Electrical characterisation of liquid crystals at millimetre wavelengths using frequency selective surfaces

Accurate and Efficient Modeling to Calculate the Voltage Dependence of Liquid Crystal-Based Reflectarray Cells

“…2 shows the solution of (5) for the structure in Fig.1 at different RMS voltages (at room temperature and 1 kHz AC-signal), assuming a separation of z = 75 µm, pretilt angles of 4º on both surfaces, and LC material type GT3-23001, which is manufactured by Merck for microwave applications. The LC characteristic data given by Merck is shown in the figure caption, and the RF parameters ( ⊥ ) and ( // ) have been measured by the authors in the band from 140 to 165 GHz [15]. As can be seen, the molecular tilt angle takes the value = 4º at the extremes, increasing its value with the separation until it reaches the maximum at the center of the LC layer.…”

“…most important parameter at antenna level) would be around 20º, which can be used in most applications. However, if a very small phase error is required and the cell structure provides a relatively large effect due to the transversal inhomogeneity, this latter can be suppressed by depositing a thin conductive layer (ITO, PDOT) across the surface of the entire cell [15], similar as in LC Displays.…”

Design and Demonstration of an Electronically Scanned Reflectarray Antenna at 100 GHz Using Multiresonant Cells Based on Liquid Crystals

“…1, can be made identical over the entire surface. The LC used is the mixture GT3-23001, which is manufactured by Merck and whose parameters are: e r// (100 GHz)=3.25, e r ±(100 GHz)=2.47, tan5//(100 GHz)= 0.015, tan5±(100 GHz)= 0.02 (measured in [10]), and 8^/(1 KHz)=8.1, Ae (1 KHz)=4.6 (givenby Merck).…”

“…The dielectric anisotropy at RF also has an influence on the accuracy of the method used. However, an FSS has previously been used to extract this parameter above 100 GHz [10], and since the LC does not present transversal inhomogeneity, the values obtained for Ae r (100 GHz) are considered to be sufficiently accurate. The uncertainty associated with the value of Ae r (0.33 Hz) can produce average phase errors after voltage synthesis, of around ±10°.…”

Electronically Reconfigurable Liquid Crystal Based Mm-Wave Polarization Converter

“…In order to reduce the possibility of breakage during processing, the thickness of the quartz substrate is chosen to be 250 μm and a metalized silicon wafer is used to form the ground plane. A thin (100 nm) resistive boron diffused polycrystaline silicon film [19] was deposited by a low pressure Chemical Vapour Deposition process at 620 o C on the un-patterned side of the quartz wafer to give an almost mmwave transparent but low frequency conductive layer. This layer is used for the establishment of a low frequency quasistatic electric field in the cavity to bias the liquid crystals; it has been experimentally determined that a low frequency field is best suitable for the biasing of the LC [13].…”