Circularly polarized HTS microstrip antenna array

A four-element, 11.67 GHz, high-T_c superconducting (HTS) microstrip antenna array with corporate feed network and circular polarization for direct broadcasting satellite (DBS) system was designed and built on a 0.5 mm thick MgO substrate. One antenna pattern was fabricated from gold thin film, and a second pattern was fabricated from YBa₂Cu₃O_7-x (YBCO) superconducting thin film. To improve the axial ratio of circularly polarized arrays, sequential rotation technique were used. Efficiency, radiation pattern, return loss and bandwidth were measured for both antennas at room temperature and at cryogenic temperatures. The array produced good circular polarization, and the gain of the array at 77 K, relative to a gold array at room temperature was approximately 1.54 dB. The measured return loss of our HTS antenna array was -35.79 dB at the resonant frequency of 11.67 GHz and the total effective bandwidth was about 3.4%. The results showed that high-temperature superconductors, when used in microstrip arrays, improved the efficiency of the circularly polarized HTS antenna array.