Design of multiband/broadband software-defined super-sparse digital beam forming array for down-link satellite communications

Conventional RF beam forming arrays are severely limited in bandwidth by the grating lobe problem, which emerges when the array element spacing exceeds about 0.6/spl lambda/ at the operating frequency. Furthermore, the complexity and cost of multiband phase-shift (or time-shift to deal with beam squint), and the lack of operational flexibility and features, also are their fundamental shortcomings. For the present design of a moving ground-based receive array for a satellite down-link spanning L, S, and X bands, a software-defined receive array approach using digital beam forming (DBF) offers an increasingly practical solution to overcome these shortcomings in a manner analogous to the software radio solution over conventional radios. The grating lobe problem can be alleviated by creating virtual array element signals in the digital signal processor (DSP). The super-sparse software-defined DBF array is shown to be feasible and increasingly practical. This approach not only overcomes the fundamental limitations of RF beam forming, but also offers cost and operational advantages mandated by the proliferation and rapid changes in modern antenna systems design.