Current Status of Time-Domain Metrology in Material and Distributed Network Research

The current status of time-domain metrology (TDM) in material and distributed network research is described. After a brief summary of earlier work, the operation and features of two prototype material measurement units are discussed. These semiautomated systems utilize a 5-V step recovery diode pulse generator and computer-controlled scanning procedures incorporating time-window stabilization and variable-dwell-time averaging. The larger, 10-ns time-window unit measures the complex permittivity and permeability over a frequency range of 0.1-10 GHz in about 10 min. The causes and magnitude of system errors are discussed along with continuing work to improve system performance. In distributed network research, the capabilities of TDM for calibration are being determined. From measured signal-to-noise ratios, it was calculated that random noise contributes less than 1 percent error for insertion loss measurements up to 50 dB over the frequency range 0.4-8 GHz. Other topics discussed include: identification and evaluation of error sources, pulse generator development, measurement configurations and procedures, and testing of waveguide and ferrite components.