Additional constraints in the maximum likelihood method to protect against element perturbation

The maximum likelihood method (MLM) provides high resolution direction-of-arrival (DOA) performance for an array of sensor elements. Its performance, however, is significantly degraded under conditions of individual element phase errors. Such phase perturbations can be caused by channel phase errors, array element placement errors, and frequency errors. By introducing robust constraints into the MLM structure, a phase-robust DOA algorithm is developed. The algorithm protects output signal-to-noise performance of signals impinging on the array against phase errors. Simulations of the algorithm are presented in the presence of random element placement errors