A BST-Integrated Capacitively Loaded Patch for - and -band Beamsteerable Reflectarray Antennas in

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.