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An insertion loss and phase measuring set has been developed for making small‐signal measurements on transistors and general two‐port networks with maximum inaccuracy of 0.1 db and 0.5 degree over a frequency range from 5 to 250 mc. In order to realize accuracy substantially independent of test frequency, the measurement information is heterodyned to a fixed intermediate frequency, where detection is performed with the aid of adjustable loss and phase‐shift standards. Use of a rapid sampling technique to compare the unknown with a high‐frequency standard eliminates errors from circuit drifts and also reduces the magnitude of the “instrument‐zero line” to a small value. Besides discussing the over‐all operation of the new test set, the paper presents the design approaches used in solving problems related to purity of terminations as seen from the unknown, automatic control of beat oscillator frequency, conversion, signal‐to‐noise, and design of loss and phase standards. Particular attention is given to the features of the set which especially adapt it to the measurement of transistor parameters.

A new insertion loss, phase and delay measurement tool has been developed for characterizing gigacycle bandwidth transistors and general two‐port networks on a small signal basis over a frequency range from 0.25 to 4‐2 gc. Maximum inaccuracies are 0.1 db, 0.6 degree (over a 40‐db loss range), and 0.5 nanosecond (over a 20‐db loss range). Above 2.0 gc, the errors may double. The particular parameters selected for measurement are closely related to the scattering coefficients of the device under test, evaluated with respect to a 50‐ohm impedance level. When measuring transistors, measurement data are corrected for the residuals of jig and bias fixtures. Transformation from the measured parameters to other sets (e.g., h, y, or z matrices) is routine. In order to minimize “instrument zero‐line” and eliminate errors from circuit drift, a rapid sampling technique sequentially compares the unknown with a high‐frequency reference. Measurement accuracy is held substantially independent of test signal frequency by heterodyning the measurement information to a fixed IF, where detection is performed by “IF substitution”, using adjustable standards of loss, phase, and delay. Substantial use of automatic control circuitry contributes to an easy and facile interface between machine and operator. This paper discusses the operation and design of the test set and its use as a tool in characterizing transistors.