Low-phase-noise, phase-locked tunable millimeter-wave signal source for calibration of W-band low-noise astronomical heterodyne receivers

One of the solutions to overcome the problem introduced by larger characteristic parameter variation is to calibrate the characteristics of the system by a known weak signal periodically. The calibration signal can be either a signal from know celestial objects or an artificial signal source build in the telescope system. The disadvantage of the celestial calibration sources is that their orientations may be far from the observing area, which takes longer time on the pointing and alignment before and after calibration. The system build-in calibration signal source can omit such kind of inconvenience. The system considered in this paper is the Array of Microwave Background Anisotropy (AMiBA), which is with 13-element millimeter-wave telescope array with HEMT based heterodyne receivers operated in 85-104 GHz band. In this paper, a frequency selectable CW source for AMiBA system calibration is presented.