A network description for antenna problems

A complete network description for an antenna is realized via a modal decomposition of the electromagnetic fields surrounding the structure. The representation contains the transmitting, receiving, and radar scattering properties of the antenna. A scattering formulation permits the antenna´s power gain, directivity, effective area, and radar cross section to be expressed as a functional on the elements of its scattering matrix. For an array of antennas, the excitations which optimize its power gain and the loading network which maximizes its radar cross section are determined. The philosophic approach of circuit theory is employed for describing physical antennas. A set of canonical antenna elements having simple properties is first defined; in addition, an actual physical structure is represented as an array of canonical elements. The method is applied to the case of a Yagi-Uda array. The possibility of loading the array with active impedances is investigated.