Tunable liquid crystal metamaterial filter with polarization-insensitive characteristic

Abstract

ABSTRACT In this paper, a systematic design method for polarization-insensitive tunable liquid crystal (LC)-based metamaterial filter with the passband of flat-top and sharp roll-off is proposed. A compact LC-based bandpass metamaterial filter unit cell with a dimension of 0.09 λ × 0.09 λ is designed. The metamaterial filter element consists of a pair of planar pinwheel-shaped metallic structures with four symmetrically distributed isosceles triangular patches. LC is sandwiched in this pair of metallic structures. The metal pattern on each layer is 90° rotationally symmetrical leading that the LC-based metamaterial filter is insensitive to the polarization of incident waves. In order to obtain the transmission characteristics of flat top and sharp roll-off, a double-layer LC-based metamaterial filter structure is proposed. Full-wave simulations show that the central frequency of the metamaterial filter is tuned from 10.88 GHz to 11.78 GHz, and the tuning range reaches up to 7.9%. Meanwhile, under TE and TM polarizations, the double-layer LC-based metamaterial filter structure achieves filtering characteristics with a flat-top passband of not less than 997 MHz and sharp roll-off for arbitrary LC states. Moreover a prototype sample is designed, fabricated, and measured to verify the proposed design method.