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Array-Fed RIS: Validation of Friis-Based Modeling Using Full-Wave Simulations

K.K. Tiwari1, T. Flisgen2,3, W. Heinrich1,2, G. Caire1

Published in:

16th German Microwave Conference (GeMiC 2025), Dresden, Germany, Mar. 17-19, ISBN 978-3-9820397-4-9, pp. 611-614 (2025).

Abstract:

Space-fed large antenna arrays offer superior efficiency, simplicity, and reductions in size, weight, power, and cost (SWaP-C) compared to constrained-feed systems. Historically, horn antennas have been used for space feeding, but they suffer from limitations such as bulky designs, low aperture efficiency (≈ 50%), and restricted degrees of freedom at the continuous aperture. In contrast, planar patch arrays achieve significantly higher aperture efficiency (> 90%) due to their more uniform aperture distribution, reduced weight, and increased degrees of freedom from the discretized aperture. Building on these advantages, we proposed an array-fed Reflective Intelligent Surface (RIS) system, where an active multi-antenna feeder (AMAF) optimizes power transfer by aligning with the principal eigenmode of the AMAF-RIS propagation matrix T. While our previous studies relied on the Friis transmission formula for system modeling, we now validate this approach through full-wave simulations in CST Microwave Studio®. By comparing the Friis-based matrix, TFriis, with the full-wave solution, Tfull.wave, we validate the relevance of the Friis-based modeling for top-level system design. Our findings confirm the feasibility of the proposed AMAF-RIS architecture for next generation communication systems.

1 Technische Universität Berlin, Germany
2 Ferdinand-Braun-Institut (FBH), Germany
3 Brandenburgische Technische Universität, Germany

Keywords:

Array-fed reflectarrays, reflective intelligent surface (RIS), full-wave simulations, Friis-based modeling validation, D-band communications.

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