High performance radomes

Antenna casings with low insertion loss and enhanced radiation patterns

Communications Materials

The geometry of the spherical impedance metasurface with the interior visible. r0 is the radial distance to the metasurface, r1 is the radial distance to the spherical image surface, θ is the elevation angle, and ϕ is the azimuthal angle.

Antenna casings are commonly used to protect antennas from physical interaction with the environment. For example, traditional radomes shield antennas from rain, wind, and moving objects which could strike and harm the structure of the antenna. Conventionally, these radomes have been constructed of a dielectric material, with the goal being to minimize the effect on the radiation pattern of an antenna over the operational frequency band. This method protects the antenna from the environment, but there are inherent costs to antenna performance in using the dielectric material. For instance, using a dielectric radome will cause some insertion loss and scatter a portion of the radiated energy emitted from the antenna, altering the antenna performance from expectations. Further, the amount of power in the main lobe of the radiation pattern will decrease and the sidelobe levels of the antenna will increase, changing the shape of the radiation pattern. Currently, the performance degradation caused by using a radome is outweighed by the benefits of protecting the antenna from the environment, so degradation is tolerated.

Existing methods addressing the above require the antenna and radome structure be designed concurrently to achieve the desired performance, increasing the risk that design limits of one would require re-designs of the other. Additionally, these methods usually require that the shape of the radome or antenna be modified from the standard spherical or cylindrical geometry, limiting the use of these products to new systems that can incorporate this shape change. Finally, these methods cannot form truly arbitrary radiation patterns and there is no explicit design procedure to directly synthesize these patterns.

The Navy has developed a system for creating antenna casings, such as radomes, that can reshape the distribution of electromagnetic energy emitted by an antenna into an arbitrarily defined pattern. The novel casings include cylindrical patterns with only azimuthal variation and antenna casings with spherical patterns having both azimuthal and elevation variations, each accomplished with an antenna casing of a fixed radial distance in the given coordinate system (either cylindrical or spherical). While the achievable amplitude variation of the desired angular pattern is dependent on the size of the antenna casing, the near-field scattering antenna casing can enhance the radiation pattern of a given antenna rather than degrade it like a standard antenna casing. This function is achieved by fabricating designed scatterers either within or on the surface of the material constituting the antenna casing. An advantage of these antenna casings is the ability to alter the source radiation pattern into any desired radiation pattern at any distance.

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