Limitations on the design, monitoring and diagnosis of complex microwave systems due to insufficient models, the reality of imperfect physical conditions, and the reliance on trial-and-error iteration for system improvement serve to increase the time and costs of radar development. While microwave characterization is traditionally the realm of conventional, port-based measurements, the proposed concept suggests an alternative: the development of a novel network of electro-optic sensors that probe the near-field amplitude and phase of microwave signals at strategic locations within prototype or field-deployed radar systems. Such a sensor network, which would rely on optically-coupled, non-conductive, ultrawideband probes, would provide an unprecedented combination of negligible invasiveness, freedom from electrical interference, and the ability to capture signal information at frequencies from UHF to W-band. It would impact the development of virtually the entire range of technologies relevant to active microwave earth-science instruments. The proposed program will thus lead to the development of an instrument that can aid in areas such as deployment, calibration, and phase correction in large arrays, as well as in the identification of sources of electromagnetic-interference signals and the isolation of faults and failures.