The Design of Internal Calibrator in Ka-band FMCW Space-Borne SAR

In this paper, the design and the features of the Radio frequency (RF) module which is part of a novel Ka-band FMCW SAR system calibrator for both satellite and airborne prototypes is presented. According to controller instructions, this RF module which composed switch array has a function of RF link switching. At the same time, every indexes of RF link meet to calibration mode requirements for radar system. A prototype of the calibrator has been fabricated. The isolation of each channel is above 40dB over the specified operation frequency of 35.4GHz to 36.1GHz. In this scheme, closing the amplifier power and using isolator is effective measure to improve isolation. In this module, a serious problem of flat gain and stability is unpredictable since manufactures cannot provide detailed MMW component data due to bad consistency. To solve this problem, unpredictable flat gain and stability of output signal due to operating temperature between −20 and +45°C is examined both experimentally and theoretically. The developed calibrator features low cost, good flat gain and good stability of output signal. And it has been applied in a FMCW SAR imaging System.