A Calorimetric Method for Measuring High Reflection Coefficients at Microwave Frequencies

The measurement of high reflection coefficients is rather difficult. Several methods have been described for this purpose, mostly using slotted-line techniques. The knowledge of the reflection coefficient of standard waveguide short-circuits is especially useful when the reflectometer method is used for impedance measurements. In this case the error due to the non-ideal behavior of the reference short circuit is one of the most important factors that influence the accuracy of the measurement. The paper analyzes several methods of measurement with particular consideration to sources of error. Special reference is made to a calorimetric method that is capable of high accuracy. Some experimental results obtained on standard ¿/4 short circuits fabricated at the Istituto Elettrotecnico Nazionale (Turin, Italy) are shown and compared with calculated values found in the literature.