Normally, the signals from an n-element phased array are combined by adding the voltage signals from the different antennas after proper delay and phase compensation. This summed voltage signal is then put through a square-law detector and an output proportional to the power in the summed signal is obtained. For identical elements, this phased array gives a sensitivity which is times the sensitivity of a single element, for point source observations. The beam of such a phased array is much narrower than that of the individual elements, as it is the process of adding the voltage signals with different phases from the different elements that produces the narrow beam of the array pattern. For some special applications, it is useful to first put the voltage signal from each element of the array through a square-law detector and then add the powers from the elements to get the final output of the array. This corresponds to an incoherent addition of the signals from the array elements, whereas the first method gives a coherent addition. In the incoherent phased array operation, the beam of the resultant telescope has the same shape as that of a single element, since the phases of the voltages from individual elements are lost in the detection process. This beam width is usually much more than the beam width of the coherent phased array telescope. The sensitivity to a point source is higher for the coherent phased array telescope as compared to the incoherent phased array telescope, by a factor of .
The incoherent phased array mode of operation is useful for two kinds of astronomical obervations. The first is when the source is extended in size and covers a large fraction of the beam of the element pattern. In this case, the incoherent phased array observation gives a better sensitivity. The second case is when a large region of the sky has to be covered in a survey mode (for example, in a survey of the sky in search for new pulsars). Here, the time taken to cover the same area of sky to equal senstivity level is less for the incoherent phased array mode. Only for a filled aperture phased array telescope are these times the same. For a sparsely filled physical aperture such as an earth rotation aperture synthesis telescope, this distinction between the coherent and incoheret phased array modes is an important aspect of phased array operation.