A BST-Integrated Capacitively Loaded Patch for ${K_a}$- and ${X}$-band Beamsteerable Reflectarray Antennas in Satellite Communications

Tunable reflectarray unit cells operating at K_a^- and X-bands are presented in this paper using barium strontium titanate (BST) technology. A patch antenna is capacitively loaded with a narrow gap in the middle and a thin-film BST layer is deposited under the patch. By tuning the dc-bias voltage across the gap, the dielectric properties of the BST layer are changed and then an integrated tunable capacitor is realized. The proposed design is evaluated using both full-wave simulations and measurements. Due to the monolithic integration of the tuning mechanism with the unit cell, the antenna element can be applied at millimeter-wave frequencies without suffering from packaging and bonding problems. The effects of substrate thickness, system pressure, and operating frequency on the performance of the BST-integrated unit cell are presented. An overall phase range of 298° and 263° with maximum reflection losses of 16 and 8.8 dB at K_a^- and X-bands, respectively, are measured when the unit cells are operated for maximum phase range. By judiciously selecting the frequency of operation, a phase range of 250° with maximum reflection losses of 5.6 and 5.8 dB at 30.7 and 10.27 GHz are achieved. The presented analysis provides guidelines for optimizing the unit cell's performance required for efficient beam-scanning reflectarray antennas.