A Comparative Study of Paraelectrics and Novel Liquid Crystals for Tunable Microwave Devices

Weil, Garsten; Müller, Stefan; Scheele, P.; Jakoby, Rolf

doi:10.1515/freq.2004.58.7-8.162

Cited by 3 publications

(3 citation statements)

References 14 publications

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“…Up to now, various methods have been reported in the literature for realizing tunable devices. [1][2][3][4][5][6][7][8][9][10][11][12] One is the use of frequency-tunable devices obtained using varactor, PIN or Schottky diodes in patch antennas. The resonance frequency of these antennas could be modified using an external continuous voltage.…”

Section: Introductionmentioning

confidence: 99%

“…2) Another method uses specific substrate materials whose microwave electromagnetic properties (" 0 or 0 ) can be modified using an external electric or magnetic field. [2][3][4][5][6][7][8][9][10][11][12] Ferrite-type materials were used for magnetic field driving. 2) For these devices, the main problem to solve in new applications is to produce a driving magnetic field.…”

Section: Introductionmentioning

confidence: 99%

“…7) Among materials whose properties can be electrically controlled, we find liquid crystals. [8][9][10][11][12] Generally used in displays for their electro-optical properties, liquid crystals are anisotropic materials. They have a tensorial permittivity whose components vary under the influence of an electric or magnetic field.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Large Microwave Birefringence Liquid-Crystal Characterization for Phase-Shifter Applications

Dubois¹,

Krasinski²,

Splingart³

et al. 2008

jjap

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This work is concerned with the improvement of a microwave liquid-crystal phase shifter using a large birefringence nematic liquid crystal. This material is a eutectic mixture of isothiocyanatotolane molecules. Microwave dielectric properties are reported and compared to the data obtained with the 5CB cyanobiphenyl material in the 26 -40 GHz frequency range using a rectangular waveguide. The phase-shifter design consists of a central cavity, where a liquid crystal is inserted, and two coplanar strip lines accesses. Its dimensions were calculated by electromagnetic simulation, using measured dielectric permittivities of the liquid crystal. The measurements were performed with a commercial Wiltron 3680 K probe test fixture. Phase-shift variations with and without bias voltage versus frequency are presented. As expected, the large-birefringence nematic liquid crystal exhibits a higher microwave dielectric anisotropy (Á" 0 ¼ 1:06 against 0.34) and the tunability of the phase shifter strongly increases (1.8 degÁcm À1 ÁGHz À1 against 0.8 degÁcm À1 ÁGHz À1 ).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Large Microwave Birefringence Liquid-Crystal Characterization for Phase-Shifter Applications

Dubois¹,

Krasinski²,

Splingart³

et al. 2008

jjap

View full text Add to dashboard Cite

show abstract

Liquid Crystals for Advanced Smart Devices with Microwave and Millimeter‐Wave Applications: Recent Progress for Next‐Generation Communications

Choi

Park

et al. 2023

Advanced Materials

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Liquid crystals (LCs) technology have a well‐established history of applications in visible light, particularly in the display industry. However, with the rapid growth in communication technology, LCs have become a topic of current interest for high‐frequency microwave (MW) and millimeter‐wave (mmWave) applications due to promising characteristics such as tunability, continuous tuning, low losses, and price compatibility. To improve the performance of future communication technology using LCs, it is not sufficient only with the perspective of radio‐frequency (RF) technology. Therefore, it is imperative to understand not only the novel structural designs and optimization of MW engineering but also the perspective of materials engineering when implementing advanced RF devices with maximum performance for next‐generation satellite and terrestrial communication. Herein, based on advanced nematic LCs, polymer‐modified LCs, dual‐frequency LCs, and photo‐reactive LCs, this article summarizes and examines the modulation principles and key research directions for the design strategies of LCs for advanced smart RF devices with improved driving performance and novel functionality. Furthermore, the challenges in development of state‐of‐the‐art smart RF devices that use LCs are discussed.

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Liquid‐Crystal High‐Frequency Microwave Technology: Materials and Characterization

Zografopoulos

Ferraro

Beccherelli

2018

Adv Materials Technologies

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Ever since the advent of microwave technology, tunable devices, such as phase shifters, resonators, and antennas, have been indispensable in applications requiring radiofrequency signal filtering, beam shaping, or steering. This necessity becomes even more relevant in view of a new era in high‐bandwidth wireless communications in 5G networks, satellite links, and advanced radars for sensing and safety. As the operating frequency is pushed toward the millimeter‐wave range or beyond, the performance of traditional microwave tunable elements, such as PIN diodes, micro‐electromechanical system switches, ferrites, or ferroelectric films, degrades, while their fabrication complexity and cost increases. In this respect, liquid crystals present a promising solution, as they provide continuous tuning, low dielectric constants, moderate losses, low dispersion, and potentially low cost. Here, a comprehensive overview of the available microwave liquid crystal materials is provided, including their key application‐relevant properties, and the techniques employed for their characterization, focusing on the spectrum above 1 GHz. Their performance metrics in terms of dielectric constant tunability, response speed, insertion losses are discussed and guidelines for their selection in different microwave applications are provided. Moreover, the differences observed in the experimental data regarding their characterization are highlighted and possible sources of the observed discrepancies are discussed.

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A Comparative Study of Paraelectrics and Novel Liquid Crystals for Tunable Microwave Devices

Cited by 3 publications

References 14 publications

Large Microwave Birefringence Liquid-Crystal Characterization for Phase-Shifter Applications

Large Microwave Birefringence Liquid-Crystal Characterization for Phase-Shifter Applications

Liquid Crystals for Advanced Smart Devices with Microwave and Millimeter‐Wave Applications: Recent Progress for Next‐Generation Communications

Liquid‐Crystal High‐Frequency Microwave Technology: Materials and Characterization

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