Future satellite platforms and 5G millimeter wave systems require Electronically Steerable Antennas (ESAs), which can be enabled by Microwave Liquid Crystal (MLC) technology. This paper reviews some fundamentals and the progress of microwave LCs concerning its performance metric, and it also reviews the MLC technology to deploy phase shifters in different topologies, starting from well-known toward innovative concepts with the newest results. Two of these phase shifter topologies are dedicated for implementation in array antennas: (1) wideband, high-performance metallic waveguide phase shifters to plug into a waveguide horn array for a relay satellite in geostationary orbit to track low Earth orbit satellites with maximum phase change rates of 5.1°/s to 45.4°/s, depending on the applied voltages, and (2) low-profile planar delay-line phase shifter stacks with very thin integrated MLC varactors for fast tuning, which are assembled into a multi-stack, flat-panel, beam-steering phased array, being able to scan the beam from −60° to +60° in about 10 ms. The loaded-line phase shifters have an insertion loss of about 3 dB at 30 GHz for a 400° differential phase shift and a figure-of-merit (FoM) > 120°/dB over a bandwidth of about 2.5 GHz. The critical switch-off response time to change the orientation of the microwave LCs from parallel to perpendicular with respect to the RF field (worst case), which corresponds to the time for 90 to 10% decay in the differential phase shift, is in the range of 30 ms for a LC layer height of about 4 µm. These MLC phase shifter stacks are fabricated in a standard Liquid Crystal Display (LCD) process for manufacturing low-cost large-scale ESAs, featuring single- and multiple-beam steering with very low power consumption, high linearity, and high power-handling capability. With a modular concept and hybrid analog/digital architecture, these smart antennas are flexible in size to meet the specific requirements for operating in satellite ground and user terminals, but also in 5G mm-wave systems.

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 paper presents the integration of frequency selective surfaces (FSSs) with retroreflectors for the realization of chipless wireless indoor localization tag landmarks. As an example, the high radar cross-section (RCS) of a trihedral corner reflector is signed with an FSS-based stop-band filter, so that the backscattered power from several corner reflectors can be distinguished by a mobile reader according to the frequency response of the FSS. Measurement results with a ${3\times3\times3 cm^{3}}$ trihedral corner reflector and a stop-band FSS in a Rogers RT/Duroid® 5880 high-frequency laminate at 90 GHz shows an RCS above -25 dBsqm for 90 degrees coverage in the TM plane. Due to the high RCS, measurements at distances up to 4 meters with a standard 25 dBi gain horn antenna and a vector network analyzer as a reader are shown. These preliminary results show the potential of the concept for applications such as indoor localization with sub-mm accuracy, where high-bandwidths, but only a low number of bits, are needed for the identification of the tag landmarks.

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.