In Physical Optics (PO) we find an approximation for the current on a metallic surface and perform a brute force integration over each tiny incremental current element to obtain the field at some location. The method is closely related to Huygens principle. As such, the integration is very time consuming on normal CPUs but can be carried out in a reasonable time using a GPU. Essentially each field integration can be carried out simultaneously by 480 cores in the case of the GTX480. The method is ideal for demonstrating the incredible power of today´s GPUs.
The following example shows the field calculated by PO for the Cassegrain antenna discussed in the Phase Retrieval section. There are 1024x1024 field points. The main reflector is 292 wavelengths in diameter and the integration interval is 1/8 of a wavelength, meaning that well over 4 million elements were integrated at each of over one million field points. The time taken was about 17 minutes.
In the following picture B shows the field scattered by a metallic head illuminated at 94GHz (the head model has been compressed to about 5cm in the axial direction), A shows the original polygon head model, C and D is the reconstructed field at the plane through the center of the head. The phase D gives depth axial information.