INTERFERENCE CANCELLATION IN SELF-COHERING ARRAYS
This dissertation is devoted to self-cohering of a large, random, nonrigid antenna array in the presence of interference. The techniques of self-cohering by self-survey and by adaptive beamforming are addressed. Both of these techniques make use of phase information from beacon signals. In such self-cohering techniques, interference must be cancelled locally at each array element where phase measurements are made. Three interference cancellation schemes which meet this local cancellation requirement are introduced: an element-pair approach, an approach focusing on single elements with injected reference, and an approach focusing on single elements (subarrays) with controllable radiation patterns.^ Two issues which are not directly related to interference cancellation are also addressed. The essence of the phase center concept in an antenna array sheds light on the self-survey process. Two techniques, a multiple frequency method and a minimum least square method, are developed for resolution of the phase-measurement ambiguities associated with self-survey.^ The self-survey process employs a radio navigation technique (i.e., phase multilateration) to accurately locate the flexible array elements and calibrate the cable delays, aiming at an application for wide-angle scanning with high angular resolution and accuracy. The self-survey system in effect determines a least-square phase-error fit for the relative phase centers of the array elements and therefore reduces the power gain loss of the array to a minimum value. The best-fit phase centers partially compensate for the actual phase profile of a nonideal radiator and also reduce the effect of phase perturbations; e.g., those caused by a turbulent transmission medium.^ A least-mean-square (LMS) steepest descent method is used to derive a phase-shift control loop and a gain-phase-shift control loop. The control loops are applied throughout for interference cancellation. The control loops have similarities to a phase-locked loop (PLL), a squaring loop and a Costas loop. Each loop is a power inversion loop in principle. It is found that complex weight control and gain-phase-shift control have comparable transient performance and lead to equivalent error-free steady-state solutions. The interference residue associated with such (gain-) phase-shift control loops is shown to result in a tolerable beacon signal phase distortion.^ The interference cancellation scheme using single elements (subarrays) with controllable radiation patterns is applied to an element-pair subarray, a linear subarray and a circular subarray. This scheme is essentially a spatial filtering technique (adaptive array processing) and is the most promising scheme for application in self-cohering arrays. ^
Engineering, System Science
CHUNG HSIN LU,
"INTERFERENCE CANCELLATION IN SELF-COHERING ARRAYS"
(January 1, 1980).
Dissertations available from ProQuest.