| Abstract: | The role of frequency is very important in electromagnetics since it may significantly change how a material interacts with an incident wave if the frequency spectrum varies. Here, a new kind of microwave window is demonstrated that has the unique property of controlling transmission and reflection based on not only the frequency of an incoming wave but also the waveform or pulse width. This is achieved by designing a planar periodic surface with circuit elements including diodes, which convert most of the incoming signal to zero frequency. This surface can preferentially pass or reject different kinds of signals, such as short pulses or continuous waves, even if they occur at the same frequency. Such a structure can be used, for example, to allow long communication signals to pass through, while rejecting short radar pulses in the same frequency band. It is related to the classic frequency selective surface, but adds the new dimension of waveform selectivity, which is possible only by introducing nonlinear electronics into the surface. Thus, the study is expected to provide new solutions to both fundamental and applied electromagnetic issues ranging from traditional antenna design and wireless communications to emerging areas such as cloaking, perfect lenses, and wavefront shaping. |
