Phased array antenna with coarse/fine electronic scanning for ultra-low beam granularity 



An antenna and scanning means therefor particularly useful in an aircraft landing system operating in the microwave frequency range. The antenna is of the line phased array type which includes digitally controlled phase shifters for each of the radiating elements of the array. The beam formed by the antenna is steered by incrementing the phase shift applied at each of the array radiating elements by an amount of phase which is dependent in part upon the position of the radiating element in the array. Phase increments sufficient to shift the beam position by one coarse step (0.1.degree.) are applied to symmetrically located radiating element pairs, pair by pair, until all elements have been incremented. The beam is thereby caused to move through one coarse step in a number of fine steps equaling the number of pairs of elements in the array. An additional feature of the scanning means is the application of phase increment to the array elements in a pseudo-random sequence. 

Phased array antenna with reduced phase quantization error 



Phase quantization errors in a phased array antenna are reduced by providing phase control signals which approximate ideal phase functions for symmetrical pairs of elements having an average phase value which is displaced from a nominal phase quantization value by one-quarter the smallest phase step. 

Distributed beam steering computer 



A distributive beam steering computer network for a radar phased array antenna is disclosed which provides direct drive for individual antenna phase shifter elements using a plurality of microcomputers co-located with each phase shifter. The microcomputers calculate the phase shift based on constants stored in a ROM which is located in each microcomputer and phase shift data comprising sin .alpha., sin .beta., and 1/.lambda. signals are distributed to all microcomputers over a single serial data line. The constants required for each shifter are different, and therefore, the ROM in each microcomputer is programmed for a specific location in an array antenna. A phase shift steering command for each element of the phased array antenna is calculated using a shift-and-add multiplication algorithm which is hard-wired into each microcomputer.