A flexible miniature electric field probe for microwave tube measurements

In the past, the characterization of slow wave structures and tuning cavities in microwave tubes has been quite difficult because of the inability to directly measure field strengths within the microwave cavity. The field probe presented in this paper consists of a 0.6-mm dipole antenna, a zero-bias Schottky barrier diode, and a unique highly resistive output transmission line on a Mylar¹ substrate. Using the highly resistive output transmission line to minimize field perturbation and lead reception, such a field probe will provide for the first time the possibility of directly measuring electromagnetic fields in microwave tubes. Further, the Mylar substrate provides flexibility and makes the field probe much less fragile than the previous designs. This paper describes the field probe, its response when rotated about an incident electric field, and measured electric field strengths in an s-band cross-field amplifier, which is representative of modern microwave tubes.