The objectives of the activity are to perform antenna system trade-offs relevant to the realization and in-orbit assembly of large arrays in Frequency Range 1 (FR1), to identify critical functions and technologies, to provide some demonstration of critical functions and to define a roadmap to make such antenna systems available. Targeted Improvements: Enabling satellite communications for unmodified terrestrial 5G user equipment operating in FR1. Description: There are on-going developments of very large deployable arrays in UHF for direct access to unmodified user equipment (e.g., smartphones). This has been triggered by various on-going studies initiated by 3GPP to assess scenarios of interest integrating terrestrial and non-terrestrial networks. As expected, the link budget isthe main challenge due to the limited performance of unmodified UEs. This requires large antenna apertures, even in low Earth orbit, while the wide field of view limits the use of reflector-based solutions. Some reported developments consider aperture diameters up to about 30 m in diameter which pose serious challenges for stowage and launch. In parallel, there has been a growing interest forin-orbit assembly and manufacturing, with various activities supported by ESA on this topic. In-orbit assembly may bring a solutionto the technological limitations encountered by large deployable array antennas, enabling a modular approach compatible with smaller launchers, possibly reducing cost and deployment complexity. The antenna would be constituted of deployable array modules, which would interconnect once in orbit, each having a simpler deployment when compared to a single antenna approach (e.g. 1D deployment instead of 2D deployment). However, in-orbit assembly may lead to some constraints on the radiating element distribution and the large spacing between them may produce grating lobes over the field of view; hence it is important to assess the feasibility of the overall system while analysing associated antenna performance to ensure a successful product. This activity will therefore carry out a system study about the feasibility and performance of large antenna systems assembled in orbit for 5G communications in FR1 including an assessment of the overall system complexity versus alternative approaches. In particular, the activity will identify critical elements, which may include antenna panel technology, in-orbit assembly equipment (e.g., docking radars, latching mechanisms), attitude control and beam forming techniques to avoid stringent requirements on the resulting ensemble to name a few. Demonstrators of critical functions shall be manufactured and tested, to de-risk the concept and a technology roadmap shall be elaborated.