Suppression of spurious modes in high power travelling wave tubes

The main task of this work was to establish suitable means to suppress band edge oscillations in broad band coupled-cavity TWT´s. The electric field flux lines in the slow wave structure have been calculated by means of conformal mapping. In the operating range, only transversal waves are existent, whereas at the upper cut-off frequency also E-modes are stimulated, esp. in the corner of the cavities. This fact can be utilized for suppression by inserting H111- resonators tightly coupled to the E-wave. A successfull application of these considerations has been demonstrated in a 30 GHz/1,5 kW TWT.