Image simulator for one-dimensional synthetic aperture microwave radiometer

Calibration for a one-dimensional synthetic aperture microwave radiometer is critical. Phase and amplitude calibration of the visibility samples must be carried out to compensate for system bias before measurement. This bias mainly comes from the un-uniform characteristics and the couplings between the receiving channels. To take into account this problem, a numerical image retrieving method is considered using an intermediate transformation matrix called the gain matrix or simply G-matrix. This matrix takes into account all the couplings and un-uniformed amplitude and phase between the channels. However, measuring the G-matrix is not an easy job. One has to set up a point source in the far field and rotate the system in the fan beam direction. The difficulty is mainly due to the incomplete test environment. A measurement set-up called image simulator is present. It is a circuit network composed of a number of high accurate microwave I-Q vector modulators and a noise generator. It simulates the incoming waves to the thinned antenna array corresponding to any image scene to be measured. While in measurement, the simulator´s outputs are connected to the RF inputs of each channel. The incoming wave is then simulated by computer program to drive each of the digital I-Q vector modulators. The design and test of the image simulator are presented followed with test results of G-matrix.