The sixth-generation (6G) wireless communications require substantial research and development in antennas, Radio-Frequency (RF) front-ends, and wave propagation characterization intended for frequencies ranging from 100 GHz to 1 THz. Sub-THz communications utilize new innovations in air interfaces and RF front-ends, such as massive antenna arrays, lens antennas, filter design, ultra-massive Multiple-Input Multiple-Output (MIMO), metasurface-based antennas, and reconfigurable intelligent surface technologies. In addition, antenna technologies will need to be tightly integrated, e.g., by using Antenna-in-Package (AiP) and on-chip antenna technologies, and the required signal integrity will necessitate high-performance vertical and horizontal interconnections and feed networks. Transmissions in the sub-THz band require low loss, low permittivity propagation, and high manufacturing tolerances for relevant antenna packages, whereas semiconductor substrates have typically higher permittivity and higher RC-delays in the package.

Currently, semiconducting and conducting structures are more often constructed with 2D metamaterials rather than pure metals. Sustainable green electronics also introduce new rules into the antenna and RF front-end development. To overcome previous technology thresholds, innovative multidisciplinary investigations, as well as research on theoretical models and experimental validation, are required. In addition, accurate and fast simulation models constitute an important part of future research.

This Special Issue welcomes the submission of original research and reviews articles that highlight new approaches to the research, design, and modelling of the characteristics of 6G wireless communication system applications and technologies. Articles focusing on radio channel modelling, antennas and antenna arrays, pattern synthesis, and the combination of these thematic areas towards 6G wireless communications systems will be considered.

Potential topics include but are not limited to the following:

• Research, design, and measurement of antenna arrays and lens antennas from 100 GHz to 1 THz
• Ultra-massive multiple-input multiple-output (MIMO) and hybrid analog and digital beamforming
• Beamforming architectures with optical interconnections
• Metasurface-based antennas and reconfigurable intelligent surfaces
• Antenna architectures for simultaneous communication and sensing/control
• Radio propagation measurement, modelling, and simulations
• Antenna-in-Package (AiP) and Antenna-on-Chip (AoC) technologies with proper technology solutions
• RF/microwave filter design for 6G applications