Significant interest in reducing the antenna blockage in high-complexity or crowded communication systems has been recently highlighted by several authors. In this context, reducing the electromagnetic presence of an antenna or a sensor by tailoring its geometry, loading, or cover has been explored and demonstrated in several examples. Recently, it has been shown that ultrathin impedance surfaces may be applied to cover dielectric and conductive objects in order to suppress their overall scattering signature at the frequency of interest. These ultrathin surfaces may significantly reduce the total integrated scattering cross-section (SCS) of targets of moderate size (2 a≦λ), where a is the cross-sectional radius and λ is the free-space wavelength. For conducting objects, the bandwidth and suppression level of such “mantle cloaks” is mainly dependent on the conformability of the cover to its target, where more conformal designs lead to a stronger scattering suppression (>15 dB) over a narrow bandwidth (˜3%). Conversely, covers with a larger separation from the target, may achieve a more shallow suppression (˜5 dB) up to 30% fractional bandwidths.
A key feature of the scattering cancellation technique is the ability of the cloaked object to interact with the background region rather than being isolated as in other approaches to cloaking. These features are ideally suited for antenna applications, including blockage reduction from passive obstacles, elimination of the mutual coupling between closely spaced antennas, and the realization of low-visibility receiving antennas for sensing and monitoring applications. These electrically transparent antennas and sensors may be of great interest for tomography, imaging, and energy harvesting, in addition to exciting applications in crowded communication systems. However, there is not currently a means for utilizing such mantle cloaks in realizable antenna systems.
Researchers at The University of Texas at Austin have developed a communication system that reduces the mutual influence of antennas operating in similar or different frequency bands. The communication system includes a first and a second antenna operating in a first and a second frequency band, respectively, and placed in close proximity to each other. The first antenna is covered by a conformal mantle metasurface with anti-phase scattering properties, thereby canceling the scattering in the second frequency band. The conformal mantle metasurface consists of a patterned metallic sheet comprising slits both in an azimuthal and a vertical direction to reduce both vertical and horizontal polarization scattering. When the first antenna is a low-band dipole antenna and when the second antenna is a high-band dipole antenna, the conformal mantle metasurface reduces the low-band blockage without disrupting the performance of both antennas in terms of radiation pattern and impedance matching.
It is noted for clarity that the technique of the present invention is fundamentally different from radar cross section (RCS) reduction or low-observability stealth techniques; namely, the scattering cancellation technique herein achieves significant scattering reduction at all angles, also in the forward direction, which is particularly relevant in the context of antenna communications.