Alexander Moessinger

Liquid Crystal-Reconfigurable Antenna Concepts for Space Applications at Microwave and Millimeter Waves

Novel approaches of tunable devices for millimeter wave applications based on liquid crystal (LC) are presented. In the first part of the paper, a novel concept of a tunable LC phase shifter realized in Low Temperature Cofired Ceramics technology is shown while the second part of the paper deals with a tunable high-gain antenna based on an LC tunable reflectarray. The reflectarray features continuously beam scanning in between . Also first investigations on radiation hardness of LCs are carried out, indicating that LCs might be suitable for space applications.

Compact tunable Ka-band phase shifter based on liquid crystals

This paper presents the design and realization of a compact phase shifter based on a tunable dual-mode ring filter at 35 GHz. The tunability is achieved by employing a thin liquid crystal layer as a tunable dielectric substrate. By applying a bias voltage in the range of 0… 40V, a tunable phase range of 117° is measured. The figure of merit of the realized phase shifter is 30.6 °/dB at 34.3 GHz.

Investigations on 77 GHz tunable reflectarray unit cells with liquid crystal

This paper presents investigations conducted with tunable reflectarray unit cells based on nematic liquid crystals (LC), at frequencies around 77 GHz. The structure of the cells is presented, as well as their performance as measured in a waveguide simulator setup. Encouraging results with tunable phase ranges as high as 280° with tuning voltages of up to 15V have been achieved. The investigated tunable unit cells will be used in electronically reconfigurable reflectarrays.

Realization and characterization of a 77 GHz reconfigurable liquid crystal reflectarray

A tunable microstrip reflectarray with beam reconfiguration capability at 77 GHz is presented. Tunablility is achieved by using anisotropic liquid crystal as RF-substrate, tunable by a biasing voltage below 15V. The reflector has been characterized by utilizing a lens setup forming a gaussian beam. The reflector properties has been extracted in terms of its reflected phase and magnitude: While it is possible to tune about 280. of phase, the associated losses are still quite high. Nevertheless, pattern measurements of the reflectarray showed distinct beam collimation towards different angles when appropriate DC control voltages are applied.

Liquid crystal based electronically steerable 4×4 antenna array with single horn feed at Ka-Band

This paper presents the design setup of an 4times4 array, each element consists of two Vivaldi antennas connected by an overlapped antipodal finline phase shifter. Simulations of an infinite expanded array showed a good matching in the whole investigated frequency range and fairly low insertion losses of less than 7.7 dB at 35 GHz. The phase can be continuously tuned up to 465deg. Measurement results of the realized array will be presented in the full paper. The presented results depict the first investigations of electronically steerable arrays fed from the back, based on liquid crystals. The results are very promising, encouraging further research: Rising the number of element cells and adding orthogonal arranged Vivaldi antennas for dual polarized signals, [8]. The setup can easily scaled down to rise the frequency. It is aimed to process the structure on fused silica, which improves the mechanical strength as well as excellent microwave properties.

Characterization of Reconfigurable LC-Reflectarrays Using Near-Field Measurements

A new measurement method for characterization of liquid crystal reflectarrays (LC) is presented. The phase and amplitude characteristics are determined by near-field measurements close to the antenna surface, using high resolution probes, which have been developed to resolve individual patches on the reflectarray. Measurement results showed a phase angle range of 280° of individual detected LC patches. The measurement setup and corresponding measurement results at 35 GHz are presented. The procedure used for measurement automation is also explained.

Liquid Crystals — Microwave Characterization and Tunable Devices

Liquid crystals (LCs) in the nematic mesophase are investigated in the microwave region. A characterization method based on a rectangular waveguide resonator is shown, which is able to extract the anisotropy of LCs. Various LCs are measured their properties at 30GHz is presented. They can be used in microwave devices to change the effective permittivity and therefore tuning the device properties. A broadband phase shifter device between 1.125GHz and 35GHz and a reflectarray operating at 35GHz is discussed. Additionally, the measurement results of unit-cells of reflectarrays at 77GHz are also presented, encouraging a realization of reflectarrays at W-Band. Index Terms – Liquid crystal, tunable device, phase shifter, reflectarray, Microwave device, Reconfigurable devices