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 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.

A novel liquid crystal (LC) based hollow waveguide phase shifter with an LC section of 14.6 mm is presented, operating at 80–110 GHz. As a proof‐of‐concept, the phase shifter is biased by using permanent magnets, which results in a differential phase shift of 307°–318° and an insertion loss of 2.1–2.7 dB in the desired frequency range of 99–105 GHz. Hence, a phase shifter figure of merit of 118°–148°/dB is determined, which are to the authors’ knowledge the highest values in this frequency range for passive phase shifters.

This study presents the first continuously tuneable, interference‐based W‐band single‐pole double‐throw (SPDT), fully implemented in subwavelength (sWL) dielectric fibre topology. Key components are the phase shifters in the two branches of the SPDT, which are realised as line sections filled with liquid crystal. They allow not only to adjust the signal ratios at the two output ports but also to tune the operating frequency between 93 and 110 GHz with isolation >25 dB. The first proof‐of‐concept SPDT demonstrator is realised and characterised at W‐band. However, concept and technology are scalable to higher frequencies. The complete SPDT with the WR10‐to‐sWL fibre transitions exhibits an insertion loss (IL) at the thru‐port between 5 and 7 dB in the frequency range from 85 to 110 GHz, where back‐to‐back measurements of the transitions itself already indicate an IL of up to 1.6 dB. The measurements at the isolated port of the SPDT exhibit transmission coefficients of less than −25 dB between 93 and 110 GHz with a minimum of −40 dB.