Design and Cold Test of a W-Band High Power Modified Sine Waveguide Traveling Wave Tube

The modified flat-roofed sine waveguide (MFRSWG) two-section slow wave circuit for the W-band high power sheet electron beam (SEB) traveling-wave tube (TWT) has been designed and fabricated. The long-distance transmission of SEB presents a significant challenge that impedes the advancement of SEB devices. To mitigate this issue by reducing the length of the slow wave structure (SWS), a type of modified coupled structure which allows a direct transition from the MFRSWG to rectangular waveguide has been investigated. The introduction of this modified coupled structure has led to a notable reduction of 30 mm in the length of the two-section SWS. Cold test results indicate that the reflection coefficient of the slow wave circuit, fabricated using Nano CNC technology, is below -15.2 dB from 90 to 96 GHz, showing a general agreement with simulation results. Within the same bandwidth, beam-wave interaction simulation results indicate that the designed MFRSWG TWT, operating at a beam current of 630 mA and a beam voltage of 33 kV, achieves an output power exceeding 1000 W, with a peak power of 1310 W at 93 GHz. Furthermore, we have developed an electron gun capable of generating a current of 630-mA SEB at a voltage of 33 kV. To focus the SEB for this TWT, a periodically cusped magnetic (PCM) system has been designed. Simulation results confirm that the SEB can propagate through the 130-mm-long beam tunnel without interception.