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Crystals
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Microwave Liquid Crystal Technology
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Microwave Liquid Crystal Technology

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Liquid Crystals".

Deadline for manuscript submissions: closed (31 March 2020) | Viewed by 45213

Special Issue Editor

Dr. Holger Maune

E-Mail Website
Guest Editor
Technische Universität Darmstadt, Institut für Mikrowellentechnik und Photonik, Merckstrasse 25, 64283 Darmstadt, Germany
Interests: reconfigurable RF systems; functional materials; liquid crystal; ferroelectrics; tunable antenna; tunable filters; phased arrays; material characterization

Special Issue Information

Dear Colleagues,

Liquid crystals (LCs) specifically synthesized for microwaves are dielectric materials with highly anisotropic characteristics and low microwave losses, which can be used to realize tunable RF and microwave components-based reconfigurable systems. Tunable components are indispensable in applications requiring adaptive signal filtering, beam shaping, or steering. This necessity becomes even more relevant in view of the upcoming new era of communication systems in the context of Internet of Things (IoT) and Internet of Space (IoS). In this respect, microwave liquid crystal technology presents a very promising hardware solution, as it provides continuous tuning, low dielectric losses, high linearity, low power consumption, and potentially low cost. Within the last 20 years, tremendous progress has been made on the material synthesis on the one hand, but also on device and technology concepts on the other hand.

We invite investigators to submit papers which discuss recent development of high-performance liquid crystal materials and liquid crystal-based microwave components.

The potential topics include but again are not limited to:

  • Material synthesis;
  • Material characterization (e.g., dielectric properties);
  • Characterization of the properties under harsh environments, such as large temperature ranges, vacuum, hard radiation (gamma or neutron), etc.;
  • Modeling of liquid crystals and components;
  • Reliability and stability of the properties, including aging and fatigue, etc.;
  • Devices and device concepts based on microwave liquid crystal technology;
  • Biasing concepts for LC-based microwave devices;
  • Applications of microwave liquid crystals and prototype demonstration.

Dr. Holger Maune
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Reconfigurable RF and microwave systems
  • Functional materials
  • Liquid crystals
  • Phase shifters
  • Material synthesis
  • Material characterization
  • Tunable components
  • Modeling

Published Papers (7 papers)

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Editorial

Jump to: Research, Review

2 pages, 162 KiB  
Editorial
Microwave Liquid Crystal Technology
by Holger Maune
Crystals 2020, 10(8), 716; https://doi.org/10.3390/cryst10080716 - 18 Aug 2020
Cited by 5 | Viewed by 1976
Abstract
Information and communication technologies (ICT) are the foundation of growth and development in the modern global economy [...] Full article
(This article belongs to the Special Issue Microwave Liquid Crystal Technology)

Research

Jump to: Editorial, Review

14 pages, 3825 KiB  
Article
Tunable RF Filters Based on Liquid Crystal for Space Applications
by Tobias Kaesser, Carsten Fritzsch and Michael Franz
Crystals 2020, 10(6), 455; https://doi.org/10.3390/cryst10060455 - 31 May 2020
Cited by 5 | Viewed by 3204
Abstract
On board of communication satellites, there are numerous RF filters in the payload used for guiding wanted signals as desired and for rejecting unwanted signals such as not to interfere with wanted signals. At present, satellites have a long lifetime (15 years at [...] Read more.
On board of communication satellites, there are numerous RF filters in the payload used for guiding wanted signals as desired and for rejecting unwanted signals such as not to interfere with wanted signals. At present, satellites have a long lifetime (15 years at least for a typical geostationary communication satellite) and there is also time elapsing between its design and the start of in-orbit service (2 years at least). On the other hand, conventional RF filters for satellite applications are fixed frequency. Therefore, there is a growing demand for in-orbit tunable filters to be able to cope with changes in the market situation during that long time. Also, there are communication systems evolving that rely on tunable devices used for adaptive filtering or steering. This article reports on in-orbit tunable bandpass filters employing liquid crystal material and operating at 20 GHz, and especially on design aspects dealing with the harsh space environment, on the operating principles for commanding the filters on board the satellite, and on a qualification campaign passed successfully. A demonstrator unit is in manufacturing for in-orbit verification. Full article
(This article belongs to the Special Issue Microwave Liquid Crystal Technology)
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39 pages, 15367 KiB  
Article
Reconfigurable Millimeter-Wave Components Based on Liquid Crystal Technology for Smart Applications
by Ersin Polat, Henning Tesmer, Roland Reese, Matthias Nickel, Dongwei Wang, Peter Schumacher, Rolf Jakoby and Holger Maune
Crystals 2020, 10(5), 346; https://doi.org/10.3390/cryst10050346 - 27 Apr 2020
Cited by 25 | Viewed by 5179
Abstract
This paper presents recent development of tunable microwave liquid crystal (LC) components in the lower millimeter wave (mmW) regime up to the W-band. With the utilization of increasing frequency, conventional metallic waveguide structures prove to be impractical for LC-based components. In particular, the [...] Read more.
This paper presents recent development of tunable microwave liquid crystal (LC) components in the lower millimeter wave (mmW) regime up to the W-band. With the utilization of increasing frequency, conventional metallic waveguide structures prove to be impractical for LC-based components. In particular, the integration of the electric bias network is extremely challenging. Therefore, dielectric waveguides are a promising alternative to conventional waveguides, since electrodes can be easily integrated in the open structure of dielectric waveguides. The numerous subcategories of dielectric waveguides offer a high degree of freedom in designing smart millimeter wave components such as tunable phase shifters, filters and steerable antennas. Recent research resulted in many different realizations, which are analyzed in this paper. The first demonstrators of phased array antennas with integrated LC-based phase shifters are reviewed and compared. In addition, beam steering with a single antenna type is shown. Furthermore, the possibility to realize tunable filters using LC-filled dielectric waveguides is demonstrated. Full article
(This article belongs to the Special Issue Microwave Liquid Crystal Technology)
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16 pages, 5921 KiB  
Article
Response Improvement of Liquid Crystal-Loaded NRD Waveguide Type Terahertz Variable Phase Shifter
by Trong Nghia Lang, Van Bao Bui, Yo Inoue and Hiroshi Moritake
Crystals 2020, 10(4), 307; https://doi.org/10.3390/cryst10040307 - 16 Apr 2020
Cited by 7 | Viewed by 2925
Abstract
Liquid crystals, which have high dielectric anisotropy even in the terahertz region and are easily controllable for dielectric permittivity by applying an electric field, have become increasingly attractive in recent years. The non-radiative dielectric (NRD) waveguide has a structure in which a dielectric [...] Read more.
Liquid crystals, which have high dielectric anisotropy even in the terahertz region and are easily controllable for dielectric permittivity by applying an electric field, have become increasingly attractive in recent years. The non-radiative dielectric (NRD) waveguide has a structure in which a dielectric line is sandwiched between two metal plates and by replacing the dielectric part with liquid crystal, a low loss liquid crystal-loaded NRD waveguide type terahertz phase shifter can be obtained. However, since the thickness of the liquid crystal layer is several hundred micrometers, it has a response time of as long as several hundred seconds when the driving voltage is removed. It is necessary to devise improvements for practical application. By inserting two polyethylene terephthalate (PET) films and reducing the thickness of the liquid crystal layer, the decay time was improved well, but the phase change was significantly reduced. In this study, we report improving both decay time and phase change with aligned nanofiber/liquid crystal complex. In addition, we demonstrate liquid crystal-load phase shifter, which has 360° phase change and the response time below one second. Full article
(This article belongs to the Special Issue Microwave Liquid Crystal Technology)
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9 pages, 3228 KiB  
Article
The Characterization and Application of Two Liquid Crystal Mixtures in the Low THz Region
by Andong Zheng, Xiujun Chu, Pengjun Wang, Peng Wang, Sheng Gao, Jun Yang, Hongbo Lu, Guangsheng Deng and Zhiping Yin
Crystals 2020, 10(2), 99; https://doi.org/10.3390/cryst10020099 - 9 Feb 2020
Cited by 3 | Viewed by 2915
Abstract
In the previous work, two new nematic liquid crystal (NLC) mixtures, E7-2 and S200-2, were produced by adding eight LC monomers to two commercial LCs S200 and E7, respectively. At λ = 589 nm, the birefringence (Δn) characteristics of the two [...] Read more.
In the previous work, two new nematic liquid crystal (NLC) mixtures, E7-2 and S200-2, were produced by adding eight LC monomers to two commercial LCs S200 and E7, respectively. At λ = 589 nm, the birefringence (Δn) characteristics of the two LC nematic mixtures E7-2 (Δn = 0.260) and S200-2 (Δn = 0.298) are greater than those of the commercial LC E7 (Δn = 0.224) and S200 (Δn = 0.266). The properties (TN-I, ε//, Δɛ, K11, and K33) of these four NLCs were measured. A double-layer metal loop arrays modulation structure based on metamaterial (MM) metal–dielectric–metal (MDM) was designed and fabricated for use in the THz frequency range. The results show that the LC mixtures E7-2 and S200-2 have greater modulation depth (MD) and less modulation insertion loss (IL) than E7 and S200 at THz frequencies. The results show that LC mixtures have significant potential for designing active tunable LC-based devices in the THz and visible light range. Full article
(This article belongs to the Special Issue Microwave Liquid Crystal Technology)
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15 pages, 7129 KiB  
Article
Liquid Crystal-Based Enclosed Coplanar Waveguide Phase Shifter for 54–66 GHz Applications
by Jinfeng Li and Daping Chu
Crystals 2019, 9(12), 650; https://doi.org/10.3390/cryst9120650 - 6 Dec 2019
Cited by 53 | Viewed by 11291
Abstract
A 0–10 V bias voltage-driven liquid crystal (LC) based 0°–180° continuously variable phase shifter was designed, fabricated, and measured with insertion loss less than −4 dB across the spectrum from 54 GHz to 66 GHz. The phase shifter was structured in an enclosed [...] Read more.
A 0–10 V bias voltage-driven liquid crystal (LC) based 0°–180° continuously variable phase shifter was designed, fabricated, and measured with insertion loss less than −4 dB across the spectrum from 54 GHz to 66 GHz. The phase shifter was structured in an enclosed coplanar waveguide (ECPW) with LC as tunable dielectrics encapsulated by a unified ground plate in the design, which significantly reduced the instability due to floating effects and losses due to stray modes. By competing for spatial volume distribution of the millimeter-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics, the ECPW’s geometry and materials are optimized to minimize the total of dielectric volumetric loss and metallic surface loss for a fixed phase-tuning range. The optimized LC-based ECPW was impedance matched with 1.85 mm connectors by the time domain reflectometry (TDR) method. Device fabrication featured the use of rolled annealed copper foil of lowest surface roughness with nickel-free gold-plating of optimal thickness. Measured from 54 GHz to 66 GHz, the phase shifter prototype presented a tangible improvement in phase shift effectiveness and signal-to-noise ratio, while exhibiting lower insertion and return losses, more ease of control, and high linearity as well as lower-cost fabrication as compared with up-to-date documentations targeting 60 GHz applications. Full article
(This article belongs to the Special Issue Microwave Liquid Crystal Technology)
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Review

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56 pages, 65518 KiB  
Review
Microwave Liquid Crystal Enabling Technology for Electronically Steerable Antennas in SATCOM and 5G Millimeter-Wave Systems
by Rolf Jakoby, Alexander Gaebler and Christian Weickhmann
Crystals 2020, 10(6), 514; https://doi.org/10.3390/cryst10060514 - 16 Jun 2020
Cited by 77 | Viewed by 16766
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 [...] Read more.
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. Full article
(This article belongs to the Special Issue Microwave Liquid Crystal Technology)
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