Self-Sustained Rigid Fully Metallic Metasurfaces to Enhance Gain of Shortened Horn Antennas
Foez Ahmed, Muhammad U. Afzal, Touseef Hayat, Karu P. Esselle, Dushmantha N. Thalakotuna
Abstract
This paper presents mechanically robust, low-cost, lightweight, and polarization-independent metallic metasurfaces (MMs) to enhance the gain and directivity of shortened horn antennas. The MM was designed based on the strategy of correcting the actual phase errors probed on the aperture of the horn using the near-field phase-transformation principle. The fundamental unit cell of the MM is made of a pair of cross slots created in a monolithic thin conductive sheet and is entirely free from high-cost dielectrics. The lack of dielectrics makes MM lightweight, cost-efficient and easy to fabricate the prototype for mass production. The MM has a 2D array of unit cells arranged to increase the gain of the shortened horn by improving aperture efficiency through local phase transformation in a wide frequency band. The concept is demonstrated by designing MMs for shortened horns with different heights and the same physical aperture at the center operating frequency of 12.5 GHz. The maximum gain-bandwidth with MM is achieved for the shortest horn, which is validated by measuring the physical prototype. The results indicate that horn gain with MM increases by 9.2 dB (from 11.1 to 20.3 dBi) and has a 3-dB fractional gain-bandwidth of 10.4%. The weighted density of the fabricated MM is only 0.87 g/cm<sup>2</sup>. Including MM, the total antenna height is around 61% shorter than a conventional air-filled horn having a similar peak gain.