3700-4200-MHz Computer-Operated Measurement System for Loss, Phase, Delay, and Reflection

A computer-operated transmission measurement set intended to support development work on microwave components for FM radio systems in the 3700-4200-MHz range is described. The instrument is capable of measuring the complete S-parameter set of the device under test, over a range from 20-dB gain to 70-dB loss. Accuracies of transmission parameters for small loss are ±0.002 dB, ±0.01°, and ±0.1 ns. The basic measurement technique is that of "IF substitution," combined with rapid cyclic comparison (30-Hz rate) of the parameters of the unknown with those of a stable microwave reference. The comparison feature eliminates errors from circuit drift, thus allowing attainment of the high accuracies sought. The test set design, the control of error sources, and the validation of accuracy are discussed.