On screening of antenna near fields by a finite ground plane

Compact back-to-back antennas are proposed for in-band full duplex relays to improve spectral efficiency and increased end-to-end data rates of a wireless link. The main technical problem in realization of these systems is the requirement for high isolation between closely located back-to-back antennas. One needs to understand how the electromagnetic near fields below a finite ground plane contribute to the mutual coupling between compact back-to-back antennas. In this paper, we present an analysis of the electromagnetic fields below a finite ground plane when excited by basic electric and magnetic sources with both horizontal and vertical orientations. The image theory and physical optics approximation are used for direct computations of the fields at close distances below the ground plane for various ground plane dimensions. This provides an insight on coupling mechanisms and isolation obtained for different ground plane dimensions for different types of sources. The analysis is scalable to all frequencies of operation. It is observed that a combination of vertical electric and magnetic dipoles on different sides of the ground plane or horizontal electric dipoles used in conjunction with any other radiating elements can improve the isolation between back-to-back antennas.