Reconfigurable Millimeter-Wave Tri-Band Antenna Based on VO2-Films-Embedded Co-Aperture Metasurface Structures

A novel reconfigurable millimeter-wave tri-band antenna using co-aperture metasurface structures embedded with electrically controlling vanadium dioxide (VO2) films is proposed. A co-aperture metasurface structure is designed by loading a large square ring surrounded by eight small square patches in the same aperture. By embedding the VO2 film into the large ring, two lower frequencies of 22 and 28 GHz can be excited and switched when the film operates in metallic and insulating states respectively. Meanwhile, an extra higher mode resonance at 40 GHz is produced by the small patches. Benefiting from the reasonable co-aperture layout, the three frequency bands exhibit good independent tunability. Furthermore, the tri-band metasurface structure is used as a radiation element to construct a reconfigurable antenna. To realize good feeding coupling at three bands with a large frequency ratio for the antenna, a new kind of combined slot is proposed and etched on the transverse surface of the feeding waveguide. The combined slot contains a loop slot, a dumbbell-shaped slot, and two U-shaped slots, corresponding to low, medium, and high frequencies, respectively. In addition, a simple coplanar direct current (dc) bias circuit with little effect on radiation is designed. As a result, when the VO2 film is in an insulating state, the antenna can simultaneously cover two bands of 27.7–29.8 and 38.8–40 GHz with a maximum gain of about 8.7 and 9.5 dBi, respectively; when the film is activated to a metallic state, it can also work in two bands of 21.1–21.6 and 38.6–40 GHz with the maximum gain of about 7.2 and 9.3 dBi. Compared with other reported VO2-based antennas, the proposed antenna can work in three different bands with an adjustable frequency ratio and superior radiation performance.