Felix Goelden

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.

Modeling and Applications of Ferroelectric-Thick Film Devices With Resistive Electrodes for Linearity Improvement and Tuning-Voltage Reduction

Low-cost planar high-Q ferroelectric-thick film varactors (Qap90) are realized and component architectures using resistive electrodes for dc bias are investigated. A basic model for planar capacitors with resistive electrodes in the gap is developed and verified by finite-difference time-domain simulations and measurements of interdigital capacitors with high-resistivity indium-tin-oxide bias electrodes in the gap. An optimized high-Q capacitor design based on a series connection of ferroelectric varactors with resistive bias decoupling is presented. The approach allows the increase of device linearity and the reduction of tuning voltages. Based on this technology, a continuously tunable high-power impedance-matching network for 1.875 GHz with tuning voltages below 60 V was developed, realized, and characterized by small- and large-signal measurements with up to 33-dBm input power. The device requires no external dc-block or RF decoupling and features separated RF and dc contacts. The output IP3 of up to 47.8 dBm verifies the excellent device linearity

Passive Phase Shifter for W-Band Applications using Liquid Crystals

In this paper a ridged waveguide phase shifter at W-band frequencies is presented. A taper matches the ridged waveguide phase shifter to the rectangular waveguide feed. Three different liquid crystals (LC) are used: a quasi-standard LC K15, a highly anisotropic mixture MDA-03-2844, and a dual-frequency switching LC MDA-05-1132, all synthesized by Merck KgaA. The return loss of the phase shifter device is always below -10dB in the whole W-band. The maximum achievable figure-of-merit of these materials is 78deg/dB at 108 GHz

Modeling of electrically tunable transmission line phase shifter based on liquid crystal

This paper present the numerical modeling of transmission lines taking into account the special material properties when liquid crystals (LC) are used as steerable anisotropic dielectrics. At first a short introduction of the properties of LC is given as well as the theoretical models used for the physical simulation of LCs in terms of molecular dynamics. Then, a full wave method to analyze the electrical behavior of LC filled waveguide structures is described. The combination of molecular dynamic and full wave simulation allows finally a systematic investigation of these structures.

IP3 Measurements of Liquid Crystals at Microwave Frequencies

The nonlinear behaviour of a phase shifter employing two different nematic liquid crystals (NLCs) as a tunable dielectric is investigated in this work. The NLCs used are the quasi-standard NLC 5CB and a highly anisotropic mixture MDA-03-2844. The third order intercept point IP3 was measured at 7.4 GHz. The utilized measurement setup allows the application of 40 dBm total power to the device under test (DUT) with an IP3 of the empty setup of at least 60 dBm. The output IP3 is at least 52 dBm for 5CB and 58 dBm for the mixture. The proposed phase shifter design therefore exhibits high linearity

W-Band Characterization of Anisotropic Liquid Crystals at Room Temperature

This paper describes the characterization of Liquid Crystals (LCs) at W-Band using the standard WR-10 rectangular waveguide. The reflection parameter of a 10 mm long waveguide - terminated by a short-circuit - is measured. The LC is oriented with a homogeneous magnetostatic field strength of 400 A/mm, generated with an air-cooled coil. The extracted complex permittivity of the LC K15 from Merck KgaA (also known as 5CB) is presented, showing permittivities well below 3 with a dielectric anisotropy of Deltaepsiv<0.19 (equivalent to tau=Deltaepsiv/epsivmax<8.5%) and dielectric losses less than tandelta<0.023, all at W-Band.

Tunable loaded line phase shifters for microwave applications

This paper presents the design and realization of a tunable periodically loaded slot line phase shifters. The tunability is achieved by using liquid crystal (LC) as a tunable dielectric. Two prototypes are fabricated based on a printed circuit board (PCB) - LC - PCB structure for 12 GHz and a glass - LC - glass structure for 18 GHz. Measurements are performed and the figure of merits of the phase shifters are determined as 47 °/dB and 42 °/dB, respectively.

Direct simulation of material permittivities by using an eigen-susceptibility formulation of the vector variational approach

This paper presents a new method for the extraction of material parameters, in this case the permittivity, by formulating the Maxwell equations as an eigen-susceptibility problem of the considered sample. This offers a direct solution of the desired material parameters by utilizing adequate and well proven numerical techniques. Hence, it is very useful if analytical approaches do not provide the aimed accuracy or even fail completely. The procedure will be demonstrated by applying the variational approach to a triple mode cavity perturbation method for the characterization of the complex permittivity tensor of general biaxial anisotropic media.

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.

Triple-Mode Cavity Perturbation Method for the Characterization of Anisotropic Media

This paper presents a novel triple mode cavity perturbation method for the characterization of the permittivity and dielectric loss tensor of general biaxial anisotropic media. At first the basic theory of the cavity perturbation method is introduced. Then, an enhanced extraction procedure will be developed which leads to a set of equations for every resonator mode. Finally, a comparison of the extracted results of known material shows the validation of the developed procedure.