The following paper presents an application of the principle of collapsed distributions to the diagnosis of square grid planar antenna arrays. The principle states that each azimuthal cut of a planar array pattern (array factor), with \(\phi = \phi _o\) , is equivalent to the pattern generated by a linear array. The linear array is obtained by projecting all of the excitations of the planar antenna on to the line \(\phi = \phi _o\) . This idea is used to develop an algorithm for detecting faulty elements in damaged planar arrays, where only on-off faults are considered. The algorithm uses far-field complex samples of the damaged pattern taken along the \(\phi = 0^{\circ }, 45^{\circ }, 90^{\circ }\) cuts. It uses this information to perform an exhaustive search to find the three collapsed linear arrays (in the specified directions) that best match the samples of the damaged pattern. Thus, the coordinates of the faulty elements along the three mentioned axes can be easily obtained. The algorithm was applied here to the diagnosis of a 76-element square grid antenna with circular boundary and quadrantal symmetry.
