Characterization Method for Digital Correlator of Interferometric Radiometers Based on Correlated Noise Source

Digital correlator is the central signal processing unit for an interferometric radiometer system. The core function of the digital correlator is to quantitatively measure the correlation coefficients of all the receiver output combination pairs, and then generate the visibility functions together with the system noise temperatures obtained by single-channel total-power measurements. In this letter, a comprehensive quantitative characterization method is proposed for a 30-channel, three-level quantized digital correlator unit (DCU), which will be used for the microwave imager combined active and passive (MICAP) C- and K-bands radiometers, on-board Chinese ocean salinity mission (COSM). First, several key performance characteristics of DCU, including correlation offset and correlation efficiency, are defined and discussed based on a segmented error model. Second, a test platform based on an arbitrary waveform generator (AWG) is established and applied for the test and evaluation of the DCU engineering model (EM). Orthogonal in-phase and quadrature bandlimited noise signals are generated via a newly proposed approach based on Hilbert transform, facilitating the joint tests of correlation efficiency and phase error. Moreover, the influences of the correlator's input power level on correlation offset and correlation efficiency are also investigated during the test of DCU. DCU test results show that the correlation offset is smaller than -40 dB, the correlation efficiency is better than 0.996, and the phase error is less than 5 degrees. The result can provide an important reference for the digital correlator test in COSM.