6G LICRIS research project

6G LICRIS project overview

RIS are thin, energy-efficient surfaces made up of many individually adjustable unit cells. By tuning the reflection coefficient of each cell, an RIS can redirect a base station’s radio wave toward a user device, including into areas without a direct line of sight (NLOS). This makes RIS a candidate technology for 6G coverage and capacity improvement, particularly in the millimeter wave range, where path loss is high.

Unlike a classic RF amplifier or repeater, an RIS works passively and needs no active RF amplification. Its use only makes economic sense once manufacturers can produce it cost-effectively and at scale. That’s why the 6G LICRIS project therefore combined the development of new liquid crystal RIS technology with the development of compact, cost-efficient measurement and characterization methods.

Rohde & Schwarz coordinated the consortium, which included Ericsson Antenna Technology Germany, Merck KGaA, IMST GmbH, brown-iposs GmbH, Fraunhofer HHI, the University of Stuttgart (Institute for Large Area Microelectronics) and Technische Universität Berlin. Associated partners included Ericsson GmbH, Airbus Defence and Space, Robert Bosch, NXP Semiconductors Germany and m4 wireless.

Why RIS matters for 6G

RIS are a type of metamaterial: engineered structures whose electromagnetic properties go beyond those of natural materials. An RIS arranges many small unit cells - or meta-atoms - across a smart surface and addresses each one individually, similar to the pixels of a display. Adjusting the state of each cell steers the reflected wave in a controlled direction, a principle known as RIS beam steering. Because each cell can shift the phase of the reflected wave, an RIS functions as a phase shifting surface for RF signals.

Until now, engineers have largely treated the radio channel between base station and device as fixed and passive. RIS technology lets operators actively adjust the radio channel during operation. This kind of RIS radio channel control can improve coverage and data throughput while reducing energy consumption, and it opens up optimization approaches beyond the classic Shannon model of wireless communications.

The 6G LICRIS project focused on a liquid crystal metamaterial approach. A liquid crystal RIS follows the same basic design as a liquid crystal display: the liquid crystal acts as a tunable dielectric between metal electrodes, and a control system sets the state of each unit cell across a large matrix. RIS designers can transfer concepts already established for LCD manufacturing to RIS, with adaptations for RF use. In addition, existing LCD production lines can, in principle, also manufacture liquid crystal RIS. This directly supports the cost efficiency that RIS for wireless communication needs to become commercially viable.

Rohde & Schwarz contribution to the LICRIS project

The project organized its work into seven work packages. There was the cross-cutting management package AP0 and six technical packages, AP1 to AP6, which covered:

• Use cases and requirements
• RIS technology and development
• Simulation and characterization
• Radio environment and channel modeling
• Network integration and proof of concept
• Rohde & Schwarz led AP0 and contributed to AP1, AP2, AP3, AP4 and AP6.

The most important RIS measurement parameter is its angle-dependent reflection or scattering pattern. Measuring this pattern requires far-field conditions. This is challenging because RIS components are electrically large and frequency-selective. For a 20 cm × 20 cm module at 28.35 GHz, a direct far-field measurement would need a minimum distance of about 15 meters. To cover the full upper hemisphere, a measurement system would need to be roughly 30 meters in diameter. Scaled-down measurements are not possible due to the frequency selectivity of RIS.

Monostatic measurement method and 2-D MBET

In work package AP3.2, Rohde & Schwarz developed and validated a monostatic radar cross-section (RCS) measurement setup with a collocated transmitter and receiver. Rohde & Schwarz combined it with a two-dimensional extension of the Monostatic-to-Bistatic Equivalence Theorem (MBET), which reconstructs the bistatic reflection pattern for any angle of incidence from a single monostatic measurement. This method enables the characterization of RIS as phase shifting surfaces using standard, commercially available compact antenna test range (CATR) chambers. This leads to a total measurement footprint of less than 1.5 m² instead of the 50+ m² a conventional bistatic far-field setup needs.

Rohde & Schwarz validated the method against full-wave simulations, an analytical metal-plate reflection model and a purpose-built bistatic reference setup using two R&S®ATS800B CATR systems on a custom circular rail system.

Across three measurement campaigns in 2024 and 2025, Rohde & Schwarz and project partners characterized 10 liquid crystal RIS demonstrators, running a total of 90 calibration and 96 far-field measurements. Tests with modulated 5G signals showed EVM deviations below 0.45 dB, confirming that an RIS behaves as a passive reflector without EVM-relevant nonlinearities, so simpler continuous-wave measurements are sufficient for qualification.

Additional Rohde & Schwarz contributions to 6G LICRIS

At the Teisnach manufacturing site, Rohde & Schwarz developed and prototyped semiconductor-based RIS module concepts for frequency ranges below 10 GHz (work package AP2.1.3), including a 6 GHz, 1-bit RIS with semiconductor RF switches and a waveguide-based measurement method for characterizing individual RIS unit cells. Rohde & Schwarz also manufactured the 4×4 subarrays for a dual-polarized 6 GHz PCB-based RIS developed with TU Berlin and brought its OTA test and measurement methodology into the definition of the project’s reference standard in AP1.

Key results of the 6G LICRIS research project

At project completion, the 6G LICRIS consortium reported the following main results:

• Material (Merck): New liquid crystal mixtures were optimized for the millimeter wave range, with tunability increased by around 20 %, losses reduced by around 8 % and stability down to −20 °C.
• RIS hardware (University of Stuttgart, TU Berlin): The first liquid-crystal-based active-matrix 3D RIS designed and manufactured in Europe has a 20 µm liquid crystal layer and switching times of about 20 ms. The partners built more than 20 functional RIS demonstrators.
• Measurement technology (Rohde & Schwarz): The monostatic measurement method with 2-D MBET post-processing enables RIS characterization in compact, commercial CATR chambers.
• Simulation (IMST): A full-wave RIS simulation model was integrated into the commercial simulator EMPIRE XPU.
• Channel and system level (Fraunhofer HHI, brown-iposs, TU Berlin): Indoor channel measurements at 28 GHz and 160 GHz, using an emulated RIS, showed an average path loss reduction of 11.9 dB in the D-band. The partners also extended the QuaDRiGa channel model with a scalable RIS model, added a system-level simulation framework and developed an O-RAN-compliant integration concept.
• Demonstration (Fraunhofer HHI and partners): A live 5G-NR end-to-end transmission using a steerable liquid crystal RIS in the FR2 band n257 was demonstrated at the project’s closing event.
• Standardization and IP: Rohde & Schwarz contributed the monostatic measurement method to the ETSI ISG RIS group specification GS RIS 008 on standardized RIS testing. It also secured the results through several patent applications.

The 6G LICRIS project concluded with a closing meeting and workshop on December 18–19, 2025, at the Fraunhofer HHI Science-Tech Space in Berlin, where the consortium presented its final results and demonstrators.

Building on the AP3 measurement work, Rohde & Schwarz plans to bring the monostatic RIS measurement method into its established measurement and antenna test product lines, with a compact RIS measurement system in preparation. The results also support RIS integration into mobile networks by feeding into ongoing ETSI and ITU-T standardization work.

Beyond RIS characterization, engineers can also apply the MBET method to other tasks, such as RCS estimation of large objects, radar target simulation and ray-tracing tools used for network planning.