Abstract
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.
Highlights
Recent developments in new wireless platforms and network architecture together with innovative wireless technologies promise improved coverage, greater capacity, higher data rates, more efficient use of spectrum resources, much quicker round-trip times or lower latency, higher system reliability, and more flexibility for the effective delivery of services
The objective of this paper is to review the fundamentals and progress of the Microwave Liquid Crystal (MLC) technology, dedicated to the deployment of MLC phase shifters and passive phased arrays
Delay lines toward innovative loaded line and nanowire membrane-filled Liquid Crystals (LCs) concepts with the newest concepts with the newest results, featuring different microwave performances and response times, results, featuring different microwave performances and response times, ranging from tens of seconds ranging from tens of seconds down to few tens of milliseconds
Summary
Recent developments in new wireless ( satellite and 5G communication) platforms and network architecture together with innovative wireless technologies promise improved coverage, greater capacity, higher data rates, more efficient use of spectrum resources, much quicker round-trip times or lower latency, higher system reliability, and more flexibility for the effective delivery of services. Their implications in communications, including major market drivers, which trigger a massive number of use cases, future mobile traffic, economical perspectives, spectrum allocation, Crystals 2020, 10, 514; doi:10.3390/cryst10060514 www.mdpi.com/journal/crystals Crystals. AreThere two future and key technologies areindescribed in some detail in Appendix are twoscenarios. future
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