Miniaturized high-temperature superconductor microstrip patch antenna

Experimental as well as computational results are presented for 2.4 GHz microstrip antennas which are miniaturized (total length, 6 mm) by both a new, stepped impedance patch shape and a relatively high substrate permittivity. The antennas investigated were fabricated from YBa₂Cu₃O_7-δ thin films epitaxially grown on single-crystalline LaAlO₃ substrates by pulsed excimer laser ablation or by high-pressure oxygen DC sputtering and, for comparison, from copper on the same substrate material. It is shown that the radiation efficiency of this antenna structure is only about 1% to 6% for copper at 77 K but is increased to values between 35% and 65% for HTS films. From experimental investigations of the power dependence of the antenna gain at 77 K, nonlinearities, especially a sharp drop at a current density of about 2×10⁶ A/cm², were observed