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.