Off-axis cold-test probe for W-band cavities

A pair of probes that can excite and detect oscillation-threatening modes in W-band gyroklystron cavities was built and tested. The probes, positioned inside 0.122-inch diameter beam tunnels that adjoin the cavity, either radiate or absorb RF from a 0.020" x 0.040" iris located off-axis on each probe tip. Each iris is joined to a WR-10 type flange on the opposite end of the probe by a rectangular waveguide that tapers in both transverse directions inside the probe body. This guide is filled with high-value dielectric powders that are layered along the taper to restrict RF propagation to the dominant rectangular TE/sub 10/ mode for frequencies between 75 GHz and 110 GHz.