The availability of several licensed and unlicensed frequency spectra in the millimeter (mm)-wave frequency range has created new opportunities in the area of high data rate applications. This has led to demands for mm-wave devices, especially high gain antennas, which are adaptive (reconfigurable), compact and cheap to manufacture.
In our previous publications on the matter of Liquid Crystals (LCs), we presented an accurate analytical technique based on the Finite Element Method (FEM), which can be used for the extraction of unknown dielectric properties of anisotropic media, including LCs [1]. In addition, we have also presented how such a technique can be used in the context or well-known LC mixtures, such as K-15.
In this paper, a new method, a planar transmission line method, for the characterization of nematic LCs in the frequency range of 57- 62 GHz is presented. The LC cell used for the dielectric characterization consists of a finite length balanced stripline where a layer of LC is sandwiched between the two strips of the line. Unlike the previous methods where the LC is magnetically biased, one of the novel features of the present characterization is the direct application of an electric field to the LC through the strips using a low voltage source, Fig. 1. This feature allows gradual variation of the bias voltage, and hence, partial switching of the LC. With a detailed account of the spatial variation of the dielectric properties through the LC layer, which can be obtained through accurate LC modeling [1] a precise determination of the anisotropic dielectric constants is possible. In the present measurement device, a new special transition from the balanced stripline to the finite ground coplanar waveguide (FGCPW) is used, Fig. 1. This transition facilitates the probe-station measurement and eases the application of an external electric field to the LC under test. The LC investigated in this paper is the E7 mixture.
[1] R. James, S. E. Day, F. A. Fernandez, S. Bulja, M. Yazdanpanahi and D. Mirshekar-Syahkal, “Finite-element analysis of a balanced microstrip line filled with nematic liquid crystal”, IEEE IMS 2009, Boston, USA, 133-136, June 2009.
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