How does the tunability of a metamaterial work

Alternative abstract:
Alternative abstractLanguage

In this work, continuously electrically tunable metamaterial leaky wave antennas for Ka-band applications with one-dimensional beam swiveling are designed, manufactured and investigated.

The antenna concept developed is based on the combination of leaky wave antennas and metamaterials. Leaky wave antennas offer high directivity with a low overall height, while metamaterials enable flexibility in the design process based on their dispersion properties.

In addition, through the use of liquid crystals as controllable material, voltage-controlled beam swiveling is achieved. The design, implementation and characterization of voltage gated metamaterial unit cells that make up the leaky wave antenna are described in detail. The design process and the analysis of the dispersion properties as well as the controllability of unit cells are carried out using equivalent circuit diagrams and analytical and full-wave models. Furthermore, tolerance and loss analyzes as well as far-field examinations are carried out. In addition, technological boundary conditions that limit the feasibility of the examined unit cells as well as the influence of design and manufacturing tolerances on the antenna are examined. In addition, a manufacturing process for combining the microwave structures with resistive feed networks and liquid crystal cavities is extensively investigated and presented in this thesis.

Different built antenna prototypes are presented. Using a magnetically controllable leaky wave antenna for 27 GHz, which uses a static magnetic field to pivot the beam, the presented unit cell concept is demonstrated and investigated. In addition, an electrically controllable leaky wave antenna will be presented, in which the orientation of liquid crystal molecules and thus beam swiveling at around 27 GHz is achieved by applying a variable voltage. Simulation results, vector network analyzes and far-field measurements of both prototypes are compared and a detailed analysis of the magnetic and electrical control is carried out. In addition, the control times of the electrically controllable leaky wave antenna installed with the liquid crystal used in this work are determined.

The concepts presented in this thesis in connection with manufactured prototypes show that the use of continuously tunable metamaterials offers a reliable possibility to realize electrically controllable leaky wave antennas for the Ka-band. Due to the good electromagnetic properties of liquid crystals at higher frequencies, the antenna concept and design methods shown can be used for frequencies up to at least 4 THz. This is of great importance in particular for current and future applications in modern, wireless communication systems.

German