Experimental Test of a New Precision Model for Microwave Rotary Vane Attenuators

Detailed measurements of scattering parameters have been made on a precision rotary vane attenuator (RVA) with high-resolution, direct angular readout. The aim of the measurements has been to test if the RVA can be used as a primary standard of attenuation by taking advantage of a precision model described recently by one of the authors (T. Guldbrandsen). Precision attenuation measurements have been made versus angle of rotation by means of a modulated subcarrier system. Within the uncertainty, the attenuation measurements agree with the functional dependence predicted by the model. Reflection coefficients have been measured versus angle of rotation by means of a computer-corrected automatic network analyzer and, within the uncertainty, they agree with the model. From the reflection measurements, corrections to the attenuation were calculated using relations derived from the model. The corrections were compared with the measured attenuation values. So far the agreement is not quite satisfactory and additional diagnostic measurements are planned.