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

TU Darmstadt在过去十年中创新地采用了超越光学的新型液晶(LC)技术，由于液晶损耗随着频率的降低而降低，因此似乎是最有前途的毫米波可调谐元件的方法。在30 GHz下，它的介电损耗非常低，仅为0.006，连续可调谐性高达27%，在所有调谐状态下，最大微分相移与最高插入损耗之比分别约为2 0 0°/分贝或1 1 0°/分贝。尽管平面技术本身具有比中空波导拓扑结构更高的系统损耗，但它们是低轮廓的，可以很容易地实现，利用类似于成熟的LCD技术的自动化制造技术。这使得能够低成本制造更大的阵列，即使对于小批量生产也是如此。由于LC是一种介质，其调谐功耗极低。然而，LC移相器面临两个关键参数：对于360°相移来说，长度太大，远远大于天线元件下方的受限空间；以及响应时间太慢(通常为&gt；1分钟)，在移动应用中，高波束控制速率至少需要不到30ms。为了克服这些问题，拟议的项目旨在开发一种新技术，能够满足所有已解决的要求，即高FOM、低插入损耗、快速响应时间、低功耗、高线性度、低成本、可靠性、轻量化、紧凑化(微型化)和扁平(低调)，同时通过首次在全球范围内合并两项独立开发的创新技术：液晶(LC)和纳米线填充膜(NAM)技术。组合的LC-NAM技术使移相器等可调谐微波器件能够利用慢波效应，小型化至少三倍。作为这一新技术的概念验证，将首次设计、实现和研究可调谐的无源慢波微带线移相器，这是60 GHz WPAN应用的典范。其目标是仅在纳米线顶部和信号电极之间获得几微米的有效LC层厚度，从而在60 GHz下保持FOM至少为70°/dB的平面微带拓扑的高性能。同时，与偏置电极之间距离为50至150微米的传统可调LC微带线相比，该器件的响应时间将从1分钟以上大幅缩短至30毫秒。因此，利用这种技术实现新一代小型化移相器是可行的，它在毫米波具有快速的响应时间和高的FOM，并且功耗非常低，并且可以很容易地集成到大型波束控制天线阵的每个天线单元中。

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.