MINIATURIZED HIGH-TEMPERATURE SUPERCONDUCTOR MICROSTRIP PATCH ANTENNA

This paper present experimental as well as computational results 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 investigated antennas were fabricated from YBa2Cu3O7-delta 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% (depending on the substrate height) for copper at 77 K but is increased to values between 35% and 65% for HTS films. In the latter case, considerable improvements could be obtained if a substrate compatible with a high-temperature superconductor with a lower loss tangent were available. From experimental investigations of the power dependence of the antenna gain at 77 K, nonlinearities, especially a shapr drop at a current density of about 2.10(6) A/cm2, were observed.