Liquid Crystal Dielectric Image Lines for Integrated Reconfigurable Millimeter-Wave Beamsteering Applications

This work investigates the capabilities and performance of liquid crystal based dielectric image lines as a basis for reconfigurable millimeter-wave components and their use for beam-steerable antennas. The components, which are operated at W-band (75 GHz to 110 GHz), are designed, manufactured and characterized. The dielectric image line topology is well suited to combine the advantages of fully dielectric waveguides with the integrated character of commercial devices. Especially, the integration of liquid crystal can be easily achieved, and does not require modifying the printed circuit board on which the dielectric image line is placed. As a basis for the components, suitable materials are analyzed first, before an adaptive measurement setup is introduced. Two modes of the dielectric image line are of particular interest in this dissertation: the fundamental Ey 11-mode and the orthogonally polarized higher-order Ex 11-mode. The first components are liquid crystal phase shifters of low permittivity (εr = 2.53). In the fundamental mode, a low profile, a maximum figure-of-merit of 136 °/dB, response times of 6 s to 9 s and linear performance in a temperature range from −10° to 80° are achieved. With the orthogonally polarized mode, a higher figure-of-merit of 188 °/dB is obtained at the cost of higher response times. Utilizing a special design, the electrodes can be employed directly on the dielectric. This results in fast switch-on response times in the range of milliseconds, which is the fastest time obtained with dielectric waveguides up to today. This high decrease in switch-on response time represents a 99% and 97% improvement when compared to a fully dielectric liquid crystal phase shifter and a classic electrode placement besides the dielectric image line, respectively. On the basis of the phase shifters, reconfigurable antennas are investigated in the dielectric image line topology. With broadband rod antennas, 1×4 array demonstrators are realized. By utilizing multimode-interference for the first time in the dielectric image line topology at millimeter-waves, compact power dividers are realized. Combining the array with the aforementioned phase shifters leads to the first liquid crystal dielectric image line rod antenna phased array. It shows gain of 17 dBi to 18 dBi and has a beam steering range of ±10°. As a less complex and more narrowband alternative, a liquid crystal leaky wave antenna is introduced, too. By allowing the bias electrodes to contribute to the radiation characteristics, a simple antenna is realized, with a gain of 15 dBi, capable of scanning 10° by applying only one bias voltage. Furthermore, novel additive manufacturing techniques are evaluated to allow automated fabrication of the investigated components. An innovative guiding mechanism, which enables the combination of liquid crystal with high permittivity materials (εr = 9), is introduced as a means of enabling smaller components