arrays (DRAs) present favorable solutions for high-throughput flexible coverage in geostationary (GEO) broadband satellite missions. The ultimate constraint in these architectures is the high number of digitally controlled antenna ports, which renders fully digital architectures impractical for the immediate future. Instead, hybrid analog–digital DRAs are being considered as a promising trade-off in terms of performance/flexibility and digital processing demands. These architectures commonly involve subarrays with analog beamforming, which form broad (regional) beams, which are then digitally beamformed at a second level to produce a multitude of narrow beams used for broadband connectivity. Due to the large size of the subarrays, these architectures are subject to undesired grating lobes that can lead to interference and reduce the gain of the main beam, thereby compromising overall performance. Partial mitigation of the grating lobes is attainable by subarray overlapping. This paper presents a comparative assessment of three different hybrid analog–digital DRA architectures in terms of the coverage characteristics and discusses their practical implementation. It is demonstrated that improved performance can be achieved by subarray overlapping with some additional analog hardware complexity but otherwise maintaining the number of digitally controlled antenna ports.