Project C12 - Passive Beam-Steering Reflector Arrays

Principal Investigator: Prof. Dr. Martin Hoffmann

As MARIE aims for mobile characterization and localization by electromagnetic sensing, beam steering of electromagnetic waves in the millimetre and submillimetre range is an important part. The beam steering devices have to be lightweight and energy-efficient for high mobility, and precise in their directivity for localized measurements. The increasing frequencies / decreasing wavelengths complicate conventional phased array antennas, but also open up new options for beam steering by MEMS. Especially a reflective beam steering comes into focus as it can easily be combined with the currently investigated MARIE on-chip antennas. For “light”, deflectable mirrors are well-known, but the required size for THz radiation would be too large for a MEMS solution. Alternatively, reflectarrays with individual phase tuning can be used. E. g. metamaterials-based MEMS systems have already been demonstrated, but the exact control of the directivity is still difficult. If the mechanical throw achieves at least Lambda/2 (resulting in a total phase shift of Lambda in free space), also a mechanical movement of individual reflectors in an reflectarray comes into focus. A passive reflectarray with mechanical phase shifting is proposed here. The goal is to investigate single reflectors first, that are switched stepwise with a resolution of 5 bit / 32 steps. In a second phase, the reflectors are integrated into rows by chip stacking and finally in reflectarrays. The frequency range at MARIE is well-suited for MEMS-based actuation.

A single reflector element requires electrostatic stepping drives, that allow for a total mechanical travel range of Lambda/2, here 600 μm or less. The intended technology focusses on an SOI approach that is already established and seems to be most suitable for this application.

Nevertheless, the actuation concept is challenging from the MEMS perspective: so far, no fully integrated stepping drives with a total throw of 600 μm are known for this application. Key challenges are the bearing of the reflectors with solid-state springs and the in-plane integration of a high number of actuators as well as the required chip stacking for rows / reflectarrays. Therefore, different approaches for the actuators and the springs have to be investigated before the most suitable design(s) are selected, realized and tested in MARIE.