Dielectric Properties Of Substrate Research Articles

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

The complex surface impedance ( Z s) of a superconductor is comprised of two unequal components, surface resistance ( R s) and surface reactance ( X s). We have investigated the effects of R s and X s on the YBa 2Cu 3O 7− x (YBCO) superconducting microstrip antenna properties (resonant frequency, input impedance, and gain) by theoretical analysis and experimentation. The antennas were fabricated from YBCO thin films on (100) MgO single crystal substrate at 11.7 GHz. The investigation of the antenna properties reveals that the X s of the superconducting thin film mainly influences the antenna resonant frequency ( f r) and has small influence on the antenna input impedance ( R in). On the other hand, R s mainly affects the input impedance of the antenna. The antenna gain, and hence the efficiency, is found to be influenced by the film surface resistance. The antennas were characterized in the temperature range of 10–90 K. Possible influences of the substrate dielectric properties (permittivity, ε r and loss tangent, tan δ) on the antenna properties were also considered in the investigation.

Dielectric properties of substrates for deposition of high-T/sub c/ thin films up to 40 GHz

Dielectric properties of CaNdAlO/sub 4/, LaAlO/sub 3/, SrLaAlO/sub 4/, SrLaGa/sub 3/O/sub 7/, and NdGaO/sub 3/ monocrystals, prospective substrate materials for the deposition of thin films of high-temperature superconductors, were measured with high accuracy at frequencies up to 40 GHz in the temperature range 10 to 300 K. Most materials exhibit uniaxial anisotropy with epsilon '/sub r/ ranging from 8.88 (SrLaGa/sub 3/O/sub 7/ along optical c-axis) to 24.18 (LaAlO/sub 3/). A decrease of epsilon 'r with temperature decrease was observed in all materials CaNdAlO/sub 4/ (perpendicular to c-axis) where epsilon 'r increases. Microwave losses in LaAlO/sub 3/, SrLaAlO/sub 4/ and SrLaGa/sub 3/O/sub 7/ decrease with temperature while CaNdAlO/sub 4/ and NaGaO/sub 3/ pronounced loss increase was found at temperatures below 100 K. The authors suggest that in the latter materials at lower temperatures, neodymium ions become magnetically ordered and are responsible for the observed effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>