Characteristic Modes Analysis of Non-Uniform Metasurface Superstrate for Nanosatellite Antenna Design

This work addresses the use of the Characteristic Modes Analysis (CMA) for tailoring a Metasurface (MTS) in view of exploiting it in compact, low-profile, Circularly Polarized (CP) antennas. The investigated non-uniform MTS is exploited as a superstrate in the design of a novel compact and low-profile antenna for nanosatellite applications. The MTS consists of a $3\times 4$ array of unequal patches arranged in a rectangular lattice. The antenna parameters are carefully tailored by using the CMA to achieve a significant performance enhancement with respect to a uniform MTS in terms of both Axial Ratio (AR) bandwidth and aperture efficiency. The reliability of the CMA approach is verified by assessing the overall performance of the whole radiating structure comprising the stripline feeding excitation. The proposed MTS antenna is compact ( $0.068~\lambda 0$ ) provides a remarkable aperture efficiency going from 86 % up to 96 % and an AR coverage in the upper hemisphere greater than 84 % within the desired S-band (2.025 – 2.29 GHz).