Roter rotational noise is analyzed in frequency domain for various geometric factors of blade; blade number, angle between the blades, chordwise shape and spanish tip shape. Hanson's method for rotor noise, originally developed for equally spaced rotors, is extended here to study the phase interference effects on the acoustic signals for the geometric factors including unequally spaced rotors. Monopoly and dipole terms are used to represent the source of the rotational noise. Acoustic signals at the far field and thear spectra are calculated at selected rotor tip Mach numbers.