Generating Microwave Spatial Fields With Arbitrary Patterns

Resorting to the temporal excitation synthesis of a time-reversal mirror (TRM), we develop a method of how to physically generate the desired microwave fields in a predefined area. The new method composes the desired field patterns with a number of the time-reversal (TR) focusing fields generated by a TRM. We first decompose the region of the desired pattern into a number of spatial grids and then probe the system by situating a probe antenna at these grids one by one. After all TRM elements capture their responses to the probing signals emitted from all grids, we synthesize the TRM excitation with these responses based on the TR method. Thanks to the space-time focusing property of TR, a set of TR focusing fields is simultaneously generated when the TRM is excited by the synthesized excitation. These focusing fields are spatially distributed with their focal spots spaced by the grids. If the grids are closely spaced, the focal spots will overlap with each other and eventually produce a smooth microwave field of the desired shape. We successfully demonstrate the generation of different desired microwave fields in an aluminum cavity. Theoretically, this method can be exploited to generate arbitrary electromagnetic fields.