  Devices relying on microwave circuitry form a cornerstone of many classical
and emerging quantum technologies. A capability to provide in-situ, noninvasive
and direct imaging of the microwave fields above such devices would be a
powerful tool for their function and failure analysis. In this work, we build
on recent achievements in magnetometry using ensembles of nitrogen vacancy
centres in diamond, to present a widefield microwave microscope with few-micron
resolution over a millimeter-scale field of view, 130nT/sqrt-Hz microwave
amplitude sensitivity, a dynamic range of 48 dB, and sub-ms temporal
resolution. We use our microscope to image the microwave field a few microns
above a range of microwave circuitry components, and to characterise a novel
atom chip design. Our results open the way to high-throughput characterisation
and debugging of complex, multi-component microwave devices, including
real-time exploration of device operation.
