Effect of surface impedance on the antenna properties in superconducting microstrip antenna

The complex surface impedance (Z(s)) of a superconductor is comprised of tw o unequal components, surface resistance (R-s) and surface reactance (X-s). We have investigated the effects of R-s and X-s on the YBa2Cu3O7-x (YBCO) superconducting microstrip antenna properties (resonant frequency, input im pedance, and gain) by theoretical analysis and experimentation. The antenna s were fabricated from YBCO thin films on (100) MgO single crystal substrat e at 11.7 GHz. The investigation of the antenna properties reveals that the X-s of the superconducting thin film mainly influences the antenna resonan t frequency (f(r)) and has small influence on the antenna input impedance ( R-m). On the other hand, R-s mainly affects the input impedance of the ante nna. The antenna gain, and hence the efficiency, is found to be influenced by the film surface resistance. The antennas were characterized in the temp erature range of 10-90 K. Possible influences of the substrate dielectric p roperties (permittivity, epsilon(r) and loss tangent, tan delta) on the ant enna properties were also considered in the investigation. (C) 1999 Elsevie r Science B.V. All rights reserved.