Design of 825 GHz square helix travellingwave tube

A helix travelling-wave tube for 825 GHz has been designed and its broadband amplification performance has been demonstrated with 3D particle-in-simulations. The design utilises a helix slow-wave structure with a square form and input/output couplers based on a transition from the helix to a coplanar waveguide and further to a rectangular waveguide with a through-substrate post coupler. A simulated small-signal gain of 18.3 dB with an output power of over 25 dBm at 1 dB compression point and a 3 dB instantaneous bandwidth of 8% have been obtained.