Superconducting microresonators are powerful tools for measuring electron paramagnetic resonance in very small sample volumes. By keeping the thickness of the superconductor below a penetration depth, and aligning the DC magnetic field in the plane of the superconductor, high fields (much larger than the critical field) are possible. With transmission-line geometry resonators (typically coplanar waveguide structures) the mode volume can be a few microns in two dimensions, while of order a wavelength in the third dimension. By utilizing unique properties of superconductors, such as large kinetic inductance, the length of the resonators can be substantially reduced, and planar lumped-element structures can be smaller still. Here we will discuss transmission-line structures which employ "mirrors" consisting of a periodically modulated impedance transmission line. Coplanar waveguide based structures of this variety have a continuous center conductor, allowing DC and low-frequency driving signals, as well as the microwaves for the EPR. A DC current can be used to electrically tune a resonator, using kinetic inductance, though here we will discuss ENDOR experiments in which the RF current is driven through the center conductor. We demonstrate this ENDOR microresonator using phosphorus and arsenic donors in isotopically enriched silicon. Surprisingly, the nuclear spin transitions can also be driven by a resonant electric field (no current) applied to the center pin. For Si:P the effect appears to be mediated by the hyperfine interaction between the donor electron and the nuclear spin. In the case of Si:As, however, the nuclear spins are being driven directly through the nuclear quadrupole interaction. These appear to be the first observations of quadrupolar nuclear electric resonance in a nonpolar crystal.