Array processing for passive localization of a source in the near field

This publication presents a coherent processing method for RF (radio frequency) source localization in a plane by employing a passive sensor array, widely distributed over a given area. The context of the localization technique discussed involves placement of the source in the near field of the sensor array and unknown character of the source in the sense that the transmitted signal, its power spectral density, and its timing are unknown to the sensors. However, the sensors have ideal mutual time and phase synchronization, highly precise knowledge of their own location, and ideal communication link to a fusion center. The source location is centrally estimated by coherently processing the received signals. For this, an estimator is derived exploiting the source location information in the phase difference of the received signals at pairs of sensors. An analytical expression is developed for the Cramer Rao lower bound (CRLB) relating the mean square error (MSE) of the location estimates to the source signal parameters and sensors layout. Numerical examples and Monte Carlo analysis validate the close form expression developed and show the high accuracy capabilities of the source localization via the presented coherent processing method.