Voltage-Tunable Artificial Gradient-Index Lens Based on a Liquid Crystal Loaded Fishnet Metamaterial

In this letter, a voltage-tunable gradient-index fishnet metamaterial is presented. The unit cells of the fishnet are loaded with nematic liquid crystal material providing a continuous tuning of each column of the array. By introducing a voltage gradient over the width of the fishnet, the phase distribution over the aperture can be tuned, and thus the radiation direction can be controlled. The beam-scanning capability is demonstrated by simulation and measurements, and their comparison is discussed. The maximum measured scan angle using an $8 \times 8$ array at a frequency of 27.5 GHz is $\pm {5^ \circ }$ requiring a maximum tuning voltage of only 20 V. The presented prototype including the biasing scheme, fabricated with standard technology processes, features a low weight compared to conventional lenses.