Frequency domain analysis and performance of a true time delay fiber optic beam forming network for array antennas

The true time-delay behavior of a fixed-scan fiber-optic beamforming network is analyzed using the microwave scattering parameters of the fiber-optic components within the network. Pseudooptical domain-scattering parameters are measured with respect to the microwave modulation of the optical carrier for signals in various paths of the optical beamforming network. The measurement technique is described, which uses a vector network analyzer outfitted with an optical test set, and results show microwave reciprocity and RF phase linearity over the measured frequency range from 2.0 to 3.0 GHz. Optical standing wave ratio and isolation between delay lines are also determined. The electrical scattering parameters of the beamformer were measured, and far-field radiation patterns measured in an anechoic chamber demonstrate ideal true-time delay behavior, with nonsquinted main beam radiation over a 50 percent instantaneous bandwidth at S-band.