Radio astronomical phased arrays with fiber-optic design architecture

Fiber optics and microwave photonics are considered to be the technological basis for the solution of at least the two main design problems in large radio astronomical active phased arrays (RAAPA): phase stabilized LO reference signal transmission to each antenna element or subarray; antenna array beamforming. We describe in detail the solution to the former problem. It is the experimental version of a new fiber-optic link, operating in the remote heterodyning mode, with phase stability (<1/spl deg/ of phase) and full compensation of the insertion loss in the RF, microwave and millimeter wave frequency regions. Two principal methods of fiber-optic beamforming in a big RAAPA are also described in detail. The first one is based on an optical true-time delay (TTD) technique to realize the classic beamforming strategy by optical means. Systems of the second kind actively use hybrid coherent optical processors, replacing the classic beamforming strategy by holographic principles and avoiding the necessity of microwave radiation delay or phase shift evaluation in every array radiator in the real-time domain.