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The use of liquid crystals for tunable devices has already been investigated for phase-shifters and antennas in planar technology. Here, the focus is, first, on a half-wavelength open-circuited stub resonator, then on a second-order dual behavior resonator filter. To have the benefit of liquid crystal anisotropy and thus obtain agility, a bias voltage is applied to the device under study. In order to avoid the shift observed between simulated and measured results of the half-wavelength open-circuited stub for the first structure, the technological process has been improved for the second one in the aim to reduce mismatching and LC leaking.Index Terms -Liquid crystal, tunable filter, dual behavior resonator.

This article deals with liquid-crystal-based tunable components: phase-shifters and patch-antennas. It reports on investigations about the influence of design on their characteristics. For phase-shifters based on an inverted microstrip line, the line design is paramount for improvement of phase-shift and Figure-Of-Merit. Moreover, the use of liquid crystal in the design of patch antennas allows adjustment of the resonance frequency, and slot insertion results in size reduction with no decrease of performances. Both cases highlight the interest of liquid crystal in millimeter frequency devices.

Tunable coplanar waveguide stub resonators deposited on various ferroelectric/dielectric heterostructures are studied in the 10-GHz band. A frequency tunability up to 45% is achieved under a moderate biasing field (E bias < 100 kV/cm) when the resonator is printed on KTa 0.5 Nb 0.5 O 3 (KTN) ferroelectric thin film alone: this comes from the large permittivity agility of the KTN material ( r(KTN) varies from 700 to 200). Nevertheless this also leads to significant insertion loss due to the dielectric loss of the ferroelectric material itself (tan r(KTN) ≈ 0.15-0.30 at 10 GHz). In this paper, an original route has been considered to reduce the device loss while keeping up a high frequency tunability. It consists in associating the KTN film with a dielectric film to elaborate ferroelectric/dielectric multilayers. The * Corresponding author. Tel.: +33 2 96 60 96 53; fax: +33 2 96 60 96 52. E-mail address: xavier.castel@univ-rennes1.fr (X. Castel).2 Bi 1.5 Zn 0.9 Nb 1.5 O 7- (BZN) oxide material is selected here for two main reasons, namely its low dielectric loss (tan r(BZN) ≈ 0.005-0.0075) and its moderate relative permittivity ( r(BZN) ≈ 95-125) at 12.5 GHz. The relevance of this approach is studied numerically and experimentally.We compare numerically two different heterostructures for which the ferroelectric film is grown on the dielectric film (KTN/BZN), or vice versa (BZN/KTN). A stub resonator printed on the most relevant heterostructure has been fabricated, and experimental data are discussed and compared to the numerical results.

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This letter presents the design, fabrication, and measurement of a KTa1‐xNbxO3‐ (KTN‐) based phase shifter. This loaded‐line phase shifter has insertion losses of about 7.36 dB at zero bias and 10 GHz, a return loss greater than 12 dB over the frequency range 1–16 GHz and a relatively high differential phase shift of about 88° for a 120 V DC bias at 10 GHz. The enhancement of performances observed by comparison with those presented by the KTN‐based phase shifters positions KTN materials as a serious alternative to Ba1‐xSrxTiO3 ones for microwave agility applications. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1148–1150, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25104

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The study of electrically tunable phase-shifters based on the use of liquid crystals is under consideration. First, the dielectric characterisation of a commercial liquid crystal involved in this study is reported. The anisotropy of such substrates is given by the permittivity tensor. Second, two phase-shifter configurations are studied. Both structures propose inverse strip-line but different accesses and substrates. In addition, phase variation measurements corresponding to these two configurations improve performances.