Abstract: A new beam synthesis technique of array antennas, namely Projection Matrix Algorithm (PMA), is investigated. The methods used for complex excitations optimization, and single beam synthesis under phase-only control are introduced firstly. Then the amplitude-only beam synthesis using improved PMA is presented. Furthermore, improved PMA is applied to the simultaneous synthesis of multiple object beams. Several engineering application examples are analyzed, including multi-beam synthesis of array antenna with the whole aperture and several sub-apertures under amplitude-only control, and multi-beam synthesis of array antenna under phase-only control with the common amplitude excitations. The patterns of the array antenna are effectively synthesized optimizing the excitations. The beam direction, beam-shape and side-lobe level requirements are all met. It is demonstrated that PMA is of effectiveness and wide applicability.