u03bb d sin u03b8 0 thus the signals from the various radiators can be adjusted to be in phase along the a a plane if the phase of each radiator is increased by 2 u03c0 u03bb d sin u03b8 0 consequently at a point on the wavefront in the far field of the transmitter array the signals from the n radiators will add up in phase i e the intensity of the total normalized signal is a sum of the signals from the individual sources the constructed pattern has a well defined directional characteristic and a well pronounced angular dependence i e the transmitter pattern has a well defined transfer characteristic of the transmitter with respect to the angle u03b8 0 fig2 b depicts an arrangement of phases for the sources the system of fig2 operating in one preferred mode of operation the array of five sources is divided into two or more portions that are phased 180 u00b0 apart each portion has at least one source the sources of each portion radiate amplitude modulated light of equal intensity and are spaced so that the resulting beam of two or more equally phased sources has a substantially flat wavefront i e no gradient of photon density on the other hand there is a sharp 180 u00b0 phase transition a large gradient in photon density between two antiphased portions of the array thus the radiated field possesses an amplitude null and a phase transition of 180 u00b0 i e crossover phase which is due to the large gradient of photon density electronic scanning is performed by appropriately varying the apportionment of 0 u00b0 and 180 u00b0 phases on the sources the five element array of fig2 b can have the 180 u00b0 phase transition along four different parallel planes extending.