Measurement of array element excitations using a planar near-field range

It is often useful to know the element excitations of an array antenna. This information may be used to adjust the phase shifters of an electronically scanned array, or to verify the design of an antenna with a fixed excitation. It can be difficult, however, to measure the element excitations directly without disturbing the field fo the antenna. This paper describes a procudure to calculate the excitation of each radiator from a near-field scan of the antenna. First, the plane wave spectrum of the antenna is computed from the near-field data. This is divided through by the spectrun of a typical array element. Integration then yields the complex element excitations, which include any mutual coupling effects that may be present. The precise location of each radiator relative to the near-field data is essential for this calculation. Results are given for measurements of a C-band circularly polarized array of potter horns fed by a squareax network.