Fresnel inspired superstrate

Miniaturization of axial-mode helical antennas often leads often to a significant degradation of gain and directivity due to the reduced effective aperture and disturbed current distribution. In this work, a compact and lightweight approach for compensating these drawbacks is proposed using Fresnel-inspired dielectric superstrates fabricated by 3D printing techniques. Unlike classical Fresnel lenses, the presented superstrates are designed to operate in close proximity to the antenna aperture. Several superstrate geometries with discretized phase-correcting zones were developed based on analytical Fresnel formulations. The influence of key design parameters was systematically investigated. Simulation results demonstrate that all proposed superstrates significantly enhance the gain of a miniaturized helical antenna, restoring or even exceeding the performance of a full-size reference antenna. Experimental validation was carried out in a semi-anechoic chamber over the 2.5 - 3.5 GHz frequency band, confirming the simulation trends despite expected measurement losses. Among the tested designs, compact superstrates provide a favorable trade-off between size, weight, and radiation performance, while larger structures offer maximum gain improvement. Transmission measurements further confirm improved performance across a wide bandwidth. The presented solution enables antenna size reduction without sacrificing radiation efficiency, making it attractive for satellite communication systems, compact RF terminals, and space-constrained wireless applications.