Concepts for and Synthesis of Liquid Crystal-Tunable Ka-band Filters with Independently Tunable Center Frequency and Bandwidth

无线电业务的数量正在稳步增加，在频带分配和按需带宽方面的需求也在迅速变化。为了满足这些要求，未来的通信系统如卫星以及4。和5。由于下一代基站的实现需要较长的运行时间，因此不仅在基带上需要灵活性，而且在射频前端也需要灵活性，例如通过使用可重构组件。一个关键组件是输入过滤器。最先进的滤波器组包含大量带通滤波器，覆盖多个参数，如中心频率和带宽。该设计基于固定数量的控制状态（即滤波器），这些控制状态只能谨慎地设置，并且不允许随后重新配置滤波器或频段分配。此外，滤波器组的大体积和重量是一个主要问题，特别是对卫星。通过采用电子可控滤波器，可以在一定的调谐范围内连续调节中心频率和带宽等参数。这允许射频前端几乎无限次的重新配置。此外，过滤器的体积和重量只是过滤器组的一小部分。本研究计划的主要目标是分析和合成可在中心频率和带宽上重新配置的基于液晶（LC）的滤波器，用于ka波段的卫星通信应用。在达姆施塔特工业大学建立的LC技术为卫星通信有效载荷的期望应用提供了两个主要优点：(1)液晶已针对毫米波应用进行了优化，显示出非常低的损耗，因此可以实现高滤波器质量。(2)这些液晶已经被太空认可，也就是说，它们是抗辐射的，因此，适合在卫星有效载荷的组件中实施。本课题所合成的lc滤波器在中心频率和带宽上都是可控的。因此，有必要研究实现可调谐耦合孔径和谐振腔结构的不同方法。开发合适的控制电极，以达到最高的质量因子和最大的调谐范围。基于lc的高阶滤波器是由单个研究的孔径和谐振器几何形状合并而成的。利用耦合矩阵法研究了最适合的滤波器拓扑结构。在合成过程结束时，整个滤波器结构的微调是在全波模拟器中完成的。因此，必须对模型进行简化，以便在合适的时间内完成模拟。在本项目的最后，对运行模式下滤波器的重新配置进行了研究，并实现了热稳定性的诊断算法。

The number of radio services is steadily increasing with rapidly changing requirements in terms of frequency band allocation as well as bandwidth on demand. To meet these requirements, future communication systems such as satellites as well as 4. and 5. generation´s base stations, which have long operational times by implementation, require flexibility not only in the baseband, but also in the RF-frontend, e.g. by using reconfigurable components. A key component is the input filter. State-of-the-art are filter banks with a multitude of bandpass filters, which cover a plurality of parameters such as center frequency and bandwidth. The design is based on a fixed number of control states (i.e. filters) that can only be set discreetly and do not allow subsequent reconfiguration of filters or frequency band allocations. Furthermore, the large volume and weight of filter banks is a major problem especially for satellites. By using electronically controllable filters, parameters such as center frequency and bandwidth can be adjusted continuously within a certain tuning range. This allows an almost unlimited number of reconfigurations of the RF frontend. Furthermore, the volume and the weight of the filter is only a fraction of a filter bank. The primary objective of this research proposal is the analysis and synthesis of electrically-controllable liquid-crystal (LC) based filters reconfigurable in center frequency and bandwidth for satellite communication applications in the Ka-band. The LC technology, which had been established at TU Darmstadt provides two major benefits for the desired application in a satellite communication payload: (1) The liquid crystals have been optimized for millimeter-wave applications, showing very low losses, and thus, allowing a high filter quality. (2) Those liquid crystals are already space-approved, i.e. they are radiation hard, and therefore, suitable for the implementation into components of a satellite payload. The LC-filters to be synthesized in this project are controllable in center frequency as well as in bandwidth. Therefore, it is necessary to investigate different approaches for the realization of tunable coupling apertures and resonator structures. Suitable control electrodes are than developed with the aim to achieve the highest possible quality factor and a maximal tuning range. The LC-based higher order filter is than merged from individual investigated apertures and resonator geometries. The best suited filter topology is investigated using the coupling matrix approach. The fine tuning of the complete filter structure at the end of the synthesis process is done in a full-wave simulator. Therefore, the model has to be simplified in such a way that simulations can be accomplished in a suitable time. An investigation of the reconfiguration of the filter in operation mode as well as the implementation of a diagnosis algorithm for the realization of the thermal stability is provided at the end of this project.