Synthetic array autofocus system

Abstract

A system for automatically focusing a synthetic array through derivation of focus error signals which may be used such as by summing a priori data so that the synthetic array data may be optimally focused. Focus error data is derived by forming the synthetic array in three sub-array. The resultant outputs of these three sub-arrays are further processed together to extract data corresponding to the degree of total array defocus. For purposes of imagery generation, the phase and amplitudes of these three sub-array resultants are vectorially summed together and the resultant is magnitude detected to yield imagery output corresponding to the full synthetic array. For derivation of focus error data, the mean (bisector of the relative phase angle between the two end sub-array resultant vectors is measured. This derived bisector's phase angle is compared to the phase angle of the central sub-array resultant vector. The angle of the bisector relative to the central sub-array resultant is representative of the degree of defocus, and the sign of the angle is indicative of whether the array is over or under-defocused. For a properly focused array, the bisector of the two outer subarray resultants is in phase with the resultant vector of the center sub-array.