As outlined in the Network 2030 vision of the International Telecommunication Union, the integration of space-based and terrestrial networks is expected to be a cornerstone of communication systems beyond 5G (5G+). In this context, the rapid expansion of satellite networks introduces significant challenges, particularly in terms of interoperability with existing infrastructures and the need for new management strategies adapted to highly dynamic network topologies.

To address these challenges, wireless communications operating in millimeter-wave frequency bands are emerging as a key technological solution. In an increasingly connected society, where extremely high data traffic densities are expected, future 5G+ networks must achieve unprecedented levels of connectivity, capacity, and scalability. Within this framework, the satellite segment becomes an essential component of the overall communication ecosystem.

Globally, several frequency bands have already been allocated for 5G deployment, initially focusing on frequencies below 6 GHz. However, higher frequency bands such as 26, 38, 60, and 86 GHz are already in use, with significant technological progress. The natural evolution of wireless communications points toward even higher frequencies, where the sub-THz spectrum is expected to play a key role in future 6G systems, both for terrestrial and satellite applications.

In this regard, the International Telecommunication Union has recently identified several sub-THz frequency ranges for 6G research. In particular, Resolution COM6/17 from the World Radiocommunication Conference 2023 defines bands such as 102–109.5 GHz, 151.5–164 GHz, 167–174.8 GHz, 209–226 GHz, and 252–275 GHz. The development of technologies operating in these frequency ranges is therefore crucial to address the challenges of next-generation communication systems.

The sub-THz band (92–275 GHz) offers the potential for ultra-high data rates and advanced sensing capabilities. However, it also presents significant challenges, particularly due to increased propagation losses, which complicate reliable signal transmission.

According to the European Vision for the 6G Ecosystem published by the 5G Public Private Partnership, sub-THz technologies are part of two key enabling areas for the future 6G air interface:

• Millimeter-wave (mmWave) communications: These bands provide large bandwidths, which are essential for 6G. While currently used in 5G NR (below 50 GHz), frequencies above 100 GHz are expected to be required in the future. Applications include access networks, fronthaul, autonomous driving, and smart manufacturing. Key challenges involve efficient beamforming, energy efficiency, and achieving high performance at low cost.

• THz communications and advanced materials: To reach even higher data rates (0.1–10 THz), advances in semiconductor technologies, new materials, and RF architectures are required. Overcoming current efficiency and fabrication limitations will be essential to balance performance and cost.

Designing antennas at sub-THz frequencies involves significant challenges. While these antennas offer major performance improvements, fabrication and measurement processes introduce important constraints.

The scientific community has explored multiple approaches to address these challenges. Many solutions are based on adapting conventional microwave designs to higher frequencies, including horn antennas, planar structures, dielectric lenses, reflectarrays, and resonant cavities.

However, although design methodologies can often be scaled, fabrication techniques require fundamentally new approaches:

• CNC micromachining
• Electrical discharge machining (EDM)
• Additive manufacturing
• Advanced photolithography
• Substrate Integrated technologies
• Silicon micromachining

Building on the expertise of the research team, this project aims to advance the development of antenna systems for future 6G communications by focusing on:

• High-gain antenna design
• Advanced manufacturing techniques
• Cost-effective and high-performance solutions
• Experimental validation of prototypes

The project targets both terrestrial and inter-satellite applications, operating in the D and G bands (110–220 GHz), with potential extension to even higher frequencies.

The technologies for future 6G applications require a significant technological advance with respect to the current state of the art, therefore the starting assumptions of this project are the following:

• Hypothesis 1: New design and manufacturing techniques for future RF components

  By combining the synthesis methods developed in previous projects, optimal and competitive designs can be achieved that meet the demands of future radio systems in the microwave and millimeter bands, both in waveguide and planar technology. Another option for developing components in the millimeter band is to use advanced non-contact design technologies that eliminate the problem of alignment or perfect contact that is required between parts when working at very high frequencies. These developments are of interest not only to the radio system, but also to those working with multilayer structures and THz measurement techniques, such as the aerospace/aeronautics industry. As for advanced manufacturing approaches, higher precision additive manufacturing techniques, such as micro-resolution 3D printing, or photolithography, deposition or coating techniques can be employed.

• Hypothesis 2: Antenna Technologies for the Hyperconnected Future

  Identify research scenarios for devices linked to applications of future 6G communications systems. From this identification, antenna technologies will be developed to meet the requirements of both terrestrial and satellite communication applications, point-to-point and point-to-multipoint mobile communications, for D and G bands (110GHz – 220 GHz) and above.

• Hypothesis 3: New evaluation scenarios to promote innovation and transfer in communication systems

  The generation of knowledge and the development of emerging technologies, which have an impact on the resolution of present and future needs of our society, through the creation of technology, has shown that any technology must be properly evaluated. Thus, this project will develop the prototypes and demonstrators necessary to validate the disruptive technologies and techniques developed in the project. The starting hypothesis is that these devices will be available to society and this project will promote collaboration with companies in the design, manufacturing and measurement processes of radiant systems in the future Sub-THz bands to which 6G is intended to reach.

In view of the starting hypotheses, the general objective of the project is based on the development of passive antenna technologies and RF subsystems in sub-terahertz bands, including both design, manufacturing and measurement, and propose solutions for the future terrestrial and space-based communications ecosystem for the road to 6G. The specific objectives (SO) are:

• SO1. Analysis and specification of requirements for characterization of future 6G communications environments for two types of scenarios: short-range terrestrial communications and inter-satellite communications.
• SO2. Development of design techniques and procedures for radiating devices based on field confinement in D-band and G-band.
• SO3. Application of new manufacturing technologies for D and G band antenna systems based on additive manufacturing, microprecision laser cutting or photolithography, among others.
• SO4. Development of new antenna measurement techniques designed and manufactured with innovative technologies in D, G and higher bands, as well as improvement of the performance of measurement systems in these bands.
• SO5. Transfer research results to the business and productive sector and ensure long-term scientific cooperation of the two participating research groups.