Frequency selective surfaces (FSS) are used as filters through which electromagnetic energy within a specific frequency range and having a prescribed polarization may be selectively propagated or not propagated. FSSs generally consist of an electrically conductive layer in which patterns of frequency scattering elements, generally in the form of apertures, are formed. The electrically conductive layer is usually supported by a dielectric substrate.
Radomes are enclosures, which protect antennas from the environment and may incorporate FSSs. A typical radome is constructed of a dielectric layer or a combination of dielectric layers which include an FSS to provide frequency selective attributes. However, the FSS is in general static, yielding a fixed pass/stop band performance. A further limitation of conventional radomes is that the enclosed antenna is exposed to many different types of electromagnetic threats, i.e., jammers generating signals in the operating band of the antenna. The radome must pass signals in the antenna operational frequency band for proper functioning of the antenna and associated systems. This exposes the enclosed antenna to jamming signals and other types of interference. Therefore, it is desirable to be able to selectively filter out signals having particular wavelengths over certain intervals of time (e.g., when the enclosed antenna is non-operating or receiving only at a particular wavelength). Moreover, a further need exists for an FSS that has frequency scattering characteristics that may be selectively modulated in time.
USPTO Backgrounds
USPTO Backgrounds