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.

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.

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A liquid crystal filled continuously tunable substrate integrated waveguide filter is proposed which has a high‐quality (Q) factor. To measure the Q‐factor, a single resonator measurement is performed by using magnetic biasing in a lab demonstrator for a proof of concept. The unloaded Q‐factor is 102–105.6. The resonator is employed to create a three‐pole Chebyshev filter with a centre frequency of 22 GHz and a bandwidth of 600 MHz. Measurement results show a 6 dB insertion loss with a return loss of about 10 dB. The filter is continuously tunable within a tuning range of 610 MHz.

The dielectric properties of nematic liquid crystal (LC) mixtures are measured from 300 GHz to 1500 GHz. Measurements are performed in a standard THz TDS setup. Refractive index and extinction coefficient for parallel and perpendicular orientation are calculated and compared to results

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Modern communication platforms require a huge amount of switched RF component banks especially made of different filters and antennas to cover all operating frequencies and bandwidth for the targeted services and application scenarios. In contrast, reconfigurable devices made of tunable components lead to a considerable reduction in complexity, size, weight, power consumption, and cost. This paper gives an overview of suitable technologies for tunable microwave components especially for SatCom applications. Special attention is given to tunable components based on functional materials such as barium strontium titanate (BST) and liquid crystal (LC).