  A split post dielectric resonator in a copper enclosure and a single post
dielectric resonator in a cavity with superconducting end-plates have been
constructed and used for the complex permittivity measurements of single
crystal substrates. (La,Sr)(Al,Ta)O3, LaAlO3, MgO and quartz substrates have
been measured at temperatures from 20 K to 300 K in the split post resonator
and from 15 K to 80 K in the single post resonator. The TE01delta mode resonant
frequencies and unloaded Qo-factors of the empty resonators at temperature of
20 K were: 9.952 GHz and 25,000 for the split post resonator and 10.808 GHz and
240,000 for the single post resonator respectively.
