Design and Measurement of Reconfigurable Millimeter Wave Reflectarray Cells with Nematic Liquid Crystal

Numerical simulations are used to study the electromagnetic scattering front phase agile microstrip reflectarray cells which exploit the voltage controlled dielectric anisotropy property of nematic state liquid crystals (LCs). In the computer model two arrays of equal size elements constructed on a 15 mu m thick tuneable LC layer were designed to operate at center frequencies of 102 GHz and 13 GHz. Micromachining processes based on the metallization of quartz/silicon wafers and in industry compatible LCD packaging technique were employed to fabricate the grounded periodic structures. The loss and the phase of the reflected signals were measured using a quasi-optical test bench with the reflectarray inserted at the beam waist of the imaged Gaussian beam, thus eliminating sonic of the major problems associated with traditional free-space characterization at these frequencies. By applying a low frequency AC bias voltage of 10 V, a 165 degrees phase shift with a loss 4.5-6.4 dB at 102 GHz and 130 degrees phase shift with a loss variation between 4.3-7 dB at 130 GHz was obtained. The experimental results are shown to be in close agreement with the computer model.