A cryogenic set-up for accurate characterization of microwave components for astrophysics

State of the art instruments for astrophysics in the millimeter and submillimeter domain adopt cryogenic front-ends. Temperatures in the range 4-20 K are necessary to almost nullify the thermal noise from lossy passive components and operate low noise amplifiers in their proper regime. Extremely high accuracy in the control of systematics is an unavoidable step towards the realization of ultra high sensitive instrumentation. For this reason a corresponding precision must be used in the characterization of the cryogenic front-end key components like feed horns, phase shifters, orthomode transducers and amplifiers. In this contribution we give a detailed description of the cryogenic set-up we have realized in our microwave lab to characterize at ultra low temperature (4 K) by means of a VNA both active and passive devices.