A Bidirectional Ray-Tracing Method for Antenna Coupling Evaluation Based on the Reciprocity Theorem

Abstract

A novel bidirectional ray-tracing method for solving antenna coupling problems is presented where the transfer function between the transmit and receive antennas is obtained by evaluating surface interaction integrals according to the reciprocity theorem. In order to eliminate the limitations of the reception spheres in the traditional unidirectional shooting and bouncing rays (SBR) method, both the transmitter and receiver are used for ray launching. The resulting rays are captured on an interaction surface, which is much more flexible in terms of size and shape than a reception sphere. The transfer function between two antennas is obtained by evaluating the reciprocity integral on this interaction surface by a specifically designed numerical integration procedure. It is shown that the new method has two advantages compared to the traditional unidirectional ray tracing. First, flexible interaction surfaces help to retain the accuracy in large geometries where the traditional unidirectional SBR fails due to reception spheres being limited in size and being missed by the rays. Second, explicit computation of single and multiple diffraction effects by the uniform theory of diffraction can be avoided and replaced by a physical optics like integration over the reciprocity interaction surface. Numerical results demonstrate the capabilities and advantages of the new approach.