Joint Multierror Calibration by Merging Errors in Distributed Coherent Aperture Radar Using Strong Scatter Echoes

Full coherence needs strict phase synchronization in distributed coherent aperture radar (DCAR). However, DCAR suffers from various types of errors, including gain-phase, time alignment, and antenna position errors (APEs), which seriously damage phase synchronization. In addition, they are coupled and difficult to estimate individually. Thus, calibrating these coupled errors is still an intractable problem in improving coherence performance. In this article, we propose a joint multierror calibration method by merging errors using echoes of several inaccurate-position strong scatters. First, orthogonal waveforms are transmitted in DCAR to obtain transmitting degrees of freedom (DoF), and its echoes from strong scatters are investigated to estimate the coupled errors jointly. Second, parameter extraction is applied to acquire time delays (TD) and gain-phase of echo peaks as measurements in error estimation. In particular, gain-phase and time alignment errors are merged as equivalent gain-phase errors, avoiding the high precision requirement of time alignment errors. Then, a practical approximation of the maximum a posteriori (MAP) estimator and singular value decomposition (SVD) are employed to obtain estimation solutions for balancing efficiency and precision. Finally, the Cramér–Rao lower bounds (CRLB) of the required parameters and critical unknowns (e.g., antenna positions, radar positions, and attitude angles) are derived to analyze the estimation performance. Simulations are employed to validate the necessity of joint calibration, the advantages of merging errors, and the effectiveness of the proposed method.