Twelve versions of physical optics: how do they compare?

The physical optics (PO) theory is best known by its PO surface current, but this is only one of many possible versions of PO. Other versions of PO are generated by making one choice from each of the following three considerations: (a) defining the lit region according to the transmitter, or according to the receiver; (b) in the lit region, three possible current sources can in turn be formulated depending on the incident and scattered fields used; and (c) fields calculated by PO generally do not satisfy reciprocity. To overcome this deficiency, the problem can be solved twice; once with the original transmitter and receiver positions, and again with their positions interchanged. The average of these two solutions does satisfy reciprocity and is called the reciprocal solution. The above combination results in 12 (=2*3*2) versions of PO. Extensive numerical results are presented to illustrate the relative merits of the different versions.<>