A highly stable, phase coherent, wideband microwave synthesizer for radio astronomy applications

A description is given of a wideband microwave synthesizer that is used as a local oscillator in a novel front-end design. This front-end design is used in a synthesis radiotelescope operating in the frequency range up to 8.6 GHz. The aperture synthesis principle on which this radiotelescope is based, as well as Very Long Baseline Interferometry (VLBI) techniques require exceptional phase and frequency stability which are fulfilled by the presented oscillator design. A phase stability of better than 5/spl deg/ r.m.s., averaged over 60 seconds, is obtained at 5 GHz over periods of 12 hours. Allan-variance values approaching 10/sup -14/ are measured for /spl tau/=1000 seconds. The output signals among two synthesizers tuned to the same frequency are always phase coherent with a fixed phase offset.