Impact of Multiple RIS on Channel Characteristics: An Experimental Validation in Ka Band.

In this work, we present the results of an experimental validation of the use of multiple Reconfigurable Intelligent Surfaces (RISs) in indoor scenarios. The setup employs a Transmitting and a Reflecting RIS in the Ka band with more than 400 elements each. Two different 1-bit Unit Cell (UC) based on PIN-diode technologies have been designed to realize the RISs. The Transmitting RIS (T-RIS) is used on the Base Station (BS) side to perform steering towards the User Equipment (UE), or the Reflecting RIS (R-RIS) acting as extender. The channel responses are analysed over a wide band (25-35 GHz) to investigate the impact of the phase distribution over RISs, as well as the antenna employed on the BS or UE side. Finally, the Multi Path Components (MPCs) in different Line of Sight and Obstructed Line of Sight, are estimated by means of space-alternating generalized expectation-maximization (SAGE) wideband algorithm, and analysed to highlight the use of RISs.