Improved interferometric method to measure near-carrier AM and PM noise

An improved version of the interferometric method to measure near-carrier A M and PM noise is being presented. The main feature of this scheme is the c apability to reduce the instrument noise by correlating the output of two e qual interferometers built around the same device to be tested, thus enhanc ing the sensitivity. Two double interferometers are described, operating in the microwave and VHF bands. The latter shows a noise floor of -194 dB rad (2)/Hz when the signal power is + 8 dBm. The sensitivity of both the instru ments turns out to be significantly higher than the ratio of the thermal no ise divided by the carrier power.