Abstract: Electromagnetic resonators according to the invention comprise a first body, exemplarily a split thin ring, that is disposed between two planar field confining plates. The thickness (t) of the first body is less (typically less than 1/2 or 1/10) of the outer radius (R) of the body, and the distance between the first body and the confining plates is less than R. In preferred embodiments the first body comprises superconducting material. Resonators according to the invention can be readily assembled into relatively compact filters that are easily tunable, can have large quality factor, and offer the possibility of single mode operation. Such filters can advantageously be used in, e.g., wireless communications systems.