The study of the interaction of a microwave field with a conventional superconducting surface is a rich topic for both application and science. The basic interaction with a small signal is understood and was quantitatively described decades ago. These descriptions rapidly break down in the presence of large amplitude microwave fields. The resulting interaction is difficult to model and depends strongly on the surface features and properties. A variety of behaviors are observed as the field amplitude is increased. The nature of the behavior changes for different materials, surface structures, and frequencies. Theoretical models describing the interaction of a large microwave signal with a superconductor have been proposed, attacking the issue from a variety of perspectives. At this time, no microscopic models exist that are able to even qualitatively explain the variety of behaviors that are observed. Beyond the scientific intrigue of better-describing the microscopic origin of the various observed behaviors of superconductors in these extreme conditions, there exists practical motivation. Particle accelerators employ resonant cavities with superconducting surfaces as a means of transferring energy to the particles. For this application, the goal is minimizing the dissipation of the microwave energy in the superconducting surface while maximizing the applied surface field. To engineer increasingly high performance surfaces, it is required to understand what features/properties are desirable or detrimental for obtaining the application goals. Realizing a large microwave field on a surface is nontrivial. In this work, a driven resonant cavity was used to create the high amplitude fields. This structure was a sample host cavity, designed with an opening such that a flat sample plate could be attached to close the volume. This scheme allows for exposing a detachable flat sample to a large microwave field. It is nontrivial to measure the response of the sample to the microwave field, as it must be decoupled from that of the system as a whole. The method used for this purpose is sensitive to systematic and measurement uncertainty, especially for samples of direct interest for accelerator application. Attempts were made to modify the system to improve its measurement quality and range. The implemented changes led to a significant improvement in performance. Using this sample host cavity, an attempt was made to improve the understanding of a common feature of superconducting surfaces, the native oxide. Specifically, the surface oxide that is present on the best materials known for accelerator application, niobium and niobium-tin. The niobium oxide contains a metallic phase that electrically couples to the superconducting bulk. This coupling, referred to as proximity-coupling, results in the normal conducting oxide layer taking on some superconducting properties. Conversely, the normal conducting layer will influence the properties of the superconductor near the surface. Models and experiments indicate that this metallic oxide may have an important role in the amplitude-dependence of the microwave dissipation in superconducting cavities used for applications. But it is difficult to control the relevant properties of the oxide, and to do so without altering other surface features. This makes it difficult to study the impact of metallic surface oxide phases on the microwave interaction directly. In this study, the choice was made to remove the oxide and replace it with an easier-to-control gold layer. This allowed for a more controlled study of the microwave response of a proximity-coupled system. Using the sample host cavity, high-field RF measurements were performed on these gold-superconductor samples for a range of gold layer thicknesses. A model describing the influence of proximity-coupling on the microwave response was implemented to assist with interpreting the measurements. The data was well-described by this model for small amplitude fields, but the agreement was lost as the field strength increased. It was found that replacing the niobium oxide with a minimal thickness gold layer enhanced the maximum field limitations of the system. This result indicates that the niobium oxide could also be a limiting factor in accelerator applications.