Novel continuously tunable and miniaturized passive "slow-wave" phase shifters with fast response time for millimeter wave applications based on a combined Liquid Crystal (LC) and Nanowire-filled Membrane (NaM) technology

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Novel Liquid Crystal (LC) technology, which has been innovatively adapted beyond optics during last decade by TU Darmstadt, appears to be the most promising approach for tunable components at millimeter waves, since LC losses decrease with frequency. At 30 GHz, it features very low dielectric losses of tand < 0.006 and continuous tunability up to 27 %, resulting in a Figure-of-Merit (FoM) defined by the ratio of the maximum differential phase shift over the highest insertion loss in all tuning states of about 200°/dB or 110° /dB for hollow waveguide or microstrip line phase shifters, respectively. Although planar technologies own system-inherently higher losses than hollow-waveguide topologies, they are low-profile and can easily be realized, utilizing automated manufacturing techniques similar to well-established LCD technology. This enables a low-cost fabrication of larger arrays even for a low-volume production. Since LC is a dielectric, its power consumption for tuning is extremely low. However, LC phase shifters face two critical parameters: too large length for 360°-phase shift, much more than for the restricted space beneath the antenna elements, and too slow response time (typically > 1 min), where at least less than 30 ms is required for high beam-steering rate in mobile applications. To overcome these problems, the proposed project aims for a new technology, enabling to satisfy all the addressed requirements, i.e. high FoM, low insertion loss, fast response time, low-power consumption, high linearity, low-cost, reliability, light-weight, compact (miniaturized) and flat (low-profile), simultaneously, by merging for the first time worldwide two independently developed innovative technologies: Liquid Crystal (LC) and Nanowire-filled Membrane (NaM) Technologies. The combined LC-NaM technology enables in general tunable microwave devices such as phase shifters miniaturized by factor of at least three, utilizing the slow-wave effect. As a proof-of-concept of this new technology, tunable passive slow-wave microstrip line phase shifters will be designed, realized and investigated for the first time, exemplary for WPAN application at 60 GHz. The objective is to achieve effective LClayer thickness of few µm only between the top of the nanowires and signal electrode, thus, keeping high performances for the planar microstrip topology with FoM of at least 70°/dB at 60 GHz. At the same time, the device's response time will be reduced dramatically from more than 1 min down to 30 ms compared to conventional tunable LC-based microstrip lines with 50 to 150 µm distances between the biasing electrodes. Thus, with this technology, it is feasible to realize a new generation of miniaturized phase shifters, having a fast response time and high FoM at millimeter waves with very low power consumption, and which could easily be integrated into each antenna element of a large beam-steering antenna array.