An adaptively phased, four-element array of thirty-foot parabolic reflectors for passive (Echo) communication systems

A description is given of an adaptively phased receiving antenna array consisting of four independently steered thirty-foot parabolic reflectors capable of operation to 15 Gc. The array has been designed as a research tool to demonstrate the principle of adaptively phasing the signals from independent array elements to achieve the same performance as would be obtained from a single equivalent aperture. The initial operating frequency has been chosen at 2270 Mc so that the array may be used in communication experiments using Echo I and Echo II passive satellites. The adaptive phasing principle is obtained by the use of a phase-locked receiver associated with each array element. The phase reference for each receiver is supplied from a common reference signal which may be obtained in three ways depending on signal characteristics. Among the advantages of this type of array are 1) ability to make separate phase corrections for each antenna, thus allowing for atmospheric inhomogeneities or for differential Doppler shift between the source and the individual antennas; 2) indifference to which particular grating lobe is chosen, because the adaptive nature of the individual phase-locked loops will always provide maximum gain; 3) potential for simple modifications to achieve interferometer or "data-processing" antenna behavior; 4) mechanical and electrical simplicity; 5) increased acquisition range for signal sources which are not known accurately in position. A detailed discussion is given of the design and various modes of operation of the phase-locked loops and receiver combining system. This is followed by a description of the automatic search and tracking functions, and their operational advantages in use with a moving target, the position of which is not known accurately. Finally, some results of preliminary tests with the system are given, which indicate that it will achieve its designed performance characteristics.