High Precision Time Delay Calibration for Radio Astronomy Radars Based on Maximum Likelihood Iteration

In the calibration of distributed radar for radio astronomy, deep space radio sources are commonly used as calibration sources to correct inter-array delay errors, and accurate delay estimation is critical. Traditional correlation methods are limited by sampling frequency, achieving accuracy only at the sampling interval level. To achieve higher accuracy, sub-sample estimation is necessary. This letter proposes a precise delay calibration method using maximum likelihood iteration for sub-sample delay estimation. The proposed algorithm starts with the frequency domain features, first transforming the delay estimation problem into a phase estimation problem, and then calculating the likelihood function of the phase difference. A cost function is established based on the maximum likelihood criterion, and the optimal solution is obtained using the Newton iteration method. Compared to other algorithms, the proposed algorithm achieves superior accuracy in sub-sample delay estimation, meeting stringent calibration requirements in radio astronomy. Simulation and experimental results verify the validation of the algorithm.