An electromagnetic field sensor or generator employing a radio frequency microstrip transmission channel formed by a low-loss dielectric substrate sandwiched between a non-resonant microstrip conductor and a conductive ground plane. A discontinuity in said microstrip conductor that substantially alters its cross-sectional dimensions causes electrical signals in the microstrip conductor to be inductively coupled to near field electromagnetic radiation in the vicinity of the discontinuity. The discontinuity may be defined by one or more holes, slots, slits or stubs in the microstrip. The sensor/generator may be used in numerous applications, including NMR spectrometry, as a near field scanning device to inspect operating integrated circuits, or to read or write data on magnetic materials.