Frequency following imaging of electric fields from resonant superconducting devices using a scanning near-field microwave microscope

We have developed a scanning near-field microwave microscope that operates at cryogenic temperatures. Our system uses an open-ended coaxial probe with a 200 /spl mu/m inner conductor diameter and operates from 77 to 300 K in the 0.01-20 GHz frequency range. In this paper, we present microwave images of the electric field distribution above a Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ microstrip resonator at 77 K, measured at several heights. In addition, we describe the use of a frequency-following circuit to study the influence of the probe on the resonant frequency of the device.