A multi-resonant unit-cell based on liquid crystals is proposed for reconfigurable reflectarray antennas. The proposed reflectarray element is made up of three parallel dipoles in the same cell and a tunable liquid crystal as substrate. The performance of the multi-resonant unit cell is compared with that of a single-resonant element in a frequency band from 30 to 40 GHz, showing a significant improvement in bandwidth, range of phase and losses. For a commercial liquid crystal, the proposed element provides a phase range greater than 360 within a 7.4 bandwidth and losses lower than 4.7 dB. These results represent a significant improvement with respect to the single-resonant unit cell based on the same liquid crystal. Finally, the proposed multi-resonant element is validated by measuring the phase response and losses in an X-band waveguide simulator.
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