Recent progress in millimeter-wave tunneladder TWTs

Two millimeter-wave TWT designs have been developed for operation at 29 and 39.5 GHz, respectively. To obtain high interaction impedance, a non-space-harmonic ladder-type interaction circuit, modified to accommodate a cylindrically symmetrical electron beam and Pierce gun, is employed. This interaction circuit consists of paired, chemically milled copper ladder sections and diamond dielectric supports. Beam focusing is provided by a radially magnetized permanent-magnet structure. Several modifications to the initial mechanical design approach have now been incorporated, enhancing the tube's robustness and ease of manufacture. Enough data are now available to confirm the cold-test data presented previously. In addition the cw operation of a tube at 28.33 GHz and 209 W rf output power verifies the calculations of power handling capacity for the diamond-supported copper circuit sections.