An NMR
resonator for receiving RF signals at desired
resonance frequencies from a measuring sample in a volume under investigation disposed about a coordinate origin (x,y,z=0), with a means for producing a
homogeneous magnetic field B.sub.0 in the direction of a z axis, wherein superconducting conductor structures are disposed between z=-.vertline.z.sub.1.vertline. and z=+.vertline.z.sub.2.vertline. on a surface which is translation-invariant (=z-invariant) in the z direction at a radial separation from the measuring sample, is characterized in that a compensation arrangement is additionally provided on the z-invariant surface, which extends to values of at least +.vertline.z.sub.2.vertline.+0.5.vertline.r.vertline.>z> -.vertline.z.sub.1.vertline.-0.5.vertline.r.vertline., wherein .vertline.r.vertline. is the minimum separation between the measuring sample and the compensation arrangement, wherein the compensation arrangement comprises further superconducting conductor structures which are RF-decoupled from the RF
resonator, with the conductor structures of the compensation arrangement and of the RF
resonator being composed of individual surface sections ("Z-structures") which comprise superconducting structures and are disposed in the z-invariant surface to each extend along the entire length in the z direction of the conductor structures of the compensation arrangement and of the RF resonator, those superconducting structures being disposed such that
decomposition of the surface of the Z structures into a plurality of small equally sized surface elements and application of a homogeneous test
magnetic field along the surface normal of each
surface element for all surface elements which differ only with respect to their z position, induces a
magnetic dipole moment of the same strength. In this manner, the disturbing influence caused by
magnetization of the superconductor is very well compensated for.