Tunable Liquid Crystal (LC)-based microwave components are of increasing interest in academia and industry. Based on these components, numerous applications can be targeted such as tunable microwave filters and beam-steering antenna systems. With the commercialization of first LC-steered antennas for K_u-band e.g., by Kymeta and Alcan Systems, LC-based microwave components left early research stages behind. With the introduction of terrestrial 5G communications systems, moving to millimeter-wave communication, these systems can benefit from the unique properties of LC in terms of material quality. In this paper, we show recent developments in millimeter wave phase shifters for antenna arrays. The limits of classical high-performance metallic rectangular waveguides are clearly identified. A new implementation with dielectric waveguides is presented and compared to classic approaches.

For the first time, a liquid crystal (LC) filled lens antenna is investigated for beam steering in this paper. The LC’s anisotropy is applied inside a semicircular shaped parallel plate waveguide to achieve a deflection of the propagating electromagnetic wave at the interface of lower and higher permittivity. Using an electrode network, the direction of the sector of higher permittivity can be adjusted, and therefore, the beam direction. Main advantage of this antenna concept is that neither phase shifters nor switching networks are needed, resulting in a very simple approach for beam steering Operating at V-band, from 50 to 75 GHz, the first demonstrator proves the antenna concept by reconfiguring the beam in pre-defined directions of −30°, 0° and +30° to simplifiy the electrode biasing network. Furthermore, it is feasible and being demonstrated to adjust the beam width and to generate multiple beams In the measurements, the antenna exhibits a measured input reflection below −10 dB over the complete frequeny range. For the unsteered radiation pattern, the side lobe level is between −8 to −12 dB, while these values degrade to −4.5 to −6 dB for the steered radiation pattern at ±30°. The measured gain is between 13 to 15 dBi.

This letter presents the realization of a miniaturized liquid crystal slow wave phase shifter at V-band. It is based on a microstrip topology, where the ground plane is realized by a porous alumina membrane filled with metallic nanowires, all of them being connected with each other by a metallic ground plane at the membrane's back. While the magnetic field can pass the nanowires almost unperturbed, the electric field is confined in between the signal electrode and the tips of the nanowires. After deembedding, the meander line phase shifter shows a matching always better than -10 dB, while exhibiting an insertion loss between 1.5 and 2.5 dB from 40 to 67 GHz. This results in a figure-of-merit for passive phase shifters of 33 dB to 45°/dB, accompanied with a phase shift of 55°-100°.

This letter presents a highly miniaturized continuously tunable microstrip line phase shifter from 10 to 67 GHz. The design takes the advantage of the microstrip line topology by a ground plane with defected ground structures (DGSs). This leads to slow wave (SW) effect of the transmission line (TL), thus the TL can be physically compact, while maintaining its electric length. By applying tunable microwave liquid crystal (LC) with an anisotropic permittivity as dielectric, a delay line phase shifter is realized. The proposed microstrip LC phase shifter with DGS and a standard microstrip LC phase shifter as reference are both filled with 20-mm-thick high-performance LC GT3-23001. By comparison, the one with DGS exhibits a significant SW effect and an improved LC tuning efficiency which leads to a remarkable enhancement of figure of merit (FoM) and compactness than the reference. A second microstrip LC phase shifter utilizing DGS filled with 5-mm thick more advanced GT7-29001 LC shows outstanding FoM of 55°/dB, compactness of $201^{\circ }/{\lambda }_{0}$ , and response time of 210 ms.

This article presents the design of a Ka-band beam-switchable and beam-steerable endfire planar Yagi–Uda antenna array fed by a wideband Butler matrix, combining continuously tunable phase shifters based on a liquid crystal (LC) technology. The proposed array consists of four wideband 3 dB 90° branch-line couplers, two novel wideband via-less crossovers, LC-based 135° microstrip (MS) delay line phase shifters, and planar endfire Yagi–Uda antennas. The Butler matrix realizes beam switching, while LC phase shifters enable continuous beam steering inbetween the discrete beam positions. In this way, long delay line phase shifters are avoided for achieving 360°, reducing the phase shifter insertion losses (IL). Besides, such a hybrid beam steering method is expected to respond faster and more accurate. The array has two metallized layers, which can be easily fabricated by standard photolithography procedures. The fabricated array demonstrator is measured in terms of $S$ -parameters and far-field patterns. The measured return loss and isolation of the array are both ≥15 dB from 26 to 30 GHz. The beam is switchable among ±15° and ±45° in E-plane. By applying bias voltage up to 5 V to the LC phase shifters, the beam can be further continuously steered, covering almost −60° to +60° with acceptable sidelobe level. The maximum gain of the array is estimated to be 5.6 dBi. The radiation efficiency is 12%.

This letter presents a continuously tunable nonradiative dielectric waveguide three-pole bandpass filter based on liquid crystal (LC) technology at 60 GHz. LC is used as tunable material to obtain a continuous tunable center frequency. For the LC’s orientation, an electrode network with parasitic mode suppressive structure is realized. The measurements are performed with magnetic and electric biasing to verify the performance of the filter design. A maximum fractional bandwidth of 1% and a tunability of 2.5% were measured with electrical biasing. Furthermore, the filter’s insertion loss is between 4.9 and 6.2 dB over the tuning range. The extracted unloaded quality factor for electrical biasing ranges from 96 to 141.