Coaxial-to-helix transducers for traveling-wave tubes

Transitions from coaxial lines to helices are described. These either have the coaxial tapered to a high impedance for the junction, or have the lay of the helix tapered to reduce its impedance. With the aid of a matching stub a transition with voltage standing-wave ratio 2:1 over a 3:1 frequency band can be made. A tapered shell transition has been made with a match of better than 1:5:1 from 400-1200 Mc/s.