Bistatic Far Field Fraunhofer Distance Versus the Transmitter and Receiver Spherical Angles and the Target Parabolic Profile Features

For radiation or scattering problems, the Fraun-hofer distance allows us to define the far field zone. It dependson the largest dimension of the target or aperture and on thewavelength. This article shows that this distance can be expressedfrom this conventional Fraunhofer distance multiplied by a newfunction. It depends on the transmitter and receiver sphericalangles and on the target or aperture profile features, assumed tobe a paraboloid. This function is positive and smaller or equalto one, which means that the conventional Fraunhofer distancecan be overestimated. In addition, the criterion is generalizedto the case where the receiver and transmitter must be bothin far field. From the Rao-Wilton-Glisson Galerkin method ofmoments, the comparison of the scattered field computed bothin near and far fields validates the closed-form expressions of thenew Fraunhofer criterion.