[en] High-frequency applications of high- temperature superconductors generally fall into two categories: 1) devices that require low values (relative to Cu) of surface resistance R_S in ambient surface magnetic fields H_rf; and 2) devices that require low R_S in modest fields (H_rf ∼ 250 Oe). Moreover, many applications can be realized with small- surface-area films (∼ 1 cm²) whereas others require larger areas - radiofrequency (rf) cavities, for example. Regardless of the application, the potential of HTS films is predicted on satisfying one or both of the above-stated requirements. The authors have measured the surface resistance of small-area (1 cm²) and large-area (6.5 cm²) YBa₂Cu₃O₇ (YBCO) films that have been laser ablated onto LaA ell O₃ substrates, large-area (5.1 cm² YBCO films that have been e-beam deposited onto LaA ell O₃, and large-area (11.4 cm²) T ell-based films that have been magnetron sputtered onto metallic substrates. The best R_S values are obtained from the 1-cm² laser-ablated films; they are 40 μΩ and 340 μΩ at 4 K And 77 K, respectively (ω/2π = 10 GHz). Comparable values for Cu are 6 and 13 mΩ, respectively. Large-area T ell-based films yield typical R_S values of 4 mΩ and 14 mΩ at 4 K and 77 K, respectively (ω/2π = 18 GHz). The dependence of R_S on H_rf for these films indicates that surface fields as large as 55 Oe can be achieved with R_S increasing only by a factor of 10. This field dependence is associated with c-axis texturing