High-Performance TE10-Waveguide Phase Shifters for Millimeter Waves - Generic Concepts Towards Liquid Crystal (LC) filled MultiGap WaveGuides (MGWG)

该方案旨在为Ka波段基于压控液晶（LC）的TE 10槽多间隙波导（MGWG）移相器创建一个新的通用概念。它将是第一个专门为高性能应用设计的低损耗可调谐RF构建模块，使用微波LC的低损耗独特功能，随频率略有下降，以及间隙波导（GWG）的关键优势，即其电流隔离壁及其与TE 10矩形波导相当的低损耗性质。一个技术目标是实现可能的最高移相器品质因数（FoM），在30 GHz下在200°/dB的范围内，与在顶壁和底壁处具有相同LC和电极箔以通过偏置电压控制LC取向的分裂块设计中的矩形波导移相器的大约120°/dB相比。这个特殊的目标是可行的，因为矩形波导移相器的FoM对于磁偏置大于200°/dB（没有电极），其中差异归因于由电极引起的损耗，包括耦合到带状线模式中，来自用于引出电极箔的小间隙的场泄漏，并且因为电场的调谐效率不能像磁场那样被充分利用。上述问题可以通过使用GWG来克服，GWG在顶部和底部具有两个电隔离的金属板，其中一个具有人工磁导体表面，其可以通过钉床（BoN）来实现。这两个DC十重金属板可以用作偏置电极。此外，由于不需要接合工艺，因此不会发生明显的场泄漏。然而，对于移相器，需要两个以上的电极来完全控制LC取向。为此，多个具有BoN的GWG元件堆叠在一起，而没有任何电流耦合。基于这种新的MGWG概念，设想的实验室规模演示器由四个凹槽GWG元件组成，以构建具有LC填充Rexolite容器的TE 10波导移相器，同时使用它们作为电极，以完全控制LC取向，从平行到垂直于RF场，从而控制其相移。远远超出最先进的，这种新的电气方案可以实现类似的调谐效率的磁偏置。为了将该MGWG移相器连接到其他标准波导元件，WR-28法兰与适配器法兰和特殊的DC块法兰一起使用，以避免偏置电极的电流连接。这些凸缘也是该项目的一部分，使用三种不同的方法，依赖于BoN原理，蘑菇型结构和光子晶体。最有前途的一个将被实施到最终的演示，以评估这种新的MGWG概念的潜力与固有的电流解耦电极作为可重构毫米波系统的平台。

This proposal aims to create a new generic concept towards voltage-controlled Liquid Crystal (LC)-based TE10-groove MultiGap WaveGuide (MGWG) phase shifters at Ka-band. It will be a first low-loss tunable RF building block specifically-designed for high-performance applications, using the unique feature of microwave LCs with low losses, slightly decreasing with frequency, and the key advantages of Gap WaveGuides (GWGs), that are its galvanic-isolated walls and its low-loss nature comparable with TE10-rectangular waveguides. One technical goal is to achieve the highest phase shifter Figure-of-Merit (FoM) possible, in the range of 200°/dB at 30 GHz, compared to around 120°/dB of rectangular waveguide phase shifters in split-block design with the same LC and electrode foils at the top and bottom walls to control the LC orientation by a bias voltage. This exceptional goal is feasible, since the FoM of the rectangular waveguide phase shifters was more than 200°/dB for magnetic biasing (without electrodes), where the difference is accounted to the losses caused by the electrodes, including coupling into stripline modes, the field leakage from the small gaps for the electrode foils to be led out, and because the tuning efficiency by electric fields could not fully be exploited as for magnetic fields. The issues above can be overcome by using GWGs, having two electrically isolated metal plates at the top and bottom, where one has an artificial magnetic conductor surface, which can be realized by a Bed of Nails (BoN). These two DC-decupled metal plates can be used as biasing electrodes. Moreover, since no joining process is necessary, no appreciable field leakage occurs. However, for a phase shifter, more than two electrodes are required to fully control the LC orientation. For this, multiple GWG elements with BoN are stacked together without any galvanic coupling. Based on this new MGWG concept, the envisaged lab-scale demonstrator consists of four groove GWG-elements to build up TE10-waveguide phase shifters with LC-filled Rexolite containers, using them at the same time as electrodes to fully control the LC orientation continuously from parallel to perpendicular with respect to the RF-field, thus, controlling its phase shift. Far beyond state-of-the-art, this new electrical scheme could achieve similar tuning efficiency as for magnetic biasing. To connect this MGWG phase shifter to other standard waveguide components, WR-28 flanges are used with adapter flanges and special DC-block flanges in-between to avoid the galvanic connection of the biasing electrodes. These flanges are also part of this project, using three different approaches relying on the BoN principle, a mushroom-type structure and on photonic crystals. The most promising one will be implemented into the final demonstrator to evaluate the potential of this new MGWG concept with inherently galvanic-decoupled electrodes as a platform for reconfigurable millimeter-wave systems.