Reconfigurable transmitarrays for beam steering and beam forming at millimetre waves – TRANSMIL

TRANSMIL is a fundamental research project aiming at making major innovations in modeling, design and demonstration of electronically-reconfigurable transmitarrays (TAs) with beam-steering and beam-forming capabilities at millimeter-wave frequencies (Ka band). It fits in the thematic frame “Société de l’information et de la communication/Réseaux numériques à haute performance” (mobility, high data rate, new broadband terminals).

A TA is typically composed of one or more focal sources illuminating a first antenna array operating in receive mode and connected, using phase-shift elements, to a second antenna array operating in transmission mode. P-i-n diodes, RF-MEMS switches, varactor diodes, ferroelectric varactors, liquid crystal, etc. can be integrated in the unit-cell in order to electronically control the unit-cell transmission phase, and thus reconfigure the antenna beam.

TAs are a recent cutting-edge antenna concept for the development of new-generation smart and high-performance telecommunication systems (high data-rate point-to-point and multi-point wireless link, heterogeneous networks, etc.) and radar systems (imaging, surveillance, security, intelligent transport systems, etc.). TAs are high-gain antenna systems realized using multilayer printed circuit technology, which leads to a cost-effective, robust, reliable and ultra competitive solution for high-volume applications. Thanks to their spatial feeding technique, TAs (as reflectarrays as well) are extremely attractive compared to traditional phased arrays that suffer from large insertion loss in their lossy and bulky beam-forming network. TAs exhibit also a unique advantage compared to reflector antennas and reflectarrays: they can be integrated onto various platforms (buildings, vehcles, aircrafts, UAV, high speed trains, public transportation systems, etc.) since they do not suffer from any feed blockage effect (in contrast to reflectarrays), thus leading to smart skins systems.

Several proofs of concept have been presented in the literature, but major theoretical and practical aspects are not studied yet. In the current state-of-the-art, there is no demonstration of electronically-reconfigurable TA at Ka-band based on mature technology with beam-steering and beam-forming capability. Advanced techniques and numerical tools for beam-synthesis applications must be demonstrated and developed to study and optimize their performance in terms of bandwidth and sensitivity to the phase quantization, F/D ratio, and unit-cell geometry. New concepts must be investigated to reduce the total volume of TAs and facilitate their integration onto host platforms. Multi-facetted TAs are not yet demonstrated.

The TRANSMIL global objectives are twofold: i) implementation (for the first time) of advanced numerical tools for the design and optimization of complex TAs with multi-facetted or conformal configurations, and ii) first worldwide demonstration of an electronically-reconfigurable conformal TA in Ka-band (26 - 40 GHz) built on mature technologies. Several experimental demonstrations are planned to reach these ambitious goals: unit-cells, passive and electronically-reconfigurable TAs.

The TRANSMIL project is composed of 4 workpackages (WP): project coordination and results exploitation (WP1); specification and design of TAs (WP2); passive and electronically-reconfigurable unit-cell design (WP3); and advanced TA design (WP4). The total effort equals 120 persons.month (duration: 36 months).

The consortium gathers two partners (one research institute and one academic institution): CEA LETI and IETR, both with a very strong and unique expertise on TAs. Indeed CEA LETI and IETR have been collaborating very closely on this topic since 2006 and are the authors of one patent and several journals and conferences papers on TAs. Our recent demonstration on electronically-reconfigurable TA at X-band defines today the state-of-the-art at the international level.