Microwave dissipation due to vortices in YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films for magnetic fields applied at small angles from the ab-planes

YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films patterned in a meander line resonant structure are used to probe vortex dynamics at microwave frequencies. We perform highly sensitive measurements of the changes in surface resistance /spl Delta/R/sub s/(H,T,/spl theta/) of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films as a function of applied dc field, temperature, and angle of the applied field relative to the ab-planes. We observe that the component of the magnetic field normal to the planes produces substantially more dissipation than the component parallel to the planes. Also, the surface resistance R/sub s/ vs. H data for magnetic fields applied at small angles from the ab-planes shows two regions of markedly different field dependence separated by a crossover field H*. For applied fields H>H* we have linear dependence of R/sub s/ on applied field with a steep slope. For applied fields H>