Demonstration of a Modified Angular Log-Periodic Folded Waveguide Traveling Wave Tube at Ka-Band

This article demonstrates a Ka -band prototype traveling wave tube (TWT) with a single-stage gain of more than 35 dB, employing our previously proposed modified angular log-periodic folded waveguide (MALP-FW) slow wave structure (SWS). The basic operating principle of the MALP-FW SWS has been thoroughly investigated in our previous work, where its advantage of suppressing oscillations has been demonstrated by particle-in-cell (PIC) simulations. Guided by the principles, a prototype MALP-FW TWT operating at Ka -band is designed, fabricated, and tested. A 1600-G periodic permanent magnetic (PPM) focusing system is designed to focus the 12-kV and 100-mA electron beam. The measured maximum gain of the TWT is more than 35 dB at 32.5 GHz, and the output signal spectrum is noise-free. These results are in good agreement with the simulation results, which show that a maximum gain of 39.1 dB can be obtained at 32.4 GHz with an input power of 7 mW. This article validates the ability of MALP-FW SWS to suppress oscillations at the experimental level and its potential for future applications in terahertz TWTs.