System Design Considerations in Fiber-Optic Networks for Active Array Satelite Antenna

Multiple pencil-beam scanning/hopping antenna systems provide a powerful approach to increase the satellite´s capacity by the frequency reuse, the increased e.i.r.p. and G/T of each of the pencil beams, and also by the efficient satellite resources utilization through matching the antenna beams´ dwelling times to the traffic and connectivity requirments. Since this permits also to use very small and inexpensive earth stations, a significant reduction in cost per communication channel can be obtained. One of the problem areas still existing and requiring an innovative solution is the distribution of the broadband microwave communications and control signals to the very large number of the active antenna moduls. Each module consists of a digital phase shifter and gain control, amplifier, and a radiating element. Recent advances in fiber optics technologies for microwave applications in the over-l0-GHz region, make it a very attractive candidate for signal distribution networks in large satellite antenna arrays. The main advantages of a fiber optic network are the very small size and weight, the capabillity to be integrated with MMIC devices, and immunity to electromagnetic interference, while the main disadvantages are the high insertion loss and high noise figure. In this paper some system design considerations are evaluated, in applying the fiber optic technologies and techniques to multibeam scanning Ku-band satellite antenna signal distribution and control networks. It is demonstrated that the fiber optic links can provide a feasible solution.