Recent Achievements on Passive and Beam Steering Transmitarrays at Millimeter Waves

Abstract

This paper reports an overview of recent advancements on transmitarray antennas at CEA-Leti in collaboration with IETR. Two fixed-beam and an electronicallysteerable prototypes are presented. The first fixed-beam transmitarray radiates orthogonal linear polarizations at K/Kaband. The second achieves wideband high-gain performance at 300 GHz using low-cost vialess technology. The reconfigurable transmitarray leverages on an efficient and low-power solution to attain beam steering and switchable circular polarization at Ka-band. Excellent scanning capabilities in a field of view of ±60°, with low axial ratio are experimentally demonstrated.

Hybrid Precoding Applied to Multi-Beam Transmitting Reconfigurable Intelligent Surfaces (T-RIS)

“…In practice, the equivalent channel is not perfectly known by the receiver and is estimated from known reference signals and time/frequency interpolation. The imperfect knowledge of the estimated channel Ĥeq can be represented by adding white Gaussian noise to the instantaneous channel, as expressed in (13):…”

“…For the rest of this work, we consider imperfect channel knowledge by performing a channel state estimation (13) with additional thermal noise (temperature of 25 • C).…”

“…The surface is composed of unit elements named unit cells. Unit cells based on Antenna-Filter Antennas (AFAs) are widely employed up to 140 GHz [13] because they can perform beamforming. They consist of a receiving antenna, a phase shifter, and a transmitting antenna.…”